Frequency Spectrum

The SOL108 (direct frequency response) and SOL111 (modal frequency response) are supported for MSC Nastran®. Gravity loading and temperature loading are not allowed in finite element modeling.

Solution excitation frequencies defined using FREQ, FREQ1 and FREQ2 are allowed in the finite element input deck. The solution excitation frequencies defined using FREQ3, FREQ4 and FREQ5 should be used with care because the eigenvalues usually change a lot during optimization.

In frequency response, structural damping PARAM,G and GE on the MATi are allowed for all design elements. Note, that the structural damping should be the same for all design elements and that the structural damping for the design elements should also be defined using OPT_PARAM yielding

OPT_PARAM
 ...
 DAMP_STRUCTURAL_STIFF = G or GE 
 ...
END_

where G or GE is the structural damping of the design elements.

Important: All kind of discrete damping elements and other kind of damping are allowed outside the design domain as long as they are not of function of the eigenfrequencies or eigenmodes. Meaning that modal damping e.g. defined using SDAMPING is prohibited.