Mechanical APDL Structural Analysis Guide

Because a linear perturbation analysis can be understood as an extra iteration of the base analysis, all
history-dependent results of the base analysis are inherited in the results of the linear perturbation
analysis. Therefore, any plastic strains, creep strains, swelling strains, and contact results from the base
analysis are available in the results data of the linear perturbation analysis.

The total strain is the sum of all strains (for example,PLNSOL,EPTO). The nonlinear solution quantities
such as equivalent stress, stress state ratio, and plastic state variable are also available. For detailed in-
formation about element results from a linear perturbation analysis, see Interpretation of Structural
Element Results Aft er a Linear Perturbation Analysis in the Element Reference.

For contact elements, the contact status or contact forces are frequently of interest. The program uses
the same contact status in calculations of both the stiffness matrix for the linear perturbation analysis
and contact results for the expansion pass.

9.2.6. Reviewing Results of a Linear Perturbation Analysis

In the linear perturbation analysis, the program calculates all requested results, including stresses and
strains, and stores them in the Jobname.RSTP file. One reason for the creation of the Jobname.RSTP
file is that all the existing restart files from the base analysis are preserved for possible future use. The
same linear perturbation or restart analysis can be performed repeatedly from the same restarting point.
The Jobname.RSTP file only stores the results of the linear perturbation analysis. Results of the base
analysis are still stored in the Jobname.RST file.

The stresses at the restarting point of the base static or full transient analysis should be obtained from
the Jobname.RST file of the base analysis.

Note

When postprocessing results obtained in a separat e session, you must resume the database

saved after the linear perturbation analysis solution is finished, because the node coordinates

have been updated with the base analysis displacements during the solve.

Note

When postprocessing the base analysis results, you must resume the database that was

saved before the linear perturbation analysis.

9.2.7. Downstream Analysis Following the Linear Perturbation Analysis

Following the linear perturbation analysis, other analysis types can be performed by using the information
from the linear perturbation analysis.

If the linear perturbation analysis is a modal analysis, the following analysis types are possible by using
the Jobname.MODE file generat ed by the perturbation and the database of the model:

• Harmonic or transient analysis using the mode superposition method (Method=MSUP on the HROPT
  or TRNOPT command). Mode superposition analysis based on QRDAMP eigensolver is not supported.


• The eigenmode reuse procedure (Restarting a Modal Analysis (p. 69)) is also available for linear per-
  turbation analysis.


• Response spectrum analysis

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General Procedure for Linear Perturbation Analysis