Question about WaveElev Output in FAST

Wind & Water Computer-Aided Engineering Software Tools
1

Hello!

I’m looking at the OC3 results (LC 5.1 with regular 6m waves) and I have a question about the WaveElev output. I can’t seem to find this output in the manual anywhere so I’m asking on this forum. In the results it says, in the variable description, that WaveElev is "Wave Elevation at Platform Centerline ". Does that mean it’s measured at the moving tower? Looking at the signal (and an FFT) I see only the wave frequency in its content. However, if it was moving with the tower I’d expect to see, at the very least, the surge and pitch frequencies in its content, so I’m assuming that this output is actually measured at a fixed point (probably the initial point at the SWL?). Can someone verify and/or clear this up for me?

Thanks!
Sean Quallen

2

Dear Sean,

I’m assuming you are using FAST v7, which never had formal hydrodynamic documentation. WaveElev in FAST v7 is the wave elevation of the incident waves at the intersection of the SWL and the undisplaced tower centerline–i.e., the location where the wave elevation is output does not move with the platform.

The hydrodynamic-related outputs in FAST v8 are well documented in the Draft HydroDyn User’s Guide and Theory Manual: nwtc.nrel.gov/system/files/Hydr … nual_0.pdf. But again in FAST v8, the locations where the wave elevation are output do not move with the platform.

Best regards,

3

Jason,

Thanks for verifying that!

Sean Quallen