Thanks for your help !
It works now, but it seems that the function "f=f0*r^(k-1)" for k=1..NF plays a big role in the wave generated by the wind.
With the different test I made you have to select good values for keywords "nombre de frequences, frequence minimale, raison frequentielle" to have good results.
In fact the frequency generated by windwaves should be in the intervall of frequencies you choose in the spectrum at the limit.
I don't know if I am clear but these parameters are very important