- For RangeKey, specify either CENTER or RANGE. When RangeKey = CENTER, the program
computes NMODE buckling modes centered around SHIFT in the range of (-LDMULTE, +LDMULTE).
When RangeKey = RANGE, the program computes NMODE buckling modes in the range of
(SHIFT,LDMULTE).
Specify expansion pass options.
Command(s):MXPAND,NMODE,,,Elcalc
GUI: Main Menu> Solution> Load Step Opts> ExpansionPass> Expand Modes
Regardless of whether you use the command or GUI method, the following options are required
for the expansion pass:
- For NMODE, specify the number of modes to expand. This argument defaults to the total number
of modes that were extracted.
- For Elcalc, indicat e whether you want ANSYS to calculate stresses. "Stresses" in an eigenvalue
analysis do not represent actual stresses, but give you an idea of the relative stress or force distri-
bution for each mode. By default, no stresses are calculated.
- Specify load step options.
The only load step options valid for eigenvalue buckling are output controls.
Database and Results File Output:
Command(s):OUTRES
GUI: Main Menu> Solution> Load Step Opts> Output Ctrl> DB/Results File
Output File:
Command(s):OUTPR,NSOL,ALL
GUI: Main Menu> Solution> Load Step Opts> Output Ctrls> Solu Printout
Note
The FREQ field on OUTPR OUTRES can be only ALL or NONE, meaning that the data
are written for all modes or no modes. For example, you cannot write information
for every other mode.
- Save a backup copy of the database to a named file.
Command(s):SAVE
GUI: Utility Menu> File> Save As
- Start solution calculations.
Command(s):SOLVE
GUI: Main Menu> Solution> Solve> Current LS
The output from the solution mainly consists of the eigenvalues, which are printed as part of
the printed output (Jobname.OUT). The eigenvalues represent the buckling load factors; if
unit loads were applied in the static analysis, they are the buckling loads. No buckling mode
shapes are written to the database or the results file, so you cannot postprocess the results yet.
To do this, you need to expand the solution (explained next).
Sometimes you may see both positive and negative eigenvalues calculated. Negative eigenvalues
indicate that buckling occurs when the loads are applied in an opposite sense.
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information
Procedure for Eigenvalue Buckling Analysis
