Reference points for wave excitaions and platform movements

Dear Jason,

I’m simulating a triple-spar in FAST and I recognized there is a phase difference between my wave elevation and surge and pitch motions. I could say that a part of this is probably because of the inertia but I wonder if there are other reasons for that. So my question is, as I’m importing the wave elevations in FAST, which point of the floater is experiencing this wave elevation at t=0 and if the surge motion that I’m getting from the output channel is from the same point at t=0.

Best regards

Dear Masih,

When using externally generated wave-elevation time series in FAST/HydroDyn (WaveMod = 5), the wave elevation is specified at (xi,yi) = (0,0). You can output the wave elevation at up to 9 locations (including (0,0)), as determined by inputs NWaveElev, WaveElevxi, and WaveElevyi in the HydroDyn input file. The platform motion (including surge motion) is output from FAST relative to the platform reference point (xi,yi,zi) = (0,0,0).

Best regards,