The results in my Spectrum dynamic analysis (water hammer type) look strange because all my maximum responses occur in missing masss mode. I have exytended the frequency cut off way beyond the max. table frequency of my spectrums; the included mass output shows a 98% force contribution of the Spectrum and yet the missing mass modes persists in my output. can anyone explain why this happens?


second question: on a different note, does it matter at all to define the (+/-) direction of the acting force in the spectrum analysis?