WECCCOMP – Forums WECCCOMP forum Restoring force is shifted up? Reply To: Restoring force is shifted up?

Tom Nathan

Thanks for clarifying some of my questions:

1. Yes, the restoring force in Figure 3 hovers at 1.8 N. This is because this force is only
calculated from the hydrostatic stiffness and the difference between the mass and buoyancy of
the float (The center of gravity sits farther forward than the center of buoyancy).
Therefore, this is the rotational restoring force on the float itself and should not be
compared against the restoring torque about Point A. In this plot, all lines correspond to
torque so N.m, the labeling is not modified in the function plotForces that is used in the
userdefined function to plot results.
2. Thank you, this value was calculated about Point A. This value is close to the heave
hydrostatic stiffness of the float multiplied by the lever arm between the float and Point A.
Again, there is a slight difference in the displaced volume, so the float/arm pair does
rotate slightly in the WEC-Sim model.
3. Thank you, the 1 kg.m2 was converted about the center of gravity of the arm EC and the float.

The organizers agree that the WECCCOMP model should be as accurate as possible in modeling the
real system. We have completed several validation cases using the WEC-Sim model and experimental
tests to tune the WEC-Sim model. We will provide access to this report once it is ready.

Please let me know if this doesn’t answer your questions or want clarification on any other parts of the model.

Nathan Tom
National Renewable Energy Laboratory