Could you elaborate on what do you mean with "For the vibrational force, i used tabulated pressure vs. time data at one frequency.". Do you mean you used a so called time history, with a given sampling frequency? because to me it is unclear what does "at one frequency" mean. The time history, if sufficiently sampled, will contain all frequencies up to the Nyquist frequency. With time history I mean a long list of couples of data points: for example t=0, p=p0; t=0.001, p=p1, and so on...
I am not familiar wiht FSI. But for simply mechanical analysis the input of a PSD as vibration excitation is certainly possible. Differently from a time history, a PSD is a statistical approach, though.
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