The paper deals with the presentation of a numerical model to predict performance characteristics of tight moored vertical axisymmetric wave energy converters that are allowed to move in the heave, pitch and sway modes of motion. The first-order hydrodynamic characteristics of the floater, i.e. exciting wave forces and hydrodynamic parameters, are evaluated using a linearized diffraction – radiation semi-analytical method of analysis that is suited for the type of bodies under consideration.
The floating WEC is connected to an underwater piston that feeds a hydraulic system with pressurized oil.
The performance of the system under the combined excitation of both first- and second-order wave loads is here analyzed. To this end, the diffraction forces originated from the second-order wave potentials are computed using a semi-analytical formulation which, by extension of the associated first-order solution, is based on matched axisymmetric eigenfunction expansions.