Hi,

I have a question concerning the wave spreading implemented in HydroDyn: As far as I understand the theory behind the cos-2s-spreading function, the wave direction spreading coefficient (s) controls the “concentration” of the directional distribution of the wave energy. A small “s” leads to a relatively wide distribution of wave energy from nearly all directions. A large spreding coefficient centers the energy more to the mean wave direction.

I read about several approches (Mitsuyasu (1975), Hasselmann(1980), Donelan(1985)) where s is frequency dependent and, consequently, the directional spreading function varies over the frequencies as well. E.g.:

s(omega)=s_max*(f/f_p)^5 , if f<f_p and s(omega)=s_max*(f/f_p)^(-2.5), if f>f_p

As far as I understood the directional spreading function in HydroDyn remains constant with the same spreading coeffiencent across all frequencies. Is that right? I tried to find the implementation in the HydroDyn routine, but I’m not sure if I understood it correctly.

Therefore I have to choose a spreading coefficient, which is valid for the directional spreading function across all frequencies of the wave spectrum?

Many thanks in advance and kind regards,

Manuela