Mechanical APDL Structural Analysis Guide

Figure 9.4: Flowchart of Linear Perturbation Full Harmonic Analysis

1st Phase of Linear Perturbation (SOLVE, ELFORM)

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

(2) Regenerate [K ].

(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) Generate [M] and [C] matrices.

(4) Perform full harmonic analysis using matrices

[K ], [M], [C], and load vector {F },

where [C] and {F } can be frequency

dependent.

T i

perturbed perturbed

T j

perturbed

For advanced usage of the above analysis types, controls are available to affect how the snapshot
matrices are modified to reflect the real-world engineering applications. These include nonlinear mater-
ial controls, contact status controls, and loading controls.

9.2.2. The Base (Prior) Analysis

The base analysis (the analysis prior to the linear perturbation analysis) can be a linear or nonlinear,
static or full (TRNOPT,FULL) transient analysis. The nonlinearity in the base analysis can be due to
nonlinear materials, geometric nonlinearity, or nonlinear contact elements being used.

If the base analysis is linear static only (that is, only prestress effects are to be included in the model),
the multiframe restart option must be invoked by using the RESCONTROL,LINEAR command, which is
a non-default option for linear static analysis.

If the base analysis is a nonlinear static analysis or a nonlinear or linear full transient analysis, the mul-
tiframe restart is automatically invoked. However, you can use the RESCONTROL command to tell the

General Procedure for Linear Perturbation Analysis