[sinatahmooresi]

Hello dear foamers,



I am trying to use fast Fourier transform to build the energy spectrum in certain point. I have the free surface elevation on the point of verification, which is the result of integrating on the volume fraction (alpha.water). I was wondering if anybody with experience on the this process can provide me with some hints. I am curious about:



1-What is the exact relationship between the FFT of free surface elevation (eta) and the spectrum of energy (S): S = FFT(eta^2)?

I saw on "Wave Mechanics" by G.Dean that S = FFT(0.5*eta2)


2- What is the normalization process in this regard. when I plot only the FFt against the frequencies, shows hundreds of time higher values of the initial spectrum at the inlet of the channel.



I can provide more information on the detail. I hope some foammer are happy to engage and give me some hints on this.



Thank you, Sina