A WEC-Sim model was developed for the 1:7 scale Aquaharmonics WEC. The original WEC geometry was defeatured to facilitate the BEM simulations to calculate the hydrodynamic coefficients. The team faced some issues during this stage of the project because the WEC device has water inside its hull. This led to multiple simulations with different versions of the defeatured geometry. The hydrodynamic coefficients were calculated using both WAMIT and Capytaine with good convergence and similarities between the results. The Capytaine simulations were done in order to provide an open source option for BEM simulations.
The PTO parametric model and the ESS model were coupled to the WEC-Sim simulation. The inputs of the parametric model are the WEC speed and position from WEC-Sim, which are used to calculate the PTO response. The ESS was also coupled and is an open loop model which receives as inputs the mechanical torque and speed in the generator from the PTO model.
An optimization function was written in MATLAB using the average grid power during steady state operation as the objective function. The values for the spring coefficient for the optimization routine are constraint to the range [-80, -20]. The range for the damping coefficient is [40, 120].. During the optimization process for each wave condition, the only variables that change were the damping and the spring coefficient, all the other parameters remain constant.
The time domain results for the PTO and the ESS shows that the power is exported to the grid when the WEC velocity is positive, which was expected from the beginning of the project. The grid voltage decreases when the power is being exported to the grid, whereas the grid current increases during the same period of time.