Specify the number of modes to use from the modal analysis. It is suggested to have modes that span 1.5 times the maximum frequency defined in input excitation spectrum.

Specify either Single Point or Multiple Points. If two or more input excitation spectrums are defined on the same fixed degree of freedoms, use Single Point, otherwise use Multiple Points.

Specify a method to be used for response spectrum calculation. Choices are SRSS, CQC, and ROSE. In general, the SRSS method is more conservative than the other methods.

The SRSS method assumes that all maximum modal values are uncorrelated. For a complex structural component in three dimensions, it is not uncommon to have modes that are coupled. In this case, the assumption overestimates the responses overall. On the other hand, the CQC and the ROSE methods accommodate the deficiency of the SRSS by providing a means of evaluating modal correlation for the response spectrum analysis. Mathematically, the approach is built upon random vibration theory assuming a finite duration of white noise excitation. The ability to account for the modes coupling makes the response estimate from the CQC and ROSE methods more realistic and closer to the exact time history solution.