Designing Short Term Wave Traces to Assess Wave Power Devices

摘要

In recent years modern numerical methods have been employed in thedesign of Wave Energy Converters (WECs), however the high computationalcosts associated with their use makes it prohibitive to undertakesimulations involving statistically relevant numbers of wave cycles. Experimentaltests in wave tanks could also be performed more efficientlyand economically if short time traces, consisting of only a few wave cycles,could be used to evaluate the hydrodynamic characteristics of a particulardevice or design modification. Ideally, accurate estimations ofdevice performance could be made utilizing results obtained from investigationswith a relatively small number of wave cycles. However thedifficulty here is that many WECs, such as the Oscillating Wave SurgeConverter (OWSC), exhibit significant non-linearity in their response.Thus it is challenging to make accurate predictions of annual energy yieldfor a given spectral sea state using short duration realisations of that sea.This is because the non-linear device response to particular phase couplingsof sinusoidal components within those time traces might influencethe estimate of mean power capture obtained. As a result it is generallyaccepted that the most appropriate estimate of mean power capture for asea state be obtained over many hundreds (or thousands) of wave cycles.This ensures that the potential influence of phase locking is negligiblein comparison to the predictions made. In this paper, potential methodsof providing reasonable estimates of relative variations in device performanceusing short duration sea states are introduced. The aim of thework is to establish the shortness of sea state required to provide statisticallysignificant estimations of the mean power capture of a particulartype of Wave Energy Converter. The results show that carefully selectedwave traces can be used to reliably assess variations in power output dueto changes in the hydrodynamic design or wave climate.