Chapter 4: Node-based Mode File Scoping for Mode-Superposition Analysis

To reduce the .mode file size and improve efficiency in the mode-superposition (MSUP) step, the .mode file can be scoped based on a subset of nodes. To activate node-based .mode file scoping, the following are required:

  • The FASTLV option on the MODCONT command must be set to NOEXP (a new, beta option). The FASTLV option activates fast load vector generation without activation of the element result superposition key (MSUPkey = YES on MXPAND).

  • A nodal component must be specified for Cname on the OUTRES command.

  • The beta keyword must be activated (KEYW, BETA,1).

Some node-based .mode file records are written only for nodes that are in the nodal component specified on the OUTRES command. The records written for scoped nodes are: SHP, RES, RESMOD, Ef1 and Ef2. Some quantities, such as loads, are not written based on node scoping because the downstream MSUP analysis will be incorrect without the complete set of information. To handle this, the quantities that require complete nodal information are projected into the generalized modal coordinates and written as modal data (e.g. modal force). The quantities written as modal data are LOD and Ef3. Additionally, a record is written that has the scoped nodes, NSCOP. These scoped nodes are written in internal (not user) node numbering.

Limitations

Modal Solution Limitations:

  • Damped (MODOPT,DAMP) and Unsymmetric (MODOPT,UNSYM) modal eigensolvers are not permitted. The QR algorithm damped eigensolver (MODOPT,QRDAMP is supported.

  • Inertial loads are not supported (e.g. OMEGA, CMOMEGA, ACEL, CMACEL).

  • Only loads from the original modal solve are supported. Loads created during a modal restart are not supported.

  • ELCALC = Yes on the MXPAND command is not supported.

  • Modal results are not written to the results file and cannot be postprocessed

Mode-superposition (MSUP) Solution Limitations:

  • MSUP transient analyses are not supported.

  • Spectrum/PSD analyses are not supported.

  • The residual response method (RESVEC,,,,,ON) is not supported.

  • All modes are required, that is, no use of MAXMODE on the HROPT command.

  • Only loads from the .mode file are allowed. No direct force (F) or acceleration (ACEL) are allowed.

  • MSUP expansion (EXPASS) is not supported.

  • Postprocessing is limited to printout of the modal coordinates (PRMC, PLMC).