Mechanical APDL Structural Analysis Guide

• PCG Lanczos (MODOPT,LANPCG)


• Supernode method (MODOPT,SNODE)


• Subspace method (MODOPT,SUBSP)


• Unsymmetric method (MODOPT,UNSYM)


• QR damped method with no complex solutions (MODOPT,QRDAMP,,,,OFF)

Mechanical APDL stores the generat ed load vectors in the Jobname.MODE file so that they can be
used in the subsequent mode-superposition analysis.

3.9.3.2. Using the Multiple Loads Method

The procedure for generating multiple load vectors is as follows:

1. Build the model.


2. Specify the mode-extraction method (MODOPT,LANB; LANPCG; SNODE;SUBSP; UNSYM; or QRDAMP).


3. Activate multiple load vectors generation (MODCONT,ON). Use the THEXPAND command if you wish
   to ignore thermal strains in the generat ed load vector.


4. Specify the first set of loads (F,BF,SF, etc.).


5. Issue SOLVE. This first solution performs the modal extraction and generat es the first load vector.


6. Delete the first set of loads and apply the second set of loads.


7. Issue SOLVE. This solution generat es the second load vector.


8. Repeat step 6 and 7 for any additional load vectors.


9. Issue a FINISH command.

The load vectors calculation can be performed during a modal analysis restart. Refer to Modal Analysis
Restart in the Mechanical APDL Basic Analysis Guide for more details.

The load vectors can then be used in a mode-superposition analysis as follows:

1. Set up a mode-superposition transient,harmonic, or PSD analysis. Ensure that any loads used in the
   creation of the load vector in the modal analysis are deleted; otherwise, duplicat e loads may result.


2. Scale the load vectors by using LVSCALE command. All load vectors must be scaled before the first
   SOLVE. Use a zero scale factor if load vectors are not actually used in this first load step.


3. Solve the mode-superposition analysis. Ensure that the load vectors that are not used at a particular load
   step have a zero scale factor on the LVSCALE command.

3.9.4. Restarting a Modal Analysis

Reusing eigenmodes that have already been generat ed can save significant time in an analysis. Modal
extraction typically requires more time than element loads generation, residual vector calculation, and
enforced static modes calculation. The procedure for restarting the modal analysis to enrich the Job-
name.MODE file is described in Modal Analysis Restart.

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

Modal Analysis Tools for Subsequent Mode Superposition Analysis