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

Tom Nathan

Mustafa Abdelrahman,
Thank you for your comment. I have a few questions to try in order to better understand your question.

1) Can your clarify what “2 units” refers to as vertical or rotational displacement. There is a
slight offset when running the WECCCOMP WEC-SIM model with no waves (~1/2 a deg). This is
because the hydrostatic restoring forces are taken from WAMIT. There will be inevitably some
uncertainty between the numerical and experimental models that competitors should try to
account for in their control algorithm.
2) The restoring force constant 92.33, is this rotation about hinge A?
3) Are the values of Moment of Inertia of 1 kg.m2 and the state space values being obtained from
Ringwood 2017?

The values presented in Ringwood 2017 assume the equation of motion was derived at hinge A as a one-degree of freedom equation of motion. The WEC-Sim model is a multi-degree of freedom system as each body and link is modeled as a separate body and the hydrodynamic and mass properties are defined at each center of gravity.

Please let me know if this has helped to resolve your questions. If not, please add further comments and questions so we can find the clarify the issues you are having.

Nathan Tom
National Renewable Energy Laboratory