nonlinear FK force implementation about wec-sim HOT 5 CLOSED

Hi Brain

If the nonlinear model is used (simu.nlHydro = 2), it calculates the FK force and the bounce force based on the instantaneous position of the body and wave elevation and integrates the corresponding static and dynamic components of the pressure field from each submerged panel on the body surface.

Thanks,

Yi-Hsiang Yu, Ph.D.
Senior Research Engineer | Water Power Program
National Renewable Energy Laboratory (NREL)
[email protected]:[email protected] | Phone: (303) 3847143

from wec-sim.

Thanks Yi-Hsiang -

That makes sense. But if the body is moving, wouldn't there be a dynamic pressure in addition to the dynamic pressure from the incoming wave field (assuming a stationary body)?

Or phrased another way - If the body is stationary, the boundary condition at each panel is that the normal velocity is zero (no-flux). If the body is moving, then the boundary condition is that the fluid normal velocity equals the panel normal velocity.

So, my question is, does the FK calculation consider the velocity of each panel, or just the position?

Let me know if I'm unclear, and I'd be happy to rephrase!

Thanks!

from wec-sim.

Hi Brain

For FK force, it is directly calculated from the pressure of the flow field based on wave theory based on the instantaneous body position and free surface. However, the diffraction part is still calculated based on linear theory, which assumes the body does not move. This means the dynamic pressure due to the change of the flow field is directly represented in the nonlinear FK force. However, the dynamic pressure due to the instantaneous body position and the body motion is not included. This is just the assumption given in this type of method, which is just a weakly nonlinear approach.

Thanks,

--Yi-Hsiang

from wec-sim.

Thanks Yi-Hsiang. That was a helpful explanation of the modeling approach.

So, if nonlinear hydro is used (simu.nlHydro = 2), then WECsim calculates the FK force internally and ignores the FK load component specified by the BEM? However, WECsim will use the diffraction force specified by the BEM?

from wec-sim.

That is correct.

Thanks,

from wec-sim.