reference temperature used in the linear perturbation is the TREF temperature from the base analysis.
See Loads, Initial Conditions, and Other Limitations in Linear Perturbation in the Element Reference for
more information.
In the stress expansion pass of a linear perturbation modal or buckling analysis, thermal effects contribute
no strain in the total strain calculation; that is, the thermal strain is zero in this expansion pass.
9.4. Considerations for Perturbed Stiffness Matrix Generation
The first phase of a linear perturbation analysis depends heavily on the multiframe restart procedure;
it also inherits the limitation of the multiframe restart (see Multiframe Restart Limitations in the Basic
Analysis Guide). These limitations include the following:
- The Jobname.Rnnn file does not save the EKILL and EALIVE commands. If EKILL or EALIVE com-
mands are required in the first phase of the linear perturbation analysis, you must reissue these
commands before the SOLVE,ELFORM command is executed. - The Jobname.RDB file saves only the database information available at the first substep of the first
load step. If you input other information after the first load step and need that information for the
restart, you must input this information in the first phase of the linear perturbation analysis. This
situation often occurs when APDL parameters are used. You must use PARSAV to save the parameters
during the initial run and use PARRES to restore them in the restart. The situation also occurs when
you want to change element real constants values; reissue the R command in the first phase of the
linear perturbation analysis.
This limitation also applies to all other commands which modify element material properties or
real constants from the base analysis in the second or later load step(s).- All loading and boundary conditions from the base analysis are stored in the Jobname.LDHI file;
therefore, upon the first phase of a linear perturbation analysis, changing the boundary conditions
is not allowed. At the end of the first phase (after the SOLVE,ELFORM operation is completed), the
program automatically manipulates the boundary conditions according to the specification of the
LoadControl key on the PERTURB command; however, any type of load manipulation is allowed
in the second phase of the linear perturbation analysis so that the desired perturbation loads can be
easily obtained.
Before execution of the SOLVE,ELFORM command, the settings for regeneration of prior solution matrices
with additional or specific requirements should be made. These specific requirements can be met by
using the following commands (these are optionally needed):
CMROTATE -- Used to specify the rotational velocity of an element component about a user-
defined rotational axis. It is needed in brake squeal analysis in conjunction with the QR damped
eigensolver (MODOPT,QRDAMP).
QRDOPT -- Used by QR damped eigensolver for reuse of symmetric eigenmodes from the Block
Lanczos eigensolver (LANB).
CNKMOD -- Used for modifying contact status from the base analysis locally for each contact
pair. The ContKey parameter on the PERTURB command can modify the contact status
globally.
MP -- Used for modifying contact frictional coefficient, MU.
TBMODIF -- Used for modifying frictional coefficients only (similar to MP command usage).
EALIVE,EKILL,ESTIF -- These are used for reproducing the element birth/dead status at the
point of the multiframe restart. They may not be used to change element status from the re-
started point.Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationLinear Perturbation Analysis