Results from a modal analysis (that is, the modal expansion pass) are written to the structural results file, Jobname.rst. Results consist of:
Natural frequencies
Expanded mode shapes
Relative stress and force distributions (if requested).
You can review these results in POST1 (/POST1), the general postprocessor. Some typical postprocessing operations for a modal analysis are described below. For a complete description of all postprocessing functions, see An Overview of Postprocessing in the Basic Analysis Guide.
If you want to review results in POST1, the database must contain the same model for which the solution was calculated.
The results file (Jobname.rst) must be available.
Read in results data from the appropriate substep (SET,
Lstep,Sbstep). Each mode is stored on the results file as a separate substep. If you expand six modes, for instance, your results file will have one load step consisting of six substeps.If the results data are complex, you can retrieve the real part, the imaginary part, the amplitude or the phase via this command:
SET, LSTEP, SBSTEP , , KIMG
Perform any desired POST1 operations. Typical modal analysis POST1 operations are described below:
You may want to list the frequencies of all modes expanded (SET,LIST). A sample output from this command is shown below.
***** INDEX OF DATA SETS ON RESULTS FILE *****
SET TIME/FREQ LOAD STEP SUBSTEP CUMULATIVE
1 22.973 1 1 1
2 40.476 1 2 2
3 78.082 1 3 3
4 188.34 1 4 4Use the KUND field on
PLDISP to overlay the nondeformed shape on the display.
For line elements, such as beams, spars, and pipes, issue ETABLE to access derived data (stresses, strains, etc.). Results data are identified by a combination of a label and a sequence number or component name via ETABLE. For more information, see The General Postprocessor (POST1).
Use PLNSOL or PLESOL to contour almost any result item, such as stresses (SX, SY, SZ...), strains (EPELX, EPELY, EPELZ...), and displacements (UX, UY, UZ...).
The KUND field on PLNSOL and PLESOL gives you the option of overlaying the nondeformed shape on the display.
You can also contour element table data (PLETAB) and line element data (PLLS).
Caution: Derived data, such as stresses and strains, are averaged at the nodes via PLNSOL. Averaging results in smeared values at nodes where elements of different materials, different shell thicknesses, or other discontinuities meet. To avoid the smearing effect, use selecting (described in Selecting and Components in the Basic Analysis Guide) to select elements of the same material, same shell thickness, and so on before issuing PLNSOL.
Issue PRNSOL, PRESOL, and PRRSOL to print nodal results, element results, and constrained node reaction data, respectivelydo . To sort the data before listing them, issue NSORT and/or ESORT.
Many other postprocessing functions - mapping results onto a path, load case combinations, and so on - are available in POST1. See The General Postprocessor (POST1) in the Basic Analysis Guide for details.