Applying an external force to a floating platform in OpenFAST

[juleshd]

Hello,
I am starting to work with OpenFAST to simulate the hydrodynamic response of a floating semi-submersible platform with semi-taut moorings (SeaState + HydroDyn + MoorDyn) in various sea states.
In my use case, I would like to apply a prescribed external force acting on the platform center of gravity (for example, a vertical force acting upward), in addition to the usual hydrodynamic and mooring loads. The force can be constant or time-dependent, but it is not related to rotor aerodynamics or turbine control.
For now, I do not see a straightforward way to apply a user-defined external force or moment directly to the floating platform. Could you please clarify if it is possible or not. And if not, what approach would you recommend for such an use case ?
Thank you in advance,
Jules

[jjonkman]

Dear @juleshd,

The Structural Control (StC) submodel of ServoDyn allows the user to specify precomputed constant or time-dependent loads (3 forces, 3 moments) at any point the blades, nacelle, tower, or substructure. See the StC documentation OpenFAST readthedocs for more information: https://openfast.readthedocs.io/en/main/source/user/servodyn-stc/StC_index.html. For a single point load in the floating platform, you should set NumSStC = 1 in ServoDyn and use StC_DOF_MODE = 4 in StC.

Best regards,

[juleshd]

Dear @jjonkman,

Thanks a lot for your quick answer ! I am going to look forward for this submodel and se how can I adapt it for my need though.

Have a great day,

Jules