On the S-shaped floaters for a Wavestar-like wave energy converter with an I-shaped mechanical power take-off

Abstract

A numerical wave energy converter (WEC) similar to the Wavestar WEC with eight units, each comprising an I-shaped power take-off (PTO), was studied with the cylindrical-hemispherical (C-HS) and S-shaped floaters. Efforts were made to examine the effects of the floater-geometry change on the PTO power performance and to study the significance of replacing a C-HS with an S-shaped floater of the same size and resonance characteristics using a hybrid algorithm based on ANSYS AQWA and MATLAB Simscape. The pure floater-shape-change effects on their heave responses were evaluated through the time-domain simulations in ANSYS AQWA and imported into a MATLAB-Simscape-based algorithm of the PTO to investigate the performance of the PTO and the overall WEC model under those effects. The buoys on the model scale were tested in a lab-scale facility, followed by a CFD analysis to study how the surrounding fluid interacts with the C-HS and the S-shaped floaters. The spectral modeling showed that the S-shaped floater could achieve a 5.5% greater RMS heave response than the C-HS in irregular waves. Replacing a C-HS with an S-shaped floater, the maximum increase in the PTO force was recorded to be 14%. A PTO integrated into an S-shaped floater attained 26% greater input power than one integrated into a C-HS floater. At an energy conversion efficiency of 55%, the PTO output power with an S-shaped floater tends to be 25–26% greater than with a C-HS floater. Replacing a C-HS with an S-shaped floater in the Wavestar-like WEC could be an optimal choice.