Wavelet analysis applied to the wave energy resource at an irish west coast site

Abstract

The wave spectral density function, more commonly known as the wave spectrum, has seen widespread use as a tool to measure the wave energy resource at possible sites for the deployment of Wave Energy Converters (WECs). The wave spectrum provides a useful means to calculate summary statistics such as significant wave height and average period from measured time series of surface elevation, which allows the time-averaged incident power to be estimated. This approach, however, has a limited capacity to monitor the temporal variability of both energy and peak frequency, which may impact on the power captured by WECs, and is thus more suited to stationary signals rather than the case of ocean waves. In this paper the wavelet transform is utilized to assess the temporal variability of wave energy at a typical location for a potential WEC deployment off the West Coast of Ireland using real wave data obtained from Datawell Waverider measurement buoys. The limitations of the wave spectrum, and the associated windowed Fourier transform, in demonstrating the fluctuations of incident energy at a point are illustrated by comparison with the results obtained from wavelet analysis. The variation of instantaneous peak frequency in the time domain is quantified using the wavelet transform and the relevance of this variation to the energy absorbed by WECs determined. The wavelet transform is also applied to readings of wave elevation taken from two concurrently deployed buoys in order to assess whether there is deviation in the short term variation of the wave resource due to spatial separation, which may be of relevance to arrays of WECs.