Wave Direction In HydroDyn

Hi Jason:
I changed the wave direction in HydroDyn, WaveDir, from 0 to 30 degrees and attempted to run a simulation and got this error:
[b]"FAST_InitializeAll:HydroDyn_Init:WAMIT_Init:All Wave directions must be within the wave heading
angle range available in “.\HydroData/IEA-15-240-RWT-UMaineSemi.3” (inclusive).

FAST encountered an error during module initialization.
Simulation error level: FATAL ERROR

Aborting OpenFAST."[/b]

Does this mean that I have to change the wave direction in the WAMIT output IEA-15-240-RWT-UMaineSemi.3 from 0 degrees to 30 degrees? I see in the second column of said output, some zero values, which I have assumed to be the wave direction.

Thank you.

Regards,
AOAW

Dear Andre,

The WAMIT data for the UMaine semisubmersible was only generated for zero-degrees wave heading. The HydroDyn module of OpenFAST will not allow you to specify the wave heading to be outside the range of the WAMIT data. So, you’ll have to run WAMIT (or an equivalent frequency-domain wave-body interaction potential-flow solver) for the range of wave headings that you want to simulate in OpenFAST/HydroDyn.

Best regards,

Noted Jason. Thank you.

Regards,
AOAW

Hi Jason:
I would like to confirm if the wind direction from the east in InflowWind is 180 degrees and from the west 0 degrees; with south being 270 deg and North 90 deg. The +ve wind direction is clockwise viewing from above.

I have attached a sketch for clarity.

Thank you.

Regards,
AOAW

Dear Andre,

The InflowWind module does not use East-West, North-South convention, but I agree that the wind direction specified in InflowWind is positive clockwise when viewed from above (following meteorological convention). This is in contrast to most other OpenFAST modules that define the direction (e.g., yaw in ElastoDyn and the wave propagation direction in HydroDyn) to be about positive Z, which is counterclockwise when viewed from above.

Best regards,

Noted.
Thanks Jason.

Regards,
AOAW

Hi @Jason.Jonkman:
Two queries about HydroDyn Wave inputs;

  1. Is the wave directional spreading function WaveDirMod dependent on the wave direction?
  2. Can you please clarify the range of values of WaveDirMod? It says from 1: Cos2S. Is S the same as WaveDirSpread. ?
  3. Is there a range of values of WaveDirSpread?

I am attempting to change the wave directionality in my model and trying to understand how it is done.

Thank you.

Regards,
AOAW

Dear @Andre.White,

Here are my answers to your questions:

  1. When WaveDirMod = 1, a cosine spreading function is used centered about the specified (mean) wave direction, WaveDir.
  2. Yes, the cosine spreading function involves cosine()^(2*S), where the wave spreading parameter, S = WaveDirSpread.
  3. The wave spreading parameter is likely site dependent, but you can find typical values in the literature.

For more information, see our related OMAE 2014 paper: https://www.nrel.gov/docs/fy14osti/61161.pdf.

Best regards,

Many thanks @Jason.Jonkman

AOAW