201051792337561

Applications of Advanced Simulation Student Guide July 2006 MT15020 — NX4.0.2

Publication Number mt15020_g NX 4

Copyright and trademarks Proprietary and Restricted Rights Notices This software and all related documentation are proprietary to UGS Corp. Copyright ©2006 UGS Corp. All Rights Reserved. All trademarks belong to their respective holders.

©2006 UGS Corporation All Rights Reserved. Produced in the United States of America. 2

Applications of Advanced Simulation — Student Guide

mt15020_g NX 4

Contents

Course overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Course description . . . . . . . . . Intended audience . . . . . . . . . Prerequisites . . . . . . . . . . . . . How to use this manual . . . . . Symbols used in this guide

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9

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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 Advanced Simulation overview . . . . . . Advanced Simulation file structure . . . Advanced Simulation workflow . . . . . . Simulation Navigator . . . . . . . . . . . . . Nodes in the Simulation Navigator Simulation File View . . . . . . . . . . . Activity . . . . . . . . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . . . . . . . . .

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1- 1 1- 2 1- 4 1- 5 1- 6 1- 8 1-10 1-10

Geometry idealization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 Geometry idealization overview . . . . . . . Modifying features . . . . . . . . . . . . . . . . . Edit Feature Parameters . . . . . . . . . . Suppress Feature/Unsuppress Feature Master Model Dimension . . . . . . . . . . Modifying geometry . . . . . . . . . . . . . . . . Idealize Geometry . . . . . . . . . . . . . . . Defeature Geometry . . . . . . . . . . . . . Partition Model . . . . . . . . . . . . . . . . . Midsurface . . . . . . . . . . . . . . . . . . . . Face Pair midsurface method . . . . . . . Offset midsurface method . . . . . . . . . User Defined midsurface method . . . . Sew . . . . . . . . . . . . . . . . . . . . . . . . . . Subdivide Face . . . . . . . . . . . . . . . . . Activities . . . . . . . . . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . . . . . . . . . . .

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2- 1 2- 1 2- 2 2- 2 2- 5 2- 7 2- 7 2-10 2-11 2-14 2-15 2-16 2-18 2-19 2-22 2-23 2-23

3D meshing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 3D Tetrahedral Mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3- 1 ©UGS Corporation, All Rights Reserved


3

Contents

3D Swept Mesh . Solid from Shell Activity . . . . . . Summary . . . . .

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3333-

4 6 8 8

2D meshing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 2D meshing overview Editing a 2D mesh . . Activity . . . . . . . . . . Summary . . . . . . . . .

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4444-

1 4 5 5

1D and 0D meshing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 1D Mesh . . . . . . . . . . . . . . . . . . . 1D element meshing methods Create Weld Elements . . . . . . . . 1D Element Section . . . . . . . . . . 0D Mesh . . . . . . . . . . . . . . . . . . . Activity . . . . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . . . . .

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5- 1 5- 2 5- 5 5- 7 5- 9 5-11 5-11

Mesh points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1 Mesh points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6- 1 Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6- 2 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6- 2 Mesh and object display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 Mesh Display preferences Object display . . . . . . . . . Activity . . . . . . . . . . . . . Summary . . . . . . . . . . . .

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7777-

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Geometry abstraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1 Geometry abstraction overview . . . . . . . . . . . . . . . . . . . . . . Comparing geometry idealization and geometry abstraction Understanding polygon geometry . . . . . . . . . . . . . . . . . . . . Understanding the geometry abstraction process . . . . . . . . . Fillet identification process . . . . . . . . . . . . . . . . . . . . . . . . . Auto Heal Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Split Edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Split Face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Merge Edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Merge Face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Match Edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Collapse Edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Face Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4


©UGS Corporation, All Rights Reserved

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8- 1 8- 2 8- 2 8- 3 8- 6 8- 9 8-10 8-11 8-13 8-13 8-14 8-17 8-19

mt15020_g NX 4

Contents

Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-20 Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-21 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-21 Element attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1 Element attributes . . . . . . . . . . . . . . . . . . . . . . . . . . Attribute Editor . . . . . . . . . . . . . . . . . . . . . . . . . . . . Attribute Editor – point selection . . . . . . . . . . . . . Attribute Editor – curve/element selection . . . . . . Attribute Editor – face selection . . . . . . . . . . . . . Attribute Editor – body selection . . . . . . . . . . . . . Attribute Editor – 3D mesh selection . . . . . . . . . . Attribute Editor – 2D mesh selection . . . . . . . . . . Attribute Editor – 1D mesh selection . . . . . . . . . . Attribute Editor – 0D mesh selection . . . . . . . . . . Attribute Editor – Contact mesh selection . . . . . . Attribute Editor – Surface contact mesh selection Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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9- 1 9- 3 9- 3 9- 4 9- 6 9- 7 9- 8 9- 9 9-10 9-11 9-13 9-15 9-16 9-16

Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1 Materials overview . . . . . . . . . . . Customizing the material library Activity . . . . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . . . . .

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10101010-

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Boundary conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1 Boundary conditions overview . Supported boundary conditions Creating loads . . . . . . . . . . . . Creating constraints . . . . . . . . Activity . . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . . .

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2 2 5 6 6 6

Model information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1 Model information overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12- 2 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12- 4 Model checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-1 Model Check overview . . . . . . . . Comprehensive check . . . . . . . . . Element Shapes check . . . . . . . . Element Shapes Threshold Values Element Outlines check . . . . . . . Nodes check . . . . . . . . . . . . . . . . ©UGS Corporation, All Rights Reserved

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13- 2 13- 2 13- 3 13- 3 13-10 13-10


5

Contents

2D Element Normals checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-11 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-11 Solving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-1 Solving overview . . . . Solving the model . . . Analysis Job Monitor Batch solving . . . . . . Activity . . . . . . . . . . Summary . . . . . . . . .

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2 2 3 3 4 4

Post-processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-1 Post-processing introduction . . . . . . Results in the Simulation Navigator The Post Control toolbar . . . . . . . . . Import Results . . . . . . . . . . . . . . . . Post View . . . . . . . . . . . . . . . . . . . . Post view templates . . . . . . . . . . . . Post view layouts . . . . . . . . . . . . . . Overlay . . . . . . . . . . . . . . . . . . . . . Combining load cases . . . . . . . . . . . Animation . . . . . . . . . . . . . . . . . . . Identify . . . . . . . . . . . . . . . . . . . . . Generating reports . . . . . . . . . . . . . Activity . . . . . . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . . . . . . .

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15- 2 15- 2 15- 3 15- 4 15- 6 15- 7 15- 7 15- 8 15- 9 15-10 15-10 15-12 15-12 15-12

Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-1 Overview . . . . . . . . Creating the report . Exporting the report Activity . . . . . . . . . Summary . . . . . . . .

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1616161616-

2 4 4 4 4

Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-1 Units overview . Units Manager . Units Converter Activity . . . . . . Summary . . . . .

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2 2 4 5 5

Mesh connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-1 Mesh Mating Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18- 2 Edge Face Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18- 5 Weld Mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18- 6 6



mt15020_g NX 4

Contents

Contact Mesh . . . . . . Surface Contact Mesh Activity . . . . . . . . . . Summary . . . . . . . . .

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18- 9 18-10 18-11 18-11

Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-1 Optimization overview . . . . . Optimization Setup . . . . . . . . Optimization analysis options Objectives . . . . . . . . . . . . . . . Constraints . . . . . . . . . . . . . Design Variables . . . . . . . . . . Activity . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . .

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Durability (fatigue) analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-1 Durability overview . . . . . . . . . . . . . . . . . . . Preparing the model for a durability analysis Creating a durability solution . . . . . . . . . . . . Evaluating fatigue results . . . . . . . . . . . . . . . Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Buckling analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-1 Linear buckling overview . . . . . . Loads in linear buckling analysis Supported environments . . . . . . . Activity . . . . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . . . . .

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Modal analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-1 Modal analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22- 2 Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22- 4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22- 5 Thermal analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-1 Thermal analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23- 2 Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23- 4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23- 4 Contact and gluing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-1 Surface to Surface Contact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24- 2 Advanced Nonlinear Contact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24- 3 Surface to Surface Gluing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24- 5 ©UGS Corporation, All Rights Reserved


7

Contents

Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24- 6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24- 6

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Course overview Course description Applications of Advanced Simulation introduces the finite element modeling and analysis tool integrated in NX. It is intended for design engineers and analysts who want to learn the details of how to do finite element analysis on NX models. This course covers the details of the FEA processes from model preparation, mesh generation and manipulation, material definition, loads and boundary conditions, FEA model checking and solving, to postprocessing the results.

Intended audience •

Design engineers

•

Analysts

Prerequisites •

Practical Applications of NX course or self-paced equivalent.

•

Working knowledge of NX Modeling.

•

Basic understanding of finite element analysis principles.

How to use this manual The general format for lesson content is: •

presentation

•

activity in the Applications of Advanced Simulation Workbook

•

summary

It is important that you use the Student Guide and Workbook in the sequence presented. Later lessons assume you have learned concepts and techniques taught in earlier lessons. If necessary, you can always refer to any previous activity where a method or technique was originally taught. ©UGS Corporation, All Rights Reserved


9

How to use this manual

Symbols used in this guide The following symbols are used throughout this guide: This is a tip. This is a note. This is a warning.

10



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1

Lesson

1

Introduction Objective •

This lesson is a fundamental introduction to Advanced Simulation.

Advanced Simulation overview Advanced Simulation is a comprehensive finite element modeling and results visualization product that is designed to meet the needs of experienced analysts. Advanced Simulation includes a full suite of pre-and post-processing tools and supports a broad range of product performance evaluation solutions.

Advanced Simulation provides seamless, transparent support for a number of industry-standard solvers, such as NX Nastran, MSC Nastran, ANSYS, and ABAQUS. For example, when you create either a mesh or a solution in Advanced Simulation, you specify the solver you plan to use to solve your model and the type of analysis you want to perform. The software then presents all meshing, boundary conditions, and solution options using the terminology or “language” of that solver and analysis type. Additionally, you ©UGS Corporation, All Rights Reserved


1-1

Introduction

1

can solve your model and view your results directly in Advanced Simulation without having to first export a solver file or import your results. Advanced Simulation provides all the functionality available in Design Simulation, plus numerous additional features that support advanced analysis processes. •

Advanced Simulation features data structures, such as the separate Simulation and FEM files, that help facilitate the development of FE models across a distributed work environment. These data structures also allow analysts to easily share FE data to perform multiple types of analyses.

•

Advanced Simulation offers world class meshing capabilities. The software is designed to produce a very high quality mesh while using an economic element count. Advanced Simulation supports a complete complement of element types (0D, 1D, 2D, and 3D). Additionally, Advanced Simulation gives analysts control over specific meshing tolerances which control, for example, how the software meshes complex geometry, such as fillets.

•

Advanced Simulation includes a number of geometry abstraction tools that give analysts the ability to tailor the CAD geometry to the needs of their analysis. For example, analysts can use these tools to improve the overall quality of their mesh by eliminating problematic geometry, such as tiny edges.

•

Advanced Simulation features the new NX Thermal and NX Flow solvers. –

NX Thermal is a fully integrated finite difference solver. It allows thermal engineers to predict heat flow and temperatures in systems subjected to thermal loads.

–

NX Flow is a Computational Fluid Dynamics (CFD) solver. It allows analysts to perform steady-state, incompressible flow analysis and predict flow rates and pressure gradients for movement of fluid in a system.

You can use NX Thermal and NX Flow together to perform coupled thermal/flow analyses.

Advanced Simulation file structure As you progress through the Advanced Simulation workflow, you will use four separate, yet associated, files to store information. To work efficiently in Advanced Simulation, you need to understand what data is stored in which file, and thus which file needs to be the active work part when you create that data. These four files parallel the simulation process. 1-2



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Introduction

1

The original design part file being analyzed A part file has a .prt extension. For example, a part might be named plate.prt. The part file contains the master part or an assembly, and the unmodified part geometry. If you start with a model designed by someone else, you might not have permission to modify it. The master part file is generally not modified during the analysis process.

The idealized copy of the design part file An idealized part has a .prt extension. By default, when an idealized part file is created, fem#_i is appended to the part name. For example, an idealized part would be named plate_fem1_i.prt if the original part was named plate.prt. An idealized part is an associative copy of the original, and you can modify it. The idealization tools let you make changes to the design features of the model using the idealized part. You can perform geometry idealization as needed on the idealized part without modifying the master part. For example, you may remove and suppress features such as small geometry details that can be ignored in the analysis. You can use multiple idealized files for different types of analysis of the same original design part file.

The FEM file



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Introduction

1

A FEM file has a .fem extension. By default, when a FEM file is created, _fem# is appended to the part name. For example, a FEM file may be named plate_fem1.fem if the original part was named plate.prt. A FEM file contains the mesh (nodes and elements), physical properties, and materials. Once you create the mesh, you can use the abstraction tools to remove design artifacts that can affect the overall quality of the mesh such as sliver faces, small edges, and isthmus conditions. The abstraction tools allow you to mesh the geometry at a level of detail that sufficiently captures the design intent relevant to a particular finite element analysis. The geometry abstraction occurs on polygon geometry stored in the FEM, not in the idealized or master part. Since multiple FEM files can reference the same idealized part, you can build different FEMs for different types of analyses.

The Simulation file A Simulation file name has a .sim extension. By default, when a Simulation file is created, _sim# is appended to the part name. For example, a Simulation file may be named plate_sim1.sim if the original part was named plate.prt. The Simulation file contains all the simulation data, such as solutions, solution setup, loads, constraints, element-associated data, physical properties, and overrides. You can create many Simulation files associated to the same FEM file.

Advanced Simulation workflow Before you begin an analysis, you should have a thorough understanding of the problem you are trying to solve. You should know which solver you will be using, what type of analysis you are performing, and what type of solution is needed. The following outline summarizes the general workflow in Advanced Simulation. 1. In NX, open a part file. 2. Open the Advanced Simulation application. Specify the default solver (which sets the environment, or language) for working in the FEM and Simulation files. You could also choose to create only the FEM file first, and then create a Simulation file later. 3. Create a solution. 1-4



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Introduction

Select the solver (such as NX Nastran), analysis type (such as Structural), and solution type (such as Linear Statics). 4. If necessary, idealize the part geometry. Once you make the idealized part active, you can remove unnecessary details such as holes or fillets, partition the geometry to prepare for solid meshing, or create midsurfaces. 5. Make the FEM file active, and mesh your geometry. It is a good practice to first mesh your geometry automatically using the software defaults. In the great majority of cases, the software defaults provide a robust, high-quality mesh you can use without modification. 6. Check your mesh quality. If necessary, you can refine your mesh by returning to the idealized part and further idealizing the part geometry. In addition, in the FEM you can use the abstraction tools to eliminate issues with the CAD geometry that can cause undesirable results when you mesh your model. 7. Apply a material to the mesh. 8. When you are satisfied with your mesh, make the Simulation file active, and apply loads and constraints to your model. 9. Solve your model. 10. Examine your results in Postprocessing.

Simulation Navigator The Simulation Navigator provides you with a graphical way of viewing and manipulating the different files and components of a CAE analysis within a tree structure. Each file or component is displayed as a separate node in the tree. The Simulation Navigator provides direct access to the entities in it through shortcut menus. You can perform most operations directly in the Simulation Navigator instead of using icons or commands. For example, to create a new solution definition, you can drag loads and constraints from one container to another in the Simulation Navigator.



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Introduction

1

Nodes in the Simulation Navigator The top panel of the Simulation Navigator shows the contents of the displayed file. The figure below shows an example of the containers that can be displayed within a top-level Simulation file. The check boxes let you control the display of the items.

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Introduction

The following table presents a high-level overview of the various nodes in the Simulation Navigator. Icon

Node Name

Node Description

Simulation

Contains all the simulation data, such as solutions, solution setup, solver-specific simulation objects, loads, constraints, and overrides. You can have multiple Simulation files associated with a single FEM file.

FEM

Contains all the mesh data, physical properties, material data, and polygon geometry. The FEM file is always associated to the idealized part. You can associate multiple FEM files to a single idealized part.

idealized part Contains the idealized part that the software creates automatically when you create a FEM. master part

When the master part is the work part, right-click on the master part node to create a new FEM or display existing idealized parts.

Polygon Geometry

Contains the polygon geometry (polygon bodies, faces, and edges). Once you mesh the FEM, any further geometry abstraction occurs on the polygon geometry, not the idealized or the master part.

0D Meshes

Contains all 0D meshes.

1D Meshes


2D Meshes


3D Meshes


Simulation Object Container

Contains solver- and solution-specific objects, such as thermostats, tables, or flow surfaces.

Load Container

Contains loads assigned to the current Simulation file. In a Solution container, the Load Container contains the loads assigned to given subcase.

Constraint Container

Contains constraints assigned to the current Simulation file. In a Solution container, the Constraint Container contains the constraints assigned to the solution.



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1

Introduction

1 Icon

Node Name

Node Description

Solution

Contains the solution objects, loads, constraints, and subcases for the solution.

Subcase

Contains solution entities specific to each subcase within a solution, such as loads, constraints, and simulation objects.

Step Results

Contains any results from a solve. In the post processor, you can open the Results node and use the visibility check boxes within the Simulation Navigator to control the display of various results sets.

Simulation File View The bottom section of the Simulation Navigator contains the Simulation File View panel, which shows the overall “roadmap” of the files you have open. To work on a particular file, double-click it make it active.

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Introduction

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Part file bracket.prt

Idealized part file bracket_fem_i.prt

FEM file bracket_fem1.fem

Simulation file bracket_sim1.sim



1-9

Introduction

1

Activity See the “Introduction” activity in the Applications of Advanced Simulation Workbook. In this activity you will work through the Advanced Simulation workflow by analyzing a part — a connecting rod — using a 3D (solid) mesh.

Summary In this lesson you:

1-10

•

Learned about the capabilities of Advanced Simulation.

•

Learned about the files that are used by Advanced Simulation.

•

Learned about basic workflow for using Advanced Simulation.

•

Created FEM and Simulation files.

•

Worked with files in the Simulation Navigator.

•

Worked through the finite element analysis workflow in Advanced Simulation.



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Lesson

2

Geometry idealization

2

Objective •

Learn how to use model preparation tools to simplify your model before meshing.

Geometry idealization overview Geometry idealization is the process of removing or suppressing features from your model prior to defining a mesh. You can also use geometry idealization commands to create additional features, such as partitions, to support your finite element modeling goals. For example, you can use geometry idealization commands to: •

Remove features, such as bosses, that aren’t significant to your analysis.

•

Modify the dimensions of the idealized part using interpart expressions.

•

Partition a larger volume into multiple smaller volumes to facilitate mapped meshing.

•

Create midsurfaces to facilitate shell meshing of thin-walled parts.

The software performs all geometry idealization operations on the idealized part, which is an assembly instance of your master model. No idealization is performed directly on the master model. You can use the commands on the Model Preparation toolbar to idealize the geometry in your model. To use the commands on the Model Preparation toolbar, you must make the idealized part the displayed part.

Modifying features Several tools let you modify features of the idealized part: •

Edit Feature Parameters

•

Suppress Feature and Unsuppress Feature



2-1


•

Master Model Dimension

Edit Feature Parameters

2

In Advanced Simulation, when you use the Midsurface tool, you create a midsurface feature parameter that you can edit using Edit Feature Parameters

.

Additionally, you can edit any existing feature parameters in your model based on the method and parameter values used when it was created. The interaction depends on the type of feature you select.

Suppress Feature/Unsuppress Feature Use Suppress Feature to automatically select features to be suppressed, or to manually select one or more features and temporarily remove them from the target body and the display. To successfully access features for suppression, you must first enable suppression for the relevant part features in Modeling (Modeling application → Edit → Feature → Suppress by Expression).

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A suppressed feature still exists in the database but appears to be removed from the model. You can retrieve any suppressed features using Unsuppress Feature

.

2

Use Suppress Feature to: •

Reduce the size of large models, thereby reducing the creation, object selection, edit, and display time.

•

Remove non-critical features such as small holes, blends, and chamfers from your model for analysis work. Note that suppressed features are not meshed in Advanced Simulation.

•

Create features in locations where there is conflicting geometry. For example, if you need to position a feature using an edge that has already been blended, you do not need to delete the blend. You can suppress the blend, create and position the new feature, and then unsuppress the blend. UGS recommends that you do not create new features where a suppressed feature exists.



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2

Suppressing associated features When you suppress a feature that has associated features, the associated features are also suppressed (see figure below).

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Suppressing features 1. Click Suppress Feature

.

2. Select the feature(s) to be suppressed, either from the list in the dialog or in the graphics window. You can also click the Selection Criteria button for automatic selection of suppressable features using a criteria filter. 3. If you do not want the Suppress Feature selection dialog to include any dependents in the Selected Features list, turn the List Dependents toggle switch to Off. (Doing so can noticeably improve performance time if the selected features have a lot of dependents.) 4. Click OK or Apply to suppress the selected features.

Master Model Dimension The Master Model Dimension tool launches the Edit Dimension dialog box. Edit Dimension lets you modify the idealized part’s dimensions, taking advantage of interpart expressions. Use the Edit Dimension dialog box to modify any feature or sketch dimension without affecting the master part dimensions. ©UGS Corporation, All Rights Reserved


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2

Editing master model dimensions to open the Edit Dimension dialog 1. Click Master Model Dimension and select a feature. Associated expressions or descriptions display in the list window.

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2. Use the Expression or the Description option to display the selected feature’s dimensions as either an interpart expression or as standard descriptions for the feature type.

2

3. Select a dimension from the list to modify. 4. (Optional) Click Used By to view a list of where the selected expression is used. 5. Enter a new value for the selected dimension. 6. Click Apply to apply the new dimension value, and repeat steps 3 – 5 for the remaining features and dimensions. Click OK to apply the new value and close the Edit Dimensions dialog.

Modifying geometry Several tools let you modify the geometry of the idealized part: •

Idealize Geometry

•

Defeature Geometry

•

Partition Model

•

Midsurface

•

Sew

•

Subdivide Face

Idealize Geometry

Use Idealize Geometry to simplify a model’s geometry by removing features from a body or a region of a body that satisfy certain criteria, or that you explicitly select for removal. For example, you may want to remove small geometric features that would otherwise cause too many additional elements to be created.

To use Idealize Geometry , you must have the idealized part displayed in the graphics window.



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2

Idealizing Geometry on a Body 1. With the idealized part displayed in the graphics region, click Idealize Geometry

.

2. In the Idealize dialog, click Body

.

3. In the graphics window, select the body. You can now select options that identify features to be removed. 4. (Optional) To remove specific faces, click Removed Faces (Optional) , and select faces to remove. 5. (Optional) To remove blends, select Chain Selected Blends. In the graphics window, select a blend. The software selects adjacent blends with the same radius. 2-8



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6. (Optional) To automatically remove features, select Holes or Blends in Automatic Feature Removal. Enter a value for the criteria. The software selects all features in the body that meet the criteria.

2

7. Click OK. The selected features are removed. Idealizing Geometry in a Region 1. With the idealized part displayed, click Idealize Geometry

2. In the Idealize dialog, click Region

.

.

3. In the graphics window, select a seed face (the first face in the region). You can now select features to be removed. 4. (Optional) To define an outer boundary for the region, click Boundary Faces (Optional)

and select the face or a set of faces.

5. (Optional) To automatically select adjacent faces to include in the region, select Tangential Edge Angle, and enter an angle value. The software selects faces adjacent to the seed face if the angle between the normal to the seed face and the normal of an adjacent face is less than or equal to the angle value. 6. (Optional) To remove specific faces, click Removed Faces (Optional) , and select faces to remove. 7. (Optional) To remove blends, turn on Chain Selected Blends. Select a blend. The software selects the adjacent blends with the same radius. 8. Click Preview Region to see the outline of the region to be simplified. 9. (Optional) To automatically remove features, select Holes or Blends in Automatic Feature Removal. Enter a value for the criteria. The software selects all features that meet the criteria. 10. Click OK. ©UGS Corporation, All Rights Reserved


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All selected features are removed.

Defeature Geometry

2 provides a streamlined method for feature Defeature Geometry removal. When you defeature a model, you simplify geometry by using selections in the graphics window to remove a face or set of faces. This is a quick way to remove larger model features such as bosses containing multiple faces. Defeaturing geometry To remove a feature or set of features, follow these basic steps: 1. Click Defeature Geometry

.

If the Selection Intent toolbar is not visible in the graphics window, position the cursor in the toolbar area outside the graphics window and click MB3 to enable Selection Intent. 2. Select Add Region Boundary from the Face drop-down list in Selection Intent. In the graphics window, the cursor becomes available for face selection. 3. Select a seed face for the feature you want to remove. 4. Select a boundary face as the outer limit for feature removal. 5. Click MB2 to update the surface region. The second figure in the following graphic shows an example of a resulting surface region.

on the Defeature dialog bar, or click MB2 again to execute 6. Click feature removal. To edit the removed feature, click on the Part Navigator tab in the Resource Bar and locate the Defeature node. Use MB3 menu options to edit feature parameters.

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2

Partition Model Partition Model provides a way to associatively partition solid bodies in a simulation model. This feature is most often used to partition bodies into sweepable solids to create a swept mesh model. This feature creates a named group of features, which can be seen in the model navigation tool. The objects selected for the trimming operation determine the contents of the named feature. Furthermore, the grouped feature allows users much greater flexibility in editing. In addition to the geometric operation of splitting the body, a glued mesh mating condition is automatically created at the partitioning geometry location, so that applied meshes are continuous from one body to the other. The model partitioning function is also useful for controlling a tetrahedral mesh using, for example, different global element sizes on sub-bodies. Because of this, the geometry model needs to be broken down into smaller units that can be more easily and automatically meshed. Model partitioning breaks down a volume into sub-volumes associatively.



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2

Partition Model provides a way to associatively partition solid bodies in a simulation model. This feature is most often used to partition bodies into sweepable solids to create a swept mesh model. This feature creates a named group of features, which can be seen in the model navigation tool. The objects selected for the trimming operation determine the contents of the named feature. Furthermore, the grouped feature allows users much greater flexibility in editing. In addition to the geometric operation of splitting the body, a glued mesh mating condition is automatically created at the partitioning geometry location, so that applied meshes are continuous from one body to the other. The model partitioning function is also useful for controlling a tetrahedral mesh using, for example, different global element sizes on sub-bodies. Because of this, the geometry model needs to be broken down into smaller units that can be more easily and automatically meshed. Model partitioning breaks down a volume into sub-volumes associatively.

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2

Partitioning the model 1. Click Partition Model

.

The Partition Model dialog is displayed.

2. Click Body to Partition

and select the solid body to be partitioned.

3. Click Partitioning Geometry , and select the desired partition geometric tool (datum plane, sheet body, curve/edge, etc.) to subdivide the body or bodies. Select an option from the Filter drop-down menu to aid in selection. When Blank Partition Geometry is selected (the default), partitioning geometry is blanked following the partitioning operation.



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4. If necessary, click Direction and choose a Vector Method to define a direction vector to extrude or revolve a selected section.

2

5. Click Apply to create the partition. If you are partitioning the model to prepare for swept meshing, click Show Unsweepable Solids require further partitioning.

to highlight bodies that

Repeat steps 2 – 4 to fully partition the model.

Midsurface Use Midsurface to simplify thin-walled geometry and create a continuous surface feature that resides between two opposing faces within a single solid body. The points and normals of the parent faces (surface pairs) are averaged at corresponding parameters. The new surface, or midsurface, contains information about the geometric thickness of the surface pairs.

Midsurface creation methods Use one of the following methods to create a midsurface feature:

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•

Face Pair: This method creates a midsurface halfway between the opposing face pairs. The face pair method is useful for creating midsurfaces for thin-wall geometries with ribs.

•

Offset: This method offsets the midsurface from one side of the solid body by a depth ranging from 0 to 100% (the thickness of the solid).



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•

User Defined: This method defines a sheet body you’ve previously created as the midsurface of a part. That is, you can manually model a sheet body to approximate the midsurface of a thin-walled part, and then define that body as a midsurface feature of your part.

Face Pair midsurface method The Face Pair method uses opposing face pairs to create a midsurface located halfway between the two faces. This type of midsurface can only be created from a single solid body that contains opposing faces.

Automatically Creating a Face Pair

1. Click Midsurface

.

2. In the dialog, choose Method →Face Pair. ©UGS Corporation, All Rights Reserved


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2


3. Select a face for side one and click MB2. Note that the solid body is promoted at this point. 4. Choose AutoCreate.

2

The software creates as many face pair features as possible. 5. Manually define or edit any remaining face pair features, if necessary. Manually Creating a Face Pair Midsurface 1. Click Midsurface

.

2. In the dialog, choose Method →Face Pair. 3. Select a face for side one and click MB2. Note that the solid body is promoted at this point. 4. Select an opposing face for side 2. Alternatively, select the Automatic Progression check box. When this option is turned on, the software selects the most likely side 2 face for each side 1 face you select. 5. Continue to select pairs in this manner until all face pair features are defined. Watch the cue line to ensure that you select the correct corresponding face at the right time.

Offset midsurface method With the Offset method, a midsurface generated from a seed face is positioned midway between the seed face and its opposing face. The distance between the seed face and the opposing face is the thickness of the solid. The offset method requires a solid of uniform thickness. You can define any number of faces to be offset, but you first must select a seed face. Once you begin, you cannot switch from the offset method to the face pair method. The midsurface thickness created using the offset method is added as an NX attribute attached to the midsurface sheet body. The name of the attribute is "Midsurface_thickness." You can verify the thickness using Format → Attribute → Object. 2-16



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2

Defining a midsurface with the offset method 1. Click Midsurface

.

2. In the Midsurface dialog, choose Method → Offset. 3. Select the solid body and click MB2 to advance to the next selection step.

4. Click Target Body

5. Click Seed Face

and select the body.

and select a seed face for the midsurface.

6. Set the Cliff Angle. The default is 75 degrees.



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7. Preview the generated face to be offset by clicking the Region or Full Boundary preview buttons. 8. If necessary, adjust the Cliff Angle to ensure that the correct face is selected. When the previewed face is correct, click OK.

2

If Blank Original is selected, the original solid body is blanked; only the sheet body is displayed.

User Defined midsurface method With the User Defined method, you use an existing sheet body to create a midsurface in a solid body. This method can be useful in situations where alternate methods of midsurface creation did not produce satisfactory results. If the sheet body you create is within the confines of the solid body, the software will automatically generate the midsurface, even if the body is not uniformly thick.

All faces connected to the seed face that satisfy smoothness and boundary face criteria are offset as a midsurface half the thickness into the solid. The software terminates midsurface creation when it encounters a boundary face. A boundary face is defined as a face oriented in the thickness direction, at an angle greater than or equal to the cliff angle value. The seed face will propagate in all directions until it reaches the edge on a boundary face. Thickness Outside Body guidelines The user-defined midsurface can contain surfaces that extend. For example, if you have a sheet body containing small holes and you want the holes to be ignored in the midsurface creation, enter a value for the Thickness Outside Body option. This value tells the software how thick to define the "virtual" solid body when it encounters what are actually the small holes. 2-18



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Note that an outside body thickness value of greater than zero is recommended. Although it is unlikely that a zero value will cause midsurface creation problems, the solve could fail, especially if the midsurface extends beyond the solid body, because the shell thickness will be interpreted as zero. In the following graphic, the yellow portion of the midsurface ignores the hole in the solid, while the dark green area extends beyond its boundaries. The software approximates a thickness for these regions, which you can modify.

Defining a midsurface with the user defined method 1. Click Midsurface

.

2. In the Midsurface dialog, choose Method → User Defined. 3. Select the solid body and click MB2 to advance to the next selection step. 4. Select the sheet body. If some part of the selected sheet body is not fully contained within the solid body, enter a value in the Thickness Outside Body field for the software to use when formatting the element thickness for a solve.

Sew Use Sew

to join together selected sheet or solid bodies.

You can use Sew to join together: ©UGS Corporation, All Rights Reserved


2-19

2


2

•

Two or more sheet bodies to create a single sheet. If the collection of sheets to be sewn encloses a volume, the software creates a solid body.

•

Two solid bodies if they share one or more common faces.

Creating a solid vs. sheet body If you want to create a solid body by sewing a set of sheets together, the selected sheets must not have any gaps larger than the specified Sew Tolerance. Otherwise, the resulting body is a sheet, not a solid.

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2

Sewing two solid bodies together You can sew two solid bodies together only if they share one or more common (coincident) faces. When you use Sew, the software deletes the common face(s) and sews the solid bodies into a single solid body. Sew All Instances •

If a selected body is part of an instance array and you select the Sew All Instances option, the software sews the entire instance array.

•

If you deselect the Sew All Instances option, the software only sews the selected instance.

Sew Tolerance The software sews edges together, whether there is a gap between them or whether they overlap, if the distance between them is less than the specified Sew Tolerance. If the distance between them is greater than this tolerance, the software cannot sew them together.



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2

Subdivide Face Subdivide Face lets you automatically subdivide multiple faces while maintaining associativity, using a variety of subdividing geometries. This function allows you to control a 2D mesh using global element size for a portion of the model. It is also useful if you want to subdivide a face into four-sided regions to facilitate mapped meshing with quadrilateral elements. The edges and faces of a subdivided face are associative and are combined into a group feature.

For simple edges and curves, the behavior will be as follows:

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•

Where a datum plane, sheet body, or face is used as a tool, the tool is intersected with the selected face to be subdivided, and the resulting curves are used for subdividing. These intersect curve features will show up in the grouped feature.

•

Where the Two Points option is chosen in the filter, you can specify the end points of a line. The last two points selected are used to create the line. The end points are associative to the underlying geometry. The resulting line will be used to subdivide the face, projecting the line as required.

Geometry objects that are associated with the subdivided face feature cannot be deleted. If you transform the objects associated with a subdivided face, the face itself is also updated. If you transform the solid body on which any subdivided faces reside, their associated curves do not move. However, the subdivided faces are updated accordingly.

Activities See the “Geometry idealization” activities in the Applications of Advanced Simulation Workbook. In these activities, you will idealize a part.

Summary In this lesson you: •

Learned about tools for modifying features in the idealized part, including Edit Feature Parameters, Suppress Feature, Unsuppress Feature, and Master Model Dimension.

•

Learned about tools for modifying geometry in the idealized part, including Idealize Geometry, Defeature Geometry, Partition Model, Midsurface (three methods), Sew, and Subdivide Face.



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2

2

Lesson

3

3D meshing 3

Objectives •

Learn how to mesh solid bodies using 3D tetrahedral elements.

•

Learn how to mesh solid bodies using 3D swept mesh elements.

•

Learn how to mesh solid bodies by creating a solid mesh generated from shell elements.

3D Tetrahedral Mesh The 3D Tetrahedral Mesh function supports the creation of 4-noded and 10-noded tetrahedral elements. You can create a 3D mesh on solid bodies for all supported solvers.



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3D meshing

3

3D Mesh Options The 3D Mesh Options dialog box defines how the meshing algorithm processes small features and fillets.

3-2



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3D meshing

3

Failed elements After meshing, the element quality is checked against the Maximum Jacobian threshold: •

If the quality measure violates this threshold, the element is highlighted in red.

•

If the quality measure is within 10% of the this threshold, the element is highlighted in yellow.

If you have a high number of poor quality elements, you can: •

Further idealize the part’s geometry to remove problematic areas.

•

Modify surface or solid mesh size variation to improve node distribution.

•

Use the abstraction tools to improve the quality of the polygonal geometry.



3-3

3D meshing

•

Increase the threshold value for Maximum Jacobian if element quality is not critical in that area of the model.

Creating a 3D mesh

1. Click 3D Tetrahedral Mesh

.

2. In the graphics window, select the solid body to mesh.

3

3. In the dialog, choose an element type from the drop-down list.

4. Enter an element size. Or, click calculate an appropriate element size.

to have the software

5. (Optional) Click Preview to view the resulting nodes on edges for the mesh. If you are not satisfied, you can modify the Overall Element Size value. 6. (Optional) To specify small feature tolerances and fillet processing parameters, click the Mesh Options button. 7. Click OK or Apply to generate the mesh.

3D Swept Mesh 3D Swept Mesh generates a mesh of either 8– (linear) or 20–noded (parabolic) hexahedral elements on any two-and-one-half dimensional solid by sweeping the mesh from a source face through the entire solid. When you create a swept mesh, the software first meshes the specified source face of the volume with linear quadrilateral elements. The software then propagates that mesh into the volume layer by layer with the first layer resulting in the first set of hexahedral elements, and so on. You can also use an existing (linear or parabolic) triangular or (linear or parabolic) quadrilateral surface mesh to generate (linear or parabolic) wedge or (linear or parabolic) hexahedral swept mesh elements. The mesh generation proceeds from the selected source face to the target face, which the software determines by evaluating the volume. If the initial mesh originating from the source face contains one or more triangular elements, the swept mesh will also contain corresponding wedge elements. 3-4



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3D meshing

3

System checks Once you click OK or Apply on the dialog box, the software: •

Checks whether the solid is geometrically sweepable and generates an appropriate error if not.

•

Checks whether the meshes on the solid’s faces or mated faces can be used for sweeping and generates an appropriate error if not.

•

Checks whether the target face has already been meshed and generates an error if yes.

Mesh mating conditions For each face in the solid, the software checks to see whether mesh mating conditions on an adjacent solid are satisfied. If they are and if a mesh is found on the face adjacent to the source face for the swept mesh, this will be used for mesh mating conditions as long as it matches the defined swept mesh, as follows. •

For a linear or parabolic wedge swept mesh, the adjacent body must have an existing linear triangular/wedge or parabolic triangular/wedge mesh.

•

For a linear or parabolic hexahedral swept mesh, the adjacent body must have an existing linear quadrilateral/hexahedral or parabolic quadrilateral/hexahedral mesh.



3-5

3D meshing

If no mesh is found on the adjacent body that satisfies other mesh mating conditions, a surface mesh is created. Free mesh or mapped mesh will be determined based on whether the face is a wall face. (All wall faces must be map-meshed.) For each edge, the same logic is applied. Generating a swept mesh from a sweepable solid

1. Click 3D Swept Mesh

3

.

2. In the graphics window, select the sweepable solid body to mesh. 3. In the dialog, select an element type from the drop-down menu.

4. Enter an element size, or click calculate an appropriate element size.

to have the software

5. (Optional) Click Preview to view the resulting nodes on edges for the mesh. If you are not satisfied, you can modify the Overall Element Size value. 6. Click OK or Apply to generate the mesh. Generating a swept mesh from a meshed surface

1. Click 3D Swept Mesh

.

2. In the graphics window, select an existing meshed surface on a sweepable solid. 3. Select an element type from the drop-down menu. Note that the element size is determined by the size of the seed mesh. 4. Click OK or Apply to generate the mesh.

Solid from Shell Use Solid From Shell triangular shell mesh. 3-6

to generate a solid tetrahedral mesh from a



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3D meshing

3

Solid meshes created from shell elements have no associativity to the bounding shell mesh or the underlying geometry. Solid meshes created by the Solid From Shell command are not editable. In addition, if any shell mesh bounding a 3D mesh created by Solid from Shell requires an update, the 3D mesh is automatically deleted. You must re-create the solid mesh following the shell mesh update. To generate a solid mesh, the shell mesh must meet the following requirements: •

All 2D triangular elements must be of the same order (linear or parabolic). Use caution when generating a solid shell from parabolic elements. Unless the parabolic triangular shell elements have straight edges, the resulting parabolic tetrahedral mesh will likely contain elements that fail Jacobian tests.

•

The shell elements must completely enclose a volume. Otherwise, the software can’t generate the solid elements.

•

There are no coincident triangular elements in the shell mesh.



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3D meshing

Use Check Nodes to identify duplicate nodes. This is a good check for coincident elements. Use Element Outlines to check for element free edges. A free-edge check will reveal any gaps in volume boundary. You can use the 2D Edit Mesh commands to repair any gaps in your shell mesh. When selected, Mesh Interior Volumes generates multiple solid meshes from selected shell meshes that enclose interior volumes. This is useful for modeling thermal or flow problems, in which the interior volumes would typically represent a heat sink or source, or a flow obstacle.

3

Creating a solid mesh from shell elements To create a solid tetrahedral mesh from triangular shell elements 1. Choose Solid from Shell

.

2. Review and modify the dialog options as needed. 3. Select one or more 2D, triangular shell meshes that completely enclose one or more volumes. 4. Click OK.

Activity See the “3D meshing” activity in the Applications of Advanced Simulation Workbook. In this activity, you will generate and refine a 3D mesh.

Summary In this lesson you learned about the three 3D meshing commands:

3-8

•

3D Tetrahedral Mesh

•

3D Swept Mesh

•

Solid from Shell



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Lesson

4

2D meshing

Objectives •

Learn how to generate a 2D mesh.

•

Learn about tools for editing a 2D mesh.

4 2D meshing overview 2D Mesh generates 3- and 6-noded triangular elements as well as 4and 8-noded quadrilateral elements. 2D elements are also commonly known as shell or plate elements. For Tri6 and Quad8 elements, midnode snapping and a specified Jacobian ratio are supported. The default element size does not specify the final size of the elements but defines the parameter used to control the edge length of the element. Actual element edge lengths are approximately equal to the specified overall element size. The software automatically adjusts for problematic element sizes on rectangular or nearly rectangular surfaces (non-planar included). The resulting element size will be "safe" and yield a higher quality mesh.



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2D meshing

4

Mesh Options The 2D Mesh Options dialog box specifies how the meshing algorithm processes small features and fillets. 4-2



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2D meshing

4

Creating a 2D mesh 1. Click 2D Mesh

.

2. Select the midsurface or faces you want to mesh. In the dialog, use the Filter drop-down menu to help you select from faces, bodies, or an existing mesh. 3. From the Type drop-down menu, choose the element type. 4. Enter a size for the Overall Element Size, or click automatically calculate a suggested element size.

to

5. If necessary, click the More Options arrow to display additional options for this mesh. ©UGS Corporation, All Rights Reserved


4-3

2D meshing

6. To specify small feature tolerances and fillet processing parameters, click the Mesh Options button. 7. Click Preview to view the resulting nodes on edges for the mesh. If you are not satisfied with the node number and location, you can modify the Overall Element Size value. 8. Click OK or Apply to generate the mesh.

Editing a 2D mesh The 2D Edit Mesh functionality provides you with a basic set of shell element and/or node editing capabilities for the purpose of fixing elements of poor and unsatisfactory quality produced by the automatic mesh.

4

Edit Mesh features the following options: Icon

Label

Description

Split Quad

Allows you to divide quadrilateral elements (quads) into triangular elements (tris). Splitting occurs along the smaller of the two diagonals.

4-4

Combine Tris

Allows you to combine triangular elements (tris) into quadrilateral elements (quads).

Move Node

Allows you to relocate a nodal position.

Delete Element

Allows you to delete elements of your choice.

Create Element

Allows you to create a quad or tri element that will be added to the existing 2D mesh. If the mesh has higher order elements, the newly created element will also have midnodes.

Unlock Mesh

Allows you to unlock the edited mesh for an update operation.

Assign Nodal Displacement Coordinate System

Allows you to manually define a nodal displacement coordinate system for selected nodes or geometry.



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2D meshing

Icon

Label

Description

Assign Nodal Displacement Coordinate System

Allows you to determine the coordinate system assigned to nodes, or the nodes to which a coordinate system is assigned.

Activity See the “2D meshing” activity in the Applications of Advanced Simulation Workbook. In this activity, you will generate and refine a 2D mesh.

4 Summary In this lesson you: •

Learned how to generate a 2D mesh.

•

Learned about tools for editing a 2D mesh.



4-5

4

Lesson

5

1D and 0D meshing

Objectives •

Learn how to create a mesh of 1D elements.

•

Learn how to create weld elements.

•

Learn how to create a 1D element section.

•

Learn how to create a 0D mesh.

5

1D Mesh 1D Mesh lets you create a mesh of one-dimensional elements. You can create or edit one-dimensional elements, along or between points, curves, or edges. One-dimensional elements are two-noded elements which, depending on type, may or may not require an orientation component. A one-dimensional element is one in which the properties of the element are defined along a line or curve. Typical applications for the 1D element include beams, stiffeners, and truss structures.



5-1

1D and 0D meshing

5

1D element meshing methods The following section describes methods available for creating different types of 1D mesh. These methods are based on the way you select geometry using Selection Step icons in the 1D Mesh dialog. Ordered Nodes method Using this method (which requires selection of a point or points for Group 1 as well as Group 2), two ordered sets of point locations are created. These point locations are associated to the parent data from which they were selected.

5-2



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1D and 0D meshing

Depending on the quantity of data selected for this method, several outputs are possible: •

If the number of points created in each set (Group 1 and Group 2) are equal, then a single 1D element is generated between each set of corresponding points, as shown in the graphic above.

•

If the number of points created in each set are unequal, then 1D elements are created from all of the points in Group 1 to all points in Group 2. This option provides a "one to many" type of connection, as shown in the following figure.

Point-to-Point Chaining method This method, which requires Group 1 selection only, generates a chain of 1D elements between the points that you select. The elements that are created form a consecutive link between the successive point locations.



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5

1D and 0D meshing

Along a Curve (Edge) method This method, which requires Group 1 selection only, generates a series of 1D elements along single or multiple curves or edges. You can specify a total number of elements or an element size for the elements. Nodes created at coincident point locations on adjacent curves/edges are shared.

5

Point-to-Curve (Edge) method For this method, which requires selection of a Group 1 point and a Group 2 curve, elements are created similarly to the Ordered Nodes method. In the Point-to-Curve method, however, the curve you select for Group 2 infers the second curve set, as shown in the following figure.

Curve-to-Curve method This method, which requires selection of a curve for both Group 1 and Group 2, generates 1D elements between two curves or edges. The point 5-4



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1D and 0D meshing

locations associated to the parent curve/edge will be used to determine the corresponding node locations.

If the two sets of point locations do not contain the same number of points, the software matches all possible points and build the rest of the elements between a point on one curve and the remaining points on the other curve. Creating a 1D mesh

1. Click

(1D Mesh).

5

2. In the dialog, choose an element type. 3. Choose either Default Element Number or Size and enter a value: •

If you select Number, enter an element density. If you enter 9 for example, and select an edge, the software will distribute nine elements along the selected edge.

•

If you select Size, enter a size in model units.

4. (Optional) Select Create Mesh Points to create selectable mesh points on or relative to CAE geometry. For example, you could create a mesh point at an arc centerpoint to create a spider mesh at a large hole. Or you could create mesh points to force a node location on an edge or improve node distribution on a curve. 5. Use the Selection Steps (Group 1, Group 2) to define sections. 6. Choose Apply or OK. 1D elements are built along or between the objects you selected for meshing.

Create Weld Elements Create Weld Elements allows you to model welds by projecting a set of points to top faces and using the resulting points to project to bottom faces, using the Normal to Face option in both projections. ©UGS Corporation, All Rights Reserved


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1D and 0D meshing

Weld mesh effect on 1D mesh When you exit the Create Weld Elements dialog box, the ordered set of points from the top faces will be added to Group 1 selection step of the 1D Mesh dialog, and the ordered set of points from the bottom faces will be added to Group 2. You can then create any type of 1D element available. In addition, the software honors the weld elements during 2D face meshing.

5

Support for interior hard curves in meshing This feature gives you the ability to associate curves to faces to represent weld locations in the Create Weld Elements dialog. These weld points are treated as interior hard curves. The point locations on the hard curves are honored by the software during 2D meshing. Creating a weld element mesh 1. Click 1D Mesh

.

2. Choose an element type. 3. Choose either Default Element Number or Size and enter a value: •

If you select Number, enter an element density. If you enter 9 for example, and select an edge, the software will distribute nine elements along the selected edge.

•

If you select Size, enter a size in model units.

4. Click Create Weld Elements. The Create Weld Elements dialog is displayed. 5. Using the Points/Curves selection step, select points, curves, or edges. Use the Filter menu to pinpoint selection. Click OK to confirm the selection. 5-6



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1D and 0D meshing

6. Use the Top Faces selection step to project the points, curves, or edges. Click OK to confirm the selection. 7. Use the Bottom Faces selection step to choose the bottom face and click OK to confirm the selection. Temporary points are displayed at the projected locations. 8. Click OK or Apply to return to the 1D Mesh dialog. The Top Faces selection is added to Group 1 and the Bottom Faces selection is added to Group 2. 9. Click OK or Apply to project the points and create weld elements. The elements are created between each pair of points (the point on the top face and the corresponding point on the bottom face).

1D Element Section

5

1D Element Section helps you create sections, which you can then assign and analyze for comparison to a bar or beam element mesh, curves/edges, or points, and display the results. This feature also lets you create associative section properties from the analysis, which can then be used for beam model analysis. Since section properties are associative, they are updated whenever changes are made to the data from which they are derived.



5-7

1D and 0D meshing

5

5-8



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1D and 0D meshing

Types of sections include: •

thin wall rectangle

•

hollow circle

•

thin wall channel

•

thin wall hat

•

thin I-beam

•

solid cylinder

•

solid rectangle

•

user–defined properties

•

user–defined thin wall

•

user–defined solid

5

Order of precedence when using sections The following is the order of precedence for each section type when there are conflicts in the section assignment: •

Section on points (smart points for the Along a Curve option)

•

Section on curves/edges

•

Section on bar/beam mesh

A section assigned to a hard point on a curve will be used in place of the section on the curve. A section on a curve/edge will precede a section found on a beam mesh. A warning message will be issued by both the Section dialog and the Attribute Editor when you attempt to add a section to a beam mesh if the underlying curve/edge already has a section. You can align the sections to bar or beam elements by specifying the desired orientation vectors.

0D Mesh 0D Mesh provides you with the tools to create concentrated mass elements at specific nodes. Zero-dimensional elements are also referred to as scalar elements. To create concentrated mass elements on nodes, you can select points, lines, curves, faces, edges, solids, or meshes. ©UGS Corporation, All Rights Reserved


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1D and 0D meshing

5

Creating a 0D mesh To create a concentrated mass using a mesh of 0D elements: and select the entity for the mass in the graphics 1. Click 0D Mesh window, or choose Create Mesh Point to concentrate the mass on a point. 2. If necessary, choose an element type. 3. In the dialog, choose either Default Element Number or Size and enter a value: •

If you select Number, enter an element density. If you enter 9, for example, and select an edge, the software will distribute nine elements along the selected edge.

•

If you select Size, enter a size in model units. This size is the average distance between 0D elements.

4. Click either Apply or OK. Notice that 0D elements are built along the grids of the object you selected for meshing.

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1D and 0D meshing

5. To specify mass properties for the 0D mesh, with the FEM file as the active part, select Simulation Navigator → FEM node → 0D Meshes → the 0D mesh → RMB → Edit Attributes. Specify total mass, CG, and inertial properties attributes on the Element tab. Specify mass distribution and mesh density attributes on the Mesh tab.

Activity

5

See the “1D and 0D meshing” activity in the Applications of Advanced Simulation Workbook. In this activity, you will generate beam (1D) elements and define a beam cross section.


Learned how to create a mesh with 1D elements.

•

Learned how to create a mesh with 0D elements.

•

Learned how to create a 1D element section.

•

Learned how to create a 0D mesh.



5-11

5

Lesson

6

Mesh points

Objectives •

Learn how to use mesh points.

Mesh points When you mesh your model, the software automatically creates a node at all mesh point locations. You create mesh points directly on the polygon geometry in your FEM file. You can position them using the standard NX Snap Point toolbar icons. Mesh points are useful for ensuring that the software creates nodes at specific locations. You can also define point-based loads or boundary conditions on mesh points. The following example illustrates one use of mesh points. Suppose you want to transfer a load from the centerpoint of the hole to the nodes on the edge. You could use the Mesh Point to create a mesh point at the centerpoint of the hole and then use the Arc Center tool on the Snap Point toolbar to constrain the new point.



6-1

6

Mesh points

You could then create a spiderweb mesh of rigid bar elements to connect the mesh point to the nodes on the edge of the hole and define a fixed constraint at the mesh point.

Where do I find it? (With the FEM file active in the Simulation Navigator) Insert→ Model Preparation→ Mesh Point

6

Activity See the “Mesh points” activity in the Applications of Advanced Simulation Workbook. In this activity, you will create mesh points.


6-2

Learned how to use mesh points.



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Lesson

7

Mesh and object display

Objectives •

Learn how to set mesh display preferences.

•

Learn how to control object display.

Mesh Display preferences Mesh Display lets you define preferences for basic finite element model visualization capabilities such as color, element shrink, and 2D element normals.

7



7-1


Where do I find it?

7

Preferences→ Mesh Display

Object display Two commands help you manage and control your display: •

•

Show Only

Show Adjacent

Both commands are designed to make it easier to limit and control the objects being displayed, which is particularly useful when you’re working with a very complex finite element model. 7-2



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•

•

Show Only lets you easily display only the entities you select. For example: –

When you’re working with a mesh in a FEM file, you can use Show Only to display only selected polygon faces.

–

When you’re working with boundary conditions in a Simulation file, you can use Show Only to display selected polygon geometry and associated simulation objects, such as points, splines, conics, meshes, loads, boundary conditions, and mesh points.

Show Adjacent works with the Show Only command. Show Adjacent shows all faces adjacent to the selected face. For example, once you’ve used Show Only to limit your display, to only a selected set of polygon faces, you can then use Show Adjacent to selectively add additional adjacent faces to that display. This process can be useful, for example, for examining an area where you might want to create a mesh mating condition.

In the following example, we used Show Only (A) to display only the polygon face on the selected fillet. (B) shows the resulting display.

7

We then used Show Adjacent (C) to add all adjacent faces (all faces that share an edge with the displayed face) to the current display. (D) shows the resulting display.



7-3


Show Only and Show Adjacent work similarly to the Blank commands in the Edit menu, but they require far fewer clicks to display only selected geometry of interest.

Activity See the “Mesh and object display” activity in the Applications of Advanced Simulation Workbook. In this activity, you will learn how to modify the display of a mesh.


7

7-4

•

Learned how to set mesh display preferences

•

Learned how to control display of objects such as geometry, meshes, loads, and constraints



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Lesson

8

Geometry abstraction

Objectives •

Learn about geometry abstraction techniques.

•

Understand the difference between geometry idealization and geometry abstraction.

•

Learn about polygon geometry.

•

Learn how to detect fillets before meshing.

•

Learn about various geometry abstraction tools.

Geometry abstraction overview The Model Cleanup toolbar contains a set of commands that let you perform geometry abstraction operations on your model. Geometry abstraction lets you eliminate issues with the CAD geometry that can cause undesirable results when you mesh your model. For example, you can use geometry abstraction tools to: •

Improve the quality of your mesh by manually eliminating problematic geometry.

•

Create boundaries on which to define loads and constraints.

The Model Cleanup toolbar contains a set of commands that let you perform geometry abstraction operations on your model. Geometry abstraction lets you eliminate issues with the CAD geometry that can cause undesirable results when you mesh your model. For example, you can use geometry abstraction tools to: •

Improve the quality of your mesh by manually eliminating problematic geometry.

•

Create boundaries on which to define loads and constraints.



8-1

8


Comparing geometry idealization and geometry abstraction Geometry idealization and geometry abstraction operations are similar in their intent in that both allow you to specifically tailor the geometry to the needs of your analysis. However, the two are fundamentally distinct processes that operate on different aspects of your model. •

•

You perform geometry idealization operations on the idealized part. Geometry idealization lets you simplify and streamline your model by removing or suppressing unnecessary features. For example, you can: –

Add features to the idealized part to facilitate the analysis.

–

Partition a large volume to facilitate the meshing of that volume.

–

Create a midsurface on a thin-walled part to facilitate 2D meshing

You perform geometry abstraction operations on the polygon geometry within the FEM file. Geometry abstraction lets you eliminate issues with the CAD geometry that can cause undesirable results when you mesh your model. For example, you can use geometry abstraction commands to: –

Remove very small surfaces or small edges from your model that can degrade element quality in that region.

–

Add geometry to your model for use in the analysis. For example, you can add edges to the polygon geometry to either control the mesh in that region or to define additional edge-based loads or constraints.

Understanding polygon geometry When you create a FEM file, the software automatically creates “polygon” geometry from the idealized part. Polygon geometry is a faceted representation of the geometry in the master part. Polygon geometry allows you to:

8

•

Tailor the design geometry to fit the needs of your CAE analysis.

•

Repair issues with the design geometry, such as narrow regions or tiny edges, that can prevent the software from meshing or solving your model.

Changes you make to the polygon geometry do not affect the master part. This gives you the flexibility and control to idealize the geometry to suit the needs of your analysis, without impacting the CAD design process and without requiring that you own the CAD part. The polygon geometry is initially a one-for-one representation of your original master part. That is, for every body, face, and edge in your model, the software creates a corresponding polygon body, polygon face, and polygon edge. 8-2



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In some cases with particularly complex geometry, the software may be unable to generate a complete, faceted representation of the master part. In those cases, the polygon geometry may contain missing faces. When this occurs, you can use the Face Repair command on the Model Cleanup toolbar to construct a new face.

Understanding the geometry abstraction process There are two different ways you can abstract the polygon geometry in your FEM file to optimize it for meshing: •

You can use the software’s automatic abstraction capabilities (available through the Mesh Options form) during either 2D or 3D meshing.

•

You can use the Auto Heal Geometry command on the Model Cleanup toolbar to manually abstract your model.

Whether you choose to perform the abstraction during meshing or by using Auto Heal Geometry, the abstraction process is the same. In both cases, the software searches your model for geometric features that are so small that they can prevent the software from being able to mesh or solve your model. During the abstraction process, the software eliminates: •

Short edges.

•

Sliver faces.

•

Highly pinched regions of the geometry.

Small feature tolerance The key difference between the different ways to perform the abstraction is in how you define the small feature tolerance. The software uses the small feature tolerance to determine which features to eliminate during the abstraction. •

On the Mesh Options dialog, you define the small feature tolerance as a percentage of your overall element size.

•

On the Auto Heal Geometry dialog, you define the small feature tolerance as an absolute measurement.

In general, the abstraction process is designed to abstract features that are smaller than 10% of your overall element size. Removing features below that size helps ensure that your model will mesh with elements that have an aspect ratio greater than 10:1, which is required by many solvers. However, you should always use caution not to set the small feature tolerance too high. ©UGS Corporation, All Rights Reserved


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In general, the small feature tolerance should not be larger than 20% of the element size you intend to use to mesh the geometry. Abstraction process limitations The abstraction process is limited to abstracting away small features. The abstraction process does not: •

Suppress holes.

•

Transform radius corners of fillets into 90° angles.

•

Turn sheet bodies into solid bodies.

Removing short edges The software abstracts any edges that are shorter than the specified small feature tolerance. This prevents the software from creating an element with a very short edge on that portion of the geometry. Removing sliver faces The software abstracts any sliver faces whose width (W) is smaller than the specified small feature tolerance.

The following graphic shows an example of a sliver face on polygon geometry.

8

When the software meshes the geometry, the software abstracts away the sliver face. Notice how the software doesn’t include this face in the mesh.

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Eliminating pinched regions The software also abstracts away any highly pinched regions of the geometry. A pinched region is a very narrow region of a surface whose width is smaller than the specified small feature tolerance.

In the case of a pinched region, the software evaluates the extent of the pinched region, isolates the pinched region, and then tries to merge it with the adjacent geometry. The following graphic shows an example of a pinched region.

8



8-5


When the software meshes the geometry, the pinched region is absorbed into the adjacent geometry.

8 Fillet identification process The software’s meshing and geometry abstraction operations contain a capability that allows the software to intelligently detect fillets within your model. By identifying fillets prior to meshing, the software can create a better discretized, mapped mesh in those regions.

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The software always tries to create a mapped mesh on fillet surfaces. However, this is not possible in all cases. If the software cannot create a mapped mesh on a fillet, the software tries to create a size consistent free mesh. If you select Fillet Processing on either the Mesh Options or Auto Heal Geometry dialogs, the software searches your model for fillets that meet criteria you specify (minimum and maximum radius dimensions). Importantly, this search is not based on the part’s history data. Rather, the software detects fillets by searching for surfaces whose boundary edges meet certain characteristics. There are two stages in the fillet identification process. The software: •

Searches the faces in the model to identify fillets.

•

Categorizes any detected fillets into inside and outside radius fillets.

Process of identifying fillets In general, fillets have four logical sides and are defined by a chain of edges that form a closed loop. The edges of fillets must also have a radius that falls between the minimum and maximum fillet radii values you specify on either the Mesh Options or the Auto Heal Geometry dialogs. If 30% of the edges on a face are fillet edges, the software considers the face to be a fillet. Categorizing fillets into inside and outside radius fillets Once the software identifies the faces that are fillets, it categorizes them as either inside or outside radius fillets. During this process, the software constructs a vector between the centerpoint of the fillet’s edge and a point on the edge. The software then compares the direction of this vector against the normal of the surface at the point on edge. •

If the vector’s direction is different from the direction of the surface’s normal, then the software categorizes the fillet as an inside radius fillet.

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•

If the vector’s direction is the same as the direction of the surface’s normal, then the software categorizes the fillet as an outside radius fillet.

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Auto Heal Geometry Auto Heal Geometry lets you abstract certain types of features from your model that may be problematic for meshing. When you create a 2D or 3D mesh on your model, the software automatically abstracts the polygon geometry to repair problematic topology, such as small features, that can degrade the quality of your mesh. With both 2D and 3D meshing, you use the options on the Mesh Options dialog to control the abstraction.

The Auto Heal Geometry command gives you an alternative way of performing the same abstraction operations that are embedded within the 2D and 3D meshing commands. However, there are some subtle differences between the two methods. •

How you specify the Small Feature Tolerance on the Auto Heal Geometry dialog is different from the way you specify it on the Mesh Options dialog. On the Auto Heal Geometry dialog, you define the small feature tolerance as an absolute measurement. On the Mesh Options, you define the small feature tolerance as a percentage of overall element size.

•

Auto Heal Geometry lets you abstract the geometry without generating a mesh on it. This can be advantageous if you intend to perform more manual abstraction operations on your model prior to meshing.



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You can use Auto Heal Geometry to abstract your model at any point in the finite element modeling process prior to meshing. Additionally, if you use Auto Heal Geometry to abstract your model, the software won’t abstract the part again during meshing. Limitations Auto Heal Geometry does not: •

Suppress through holes or features.

•

Turn sheet bodies into solid bodies.

•

Transform manifold bodies into non-manifold bodies.

Automatically healing polygon geometry 1. Click Auto Heal Geometry

.

2. On the dialog, specify a Small Feature tolerance value in model units. Features smaller than this value are abstracted during meshing. 3. If you want special processing to apply to filleted faces during meshing, choose whether you want special processing applied to inside-radius fillets, outside-radius fillets, or all fillets. Otherwise, select No Fillets. 4. Enter the minimum and maximum radius that you want the software to use during the fillet identification process. 5. Click OK or Apply.

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Split Edge Split Edge you specify.

splits a single edge into two separate edges at the location

Split Edge lets you split any polygon edge in your model into two separate edges. You may want to split an edge when:

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•

You want to define separate boundary conditions on different portions of an edge.

•

You’re preparing to split a face.



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Splitting an edge 1. Click Split Edge

.

2. Select the polygon edge you want to split. 3. Use the selection mode icons on the Snap Point toolbar to select the location where you want to split the edge. •

Mid Point lets you select a location at 50% of the total length of the curve.

•

Quadrant Point lets you select a point at the quarter points of an arc or ellipse.

•

Point on Curve lets you select any point along the curve.

4. Click MB2 or click OK on the Split Edge dialog bar to split the edge at the selected location.

Split Face Use Split Face

to divide a selected polygon face into two separate faces.

For example, you can use Split Face to: •

Add an edge to divide a face so that you can apply an edge-based load.

•

Divide an irregular face into several smaller faces on which you can define mapped meshes.

•

Restore an edge that was previously removed by another abstraction command, such as Merge Face or Auto Heal Geometry, or by the automatic abstraction that occurs during 2D or 3D meshing.

8

Splitting faces by points or suppressed edges The Split Face command has two separate modes of use. •

mode to split a polygon face by selecting Use the Split face by points two points on one of the face’s edges.

•

mode to split a polygon face Use the Split face by suppressed edges by restoring an edge that was previously removed by another abstraction command or process.



8-11


Splitting a face by selecting points 1. Click Split Face

2. Click

.

Split face by points on the Split Face dialog bar.

3. Select the first point on a polygon edge. The selection mode icons on the Snap Point toolbar help you select the point. •

End Point lets you select a point at the end of a curve.

•

Mid Point lets you select a point at 50% of the total length of the curve.

•


•


4. Select the second point on a polygon edge on the same face. 5. The software creates a new polygon edge between the two selected points. Click MB2 or click OK on the dialog bar to accept the new edge and split the face at that location. Splitting a face by selecting suppressed edges 1. Click Split Face

.

2. Click Split face by suppressed edges

8

on the Split Face dialog bar.

The software displays any previously suppressed polygon edges in the graphics window. 3. Select a suppressed edge. 4. Click MB2 or click OK to restore the edge and divide the face at that location.

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Merge Edge Use Merge Edge location.

to merge two edges together at a selected end-of-edge

Merge Edge allows you to combine selected polygon edges at a selected endpoint. This is useful, for example, when you want to create a larger or more continuous boundary edge prior to meshing. You can also use Merge Edge to recombine edges that you had previously divided with the Split Edge command. You cannot use Merge Edge to combine edges when more than two polygon edges intersect at a single endpoint. Merging edges 1. Click Merge Edge

.

2. Select the point at the end of the polygon edge that you want to merge with the adjacent edge. The End Point option on the Snap Point toolbar lets you easily select points at the end of polygon edges. 3. Click MB2 or click OK on the Merge Edge dialog bar to merge the two edges together at the selected location.

Merge Face Merge Face lets you merge two separate polygon faces into a single polygon face along a common polygon edge. You can use Merge Face to combine two adjacent polygon faces into a single face. This is useful, for example, if you want to create larger faces prior to meshing. You can also use Merge Face to recombine faces you previously divided with Split Face. Manual or Automatic Face Merging With the Merge Face command, you can either manually combine faces at locations you select, or you can have the software automatically combine faces based on criteria you specify. The options on the Merge Face dialog let you choose between the manual and automatic methods. You can also use options on the Merge Face dialog to specify the criteria the software should use when automatically merging faces. ©UGS Corporation, All Rights Reserved


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Merging adjacent faces manually 1. Click Merge Face

.

2. Click Merge Faces on the Merge Face dialog bar to display the Merge Faces dialog. 3. Use Auto Remove Vertices to control whether the software automatically removes associated vertices (end-of-edge points) when you remove an edge between two faces 4. Click Merge and then select the polygon edge between the two adjacent faces you want to merge together. 5. Click OK or Apply on the Merge Faces dialog. Automatically merging adjacent faces 1. Click Merge Face

.

2. Click Merge Faces on the Merge Face dialog bar to display the Merge Faces dialog. 3. Click Auto Merge. 4. Use Auto Remove Vertices to control whether the software automatically removes associated vertices (end-of-edge points) when you remove an edge between two faces 5. Specify the maximum Edge Angle and Vertex Angle in degrees. 6. In the graphics window, select the faces that you want to have the software automatically evaluate for merger using the edge and vertex angle criteria you specified.

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7. Click OK or Apply on the Merge Faces dialog.

Match Edge Use Match Edge you select. 8-14

to match the first edge you select to the second edge



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Match Edge lets you repair small cracks or gaps in your model by matching an edge (the source edge) to another edge (the target edge). You can use Match Edge on any solid polygon body that contains free (unstitched) edges. •

If you use Match Edge to connect free edges within the same solid or sheet body, the software stitches the free edges together and creates a single, common edge. When you mesh these edges, the software creates duplicate nodes along the area where the edges were matched.

•

If you use Match Edge to connect free edges between different solid or sheet bodies, the software matches the free edges together. This results in two coincident, but separate edges.

Projecting versus not projecting edges You can choose from two different methods on the Match Edge dialog to control how the software matches the first edge to the second edge. •

With Project, the software projects the source edge onto the target edge.



8-15

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•

With No Project, the software interpolates the source edge point-by-point onto the target edge.

Match Edge limitations

8

•

You cannot use Match Edge to stitch together the free edges between separate solid bodies.

•

You cannot use Match Edge to stitch together the free edges between separate sheet bodies.

•

You can’t use the Match Edge method when the source edge is unstitched and the target edge is stitched within the same sheet or solid body. You can only use Match Edge when the source edge is stitched and the target edge is stitched within a different sheet or solid body.

Matching edges 1. Click Match Edge 8-16

.



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2. Select the edge to match (the source edge). 3. On the Match Edge dialog, set the Project Switch: •

Click Project to project the source edge to the target edge without changing its length or shape.

•

Click No Project to map, endpoint-to-endpoint, the source edge onto the target edge.

4. Select the edge to match to (the target edge). 5. Click OK or Apply.

Collapse Edge to collapse an edge to either one of its end points or Use Collapse Edge to a specified point along the edge. Collapse Edge lets you manually remove very small edges, such as those shown below, from your model by collapsing them to a point.

8 You can use Collapse Edge to collapse a selected polygon edge to any point along that edge. For example, the following graphic shows an example of a very small polygon edge.



8-17


We then used Collapse Edge to collapse the edge to its end point, as shown below.

8

Collapsing an edge to a point

1. Click Collapse Edge

.

2. In the graphics window, select the polygon edge to collapse. 3. Use the tools on the Snap Point toolbar to help select the point to which you want to collapse the edge. • 8-18

End Point lets you select a point at the end of a curve.



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•

Mid Point lets you select a point at 50% of the total length of the curve.

•


•


4. Click MB2 or click OK on the Collapse Edge dialog bar to collapse the edge to the selected point.

Face Repair Use Face Repair to create new polygon faces from free polygon edges on the surrounding body. When you first create a FEM file, the software creates polygon geometry from the idealized part. The polygon geometry is a one-for-one, faceted (tessellated) representation of your original geometry. Occasionally, the software may encounter problems during this process and may be unable to completely or properly tessellate certain faces. Face Repair lets you repair polygon faces that are either damaged or missing entirely. For example, you can use Face Repair to: •

Repair a corrupt or poor quality polygon face that did not tessellate properly when the software created the polygon geometry.

•

Create a new polygon face to fill a missing void in your model.

Repairing and replacing damaged faces 1. Click Face Repair

.

2. Set the Type Filter in the Selection toolbar to the type of polygon geometry you need to select. •

To create a new polygon face from a set of free edges, set the Type Filter to Polygon Edge.

•

To replace a damaged polygon face with a new face, set the Type Filter to Polygon Face

3. With the Pick Loops selection step active: •

If you’re creating a new face from a set of free edges, select a free edge. The software constructs a loop of free edges.



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•

If you’re replacing a damaged face, select the damaged face. The software automatically deletes the face, leaving a loop of free edges.

4. Subdivide the loop as necessary: a. Click the first Point selection step icon, and select a point along a free edge of the loop. b. Click the second Point selection step icon. Select a second point to define a curve that subdivides the free loop so that you can create a quality face. Use the Snap Point toolbar options to help select specific points. c. Click Create Face from Loops. Select an edge to define an outer loop, and, if necessary, select a second edge to define an inner loop (i.e., a hole). d. Click Complete Set and Start Next Set to generate the face and return to the Point selection step. 5. Repeat step three until you’ve defined a new polygon face to connect the free edges. 6. Click OK.

Reset Use Reset

to restore abstracted polygon geometry to its original state.

Reset lets you remove changes you have made to the polygon geometry with the geometry abstraction tools, such as Split Face and Match Edge. When you use Reset, the software returns the portion of the polygon geometry you select to its original state prior to any modifications.

8

Collapse Edge limitation In general, Reset removes all changes to the polygon geometry from the geometry abstraction commands. The one exception to this is the Collage Edge command. Because Collapse Edge can cause fundamental changes in the polygon geometry, the software can’t always reset all the changes caused by the Collapse Edge command. Resetting geometry 1. Click Reset 8-20

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2. Select the polygon geometry on which you want to remove changes caused by the geometry abstraction commands. You can: •

Select one or more faces or bodies to reset the abstractions made to those faces or bodies.

•

Choose Edit → Selections → Select All to reset all abstractions made to the polygon geometry.

3. Click OK to reset the selected geometry.

Activity See the “Geometry abstraction” activity in the Applications of Advanced Simulation Workbook. In this activity, you will simplify geometry to improve mesh quality.


Learned about geometry abstraction techniques.

•

Learned the difference between geometry idealization and geometry abstraction.

•

Learned about polygon geometry.

•

Learned how to detect fillets before meshing.

•

Learned about various geometry abstraction tools.

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Lesson

9

Element attributes Objectives •

Learn how to modify element attributes.

•

Learn how to override element attributes.

•

Learn how to use the Attribute Editor to modify element attributes.

Element attributes The Element Attributes dialogs let you define and modify the materials and physical properties for the elements, as well as additional mesh properties. The default language Solver setting for the FEM file determines which elements can be used, as well as their corresponding element attributes. The dialog below shows the element attributes for a beam element.

9 In the same dialog, if you pick the mesh tab, you can modify additional mesh attributes: ©UGS Corporation, All Rights Reserved


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Element attributes

Where do I find it? Simulation Navigator→mesh node→right click→Edit Attributes Element attribute overrides When you’re working in a Simulation file, you can define element “overrides.” Element overrides let you change the value of selected element attributes, such as materials or physical properties, without requiring that you copy the entire mesh (FEM file). When you solve a model that contains an override, the software uses the values you modified in the override instead of the values you defined in the original model. For example, this allows you to use a single FEM model to perform a series of material studies, which saves disk space as well as modeling time and effort. You can also use overrides to quickly analyze the effect of varying the element thickness within a 2D mesh. The graphic below shows an example of an element override that is used to vary the element thickness. When we initially created the original FEM file, we didn’t define a thickness value. However, we then created two different overrides in the files SIM1 and SIM2 in which we defined override values for the element thickness of 2mm and 2.5mm, respectively.

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Element attributes

Attribute Editor The Attribute Editor lets you select any editable FEM entity and review and revise its attributes. The entities that you can select include: •

Meshes, including 0D, 1D, 2D, 3D, contact meshes, and surface contact meshes. Once you select a mesh, you can edit the element attributes and materials assigned to the elements. The attributes that you can edit depend on the element type. These properties are the same ones that you can modify through the Element Attributes dialogs available in the Simulation Navigator.

•

Geometry, including point/mesh point, curve/edge, face, and body. Once you select geometry, you can edit attributes that will help you control the mesh definition on this geometry.

Attribute Editor – point selection The following illustration shows the Attribute Editor dialog that displays after selecting a point. The dialog presents a variety of point attributes that may be reviewed and edited.



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Element attributes

Attribute Editor – curve/element selection The following illustration shows the Attribute Editor dialog that displays after selecting a curve or edge. The dialog presents a variety of curve/edge attributes that may be reviewed and edited.

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Element attributes

Edge Density Type and Edge Density value These two options work in combination, allowing you to specify density control for the 2D mesher on local edges. You can apply or assign edge densities to model edges and curves using any of the following: •

Edge Density Number

•

Edge Density Size

•

Edge Density Chordal Tolerance

•

Edge Density Geometric Progression

Number When the Edge Density Type is set to Number, the number entered in the Edge Density field reflects the number of elements on the edge. Edge Density Size When the Edge Density Method is set to Size, the value entered in the Edge Density field reflects the approximate size of the element on the edge. The number of elements is rounded to the closest integer. Edge Density Chordal Tolerance Chordal tolerance is defined as the maximum distance between an arc along the curve and the curve itself. The Chordal Tolerance option allows you to produce a parametric set of node locations that are derived from equations related to the curvature of the curve or edge. Nodes are placed in high curvature areas (where curvature is greater) and in lower curvature areas. Edge Density Geometric Progression Geometric Progression allows you to specify a ratio of node locations along an edge or curve. This produces a series of node locations that are more dense at one end and less dense at the other. This option should be used to define critical areas of interest. Finer, more controlled meshes are produced in these critical areas, allowing a coarser mesh to be generated in less critical areas of the part. Edge Density Ratio The Edge Density Ratio field becomes active when the Geometry Progression option is selected. The default value for Edge Density Ratio is 1.0. With the default value, the result is the specified Number of Points value (or node locations) divided into equal parameter spacing, based on the arc length. Geometric Progression allows spacing of a set of points based on a geometric ratio. ©UGS Corporation, All Rights Reserved


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Element attributes

For example, if a ratio of 0.75 is entered, the distance from one point to the next is multiplied by 0.75 (as shown below).

It is important to note that the Geometric Progression option is dependent upon direction. The distribution of the nodes always begins at the natural start of the curve (indicated by the direction of the temporary display arrow). The arrow always points from the natural start of the edges or curves to its end. Applying the inverse value for the Edge Density allows you to reverse the direction of node distribution.

Attribute Editor – face selection The following illustration shows the Attribute Editor dialog that displays after selecting a face. The dialog presents a variety of face attributes that may be reviewed and edited. Shown below is a brief description of each option.

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Element attributes

Face Density Face Density allows you to set the approximate element size for the selected face.

Attribute Editor – body selection The following illustration shows the Attribute Editor dialog that displays after selecting a solid body. The dialog presents a variety of solid body attributes that may be reviewed and edited.

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Element attributes

Attribute Editor – 3D mesh selection The following illustration shows the Mesh tab on the Attribute Editor dialog that displays after selecting a solid (3D) CTETRA10 mesh. The dialog presents a variety of solid mesh attributes that may be reviewed and edited.

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Element attributes

Attribute Editor – 2D mesh selection The following illustration shows the Attribute Editor dialog that displays after selecting a shell (2D) CQUAD4 mesh. The dialog presents a variety of mesh and element attributes that may be reviewed and edited.

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9-9

Element attributes

9

Attribute Editor – 1D mesh selection The following is a typical Attribute Editor dialog that displays after you have selected a beam mesh. The dialog presents a variety of mesh and element attributes of the mesh for your review and/or edit, if desired.

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Element attributes

Attribute Editor – 0D mesh selection The following image shows the Mesh tab on the Attribute Editor dialog that displays after you have selected a 0D mesh (concentrated mass). The dialog presents a variety of mesh and element attributes of the mesh for your review and/or edit, if desired.

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Element attributes

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Element attributes

Mesh Density method and value Mesh Density allows assignment of a default density to the element to be created. The two options are: •

Number - Use this option to specify the number of elements to be created on the geometry.

•

Size - Enter the approximate size of the element to be created.

Mesh Density Value allows specification of a desired density value for the mesh. Distribute Mass When toggled on, the Distribute Mass option instructs the system to distribute the concentrated mass elements along the selected object (face, edge, etc.).

Attribute Editor – Contact mesh selection The following image shows the Attribute Editor dialog that displays after you have selected a contact mesh.

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Element attributes

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Element attributes

Attribute Editor – Surface contact mesh selection The following image shows the Attribute Editor dialog that displays after you have selected a surface contact mesh.

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9-15

Element attributes

Activities See the “Element attributes” activities in the Applications of Advanced Simulation Workbook. In these activities, you will improve the mesh by modifying element and mesh attributes.


Learned how to apply element attributes.

•

Learned how to modify element overrides.

•

Learned how to use the Attribute Editor.

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Lesson

10 Materials Objectives •

Learn how to assign a material to a mesh or geometry.

•

Learn how to customize the material database.

10 ©UGS Corporation, All Rights Reserved


10-1

Materials

Materials overview Use Materials to select and define materials and material properties to use in the simulations and mechanisms you build.

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Materials

From the Materials dialog box, you can: •

Create, review, and edit isotropic, anisotropic, orthotropic, and fluid materials.

•

Add, review, and edit temperature-dependent fields for these material types.

•

Control the orientation of the material by aligning it with a coordinate system.

•

Use the material library, which includes standard as well as user-defined materials.

Isotropic materials The isotropic material is the most commonly used material property. An isotropic material is defined as a material having the same material properties in any or all directions. Isotropic material types are used when certain assumptions are made. Use of an Isotropic material assumes that the material is homogeneous and that the properties (Young’s Modulus, for example) are the same in all directions. On the Materials dialog, you select the Isotropic tab to enter the isotropic material properties. Orthotropic materials An orthotropic material is a special case of an anisotropic material that may be used with plate and shell elements. It contains three orthogonal planes of material symmetry at a given location in the model structure. It is common to model composite structures (laminates) using an orthotropic material, especially when the parts are constructed from fiber composites. the Orthotropic tab on the Materials dialog shows the material properties for this material type. You may want to re-size the dialog to better see the contents of the scroll window. Anisotropic materials An anisotropic material has different properties in each direction at any given location in the model structure. No material plane of symmetry is associated with an anisotropic material (meaning that properties may vary in all directions). Anisotropic specification consists of three matrices. The two square matrices are symmetrical so that you need only enter data at the bottom half. As a convenience, the paired value is a label which will be updated automatically each time the opposite twin value is entered. When complete, the entire symmetric matrix will be shown. ©UGS Corporation, All Rights Reserved


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Materials

Fluid materials Fluid material properties are those applicable to 3D elements modeling the liquid or gas in a fluid volume. Assigning a material 1. Click Materials

.

2. On the Materials dialog, click Library

.

3. When the **Unsatisfied Title** dialog opens, click OK. A list of available materials appears. 4. Select one or more materials and click OK. Use Shift-click or Control-click to select multiple items. 5. Select the material name in the Materials dialog, then pick the geometry in the graphics window and click Apply. A status message appears, indicating that the material has been assigned.

Customizing the material library Adding a new material To add a new material to the library, use the following basic steps: 1. From ${UGII_BASE_DIR}\ugii\materials, make a backup copy of phys_material.dat. If you are running NX as a client, copy the following files to a local directory: phys_material.dat and phys_material.tcl. 2. Make sure the necessary environment variables are pointing to the location of the modified phys_material.dat file, and to locations of the current phys_material.def and phys_material.tcl files. If you are running NX as a client, you may need to set the variables manually. To add a new material to the database: 1. Open the phys_material.dat file in a text editor application. 2. Go to the bottom of the materials list. Copy the full line of the bottom-most material and paste it on the next line down. 3. Enter a new material name and unique ID.

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4. Change the values in the material property fields, as necessary. 10-4



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Materials

5. Add temperature-dependent properties. 6. Save the file and exit the text editor. 7. From a command shell or the System Properties dialog, set the appropriate environment variables for running the software with the modified file. (see Setting material library environment variables) 8. Launch the software with a test part to make sure the new material is working as intended. Setting material library environment variables To ensure that the material library database is accessed from the correct location, make sure the ugii_env.dat file has the following environment variables set correctly, or set them directly: • phys_material.def - UGII_PHYS_MATERIAL_LIB_DIR= ${UGII_BASE_DIR}\ugii\materials\${UGII_LANG}\

• phys_material.dat - UGII_PHYS_MATERIAL_LIB_DATA_DIR= ${UGII_BASE_DIR}\ugii\materials\

• phys_material.tcl - UGII_PHYS_MATERIAL_LIB_PATH= ${UGII_BASE_DIR}\ugii\materials\

• ug_metric.def or ug_english.def - UGII_DEFAULTS_FILE= [default directory ${UGII_BASE_DIR}\ugii\]

When defining the environment variable path, UGS recommends that you use an end backslash. Otherwise, you may get an error message when you try to use the updated library.

Activity See the “Materials” activity in the Applications of Advanced Simulation Workbook. In this activity you will apply a material to a mesh, and create a new material.

Summary

10

In this lesson you: ©UGS Corporation, All Rights Reserved


10-5

Materials

•

Learn how to assign a material to a mesh or geometry.

•

Learn how to customize the material database.

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11

Lesson

11 Boundary conditions

Objectives •

Learn about the boundary conditions that can be defined for a model.

•

Learn how to create loads.

•

Learn how to create constraints.



11-1

Boundary conditions

11

Boundary conditions overview Loads, constraints, and simulation objects are all considered boundary conditions. The Simulation Navigator provides tools that let you create, edit, and display boundary conditions. You can also create boundary conditions using icons on the Advanced Simulation toolbar. The options that appear on the boundary conditions dialogs are specific to the active solution and its associated solver. For example, if the active solution uses the NX Nastran solver, the Create Force dialog provides options that are specific to the NX Nastran FORCE card. You can create boundary conditions before or after you create a solution: •

If you create a solution first, the loads, constraints, and simulation objects are stored in their respective containers in the Simulation: the Load Container, Constraint Container, and Simulation Objects Container. They are also stored in the solution.

•

If you create the loads, constraints, and simulation objects first, they are stored in their respective containers in the Simulation. You can then drag and drop individual boundary conditions into solutions you create.

Supported boundary conditions The tables list the Advanced Simulation boundary conditions (loads, constraints, simulation objects), the associated analysis types, and the Nastran solver cards that they support. Icon

Load Force Moment Bearing Torque

11-2

Nastran Analysis Type Structural (all except SEMODES 103)

Supported Nastran Cards FORCE

Axisymmetric Structural Structural (all except MOMENT SEMODES 103) Structural (all except SEMODES 103) Structural (all except SEMODES 103)


FORCE FORCE


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Boundary conditions

11 Icon

Load

Pressure

Nastran Analysis Type

Structural (all except SEMODES 103)

Supported Nastran Cards PLOAD4 (Structural only) PLOAD2 (Structural only)

PLOAD1(Structural Axisymmetric Structural only) PLOADX1 (Axisymmetric Structural only)

Hydrostatic Pressure Gravity

Centrifugal

Temperature Load

Heat Flux

Radiation

Icon

Structural (all except SEMODES 103) Structural (all except SEMODES 103)

GRAV

Axisymmetric Structural Structural (all except SEMODES 103) RFORCE Axisymmetric Structural Structural (all except SEMODES 103)

TEMP

Axisymmetric Structural Thermal Axisymmetric Thermal

QBDY3 QBDY2 QHBDY

Thermal Axisymmetric Thermal

Heat Generation

Thermal

Constraint


User Defined Constraint

Structural


PLOAD4

Axisymmetric Structural

RADBC

QVOL

Supported Nastran Cards SPC (Structural only) SPC1


11-3

Boundary conditions

11 Icon

Constraint


Enforced Displacement Constraint

Supported Nastran Cards

Structural

SPCD

Fixed Constraint

Structural Axisymmetric Structural

Fixed Translation Structural Constraint Fixed Rotation Structural Constraint Simply Supported Structural Constraint

SPC SPC SPC

Pinned Constraint

Structural

SPC

Cylindrical Constraint

Structural

SPC

Slider Constraint

Structural

SPC

Roller Constraint

Structural

SPC

Symmetric Constraint

Structural

SPC

Anti-Symmetric Structural Constraint Thermal Thermal Constraints Convection

11-4

SPC

Axisymmetric Thermal Thermal Axisymmetric Thermal


SPC SPC CONV


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Boundary conditions

11 Icon

Simulation Object


Supported Nastran Cards BCRPARAM BCTPARM

Surf to Surf Contact

SESTATIC 101 (Single Constraint and Multi Constraint), ADVNL 601, 106

BCTSET BSURF BSURFS BCTPARA (ADVNL only)

Surf to Surf Gluing

Structural (all except NX Nastran ADVNL 601, 106) NLSTATIC 106

Initial NX Nastran ADVNL 601, Temperatures 106

BGSET

TEMP

NLSCH 153

Creating loads The procedure for creating most structural and thermal loads is similar. 1. In the Simulation Navigator active structural or thermal solution, right-click on Loads. 2. Choose New Load. 3. From the menu, choose the type of load that you want to create. 4. (Optional) In the dialog box, choose the type of load to create. 5. Select the object to apply the load to. Boundary conditions can be applied to geometry, including faces, edges, curves, points, mesh points, vertices, or the entire model. They can also be applied to nodes or elements. The type of boundary condition determines the objects that you can apply it to.

6. (Optional) For some thermal loads, click and select a control point.


(Optional Control Point),


11-5

Boundary conditions

11 7. (Optional) Click the arrow next to direction for the load.

(Inferred Vector) and enter a

8. Enter a magnitude for the load.

Creating constraints The procedure for creating most constraints is similar. 1. In the Simulation Navigator active solution, right-click on Constraints. 2. Choose New Constraint. 3. From the menu, choose the constraint that you want to create. 4. (Optional) On the Create (Constraint) dialog, choose the Type. 5. Select the object to apply the constraint to. Boundary conditions can be applied to geometry, including faces, edges, curves, points, mesh points, vertices, or the entire model. They can also be applied to nodes or elements. The type of boundary condition determines the objects that you can apply it to. 6. (Optional) For a convection boundary condition, click the Optional Control Point icon, and select a control point. 7. (Optional) Enter a direction for the constraint. 8. (Optional) Enter a magnitude for the constraint.

Activity See the “Boundary conditions” activity in the Applications of Advanced Simulation Workbook. In this activity, you will apply loads and constraints to your model.


11-6

•

Learned about the boundary conditions that can be defined for a model.

•

Learned how to create loads.



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Boundary conditions

•

11

Learned how to create constraints.



11-7

11

Lesson

12 Model information

12

Objectives •

Learn how to display information about your model.



12-1

Model information

Model information overview The Information feature is available with every NX application producing geometric and part relationship data. The Information→Advanced Simulation menu lets you query finite element entities or objects. In addition, you can obtain a simulation summary which gives more detailed information on mesh nodes, element numbers, etc.

12

Information options provide general and specific information for selected objects, expressions, parts, layers, etc. Data is displayed in the Information window. The Information window has its own menu bar that supports cut, copy and paste operations, as well as capability to save output to a file and/or print to the default printer. The data that is output to the Information window differs depending upon the chosen Information option(s). •

Identify lets you display element or node labels.

The image shows element and node labels displayed for 2D elements.

12-2



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Model information

12

•

When the FEM is active, you can list information on a mesh, material, section, and mesh mating condition. Finite Element Summary lists detailed information about number of nodes, elements, and other entities. The figure shows an information listing for one element.

•

When the Simulation file is active, you can list information on a mesh, load, constraint, Simulation object, solution, step, material. Identify lets you display element or node labels. Simulation Summary lists information about the solutions in the Simulation file.



12-3

Model information

12


12-4

Learned how to display information about your model.



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Lesson

13 Model checking 13

Objectives •

Learn how to perform model checks.

•

Understand threshold values.



13-1

Model checking

Model Check overview Model Check provides complete information about the model and all its finite element components. Model Check is a good predictor of whether the model is ready to solve.

13

Comprehensive check Use the Comprehensive check to see if your model contains all the necessary elements for the analysis. When you perform a Comprehensive check, the software verifies that the model contains: •

Elements

•

Element attributes (such as thickness)

•

Loads

•

Constraints

•

Materials

The software displays the results of a Comprehensive check in a separate Information window, along with an error summary for each topic.

13-2



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Model checking

Element Shapes check Use the Element Shapes check to detect elements that may be too distorted to yield good analysis results. For accurate results, finite element analysis solvers require elements that are not distorted.

13

Element Shapes Threshold Values Threshold values are the maximum allowable value for each test. Any element whose test results exceed these values will fail the test. You may also accept the software’s defaults for the threshold values. The values you enter depend on the accuracy you need from your analysis and the type of solver specified in the environment.



13-3

Model checking

13

The Jacobian zero threshold is an exception. An element fails the Jacobian zero test if its test results fall below the threshold value you enter. Note that the shape tests do not check for misplaced midside nodes. Aspect Ratio Aspect ratio is the ratio of an element’s length to its width.

13-4



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Model checking

Tri Aspect Ratio

13

The aspect ratio for a triangular element is calculated as the ratio of the length (h2) to the height (h1). This ratio (h2/h1) is then multiplied by SQRT(3)/2, such that an element in the shape of an equilateral triangle will equal 1. This procedure is repeated for the remaining two edges of the triangle and the largest value is retained as the aspect ratio for the element. Quad Aspect Ratio

The aspect ratio for a quad element is determined using a test proposed by Robinson and Haggenmacher (J. Robinson and G. W. Haggenmacher, "Element Warning Diagnostics," Finite Element News. June and August, 1982). This test is based on a projection plane created by first bisecting the four element edges, then creating a point on the plane at the vector average of the corners. The x-axis extends from the point to the bisector on edge 2. The ratio is determined as the ratio of the length from the origin to the bisector of ©UGS Corporation, All Rights Reserved


13-5

Model checking

edge 2 to the length from the origin to the bisector of edge 3. If the ratio is less than 1.0, it is inverted. Tet Aspect Ratio

13 The aspect ratio for a tetrahedral element is computed by taking the ratio of the height of a vertex to the square root of the area of the opposing face. The maximum height to area value is multiplied by a factor cf = 0.805927, which is the ratio of height to edge length for an equilateral tetrahedron. This result is the aspect ratio. With an equilateral tetrahedral element, the software report a value of 1. Aspect ratio = Max(cf(hi)/sqrt(Ai)), where i = 1,2,3,4. Warp Warp allows for measurement of out-of-plane element deviation. Quad Warp

The warp value is determined using a test proposed by Robinson and Haggenmacher which uses the following method of calculating Quad element Warp. The test is based on a projection plane created by first bisecting the four element edges, then creating a point on the plane at the vector average of 13-6



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Model checking

the corners (where the x-axis extends from the point to the bisector on edge 2). The plane normal is in the direction of the cross product of the x-axis and the vector from the origin to the bisector of edge 3. Every corner of the quad is a distance h from the plane. The length of each half edge is measured and the shortest length is assigned a value of 1. The warp angle is the arcsine of the ratio of the projection height h to the half edge length 1. Skew Skew allows for measurement of angular deviation of an element using an edge bisector method. Tri Skew Angle

Three potential skew angles are computed for each triangular element. To calculate each skew angle, the software constructs two vectors: one from a vertex to the mid-point of the opposite edge; the other between the mid-points of the adjacent edges. The software subtracts the angle between these two vectors from 90° (skew angle = 90°-a). This procedure is repeated for the other two vertices. The largest of the three computed angles is the skew angle for that element (skew factor = (90°-a)/90). Quad Skew Angle

Prior to testing for skew, the software checks each element for convexity. Elements which fail the convexity check double-back on themselves. This causes the element stiffness terms to contain either a zero or negative value. ©UGS Corporation, All Rights Reserved


13-7

13

Model checking

13

This skew test is based on a reference frame created by first bisecting the four element edges, then creating an origin at the vector average of the corners (where the x-axis extends from the origin to the bisector on edge 2). The z-axis is in the direction of the cross product of the x-axis and the vector from the origin to the bisector of edge 3. The y-axis is in the direction of the live cross product of the x- and z-axes as shown above.

The Robinson and Haggenmacher skew test uses the angle (alpha) between the edge 2 and 4 bisector and the test y-axis. The resulting angle is subtracted from 90 degrees to yield the skew angle. Tet Skew Angle Each face of the tet element is tested for skew as if it were a tri element. The highest resulting angle for each element is retained as the skew angle. Quad Taper Taper allows for measurement of the geometric deviation of a quadrilateral element from a rectangular shape. 13-8



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Model checking

13 Quadrilateral element taper is determined using a test proposed by Robinson and Haggenmacher. Four triangles are created bounded by the element edge and the edges created by connecting the element verification reference frame origin with the two nodes at the element edge. The resulting four triangular areas are calculated and summed. The ratio of the smallest triangular area to the total area of the element is the taper ratio (taper ratio = 4*a(smallest)/a1+a2+a3+a4) Jacobian A Jacobian is a determinant used to describe the variance of some characteristic at two different positions in a system. For example, a Jacobian might be used to describe the variance of slope between two points on a curve. Jacobians are useful tools for measuring distortion. A Jacobian could be used to compare the orientation between two edges of an element. For shape check the Jacobian is evaluated at each vertex. These values are then used to generate results for the Jacobian Ratio and Jacobian Zero tests. Jacobian measures the ratio between the area or volume of an element to the ideal parametric element. The software calculates this value by mapping a parent element (in computational space) against the actual element. Jacobian Ratio Jacobian Ratio is a ratio of the largest Jacobian determinant to the smallest. This ratio gives you an idea of overall distortion in an element. The Jacobian ratio test is helpful for identifying when the interior corner angles of an element deviate too much from 90 degrees. An element will fail this test if the ratio is higher than the value entered in the data field. A ratio close or equal to 1.0 is desired. Jacobian Zero The determinant of the Jacobian (J) is calculated at all integration points for each element selected. The minimum value for each element is determined. This element verification test can be used to identify incorrectly shaped ©UGS Corporation, All Rights Reserved


13-9

Model checking

elements. For a well formed element, J is positive at each Gauss point and is not significantly different from the J value at other Gauss points. J approaches zero as an element vertex angle approaches 180 degrees. The Jacobian Zero is the smallest determinant. An element will fail this test if its Jacobian Zero is below the value entered in the data field.

Element Outlines check

13

Use the Element Outlines check to display free edges (element edges that are unconnected to any other element) of 2D meshes and display free faces (element faces that are unconnected to any other element) of 3D meshes.

Nodes check Use the Nodes check to detect and merge duplicate (coincident) nodes between meshes. This check operates only between boundary nodes on your geometry (for example, edges of faces and faces of bodies, etc.). Moreover, the software only merges nodes of identical types. For example, the software will not merge a midnode with an end node. The ability to detect and merge duplicate nodes is particularly useful when you’re working with assembly models or with models that contain multiple meshes. If you try to solve a model that contains coincident nodes, singularities or other rigid body motion errors can occur during the solve.

13-10



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Model checking

13

2D Element Normals checks Use the 2D Element Normals check to display and reverse 2D element normals. You can check the normals on individual faces or within individual meshes, or you can check all 2D elements in the current part. Once you reverse an element’s normal, the software maintains that reversal across all mesh updates.

Summary In this lesson you: ©UGS Corporation, All Rights Reserved


13-11

Model checking

•

Learned how to perform model checks.

•

Learned about threshold values.

13

13-12



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Lesson

14 Solving

Objectives •

Learn how to solve the finite element model.

•

Learn how to do a batch solve.

14



14-1

Solving

Solving overview Once you have prepared your FE model by defining a mesh and applying boundary conditions, you can perform a solve. A solve formats the bulk data deck or input file, then automatically begins processing. You can also choose to write out the input file without solving it. You can also write out an input file with File →Export. This command lets you control the location of the input file, as well as the units for the file. You can write out the active FE Model and Simulation, or only the active FE Model.

14

Solving the model To ensure a successful solve and accurate results, run a comprehensive check, as well as element quality checks, before you solve the model. 1. In the Simulation Navigator, select the solution node.

2. Click

.

3. On the Solve dialog, select an option from the Submit menu. 4. To edit solution attributes, choose Edit Solution Attributes. 5. To edit solver parameters, choose Edit Solver Parameters. 6. Click OK to run the solve. The Analysis Job Monitor appears. When the analysis is complete, a Results node appears in the Simulation Navigator. 14-2



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Solving

Analysis Job Monitor The Analysis Job Monitor lets you keep track of the progress of the analysis job you submitted, and also lets you know when the analysis job is completed. The Analysis Job Monitor automatically appears after you run a solve.

14

Batch solving Solve All Solutions allows you to perform batch solves. You can choose between launching all solves simultaneously or in sequential order.



14-3

Solving

14

Activity See the “Solving” activity in the Applications of Advanced Simulation Workbook. In this activity, you will learn the process for preparing and solving a model.


14-4

•

Learned how to solve the finite element model.

•

Learned how to do a batch solve.



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Lesson

15 Post-processing

Objectives •

Learn how to use Post-processing.

•

Learn how to use the tools on the Post Control toolbar.

15



15-1

Post-processing

Post-processing introduction Use the post-processor to view the results of all analysis types supported by Advanced Simulation. You can enter Post-processing by double-clicking on any Results node in the Simulation Navigator. Opening the post-processor To open the post-processor:

15

•

Double-click on the Results node in the Simulation Navigator.

•

Click the Enter Post Processing toolbar.

•

From the main menu, choose Tools→Results→Enter Post Processing

on the Advanced Simulation

Results in the Simulation Navigator Use the Simulation Navigator to display and manage results in Post –processing. Available options include the following: Node

Name Results node

Description and Functions Result types are displayed under the Results node in the Simulation Navigator. You can expand each result type to access all data components available for the selected result type. Select or clear the visibility check box ( ) for a result type or data component, and the graphics window display updates dynamically. You can use MB3 options available from the Results node to do the following:

15-2


•

Create and append post views

•

Combine load cases


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Post-processing

Node

Name Post View node

Description and Functions Provides access to the current post view. Double-clicking on a post view in the Navigator designates that view as the new work view. To manage display features of a particular view, select the view in the Navigator, then right-click to access the following options: •

Load - Populates the graphics window with the selected post view.

•

Rename - Renames the post view.

•

Clone - Creates an identical copy of the post view in the Simulation Navigator.

•

Delete - Deletes the selected post view.

•

Overlay - Adds the post view to the current working post view.

•

Append to Display - adds the post view to the current layout.

•

Save As Template - Lets you save the selected post view as a template.

The Post Control toolbar Use the Post Control toolbar to access the following Post-processing features: Icon

Option Finish Post Processing

Post View


Description Exits Post-processing. Alternatively, you can exit Post-processing by double-clicking the FE Model node in Simulation Navigator. Controls the display of results in selected post views.


15-3

15

Post-processing

Icon

Option Identify Display Marker Display Marker Drag

15

Description Probes and displays node and element information in the work view. Switches the display of minimum and maximum result markers on and off. Allows you to reposition minimum and maximum result markers.

View Layout

Displays results in multiple layout views.

Select All Views

Selects all layout views.

Deselect All Views

Deselects all selected layout views.

Overlay

Superimposes one set of results on another in the same view.

Animation Setup

Controls animation settings.

Previous

Steps backward through the animation one frame at a time when the animation is paused. Steps forward through the animation one frame at a time when the animation is paused. Plays the animation using the current settings.

Next Play Pause

Pauses the current animation.

Stop

Stops the current animation.

Import Results You can import and access results for solves performed outside of the current set of solutions. The following file formats are supported for importing results:

15-4

•

Nastran (.op2)

•

Structures P.E. (.vdm)

•

Ansys Structural (.rst)



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Post-processing

•

Abaqus Thermal (.rth)

•

Abaqus (.fil)

•

I-DEAS results file (.unv)

•

I-DEAS Bun file (.bun)

Importing results To import and view results: 1. From the Simulation Navigator, right-click on the Simulation file and select Import Results. 2. From the Import Results dialog, name the imported results file.

15

3. Click on the File Open button to select a file type and path for the file name. Click OK. 4. Review the results units. If necessary, click Change and select new units from the Import Results units dialog. 5. Click OK. The imported results node appears in the Simulation Navigator. Using imported results Once you have successfully imported a results file, the imported results node behaves somewhat like a solution node in the Simulation Navigator. You can therefore perform the following operations on imported results: •

Post-process and view the results

•

Re-solve for new results

•

Edit attributes of the imported results



15-5

Post-processing

Post View When you enter Post-processing, the Results node expands to display all result types available. Beneath the Results node is a post view, which is created automatically by the software from solver results. A post view represents result settings displayed in the graphics window that include result type, data component, cutting plane, deformation, and so on. You can create additional post views, and save settings as templates. You can manage the settings for each view using the Post View dialog.

15

15-6

•

The Post View Display tab provides options for displaying results such as contour type, deformed display options, and where to display results. You can also manage cutting plane options from the Post View Display tab.

•

The Color Bar tab lets you select results data for post processing. Options are also provided for linear or log display and for viewing optimization results in tabular and graph form.

•

The Edges and Faces tab controls the display of element edges and faces.

•

The Preferences tab controls display marker, synchronization, dynamic viewing and text color preferences.



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Post-processing

Post view templates Post View templates provide a way to save data from one or more post views for future re-use. Depending on how many views are currently displayed, you can save the template as a single view or as a layout. Creating a Single-View Template 1. Select the post view node of the view you want to save as a template. 2. Right-click on the post view and choose Save as Template. 3. In the Save Post Template dialog, enter a Name and choose additional options, if necessary. For example, you can save this template as the default, and you can choose to use the part model image for the template icon.

15

4. Click OK. This template is stored in the Post Processing Templates palette, available from the resource bar.

Post view layouts Post-processing displays up to nine models simultaneously. The Layout view also lets you save templates in layout format. Creating a viewport layout To create a viewport layout, click the down arrow next to the layout icon on the Post Control toolbar. From the drop-down list, select a layout from one to nine views. ©UGS Corporation, All Rights Reserved


15-7

Post-processing

Overlay The Overlay icon ( ) becomes active only after you have created an overlay using the Simulation Navigator. Use Overlay to superimpose one or more sets of results on another. Use the Overlay dialog to select the view to apply changes to when modifying an overlay, and to remove overlays. Creating an Overlay Create an overlay using the Simulation Navigator. Overlay active until an overlay exists. To create an overlay display:

is not

1. Ensure that you have created at least two post views in the Simulation Navigator. 2. Ensure that the layout in the graphics window for the current work view is single-view only.

15

3. Right-click on a non-work view, and select Overlay. The non-work view is superimposed over the work view in the graphics window. 4. Select additional views to superimpose, if desired.

You can now use Overlay Overlay dialog.

15-8


in the Post Control toolbar to launch the


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Post-processing

Combining load cases You can add linear static load cases and view their combined results. You can scale results to compare the results of similar loading conditions at different loading values. This feature is useful for viewing results for varying combinations of load cases without spending analysis time, resources and disk space for every instance of a load case combination. Combined load case definitions are saved in the Simulation file and are available from session to session. Prior to using the Combine Load Cases functionality, you should give some thought to how you set up your analysis. Be sure to create a separate subcase for each load case you intend to combine. If you will be applying a scale factor, you may find it useful to define loads using unit values. Combining load cases To combine and scale load cases in the post-processor:

15

1. Right-click on the Results node in Simulation Navigator and choose Combined Loadcases. 2. Enter a short, meaningful name for the combined load case and click Create. The combined load case name appears selected in the Combined Load Cases list box. The Load Case Component list box is now active. 3. The Load Case Component list box lists the solved subcases for the solution. Select the first load case to combine. The Scale field and the Add/Edit button are now active. 4.

If you are applying a scale factor to this load case, enter a value in the Scale field.

5. Click Add/Enter. The load case, multiplied by the entered scale factor, appears in the Combined Load Case Definition list. 6. Repeat steps 3 – 5 for each load case you want to combine. 7. Click OK or Apply. The combined load case appears below the results node along with the subcases. You can create post views displaying the combined results. ©UGS Corporation, All Rights Reserved


15-9

Post-processing

Animation Animation allows you to generate and control the display of animation frames. You can animate displays to better visualize how the model responds to a particular solution. Using the animation tools You can quickly animate static displacement or stress results (using the default settings) using the Animation tools: 1. Click Play

on the Post Control toolbar.

The software first generates and steps through the individual frames of the animation, and then plays the animation. 2. (Optional) Step through the animation frame by frame. Click Pause

15

or Next , and then click Previous forward through each animation frame.

to step backward or

to delete the animation frames and return to the static 3. Click Stop displacement or stress display.

Identify Use Identify to probe and display nodal and elemental information for the Work view display. You can display the IDs or the current results value. You can also list results for selected nodes and elements, and you can save a particular selection. Identifying results at nodes or elements 1. Click Identify

15-10

.



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Post-processing

15 2. In the dialog, choose a filter from the Filter menu. •

If you select n Highest or n Lowest Nodes or Elements, enter a value for N=. For example, to view the 10 nodes with the highest values for the current result, enter N= 10.

•

If you select Node IDs or Element IDs, enter node or element ID in the IDs: field. Use commas or spaces to separate multiple node IDs.

•

If you select a geometry-based filter (or no filter), use the resulting Probe cursor to interactively select nodes or elements.

Selected elements are marked using the marker indicated in the Mark field: Values, node IDs, or just the node location highlight. 3. Click List Information in Window or List Information in Spreadsheet to generate a listing of results data for all nodes or elements matching the probe criteria. To include all data components in the listing, be sure to select the List All Components check box.



15-11

Post-processing

Generating reports The report is an HTML document containing .gif images and other FE model data. It consists of a title page and multiple chapters. Each chapter contains automatically generated information, with some sections including optional information that you can enter or edit. Use Create Report

to generate a report.

Activity See the “Post-processing” activity in the Applications of Advanced Simulation Workbook. In this activity, you will explore some of the techniques that you can use to post-process the results from a solve.

15


15-12

•

Learned how to use the post-processor.

•

Learned how to use the tools on the Post Control toolbar.



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Lesson

16 Reports

Objectives •

Learn how to generate an HTML report.

16



16-1

Reports

Overview To generate a report, use Create Report

.

The report is an HTML document containing .gif images and other FE model data. It consists of a title page and multiple chapters. Each chapter contains automatically generated information, with some sections including optional information that you can enter or edit. You can create a report at any time after you create a solution. That is, the solution need not be complete and solved. For example, suppose that you define the loads and constraints for a model that will be meshed by a colleague. You may want to create a report detailing the loading before handing off the solution to the colleague performing the meshing. The figure shows a typical report structure displayed in the Simulation Navigator.

16

16-2



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Reports

16



16-3

Reports

Creating the report 1. Click (Create Report), or right-click on the Solution node in the Simulation Navigator and select Create Report. An HTML-formatted report is automatically generated and displays as a node in the Simulation Navigator. 2. Expand the Reports node in Simulation Navigator so you can see the chapters and their contents. 3. Use MB3 options in the Simulation Navigator to modify the report, as necessary. •

Clear the visibility check box ( ) next to a report item to exclude it from the current report, or MB3 → Clear.

•

MB3 → Edit to display a text editor where you can add or edit text to the sections of the report.

Exporting the report To export the report, right-click on the Report node in the Simulation Navigator and choose Export. The report is written to a number of HTML and graphics files, and stored in your local temp directory. When the files are written, the software launches your default browser and displays the resulting report.

16

Activity See the “Reports” activity in the Applications of Advanced Simulation Workbook. In this activity, you will create an HTML report of model data, solution data, and images.


16-4

Learned how to generate an HTML report.



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Lesson

17 Units Objectives •

Learn how to create new units of measure.

•

Learn how to calculate unit conversions.

17



17-1

Units

Units overview The NX software provides two default unit system files: English and metric. You can choose one of these unit systems when you create a new part file. The settings for that unit system are then applied to and stored with the file. Within a part, you can modify the default unit settings as follows: •

In key dialogs, drop-down selections let you change the unit system dynamically rather than having to manually calculate conversions. For example, if you are creating a load set and want to enter the force in Newtons instead of pound-feet, select Newtons from the unit options and enter a value.

•

The Units Manager dialog lets you create new units and unit systems that are saved to the part and become available from all key dialogs.

•

The Units Converter dialog provides a utility to calculate unit conversions.

All unit modifications are stored with the part and are therefore preserved between sessions. In addition, the unit values are automatically converted to the NX standard or metric system when you perform a solve.

Units Manager Units Manager lets you make changes to units of measure. New information from each Units Manager session is dynamically updated in all key dialogs.

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Units

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Creating a new unit of measure To create a new unit of measure: 1. Choose Analysis → Units Custom → Units Manager. TheUnits Manager dialog opens. The default unit system is displayed, with the Default Unit option selected. 2. Choose Measure to change or add a unit of measure, such as Temperature. Each unit of measure is assigned a unique conversion equation, which appears in the Conversion Parameters section of the dialog and updates automatically whenever you change the unit of measure. 3. Select or enter a new unit name. When you switch from the original unit system, the software updates the dialog by clearing the Default Unit check box. ©UGS Corporation, All Rights Reserved


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Units

4. Enter a Unit Display Name, which is the abbreviated name for the unit. 5. Enter a full-name description for the unit of measure. 6. In the Conversion Parameters section, enter a multiplication factor and, if necessary, an addition factor for the unit of measure equation. 7. Choose New Unit. The new unit measurement is available immediately. For example, if you just defined dyne as a unit of force in the Units Manager dialog, the dyne unit appears as a selectable option the next time you open the Loads dialog. You can delete or update units you’ve manually created in the Units Manager dialog as long as they haven’t been used elsewhere.

Units Converter The Units Converter dialog provides a utility to calculate unit conversions. You can use the converted values as input in other dialogs, or to simply compare with other values.

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Calculating a conversion value 1. Choose Analysis → Units Custom → Units Converter. 2. In the dialog, select a Quantity. 3. In the From field, enter a value and select a unit system for the original unit. 4. In the To field, select the new unit system. The software automatically calculates a conversion value. 17-4



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Units

Activity See the “Units” activity in the Applications of Advanced Simulation Workbook. In this activity, you will create and work with custom units.


Learned how to create new units of measure.

•

Learned how to calculate unit conversions.

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Lesson

18 Mesh connections Objectives •

Learn how to connect parts using various tools, including Mesh Mating Condition, Edge-Face Connection, Weld Mesh, Contact Mesh, Surface Contact Mesh.

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Mesh connections

Mesh Mating Condition Use Mesh Mating Condition their associated 3D meshes.

to connect two separate solid bodies and

The Mesh Mating Condition capability lets you assemble individual meshes together at a specified interface. The software ensures that connectivity is maintained at that interface. For example, you can use Mesh Mating Condition to: •

Connect the meshes on similar bodies within an assembly.

•

Create identical meshes on two faces to facilitate contact definition.

18 Understanding the roles of the source and target faces In a mesh mating condition, the software creates a connection between the mesh on the face of one body and the mesh on the face of another body. One face serves as the source face for the mating condition, and the other face serves as the target face. The source face controls the density of the mesh at the interface. In general, the source face should have a finer mesh, and the target face should have a more coarse mesh. However, when you define a mesh mating condition, you actually select the faces of the part and not the meshes. 18-2



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Mesh connections

You can use the Reverse Direction icon at the bottom of the Mesh Mating Conditions dialog to reverse which face is the source and which face is the target. Selecting faces automatically or manually On the Mesh Mating Conditions dialog, the Type options let you choose whether you want the software to automatically search your model for appropriate source and target faces or whether you want to manually select pairs. If you select Auto Create to have the software select the pairs, you can use the Face Search option to control the criteria the software should use to find pairs. •

Choose All Pairs to have the software find all pairs of source and target surfaces within the specified Distance Tolerance.

•

Choose Identical Pairs to have the software find only pairs of source and target surfaces within the specified Distance Tolerance. that are also geometrically identical (for example, they must have the same number of edges, the same area, etc.).

Selecting a mesh mating condition type The Mesh Mating Conditions dialog lets you define the following types of mating conditions: •

A Glue Coincident condition.

•

A Glue Non-Coincident condition.

•

A Free Coincident condition.

Glue Coincident conditions With a Glue Coincident condition, if two faces are geometrically identical, the software imprints the mesh from the source face onto the target face. It then merges the nodes at the interface between the source and target so that the two faces share the same nodes. Glue Non-Coincident conditions With a Glue Non-Coincident condition, the software creates multi-point constraints (MPCs) or constraint equations between the nodes on the source and target faces. ©UGS Corporation, All Rights Reserved


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Mesh connections

You can create this type of mesh mating condition between any two faces irrespective of their relative positioning. However, the software uses the Distance Tolerance to connect the nodes at the time you solve. Therefore, if the two faces are far apart relative to the tolerance, no relationship is created between the two meshes, and the bodies are likely to move independently. Free Coincident conditions With a Free Coincident condition, the software aligns the mesh on both the source and target face but does not connect the meshes. With Free Coincident, this results in duplicate nodes at the interface between the source and target faces. This is useful, for example, for setting up surface-to-surface contact problems. Managing Mesh Mating conditions in the Simulation Navigator When you create a mesh mating condition, the software adds it to the Connection Meshes → Mesh Mating Conditions container in your FEM file in the Simulation Navigator. You can use MB3 options in the Simulation Navigator to delete, rename, and manage mesh mating conditions. Automatically Creating Mesh Mating Conditions 1. Click Mesh Mating Condition

.

2. Select Auto Create on the Mesh Mating Condition dialog. 3. Optionally, select a region of your model to limit the face pair search. If you don’t select a region of faces, the software searches the entire visible model. 4. Choose the Mesh Mating Type.

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5. Choose the Face Search Option. To limit the face pair search to coincident faces, select Identical Pairs Only. 6. Adjust the Distance Tolerance as necessary for the size and scale of your model. 7. Click Preview to highlight all face pairs that match the criterion you’ve set. If the previewed face pairs do not meet your expectations, you may need to adjust the Mesh Mating Type, Face Search Option, or Distance Tolerance. You can also change the Type to Manual and manually select the 18-4



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Mesh connections

8. Click OK or Apply to create the mesh mating condition. Manually creating mesh mating conditions 1. Click Mesh Mating Condition

.

2. Select Manual on the Mesh Mating Condition dialog. 3. Choose the Mesh Mating Type. 4. Depending on the size and scale of your model, you may want to adjust the Distance Tolerance. 5. Select the source face. 6. Select the target face. 7. Click OK or Apply to create the mesh mating condition.

Edge Face Connection Use Edge-Face Connection to define the connection between a set of edges and a set of faces. Use this feature whenever there are meshes to be connected in T-junction configuration, for example, fins or stiffeners attached to surfaces. When you use Edge-Face Connection functionality, the software ties the selected edges to the faces using rigid links and MPCs (multi-point constraints). The existing meshes on the edges or faces are not disturbed.

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Mesh connections

Understanding the edge-face connection process Once you finish making selections on the Edge-Face Connection dialog, click OK or Apply to create rigid links between the selected edges and selected faces. The software creates the connection as follows:

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If are no meshes exist on the edges, each selected edge is seeded with nodes corresponding to the number specified in the Default Element field.

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From these seeded node locations, element nodes are located (Glue Meshes) or points are projected and corresponding nodes created on the selected faces (Match Meshes).

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Rigid links are created between the face nodes and the edge nodes.

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The rigid link elements are displayed in preview.

Weld Mesh Weld Mesh lets you locate/automate the recognition of weld features (connections) and then automate the creation of their FE model representation, including consideration for midsurfaces. 18-6



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Mesh connections

Use Weld Mesh to create weld elements (1D mesh) from weld features (connections).

Resistance spot welds Resistance spot welds are used to connect multiple layers of sheet metal. The original spot weld locations (weld points) are projected onto the face, and the software creates weld elements (Rigid Link or Spring type elements) between the projection points. •

The original spot welds are first projected to the first body using a normal to the surface projection.

•

The second and subsequent bodies are projections of the first body’s locations, again projected normal to the first body’s surface.

•

The software treats the weld points as hard points. This means that the software honors the weld points during face meshing.

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Weld element process You can get spot locations for each layer of metal faces from the weld feature. The software creates hard points at the spot locations defined in the weld feature. The software sorts face pairs from top to middle, and middle to bottom. It then creates the recipe for the weld mesh recipe. Finally, the ©UGS Corporation, All Rights Reserved


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Mesh connections

software creates 1D elements between the projection points for each pair of faces.

Resistance seam welds Resistance seam welds connect multiple layers of sheet metal, just as resistance spot welds do. They differ from resistance spot welds in that the weld geometry is modeled by curve. Points on the original curves are projected on to the faces, and weld elements (Rigid Link/Spring) are created between the projected points. •

Resistance seam welds connect multiple layers of sheet metal, just as spot welds do. They differ from spot welds in that the weld geometry is modeled by a curve. As with spot welds, the points on the "original" curves are projected to the first body’s surface, and then the resulting projection points are projected to each subsequent body.

•

The software creates the rigid elements between each pair of points (point on top face and the corresponding point on the bottom face).

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The software treats the weld points as hard points. This means that the software honors the weld points during face meshing.

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Mesh connections

Contact Mesh Use Contact Mesh to create point-to-point contact between two edges or a portion of two edges defined by limiting points. Result types supported in Post Processing for contact mesh include Normal Force, Sliding Force, Element Status, and Gap/Penetration.

18 Creating a contact mesh 1. Click Contact Mesh

.

2. Select the desired contact edge and click OK. 3. Select the desired target edge. ©UGS Corporation, All Rights Reserved


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Mesh connections

4. Click Apply to build the contact mesh. 5. (Optional) You can also use the other selection step icons to control the limiting points definition. You can define or edit the element properties of the contact mesh you built using the Attribute Editor.

Surface Contact Mesh Surface Contact Mesh lets you create and define contact elements between two selected faces of a solid or between different components. The options available in the Surface Contact dialog depend on the solver environment selected as the currently active solution. Using surface contact, you can choose between four contact conditions: standard, rough, no separation, or bonded. Depending on the solver you plan to use, you define the contact elements as surface contacts or node-to-node gap elements.

18 Creating a surface contact mesh 1. Click Surface Contact Mesh

.

2. (Optional) Select Auto Create Contact Pairs, and enter the desired Capture Distance to specify the surface proximity value by which the overlapping faces can be detected. 18-10



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3. (Optional) To more specifically define contact, use the Selection Steps instead of Auto Create. First, select the source face and then the target contact face. 4. Change other properties as desired. 5. Click Apply to build the surface contact mesh, and then click OK.

Activity See the “Mesh connections” activity in the Applications of Advanced Simulation Workbook. In this activity, you will create mesh connections and generate a mesh.

Summary In this lesson you learned how to use various mesh connection tools: •

Mesh Mating Condition

•

Edge Face Connection

•

Weld Mesh

•

Contact Mesh

•

Surface Contact Mesh

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Lesson

19 Optimization

Objectives •

Learn how to use optimization.

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Optimization

Optimization overview Optimization is a process that helps you arrive at the best solution for a given design goal. To achieve the design goal, you set convergence parameters for the design objective, constraints, and design variables. The software then performs a series of iterations to converge on a solution. After you perform an optimized solve, you can access the results in Post Processing. Where do I find it? To run optimization, do one of the following: •

In the Simulation Navigator, right-click on the simulation → New Solution Process → Optimization

•

Advanced Simulation toolbar → Optimization Setup

Optimization Setup Use the Optimization Setup dialog to specify an optimization type, then define a design objective, constraints, design variables, and convergence parameters. You can also use this dialog to specify the number of iterations for the optimization run and to view defined optimization settings.

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Optimization

Optimization analysis options Two types of optimization are available: •

Global Sensitivity Studies

•

Altair HyperOpt™

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Global Sensitivity Studies Global Sensitivity Studies iterates through the limits of each selected design variable one at a time, to see how sensitive the design objective is to each variable. ©UGS Corporation, All Rights Reserved


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Optimization

The design variable values are varied over a specified number of steps. For example, if a design variable has a lower limit of 0.0, an upper limit of 10.0, and you specified 5 steps for the global sensitivity study, there will be five iterations during which the design variable is incremented by a value of 2.0 for each iteration. The total number of iterations for a global sensitivity study is equal to: ( number of steps + 1 ) * number of selected design variables The results for study are displayed in the Sensitivity Spreadsheet, which you can access from Results → Type in the Post-Processor. Upon initiating an analysis or study, a copy of the part is saved. In general, you should not attempt to modify a model while an optimization analysis is in progress. Altair HyperOpt™ Altair HyperOpt™ provides full support for shape optimization, including the use of feature parameters and expressions as design variables. Once you have defined a set of design variables, design constraints, and an optimization goal, the software stores this information and uses it during optimization to determine how many iterations are needed for a converged solution. During the optimization, a graph displays that dynamically updates for each iteration to show the objective result (y axis) vs. iteration (x axis). When the run is complete, the graph closes and quits, and the Optimization Spreadsheet automatically launches.

Objectives Use the Objective dialog to select and define a design objective to be applied to the optimization problem. Optimization objectives include response types from supported solvers. You can select:

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Volume or weight (for static analysis)

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Frequency (for modal analysis)

•

Additional selections such as stress, displacement, and temperature (for thermal analysis)



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Optimization

Constraints Use the Constraints dialog to make constraint selections for optimizing a specific problem. Constraints can be applied to the model as a whole or to specific geometries.

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Optimization

Design Variables Use the Design Variables dialog to define the design variables, which are independent quantities that you can vary in order to achieve the optimum design. Upper and lower limits define a maximum range of variation and serve as constraints on the allowable amount of change.

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Optimization

Activity See the “Optimization” activity in the Applications of Advanced Simulation Workbook. In this activity, you will use shape optimization to minimize the weight of a part.



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Optimization


Learned how to use optimization to achieve your design goals.

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Lesson

20 Durability (fatigue) analysis

Objectives •

Learn how to create a durability solution.

•

Learn about the types of durability results.



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Durability (fatigue) analysis

Durability overview Fatigue life can be defined as "failure due to repeated load...involving the initiation and propagation of a crack or cracks to final fracture" (Fuchs, 1980). Structural fatigue analysis is a tool for evaluating a design’s structural worthiness, or its durability, under various simple or complex loading conditions, also known as fatigue duty cycles. Results of a fatigue analysis are displayed as contour plots that show the duration of cyclic loading (number of fatigue duty cycles) the structure can undergo before crack initiation occurs. Fatigue analysis uses the cumulative damage approach to estimate fatigue life from stress or strain time histories. Estimation is accomplished by reducing data to a peak/valley sequence, counting the cycles, and calculating fatigue life. A library containing standard fatigue material properties is provided. Fatigue analysis process To perform a fatigue or durability analysis, prepare the model as you would for a finite element analysis and then provide certain fatigue-specific information: •

Fatigue material properties

•

Fatigue load variations

•

Fatigue analysis options

Fatigue results During the solve, the load variation parameters are combined with other fatigue criteria, and the software performs fatigue analysis calculations to evaluate the structure’s durability. Durability is assessed and displayed as contour plots in the following areas: •

Structural strength (Stress Safety Factor)

•

Fatigue strength (Fatigue Safety Factor)

•

Fatigue life (Fatigue Life)

Preparing the model for a durability analysis To prepare the model for a durability analysis, first perform the initial steps for a linear static analysis: 1. Open or create the part or assembly. 2. In Advanced Simulation, create new FEM and Simulation files.

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3. Create a linear statics solution. You will not need to perform a solve. 20-2



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4. Apply loads and constraints; mesh the model. 5. Make sure to assign a material that contains fatigue properties.

Creating a durability solution To create a durability solution: 1. With the Simulation node selected, create a new solution process (MB3 → New Solution Process → Durability Solution).

2. Assign a name to the solution and specify durability parameters. Click OK. 3. In the Simulation Navigator, select the Durability solution node. Right-click and select New Load Variation.



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4. Select the Durability solution node you just created; right-click and select Solve. 5. After the solve is complete, select the Results node in the Simulation Navigator; double-click. Post Processing opens. 6. Under the Results node, pick one of the results types.

Evaluating fatigue results The fatigue result types correspond to the fatigue evaluation options: •

Stress Safety Factor

•

Fatigue Safety Factor

•

Fatigue Life Factor

You can view each of these result sets in a post processing display. Stress safety results are displayed as linear scale by default, while fatigue safety and fatigue life results are displayed as log scale.

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Viewing fatigue results To access fatigue results: 1. After the solve is complete, select the Results node in the Simulation Navigator; double-click. Post Processing opens. 2. Under the Results node, pick one of the results types (see below for description). Stress Safety Factor results The software calculates Stress Safety Factor as a function of the time history of effective stress (von Mises, maximum or minimum principal stresses) to determine the failure index results set for the structure. Values greater than 1 are acceptable; values less than 1 indicate failure. Fatigue Safety Factor results Fatigue safety results reflect the fatigue safety factor due to the cyclic loading conditions you defined in the fatigue duty cycle. For a design to be considered feasible, the fatigue safety factor must be greater than 1. In addition: •

An area where the fatigue safety factor approaches infinity may be overly designed for this particular event. You probably don’t need to pay much attention to it.

•

An area where the fatigue safety factor is less than or equal to 1 will eventually be damaged by repeating the given fatigue duty cycle.

•

Lower fatigue safety factor values indicate that the cyclic stress range during the fatigue duty cycle was high.

Fatigue Life results Fatigue life is expressed as a real scalar results set that evaluates the number of fatigue duty cycles before crack initiation occurs.

Activity See the “Durability (fatigue) analysis” activity in the Applications of Advanced Simulation Workbook.

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In this activity, you will perform a durability (fatigue) analysis. ©UGS Corporation, All Rights Reserved


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Learned how to create a durability solution.

•

Learned about durability results types.

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Lesson

21 Buckling analysis

Objectives •

Use linear buckling in an analysis



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Buckling analysis

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Linear buckling overview Buckling analysis is a technique used to determine buckling loads and buckled mode shapes. A buckling load is the critical load at which a structure becomes unstable, and a buckled mode shape is the characteristic shape associated with a structure’s buckled response. A linear buckling analysis identifies the loading conditions that make a structure unstable and result in various buckled mode shapes, as determined by the eigenvalue extraction method and the number of modes for which the analysis is solved. In a linear statics analysis, a structural model is normally considered to be in a state of stable equilibrium. As you remove the load previously applied, the structure goes back to its original position. However, under certain loading combinations, the structure becomes unstable. When this loading is reached, the structure continues to deflect without an increase in the loading magnitude and "buckles" or becomes unstable. To build the model for a linear buckling analysis, choose the Linear Buckling analysis. Before performing the Solve operation, enter a number for the required buckled shape modes and, if desired, the upper and lower eigenvalue range. A default value (usually the lowest number of modes) is given if these values are not defined.

Loads in linear buckling analysis If the analyzed model only contains a buckling load (that is, a load, which when large enough, would cause the system to become unstable), the critical buckling load is the load multiplied by the eigenvalue. The model can contain one or more buckling loads and also other loads that would not cause buckling on their own, but instead act on the part by making it more (or less) likely to become unstable. The figure below illustrates one such case.

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Buckling analysis

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P1 is the buckling load and P2 is a load that makes the part more likely to become unstable. The part in the example will become unstable for a lower value of P1 than the same part without P2. P2 may be a known load acting on the part. You may want to find out the value of P1 at which the part becomes unstable. With a linear buckling solution, you cannot keep P2 constant and analyze the part only for buckling caused by P1. The linear buckling solution considers all loads as a system. The relation between the loads is not considered to change. For example, if the part is analyzed with P1=1 and P2=0.5 and the lowest eigenvalue turns out to be 500, the system is calculated to be unstable for the load combination: P1=500 and P2=250.

Supported environments Advanced Simulation supports the following linear buckling environments: •

Nastran - SEBUCKL105

•

ANSYS - Buckling

•

ABAQUS - Buckling Perturbation Substep



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Buckling analysis

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Activity See the “Buckling analysis” activity in the Applications of Advanced Simulation Workbook. In this activity, you will analyze a strap to determine the first three buckling modes.


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Learned how to use linear buckling in an analysis.



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Lesson

22 Modal analysis

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Objectives •

Learn how to perform a modal analysis.



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Modal analysis

Modal analysis Dynamic analysis is an important part of any design involving non-static structure. These analyses are frequently performed to ensure that the natural frequency of a given part does not coincide with that of a certain input or forcing function. These forcing functions can occur in nature from such causes as wind or other parts of a mechanical system (such as a nearby engine).

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Use of modal analysis Below are a couple reasons for running a dynamic analysis and verifying that the forcing function frequency does not coincide with the part being analyzed: •

If the natural frequency of the part happens to be the same as that of the forcing function, an amplification of vibration may result, imparting more load into the part than intended. This amplification can also carry over into any mating parts, resulting in a vibrating system.

•

If the natural frequencies are close, the product may vibrate. Although the vibration may not be detrimental to the strength of the system, it can present discomfort to the user.

Modal analysis and material properties In order to perform a dynamic analysis, the density must be specified in the material properties listing. Failure to specify the density and assign it to the mesh will yield a result without natural frequencies. Submitting a dynamic analysis Several parameters must be specified before submitting a dynamic analysis. Upon selecting Solve, choose Edit Solution Attributes, and the Edit Solution dialog is displayed.

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Modal analysis

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To submit the analysis, you must first specify the frequency range of interest and number of modes you wish to find. From the Modal Generation menu,



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Modal analysis

choose Modes/Frequency to activate the Frequency Range Lower Limit and Upper Limit fields. Knowing the input frequency, you would typically specify a broad range around it, within the range of interest field. For example, for a forcing frequency of 500 Hz, you could specify a lower limit of 0 and an upper limit of 1000. It should be noted that this frequency range is in Hertz units.

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The Number of Desired Modes corresponds with the number of mode shapes for that part. Typically there is one natural frequency that corresponds to a given mode shape. The higher the number of mode shape, the less extreme are the deflections that correspond to the frequency of that mode. The first mode shape normally results in the highest local deflection of a part. The first four mode shapes are typically requested when performing an analysis. Generally, a dynamic analysis is submitted without any type of loading; however, the part must be constrained in accordance with a real-life situation. If a structural analysis is being performed, the simplest way to transition to a dynamic analysis is to delete the loads and submit the model with constraint information only. Mode shapes of a modal analysis Mode shapes illustrate the deflection of the part when subjected to vibration. A mode shape develops when the vibration frequency reaches the natural frequency. At this point the part is considered to be in a steady state. Post processing a modal analysis For modal analysis the frequency results are displayed, ranging from lowest to highest natural frequency in the specified range. The results are ordered by mode shape, with the lowest natural frequency being the first mode shape, the next highest the second mode shape, and so on. Selection of the various results shows the mode shape. The natural frequency for that mode shape is displayed with the result selection. All post processing tools are available when processing the model results. This includes the animation tool. The animation tool is particularly useful when visualizing mode shapes. The displayed deflections are relative to other grid points in the model and should not necessarily be considered true deflections.

Activity See the “Modal analysis” activity in the Applications of Advanced Simulation Workbook. In this activity, you will perform an modal analysis on a speaker cabinet. 22-4



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Modal analysis


Learned how to perform a modal analysis.



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Lesson

23 Thermal analysis 23

Objectives •

Learn how to perform a thermal analysis.



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Thermal analysis

Thermal analysis Thermal analysis is an important part of any design intended to function over a broad range of temperatures. There are usually certain design conditions that a given part must be designed to withstand. Thermal analysis is one tool employed to verify this criterion. Thermal model preparation Preparation of a thermal model is similar to preparation of a structural model. With a structural model, the part must be both constrained and loaded to obtain a result. With a thermal model, constraints only may be specified or a combination of constraints and loads, depending on the application.

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There are a number of different types of loads and constraints available when performing a thermal analysis. One parameter that is required with a thermal analysis is the coefficient of conductivity. A value must be assigned to the mesh. Failure to enter a conductivity coefficient will yield no results as the solver does not know the rate at which heat flows through the assigned material. Post processing a thermal model Thermal models are post processed similar to dynamic and structural models. When viewing the results of a thermal model, you can animate the result and view the temperature changes throughout the model. Also helpful as an available option is the ability to target the highest temperature node or element. Determining thermal stresses and strains From various strength of materials and linear elasticity concepts, we know that thermal loading is not capable of causing direct stress, but instead causes thermal strains. Depending on how the part is constrained, these thermal strains may result in thermal stresses. For example, if a part is constrained at both ends over a length and is subjected to a positive temperature load, the part will tend to grow. Because the part is fully constrained at both ends, it is not able to grow. This results in thermal stresses. If one end of the part was free, the part would grow without incident and no thermal stress would develop. To calculate these stresses and strains the part must first be loaded with the thermal loads or constraints. The part is then structurally constrained. The model would then be run as a structural analysis and post processed. If there are no structural loads applied, the resulting stresses and strains must be due to thermal loading. It should be noted that in linear elastic analysis, 23-2



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Thermal analysis

these thermal stresses and strains are additive to the structural stresses and strains. Submitting a thermal model for analysis When submitting a thermal model for analysis, choose Edit Solution Attributes on the Solve dialog. On the Edit Solution dialog, enter the Default Initialization Temperatutre, which is a start temperature for all the nodes that do not have a temperature assigned. This gives the solver a starting point that is closer to the ending temperature, resulting in fewer iterations. This can actually lower the run time of the model.

Material considerations of temperature When considering varying ranges of temperature, attention must be paid to the material properties. Material properties typically vary with temperature. ©UGS Corporation, All Rights Reserved


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Thermal analysis

As a material is removed from room temperature, property degradation will occur. For an accurate analysis, this degradation must be accounted for. One way to accomplish this is to use multiple names of the same material with different material values. For example, aluminum may be denoted by the numbers 1 through 5. They can then be defined as being in a category of a temperature range. Consult your local material information specifications for temperature range and degradation amounts.

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Activity See the “Thermal analysis” activity in the Applications of Advanced Simulation Workbook. In this activity, you will perform a thermal analysis. You will also create and solve a second solution using the same model.


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Learned how to perform a thermal analysis.



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Lesson

24 Contact and gluing

Objectives •

Learn how to analyze surface to surface contact

•

Learn how to analyze advanced nonlinear contact

•

Learn how to analyze gluing


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Contact and gluing

Surface to Surface Contact Surf to Surf Contact

lets you define contact between two surfaces.

To define the contact, select a source region and target region in the Simulation model. On the Create Surf to Surf Contact dialog, enter the parameters to define contact between these two surfaces.

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To define additional contact parameters for the solver and solution type, use the Edit Solution dialog. These solvers and solution types support surface to surface contact: Solver

Solution Type

NX Nastran

SESTATIC 101 (Single Constraint and Multi Constraint)

ANSYS ABAQUS

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Linear Statics Nonlinear Statics Structural — General Analysis


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Contact and gluing

When the solution is set to the NX Nastran solution type SESTATIC 101, there are two commands for defining surface contact: Surf to Surf Contact, and the legacy command Surface Contact Mesh. UGS recommends that you use Surf to Surf Contact to define contact between two surfaces. Unlike Surf to Surf Contact, Surface Contact Mesh generates contact (or gap) elements between the two surfaces. Defining surface to surface contact To define surface to surface contact: 1. In the Simulation Navigator, right-click on Simulation Objects Container → New Simulation Object → Surf to Surf Contact. Make sure that your solution supports surface to surface contact.

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2. Select the first surface (the source region). 3. In the Create Surf to Surf Contact dialog, click Target Region. 4. Select the second surface (target region). 5. In the Create Initial Temperature dialog, enter parameters for the contact between these two surfaces and click OK.

Advanced Nonlinear Contact Create Advanced Nonlinear Contact lets you define surface-to-surface contacts on shell and solid element faces in an advanced nonlinear solution for NX Nastran. This dialog box is available when the Solution Type is ADVNL 601,106.



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Contact and gluing

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To define the contact, select a source region and target region in the Simulation model. On the dialog box, enter the parameters to define contact between these two surfaces. Specify the Target Region Type as FLEX (flexible) or RIGID. When you use a rigid target region (meaning the target contact surface is rigid and the rest of the target part is flexible), you can use the optional selection step, Optional node for rigid target displacement . Choose this step to select a single node or point as a “master” node to control the motion of the rigid target region. Internally, rigid links will connect all the nodes on the rigid target region to this master node. Defining advanced nonlinear contact Only NX Nastran SOL 601,106 supports advanced nonlinear contacts. 1. In the Simulation Navigator, right-click on Simulation Objects Container → New Simulation Object → Advanced Nonlinear Contact. 2. Select the first surface (the source region). 3. In the Create Advanced Nonlinear Contact dialog, click Target Region . 24-4



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Contact and gluing

4. Select the second surface (the target region). 5. If you set the Target Region Type to RIGID, you can click Optional node . Then select a single node or point for rigid target displacement as a “master” node to control the motion of the rigid surface. Internally, rigid links will connect all the nodes on the rigid target region to this master node. 6. Enter any additional parameters for the contact between the two contact surfaces and click OK.

Surface to Surface Gluing

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Create Surf to Surf Gluing lets you connect two surfaces to prevent relative motion in all directions.

To glue two surfaces, you must first define the regions where you want to create glue elements (stiff springs that connect and constrain the surfaces). A region is a collection of element free faces in a section of the model where you expect gluing (or contact) to occur. These regions can be created using shell elements and using free faces of solid elements. Select a source region and target region in the Simulation model. In the Create Surf to Surf Gluing dialog box, enter the parameters to define the contact between these two surfaces. ©UGS Corporation, All Rights Reserved


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Contact and gluing

This option is available for all structural NX Nastran solution sequences except for SOL 601 and 701. It is not supported in thermal or axisymmetric solutions. Defining surface to surface gluing Only NX Nastran supports surface-to-surface gluing. 1. In the Simulation Navigator, right-click on Simulation Objects Container → New Simulation Object → Surf to Surf Gluing. 2. Select the first surface (the source region).

3. In the Create Surf to Surf Gluing dialog, click

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Target Region.

4. Select the second surface (the target region). 5. Enter parameters for the contact between these two surfaces and click OK.

Activities See the “Contact and gluing” activities in the Applications of Advanced Simulation Workbook. In these activities, you will learn how to set up and perform contact and gluing analysis problems.


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Learned how to define surface to surface contact.

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Learned how to define advanced nonlinear contact.

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Learned how to define surface to surface gluing.



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