My best guess is that
FFT is a fast Fourier transform of a time sequence,
autospectrum is a spectral estimator (requiring averaging) using emsembles of FFTs. FFTs are useful for real time monitoring the trend, but an autospectrum is a stastistcal vaule for the supposed-to-be time variant signal...
I am not sure if I undersood your question correctly, but a simple way can be that you measure a point mobility (FRF) of the subject of interest, and then take the real part of its inverse. The inverse is the impedance and its real part is the damping(i.e., power absorbing part). Finally, you...
It is not possible to obtain a DC displacement (at 0Hz) from an accerlation measurement, but AC displacement. (suppose that an apple drops at the accerlation of gravity, where is the position now?) In the frequency domain, it can be rather easily done by dividing the accerlation by -w^2, where w...
