Support for Multi-Directional Wave Time Series Input in HydroDyn Module of OPENFAST

[Jiangyunmu]

Hi! all
I am trying to load two wave elevation files from distinct directions simultaneously using the HydroDyn module in OPENFAST. Currently, I am facing challenges in configuring multi-directional wave time series inputs effectively.

Here's what I've tried so far:

Using WaveMod=5: Attempted to input externally generated wave-elevation time series. However, it seems to support only a single wave direction at a time.

Key Requirements:
The ability to input two distinct wave time series files, each corresponding to a different direction (e.g., 45° and 135°).
Ensuring both wave directions' interactions are accurately simulated.
Is there a recommended approach or a workaround within OPENFAST for configuring multiple directional wave inputs? Any guidance or potential updates for multi-directional wave handling in HydroDyn would be highly appreciated.
Thank you

[Jiangyunmu]

@jjonkman TKS!

[jjonkman]

Dear @Jiangyunmu.

I agree that the WaveMod = 5 option of HydroDyn is meant for long-crested waves from a single direction.

You could always implement multi-directional waves through the WaveMod = 6 option if you can can calculate the full set of wave kinematics data yourself.

The WaveMod = 2, 3, 4 options of HydroDyn support directional spreading of irregular waves, but not waves from two distinct directions.

Within the new SeasState module of the upcoming v4.0 release of OpenFAST (whereby SeaState was separated from HydroDyn into its own module), a new WaveMod = 7 option has been added whereby you can define the incident waves in terms of discrete frequency components, where each frequency component can be tied to a specific direction. This would allow you to specify a sea state with waves coming from two distinct directions. The only limitation of this approach is that each frequency component must be unique, i.e., that you can't have two waves of different directions with the same exact frequency. Regardless, this feature sounds like what you want; is that correct?

Best regards,