Numerical and experimental studies on the PTO system of a novel floating wave energy converter

Experiments and several numerical studies were done on a power-take off system of a novel floating wave energy convertor. The wave energy convertor utilizes the changes in surface elevation of the waves to cause a column of water to rise and fall periodically in the caisson which creates a bi-directional flow. A cross flow turbine within the device uses this bi-directional flow to rotate in one direction. A 6 DOF ocean simulator was used to conduct experiments on the PTO system at a model to prototype scale of 1:3, for no-load conditions and loaded conditions. In the experiment, the parameters like pitching angles of the device, moment of inertia on the shaft, wave periods and rotational speeds of the turbine were varied. It was found that for all pitching angles, the device had optimum response at a wave period of 3 s. A moment of inertia of 0.053 kg m2 was found to be appropriate for all test cases. Peak hydraulic efficiencies between 35% and 45% were obtained for the range of 40–50 RPM for most test cases. Particle image velocimetry (PIV) tests then done to document and investigate the flow around the turbine and the inlet and exit nozzles. A commercial CFD software was used to carry out the numerical calculations and to observe the internal flow. Finally, a floating body simulation was conducted on to calculate the motion of the device at sea and thus calculate the overall performance of the device.