3.2. The CMS Use and Expansion Passes

The CMS use pass and expansion pass are identical to those in a substructuring analysis and support the following analysis types:

The use pass and expansion pass also support prestressed substructures with the limitations reported in Second Phase - Substructure Generation Pass. In addition to the files mentioned in the expansion pass of a substructuring analysis, the procedure for the CMS expansion pass assumes that the jobname.cms file from the CMS generation pass is available. If Elcalc = YES on CMSOPT, jobname.mlv is created instead of jobname.seld and the jobname.mlv must be available for the expansion pass. It is possible to use these files (.cms, .mlv, and .seld) created in previous releases as they are forward compatible, see Program-Generated Permanent Files in the Basic Analysis Guide.

If the use pass is performed using a mode-superposition method and you intend to perform a superelement expansion pass, do not activate the element results superposition key (MSUPkey = YES on the MXPAND command) during the modal analysis.

Note:  If the MSUPkey is left blank, the superelement nodal forces will be added to the jobname.mode file for post-processing.

Spectrum analyses (ANTYPE,SPECTR) only supports the use pass. Calculations of participation factors defined as Equation 15-57 and Equation 15-171 are not well approximated with the residual-flexible free-interface CMS method. Consequently, SPRS, DDAM, MPRS analyses and PSD analysis with base excitation (Excit = BASE on PFACT) are not supported with the residual-flexible free-interface CMS method, and the fixed-interface CMS method is preferred over the free-interface CMS method for any of those analyses.

Avoid applying degree-of-freedom constrains in the generation pass to ensure that all mass is accounted for in the substructure (the constraints are then applied at master degrees-of-freedom during the use pass).

If the superelement is based on cyclic symmetry (CYCLIC) or multistage cyclic symmetry (MSOPT) procedure, the following applies:

  • For CYCLIC procedure, modal analysis is the only use pass supported. A use pass must be performed for each harmonic index of interest. Expansion pass is not supported

  • For MSOPT procedure, only a single stage is supported.

As in substructuring, the generation and expansion passes occur for each part (CMS superelement) of the entire structure, and the use pass occurs only once because it uses all superelements together to build the full model. The use pass in a modal analysis extracts the eigenvalues of the full model (but not the eigenvectors, because the expansion pass recovers them).

In a modal analysis using the free-interface CMS method, the use pass may not always extract all of the modes requested (MODOPT). In such cases, increase or decrease the number of modes to extract and run the use pass eigensolution again.