Dear Developers,

I have doubts in simulation results of WEC-sim application of non-linear hydrodynamics for a Heaving Ellipsoid.

I ran simulation using the settting and files provided by WEC-sim application master for a heaving ellipsoid for 4 different cases, which are given below:

1. Linear hydrodynamics with PTO
2. Linear hydrodynamics without PTO
3. Non linear hydrodynamics with PTO
4. Non linear hyrdrodynamics without PTO

Here, PTO is a simple damper. Without PTO means making the damping coefficient zero in wecsim input file. I was expecting that wecsim will calculate the response of the ellipsoid using non-linear hydrodynamics when the body(1).nlHydro =2 no matter there is a PTO or no PTO. But this is not the case. The system behaves linearly even the body(1).nlHydro =2 with PTO turned off (as it can be seen in graphs below)

All other settings kept constant. Regular wave with h=12.2m and T=16.61 is simulated with simu.wave('regular').

Is there something I am missing about nonLinearHydro formulation using Froude-kryolov force? Please guide me what is happening.

I have attached the output graphs of Heave, restoring force and force exciatation for you reference in the same order below:

Workstation Information (this section MUST BE completed):

• OS: , Windows 10
• MATLAB/Simulink Release, 2021b
• WEC-Sim Release v4.4

I am not sure where is the issue. But it does not make sense to me for now. I am facing another issue with nonLinearHydro that I asked in #878 . I guess this issue is related to theory implementation.