- The unsymmetric eigensolver (MODOPT,UNSYM) supports mode expansion and multiple load vector
generation.
For a modal analysis restart, the database must contain the model data as well as the modal solution
data. The model in the database must match the initial model used to solve the first modal solution.
In addition, the following files must be available: mode file (Jobname.MODE, as well as Jobname.LMODE
if the unsymmetric eigensolver was used with MODOPT,UNSYM,,,,,,BOTH), EMAT file (Jobname.EMAT),
ESAV file (Jobname.ESAV), and database (Jobname.DB).
New elements can be added in the restart session to define the load vectors. These new elements must
have no mass or stiffness characteristics that could affect the eigenvalues obtained from the original
modal analysis. Examples of such elements include:
- Surface elements without density (SURF153,SURF154,SURF156).
- Follower elements (FOLLW201) with KEYOPT(1) = 1 (constant direction load).
- Contact elements using the multipoint constraint (MPC) approach to define surface-based constraints.
The loads must be applied to the pilot node. Please refer to Surface-Based Constraints in the Mech-
anical APDL Contact Technology Guide for more information.
During each restart solution, the load vectors generat ed will replace those generat ed during the previous
modal solution (which may be the original modal analysis or a modal analysis restart). See Ex-
ample 5.6: Modal Analysis Restart (p. 136) for a detailed example of this procedure.
The following restrictions apply to modal analysis restart:
- A modal analysis cannot be restarted if residual vectors (RESVEC command) are calculated during the
first analysis. - Modal analysis restart is not supported for cyclic symmetry analysis.
The following example demonstrat es a typical command sequence for a modal analysis restart.
Example 5.6: Modal Analysis Restart
/filnam,case1
/prep7
et,1,plane182! 2D PLANE182 elements
mp,ex,1,2.0e11! Material Properties
mp,dens,1,7800
mp,nuxy,1,0.3
rect,0,4,0,2! Rectangular area
esize,0.5
type,1
mat,1
amesh,1! Mesh area with PLANE182 elements
allsel,all
nsel,s,loc,x,0
d,all,all,0! Fix the model at location X=0
nsel,all
finish
/com,
/com, First Modal solve
/com,
/solu
antype,modal
modopt,lanb,20,0,20000! Use Block Lanczos, extract 20 modes in frequency range of 0 to 20000Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationSolution