How to chose from the modal base the optimal base of mods to be exapanded depending on their effecitves modals masses for use in transient analysis with modal superposition on Ansys?
It depends upon the frequency range of interest and the excitations' spectra. A very simple way is to keep modes up to the double of the maximum frequency available in your simulation. Also keep attention to the integration step, because, if variable, can change the frequency band on which you are focused.
well sir, i forgot to mention that my modal base contains 60 modes in witch i try to extract only the 2, 13, 28 and 31 modes to be used in modal superposition because they have the biggest mass ratio, therefor even fixing the frequency range would not help me in extracting only this 4 modes it will extract all the modes from the second to the 31 mode.
Based on your considerations, I suggest you to shrink the modal base to the wanted 4 modes before running the transient simulation, but avoiding any recalculation of the modal base. Otherwise, I suggest you add a selection criterion via a script, so that at each recalculation you exclude those not fulfilling your mass ratio ranking.