Discrepancies with WEC-Sim wave spectra

[akeeste]

As first discussed in #395 with @MShabara, there appear to be some discrepancies between how WEC-Sim and MHKiT each create wave spectra. For example, if a wave spectrum is define in WEC-Sim and MHKiT recreates that spectrum based on WEC-Sim's wave elevation timeseries, the results are not the same.

[MShabara]

When running the OSWEC example on WEC-Sim, the following spectrum in generated

However, when importing the waveform into MHKiT, the following spectrum is obtained

[akeeste]

@MShabara I found a good comparison between WEC-Sim's spectra and MHKiT's spectra created from the WEC-Sim wave elevation time series. In this case I:

• Use the RM3 example in 3 wave conditions (6s x 2.5m PM spectrum, 8s x 1.5m PM spectrum, 12s x 1m JS spectrum).
• simu.dt=0.01s; simu.rampTime=10waves.period; simu.endTime=100waves.period;
• Scale the WEC-Sim spectra from m^2*s/rad to m^2/Hz and its frequency dimension from rad/s to Hz as MHKiT uses
• sample_rate = 1/100 and nnft = 5000

The MHKiT results are a little noisy, this is like due to the relatively short timeseries from WEC-Sim. The magnitude and noise also appears very dependent on nnft.

mhkit_spectra.zip

[akeeste]

This issue is resolved. @MShabara please reopen if other issues with the wave spectra appear