Harbour resonance

Can i use [b]FFT filtering of time series tool[/b] for long wave analysis?

If you have made a MIKE 21 BW-simulation you can use the FFT tool as part of an initial analysis of harbour resonance.

What should be the minimum frequency? 0.002 is ok ? Are we considering the energy of long wave here? if so what should be the considerable wave energy for long waves inside the harbor?