Dear jason,
I am using the white-noise wave spectrum to generate irregular waves to explore the motion of the OC3 system in waves, to verify my calculations, I used openfast simulation results as a reference. When using the openfast, I set the significant wave height to 2m and got some results, the wave time curve at point (0,0) is as follows:
The significant wave height is calculated as follows:

So, when Hs = 2m, the area under the spectrum should be 0.25, my frequency range is 0-3rad/s, so the value of S(w) should always be 0.25/3 m^2*s/rad. The wave spectrum is as folows:
Later, I use this white noise spectrum to generate irregular waves, however, compared to the OpenFast’s results, my wave amplitude is small

May I ask if my understanding of this issue is wrong? I would appreciate it if you could give me some advice.
Best regards
Lin.Yang