Characterization of loads on a hemispherical point absorber wave energy converter

Large-scale experiments were carried out using a hemispherical shaped point absorber with a diameter of one meter, equivalent to scale 1:5 of the Wavestar North Sea prototype. The purpose of the experiments is to determine the hydrodynamic and dynamic loads on the Wavestar wave energy converters. With a better understanding of the loads the structural expenses can be reduced, and thereby reduce the cost of energy. The set-up consists of the hemisphere connected through a rigid arm that pivots on a non-moving main structure, which in this case is the gantry of the wave basin. The pitch motion of the hemisphere arm assembly is controlled using a linear hydraulic actuator. Wave and motion induced loads on the floating point absorber in regular waves as well as extreme conditions are presented. Drag, inertia and slamming pressure are determined directly from the experiments. Radiation, diffraction and excitation moments are determined by inviscid boundary element numerical models.