Reply To: Selecting # of Modes for good Mass Participation

[jbettinger]

So for us, the goal of the model and others like it is to subject the unit to shock and vibration. The vibration is almost always random vibe (every so often harmonic/sine vibe but not as frequent), and the shock usually splits the middle between being a time domain (transient structural "sawtooth" shock) or a frequency domain (response spectrum). I guess it makes sense not to need too many modes for rando vibe as long as I have enough to cover the frequency range and a bit above. But still, since the modal analysis feeds into the shock and vibe I figured it would be important to make sure as much of the system is described as reasonably achievable. The projects I work with vary pretty wildly in shape and size. My most previous project needed ~150 modes before I hit a 0.9 ratio, while my current one (which is larger and goofier in shape/mounting) only needs ~35 modes.