Goals This workshop will demonstrate : 1. Bearing Bearing modelin modeling g using using ASCII ASCII file file generated generated from from ROMAC* ROMAC* code. 2. Campb ampbel elll Dia Diagr gram am Log Dec 3. Orbit Plots 4. Criti ritica call spe speed ed map –
Problem Statement : The model consists of three disks mounted on two bearings at the ends Our goal is to import the bearing data from an external file using ANSYS ANSYS macro, plot the campbell diagram, critical speed map, orbit plots, logarithmic decrement & stability for the analysis anal ysis
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*The Rotating Machinery and Controls (ROMAC) Industrial Program supports coopera tive research efforts conducted by faculty, staff, and students in the Mechanical and Aerospace Engineering Department and the Electrical Engineering Department at the University of Virginia.
Project Schematic Open the Project page. From the “Units” menu verify: •
Project units are set to “US Customary (kg, m, s, C, A, N, V).
•
“Display Values in Project Units” is checked (on).
Preprocessing Retrieve the archive WS3_Three_mass_disk.wbpz in the Workshop folder
a.
b. Open Project Save the Project
c.
Geometry
Multibody part made up of Line bodies
b.
a.
Double click on Setup to open Mechanical
Disk modeled as point masses
Geometry •
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The three mass disk example is composed of one shaft divided into nodes and elements (Stations and sections) Figure 1 illustrates the finite element model of the system The model consists of 24 beam elements with 25 nodes Each node has 4 degrees of freedom in order to conduct a lateral rotordynamic analysis. The four degrees of freedom are: A. B.
Displacements in the horizontal and vertical directions Rotational (bending) displacements in the horizontal and vertical directions
Connections and Mesh
b. a.
Two Longitudinal springs are defined in Connections to model Bearings. Note : The properties of these springs will be modified later through Command Objects
Mesh is refined adjacent to the springs
Named Selection
Named Selection is defined for the vertices at the bearings and the disk locations
Analysis Settings
Set number of modes to find to 8 Set Solver to Full Damped Activate Coriolis effect and set Campbell Diagram to on Set number of points (rotational speeds) to 8.
Boundary Conditions
b.
a.
Apply Rotational Velocity
Select the Axis of Rotation by selecting any line body along + X-axis
c.
d.
Boundary Conditions
a. Apply Displacement at two bearing locations by Scoping to Named Selection Bearings
b. Only X component is fixed
Boundary Conditions
Apply Fixed Rotation about X-axis at two bearing locations by Scoping to Named Selection Bearings. This is to prevent the torsional modes
a.
b. Only X component is fixed
Bearing Modeling and Setup The macro IMPORTBEARING1.mac reads the bearing data from text file (below) created by ROMAC code THPAD
ANSYS Bearing Element COMBI214
Import Bearing Macro
b. Right click on Commands and click Import.
a.
Insert Commands
Import Bearing Macro
c.
Click Yes
d.
e.
Macro will appear in the Commands
Go to Project Directory folder, WS3_Three_mass_disk_files, select the macro IMPORTBEARING1.MAC
Change Element type The commands in the text file Change Element Type.txt in the Folder WS3_Three_mass_disk_files are used to replace linear springs defined by Mechanical with “COMBI214” bearing elements Follow the same procedure to Import the Change Element type text file through another Commands object as done for Bearing Import macro
The text file will appear as shown in the Commands
Solution
Click on the Solution to see the tabular modal results
b.
a.
Hit Solve in the Solution
Postprocessing modal results
Select the modes for the 1st rotational velocity ( Solve Point 1). Create mode shapes for the result set.
a.
Right click on Solution and select Evaluate All Results
b.
Mode Shape Mode shape for Set number 4
Orbit plot Copy the text from file Plot orbit.txt from folder WS3_Three_mass_disk_files to the Commands object
b.
The orbit plot is for the specified set number in the Commands
Insert a Commands object in Solution
a.
Orbit plot
b. a.
Clear Generated data
c.
Hit Solve
Campbell Diagram Right click on Solution and insert Campbell Diagram
a.
Details
b.
Evaluate results
Campbell Diagram – Frequency Vs Rotational Velocity
Critical Speed line
1st Critical Speed
Campbell Diagram – Stability Vs Rotational velocity
Details
Campbell Diagram – Logarithmic Decrement Vs Rotational Velocity
Critical Speed Map
a.
Drag and drop another Modal analysis on the existing one to share the first three cells
b.
Second modal analysis will appear in Project tree in Mechanical
Boundary conditions
Copy Displacement from 1st Modal analysis to 2nd Modal analysis
a.
Copy Fixed Rotation in the same way
b.
Environment Import the Change Element type Critical text file (Folder - WS3_Three_mass_disk_files) through Commands object to replace linear springs defined by Mechanical with “COMBI214” bearing elements
a. b.
Analysis Settings
Import Critical Speed Map macro
a.
Insert a Commands object in Solution
b. Import CRITSPEEDMAP.mac Rename
c.
Critical Speed Map Arguments
Fill in the argument values which are used in the CRITSPEEDMAP macro
