For calculation of Jonswap/Pierson-Moskowitz spectrum

[icnosvbovwb]

Dear @jjonkman

This figure shows that I set WaveMod=2, WaveHs=5, WaveTp=10, WavePkShp=1.835 in the hydrodyn.dat. Other settings are default. I used Jason_ PSD. m calculates the Wave1Elv PSD, but it is not as smooth as the curve shown in the next picture. I don't know why?
But waves need wind, that is, U10 mentioned below. How does it know the wind speed（U10) in openfast? I wonder if Hs and Tm are set, then openfast calculates U10 by itself and gets the corresponding wave spectrum.

These two pictures show that I used the PlotBothSpectra. m script (https://github.com/amarnathajay/SeaSpectra) to calculate the spectrum of Jonswap and Pierson-Moskowitz spectrum.

Q1: I don't quite understand the relationship between Wave1Elv PSD calculated by the Jason_ PSD.m script and the spectrum calculated by the PlotBothSpectra. m script.

[jjonkman]

Dear @icnosvbovwb,

I'm not familiar with the PlotBothSpectra.m script, which doesn't appear to be developed by NREL, so, I won't comment on that.

The spectrum plotted via Jason_PSD.m is not smooth either because (1) you have generated the sea state with WaveNDAmp enabled in HydroDyn, which randomizes both the amplitude and phase) or (2) you have resampled the wave data in some way (the time series uses a time step and/or simulation length that is different from WaveDT and WaveTMax).

HydroDyn makes use of a Pierson-Woskowitz and/or JONSWAP spectrum that depends on HydroDyn inputs WaveHs and WaveTp, but not on wind speed. (Wind speed in OpenFAST is defined within the InflowWind module, but this data is not used by HydroDyn).

Best regards,

[icnosvbovwb]

Dear @jjonkman

I modified WaveNDAmp=FALSE and set WavePkShp =1.
Data=xlsread('Wave1Elv.xlsx');
df=1/1000;
N=1000/0.0125;
[f1,Sf1]=Jason_PSD(Data,df,N);
plot(f1,Sf1)
The spectrum plotted via Jason_PSD.m is not smooth，I don't know what's wrong.