Abstract
A benign quarter scale test site for floating wave energy devices has been provided off the west coast of Ireland in a mn
semi-enclosed coastal bay, partially sheltered from the Atlantic by the Aran Islands. It is expected the provision of this site will encourage developers to progress to Phase 3 of the Ocean Energy: Development & Evaluation Protocol. The site characteristics have been determined from a hindcast model using the 3rd generation wave model SWAN for the year 2000, and a non-directional wave recording buoy in situ since the test site’s inception in late 2005. Analysis of this data has shown that there are high occurrences of twin peak spectra, comprising a local fetch limited wind sea and a long period swell which approaches the site around the Aran Islands from offshore. The method that identifies and separates these multi-modal wave generation systems into their constituent processes will be presented in this paper. Through the application of this method the wind and swell sea components will be presented in various forms to engender a thorough knowledge of the conditions at the test site.
Phase 3 of the Development Protocol bridges the end of laboratory model testing and the beginning of sea trials. As completion of the previous two phases is a prerequisite for the use of the test site, this paper explores several considerations that WEC developers will need to take into account. Phase 1 and 2 of the protocol will have involved controlled laboratory conditions, mostly being a combination of monochromatic trials with idealised irregular trials such as the standard representative formulae for JONSWAP or Pierson-Moskowitz spectra. As most floating wave energy converters have a narrow response bandwidth, a high occurrence of twin peaked spectra may not produce the expected power production from the device, especially if resonance falls within the valley between the wind and swell spectral components. What effect will a long period swell occurring at the test site have on the motions of the device, and particularly the power output?
Finally, this paper will look at the scalability of the conditions at the benign test site and compare these to a fully exposed site off the west coast of Ireland which would be typical for full scale prototype deployment.