Directional Wave Spreading

I have a question about directional wave spreading in HydroDyn. As far as I understand, HydroDyn can include directional wave spreading function using cos-2s model. A small s which is the directional wave spreading parameter is a function of frequency. However, I found that the input of s in HydroDyn is defined as a constant value. So, I would like to ask about how to define s? Could you please explain me?

Danupon Subanapong

Dear Danupon,

In the HydroDyn hydrodynamics module of FAST / OpenFAST, the wave directional spreading is not frequency dependent. We wrote a paper for OMAE 2014 when we first introduced wave directional spreading in HydroDyn; please review this paper for more information on the approach implemented:

Best regards,

Thank you so much!!!