The CMR of RS method can be set-up in an NX Nastran solution by adding a few additional solution control cards to a standard SOL 103 solution. In the case control, an RSMETHOD card is needed in addition to the standard METHOD card. The purpose of each is:
•RSMETHOD : identifies modal solution controls cards (EIGR or EIGRL) to be used for the first modal solution. Typically the control cards define a frequency range to compute the modes. Modes outside that range are neglected.
•METHOD : identifies modal solution controls cards (EIGR or EIGRL) to be used for the second modal solution. This is the modal solution of the reduced system. It is important to solve for all the modes of the reduced system. This can be done by specifying a wide frequency range on the EIGR or EIGRL cards.
The bulk data section of the input file needs definition of the t-set and q-set DOF. These are defined by these cards:
•ASET : define the connection DOFs (these are in the t-set)
•SPOINT : creates additional DOFs
•QSET : identifies SPOINT DOFs as modal reduction DOFs and places them in the q-set
For the first modal solution (RSMETHOD), it is recommended that the solved frequency range be at least twice the frequency range of interest in the MBD solution. For example, if the MBD solution is to be accurate to 1500 Hz, the first modal solution of the components should capture modes to at least 3000 Hz. The user needs to be sure that the number of q-set DOF created by QSET and SPOINT cards is larger than the actual number of modes computed from RSMETHOD.
As mentioned already, all the modes of the reduced system need to be computed for the second modal solution (METHOD). The user can verify that all the modes have been computed by confirming that the number of modes is equal to the reduced DOF set size (the sum of the number of normal modes and number of connection DOFs).