Fathom 7.0 Modules Guide

AFT Fathom™ Modules User’s Guide

AFT Fathom version 7.0 Modules Incompressible Pipe Flow Modeling

Applied Flow Technology

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CAUTION! AFT Fathom is a sophisticated pipe flow analysis program designed for qualified engineers with experience in pipe flow analysis and should not be used by untrained individuals. AFT Fathom is intended solely as an aide for pipe flow analysis engineers and not as a replacement for other design and analysis methods, including hand calculations and sound engineering judgment. All data generated by AFT Fathom should be independently verified with other engineering methods. AFT Fathom is designed to be used only by persons who possess a level of knowledge consistent with that obtained in an undergraduate engineering course in the analysis of pipe system fluid mechanics and are familiar with standard industry practice in pipe flow analysis. AFT Fathom is intended to be used only within the boundaries of its engineering assumptions. The user should consult the User’s Guide for a discussion of all engineering assumptions made by AFT Fathom.

Information in this document is subject to change without notice. No part of this User’s Guide may be reproduced or transmitted in any form or by any means, electronic or mechanical, for any purpose, without the express written permission of Applied Flow Technology.

© 2008 Applied Flow Technology Corporation. All rights reserved. Printed in the United States of America. First printing.

“AFT Fathom”, “AFT Mercury”, “Applied Flow Technology”, and the AFT logo are trademarks of Applied Flow Technology Corporation. Microsoft, Visual Basic, Excel and Windows are trademarks or registered trademarks of Microsoft Corporation.

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Contents Summary

1. Introduction .................................................................... 1 2. Using Goal Seek and Control ........................................ 7 3. Goal Seek and Control Example ................................. 33 4. Modeling Extended Time Simulation.......................... 47 5. Modeling Time and Event Based Transients ............. 81 6. Extended Time Simulation Example........................... 91 7. Working with Cost Databases................................... 113 8. Performing Cost Analysis.......................................... 137 9. Cost Analysis Example .............................................. 151 10. Using Modules Together.......................................... 169 Glossary .......................................................................... 179

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iv AFT Fathom 7.0 Modules User’s Guide

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Table of Contents v

Detailed Contents Summary..................................................................................................iii Detailed Contents ..................................................................................... v

1. Introduction .................................................................... 1 What this user’s guide covers................................................................... 1 Modeling capabilities ............................................................................... 2 GSC module ....................................................................................... 2 XTS module ....................................................................................... 2 CST module ....................................................................................... 2 Who can use AFT Fathom........................................................................ 3 Getting started with the AFT Fathom Modules........................................ 3 GSC module ....................................................................................... 3 XTS module ....................................................................................... 3 CST module ....................................................................................... 3 Using Modules together ..................................................................... 3 Example models ................................................................................. 4 Using online help...................................................................................... 4 Activating modules................................................................................... 4 Opening models with and without module data ....................................... 5 Opening models without module data in a module............................ 6 Opening models with module data without an active module ........... 6 Using modules in scenarios ......................................................... 6

2. Using Goal Seek and Control ........................................ 7 What is the GSC module? ........................................................................ 7 How does the GSC module work?............................................................ 7 Using the GSC module ............................................................................. 8

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vi AFT Fathom 7.0 Modules User’s Guide Enabling GSC use..................................................................................... 9 Goal Seek and Control Manager ............................................................ 10 GSC variables ......................................................................................... 11 Types of variables...................................................................... 11 Creating and deleting variables ................................................. 12 Applying variables..................................................................... 14 Object type................................................................................. 14 Junction type.............................................................................. 14 Junction number and name ........................................................ 14 Variable parameter .................................................................... 14 Linking variables ....................................................................... 15 Variable bounds......................................................................... 15 Reviewing junction input data................................................... 15 Editing junction input data ........................................................ 15 GSC goals ............................................................................................... 16 Types of goals............................................................................ 16 Creating and deleting goals ....................................................... 19 Applying goals........................................................................... 20 Goal types .................................................................................. 20 Object types ............................................................................... 21 Reviewing object input data ...................................................... 21 Editing object input data............................................................ 21 GSC data in Model Data......................................................................... 22 GSC feedback during the solution.......................................................... 22 GSC data in output ................................................................................. 23 Changing input values to GSC results.................................................... 24 Transferring results to initial............................................................ 24 Generating a disconnected scenario................................................. 25 When goals cannot be achieved.............................................................. 26 Physically unrealistic goals.............................................................. 27 Better starting point needed ............................................................. 27 Changing control parameters ........................................................... 27 Changing tolerance in Solution Control .................................... 28

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Table of Contents vii Changing goal seeking numerical control ................................. 29 What to do if the Solver gets stuck......................................................... 29 GSC data differences across scenarios ................................................... 32

3. Goal Seek and Control Example ................................. 33 Topics covered........................................................................................ 33 Required knowledge ............................................................................... 33 Model file ............................................................................................... 34 Problem statement .................................................................................. 34 Step 1. Start AFT Fathom....................................................................... 34 Step 2. Specify system properties........................................................... 34 Step 3. Build the model .......................................................................... 35 A. Place the pipes and junctions ................................................ 35 B. Enter the pipe data................................................................. 35 C. Enter the junction data .......................................................... 36 J1 Reservoir ............................................................................... 36 J9 Reservoir ............................................................................... 36 J3 Tee......................................................................................... 37 J6 Elbow .................................................................................... 37 J4, J7 Control Valves................................................................. 37 J5, J8 Heat Exchangers.............................................................. 37 J2 Pump ..................................................................................... 37 D. Check if the pipe and junction data is complete ................... 37 Step 4. Open the Goal Seek and Control Manager................................. 38 Step 5. Add a variable............................................................................. 38 Step 6. Add a goal................................................................................... 39 Step 7. View GSC settings in Model Data ............................................. 42 Step 8. Enable goal seeking.................................................................... 43 Step 9. Run the model............................................................................. 43 Step 10. Examine the results................................................................... 44 Analysis summary................................................................................... 45

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viii AFT Fathom 7.0 Modules User’s Guide

4. Modeling Extended Time Simulation.......................... 47 What is the XTS module?....................................................................... 47 How does the XTS module work?.......................................................... 48 Using the XTS module ........................................................................... 48 Enabling XTS transient mode................................................................. 49 Transient control window....................................................................... 51 Entering junction transient data ....................................................... 52 Initiating transients .................................................................... 53 Repeat transient ......................................................................... 53 Transient Special Conditions..................................................... 53 Entering reservoir volume data............................................................... 54 Infinite reservoirs ............................................................................. 54 Finite reservoirs................................................................................ 54 Finite open tanks........................................................................ 55 Finite closed tanks ..................................................................... 55 Known parameters initially.............................................................. 57 Entering reservoir transient data ...................................................... 58 Infinite reservoirs....................................................................... 58 Finite open tanks........................................................................ 58 Finite closed tanks ..................................................................... 59 What happens when finite tanks overflow? ..................................... 59 What happens when finite tanks drain? ........................................... 60 What happens when pipes are uncovered? ...................................... 60 Interpreting pipe depth and elevation data....................................... 61 Maximum and minimum pressures in closed tanks ......................... 61 Transient data in Model Data window ................................................... 61 Solution progress window with XTS ..................................................... 62 Transient control difference methods..................................................... 63 Forward difference method.............................................................. 64 Central difference method................................................................ 64 Relative and absolute tolerance ................................................. 65 Relaxation.................................................................................. 67

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Table of Contents ix Maximum iterations................................................................... 67 Changing parameters during the run ......................................... 67 Output values displayed with forward difference............................ 67 Output values displayed with central difference.............................. 68 Transient data in Output window ........................................................... 69 Detailed results for a time step......................................................... 69 Transient results for all time steps ................................................... 69 Quick graphs .................................................................................... 70 Transient Graph Results ......................................................................... 73 Profile graphs ................................................................................... 73 Animation of output................................................................... 74 Transient graphs............................................................................... 75 Transient Visual Report.......................................................................... 76 Special conditions................................................................................... 77 Special conditions with no transient data .................................. 77 Special conditions with transient data ....................................... 78 Pump special conditions ............................................................ 79 Transient Special Conditions ........................................................... 80

5. Modeling Time and Event Based Transients ............. 81 Time-based transients ............................................................................. 81 Event-based transients ............................................................................ 82 Single event transients ..................................................................... 82 Dual event transients: cyclic and sequential .................................... 83 Cyclic events.............................................................................. 83 Sequential events ....................................................................... 84 Junctions with inherent event logic ........................................................ 85 Check valve ...................................................................................... 86 Relief valve ...................................................................................... 86 Thought experiment to further clarify event transients .......................... 86 Other transient features........................................................................... 87 Absolute vs. relative transient data .................................................. 87 Repeat transient................................................................................ 87

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x AFT Fathom 7.0 Modules User’s Guide Add time offset................................................................................. 87 Graphing the transient data .............................................................. 87 Event messages....................................................................................... 89 Transient indicators on the Workspace .................................................. 89 Transient data in Model Data ................................................................. 90

6. Extended Time Simulation Example........................... 91 Topics covered........................................................................................ 91 Required knowledge ............................................................................... 91 Model file ............................................................................................... 92 Problem statement .................................................................................. 92 Step 1. Start AFT Fathom....................................................................... 92 Step 2. Specify system properties........................................................... 92 Step 3. Build the Model.......................................................................... 93 A. Place the pipes and junctions ................................................ 93 B. Enter the pipe data................................................................. 93 C. Enter the junction data .......................................................... 94 J1 Reservoir ............................................................................... 94 J11, J13, J15, J17, J19 Assigned Pressures ............................... 95 J10, J12, J14, J16, J18 Valves ................................................... 95 J4, J6 Valves.............................................................................. 95 J3, J5 Pumps .............................................................................. 95 J8 Control Valve........................................................................ 96 J2, J7, J9 Branches .................................................................... 96 D. Check if the pipe and junction data is complete ................... 96 Step 4. Specify transient output time units............................................. 96 Step 5. Select transient analysis.............................................................. 97 Step 6. Open transient control ................................................................ 97 Step 7. Set up the system transients........................................................ 99 A. Auxiliary pump J5 transient. ....................................................... 99 B. Valve J6 Transient..................................................................... 100 C. Valve J12, J14, J16, J18 Transients .......................................... 100 Step 8. Run the model........................................................................... 101


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Table of Contents xi Step 9. Examine the transient results.................................................... 102 Analysis summary................................................................................. 111

7. Working With Cost Databases .................................. 113 Sources of cost data supported ............................................................. 113 Types of databases supported............................................................... 113 Engineering and cost databases ............................................................ 114 Cost Database window ......................................................................... 114 One time vs. recurring costs........................................................... 115 Creating cost databases......................................................................... 116 Pipe material costs ......................................................................... 118 Non-recurring costs ................................................................. 119 Recurring costs ........................................................................ 119 Junction costs ................................................................................. 119 Deleting costs................................................................................. 119 Non-recurring costs, non-pumps and control valves ............... 119 Recurring costs, non-pumps .................................................... 120 Pump and control valve costs .................................................. 121 Costs for tees and branches ..................................................... 122 Pipe fitting & loss costs ................................................................. 122 Scale tables..................................................................................... 123 Global multipliers in cost database ................................................ 124 Global multipliers in Database Manager ....................................... 124 Using cost databases............................................................................. 125 Database Sections.................................................................... 126 How repetitive costs are handled ................................................... 126 Using the Database Sources tables................................................. 127 Pipe costs in Pipe Specifications window...................................... 127 Cost for pipe fittings & losses........................................................ 130 Junction costs in Junction Specifications window......................... 131 All databases vs. selected cost databases....................................... 132 Cost Settings window..................................................................... 133 Database locations in General Preferences .......................................... 134

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xii AFT Fathom 7.0 Modules User’s Guide Reviewing application of cost data....................................................... 135

8. Performing Cost Analysis.......................................... 137 What is the CST module?..................................................................... 137 How does the CST module work? ........................................................ 137 Using the CST module.......................................................................... 138 Accessing cost databases ...................................................................... 139 Cost databases ................................................................................ 139 Energy Cost databases.................................................................... 139 Database Manager.......................................................................... 139 Cost Application Manager.................................................................... 139 Cost Databases ............................................................................... 141 Energy Cost Databases................................................................... 141 Cost Multipliers ............................................................................. 141 Maximum Cost Groups .................................................................. 141 Service Duration ............................................................................ 142 Cost Settings window ........................................................................... 142 Cost Calculations ........................................................................... 142 Energy Cost .................................................................................... 142 Cost Definitions ............................................................................. 143 Monetary vs. non-monetary costs .................................................. 143 Engineering parameter costs .......................................................... 144 Custom monetary units .................................................................. 144 Cost Time Period ........................................................................... 144 Cost Report ........................................................................................... 145 What are maximum cost groups? ......................................................... 146 Typical usage guidelines................................................................ 147 Creating a maximum cost group for pumps ................................... 147 How cost multipliers are applied with maximum cost groups....... 148 Maximum cost is the base cost before multipliers are applied 148 Pump operates part of the time ................................................ 148 Spare pump .............................................................................. 148 Maximum cost groups for control valves....................................... 149

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Table of Contents xiii

9. Cost Analysis Example .............................................. 151 Topics covered...................................................................................... 151 Required knowledge ............................................................................. 151 Model file ............................................................................................. 152 Problem statement ................................................................................ 152 Step 1. Start AFT Fathom..................................................................... 153 Step 2. Open the model file .................................................................. 153 Step 3. Cost Settings............................................................................. 153 Cost Calculations ........................................................................... 154 Cost Definitions ............................................................................. 154 Cost Time Period ........................................................................... 154 Step 4. Create the cost databases.......................................................... 155 Create a new cost database for the pipe costs ................................ 155 Enter the pipe material costs .......................................................... 156 Create cost scale tables .................................................................. 159 Add the costs for pipe fittings........................................................ 160 Create a new cost database for the pumps ..................................... 163 Enter the pump costs................................................................ 163 Connecting the cost databases........................................................ 164 Step 5. Including items in the Cost Report ........................................... 165 Step 6. Run the model........................................................................... 166 Step 7. Examine the Cost Report.......................................................... 166 Analysis summary................................................................................. 168 Cost optimization with AFT Mercury™ .............................................. 168

10. Using Modules Together.......................................... 169 Model file ............................................................................................. 169 Problem statement ................................................................................ 169 Start AFT Fathom................................................................................. 170 Open the model file .............................................................................. 170 Variable and goal settings .................................................................... 170 Transient control settings ..................................................................... 170 Junction transient data .......................................................................... 172

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xiv AFT Fathom 7.0 Modules User’s Guide Cost settings.......................................................................................... 174 Run the model....................................................................................... 174 GSC and XTS module solutions........................................................... 175 Examine the results............................................................................... 175 Summary............................................................................................... 177

Glossary .......................................................................... 179

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CHAPTER 1

Introduction

Welcome to the AFT Fathom™ 7.0 Modules. AFT Fathom is a graphical platform for modeling incompressible flow in pipe networks. There are three optional add-on modules which extend AFT Fathom’s extensive modeling capabilities into new areas. The Extended Time Simulation (XTS) module allows the engineer to model time varying system behavior. The Goal Seek & Control (GSC) module allows the engineer to perform multivariable goal seeking and simulate control system functions. The Cost (CST) calculation module allows the engineer to calculate system costs, both initial and recurring. The modules can be used individually or together. The AFT Fathom Modules automate and organize a range of engineering functions, bringing increased productivity to the piping system engineer.

What this user’s guide covers This User’s Guide documents features in the AFT Fathom Modules which are not discussed in and are not part of the standard AFT Fathom 7.0 User’s Guide provided separately. This User’s Guide assumes the user is familiar with AFT Fathom. Please consult the AFT Fathom 7.0 User’s Guide for information on standard AFT Fathom functions.



2 AFT Fathom 7.0 Modules User’s Guide

Modeling capabilities GSC module •

Can automatically have parameters vary to meet specified goals

•

Can specify group goals to ensure a group of pipes or junctions satisfies operating criteria

•

Can link variables to force commonality in solutions

•

Can easily apply and unapply goals and variables

XTS module •

Can model transient behavior over time

•

Supports time and event transients for valve position, pump speed, pump control setpoints, pressure or flow, reservoir liquid level or surface pressure, spray CdA, control valve setpoints

•

Reservoirs can be finite with defined tank geometries so surface level changes with time can be computed

•

Reservoirs can be open or closed. If closed, surface pressure changes due to gas compression (when the liquid level changes) can be modeled.

•

Transient data shown on Output window and controlled by special Output Control features

•

Transient data can be graphed over time

•

Profile data can be animated

•

Quick Graph on Output window shows a popup graph of transient data

CST module •

Can obtain cost for entire pipe system (has all cost capabilities of AFT Mercury™)

•

Can account for non-recurring and recurring costs


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Chapter 1 Introduction 3 •

If used with XTS module, can calculate pump energy usage and cost over time

Who can use AFT Fathom AFT Fathom assumes that the user possesses a good general knowledge of engineering pipe system hydraulics. Even the most advanced and easy-to-use software package cannot make up for a lack of fundamental knowledge on the part of the user. The level of knowledge assumed by AFT Fathom is consistent with that obtained in a typical engineering undergraduate course in fluid mechanics. See the copyright page in this User’s Guide for cautionary information.

Getting started with the AFT Fathom Modules GSC module Chapter 2 discusses in detail how to use the GSC module. Chapter 3 focuses on an example application.

XTS module Chapter 4 discusses in detail how to use the XTS module. Chapter 5 discusses time and event transients. Chapter 6 focuses on an example application.

CST module Chapter 7 discusses how Cost Databases are built and used. Chapter 8 discusses in detail how to use and apply data to generate cost calculations. Chapter 9 focuses on an example application.

Using Modules together Chapter 10 discusses how the modules can be used with each other and looks at an example.

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Example models An auxiliary help file (called FathomExamples.hlp) is installed with AFT Fathom and leads the user through modeling a number of real world systems. This help file can be accessed by choosing “Show Examples” from the Help menu. The example models discussed in FathomExamples.hlp are installed in the Examples folder. It can be opened from the Help menu by choosing “Show Examples”.

Using online help To access AFT Fathom's online help, press the F1 function key or select Help from the menu bar. For convenient access, much of the content of this User’s Guide is included in the Help system. The Help button in each dialog window provides context-sensitive help on the features of that window. In the Help system you have the option of searching for information on specific topics or searching through the hierarchical layout to find more general information.

Activating modules When AFT Fathom launches, the first window displayed is the Activate Modules window (Figure 1.1 top). This allows you to select which modules you would like to activate for use in AFT Fathom. If a license is not found for a module, the selection will be disabled (Figure 1.1 bottom). Even though the Activate Modules window allows you to choose a module for activation, that does not mean that a license is available for use – it just means that a license exists. If it is in use by another user and thus not available for checkout, you will be informed after clicking the OK button. If there is a module you would like to always have activated when you start AFT Fathom, select it in the Activate Modules window and then click the Set as Default button (see Figure 1.1). If you do not want the Activate Modules window to display when you start AFT Fathom, clear the “Always Show” check box provided.


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Chapter 1 Introduction 5 If, after starting AFT Fathom, you decide you would like to activate (or deactivate) a module, you can open the Activate Modules window from the Options menu.

Figure 1.1

The Activate Modules window displays when AFT Fathom launches, showing all modules available (top) or only some available (bottom).

Opening models with and without module data What happens when you open a model that has module data without access to that module, and vice versa? This section discusses what happens to the model.

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6 AFT Fathom 7.0 Modules User’s Guide When AFT Fathom is used along with a module, that module is said to be active.

Opening models without module data in a module There is no problem opening a model without module data into AFT Fathom when one or more of the modules is active. When doing so, the model can be enhanced through the module features. However, once a model which uses module features is saved, the data can only be retained by continuing to use that model with the active module. If you want to continue to use the original model without module features, you may want to keep two versions of the model. One for use with modules and one without.

Opening models with module data without an active module If you open a model which has module data in it, and that module is not active, AFT Fathom will attempt to activate the module. If it cannot, the module related data will not be displayed in AFT Fathom. Further, AFT Fathom does not attempt to retain the original module data and it may be lost if the model is later saved. When you open the model in such cases, AFT Fathom will inform you what modules are used in the model, and warn you about lost data if you open the model and save it. You will be given a choice to cancel the model opening process at that point. Important: Opening a model created with a module into an AFT Fathom session without that module will usually result in the data being lost. Using modules in scenarios You may have a model where some scenarios use certain modules while others do not. If a module is used in any scenario, AFT Fathom considers that entire model to be using the module. Thus even if the scenario which uses the module is not opened, the data may be lost when the model is saved.


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CHAPTER 2

Using Goal Seek and Control

This chapter introduces the Goal Seek and Control Module (GSC). Detailed information regarding GSC menus and functionality is given in this chapter. Chapter 3 provides a detailed hands-on GSC example.

What is the GSC module? Many engineering modeling tasks involve more than just directly solving a system. In some cases a manual, “cut and try” method of changing input variables to achieve desired operating results is required. When a single parameter is being changed, the manual process (while tedious and time consuming) can be used successfully. However, varying two or more parameters at the same time quickly becomes impractical. The GSC module automates the process of changing input variables to achieve desired design goals. For single variable situations, the GSC module offers the advantage of being much faster than manual methods. Further, it provides a practical tool for solving cases when there are two or more variables.

How does the GSC module work? The GSC module employs numerical optimization technology like that used in AFT Mercury™. The optimization engine employed by the AFT Fathom GSC module uses state-of-the-art optimization technology licensed from Vanderplaats Research and Development, the leading



8 AFT Fathom 7.0 Modules User’s Guide company in optimization technology. However, rather than minimizing some function value such as system cost or weight, the GSC module satisfies equality criteria using “goal programming” methods. The core hydraulic solution in AFT Fathom is performed by the Hydraulic Solver. In standard AFT Fathom usage, the Hydraulic Solver is called once to solve a system. The GSC module’s Numerical Optimizer is used to call the Hydraulic Solver repeatedly, thus solving a series of models with different inputs. The Numerical Optimizer adjusts the user specified Variables (discussed later in this chapter) in order force the Hydraulic Solver output values to agree with the user specified Goals (also discussed later in this chapter). Figure 2.1 depicts the relationship between the different components. Graphical Interface Input

Output

Hydraulic Solver

Yes No

Converged on goals?

Numerical Optimizer Figure 2.1

The GSC module flowchart shows how the Hydraulic Solver is called repeatedly in an iterative loop.

Using the GSC module The user has the option of activating or not activating the GSC module when AFT Fathom first loads. After AFT Fathom is loaded, the GSC module can be activated or deactivated for use from the Options menu. Whether or not GSC is activated impacts the View menu, Analysis menu, Model Data window and Output window. If the GSC module is active, the user can still run models without goal seeking. This is selected under Goal Seek & Control on the Analysis menu. Hence there are three possibilities for GSC. 1. GSC is not active 2. GSC is active and goal seeking is ignored


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Chapter 2 Using Goal Seek and Control 9 3. GSC is active and goal seeking is performed Table 2.1 lists the three possibilities and the impact on various AFT Fathom features. Table 2.1

AFT Fathom feature accessibility based on GSC activation and GSC use

GSC Not Active

GSC Active

GSC Active

No Mode

Ignore

Use

Not Visible

Visible

Visible

"Goal Seek and Control" on Analysis Menu

Not Visible

Visible

Visible

"Goal Seek and Control" tab in General Section of Model Data

Not Visible

Visible

Visible

"GSC Variables" and "GSC Goals" tab in General Section of Output window

Not Visible

Not Visible

Visible

Feature "Goal Seek and Control Manager" on View Menu

Enabling GSC use When the GSC module is active, two new menu items appear – one on the View menu and the other on the Analysis menu. On the Analysis menu is the Goal Seek & Control menu, from which the user can select “Ignore” or “Use”. The GSC module goal seeking is enabled by selecting Goal Seek & Control -> Use from the Analysis menu (Figure 2.2). This can be selected before or after a model is built. Pre-existing models built with standard AFT Fathom can be opened with GSC and goal seeking data added. Goal seeking can be turned off at any time by selecting Ignore from the same menu. The Ignore mode causes the GSC module to function like standard AFT Fathom. One difference is that users can still enter goal seeking data and this data is retained in the model. If the model is opened in standard AFT Fathom, this data will be lost. Table 2.1 relates the differences between not using GSC and using it in Ignore mode.

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10 AFT Fathom 7.0 Modules User’s Guide The purpose of Ignore mode is that it allows the goal seeking to be quickly turned off and on without having to change data in the Goal Seek & Control Manager (discussed in the next section). When the goal seeking mode is selected, the Goal Seek and Control Manager option on the View menu is enabled.

Figure 2.2

Select “Use” from the Goal Seek & Control menu item on the Analysis menu to instruct AFT Fathom to perform goal seeking when it runs.

Goal Seek and Control Manager The Goal Seek and Control Manager is where variables and goals are defined and applied (Figure 2.3). The Goal Seek and Control Manager is opened by selecting Goal Seek and Control Manager from the View Menu.



Chapter 2 Using Goal Seek and Control 11 There are three tabs on the Goal Seek and Control Manager, and the first two will be used most frequently. These are the Variables tab and the Goals tab. Variables and goals are discussed in then next few sections.

Figure 2.3

Goal Seek and Control Manager is where you define and apply your variables and goals.

GSC variables Variables are input parameters that the GSC module will change to achieve the user's desired goals. Variables are defined and applied from the Variables tab on the Goal Seek and Control Manager window (see Figure 2.4). Generally, there must be one variable applied for each goal that is applied. Types of variables All variables are junction parameters. The variables that are available for each junction type are shown in Table 2.2. There are over 30 types of variables.

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Figure 2.4

GSC Variables are input parameters to be automatically varied.

Creating and deleting variables To create a variable, click the New Variable button on the Variables tab (Figure 2.4). This will insert a new item into the variable list. After the variable has been added, the variable data is defined by entering the necessary data in each of the data columns. Variables may also be added by duplicating an existing variable, then modifying the data for the new variable. To duplicate a variable, select the variable to be duplicated from the variable list, and click the Duplicate Variable button. To delete a variable, select the variable by clicking on the appropriate row in the variable list. After selecting the variable to be deleted, click the Delete Variable button. If you want to delete all of the variables in the list, click the Delete All Variables button.



Chapter 2 Using Goal Seek and Control 13 Table 2.2a List of object types with available variables Object Type Assigned Flow

Assigned Pressure

Branch Check Valve Control Valve General Component Heat Exchanger

Orifice

Pump

Relief Valve Reservoir

Screen Spray Discharge

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Variables Flow Elevation Temperature Pressure Elevation Temperature Imposed Flow Loss Value Control Setpoint Loss Factor Loss Factor Heat Rate Discharge Temperature Temperature Rise Enthalpy Rise Heat Transfer Area Overall Heat Transfer Coefficient Secondary Flow Secondary Inlet Temperature Diameter/Area Loss Factor Elevation Speed Flow Head Rise Impeller Size Control Setpoint Loss Value Liquid Level Surface Pressure Temperature Open Area Loss Factor Spray Area K Number Sprinklers Number Sparger Holes Elevation

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Restrictions

Only with heat transfer


Only with heat transfer Only with heat transfer Only with heat transfer Only with heat transfer Only with heat transfer Only with heat transfer Only with heat transfer Only with heat transfer


Only sprinklers Only spargers

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14 AFT Fathom 7.0 Modules User’s Guide Table 2.2b List of object types with available variables Object Type Three Way Valve Valve Venturi

Variables Open Percentage Loss Value Elevation Loss Factor

Restrictions

Only exit valves

Applying variables Once a variable has been created, the user must specify if a variable is to be used when the GSC module is run. To apply a variable, select the checkbox in the Apply column. Using the Apply feature allows the user to define multiple variables that can be used in alternate cases or analyses. Any of the variables that are not being used for a particular analysis can remain in the list for later use. Click the Apply checkbox for the variables that are to be used in the current analysis. Object type The Object Type defines whether the variable applies to a pipe or a junction. At this time, variables may only be assigned to junction object types. Junction type The Junction Type column is used to define the type of junction to which the variable is being applied. Junction number and name The specific junction to vary is selected in the Junction Number and Name column. The list will only display junctions of the type selected in the Junction Type column. Variable parameter Each junction type has a specific set of parameters that are available as variables (Table 2.2). The list will only display parameters that are available for the junction type selected in the Junction Type column.



Chapter 2 Using Goal Seek and Control 15 Linking variables The Link To column is used to force a variable on multiple junctions of the same type to solve to the same value. An example where this would be desirable would be when using pump impeller trim as a variable for several pumps in parallel. It is often desirable to solve for a condition where the pump impeller trim is the same for all of the pumps. This can be accomplished by using variable linking. A pump impeller trim variable would be defined for each of the pumps. Then, one of the pumps would be selected as the basis pump, which just means no linking is specified for this pump. The other pumps would be linked to the basis pump by selecting the basis pump from the list in the Link To column. Variable bounds During a goal search, the GSC module will modify the values for the defined variables. Sometimes it is helpful to specify upper and lower bounds for variables to provide logical extremes during the goal search. Some examples of logical bounds that can be applied would be lower and upper bounds on valve open percentage of 0% and 100%, respectively. Note that bounds can have engineering units, but these units are not displayed. It is assumed the units are the same as the junction input parameter specifications window. Reviewing junction input data If you would like to see the input data for the junction selected as a variable, press the right mouse button on the far left column in the Variables table. The inspection window will display, showing you the input data. Editing junction input data Similar to the inspection feature just described, you can open the Junction Specifications window by double-clicking the far left column in the Variables table. From there you can change any data desired.

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GSC goals Goals are output values you would like to achieve. The GSC module adjusts the applied variables until the applied goals are met. Goals are defined and applied on the Goals tab on the Goal Seek and Control Manager window (Figure 2.5). Generally there should be one goal applied for each applied variable.

Figure 2.5

GSC Goals are output parameters to be achieved by changing the variables.

Types of goals The GSC module offers over 150 goals applied to pipes, junctions or groups of pipes and/or junctions. Table 2.3 lists all of the types of goals.



Chapter 2 Using Goal Seek and Control 17 Table 2.3a List of object types with available goals Object Type Pipe

Area Change Bend Check Valve General Component Jet Pump Orifice Relief Valve Screen Valve Venturi Volume Balance Assigned Flow

Assigned Pressure

Goals Energy Gradeline Head Gradient Head Loss Heat Rate Into Pipe Hydraulic Gradeline Mass Flow Rate Pressure Drop Friction Pressure Gradient Pressure Stagnation Pressure Static Pressure Static Maximum Pressure Static Minimum Temperature Temperature Loss Velocity Volumetric Flow Rate Wall Temperature Energy Gradeline Hydraulic Gradeline Mass Flow Rate Pressure Stagnation Pressure Static Temperature Volumetric Flow Rate

Energy Gradeline Hydraulic Gradeline Pressure Stagnation Pressure Static Mass Flow Rate Net Into Jct Vol. Flow Rate Net Into Jct

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Restrictions/Comments


Only with heat transfer Only with heat transfer



Net flowrate Net flowrate

Page 17


18 AFT Fathom 7.0 Modules User’s Guide Table 2.3b List of object types with available goals (cont.) Object Type Branch

Control Valve

Dead End Heat Exchanger

Goals Energy Gradeline Hydraulic Gradeline Mass Flow Rate Pressure Stagnation Pressure Static Temperature Volumetric Flow Rate Cv Energy Gradeline Head Loss Hydraulic Gradeline Mass Flow Rate Open Percentage Pressure Loss Pressure Stagnation Pressure Static Temperature Volumetric Flow Rate Energy Gradeline Pressure Stagnation Energy Gradeline Heat Rate In Hydraulic Gradeline Mass Flow Rate Pressure Stagnation Pressure Static Temperature

Restrictions/Comments

Net flowrate

Only with heat transfer Net flowrate If Open Pct data exists Only for FCV Not PDCV Only for FCV Only for PRV, PSV If Open Pct data exists Not PDCV Only for FCV Only for FCV Only with heat transfer Only for PRV, PSV

Only with heat transfer. For nonfixed heat rate exchanger models.

Only with heat transfer. For noncontrolled temperature models.

Volumetric Flow Rate



Chapter 2 Using Goal Seek and Control 19 Table 2.3c List of object types with available goals (cont.) Object Type Pump

Reservoir Spray Discharge Tee or Wye

Three Way Valve

Group Sum (pipes and junctions)

Group Max/Min Pipes Group Max/Min Junctions

Goals Energy Gradeline Head Rise Hydraulic Gradeline Mass Flow Rate NPSH Margin Power Overall Pressure Rise Pressure Stagnation Pressure Static Temperature Volumetric Flow Rate Mass Flow Rate Net Into Jct Vol. Flow Rate Net Into Jct Mass Flow Rate Out Volumetric Flow Rate Out Energy Gradeline Hydraulic Gradeline Pressure Stagnation Pressure Static Temperature Energy Gradeline Hydraulic Gradeline Pressure Stagnation Pressure Static Temperature Head loss Heat rate in Mass flow rate Pressure loss Volumetric flow rate Uses all pipe goals Use all junction type goals

Restrictions/Comments Only for non-fixed head rise pumps Only for non-fixed flow pumps

Only for non-fixed head rise pumps

Only with heat transfer Only for non-fixed flow pumps Net flowrate Net flowrate Net flowrate Net flowrate


Only with heat transfer Only with heat transfer

Same as pipe goals Same as junction goals

Creating and deleting goals To create a goal, click the New Goal button on the Goals tab. This will insert a new item into the goals list. After the goal has been added, the

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20 AFT Fathom 7.0 Modules User’s Guide goal data is defined by entering the necessary data in each of the data columns. Goals may also be added by duplicating an existing goal, then modifying the data for the new goal. To duplicate a goal, select the goal to be duplicated from the goal list, and click the Duplicate Goal button. To delete a goal, select the goal by clicking on the appropriate row in the goal list. After selecting the goal to be deleted, click the Delete Goal button. If you want to delete all of the goals in the list, click the Delete All Goals button. Applying goals Once a goal has been created, the user must specify if a goal is to be used when GSC is run. To apply a goal, select the checkbox in the Apply column. Using the Apply feature allows the user to define multiple goals that can be used in alternate cases or analyses. Any of the goals that are not being used for a particular analysis can remain in the list for later use. Click the Apply checkbox for the goals that are to be used in the current analysis. Goal types Users may specify three types of goals when using the GSC module. •

Point Goal – A point goal is specified when the desired goal can be specified at a specific object location in the model.

•

Differential Goal – A differential goal is used when the goal value is actually determined by the difference in values between two specific object locations. An example of a differential goal might be the pressure difference between two locations in the model.

•

Group Goal – A Group goal is used when a goal is to be applied to a group of objects at the same time. In order to use a Group goal, all of the objects must be added to a Group by using the Groups command on the Edit menu.



Chapter 2 Using Goal Seek and Control 21 Object types For Point and Differential goal types, the object type indicates whether the goal is to be applied to a pipe or a junction object. If the goal is to be applied to a junction, the type of junction is selected from the list. For the Group goal type, the user must select between a Group Max/Min or a Group Sum object type. A Group Max/Min goal allows a single goal to be applied to a group of objects. The GSC module applies a Group Max/Min goal by ensuring the final goal value is either greater than or equal to (a Min goal) or less then or equal to (a Max goal) the specified value for each object in the group. For example, a Group Max/Min goal can be applied to ensure a minimum flow rate out of each spray discharge nozzle in a group of nozzles. Group Max/Min goals only work for groups where all group members are of the same type (i.e., all pipes or all valve junctions). A Group Sum goal is used to set the sum of the goal parameter for all the members in a group to a specified value. For example, the Group Sum goal can be applied to set the sum of the volumetric flow rates through all of the nozzles in a group of spray discharge nozzles to a particular value. Groups used in Group Sum goals can consist of pipes and/or junctions, with junctions of different type. Reviewing object input data If you would like to see the input data for the pipe or junction selected as a goal, press the right mouse button on the far left column in the Goals table. The inspection window will display, showing you the input data. This feature does not work for group goals. Editing object input data Similar to the inspection feature just described, you can open the Pipe or Junction Specifications window by double-clicking the far left column in the Goals table. From there you can change any data desired. This feature does not work for group goals.

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GSC data in Model Data When the GSC module is active, the Model Data window displays a list of all variables and goals in the General section. This is useful for documentation purposes. See Figure 2.6.

Figure 2.6

Model Data window shows the variable and goal input data.

GSC feedback during the solution Figure 2.1 depicted the logic flow when running AFT Fathom with goal seeking enabled. When a goal seeking model is run, the Solution Progress window displays additional information (Figure 2.7). As shown in Figure 2.7, at the far right is how many calls have been made to the Hydraulic Solver. This relates to the Figure 2.1 iteration loop from the Hydraulic Solver to the Numerical Optimizer, and how many times GSC has gone around the loop. The Best (Lowest) field shows the progress towards satisfying the GSC goals. As progress is made, this field will approach zero. This relates to



Chapter 2 Using Goal Seek and Control 23 the diamond in Figure 2.1 which checks goal convergence. This occurs when the Best (Lowest) value is sufficiently small. Number of calls to the Hydraulic Solver displayed here As progress is made, this should approach zero

GSC information displayed on this line

Figure 2.7

The Solution Progress window shows additional information when a GSC model is run.

GSC data in output When the GSC module is active and goal seeking is enabled, the Output window displays a GSC Variables tab and GSC Goals tab in the General section (see Figure 2.8). If the goal seeking was successful, the GSC Goals tab (Figure 2.8 bottom) should show the “Actual Goal Value” (i.e., the result from the hydraulic solution) close or equal to the “User Goal Value” specified in the Goal Seek and Control Manager. If the Actual Goal Value and User Goal Value differ significantly, the user is given a warning. This can occur for a variety of reasons, and is discussed in detail later in this chapter.

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24 AFT Fathom 7.0 Modules User’s Guide The GSC Variable tab (Figure 2.8 top) shows the input values that must exist in order to satisfy the goals.

Figure 2.8

Output window shows the solved variable values and the user’s goal and actual solved goal values.

Changing input values to GSC results As discussed previously, the Output window GSC Variables tab (Figure 2.8 top) indicates how the input parameters must be varied to satisfy the goals. Once you have these results, you may want to keep and use them in the model. There are two ways to do this: Transferring Results to Initial and generating a Disconnected Scenario.

Transferring results to initial In general, the Output window supports a feature called “Transfer Results to Initial Guesses”. This is available on the Edit menu. When used without the GSC module, it transfers calculated results for flow, pressure and temperature to the initial guess values of the pipes and junctions. When used after a GSC run it gives you three options: to transfer the GSC Variable Data, the calculated results, or both (see Figure 2.9). If you choose either of the first two options that transfer GSC Variable Data, the junction data on the Specifications window will be changed to the GSC Variable results (i.e., Figure 2.8 top). This means that one could



Chapter 2 Using Goal Seek and Control 25 then choose to Ignore goal seeking, rerun the model, and obtain the same results as before.

Figure 2.9

Transfer Results window opened from the Output window Edit menu allows users to transfer GSC Variable data back to the input fields

Generating a disconnected scenario Scenarios and Scenario Manager are discussed in depth in the AFT Fathom 7.0 User’s Guide. After a run is complete, a special type of scenario can be created called a disconnected scenario. A disconnected scenario itself breaks the inheritance of normal child scenarios so that it is a truly standalone scenario. This is ideal for GSC results in that it may not make sense to save the GSC results for future use if the model can otherwise be changed in arbitrary ways. For if it were changed, the GSC results would be invalidated, meaning the user would need to rerun GSC. For example, assume a GSC run is made to find the valve open position required to achieve a certain flow. If this result is saved, and then the pipe size is later changed, the valve open position would no longer supply the desired flow. The pipe size could be changed, for instance, within the particular scenario or perhaps in an ancestral scenario. What one may want in such cases is to preserve the GSC results and all input data that accompanied it. That is the purpose of the disconnected scenario. Disconnected scenarios cannot be changed by other scenarios, but only in the disconnected scenario itself.

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26 AFT Fathom 7.0 Modules User’s Guide To create a disconnected scenario, in the Output window choose Generate Disconnected Scenario from the View menu or Toolbar.

When goals cannot be achieved In some cases the GSC module may not be able to achieve a goal. This can happen for the following reasons: 1. A goal is not physically realistic 2. A better starting point is needed for the input values assigned as GSC Variables 3. Hydraulic solution tolerances or optimizer numerical parameters require adjustment In such cases, the goal will not be satisfied in the results. In other words, the Actual Goal Value and User Goal Value will differ (Figure 2.8 bottom). In all cases the user will be warned when goals were not met. Figure 2.10 shows the Output window with such a warning.

Figure 2.10

Warning display in Output window when a goal cannot be met.



Chapter 2 Using Goal Seek and Control 27

Physically unrealistic goals It may be possible that a goal is not achievable because it is not physically possible. For example, a pump may be too small to satisfy a flowrate goal at some pipe. To determine whether a goal is unrealistic, try changing the goal and rerunning the model. If the goal can be met in some cases and not others, this is an indicator that the original goal was unrealistic.

Better starting point needed In some cases the goal may be so far away from the original model that the GSC module has difficulty finding a solution. This is not common, but it is worth trying to adjust the starting point of parameters which are being varied.

Changing control parameters The Numerical Optimizer determines goal search directions by approximating a gradient based on perturbed variable values. By default it uses a central difference approximation, but forward difference can also be used. If the hydraulic solution is not converged to a sufficiently small tolerance, the gradient approximation will not be sufficiently accurate and hence a good search direction cannot be obtained. The end result is that the goal seeking fails. There are two general areas that can be changed in such cases: the hydraulic solution tolerances in Solution Control, and numerical control parameters in the Goal Seek and Control Manager. In the next few sections recommendations on how to manually change these parameters will be given. However, before making a manual change it is definitely worth trying the automated parameter adjustment feature. Figure 2.10, bottom picture, shows the warning when a goal is not met, and also shows a recommendation and suggests pressing the “F2” key. When doing so, a window appears as shown in Figure 2.11. This window will offer up to three options for automatic parameter adjustment. It is typically a good idea to accept the default changes, click OK, and rerun the model.

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28 AFT Fathom 7.0 Modules User’s Guide The purpose of the Figure 2.11 window is to simplify for the user making common changes to resolve goal seeking problems.

Figure 2.11

When goal seeking fails, pressing the F2 key will show this window which allows the user to automatically implement recommend numerical parameter adjustments.

Caution: The user should be very cautious in manually changing parameters in Solution Control and the Goal Seek and Control Manager numerical control. Making changes without a good understanding of the parameters involved can lead to incorrect results. Changing tolerance in Solution Control By default AFT Fathom uses Relative Tolerance criteria set to 0.0001 (see Figure 2.12). Goal seeking convergence can sometimes be improved by reducing these values to 0.00001 or 0.000001. For a more in-depth discussion of Solution Control see the AFT Fathom 7.0 User’s Guide, Chapter 8.



Chapter 2 Using Goal Seek and Control 29

Figure 2.12

Reducing Solution Control tolerance criteria may resolve goal seeking difficulties.

Changing goal seeking numerical control Figure 2.13 shows the Numerical Control area of the Goal Seek and Control Manager, discussed earlier in this chapter. The most useful parameter one can adjust is the Relative Finite Difference Step Size. Using values between 0.01 and 0.001 are recommended. In some cases using a value as high as 0.1 may be tried.

What to do if the Solver gets stuck Figure 2.1 depicts the logic of how the Hydraulic Solver and Numerical Optimizer work together. Discussed earlier is the issue of physically unrealistic goals. Occasionally the user may have specified a goal which is in fact physically realistic, but in the process of going from a physically realistic starting point to a similarly physically realistic goal, a physically unrealistic system may be proposed by the Numerical Optimizer. What happens in such cases?

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Adjusting finite difference step size can resolve difficulties

Figure 2.13

Changing certain numerical control parameters in the Goal Seek and Control Manager may resolve goal seeking difficulties.

When performing goal seeking with the GSC module, AFT Fathom has been designed to gracefully handle such cases. One of two things will typically happen: 1. The Hydraulic Solver will experience a computational error 2. The Hydraulic Solver will not be able to converge In the first case, AFT Fathom does not stop and tell the user of the error, but instead sets an internal flag that the system used for the particular iteration that caused the error was a poor system and should not be considered further by the Numerical Optimizer. In other words, it skips the system that caused the error. This will happen in a way which is transparent to the user and requires no intervention. The second case is of more interest here. In this case the Hydraulic Solver gets stuck on one of the systems proposed by the Numerical Optimizer and cannot progress. The Hydraulic Solver will continue trying to converge until it reaches the iteration limit. Once it reaches that



Chapter 2 Using Goal Seek and Control 31 limit, it will react in a similar way to the first case above – it will set a flag and skip that system. However, the default maximum number of iterations is 50,000 (specified in Solution Control, Figure 2.14). It is perfectly fine for one to wait until this limit is reached and allow the AFT Fathom to handle the situation automatically, but depending on the size of the model it may take awhile to get to 50,000 iterations. In such cases it may be desirable to allow AFT Fathom to more quickly conclude the model will not converge by reducing the maximum iterations to something like 5,000. Tip: If the Hydraulic Solver appears to get stuck while performing a GSC run, you can pause the Solver, open the Solution Control window, and reduce the Maximum Iterations. The default value is 50,000. Depending on the model size, a reduced value of 5,000 may be appropriate.

Figure 2.14

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It may be desirable to reduce the Solution Control Maximum Iterations when performing goal seeking.

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GSC data differences across scenarios GSC variables and goals will appear in all scenarios. In other words, you cannot create a variable or goal that will appear in some scenarios and not others. However, the application of variables and goals can differ from scenario to scenario. This allows you to perform goal seeking with different variables and goals across scenarios.

Variable and goal application can differ between scenarios

Figure 2.15

Goal Seek and Control Manager allows one to apply and unapply variables and goals. The application of goals and variables can be modified between scenarios.



CHAPTER 3

Goal Seek and Control Example

This example demonstrates the fundamental concepts of the Goal Seek and Control (GSC) add-on module by way of example. The example shows how GSC can be used to size pumps as part of a system design process. A number of other GSC example model discussions are included in a Help file distributed with AFT Fathom called FathomExamples.hlp. It can be opened from the Help menu by choosing “Show Examples”. Note: This example can only be run if you have a license for the GSC module.

Topics covered •

Using Goal Seek and Control Manager

•

Defining GSC Variables and Goals

•

Using pump head rise as a GSC Variable

•

Using Group Max/Min goals

Required knowledge This example assumes that the user has some familiarity with AFT Fathom such as placing junctions, connecting pipes, entering pipe and



34 AFT Fathom 7.0 Modules User’s Guide junction specifications, global editing, and creating groups. Refer to the AFT Fathom User's Guide for more information on these topics.

Model file This example uses the following file, which is installed in the Examples folder as part of the AFT Fathom installation: •

Pump Sizing and Selection with FCV.fth (GSC Example Scenario) – AFT Fathom model file

Problem statement The piping for a heat exchanger system is being designed. The system will pump supply water from a tank pressurized to 10 psig with a liquid surface elevation of 5 feet to a receiving tank with a pressure of 30 psig and a liquid surface elevation of 10 feet. The heat exchangers operate in parallel. The flow through the heat exchangers is controlled to 100 gal/min by two flow control valves. There is a design requirement that the control valves have a minimum pressure drop of 5 psid. Use GSC to size the pump.

Step 1. Start AFT Fathom From the Start menu, choose AFT Products and AFT Fathom.

Step 2. Specify system properties 1. Open the System Properties window by selecting System Properties in the Analysis menu 2. On the Fluid Data Tab, select the AFT Standard database and then select “water at 1 atm” in the fluids available window 3. Click “Add to Model” to select water for use in this model 4. Type in 70 degrees in the fluid temperature box 5. Click “Calculate Properties”



Chapter 3 Goal Seek and Control Example 35 6. Select “OK”

Step 3. Build the model A. Place the pipes and junctions At this point, the first four items are completed on the Checklist. The next Checklist item is to “Define Pipes and Junctions”. In the Workspace window, assemble the model as shown in Figure 3.1.

Figure 3.1

Layout of pipe system for Pump Selection with Flow Control Valves Example

B. Enter the pipe data The system is in place, but now you need to enter the input data for the pipes and junctions. Double-click each pipe and enter the following data in the Specifications window (or use the Global Pipe Editing window): All of the pipes are Steel, with standard roughness and the following data:

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36 AFT Fathom 7.0 Modules User’s Guide Pipe

Length (feet)

Size

Type

P1

20

2 inch

Schedule 40

P2

50

2 inch

Schedule 40

P3

60

2 inch

Schedule 40

P4

20

2 inch

Schedule 40

P5

100

2 inch

Schedule 40

P6

20

2 inch

Schedule 40

P7

60

2 inch

Schedule 40

P8

20

2 inch

Schedule 40

P9

100

2 inch

Schedule 40

C. Enter the junction data J1 Reservoir 1. Name = Supply Tank 2. Tank Model = Infinite Reservoir (only visible if XTS module is enabled) 3. Liquid Surface Elevation = 5 ft 4. Surface pressure = 10 psig 5. Pipe Depth (on Pipe Depth and Loss Coefficients tab) = 5 ft J9 Reservoir 1. Name = Receiving Tank 2. Tank Model = Infinite Reservoir (only visible if XTS module is enabled) 3. Liquid Surface Elevation = 10 ft 4. Surface pressure = 30 psig 5. Pipe Depth (on Pipe Depth and Loss Coefficients tab) = 10 ft (for both pipes)



Chapter 3 Goal Seek and Control Example 37 J3 Tee 1. Elevation = 0 feet 2. Loss Model = simple J6 Elbow 1. Elevation = 0 feet 2. Type = standard J4, J7 Control Valves 1. Elevation = 0 feet 2. Valve Type = Flow Control 3. Flow rate = 100 gpm Using the Groups tool on the Edit menu, add the control valves to a group named Flow Control Valves. J5, J8 Heat Exchangers 1. Elevation = 0 feet 2. Loss Model = Resistance Curve 3. Loss Curve Data = 10 psid @ 100 gal/min J2 Pump 1. Elevation = 0 feet 2. Pump Model = Fixed Head Rise 3. Fixed Head Rise = 20 feet

D. Check if the pipe and junction data is complete Turn on Show Object Status from the View menu to verify that all the necessary data is entered. If so, the “Define Pipes and Junctions” checklist item will have a check mark. If not, the uncompleted pipes or junctions will have their number shown in red. If this happens, go back to the uncompleted pipes or junctions and enter the missing data. You can also open the List Undefined Objects window from the View menu to see what data is missing.

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Step 4. Open the Goal Seek and Control Manager The GSC data is entered in the Goal Seek and Control Manager window. Open the Goal Seek and Control Manager from the View Menu. After opening the Goal Seek and Control Manager, the user specifies all of the system variables, as well as the desired goals. The Goal Seek and Control Manager is shown in Figure 3.2 below.

Figure 3.2

The Goal Seek and Control Manager is used to define GSC Variables and Goals.

Step 5. Add a variable In the GSC module, variables are the parameters that AFT Fathom will modify in order to achieve the specified goals. In general there should be one applied variable for each applied goal. Select the Variables tab on the Goal Seek and Control Manager window. The Variables tab allows users to create and modify the system variables. The object and junction type are selected, then the name and



Chapter 3 Goal Seek and Control Example 39 number of the object to which the variable applies, and the object parameter that is to be varied are specified on the Variables tab. For this example, you will be adding a variable for the Pump Fixed Head Rise. Select the “Add Variable” button, and input the following variable data: 1. Apply: Selected 2. Object Type: Junction 3. Junction Type: Pump 4. Junction Number and Name: J2 (Pump) 5. Variable Parameter: Head Rise 6. Link To: (None) 7. Lower Bound: Leave Blank 8. Upper Bound: Leave Blank The Apply column allows users to specify which of the variables that have been defined will be used. This allows the flexibility of creating multiple variable cases, while only applying selected variables for any given run. The Link To column allows users to apply the same variable to multiple objects. This allows users to force parameters for several objects to be varied identically. Upper and lower bounds provide logical extremes during the goal search. For this case, leave the lower and the upper bounds blank. After entering the data, the Variable tab should appear as shown in Figure 3.3.

Step 6. Add a goal Goals are the parameters you want to achieve. The goals are achieved as AFT Fathom modifies the variables. Typically, there should be one applied goal for each applied variable.

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Figure 3.3

GSC Variables are parameters that are changed by AFT Fathom to achieve the defined goals.

Select the Goals tab on the Goal Seek and Control Manager window. The Goals tab allows users to create and modify the system goals. The goal type, object type, and the goal parameter are selected. A criterion for determining if the goal has been met is then specified, along with a value and units for the goal parameter. The user then selects the object to which the goal applies, and, if applicable, the location on the object at which the goal applies (e.g., the inlet or outlet of a pipe object). The Apply column allows users to specify which of the goals that have been defined will be used. This allows the flexibility of creating multiple goal cases, while only applying selected goals for any given run. A Group Max/Min goal allows a single goal to be applied to a group of objects. Fathom applies a Group Max/Min goal by ensuring the final goal value is either greater than or equal to (a Min goal) or less then or equal to (a Max goal) the specified value. For this example, a Group Max/Min goal will be applied to ensure the minimum pressure drop across the flow control valves is at least 5.0 psid.



Chapter 3 Goal Seek and Control Example 41 Create a new goal for the pressure drop across the flow control valves as defined below (if the option for a group goal is not visible you may have forgotten to create a group as discussed in Step 3c above): 1. Apply: Selected 2. Goal Type: Group 3. Object Type: Group Max/Min 4. Goal Parameter: Pressure Loss 5. Criteria: >= 6. Goal Value: 5 7. Goal Units: psid 8. Object ID: Flow Control Valves (this is the name of the group) 9. Object Location: NA After entering the data, the Goals tab should appear as shown in Figure 3.4.

Figure 3.4

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GSC Goals are the parameter values the user wants to achieve.

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42 AFT Fathom 7.0 Modules User’s Guide As variables and goals are added to a model, AFT Fathom will display symbols beside the pipes and junctions that have variables or goals applied to them. The default is a “V” for variables, and a “G” for goals. The goal symbol is not displayed next to objects that are part of a group goal. This is illustrated in Figure 3.5. These symbols can be configured on the Workspace Preferences window.

“G” symbols for GSC Goals are not displayed for Group goals.

“V” symbol for a GSC Variable.

Figure 3.5

AFT Fathom displays symbols next to objects on the Workspace that have goals or variables defined.

Step 7. View GSC settings in Model Data The Model Data window provides a summary of the GSC module variable and goal definitions. Once the variable and goal information has been added in the Goal Seek and Control Manager, the information is displayed on the Goal Seek and Control tab in the General section of the Model Data Window. Figure 3.6 shows the GSC variable and goal information as it was entered for this example.



Chapter 3 Goal Seek and Control Example 43

Figure 3.6

The Goal Seek and Control parameters defined in the Goal Seek and Control Manager are displayed in the General section of the Model Data window.

Step 8. Enable goal seeking After the GSC goals and variables have been defined, goal seeking must be enabled using the Analysis menu, as shown in Figure 3.7.

Step 9. Run the model Select Run Model in the Analysis menu. This will open the Solution Progress window. This window allows you to watch as the AFT Fathom Solver converges on the answer. Note: When using the GSC module there is an area displayed in Solution Progress that shows the specific progress of the GSC module. As it makes progress, the Best (Lowest) value will decrease towards zero. The field in the far right displays how many complete hydraulic solutions have been run. After completion, click the View Output button at the bottom of the Solution Progress window.

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Figure 3.7

Select “Use” from the Goal Seek & Control menu item on the Analysis menu to instruct AFT Fathom to do goal seeking when it runs.

Step 10. Examine the results The Output window contains all the data that was specified in the Output Control window. The results of the GSC analysis are shown in the General Output section. The GSC Variables tab shows the final values for the variable parameters, as shown in Figure 3.8. The GSC Goals tab shows the values achieved for the goals, as shown in Figure 3.9.



Chapter 3 Goal Seek and Control Example 45

Figure 3.8 The final GSC Variable values are shown on the GSC Variables tab in the Output window General section.

Figure 3.9 The final GSC Goal values are shown on the GSC Goals tab in the Output window General section. The Actual and User values should be close if GSC was successful. If not, a warning will appear.

Analysis summary For this example, the minimum goal of 5 psid pressure drop across the flow control valves was achieved by applying a Group Max/Min goal. The pump head requirement for the example system was determined to be 167.3 feet, as shown in Figure 3.8. The pump head requirements for this system could also be determined without GSC by adjusting the pump head rise, and running multiple Fathom solutions until the minimum control valve pressure drop requirement was met. Alternatively, one could change the pump to a fixed flow pump, and allow Fathom to calculate the pump head requirement directly. However, this technique results in a reference pressure problem between the assigned flow pumps, and the flow control valves. To bypass this problem, one of the flow control valves must be changed to a constant pressure drop valve with a 5 psid pressure drop, until a pump head could be determined. By using the GSC module to size the pump, the head requirements can be determined directly without user iterations or modifications to the flow control valves.

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CHAPTER 4

Modeling Extended Time Simulation

This chapter discusses how one uses the XTS module to model transient system behavior. Detailed information regarding XTS menus and functionality is given in this chapter. Chapter 6 provides a detailed hands-on XTS example.

What is the XTS module? While steady-state modeling answers many design questions, some questions cannot be adequately answered without considering how systems behave over time. Questions such as how long it will take to fill a tank require a dynamic system model. The AFT Fathom XTS module answers such questions. The XTS module allows you to model transient system behavior. Users can specify the time duration of the simulation, time step size, control system parameters, and how components such as pumps and valves operate over time. Operations such as valve position changes can occur during a specified time schedule, or can occur in response to events in the system thereby simulating control system actions. Users can also specify tank volume on “finite” tanks, so that tank draining and filling can be simulated. Tanks can be open or pressurized, with the gas pressure automatically calculated as the liquid level changes. The XTS module is a powerful tool which extends AFT Fathom’s powerful modeling capabilities into the dimension of time.




How does the XTS module work? The XTS module can be described as using a lumped or quasi-steady approximation to time simulation. What it in fact does is represent the transient system behavior as a sequence of pseudo-steady-state solutions. In between each pseudo-steady-state solution it adjusts transient parameters, performs mass balances on tanks, and changes component operations as specified by the user. As a thought experiment, consider a system which you want to simulate for ten minutes in one minute increments. This would require eleven time step solutions (time zero and each minute up to ten). You could manually do this with standard AFT Fathom by running a steady-state model eleven times, and in between each run adjusting the input parameters for the next run based on the results of the previous run. The XTS module automates this manual process. Besides the automation benefits, the XTS module offers additional benefits such as transient output data management, consolidation and display, and graphing tools to review the transient results.

Using the XTS module The user has the option of activating or not activating the XTS module when AFT Fathom first loads. After AFT Fathom is loaded, the XTS module can be activated or deactivated for use from the Options menu. Whether or not XTS is activated impacts the Analysis menu, Checklist and Status Bar and multiple other AFT Fathom functions. If the XTS module is active, the user can still run models in Steady Only mode by selecting this under Time Simulation on the Analysis menu. Hence there are three possibilities for XTS. 1. XTS is not active 2. XTS is active and operated in Steady Only mode 3. XTS is active and operated in Transient mode Table 4.1 lists the three possibilities and the impact on various AFT Fathom features.



Chapter 4 Modeling Extended Time Simulation 49 Table 4.1

AFT Fathom feature accessibility based on XTS activation and Time Simulation mode

XTS Not Active

XTS Active

XTS Active

No Mode

Steady Only Mode

Transient Mode

Not Visible

Visible

Visible

"Transient Control" on Analysis Menu

Not Visible

Visible but disabled

Visible and enabled

"Transient Control" on Checklist

Not Visible

Visible but disabled

Visible and enabled

"Transient Control" on Status Bar

Not Visible

Not Visible

Visible

Feature "Time Simulation" on Analysis Menu

"Transient" tab on Junction Specifications Windows

Visible - data can be Visible - data can be Not Visible - data entered but will not be entered and will be cannot be entered used used

Transient Pipe and Jct tabs in Output Control

Not Visible

"Transient" tab in Junction Section of Model Data

Not Visible

Time control slider and buttons in Output window

Not Visible

Not Visible

Visible

Time control slider and buttons in Visual Report

Not Visible

Not Visible

Visible

"Transient" tabs on Output Window

Not Visible

Not Visible

Visible

"Transient" tab on Select Graph Data

Not Visible

Not Visible

Visible

Animation controls on Graph Results

Not Visible

Not Visible

Visible when selected

Visible

Visible

Visible only if junction Visible only if junction transient data exists transient data exists

Enabling XTS transient mode When the XTS module is active, two new menu items appear on the Analysis menu. At the top of the Analysis menu is the Time Simulation menu, from which the user can select “Steady Only” or “Transient”.

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50 AFT Fathom 7.0 Modules User’s Guide The XTS Transient analysis mode is enabled by selecting Time Simulation -> Transient from the Analysis menu (Figure 4.1). This can be selected before or after a model is built. Pre-existing models built with standard AFT Fathom can be opened with XTS and transient data added. Transient modeling can be turned off at any time by selecting Steady Only from the same menu. The Steady Only mode causes the XTS module to function like standard AFT Fathom. One difference is that users can still enter transient data and this data is retained in the model. If the model is opened in standard AFT Fathom, this data will be lost. Table 4.1 relates the differences between not using XTS and using it in Steady Only mode. When the Transient analysis mode is selected, the Transient Control option on the Analysis menu is enabled. Transient Control is a required Checklist item when in Transient analysis mode. In Steady Only mode the Transient Control menu item is visible but disabled and thus not required.

Figure 4.1

Transient mode is enabled from the Analysis menu.



Chapter 4 Modeling Extended Time Simulation 51

Transient control window When the XTS module is in Transient mode, the Transient Control menu option is enabled on the Analysis menu. This becomes one of the Checklist items, and hence the user must enter data in Transient Control. The transient simulation is controlled by information the user enters in the Transient Control window (see Figure 4.2). This window is used to specify the duration of the transient simulation, the size of the time step, and the frequency of the data saved to the transient output file.

Figure 4.2

The Transient Control window is used to specify the transient run parameters.

Also available is Forward Difference and Central Difference options for Finite Tank Liquid Level Adjustments. If finite tank reservoirs are not

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52 AFT Fathom 7.0 Modules User’s Guide used in the model, then there is no difference between the two options. The impact when one or more finite tanks do exist is discussed later in this chapter.

Entering junction transient data Transient data may be entered in the Transient tab on the Specifications windows for junctions which can have transients defined. A typical Transient tab is shown in Figure 4.3 for a Valve junction. Table 4.2 lists the different types of junction transients that can be modeled. In most cases, transient data can be entered as absolute values or as a percentage of steady-state. The distinction is made when choosing between Absolute Values and Relative to Steady-State Value (Figure 4.3).

Figure 4.3

Example Transient tab on Valve Specifications window.

The first data point always needs to match the steady-state value which is usually entered on the tab at the far left. If, for example in Figure 4.3, the steady-state data for Cv of 200 is changed to 250, the transient data will also need to be changed. However, if in Figure 4.3 the Relative



Chapter 4 Modeling Extended Time Simulation 53 option is specified, the first data point would be 100%, and if the steadystate Cv is changed from 200 to 250 there is no need to change the transient data since the first data point is still 100%. But it is now relative to a different steady-state value. Initiating transients There are four ways to initiate transients. Time based transients are based on the absolute simulation time. Single event transients are initiated by one event such as a pressure, tank liquid level, or other parameter at a specified location. Dual Event Cyclic events initiate transients in a repeating cycle based on two event parameters. Dual Event Sequential events initiate two transients that do not repeat. Table 4.2

Types of junction transients that can be modeled

Junction Type

Transient Parameters Modeled

Assigned Flow Assigned Pressure Branch Control valve Pump Reservoir Spray Discharge Three-Way Valve Valve

Flow rate Pressure Flowrate source or sink Setpoint Speed, flow rate, head rise, control setpoint Liquid level, surface pressure Flow area Position K, Cv or open percentage

Once the type of transient initiation is selected, the transient data for the component must be entered in the table, as appropriate. See the “Time and Event Transients” chapter for more details. Repeat transient If the transient data is periodic, you can enter the data for one cycle of the period and then tick the check box for Repeat Transient. This will cause the one cycle of transient data to be repeated once it has reached the end. The repetition will continue until the end of the simulation. Transient Special Conditions There may be occasions where, once having entered the transient data, you do not wish the transient to activate for a particular case. One option

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54 AFT Fathom 7.0 Modules User’s Guide is to just delete the transient data. A second option is to specify the Transient Special Condition as Ignore Transient Data. In such a case, the data can be left in the window for future use, but will not activate during the run. This is discussed further later in this chapter.

Entering reservoir volume data When running AFT Fathom in Steady Only mode (or without the XTS module), each reservoir junction is considered an infinite reservoir. This means that the liquid heights and surface pressures entered are constant. When running transients, reservoirs can be either infinite or finite. Similar to Steady Only mode, an infinite reservoir maintains its level during the transient. The differences are discussed below and summarized in Table 4.3.

Infinite reservoirs Infinite reservoirs refer to a massive body of fluid whose surface level does not change appreciably as a result of liquid inflow or outflow during the time frame of the simulation. An example is a large lake or the ocean. Figure 4.4a shows a Reservoir junction modeled as infinite.

Finite reservoirs Finite reservoirs (also called finite tanks) refer to a body of fluid which is small enough that its surface level changes significantly during the time frame of the simulation as a result of liquid inflow or outflow. An example is a tank which drains as the simulation progresses. Tanks can have constant cross-section (e.g., a pure vertical cylinder) or tank crosssection can change with height. When the cross-section changes, the tank volume at each height data point must be specified. Finite tanks can further be broken down into open or closed tanks.



Chapter 4 Modeling Extended Time Simulation 55 Table 4.3 Reservoir Junction Configuration

Various possible inputs with infinite and finite Reservoir junctions

Tank Volume Needed?

Initial surface level known?

Initial surface pressure known?

Infinite

No

Yes

Yes

Finite - Open Tank Initial Liquid Level Known

Yes

Yes

Yes

Calculated

Constant or User Specified

Finite - Open Tank Initial Liquid Level Unknown

Yes

No

Yes

Calculated

Constant or User Specified

Finite - Closed Tank Initial Liquid Level Known

Yes

Yes

Yes/No

Calculated

Calculated from PVn

Finite - Closed Tank Initial Liquid Level Unknown

Yes

No

Yes

Calculated

Calculated from PVn

Surface level over time

Surface pressure over time

Constant or User Constant or User Specified Specified

Finite open tanks Finite open tanks are open to the atmosphere or some other fixed surface pressure. Typically open tanks have a constant surface pressure with time, although users have the latitude to pre-specify time varying surface pressure. Figure 4.4b shows a Reservoir junction modeled as a finite open tank. Finite closed tanks Finite closed tanks are tanks in which, as the liquid level changes, the gas above the liquid expands or contracts and hence its pressure changes according to the gas thermodynamic laws. For closed tanks the user specifies the initial liquid level and gas pressure, but during the simulation all gas pressure and liquid levels are calculated by AFT Fathom. Figure 4.4c shows a Reservoir junction modeled as a finite closed tank.

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Figure 4.4a

Reservoir junction modeled as infinite

Figure 4.4b

Reservoir junction modeled as finite open




Figure 4.4c

Reservoir junction modeled as finite closed

Known parameters initially In some cases the liquid level may not be known initially when modeling finite tanks. An example would be a vertical standpipe. At time zero the net flow at the standpipe would be balanced, and the liquid surface would find its own level (this would equal the local hydraulic gradeline). Hence the initial liquid level would be calculated based on equilibrium. However, under transient conditions the liquid level will change, and the liquid volume in the standpipe can significantly affect pipeline behavior. This is the purpose of the features in the Known Parameters Initially area (see Figure 4.4b). By default, both the initial liquid level and initial surface pressure are assumed known. If you want to model one of them as unknown initially, clear the check box. You must have at least one of the two selected as known. If the surface pressure is selected as unknown initially, it functions similarly to the unknown liquid level except initial equilibrium surface pressure would be calculated.

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58 AFT Fathom 7.0 Modules User’s Guide This feature only affects the calculation at the initial “zero” time step. For all other time steps, the junction behaves the same as a junction in which the liquid level and surface pressure are known initially.

Entering reservoir transient data Infinite reservoirs For an infinite reservoir, the liquid level or surface pressure can be varied over time according to a user specified transient profile (see Table 4.3). This is input on the Transient tab (see Figure 4.5).

Figure 4.5

Infinite reservoirs can have user specified time varying liquid level or surface pressure.

Finite open tanks For a finite open tank, the surface pressure can be varied over time according to a user specified transient profile (see Table 4.3). This is input on the Transient tab (see Figure 4.6).



Chapter 4 Modeling Extended Time Simulation 59 Finite closed tanks For a finite closed tank with a maximum allowable pressure (this is a relief pressure), the relief pressure can be varied over time according to a user specified transient profile. This is input on the Transient tab.

Figure 4.6

Finite tanks can have user specified time varying surface pressure.

What happens when finite tanks overflow? As the transient progresses finite tanks can fill up. If the tank is open, then it is possible for the liquid to reach the top. How does AFT Fathom handle this? When a finite tank liquid level reaches the top, it is assumed that the liquid spills over the top. Hence the liquid height is maintained at the top of the tank. Note that this causes a loss of mass from the system model. If the tank is closed, the gas pressure will increase as the tank fills. Thus the tank cannot overflow. If the tank has a maximum pressure (which

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60 AFT Fathom 7.0 Modules User’s Guide represents a relief line) then it is possible for the liquid mass to be lost as it would ostensibly flow out the relief line. The liquid level in the tank would then be maintained at the top of the tank.

What happens when finite tanks drain? When a tank drains to the bottom, it cannot supply any more liquid to the connected pipes. The system behavior after a tank has drained cannot be accurately modeled by AFT Fathom. In a real system, and in the absence of a valve to stop the flow, a drained tank which continues to flow would result in the connected pipes themselves draining and a gas/liquid interface moving down the pipes. AFT Fathom assumes all pipes are liquid full, and cannot model draining pipes. Since it is not desirable in most applications to have the pipes drain, this limitation is not a significant issue. The user can, for example, use a valve in the pipe which closes when the tank drains. This would use an event transient. Since AFT Fathom cannot model a tank after it has drained, what does it do? Rather than halt the transient run, which would not be very helpful to the user, AFT Fathom assumes the connecting pipe “turns off” when it no longer has liquid to supply it. To implement this, AFT Fathom sets the pipe’s Special Condition so that it turns the pipe off.

What happens when pipes are uncovered? AFT Fathom allows multiple pipes to connect to a reservoir, all at different elevations. As a tank drains, pipes may be uncovered. AFT Fathom handles this in the same manner as described above for completely drained tank. If a pipe is uncovered, then there are two possibilities: 1. Liquid flows from the pipe and into the tank – AFT Fathom can model this case. The liquid free falls to the liquid surface, and appropriate boundary conditions are used to solve the system. 2. Liquid tries to flow from the tank and into the pipe – AFT Fathom cannot model this case. Since the pipe is not covered by liquid, then the tank cannot supply liquid to the pipe and in reality the pipe itself would drain. AFT Fathom does the same thing as described above for a completely drained tank – it sets the pipe flow to zero.



Chapter 4 Modeling Extended Time Simulation 61 Important: When a tank drains completely or sufficiently to uncover a pipe, AFT Fathom cannot adequately model the system behavior after this point unless a valve is used to stop the flow into the pipe. AFT Fathom will warn the user when this happens.

Interpreting pipe depth and elevation data When specifying pipe data at reservoirs, the pipe connection can be specified as either a depth below the liquid surface or an absolute elevation. If the liquid level changes, what is the impact on pipe depth and/or elevation? Before a transient run is started, AFT Fathom converts all pipe connection data into absolute elevations. If depth data is entered, the absolute elevation is determined from the user’s definition of bottom tank elevation (which is absolute), liquid level (which may be absolute or relative to the bottom of the tank), and pipe depth below the liquid surface. In summary, the user does not have to be concerned about AFT Fathom misinterpreting pipe depth data. Tip: Since transient models allow the liquid level to change, and the user may desire to run different scenarios with different initial liquid levels, it is better to specify reservoir pipe connections based on elevation and not depth.

Maximum and minimum pressures in closed tanks As shown in Figure 4.4c, a closed tank allows the user to specify maximum and minimum pressure. This is the pressure of the gas in the tank. The purpose of maximum and minimum pressure is to simulate relief and vent systems in the tank which represent over and underpressurization.

Transient data in Model Data window Junction transient data is displayed on the Transient tab in the Junction section of the Model Data window (Figure 4.7). As related in Table 4.1, this tab is only visible if transient input data exists.

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Figure 4.7

Transient input data is displayed in the Junction section of the Model Data window.

Solution progress window with XTS When the XTS module is run in Transient mode additional information is displayed on the Solution Progress window as shown in Figure 4.8. Some basic Transient Control information is displayed relating to the Stop Time and Time Step. The progress of the transient simulation is shown in a progress bar so you can see how much of the simulation has been completed. When the progress reaches 100% the transient simulation is finished. You can click the View Output button to view the results.




Transient control parameters are displayed for information

Transient progress bar shows how much of the transient run has been completed

Figure 4.8

Solution Progress window shows additional information when running an XTS Transient simulation.

Transient control difference methods The Transient Control window was discussed earlier in this chapter. One feature not discussed is the forward and central difference options (see Figure 4.2). The forward and central difference options are only relevant when finite tanks are modeled. They relate to what liquid levels are used in the tank for each time step calculation. If the assumed time step is small enough, then the two methods yield virtually the same results. However, as the time step is increased, the central difference method is much more accurate. The drawback is that the central difference method is iterative and takes more computation time.

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Forward difference method The forward difference method solves the pipe system as if all tank levels remain at the same value as the beginning of the time step. Since the liquid level is known at the beginning of the time step, no time-based iterations are required. (The iterations for flow and pressure common to steady-state modeling still occur. These are discussed in the AFT Fathom 7.0 User’s Guide). Once the solution is complete for the time step, the solved flowrates are used to update the tank liquid level for the next time step. Figure 4.9 depicts how this works. Since in reality the tank level changes during the time step, precision is lost by using the liquid level at the beginning of the time step. As discussed earlier, making the time steps shorter helps alleviate this problem.

Tank Liquid Level

Forward Difference Method

Liquid Level Used for Calculation Actual Liquid Level

Time Steps

Figure 4.9

Forward difference method for time calculation assumes liquid level stays constant during each time step, allowing a direct calculation for each time.

Central difference method The central difference method solves the pipe system using tank liquid levels which represent the average over the time step (see Figure 4.10).



Chapter 4 Modeling Extended Time Simulation 65 Since the liquid level changes during the time step, it is more accurate to use the average over the time step. However, the difficulty is that the average is taken between the liquid level at the beginning and end of the time step and, while the liquid level is known at the beginning, it is not known at the end. That is what we are trying to solve for. Hence the transient solution must assume a liquid level at the end of the time step and iterate on that value until convergence.

Tank Liquid Level

Central Difference Method Actual Liquid Level Liquid Level Used for Calculation

Time Steps

Figure 4.10

Central difference method for time calculation uses average liquid level during time step for calculation, requiring iteration for each time.

There are several iteration control parameters needed by the central difference method, and these are input in the Transient Control window (Figure 4.11). The central difference method attempts to converge on the liquid height at the next time step for each finite tank. Relative and absolute tolerance The relative and absolute tolerance inputs influence when AFT Fathom concludes it has converged on the new liquid height. Both of these criteria are applied, and if either one is satisfied then convergence has occurred.

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Figure 4.11

Iteration control parameters are required for by the central difference method

The relative criteria is how much the liquid level calculation changes between iterations on a relative, or percentage basis. The absolute criteria relates how much the liquid level changes between iterations on an absolute basis of height. Hence the absolute tolerance has units of length associated with it. The default values for relative tolerance is 0.00001, and the absolute tolerance is 0.0001 feet.



Chapter 4 Modeling Extended Time Simulation 67 Relaxation The relaxation applies to how fast AFT Fathom allows the liquid level to change during time steps. For a general discussion of relaxation see Chapter 8 of the AFT Fathom User’s Guide. Relaxation values must be greater than zero and less than or equal to 1. By default a value of 1 is used. This in fact means no relaxation. Setting values closer to zero will improve convergence but slow the calculation. Values less than 0.01 should never be used unless directed by Applied Flow Technology. Caution: The iteration control parameters for central difference time calculations should not be changed by the user unless they clearly understand their use or it has been recommended by Applied Flow Technology support. If changed indiscriminately, there is a danger of incorrect results being generated. Maximum iterations This is the maximum number of attempts allowed for each time calculation iteration. If it reaches this value, the transient solution will stop due to failure to converge. Changing parameters during the run As shown in Figure 4.8, the Solution Progress window displays while the transient simulation is being performed. If a central difference method is used, because of its iterative nature the simulation can get stuck. If this happens then the simulation can be paused and Transient Control parameters changed (such as reducing the relaxation parameter). With forward difference there are no parameters to change and hence this option is not available.

Output values displayed with forward difference One advantage of the forward difference method is that it is easier to reconstruct the calculation for a given time step. For example, assume you want to run a separate steady-state AFT Fathom model to represent a particular time step calculation.

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68 AFT Fathom 7.0 Modules User’s Guide To do so, just look at the reservoir levels for that time step, enter these as the reservoir levels in the steady-state model, and all results should be the same as in the transient solution.

Output values displayed with central difference When using the central difference method a somewhat strange result is that the reservoir liquid levels displayed in the output are never directly used to solve any time step (except for the initial “time zero” step). As discussed earlier, each time step is solved using an average liquid level. But this average liquid level is not displayed in the output. Instead, the liquid levels upon which the average was derived are displayed. This is depicted in Figure 4.12 where the liquid levels in the output do not correspond directly with the assumed liquid level for calculation. If for some reason you would like to construct a steady-state model to represent a time step from a transient simulation which used central difference, you must enter reservoir liquid levels which are the average of the desired time step and the previous time step.

Tank Liquid Level

Central Difference Method Actual Liquid Level Liquid Level Used for Calculation

Liquid Levels Displayed in Output

Time Steps

Figure 4.12

The squares represent the actual liquid level output values for central difference. Note that the squares do not correspond directly to the line representing the assumed liquid level for calculation.




Transient data in Output window During a transient run output data is saved to an auxiliary file in the input model’s folder. The file name is based on the input file name and uses the “.out” file extension. A numerical value is added to distinguish output among different scenarios. Output can be reviewed in the Output window, Graph Results window, or Visual Report. In the Output window, transient data is displayed in two ways as discussed next.

Detailed results for a time step When an XTS Transient mode run is complete, results are displayed in the Output window similar to steady-state runs. However, the pipe and junction output tables can only display data for one time step at a time. Initially the first time step is displayed. A slider bar and buttons at the bottom of the window allow the user to adjust the currently displayed time step (Figure 4.13). Tip: The units and format of time on the slider can be modified in the Output Control window on the Format and Action tab. The data displayed is the same as that traditionally configured in the Output Control window on the Display Parameters tab.

Transient results for all time steps Also available in the Output window are Transient tables which display data for all time steps in the same table (Figure 4.14). This data is configured in the Output Control window on the Display Parameters tab. The buttons at the top of this tab allow one to select the steady and transient table configuration. The displayed data has expand/collapse buttons for each pipe and junction (Figure 4.15) to allow easier navigation of output. Note: XTS Transient models support “accumulated” output parameters. These are integrated values over time for parameters such as flow or power, and are available in most pipe and junction output tables.

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Figure 4.13

Time slider at bottom (currently at 30 seconds) allows user to change time step of displayed results. Time is also shown at the top left of each table, as circled.

Quick graphs The Quick Graph feature can be used to conveniently plot transient data for quick examination. To use the Quick Graph feature, place the mouse cursor over the column of transient data you wish to examine. Then, right click with the mouse, and select Quick Graph from the list of options. Figure 4.16 illustrates how to do this for J10 Reservoir Liquid Height vs. Time. Figure 4.17 shows the resulting graph. The graph illustrates how the liquid level in the Reservoir rises with time. The Quick Graph necessarily has limited functionality. In contrast, the Graph Results window may be used to create a full range of graphs related to the XTS transient output.




Figure 4.14

The Transient tabs in the Pipe and Junction sections show results for all time steps. The first number in the left column is the pipe/junction number and the second (in parentheses) is the time (in minutes here). The tables can be expanded or collapsed.

Figure 4.15

The transient summary tables (such as Reservoir Transient above) can be expanded or collapsed to improve viewability.

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Figure 4.16

The Quick Graph feature can be accessed from any transient data column using the right mouse button.

Figure 4.17

The Quick Graph feature can be used to quickly plot transient data from the Output for review.




Transient Graph Results Transient data can graphed in two general ways: Profile graphs and transient graphs.

Profile graphs Profile graphs show results where the distance along the pipe is the independent, x parameter (Figure 4.18). If the pipes are connected, a sequence of pipes can be graphed in the profile. Profile graphs can only show data at a particular time or show overall maximum and minimum values for all times (Figure 4.19). Profile graphs can be created for one or more pipe sequences. Note that the x-axis on profile plots is cumulative distance along the pipe sequence. Multiple profiles can be plotted simultaneously using the Groups on the Edit menu.

Figure 4.18

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Transient graphs can show several types of output. Here a profile plot for a pipe sequence for pressure is to be generate.

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Figure 4.19

Transient max/min profile plot for pressure as specified in Figure 4.18.

Animation of output Another useful feature of profile graphs is that they allow animation of the output results. Animation is selected in the Select Graph Data window (Figure 4.18) and, when selected, reveals additional control features on the Graph Results window (Figure 4.20). At the left is the Play button, which starts the animation. Next to it are the Pause and Stop buttons. If the Pause button is pushed, the animation stops at that time step. One can print the graph or copy the data if desired or use the time slider controls (to the right of the Stop button) to set the time forward or backwards. The Stop button stops the transient and resets the time to zero. The current time (in seconds) and time step are shown to the right of the time controls. At the far right are the speed controls. Slowing the animation involves adding time delays to the data display. Increasing the speed involves skipping time steps. The default speed, right in the middle, has no delays or skips.



Chapter 4 Modeling Extended Time Simulation 75 If plotting a single path using the list of pipes in Select Graph Data, one can cross-plot on the animation design alerts (in Profile Along a Flow Path) or steady-state results (in EGL, HGL and Elevation Profile).

Figure 4.20

Animation in Graph Results displays additional controls to play and review the animation.

Transient graphs Transient graphs show how parameters vary with time (see Figures 4.21 and 4.22). Here the x-axis is time (rather than distance as in profile graphs) as shown in Figure 4.19 and 4.20. Traditional Pump vs. System Curve plots will create plots for the first time step (i.e., time zero) only. If the user wants to create a pump vs. system curve plot for some other time step, follow these steps: 1. Set the model Stop Time in Transient Control to the time for which a pump vs. system curve is desired. 2. Run the model. 3. Create a “Disconnected Scenario” using features on the View menu and Toolbar. This will create a child scenario with input data set equal to the final time step.

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76 AFT Fathom 7.0 Modules User’s Guide 4. Load and run the disconnected scenario and create the pump vs. system curve there.

Figure 4.21

Transient graphs can shown how parameters vary with time. Here the Reservoir Junction #2 liquid height is to be plotted. The generated plot is shown in Figure 4.22.

Transient Visual Report The Visual Report data will be displayed at a selected time. The slider bar and buttons at the bottom of the Visual Report work the same as the Output window time selection controls (Figure 4.13). When the user changes the current time, the displayed values change as well. In addition, color maps are updated when in use. As shown in Figure 4.23, the current time is displayed in the lower left by the time adjustment buttons, as well as on the Visual Report itself. The display on the Visual Report can be turned on and off on the Visual Report Control window as shown in Figure 4.24. It is helpful to have the time on the Visual Report when it is printed.




Figure 4.22

Transient graphs show how parameters vary with time. Here the Reservoir Junction #2 liquid height is plotted as specified in Figure 4.21.

Special conditions Some junctions have Special Conditions that alter the normal state of the junction. These are discussed in the AFT Fathom 7.0 User’s Guide. The junctions that have special conditions set are shown using a special symbol before the ID number (an “X” by default). This symbol can be customized in the Workspace Preferences window. Special conditions with no transient data If a Special Condition is applied to a junction without any transient data, then the transient solution will retain the Special Condition. For instance, if a Special Condition is set for a valve junction, the steadystate solution will solve with the valve closed. In addition, the transient solution will run the entire simulation with the valve closed as well

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78 AFT Fathom 7.0 Modules User’s Guide because there is no transient data entered which implies the valve state is not intended to change.

Time slider and time controls adjust display time

Currently displayed time can be shown for printing purposes

Figure 4.23

Visual Report has additional time adjustment controls when in AFT Fathom is in Transient mode.

Special conditions with transient data If a Special Condition is applied to a junction that has transient data, then the transient solution will ignore the Special Condition. It is then incumbent upon the engineer to relate the Special Condition to the initial transient data. For instance, assume the user wants to simulate the transient that occurs during a valve opening. The steady-state solution will have the valve closed, and this is modeled by using a Special Condition for the valve junction. In such a case, the Cv data entered on the valve junction's Loss Model tab will be ignored. On the Transient tab, a transient can be entered. The first data in the table should then be Cv = 0, which corresponds to a closed valve. From there the Cv can be increased above zero as desired to open the valve.




Figure 4.24

Visual Report Control allows you to display time on the Visual Report when in Transient mode.

If the user were to keep the Cv equal to zero, then that would be equivalent to the previous case where the user set the Special Condition but did not enter any transient data. Pump special conditions Pump Special Conditions are slightly more complicated than for valves. In fact, pump junctions have two types of Special Conditions. The first is to turn the pump off and have no flow through it. This is called “Pump Off No Flow”. The second type of Special Condition turns the pump off but allows flow to go through the pump. This is called “Pump Off With Flow Through”. Why would one want to use one Special Condition rather than the other? The simple answer is that the first Special Condition is more appropriate

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80 AFT Fathom 7.0 Modules User’s Guide for positive displacement type pumps and the second for centrifugal pumps. Here's why. When a positive displacement pump is turned off and has a pressure difference across it, it will usually act like a closed valve and not allow flow to go through it. Thus the first Special Condition would be most appropriate. For instance, assume one wants to model the transient that occurs during the startup of a positive displacement pump. The best way to do this would be to use the first Special Condition with no flow, and then input a flowrate transient in which the first data point is zero flow. On the other hand, when a centrifugal pump is turned off and has a pressure difference across it, in the absence of other valving which prevents flow the pump will usually allow flow to go through it. Thus the Special Condition that allows through flow would be most appropriate. For example, assume one wants to model the transient during the startup of a centrifugal pump. One would use the second Special Condition, and, in conjunction with a pump curve entered at 100% speed, input a speed transient with the initial speed as zero.

Transient Special Conditions Junctions which accept transient data also support Transient Special Conditions. The default for all junctions is None. The other choice is Ignore Transient Data. This allows one to have no transient initiation at that junction without having to delete the transient data. When a Transient Special Condition is set to Ignore, a # symbol is displayed adjacent to the junction number on the Workspace. This symbol can be customized in the Workspace Preferences window.



CHAPTER 5

Modeling Time and Event Based Transients

In general, transients can be initiated in one of two ways. They can be initiated according to a prescribed time schedule or according to certain events that happen in the system. These two categories are referred to as time-based and event-based transients. Event-based transients break down further into three categories: Single event, cyclic dual events and sequential dual events. The behavior of time-based and the three event-based transients are described in this chapter.

Time-based transients Time-based transients occur in accordance with the time of the transient simulation. The start and stop times of the simulation are specified in the Transient Control window. The initiation of time-based transients are pre-specified before a model is run. For example, consider a valve closure transient. Assume the valve starts to close at two seconds into the simulation, and the time it takes for the valve to close is one second. After that, the valve stays closed. If the initial valve Cv is 250, the transient would appear as in Figure 5.1. In the “Initiation of Transient” area there are four options. For timebased transients, the option is specified as Time. In the Transient Data area the data is entered. Here the Cv profile of the valve will follow the profile entered and start to close at 2 seconds.




Figure 5.1

Time-based transient specifies the transient behavior before simulation is run.

Event-based transients Event transients are initiated when some user specified criteria is met. For example, a valve can start to close when a certain pressure is reached at a point in the system. If the pressure is never reached, the transient is never initiated. Event transients are one of three types. The three types will be discussed in the following sections.

Single event transients To specify a Single Event transient, select Single Event in the Initiation of Transient area of the junction window (see Figure 5.2). An “Event” tab will appear where the event criteria is entered. In Figure 5.2, the criteria is such that the transient will be initiated when the outlet static pressure in Pipe 2 exceeds 150 psig. If the pressure at this location never



Chapter 5 Modeling Time and Event Based Transients 83 reaches 150 psig, the transient specified in the Transient Data area will not occur.

Figure 5.2

Single event transient specifies how a junction will respond if and when some condition is satisfied.

The data in the Transient table has a slightly different meaning than does a time-based transient. Here time zero is relative to the time at which the event criteria is first met. For example, if Pipe 2 reaches 150 psig at 3.65 seconds, the valve will start its transient at 3.65 seconds. The valve will close (i.e., Cv = 0) at 1 second after the event initiation, or 4.65 seconds.

Dual event transients: cyclic and sequential Dual event transients contain two different transients for the junction. Cyclic events Cyclic dual events can repeatedly switch from one to the other based on the behavior of the model. For example, these could be high and low pressures at some location. When the low pressure setting is reached a valve transient is initiated which closes the valve. The pressure may then build up to a point where the high pressure setting is reached. In this

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84 AFT Fathom 7.0 Modules User’s Guide case a second valve transient is initiated which opens the valve. Should the pressure drop to the low pressure setting again, the valve will again close. The two settings will continue to cycle the valve on and off until the end of the simulation. Cyclic dual events are specified by selecting Dual Event Cyclic in the Initiation of Transient area of the junction window (Figure 5.3). When selected, two event tabs appear. Here the first and second event can be specified. In this case the first event is a pressure at Pipe 2 inlet less than 50 psig. The transient that is initiated when this event occurs is in the table of the First Transient tab in Figure 5.3. Here the valve closes one second after the event. A second event, not shown, is specified on the Second Event tab, with the accompanying transient specified on the Second Transient tab, also not shown. Typically, the first data of the second transient should match the final data of the first transient. In other words, if the valve is closed as in Figure 5.3 by setting the Cv value to 0, the first data point of the second transient should be zero and then proceed to some higher value which represents the opening of the valve. More often than not the two events will specify the same parameter at the same location. For example, if the first event specified a pressure at a certain pipe, the second event would also specify pressure at the same pipe location. However, this is not required. You can specify the first event as pressure and the second as flowrate, for example, or you could specify the two events to be at different locations in the pipe system. Sequential events Sequential dual events progress from the first event to the second and no further. For example, these could be two high pressure settings. When the first setting is reached the valve opens partially, and when the second setting is reached, which would likely be at a higher pressure than the first event, the valve opens the rest of the way. Similar to a single event transient, if the pressure drops and then rises again, the events would not be initiated again.



Chapter 5 Modeling Time and Event Based Transients 85

Figure 5.3

Dual Event Cyclic selection for transient initiation

Sequential dual events are specified by selecting Dual Event Sequential in the Initiation of Transient area of the junction window (Figure 5.3). Similar to Cyclic Dual Events, two event tabs appear where the first and second event can be specified. The transients that are initiated when the events occur are specified in the table of the First Transient and Second Transient tab. Similar to Cyclic Dual Events, the two events do not have to be for the same parameter (e.g., pressure) or at the same location.

Junctions with inherent event logic There are two junction types in AFT Fathom which have built-in, or inherent, event logic. These are the check valve and relief valve. The user does not need to specify the nature of the events, and in fact is not allowed to. The inherent event logic is very similar to the Dual Event Cyclic logic described previously.

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Check valve The check valve has two built-in events. The first is that it closes when backflow starts to occur. The second is that it reopens when sufficient pressure differential occurs. These transients are assumed to be instantaneous.

Relief valve The relief valve has two built-in events. The first is that it opens when the cracking pressure is reached. The second is that it closes again when the pressure falls back below the cracking pressure. These transients are assumed to be instantaneous.

Thought experiment to further clarify event transients To further clarify the capabilities of event transient modeling, here we will discuss how one could use a regular AFT Fathom Valve junction to simulate a check valve. As discussed previously, check valves have inherent event logic. That logic assumes that the valve closing transient is initiated when backflow begins. Once a certain pressure differential exists across the closed check valve, the valve reopens. One could use a regular valve junction to simulate a check valve as follows. First, the valve would need to be specified as Dual Event Cyclic in the Initiation of Transient area. The first event would be a flowrate that is less than or equal to zero at the inlet of the valve's discharge pipe. A Cv transient could then be entered to simulate how the check valve closes. The second event would be a differential pressure across the check valve that is greater than or equal to the check valve's reopening pressure differential. A reopening Cv profile could be entered in the second Transient table. With the above considerations, the valve junction and check valve junction would respond identically.




Other transient features Absolute vs. relative transient data In the Transient Data area (see Figure 5.1, 5.2 or 5.3) it can be seen that there are two options: “Absolute Values” and “Relative To Steady-State Values”. In the case of a valve junction, the first option allows you to put in actual Cv values (for example) vs. time. The second option allows you to put in a percentage of the steady-state Cv value. While not shown here, the steady-state value is entered on the Loss Model tab. For junctions other than valves, different parameters are specified as the transient parameter. For example, the transient could be the steady-state pump speed, pump flowrate, spray discharge area, or boundary pressure.

Repeat transient For transients that are periodic, you can specify that the transient repeats itself. This is specified by selecting the “Repeat Transient” checkbox (see Figure 5.1, 5.2 or 5.3). When Repeat Transient is selected, the first and last data points must match. After the transient reaches the final data point, it returns to the first data point and starts over.

Add time offset There may be times you want to shift the time data points in the Transient table. For instance, assume you have a valve specified as a time-based transient where the valve starts to close after five seconds. Further assume that you wish to change the transient so that it starts to close after seven seconds. In such a case, you want to shift all time values by two seconds. If you select the Edit Table button (see Figure 5.1, 5.2 or 5.3), there is menu choice for Add Time Offset. If you select this, you are prompted to enter an offset time, and all times in the table will shift by the specified time.

Graphing the transient data It is helpful to see the transient data in graph form, and this is easily done by selecting the Show Graph button (see Figure 5.1, 5.2 or 5.3).

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Figure 5.4

The Event Messages area shows a listing of all events that occur during the simulation sorted by junction and time.




Event messages Events that are initiated during the simulation are displayed in the two Event Messages area of the Output window (see Figure 5.4). The first is a list of event messages sorted by junction. The second is a list of event messages sorted by time. If no events occur, the Event Messages tab will be hidden.

Transient indicators on the Workspace To help the user quickly see which junctions are specified with transient data, a “T” is prepended to the junction number on the Workspace. Figure 5.5 shows an example where it is seen the junction J5 has transient data. The symbol can be configured on the Workspace Preferences window.

“T” Symbol displayed for junctions which have transient data

Figure 5.5

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Junctions that have transient are shown with an adjacent “T” on the Workspace as J5 is shown here (others also have the symbol here).

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Transient data in Model Data All transient junction data can be viewed in the Model Data window junction area on the Transient tab (see Figure 5.6). In addition, if events are specified the event data will also be displayed.

Figure 5.6

All junction transient data is shown in the Model Data window on the Transient tab.



CHAPTER 6

Extended Time Simulation Example

This example demonstrates the fundamental concepts of the Extended Time Simulation (XTS) add-on module. The example shows how XTS can be used to simulate the transient behavior of a system which has demands which vary over time. A number of other XTS example model discussions are included in a Help file distributed with AFT Fathom called FathomExamples.hlp. It can be opened from the Help menu by choosing “Show Examples”. Note: This example can only be run if you have a license for the XTS module.

Topics covered •

Transient Control

•

Defining system transients

•

Time and event transients

•

Transient output

•

Animating output predictions




92 AFT Fathom 7.0 Modules User’s Guide junction specifications, global editing, and creating groups. Refer to the AFT Fathom User's Guide for more information on these topics.


Variable Demand – XTS.fth – AFT Fathom model file

Problem statement A pumping system is used to supply five separate demand points. The system has a main pump and an auxiliary pump in parallel. The main pump operates until the demand flows cause the control valve open percentage to exceed 50%. When the control point limit is exceeded, the auxiliary pump starts to ensure adequate flow in the system. Use XTS to model the demand flows starting in sequence every 30 seconds, and to model the auxiliary pump startup when the control valve open percentage exceeds 50%.


Step 2. Specify system properties 1. Open the System Properties window by selecting System Properties in the Analysis menu 2. On the Fluid Data Tab, select the AFT Standard database and then select “water at 1 atm” in the fluids available window 3. Click “Add to Model” to select water for use in this model 4. Type in 70 degrees in the fluid temperature box 5. Click “Calculate Properties”



Chapter 6 Extended Time Simulation Example 93 6. Select “Heat Transfer With Energy Balance (Single Fluid)” 7. Select “OK”

Step 3. Build the Model A. Place the pipes and junctions At this point, the first four items are completed on the Checklist. The next Checklist item is to “Define Pipes and Junctions”. In the Workspace window, assemble the model as shown in Figure 6.1.

Figure 6.1

Layout of pipe system for the XTS Variable Demand Example.

B. Enter the pipe data The system is in place, but now you need to enter the input data for the pipes and junctions. Double-click each pipe and enter the following data in the Specifications window (or use the Global Pipe Editing window). All of the pipes are Steel, with standard roughness and the following data:

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94 AFT Fathom 7.0 Modules User’s Guide Pipe

Length (feet)

Size

Type

P1

10

4 inch

Schedule 40

P2

10

4 inch

Schedule 40

P3

10

4 inch

Schedule 40

P4

10

4 inch

Schedule 40

P5

10

4 inch

Schedule 40

P6

10

4 inch

Schedule 40

P7

10

4 inch

Schedule 40

P8

50

4 inch

Schedule 40

P9

50

4 inch

Schedule 40

P10

10

4 inch

Schedule 40

P11

10

4 inch

Schedule 40

P12

10

4 inch

Schedule 40

P13

10

4 inch

Schedule 40

P14

10

4 inch

Schedule 40

P15

10

4 inch

Schedule 40

P16

10

4 inch

Schedule 40

P17

10

4 inch

Schedule 40

P19

10

4 inch

Schedule 40

P19

10

4 inch

Schedule 40

C. Enter the junction data J1 Reservoir 1. Tank Model = Finite Open Tank 2. Known Parameters Initially = Liquid Surface Level, Surface Pressure 3. Tank Conditions = Height from Bottom Elevation



Chapter 6 Extended Time Simulation Example 95 4. Liquid Height = 5 feet 5. Surface pressure = 1 atm 6. Tank Bottom Elevation = 0 feet 7. Tank Height = 5 feet 8. Cross-Sectional Area = Constant, 20 feet2 9. Pipe Depth = 5 feet (on Pipe Depth & Loss Coefficients tab) J11, J13, J15, J17, J19 Assigned Pressures 1. Elevation = 10 feet 2. Pressure = 1 atm (stagnation) J10, J12, J14, J16, J18 Valves 1. Valve Data Source = User Specified 2. Elevation = 10 feet 3. Loss Model = Cv (Constant) 4. Cv = 10 J4, J6 Valves 1. Valve Data Source = User Specified 2. Elevation = 0 feet 3. Loss Model = Cv (Constant) 4. Cv = 100 J3, J5 Pumps 1. Elevation = 0 feet 2. Pump Model = Pump Curve 3. Pump Curve Data: 80 feet at 0 gal/min 90 feet at 125 gal/min 50 feet at 250 gal/min

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96 AFT Fathom 7.0 Modules User’s Guide J8 Control Valve 1. Elevation = 0 feet 2. Valve Type = Pressure Reducing (PRV) 3. Action if Setpoint Not Achievable = Use Default Actions 4. Control Setpoint = Pressure 5. Pressure Setpoint = 45 psia 6. Loss When Fully Open = Use Cv Table on Optional Tab 7. Open Percentage Data (On Optional Tab): Cv = 0 at 0% open Cv = 100 at 100% open J2, J7, J9 Branches 1. Elevation = 0 feet

D. Check if the pipe and junction data is complete Turn on Show Object Status from the View menu to verify that all the necessary data is entered. If so, the “Define Pipes and Junctions” checklist item will have a check mark. If not, the uncompleted pipes or junctions will have their number shown in red. If this happens, go back to the uncompleted pipes or junctions and enter the missing data. You can also open the List Undefined Objects window from the View menu to see what data is missing.

Step 4. Specify transient output time units The format and units used to display the transient data in the Output window are controlled from the Format & Action tab on the Output Control window. Open the Output Control window from the Analysis Menu, and select the Format & Action tab. Set the Time Simulation Formatting units to minutes. On the General tab add the Reservoir summary data to the General Output section by selecting Detailed Reservoir Information from the General Output Options area. Click OK to close the window.



Chapter 6 Extended Time Simulation Example 97

Step 5. Select transient analysis The XTS module may be turned on and off so users can run steady-state models using AFT Fathom. It is often useful to check the model steadystate solutions before attempting to run a transient case, to ensure the model is realistic. In order to run a transient analysis using XTS, the Transient mode must be selected. This is done by selecting Time Simulation from the Analysis Menu, as shown in Figure 6.2.

Figure 6.2 Transient analyses are selected on the Analysis menu.

Step 6. Open transient control XTS module transient simulations are controlled through the Transient Control window. Open the Transient Control window by selecting Transient Control from the Analysis Menu, or by double-clicking Transient Control on the Status Bar. Transient Control will not appear on the Status Bar if AFT Fathom is set to perform steady-state analyses. When AFT Fathom is set to perform a transient analysis, the Transient Control becomes the sixth Checklist item required to run the model.

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98 AFT Fathom 7.0 Modules User’s Guide The Transient Control window is used to specify transient start and stop times, as well as the time step controls and solution parameters for finite tank liquid level calculations. Start times, stop times, and time steps can be specified in any units from seconds to years. From the Transient Control window, users can specify the number of output points that are saved to the transient output file. This allows XTS to do transient calculations with a small time step while limiting the size of the transient data output file. For this example, the simulation will run for 3 minutes, with a time step of 5 seconds. The output will be saved to the output file for every time step. The Transient Control window should appear as shown in Figure 6.3.

Figure 6.3

The Transient Control window is used to specify transient run times and time step sizes.




Step 7. Set up the system transients In the XTS module, transients can be defined for junctions. These transients include valves opening and closing, and pumps starting and stopping. Transients for junctions can be defined as either time based or event based transients. A time based transient starts at a specified absolute time. Event based transients are initiated when a defined criteria, such as a pressure in a particular pipe is reached or exceeded. See Chapter 5 for more information on time and event transients.

Figure 6.4

The Transient tab on the Pump Specifications window is used to specify the event-based transient for the auxiliary pump in the Variable Demand example.

A. Auxiliary pump J5 transient. Open the Specifications window for pump J5. The pump is not operating at the beginning of this simulation. Set the pump J5 Special Condition on the Optional tab to Pump Off With Flow Through. The transient data is entered on the Transient tab. Set an event-based transient on the auxiliary pump so the pump will start when the control

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100 AFT Fathom 7.0 Modules User’s Guide valve open percentage exceeds 50%. The transient event definition and pump startup profile are shown in Figure 6.4.

B. Valve J6 Transient Open the Valve Specifications window for Valve J6. The valve should be closed initially to prevent flow through pump J5 while the pump is not operating. Do this by setting the valve Special Condition to Closed on the Optional tab. Valve J6 will open when the Pump J5 starts. To do this, enter the same transient event as defined for Pump J5 on the Transient tab. This is shown in Figure 6.5.

Figure 6.5

The Transient tab on the Valve Specifications window is used to specify the event-based transient for the pump isolation valve in the Variable Demand example.

C. Valve J12, J14, J16, J18 Transients Initially, the only flow through the system will be through the J10 Valve. Valves J12, J14, J16, and J18 will be closed initially and then will open in sequence, 30 seconds apart. Open the Specifications window for each valve, and set the Special Condition to Closed on the Optional Tab. The



Chapter 6 Extended Time Simulation Example 101 valve opening transient for Valve J12 is shown in Figure 6.6. The same opening transient should be added to valves J14, J16, and J18 by adding 30 seconds to the Time Absolute event for each valve.

Step 8. Run the model After all of the pipes and junctions have been defined, and all of the transient data and transient control items have been specified, the transient simulation may be executed. Select Run Model in the Analysis menu. This will open the Solution Progress window. This window allows you to watch as the AFT Fathom Solver converges on the answer. When using the XTS module, the Solution Progress window displays the progress through the transient analysis. This information is displayed below the solution tolerance data, as shown in Figure 6.7. After the run has completed, the results can be reviewed by clicking the View Output button.

Figure 6.6

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The Transient tab on the Valve Specifications window is used to specify the time-based transients for valve junctions J12, J14, J16, and J18 in the Variable Demand example.

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Step 9. Examine the transient results The AFT Fathom XTS module displays transient output in a number of places in the Output window. Each of the summary tables in the General Output section has a companion transient summary tab which displays the summary data at each time step in the transient run. Each junction included in the summary is included in the transient summary. The transient summary data for each junction may be expanded or collapsed by clicking the + or – sign beside the junction data list. The entire list may be expanded or collapsed by clicking the button in the top left-hand corner of the transient summary window. Figure 6.8 shows the Pump Transient summary tab, with the data for Pump J3 collapsed, and Pump J5 expanded.

Transient progress displayed

Figure 6.7

The Solution Progress window shows the progress of the transient analysis.




Figure 6.8

The transient summary tables (such as Pump Transient above) can be expanded or collapsed to improve viewability.

The Quick Graph feature can be used to conveniently plot transient data for quick examination. To use the Quick Graph feature, place the mouse cursor over the column of transient data you wish to examine. Then, right click with the mouse, and select Quick Graph from the list of options. Figure 6.9 illustrates how to do this for J1 Reservoir Liquid Height vs. Time. Figure 6.10 shows the resulting graph. The graph illustrates how the liquid level in the Reservoir drops with time. Figure 6.11 shows a Quick Graph plot of the volumetric flow rate through pipe P8. The plot shows the change in flow rate as each of the flow demand transients takes place.

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Figure 6.9

The Quick Graph feature can be accessed from any transient data column using the right mouse button.

Figure 6.10

The Quick Graph feature can be used to quickly plot transient data from the Output for review.

The Graph Results window may also be used to create a full range of graphs related to the XTS transient output. An additional graphing feature available for XTS is transient output animation. Profile plots for flow paths can be animated to dynamically view transient effects. Figure



Chapter 6 Extended Time Simulation Example 105 6.11 shows how to animate the transient response of the Volumetric Flow Rate for the flow path from the pump J3 discharge to assigned pressure junction J11. Figure 6.12 shows the resulting animation plot at time = 90 seconds. Select the parameter to animate

Select the profile path

Select Animate to use the animation feature

Figure 6.11

The transient results for flow paths profiles can be viewed dynamically using the animation feature.

Similar to the transient summary data, the transient tabs in the Pipe and Junctions sections of the Output window are used to display the transient data for each pipe and junction at every time step, as shown in Figure 6.13. This transient data can be expanded or collapsed in the same manner as in the General Output transient summaries.

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106 AFT Fathom 7.0 Modules User’s Guide The speed of the animation can be controlled

The animation can be paused or stopped at any point

The current time step is displayed

Figure 6.12

The animation feature dynamically displays transient parameter data.




Figure 6.13

The Transient tabs in the Pipe and Junction sections show results for all time steps. The first number in the left column is the pipe/junction number and the second (in parentheses) is the time (in minutes here).

Figure 6.14 shows the output data for the pipes and junctions, found on the Pipes and All Junctions tabs, at the initial time step, Time = 0 minutes. The output for all of the pipes and junctions can be displayed at any time step by using the slider bar located at the bottom of the Output window. Figure 6.14 also shows the pipe and junction data at Time = 1 minutes. When junction event transients occur, these events are recorded and displayed in the General section of the Output window. The events are displayed on two different tabs. The first tab sorts the events by junction number, and the second tab sorts the events by time, in the order in which they occur. The tabs are shown in Figure 6.15.

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Slider bar allows current time to be changed

Time is currently zero minutes

Time is currently 1 minute

Figure 6.14

The Pipe and Junction output can be displayed at any time step using the slider bar at the bottom of the Output window (Time = 0 minutes shown above and 1 minute below).




Figure 6.15

The occurrence of event transients are recorded in the General Output section.

The event messages show the demand flow transients ocurring at 30second intervals, as expected. Figure 6.16 shows the affect of the demand transients on the volumetric flow rate through pipe P8. The plot shows how the change in flow rate corresponds to the times when the transient events occur.

Figure 6.16

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Volumetric flowrate through Pipe 8 (inlet to J8 control valve) increases over time as each of the demand point transients occur.

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110 AFT Fathom 7.0 Modules User’s Guide The event messages also show the auxiliary pump starting at just over 1 minute into the transient analysis. Figure 6.17 shows a plot of the transient pump speed, and clearly shows the pump starting at this time. The auxiliary pump startup event was based on the control valve exceeding a percent open value of 50%. Figure 6.18 shows the control valve percent open vs. time. The plot shows the valve percent open exceeded the initiation criteria at just over 1 minute. The plot also shows that the control valve percent open continues to increase, even after the last demand transient has occurred. The valve is very close to its fully open state at the end of the analysis. This is due to the fact that the supply tank continues to drain as the analysis progresses, reducing the amount of hydrostatic head available upstream of the pumps.

Figure 6.17

The auxiliary pump transient occurs at just over 1 minute into the transient analysis.




Figure 6.18

The control valve open percentage exceeds 50% at just over one minute into the analysis, which triggers the auxiliary pump startup transient.

Analysis summary This example illustrates how XTS can be used to analyze dynamic system behavior. Time and event-based transients give the user the flexibility to define a large variety of dynamic responses that can occur in piping systems. The ability to use both text and graphical means to display the transient output allows the user to clearly understand, and communicate, the impact of transient behavior on system designs.

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CHAPTER 7

Working With Cost Databases

Cost databases provide the information needed to perform cost calculations in the CST module. Users can build their own cost databases using tools in AFT Fathom. This chapter discusses how to build cost databases.

Sources of cost data supported At present, the AFT Fathom CST module supports cost data in AFT Cost Database format.

Types of databases supported AFT Fathom uses four types of databases: •

Engineering databases – Maintains equipment performance and size data

•

Cost databases – Maintains cost data for the equipment

•

Energy Cost Databases – Maintains detailed cost of energy for pump calculations




Engineering and cost databases The first part of this chapter focuses on the first two database types: Engineering Databases and Cost Databases. Energy Cost Databases are discussed in the AFT Fathom 7.0 User’s Guide. There can be multiple cost databases for each engineering database. This allows cost data sets to be maintained separately from the engineering data. This can be useful for maintaining costs in different currencies or differences based on geographical location or times of the year. AFT Fathom engineering and cost databases can be set up on local or wide area networks (see AFT Fathom 7.0 User’s Guide Chapter 7). AFT Fathom’s engineering databases are nearly identical to the traditional AFT Fathom database used in versions 5.0 and before. Figure 7.1 shows how engineering and cost databases fit into AFT Fathom.

Cost Database window The Cost Database window is opened from the Database menu. This window allows you to create a cost database for items that are in a specific engineering database. Cost can be entered for pipes, junctions, and pipe fittings & losses. The costs can be of several types: 1. Material 2. Installation 3. Maintenance



Chapter 7 Working With Cost Databases 115

Fathom Model Connected Databases

Database Manager

Available Databases

Engineering Database #3

Engineering Database #1 Cost Database #1A

Cost Database #1C Cost Database #1B

Engineering Database #2 Cost Database #2A

Cost Database #2C

Cost Database #3A

Cost Database #3C Cost Database #3B

Cost Database #2B Figure 7.1

Relationship between engineering and cost databases in AFT Fathom.

One time vs. recurring costs AFT Fathom can include costs that occur once up front (i.e., first cost or capital cost) and recurring costs such as maintenance. The Cost Settings window allows you to input the Cost Time Period. This affects all recurring costs. Typically this will not affect nonrecurring costs, except when non-recurring costs occur at some future

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116 AFT Fathom 7.0 Modules User’s Guide time. An example would be a phased project where later phases incur non-recurring costs, but these do not occur until some later time.

Creating cost databases Before a cost database can be setup, an engineering database must exist. The engineering database can be an AFT Fathom internal database, which means that it was created by AFT and included with the AFT Fathom software. An example of an internal database item is the steel pipe materials available in the Pipe Specifications window.

Figure 7.2

When creating a cost database, you must first associate it with an engineering database.

Other databases controlled by the end user are the local user database and external databases that are connected in the Database Manager. To create a cost database, open the Cost Database window from the Database menu. Here you can create a new cost database by clicking on



Chapter 7 Working With Cost Databases 117 the New button. The Open Available button allows you to open a cost database that is currently available in the Database Manager. Finally, you can open any cost database by clicking the Open Any button and browsing to the database file. When you click on the New button, you are prompted to choose the engineering database with which the cost database will be associated (Figure 7.2). Important: Make this choice carefully, because once you have made the association you cannot change it. After you have made changes to a new or exiting cost database, click the Save button to save those changes, or Close button to exit with saving the changes. Once the database is created, you should enter a meaningful description and select the cost units (see Figure 7.3).

Figure 7.3

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General information for new cost database.

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Pipe material costs The Pipe Materials tab shows all the pipes in the engineering database (Figure 7.4). Costs can be entered at several levels. You can enter costs at the material level, the nominal size level, and finally at the type (i.e., schedule) level. Costs entered at the material level apply to all nominal sizes and types in that material type. Costs entered at the nominal size level apply to all schedules within that nominal size. Costs entered at the type (schedule) level apply only to that type. To enter a new cost, navigate to the material, nominal size and type combination for which you want to enter a cost. Click the New Cost button, and a new cost item is created in the table below. The new cost item will appear as a new column.

Figure 7.4

Example of pipe material cost data

Some cells are displayed in black, which means they are not relevant to the type of entry selected.



Chapter 7 Working With Cost Databases 119 Non-recurring costs Pipe non-recurring costs can be entered as cost per length (e.g., dollars per foot) or cost per mass (e.g., dollars per pound). Enter the cost in the Cost field, and select whether the cost is per length or per mass in the “Cost Per” field. Finally, select the units of length or mass in the Cost Per Units field. Recurring costs Recurring costs are entered as cost per time per length or cost per time per mass. Because recurring costs can change over time for various reasons, a scaling table can be specified. This is done in the Time Scaling Table field. If no scaling table is selected, the costs will be assumed to be constant over time. On the other had, selection of a scaling table will cause the costs to change over time, perhaps increasing or decreasing. Scaling tables are created on the Tables tab, and will be discussed later in this chapter.

Junction costs Costs can be entered for all junction types except for Volume Balance junctions. To enter cost for a junction, it must first be in an engineering database. Cost data is entered in a cost database associated with that engineering database. Figure 7.5a shows an example of entering cost data for a bend junction. Here the bend is a standard elbow made of steel.

Deleting costs To delete a cost item, select the column in the cost table and click the Delete button. Non-recurring costs, non-pumps and control valves For non-recurring cost types for junctions that are not pumps or control valves, there are three ways to enter junction cost data that captures the diameter dependence of the junction. The diameter used for dependence is that of the upstream pipe of the specific junction. These are the three ways: 1. Specify the Use Size Table as “none”, enter the cost in the Cost field, and in the Cost Per field specify the cost as per Diameter as

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120 AFT Fathom 7.0 Modules User’s Guide shown as Cost #2 in Figure 7.5a. When the Cost is per Diameter, the Cost Per Units field will allow you to specify if the cost is per inch, per foot or otherwise. This cost will then vary linearly with diameter. This method offers the least cost precision. 2. Specify the Use Size Table as Table of Costs, enter the cost in a table of cost vs. diameter as a size scale table (on the Tables tab), and then select the table in the Size Scaling Table field. Cost #3 in Figure 7.5a uses the scaling table called “90 deg. Steel Acq.”. 3. Specify the Use Size Table as Table of Multipliers, enter the cost in the Cost field, enter a table of cost multipliers vs. diameter as a size scale table (on the Tables tab), and then select the table in the Size Scaling Table field. This is shown as Cost #4 in Figure 7.5a.

Figure 7.5a

Examples of junction non-recurring costs

Recurring costs, non-pumps Non-pump junction recurring cost types have available the same three options to account for recurring costs that vary with diameter as the preceding discussion for non-recurring costs. In addition, how the costs vary over time is specified.



Chapter 7 Working With Cost Databases 121 The cost over time variation is specified in the Time Scaling Table. If the table is specified as none, the cost over time is assumed to be constant. If you want to vary the cost over time, you can specify a Time Scaling Table to vary the cost. Scaling tables are created on the Tables tab, and will be discussed later in this chapter. Cost #5 and #6 in Figure 7.5b show examples.

Figure 7.5b

More examples of junction non-recurring and recurring costs

Pump and control valve costs The cost data for pump and control valves function differently than for other junctions. Rather than cost data that depends on diameter, pump cost data is entered as it depends on power. Control valve cost data is entered as it depends on the Cv value. This applies to both recurring and non-recurring costs. Pump junctions are also the only junction type that includes operation/energy costs. These are setup in a separate type of database called an Energy Cost Database.

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122 AFT Fathom 7.0 Modules User’s Guide Costs for tees and branches Cost data for tees and branches can be entered as a function of diameter. But with multiple connecting pipes, which diameter should be used as the cost basis? AFT Fathom always obtains the cost for tees and branches based on the largest diameter of any connecting pipe.

Pipe fitting & loss costs Pipe fittings & losses cost specification functions the same as non-pump junctions, with the exception that costs can be associated with a particular pipe material and size. Costs for Pipe Fittings & Losses from the AFT Fathom internal database can be entered when the cost database is associated with the internal engineering database. Costs for user specified Pipe Fittings & Losses would be associated with the Local User Database or other external database in which the engineering information has been saved.

Figure 7.6

Scale table example of a table of costs.




Figure 7.7

Scale table example of a table of multipliers.

Scale tables Scale tables are used to vary a cost with time, diameter (i.e., size), power, or Cv. The same scale table can be applied to multiple cost items, whether pipe materials, junctions, or pipe fittings & losses. Time scale tables are always based on a multiplier. This is the format of the table (see Figure 7.6). The diameter and power type tables can have the format of a multiplier, or the format of actual cost. When the format is a multiplier, the multiplier is obtained from the table and multiplies a base cost value of a cost item. When the format is a cost table, the actual cost is obtained from the table and then multiplied by a scalar multiplier for an item. By default, the item’s multiplier value is 1. Figure 7.6 shows an example of a table of costs, and its usage is shown in Figure 7.5a, Cost #3. Note in Figure 7.6 in the table at the right that the parameters are Diameter (in inches) vs. Cost (in U.S. Dollars here). Figure 7.7 shows an example of a table of multipliers, and its usage is shown in Figure 7.5a, Cost #4. Note in Figure 7.7 that the table shows a Diameter (in inches) vs. Multiplier (with no units).

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Figure 7.8

Cost multipliers can be entered on the General tab that multiply all items in the cost database.

Global multipliers in cost database To account for cost fluctuations perhaps due to geographic or seasonal causes, global cost multipliers for all items in the cost database can be entered in a table on the General tab. Figure 7.8 shows an example. These multipliers are built in to the database.

Global multipliers in Database Manager Multipliers on cost data can also be applied in the Database Manager (Figure 7.9). While Cost Database multipliers (discussed in previous section) are built into the database, and may be beyond control of the user, the Database Manager multipliers are more flexible and under complete control of the user. General use of Database Manager is discussed in the next section.




Figure 7.9

Global multipliers for cost databases in Database Manager.

Using cost databases To be used in an AFT Fathom model, cost databases must be connected. To connect a cost database, open the Database Manager from the Database menu (see Figure 7.10). Since each cost database depends on an engineering database, the engineering database must also be connected. To connect an engineering or cost database, first make it available using the Add Engineering Database or Add Cost Database menu selections on the Edit Available list button. This adds the database to the list of Available Databases at the top. Once available, click the Add to Connections button to add it to the list of Connected Databases below. Note how the cost databases in both the Available and Connected Database list are shown subordinate to the engineering database.

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126 AFT Fathom 7.0 Modules User’s Guide Note: More than one cost database can be related to an engineering database.

Figure 7.10

Database Manager allows you to connect to engineering and cost databases

Database Sections Each cost database has sections of data, whether pipe materials, junctions, or pipe fittings & losses and you can selectively connect to each of these sections in the Database Sections list in the lower right corner. You can choose to have the same cost section from multiple databases except for energy costs which can only come from one.

How repetitive costs are handled To maximize flexibility for the user, multiple cost databases can be connected to the same engineering database. What happens if there is cost data for the same engineering item in each database? For example, assume an engineering database exists called PUMP.DAT which has engineering data for pumps (e.g., pump curves, NPSH, etc.). In



Chapter 7 Working With Cost Databases 127 PUMP.DAT there is a database entry for a pump called “PumpCo Model 100A”. Two cost databases exist based on PUMP.DAT, one called MAXCOST.CST, and the other called BESTCOST.CST. The MAXCOST.CST database has a material cost for “PumpCo Model 100A” of $1000, while BESTCOST.CST has a material cost of $750. If both of these databases are connected in the Database Manager, and if both have their Database Sections specified to include their “Junction/Component” section, then AFT Fathom will interpret the cost for “PumpCo Model 100A” as the sum of the two, namely $1750. There will be occasions you want cost items to be summed, and other cases where you do not. Obviously, if you have two databases, one that tracks the maximum cost and the other that tracks the “best” cost of an item, you want to use only one cost at a time and not have the costs summed. However, perhaps the two material costs do not represent the same item, but rather represent partial costs of that item that you want to maintain separately. For example, one database may contain costs of the pump and its casing, while another may contain cost for the motor. A third might contain cost for a variable speed drive. When managed in this way, you want the costs to be summed.

Using the Database Sources tables AFT Fathom displays the source of all cost data in a run, and you are strongly encouraged to review this data to verify that the cost calculations were based on the appropriate cost data. In the Output window, the sources of all cost data are displayed for each pipe and junction in the Database Sources table. Figure 7.11 shows the Database Sources for an example case. Here the sources for both pipes and junctions are displayed.

Pipe costs in Pipe Specifications window To access the cost for a pipe, use the Cost tab on the Pipe Specifications window (Figure 7.12). Select the “Include Cost in Report” option and the cost will be calculated and displayed in the Output window Cost Report.

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Figure 7.11

Database source tables for pipes and junctions shows source of all cost data

To configure cost data for the pipe, click the Cost Application button (visible in Figure 7.12) to open the Cost Application Manager (see Figure 7.13). The Cost Application Manager allows you to configure pipe cost calculations in three ways: •

Cost databases accessed (these are additive)

•

Multipliers on costs

•

Service Duration

The Service Duration option deserves further explanation. This option allows you to specify when a pipe is to be installed and/or removed. Pipes that are installed in the future typically cost less in present currency than pipes installed initially. Pipes installed in the future are discounted in present currency value using the interest and inflation rates specified in the Cost Settings window.




Figure 7.12

The Cost tab shows cost data applied to the pipe. The Cost Application button opens a window where cost data can be refined.

The Cost Databases section (Figure 7.13) has two options. The first is to use all connected cost databases. The second is to use only the cost databases specified in the Cost Application Manager. Figure 7.14 diagrams the logic of how cost data is accessed for a pipe. The differences between these options are detailed later in the this chapter.

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Figure 7.13

The Cost Application Manager allows application of cost data to pipes.

Cost for pipe fittings & losses The pipe fittings & losses database resides in the AFT Fathom internal engineering database. Thus, a cost database for pipe fittings & losses must be associated with the internal database – unless you add your own custom fittings & losses to an engineering database. Then cost databases can be associated with that database as well.



Chapter 7 Working With Cost Databases 131 Start

Get Costs ?

No

Yes All Databases ?

No

Yes Database Manager

Use Databases Specified in Cost Application Manager

Return

Figure 7.14

Logic for obtaining costs for pipes. Includes material and cost for fittings & losses. Junction costs use the same logic.

Costs can be specified for different sizes of fittings & losses, and when the fittings & losses are selected in the Pipe Specifications window, the costs are obtained similar to how costs are obtained for the pipe materials.

Junction costs in Junction Specifications window Junction costs are configured in a similar manner to pipe costs. The logic is the same as for pipes (Figure 7.14). The Cost tab on junction windows may display more data than does the pipe. For example, the Cost tab on

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132 AFT Fathom 7.0 Modules User’s Guide the Pump Specifications window is shown in Figure 7.15. The additional data comes from additional features for pumps in the Cost Application Manager. More detail on the Cost Application Manager will be given in Chapter 8.

Figure 7.15

Cost tab on the Pump Specifications window allows pump cost data to be configured.

All databases vs. selected cost databases In the Pipe Specifications window and most Junction Specifications windows additional fine tuning of cost data sources is provided through access to the Cost Application Manager. The default in all cases is “All Connected Databases”. This selection means that the cost data is to be obtained from the databases connected in the Database Manager. In the lower half of the Connect to Database tab on the Database Manager window (see Figure 7.10), the connected cost databases for the current model are displayed. More specifically, the sections from those databases are specified in the lower right of the window. There can be multiple cost databases for each engineering database, and this makes it possible for multiple costs to exist for each pipe or component. The



Chapter 7 Working With Cost Databases 133 reasons for this are discussed earlier in this chapter. The point here is that when “All Cost Databases” are selected as the cost database source for a pipe or junction, this refers to the connected cost databases in the Database Manager. If you choose a selection other than “All Cost Databases”, then the selected cost databases will be the sole source of cost data for the particular pipe or junction in the model.

Cost Settings window We have discussed how cost data is entered and how it is assigned and accessed by AFT Fathom. The Cost Settings window offers one more variation to the process.

Figure 7.16

The Cost Settings window allows specification of different cost categories to be included in the cost calculation.

Of those pipes and junctions with costs that are to be included, the costs fall into different categories. There are four cost categories: Material, Installation, Maintenance, and Operation/ Energy. The Cost Settings window allows the user to specify which of these cost categories to include in the cost calculation (see Figure 7.16). This allows the user to

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134 AFT Fathom 7.0 Modules User’s Guide easily compare the cost differences, for example, between a system calculated for first cost vs. one calculated for life cycle costs. For recurring cost items, the duration of the Cost Time Period is critical. Recurring cost times are entered on a cost per time basis.

Database locations in General Preferences When performing a cost calculation, there may be many engineering and cost databases that underlie the model. These databases need to be connected in the Database Manager in order to be accessible by the model. However, to know which databases are actually needed, one needs to first load the model. This creates a dilemma.

h Figure 7.17

Database Search Locations can be defined in the General Preference window.

To help alleviate the dilemma, users can create “Database Search Locations” in the General Preferences window. Figure 7.17 shows an



Chapter 7 Working With Cost Databases 135 example. Once specified, you can set these as your default locations by clicking the Set As Default button. When AFT Fathom tries to open a model that requires certain databases, and those databases have not been connected already, AFT Fathom looks for them in the locations specified in the General Preferences. In addition, AFT Fathom looks in the model's folder. If AFT Fathom finds the databases in one of these locations, it automatically adds it to the list of connected databases in the Database Manager. If it cannot find a database, it informs you once the model is loaded.

Reviewing application of cost data The Cost Summary window (Figure 7.18), opened from the View menu shows all connected cost databases and energy cost databases, and which pipes and/or junctions are obtaining costs from each database.

Figure 7.18

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Cost Summary window shows which pipes and junctions are obtaining costs from which cost and energy databases.

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CHAPTER 8

Performing Cost Analysis

This chapter explains how to perform cost calculations using the AFT Fathom CST module.

What is the CST module? Ultimately all engineering designs are going to be translated into cost. Along the way there is an interchange between the engineering decisions and the financial implications. The AFT Fathom CST module brings these two processes together to allow the cost impact of engineering decisions to be quickly assessed. Moreover, calculation of recurring costs such as energy and maintenance can be easily included in your cost calculations. The cost data used for cost calculations can be developed and customized by the user.

How does the CST module work? The AFT Fathom CST module works by allowing the user to associate cost items from external cost sources to pipes, fittings and components and to see the cost with the output. Recurring costs are calculated over time periods specified by the user using interest and inflation rates to discount future expenditures.




Using the CST module The user has the option of activating or not activating the CST module when AFT Fathom first loads. After AFT Fathom is loaded, the CST module can be activated or deactivated for use from the Options menu. Whether or not CST is activated impacts the View and Database menus and all Pipe and Junction Specifications windows, and other AFT Fathom functions. Table 8.1

AFT Fathom feature accessibility based on CST activation and usage of costs

CST Not Active

CST Active

CST Active

Costs not used

Costs not used

Costs used

Not Visible

Visible

Visible

"Cost Summary" on View Menu

Not Visible

Visible

Visible

Cost Databases in Database Manager

Not Visible

Visible

Visible

Material, installation and maintenance costs in Cost Settings window

Not Visible

Visible

Visible

"Cost" tab on Pipe and Junction Specifications window

Not Visible

Visible

Visible

"Cost Report" tab in General Section of Output window

Not Visible

Not Visible

Visible

"Database Sources" tabs in Pipe and Junction Sections of Output window

Not Visible

Not Visible

Visible

Feature "Cost Database" on Database Menu

If the CST module is active, the user can still run models without cost calculations. Hence there are three possibilities for CST. 1. CST is not active 2. CST is active and operated without cost calculations 3. CST is active and operated with cost calculations



Chapter 8 Performing Cost Analysis 139 Table 8.1 lists the three possibilities and the impact on various AFT Fathom features.

Accessing cost databases Cost databases To perform cost calculations, cost databases must be accessed. Cost databases can be built by the user. See Chapter 7 for more information on building and connecting cost databases.

Energy Cost databases Pump energy cost calculations can be performed in standard AFT Fathom. Simple cost data for energy can be entered in the Cost Settings window, or more detailed energy cost data can be included in energy costs databases. See the AFT Fathom 7.0 User’s Guide for more information on energy costs databases.

Database Manager Cost databases and energy cost databases are accessed through the Database Manager. See Chapter 7 on Using Cost Databases and the AFT Fathom 7.0 User’s Guide, also Chapter 7, for more information on Database Manager. Once cost data is connected in Database Manager, it can be applied to pipes and junctions in the model using the Cost Application Manager.

Cost Application Manager The Cost Application Manager (CAM) is used to apply cost data to each pipe and junction in the model, and to access features which modify the data. The CAM for a particular pipe or junction is accessed by clicking the Cost Application button on the Pipe or Junction Specifications window Cost tab. It can also be opened from the View menu, where all applied cost data for all pipes and junctions is shown. See Figure 8.1.

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Figure 8.1

The Cost Application Manager can display options for a single pipe or junction (above) or all pipes and junctions (below).



Chapter 8 Performing Cost Analysis 141

Cost Databases Any or all connected cost databases can be applied to any pipe or junction by specifying the databases in the CAM. To use all of the available cost databases, choose All Connected Databases in the Cost Databases category. To choose specific cost databases, choose Selected Databases in the Cost Database category, and then select the desired cost databases from the list of available databases. Figure 8.1 (top) shows an example where all of the available cost databases were applied to a pump junction.

Energy Cost Databases Energy Cost databases may be created and used for pumps. You may apply any or all connected energy cost databases to any pump by specifying the databases in the CAM. To use all of the available energy cost databases, choose All Connected Databases in the Energy Cost Databases category. To choose specific energy cost databases, choose Selected Databases in the Energy Cost Database category, and then select the desired energy cost databases from the list of available databases. Figure 8.1 (top) shows an example where a specific energy cost database was applied to a pump junction.

Cost Multipliers Cost multipliers can be applied to all cost types in the applied cost and energy databases for each pipe or junction in the model. These multipliers can be used to account for things such as a pump not operating 24 hours a day. Cost multipliers are entered in the Cost Application Manager for each pipe or junction to which they apply. Figure 8.1 (top) shows cost multipliers of 120% applied to the pump Material, Installation, Maintenance, and Operation/Energy costs.

Maximum Cost Groups Maximum cost groups can be applied to pump and control valve junction costs. They are applied by selecting the desired group for each cost type in the Maximum Cost Group category in the CAM. Figure 8.1 (top) shows Maximum Cost Group options.

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142 AFT Fathom 7.0 Modules User’s Guide See the section on Maximum Cost Groups later in this chapter for a detailed discussion on creating and using Maximum Cost Groups for pumps and control valves.

Service Duration If a component will have a limited service time during the life of the system to be analyzed, the Service Duration can be used to define this. For example, a system expansion may be planned 3 years after the initial start of the system. The components for this expansion could be included in the total cost of the system by adding a Service Duration Start of 3 years. Alternatively, system components can be taken out of service prior to the end of the full system life. The Service Duration End is used to define this type of event. Figure 8.1 (top) shows a Service Duration Start at 1 year, and a Service Duration End at 10 years.

Cost Settings window Once cost databases are connected and applied to pipes and junctions, the cost categories need to be included in the Cost Report. To do this select Cost Settings from the Analysis menu. The Cost Settings window also allows input of the time period to calculate costs and financial assumptions such as interest and inflation rates which reduce the cost of future expenditures. The Cost Settings window is shown in Figure 8.2.

Cost Calculations By default, cost calculations are turned off. To turn on cost calculations, select Calculate Costs in the Cost Calculations area.

Energy Cost Energy cost data can be specified though an energy cost database, or by directly entering an energy cost on the Cost Settings window. Using an energy cost database allows you to specify multiple energy costs, such as energy costs at both peak and off-peak rates. Note: Energy cost calculation for pumps is also part of the standard AT Fathom version.




Figure 8.2

The cost calculations are turned on and cost categories are selected in the Cost Settings window.

Cost Definitions The Cost Definitions section allows you to specify the type of costs to be determined. You may select from engineering parameter costs, such as pipe weight, or actual monetary costs, including material and installation costs.

Monetary vs. non-monetary costs Cost data can be monetary or non-monetary. A non-monetary cost example is weight. You could create a cost database where the cost of the pipes, pumps and valves was in pounds or kilograms (pounds/ft for the pipe, pounds/HP for the pumps and pounds/Cv for the valves). With this information, you could calculate the “cost” of the system with the CST module. Broadening this concept, the CST module can be used to calculate costs for any number of non-monetary parameters.

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Engineering parameter costs CST offers built-in non-monetary cost calculation methods for several engineering parameters. •

Flow Volume – The sum off all internal pipe volumes. Pipe volume is pipe length multiplied by cross-sectional area.

•

Pipe Inner Surface Area – The sum off all pipe inner surface areas. Inner surface area is pipe length multiplied by circumference.

•

Pipe Weight – The sum of all pipe weight. Pipe Weight is pipe material volume multiplied by material density.

•

Pipe and Fluid Weight – Same as Pipe Weight, but also includes the weight of the fluid inside the pipes.

Because the geometric and material data for pipes and ducts is always available from the model input data, using engineering parameter cost calculations does not require the user to construct detailed cost databases. A design “cost” can be obtained with minimal effort by the user. Any engineering parameter calculation is not as comprehensive as rigorous cost-based calculations, but can be useful in many cases.

Custom monetary units Monetary units can be set up by the user to allow pump energy cost calculations in whatever currency is desired. On the Unit Preferences tab select Monetary units and “New” and enter data for name of the currency and conversion rate to the base units of U.S. Dollars. Once entered, the currency can be selected for monetary input and output.

Cost Time Period The system lifetime to be applied for the cost calculations is specified in the Cost Time Period section. You can also specify interest and inflation rates to be applied to the cost calculations as well. The CST module can include costs that occur once up front (i.e., first cost or capital cost) and recurring costs such as maintenance or operation. The System Life affects all recurring costs. It can also affect non-recurring costs if the Service Duration is used. See Chapter 7 for detailed discussions regarding recurring and non-recurring costs.




Cost Report The Cost Report is a detailed list of all costs for the system being analyzed (see Figure 8.3). It is displayed on the Cost Report tab in the General section of the Output window. The content of the Cost Report can be customized on the Summaries tab of the Output Control window. The grand total cost is shown on the top line. Below that, several subtotals are shown. Then below that, costs for pipes, junctions, and pipe fittings & losses are shown, with subtotals. The costs are further broken down in the columns by Material, Installation, Maintenance and Operation/Energy, with Non-Recurring and Recurring cost sub-totals.

Figure 8.3

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The Cost Report is displayed in the General section of the Output window

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146 AFT Fathom 7.0 Modules User’s Guide The Format & Action tab (on the Output Control window) allows you to hide items that have zero cost, to group pipe costs, and to show subtotals only. From this tab, you can also specify the cost unit style as whole units, or as a fractional unit, as well as specify the number of decimal places to be displayed.

What are maximum cost groups? The maximum cost group concept is virtually the same for pumps and control valves. The application to pumps will be discussed in detail, and at the end of this section, a comparison will be made to control valve applications. It is common in pipe system design for multiple pumps to be arranged in parallel. When operating in parallel, system capacity is increased. Sometimes a parallel pump is included as a backup, and under normal conditions does not operate. Whatever the case, the design will usually call for each pump to be of the same design. Therefore, each pump will have the same initial cost (i.e., material and installation). Maintenance and operation costs may be different. In the case of a spare pump, the operation cost will be zero! When sizing a pump, a generic pump modeled as a fixed flow may be used in the initial phase of the sizing process. The material and installation cost for such generic pumps are input as a function of power usage, which allows flexibility in cost calculations before an actual pump is selected. However, pumps in parallel will not always operate at the same design point because of differences in supply and discharge piping, for example. If the pump is a spare, it most certainly will not operate at the same point as the pumps that are in operation. Because the cost for each pump typically depends on its power usage, and the power for each parallel pump may be different, the cost for each pump will be different although they are the same pump design. Even more difficult is obtaining the cost for a spare pump. Since it is not operating, it is not possible to obtain a valid cost. To ignore its cost would artificially lower the total system cost. In the case of a spare, what is desired is for the spare pump's material and installation cost to be somehow linked to that of an operating pump for which a valid cost is obtainable. That is the function of maximum cost groups.



Chapter 8 Performing Cost Analysis 147 When a pump is included in a maximum cost group for a cost category, the CST module looks at each pump in the group. It then identifies the pump with the maximum cost for that cost category, and applies that cost to each pump in the group for that cost category. This accomplishes the following: •

The CST module will use the same cost for each pump in the group which is consistent with the fact that each purchased pump will actually cost the same

•

The basis for pump selection will be the pump that uses the most power and, hence, costs the most

•

It allows the cost for spare pumps to be accounted for properly by linking its cost to that of an operating pump

Typically, parallel pumps will have certain cost categories that will be the same, while other categories will be different. For instance, the material (i.e., purchase) cost of each identical pump will usually be the same, as will the installation cost. However, operating costs will likely be different unless each pump has identical suction and discharge piping, and is operated the exact same number of hours each year. Maintenance costs will differ between operating pumps and spares.

Typical usage guidelines Typically, maximum cost groups will be used as follows: •

Will be used for the material and installation cost categories

•

Will not be used for the operation cost category for pumps

•

May or may not be used in the maintenance cost category

Creating a maximum cost group for pumps Here is the procedure for creating a maximum cost group: 1. Select the pumps on the Workspace which will all be of the same design 2. On the Edit menu select Groups -> Create 3. Enter a name when prompted (it might be clearer if you named the group “Pump Maximum Cost Group”) 4. Click the OK button

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148 AFT Fathom 7.0 Modules User’s Guide 5. The Group Manager will automatically open to show you the contents of the new group. Click the OK button in the Group Manager 6. On the Workspace, open the Pump Specifications window for one of the pumps in the group 7. Select the Cost tab 8. Click the Cost Application button. In the Cost Application Manager, select the name of the group for each applicable cost type (typically this will only be material and installation) 9. When closing the pump window, AFT Fathom will prompt you to automatically change all other pumps in the group to the same settings as in Step 8. Typically, you will want to let AFT Fathom do this. If you decline, you can open each pump in the group and specify its maximum cost group.

How cost multipliers are applied with maximum cost groups In the Multipliers category of the Cost Application Manager, you can assign multipliers on the different pump cost types. The multipliers have several uses. Here are some possibilities. Maximum cost is the base cost before multipliers are applied When a maximum cost is determined for a maximum cost group cost category, the maximum cost is the base cost before multipliers are applied. This allows a design case with a zero multiplier to drive the pump cost for that category, which may happen in the case of standby pumps. Pump operates part of the time The pump operates all day Monday to Friday, but is shut down on the weekends. A multiplier of 5/7 (i.e., 71.4%) on the operation costs would represent this. Spare pump A spare pump would use a multiplier of zero on operation cost because its annual operating cost is essentially zero. However, it might still have



Chapter 8 Performing Cost Analysis 149 a maintenance cost. Because it is not operating, the maintenance might only be 10% of the cost for an operating pump. A multiplier on maintenance cost of 10% would be appropriate. The pump will probably cost just as much to purchase and install as the one that is operating, and thus multipliers of 100% would be appropriate for material and installation cost.

Maximum cost groups for control valves Whereas the cost for generic pumps during the sizing process is based on power usage, generic control valve costs are typically based on valve maximum Cv. The application of maximum cost groups for control is the same as for pumps, except control valves do not have operation costs.

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CHAPTER 9

Cost Analysis Example

This example demonstrates the fundamental concepts of the Cost (CST) add-on module by way of example. The example illustrates how the CST module can be used to calculate initial and life cycle costs for a given system design. A number of other CST example model discussions are included in a Help file distributed with AFT Fathom called FathomExamples.hlp. It can be opened from the Help menu by choosing “Show Examples”. Note: This example can only be run if you have a license for the CST module.

Topics covered •

Creating cost databases

•

Entering pipe, junction and fitting cost data into databases

•

Connecting cost databases

•

Using Cost Settings

•

Using the Cost Report




152 AFT Fathom 7.0 Modules User’s Guide junction specifications, global editing, Database Manager, and creating groups. Refer to the AFT Fathom User's Guide for more information on these topics.

Model file This example uses the following files, which are installed in the Examples folder as part of the AFT Fathom installation: •

Plant Cooling.fth (10 Year Operation Cost scenario) – AFT Fathom model file

•

Plant Cooling.dat – AFT Fathom engineering database file

There are also two cost database files for this example, which are installed in the Examples folder. These databases will be recreated as part of this problem, but they are included as reference material. These cost databases are used in the 10-Year Operation Cost (with Cost Databases) scenario of the Plant Cooling.fth model file. The database files are: •

Plant Cooling - Sch20 Steel Piping Costs (Example DB).cst – AFT Fathom cost database file

•

Plant Cooling - Circ Pump Costs (Example DB).cst – AFT Fathom cost database file

Problem statement After designing a plant cooling system, it is necessary to calculate the system cost over a 10-year period to determine the feasibility of the design. The system model consists of four circulating water pumps, schedule 20 steel pipes and fittings, and two sets of cooling tower cells. Use CST to determine the cost of the cooling system for a 10-year period. Include material, installation, and energy costs for the pumps, pipe, and fittings. The cooling tower costs are ignored here, and assumed to be calculated in some other context.



Chapter 9 Cost Analysis Example 153


Step 2. Open the model file Open the Plant Cooling.fth model file to the 10 Year Operation Cost scenario, which is located in the Examples folder in the AFT Fathom application folder. Save the file to a different folder. The model should appear as shown in Figure 9.1.

Figure 9.1

The Plant Cooling model (from the Examples folder in the AFT Fathom application directory).

Step 3. Cost Settings To select the CST module calculations, select Cost Settings from the Analysis menu. The Cost Settings window is where the types of costs to

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154 AFT Fathom 7.0 Modules User’s Guide be included in the cost calculations are specified. The Cost Settings window is shown in Figure 9.2.

Cost Calculations By default, the cost settings are turned off. To turn on the cost calculations, select Calculate Costs in the Cost Calculations area. Energy cost data can be specified though an energy cost database, or by directly entering an energy cost on the Cost Settings window. Using an energy cost database allows you to specify multiple energy costs, such as energy costs at both peak and off-peak rates. For this example, select Use This Energy Cost Information, and enter an energy cost of 0.06 U.S. Dollars/kW-hr, as shown in Figure 9.2. Note: Energy costs for pumps is also part of the standard AT Fathom version.

Cost Definitions The Cost Definitions section allows you to specify the type of costs to be determined. You may select from engineering parameter costs, such as pipe weight, or actual monetary costs, including material and installation costs. For this example, select Monetary Costs. Include Material, Installation, and Operation/Energy costs by selecting them from the list of available monetary costs, as shown in Figure 9.2.

Cost Time Period The system lifetime to be applied for the cost calculations is specified in the Cost Time Period section. You can also specify interest and inflation rates to be applied to the cost calculations as well. For this example, enter a system life of 10 years, as shown in Figure 9.2, then close the Cost Settings window by clicking the OK button.




Figure 9.2

The cost calculations are selected on the Cost Settings window.

Step 4. Create the cost databases Refer to Chapter 7 for detailed information regarding creating and using cost databases. The energy cost for the pumps was specified in the Cost Settings as a fixed cost rate. Now, the material and installation cost for the pumps, pipes, and fittings must be included. This will be done by creating two new cost databases. The first database will be for the pipe and fitting costs, and it will be associated with the engineering database that contains the pipe material data. The second cost database will be for the pump costs, and it will be associated with the engineering database that contains the pump component information.

Create a new cost database for the pipe costs Create a new cost database for the pipe costs by opening the Cost Database window from the Database menu. Create a new cost database

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156 AFT Fathom 7.0 Modules User’s Guide by clicking on the New button. When you click on the New button, you are prompted to choose the engineering database with which the cost database will be associated The piping material data used in the model comes from the default AFT internal database, so the pipe cost database will be connected to this database, as well. Select AFT DEFAULT INTERNAL DATABASE from the database list shown in the Select Database window, then click the Select button. Important: Make this choice carefully, because once you have made the association you cannot change it. Once the database is created, you must enter a meaningful description and select the cost units. Enter the following data on the General tab: 1. Cost Type = Monetary 2. Monetary Unit = U.S. Dollars 3. Description = Plant Cooling System – Sch20 Steel Piping Costs 4. Notes = This database is for the Plant Cooling CST Example File Save the cost database to a file by clicking the Save button. When prompted, choose to add the new database to the list of available and connected databases. The information on the General tab should appear as shown in Figure 9.3 Note: The database file pathnames may be different than those shown in Figure 9.3. For this example, you will enter Pipe Material costs, Junction costs for the pumps, and Fittings and Losses costs for the pipes.

Enter the pipe material costs After the pipe cost database has been created, select the Pipe Materials tab in the Cost Database window. This is where you will enter the material and installation costs for the piping.



Chapter 9 Cost Analysis Example 157 The selected database file information is displayed The cost type and monetary units are specified

A description of the cost database must be given

Descriptive notes can be added to provide additional information about the database

Figure 9.3

The Cost Database window is used to enter cost database data.

The Pipe Materials tab shows all the pipes in the engineering database (AFT DEFAULT INTERNAL DATABASE). Costs can be entered at several levels. You can enter costs at the material level, the nominal size level, and finally at the type (i.e., schedule) level. Costs entered at the material level apply to all nominal sizes and types in that material type. Costs entered at the nominal size level apply to all schedules within that nominal size. Costs entered at the type (schedule) level apply only to that type. For this example, all of the pipe material costs will be entered at the type (schedule) level. To enter a new cost, navigate to the material, nominal size and type combination for which you want to enter a cost. Click the New Cost button to create a new cost item in the table below. The new cost item will appear as a new column. Each pipe size in this example has two non-recurring costs associated with it. The costs to be entered are the material and installation costs. Figure 9.4 shows the costs entered for 8-inch Schedule 20 Steel. Enter the non-recurring pipe costs for the pipe in this example, as shown below.

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158 AFT Fathom 7.0 Modules User’s Guide All pipes are Schedule 20 Steel – Size

Material Cost Installation Cost

(inches) (dollars/foot)

(dollars/foot)

8

10.50

24.00

14

22.50

51.50

18

27.40

70.00

20

35.40

85.50

24

40.00

96.50

28

58.00

110.00

30

60.00

129.00

Figure 9.4

Non-recurring pipe costs, such as material and installation costs, are entered on the Pipe Materials tab.




Create cost scale tables The pipes in the model have 90 deg. elbows specified as fittings and losses. The cost of these 90 deg. elbow items can be included in the cost calculation. The costs for these items will be accounted for in scale tables. Scale tables can be used to vary a cost with a parameter such as diameter (i.e., size). Once created, this scale table can be applied to the fitting/loss items. The first table you will create is the scale table for the 90-deg. elbow installation costs. Select the Tables tab, and click the New Table button. Enter the following data for the scale table on the New Scale Table window: 1. Name = 90 Elbows Installation (Sch20, 8-34) 2. Table Type = Diameter 3. Table Format = Cost The window should appear as shown in Figure 9.5. After entering the data, click the OK button. After the table has been created, enter the cost data for the table. Do this by selecting the table name in the Table list, then entering the cost values in the table provided. Enter the following installation cost data into the scale table: Diameter

Installation Cost

(inches)

(U.S. Dollars)

8.125

185.50

12.250

298.00

17.376

446.00

23.250

595.00

29.000

744.00

33.000

843.00

You do not need to enter data in the scale tables for every diameter in the model. If a diameter falls between two data points in the table, the CST module will use the points on either side to linearly interpolate for a

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160 AFT Fathom 7.0 Modules User’s Guide value. If the cost function is non-linear, you may need to add additional data points to achieve a more accurate cost value. Create another scale table for the material costs using the following data: 1. Name = 90 Elbows Material (Sch20, 8-34) 2. Table Type = Diameter 3. Table Format = Cost Diameter

Material Cost

(inches)

(U.S. Dollars)

8.125

68.00

12.250

151.50

17.376

262.50

23.250

373.50

29.000

484.50

33.000

558.50

After the scale tables have been created, and the cost data entered, the Tables tab should appear as shown in Figure 9.5.

Add the costs for pipe fittings With the cost scale tables for the fittings defined, the costs for the pipe fittings can be added. Select the Pipe Fittings and Losses tab. A list of all of the available fittings and losses is displayed in the Pipe Fittings and Losses list. The fittings in the model are 90-deg. smooth flanged elbows, with an r/D ratio of 1. Navigate through the list until you find the proper selection for these fittings.




Figure 9.5

The Tables tab on the Cost Database window is used to create cost scale tables.

Add the material cost by clicking the New Cost button, and entering the following data: 1. Description = Elbow Material Costs 2. Cost Type = Material (NR) 3. Material = Steel 4. Material Size = All Sizes 5. Material Type = All Types 6. Use Size Table = Table of Costs 7. Multiplier = 1 8. Size Scaling Table = 90 Elbows Material (Sch20, 8-34) Now add the installation cost by clicking the New Cost button, and entering the following data: 1. Description = Elbow Installation Costs 2. Cost Type = Installation (NR)

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162 AFT Fathom 7.0 Modules User’s Guide 3. Material = Steel 4. Material Size = All Sizes 5. Material Type = All Types 6. Use Size Table = Table of Costs 7. Multiplier = 1 8. Size Scaling Table = 90 Elbows Installation (Sch20, 8-34) The actual cost values used for the fittings are the values that were entered in the scale tables on the Tables tab. The scale table to use for each cost is specified when the cost is defined. After the cost data is entered, the Pipe Fittings & Losses tab should appear as shown in Figure 9.6.

Figure 9.6

The Pipe Fittings & Losses tab on the Cost Database window is used to specify costs for pipe fitting/loss items.




Create a new cost database for the pumps To enter cost for a pump, or any other junction type, the junction must first be added to an engineering database. Cost data is then entered in a cost database associated with that engineering database. The pumps used in this example have been added to an engineering database. Create a new cost database associated with the Plant Cooling engineering database with the following general information: 1. Cost Type = Monetary 2. Monetary Unit = U.S. Dollars 3. Description = Plant Cooling Circ Pump Costs Save the cost database to a file by clicking the Save button. When prompted, choose to add the new database to the list of available and connected databases Enter the pump costs After the pump cost database has been created, select the Junctions tab in the Cost Database window. This is where you will enter the material and installation costs for the pumps. All of the junctions that are available in the selected engineering database will be listed. Select the Cooling Tower Circ Pump from the list of pumps. Add the material cost by clicking the New Cost button, and entering the following data: Material Cost = $28,500 Add the installation cost by clicking the New Cost button, and entering the following data: Installation Cost = $12,500 Figure 9.7 shows the pump costs entered in the cost database.

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Figure 9.7

The Junctions tab on the Cost Database window is used to specify costs for junctions.

Connecting the cost databases The cost databases should have been added to the list of available database, and been connected to the example model. If they were not, you can use the Database Manager to connect the cost databases now (see Figure 9.8). Refer to Chapter 7 for information on how to connect databases using the Database Manager.




Figure 9.8

Database Manager with connected engineering and cost databases.

Step 5. Including items in the Cost Report The final step before performing a cost analysis is to specify which pipes and junctions you want to be included in the final cost report. This is done by choosing Include in Cost Report on the Cost tab in the Specifications window for each pipe and junction to be included, as shown for Pipe 100 in Figure 9.9. Include the four circulating water pumps, and all of the pipes in the cost report. The Global Edit feature may be used to update this information for all of the pumps and pipes.

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Figure 9.9

The Cost tab on the Pipe and Junction Specifications windows is used to include the objects in the Cost Report.

Step 6. Run the model After all of the pipes and junctions have been defined, and all of the cost parameters have been specified, the cost analysis may be executed. Select Run Model in the Analysis menu. This will open the Solution Progress window. This window allows you to watch as the AFT Fathom Solver converges on the answer. After the run has completed, the results can be reviewed by clicking the View Output button.

Step 7. Examine the Cost Report The Cost Report is displayed in the General Results section of the Output window. View the Cost report by selecting the Cost Report Tab. The content of the Cost Report can be modified from the Output Control



Chapter 9 Cost Analysis Example 167 window. Figure 9.10 shows the Cost Report for this example with the Material, Installation, Operation/Energy, and Total costs displayed. The Cost Report shows the total system cost, as well as the individual totals for the material, installation, and energy costs. In addition, the Cost Report displays the detailed cost for each pipe, junction, and fitting that was included in the report. The items are grouped together by type, and a subtotal for each category is listed.

Figure 9.10

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The Cost Report in the General Output section shows the results of the cost analysis.

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Analysis summary The CST analysis for this example shows the following costs for the plant cooling system design: Total System Cost: $2,920,461 Total Material Cost:

$418,844

Total Installation Cost:

$699,341

Total Operation/Energy Cost: $1,802,276 Cost of Pipe:

$918,940

Cost of Pumps: $1,966,276 Cost of Fittings:

$35,244

Cost optimization with AFT Mercury™ AFT Mercury is a tool built on AFT Fathom technology. With AFT Mercury you can automatically size all pipes or ducts in your system to minimize monetary cost, weight, volume, or surface area. In addition, you can concurrently size the pumps and pipes to obtain the absolute lowest cost system that satisfies your design requirements. Finally, by accounting for non-recurring and recurring costs, you can optimize pipe and duct systems to minimize life cycle costs over some specified duration. By using AFT Mercury on this example, not only could the system cost be determined, but also the optimal system design could be determined.



CHAPTER 10

Using Modules Together

Previous chapters have illustrated how to use each of the AFT Fathom modules by themselves. However, AFT Fathom also allows you to use the modules together, in any combination you choose. This allows even greater flexibility in the types of analyses that can be accomplished using AFT Fathom. This chapter shows how the GSC, XTS, and CST modules can be used simultaneously by examining an example problem. Note: This example can only be run if you have licenses for the CST, GSC and XTS modules.


Fixed Head Supply Tank.fth – AFT Fathom model file

Problem statement A process plant requires the delivery of water at a fixed head, regardless of the system demand. This is accomplished by pumping the water to a supply reservoir, and maintaining a constant fill-level by varying the supply pump speed as the process demands change. Throughout any 24-



170 AFT Fathom 7.0 Modules User’s Guide hour period the process demands vary from as little as 500 gal/min to peak demands of 2500 gal/min. Use the GSC and XTS modules to analyze the system performance over a 24-hour period. Use the CST module to determine to energy costs for the pump with this daily operation over one year.

Start AFT Fathom From the Start menu, choose AFT Products and AFT Fathom.

Open the model file Open the Fixed Head Supply Tank.fth model file, which is located in the Examples folder in the AFT Fathom application folder. Save the file to a different folder. The model should appear as shown in Figure 10.1.

Variable and goal settings The GSC module is used to keep the level of the fluid in the Process Supply Tank constant by varying the pump speed. Open the Goal Seek and Control Manager and view the variables and goals (see Figure 10.2). The variable for this problem is the pump speed. The goal is defined as a point goal on the Process Supply Tank junction. The desired goal is for the net volumetric flow rate into the junction to be zero, which will keep the water level in the tank constant.

Transient control settings The XTS module is used to model the process demand changes over the 24-hour analysis period. Open the Transient Control window to view the Transient Control settings (see Figure 10.3). The transient analysis is set to run for a period of 24-hours with a time step of 10 minutes.



Chapter 10 Using Modules Together 171

Figure 10.1

Model of a Fixed Head Supply Tank (model file from the Examples folder in the AFT Fathom folder).

Figure 10.2

Goal Seek and Control variable and goal settings.

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Figure 10.3

Transient Control settings for a 24-hour period.

Junction transient data The flow variation in this model is driven by the J4 Assigned Flow junction. Open the J4 Assigned Flow Specifications window and select the Transient tab. The process flow demands are modeled as timevarying flows. The flow profile over the 24-hour period is defined in the Transient Data table (Figure 10.4). In addition, the J3 Reservoir junction is modeled as a finite reservoir (Figure 10.5). The J3 Reservoir can potentially drain and fill, and the varying pump speed (and, hence, flow) is what will keep its liquid level at 15 feet.



Chapter 10 Using Modules Together 173

Figure 10.4

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Flow demand over 24 hours at the J4 junction.

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Figure 10.5

J3 Reservoir junction is finite, which means it can drain and fill.

Cost settings For this problem, the pump energy cost for the 24-hour analysis period is entered as a fixed energy cost on the Cost Settings window. Open the Cost Settings window from the Analysis menu to view the energy cost settings (Figure 10.6). The Cost Time Period for the cost analysis is set to one year. The 24hour operation is assumed to repeat every day for this one-year period, and the total energy cost will be calculated assuming the 24-hour operation repeats non-stop throughout the year. More complicated cost variation is possible when using energy cost databases. Note that the cost calculation display is selected in the Cost Settings window by selecting the Calculate Costs option.

Run the model Select Run Model in the Analysis menu. This will open the Solution Progress window. This window allows you to watch as the AFT Fathom Solver converges on the answer.



Chapter 10 Using Modules Together 175 After the run has completed, the results can be reviewed by clicking the View Output button.

Figure 10.6

Cost Settings window applies Operation/Energy cost, can set the energy cost, and specifies the cost time period.

GSC and XTS module solutions When the GSC and XTS modules are used simultaneously, the GSC module is rerun for each time step. The GSC module variables are recalculated for the system conditions at each time step to ensure the specified goals are always met. This will typically result in longer run times, due to the increase in solution iterations that must be solved for each time step analysis.

Examine the results When using multiple modules, the goal seek, transient and cost analysis results are shown in the Output window in the same manner as when they are used individually.

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176 AFT Fathom 7.0 Modules User’s Guide The GSC variable and goal results in the General Output section can be viewed for each time step by using the slider bar at the bottom of the Output window, as shown in Figure 10.7. GSC module goal results for Time = 0 hours

GSC module goal results for Time = 12 hours

Figure 10.7

The slider bar at the bottom of the Output window can be used to view the transient results at any time step, including the GSC module variable and goal results.

Cost data is displayed in the Cost Report in the General Output section, as shown in Figure 10.8. The one-year energy cost for the supply pump in this example was $42,129.

Figure 10.8

The cost data is shown in the Cost Report in the General Output section of the Output window.

Figure 10.9 shows how the GSC module varied the pump’s speed over time with the varying process flow rate. Figure 10.10 shows that the water level in the process supply tank remains constant over time (which



Chapter 10 Using Modules Together 177 was the goal). The pump speed changes to increase and decrease the flow in order to keep the net flow into the Supply Tank zero.

Summary Individually, the AFT Fathom modules provide you with powerful analytical tools to assist you in the design of your pipe systems. The ability to combine the capabilities of these tools provides you with even greater and more powerful modeling capabilities.

Figure 10.9

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The GSC module varies the supply pump speed as the process flow rate changes over time (top).

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Figure 10.10

The water level in the process supply tank remains constant over time due to the variation in the pump speed.



Glossary

cost database A database of pipe system component costs associated with an engineering database. The CST module obtains cost data for system components from cost databases and displays the costs in the Cost Report. Cost Report The table shown in the Output window relating the total cost and individual costs for all items for the pipe system. CST module An optional add-on module to AFT Fathom which allows users to calculate non-recurring and recurring cost for the pipe system design. cyclic dual event A junction transient which has two initiation criteria which switch behavior from one transient state to the other and back Database Manager The window that allows creation and connection to network databases. Energy/operational cost A recurring cost that represents the cost of operating a pump. energy cost database pumps.

A database of energy costs that can be used with

engineering database A database which has engineering data for pipe system components such as pipe diameters and pump curves. event transient A transient which is initiated based on some criteria being satisfied in the system finite reservoir A body of fluid which is small enough that its surface level changes significantly during the time frame of the simulation as a result of liquid inflow or outflow. An example is a tank which drains as the simulation progresses.



180 AFT Fathom 7.0 Modules User’s Guide finite tanks See finite reservoir Goal See GSC goal Graph Results window The graphical window that allows preparation of plots. GSC goal Goals are the specified conditions that AFT Fathom will satisfy by changing the defined variables. Goals may be added, duplicated, and deleted from the Goals tab on the Goal Seek and Control Manager window. GSC module An optional add-on module to AFT Fathom which allows users to perform multi-variable goal seeking and simulate system control functions. GSC variable Variables are the parameters that AFT Fathom will automatically vary in order to achieve the desired goals. Variables may be added, duplicated, and deleted from the Variables tab on the Goal Seek and Control Manager window. Hydraulic Solver

See Solver

infinite reservoirs A massive body of fluid whose surface level does not change appreciably as a result of liquid inflow or outflow during the time frame of the simulation. An example is a large lake or the ocean. installation cost A non-recurring cost that represents the cost of installing a component. junction In AFT Fathom, a pressure/head solution point that connects and balances flow from pipes. maintenance cost A recurring cost that represents the cost of maintaining a component. material cost A non-recurring cost that represents the cost of purchasing a component. maximum cost group A group of pumps or control valves which are in the sizing stage but will eventually all be of the same design. The cost for each pump/control valve will therefore be the same. The maximum cost group looks for the most expensive pump/control valve in the group and uses that cost for all pumps/control valves in the group. Model Data window The text-based window where the input for the model is given in text form and input data can be entered.



Glossary 181 object A pipe system component (either a pipe or a junction) that is created, exists, and can be viewed on the Workspace. object status The state of the object, whether defined or undefined. operational cost See Energy/operational cost Output window The text-based window that shows the results of the analysis. pipe In AFT Fathom, a conduit for incompressible, steady-state fluid flow. All pipes have constant diameter and are completely filled with fluid. Primary window One of AFT Fathom's two input or three output windows. Quick Graph When using the XTS module, a feature in the Output window (activated with a right-click) which shows a graph of transient table contents relaxation A parameter that affects how the iterative solution scheme approaches a pipe flow solution. scenario A variant case of a model that is created in the Scenario Manager. Scenario Manager Window that allows one to create and manage multiple pipe flow model scenarios. These include different equipment, sizes, and operating conditions. sequential dual event A junction transient which has two initiation criteria. The first criteria will initiate a transient and the second, which will not occur until the first has occurred, will initiate a second transient. The two transients will not cycle (see cyclic dual event) but will cascade from the first to the second and then will cease Solver The part of AFT Fathom that contains the pipe flow network solution method. Specifications window are entered.

The window in which an object's properties

steady-state The condition of a system in which the rate of change of all parameters is negligibly small. time transient A transient which is initiated absolute time in the transient solution

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182 AFT Fathom 7.0 Modules User’s Guide tolerance The value at which the Solver should consider that convergence has been obtained. Variable See GSC variable Visual Report window The graphical window that allows integration of the analysis results with the pipe system schematic. Workspace The area of the Workspace window where models are visually assembled. Workspace window The graphical window where model assembly occurs and input data can be entered. XTS module An optional add-on module to AFT Fathom which allows users to simulate system transient behavior.



Repetitive costs 126

Index

Scale tables 123, 159 Using 125

A AFT DEFAULT INTERNAL DATABASE 156

Cost Report 127, 145 in Output window 166 Cost Settings window 153, 174

AFT Fathom

Specifying cost categories 133

Example models 4, 33, 91, 151 Getting started 3

Cost Summary window 135

qualifications for use 3

CST module 2 activating 4

using online help 4

setting up cost data 152

Animation 104

cyclic dual events 83, See Event transients

C Central difference method 64, 68 Check Valve junction

D Database Manager 116, 117, 127, 132, 139, 164

inherent event logic 86 Control Valve junction

Cost Databases 125

maximum cost groups 141, 146 Cost Application Manager 132 Cost Database window 114, 155

global multipliers 124 setting default database locations 134 Database Sources

Cost Databases Additional Loss costs 122

of cost data 127 Databases

Creating 116, 155, 163 Junction costs 119, 163

Cost 113, 155, 163

Multipliers 124

Energy Cost database 142, 154

Pipe Fitting & Loss costs 160

Engineering 113

Pipe material costs 118, 156

Differential Goal 20

Pump costs 121, 163

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E

Goals 16, 40

Energy Cost Database 142, 154

numerical control 27, 28, 29

Engineering parameter optimization 144

scenario differences 32

Event messages 89

View menu 10

in Output window 109

Variables 11, 38 Goals See Goal Seek and Control Manager

Event transients 82 at a pump 99

Differential Goal 20

Event messages in Output window 109

Group Goal 20

Example models 4

Group Max/Min 21 Group Max/Min example 40 Group Sum 21

F

Point Goal 20

FathomExamples.hlp 4, 33, 91, 151 Finite reservoirs 54

Graph Results window 70, 104 animation 104

Flow Volume calculations 144 Forward difference method 64, 67

Group Goal 20 Group Max/Min goal 21, 40 Group Sum goal 21

G

Groups 37

General Preferences

cross-plotting profile graphs 73

Database locations 134 Goal Seek and Control 43, See GSC module

group goal types 16 group goals 20

Enabling on Analysis menu 43

Group Max/Min goal example 40

Goals 39

maximum cost group 141, 146

Variable and goal results in Output window 44 Variables 38

GSC module 2 activating 4 setting up goal seeking 34

Goal Seek and Control Manager 10, 23, 38, 42, 43, 170, 180

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Index 185

I

creating 147

Ignore Transient Data See Transient Special Conditions

how multipliers are applied 148 Model Data window

Infinite reservoirs 54

GSC data 22, 42 transient junction data 61, 90

J

Monetary costs 143

Junction Specifications window Cost data 131

N

Including costs data 165

Non-monetary costs 143

opening in Goal Seek and Control Manager 15, 21

O

repeat transient 87

Output Control window 44

transient data 52

Cost Report formatting 145, 146, 167

transient data - absolute vs. relative 87

time formatting and units 69, 96

Junctions

transient pipe and junction data 69

assigned flow 172

Output window

assigned pressure 95

changing time formats and units 96

branch 96

Cost Report 127, 145, 166

control valve 37, 96

Database Sources 127

elbow 37

Event messages 89

heat exchanger 37

GSC Goal warning 26

pump 37, 95

GSC output 23, 44

reservoir 36, 94, 172

Quick Graph 70, 103

tee/wye 37

transient output 69, 102

valve 95

P

M

Parameter and Unit Preferences window

Maximum cost group 141, 146

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Custom monetary units 144

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186 AFT Fathom 7.0 Modules User’s Guide Monetary units and currency conversion 144 Pipe and Fluid Weight calculations 144

inherent event logic 86 Repeat transient 53, 87 Reservoir junction Modeling finite tanks during transients 94

Pipe Fittings & Losses Cost data 130

Reservoirs

Pipe Inner Surface Area calculations 144

drained 60 finite 54

Pipe Specifications window

infinite 54

Including cost data 165

Maximum and minimum pressures in closed tanks 61

opening in Goal Seek and Control Manager 21

overflow 59

Pipe Costs 127 Pipe Weight calculations 144 Point Goal 20 Pump junction maximum cost groups 141, 146 Pump Specifications window Turning pumps on and off during transients 99 Pump Transient summary report 102 Pumps

pipe depth and elevation input 61 Run Model 43, 101, 166, 174

S Scale tables 123, 159 sequential dual events 84, See Event Transients Show Object Status 37, 96 single event transients 82 Special Conditions 77

modeling transients 99

Transient 80 System Properties window 34, 92

Q Quick Graph in Output window 70, 103

T Time-based transients 81 Transient Control window 50, 51, 81, 97, 170

R Relief Valve junction

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Index 187 Changing parameters during the run 67

Specifying transient output time units and formats 96

disconnected scenarios 75

Time-based transients 81

forward and central difference 63

Transient control window See Transient control window

information in Solution Progress 62 Maximum iterations 67

Transient modeling Enabling on Analysis menu 97

Relative and absolute tolerance 65

Output window transient results 102

Relaxation 67

Setting up finite tanks which fill or drain 94

Transient data See Transient Control window, See Junction Specifications window

Specifying time units in Output window 96

Absolute vs. relative transient data in junctions 87

Transient Control window 97

animation 74, 105

Turning pumps on and off 99

entering for junctions 52 Event messages in Output 89 Event-based transients 82 graphing input in Junction Specifications window 87 in Graph Results 73

Transient Special Conditions 53, See Special Conditions

U Undefined Objects window 37, 96

V

in Model Data 90 in Model Data window 61 in Output window 69, 102 in Visual Report 76 junction transient example 99 junctions which support transient data 53 Repeat transient in junctions 87 Reservoirs 58

Visual Report window transient data display 76

W Workspace Preferences window 77, 80 GSC Variable and Goal indicators on the Workspace 42 Transient indicators on the Workspace 89 Workspace window 35, 93

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X XTS module 2 activating 4 enabling transient mode 49 Setting up a transient model 92

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Fathom 7.0 Modules Guide

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