In many engineering applications, the linear behavior of a structure based on a prior linear or nonlinear preloaded status is of interest. You can use the new linear perturbation analysis procedure to solve a linear problem from this preloaded case for modal analyses. The preloaded case can have any nonlinear materials and geometric and contact nonlinearities. You can also use the linear perturbation procedure to perform a buckling analysis if the preloaded case is linear or in the case of linear with bonded contact.

To perform a modal linear perturbation after a static or full transient analysis, restart the analysis at the load point of interest and issue the commands PERTURB,MODAL and SOLVE. If a downstream analysis is desired using a modal load vector, you can define or modify the perturbation load for the downstream analysis. The perturbed load is calculated and stored in the .FULL and .MODE files for subsequent mode-superposition, PSD, or other type of modal-based linear dynamic analysis.

For more information, see Linear Perturbation Analysis in the Structural Analysis Guide, the PERTURB command documentation, and Linear Perturbation Analysis Theory in the Theory Reference for the Mechanical APDL and Mechanical Applications.

This feature supersedes the partial-solution-based prestressed modal procedures (using the PSOLVE command).