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

Hull University

Hi Nathan

Thanks a lot for your helpful reply.

1. After running the wecSim to simulate the WECCC model the function userDefinedFunctions.m plots the response (states, forces and power). The plot for forces, figure 3, shows all forces are almost symmetric around the zero line except the restoring which is shifted up by 1.8 N (or Nm). So the 2 units refers to 2 N (or Nm). (Here I have another question please, should we consider the forces generated by the wecSim here as moments so the unit is Nm because the motion is restricted in the pitch direction only, or they literally forces so the unit is N?. The figure y-label indicate force in (N) or (Nm) without specifying which is the valid unit for this case)

I agree with you that this mismatches between the simplified one-degree-of-freedom case (Ringwood 2017) and the multi-body case (wecSim) is expected and it should be handled by the controller.

2. Yes, I take the restoring constant of 92.33 Nm/rad from Ringwood 2017 (EWTEC conference paper). It is around point A as I understand. I am trying to double check this

3. Yes, the Moment of Inertia of 1 kg.m2 and the state-space approximation of radiation force dynamic are taken from Ringwood 2017.

My point of view is that the wecSim for the WECCC model should be close to the simple ODF case (Ringwood 2017) as the motion is considered in pitch degree only. Some mismatch should exist indeed.

Thanks a lot