Mechanical APDL Structural Analysis Guide

NSEL,ALL

NSEL,...

CM, BASE2,NODE! Define component BASE2 with selected support nodes undergoing the second enforced motion

FINISH

! Generate the pseudo-static modes in Modal Analysis

/SOLU

ANTYPE, MODAL

MODOPT, LANB,10

MODCONT,, ON! Activate enforced motion

---! Define constraints

CMSEL,S,BASE1,NODE! Select nodes of component BASE1

D, ALL, UX, 1! Define enforced motion 1 to be applied on all nodes along UX

CMSEL,S,BASE2,NODE! Select nodes of component BASE2

D, ALL, UY, 2! Define enforced motion 2 to be applied on all nodes along UY

SOLVE

FINISH

! Mode-Superposition Transient Analysis

/SOLU

ANTYPE, TRANSIENT

TRNOPT, MSUP

OUTRES, ALL,ALL

KBC,1

DELTIM,...

DVAL, 1, ACC, 100.0! Define constant acceleration for enforced motion 1

DVAL, 2, ACC, %ACCTAB%! Define tabular acceleration for enforced motion 2

SOLVE

TIME,...

SOLVE

FINISH

3.9.6. Using Mode Selection

When performing a mode superposition-based analysis (spectrum, PSD, transient, or harmonic), modes
can be selected for mode expansion. The selected modes can be included in a downstream mode su-
perposition-based analysis. Consider using mode selection in the following cases:

• When spurious modes have been extracted that may lead to erroneous mode superposition results.


• When the model and/or the number of extracted modes is large.

Modes are selected before mode expansion, such that the Jobname.MODE file and the Jobname.RST
file (from the modal analysis) contain only the selected modes. By reducing the total number of modes
included in the superposition analysis, mode selection saves disk space and increases the performance
of the post-processing of the modal results. This means that mode selection can be useful even when
a downstream mode superposition analysis is not intended.

Mode selection is generally performed during a modal analysis restart. See Modal Analysis Restart in
the Mechanical APDL Basic Analysis Guide for more details.

The following methods are available for mode selection:

• Mode Selection Based on a User Defined Array (p. 72)


• Mode Selection Based on Modal Effective Mass (p. 73)


• Mode Selection Based on the Mode Coefficients (p. 74)

Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information

Modal Analysis Tools for Subsequent Mode Superposition Analysis