Mechanical APDL Structural Analysis Guide

This chapter describes both points in detail. Input examples are given to aid in understanding the pro-
cedure.

9.2. General Procedure for Linear Perturbation Analysis

A linear perturbation analysis offers simplicity and ease of use. With the aid of a restart from the base
analysis, it is easy to envision how the snapshot of the solution matrices from the base analysis is regen-
erated and used. All other control keys (commands) are optional.

The following topics related to the linear perturbation analysis procedure are available:

9.2.1. Process Flow for a Linear Perturbation Analysis

9.2.2. The Base (Prior) Analysis

9.2.3. First Phase of the Linear Perturbation Analysis

9.2.4. Second Phase of the Linear Perturbation Analysis

9.2.5. Stress Calculations in a Linear Perturbation Analysis

9.2.6. Reviewing Results of a Linear Perturbation Analysis

9.2.7. Downstream Analysis Following the Linear Perturbation Analysis

9.2.1. Process Flow for a Linear Perturbation Analysis

The following figures show the linear perturbation analysis flow for static, modal, eigenvalue buckling,
and full harmonic analyses:

Figure 9.1: Flowchart of Linear Perturbation Static Analysis

1st Phase of Linear Perturbation (SOLVE, ELFORM)

(1) Restart from base analysis (multiframe restart).

(2) Regenerate [K ] and material data.

(3) Delete most of the loads inherited from base analysis.

Base Analysis

Static or Full Transient

2nd Phase of Linear Perturbation (SOLVE)

(1) Allow modifications of perturbation loads to

generate {F }.

(2) Perform coordinate update (program automatically

executes UPCOORD) if base analysis includes

NLGEOM,ON.

(3) Perform static analysis to solve

[K ] {U }={F }.

T

i

perturbed

T

i perturbed perturbed

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Linear Perturbation Analysis