Quantification of the influence of directional sea state parameters over the performances of wave energy converters

Accurate predictions of the annual energy yield from wave energy converters are essential to the development of the wave industry. The current method based on power matrices uses only a small part of the data available from sea state estimations and it is consequently prone to inaccuracies. The research presented in this work investigates the issue of energy yield prediction and questions the power matrix method. This is accomplished by quantifying the influence of several directional sea states parameters on the performances of wave energy converters. The approach taken was to test several wave energy converters in the Edinburgh Curved tank with a large set of sea states. The selected wave energy converters are a fix OWC, a set of two OWCs acting as a weak directional device and the desalination duck model. Uni-modal and bi-modal sea states were used. For the uni-modal sea states, parameters related to the wave system shape were considered. For the bi-modal sea states, the relative position of the wave system peaks was investigated and the uni-modality index was introduced to quantify the degree to which sea states could be considered bi-modal. For all sea states, the significant wave height was kept constant. The experimental work required good spectral estimates. The MLM and MMLM were adapted to deterministic waves to improve their stability and accuracy. A routine to isolate wave systems was also developed in order to estimate parameters with respect to each wave systems. For uni-modal spectra, parametric models of the observed performances of the devices could be devised. The frequency spreading and its interaction with the energy period proved to be as important as the energy period itself, which suggests that the frequency spreading should be used for energy production prediction. For bi-modal spectra, evidence of the duck sensitivity to directionality was found while the OWCs were not affected.