Abstract
To meet the growing global demand for carbon neutral electricity, wave energy is increasingly being identified for its global prevalence and the emerging clean technologies that can harness it. To provide the scale of electricity needed, Wave Energy Converters (WECs) will need to be deployed in large arrays. However, the effects of a WEC array's layout on the surrounding wave conditions in both the near and far fields is poorly understood. The published literature describes numerous methods to model interactions of incident waves and WEC arrays. Yet, none of the published methods provide a methodology which spectrally resolves the individual WEC's energy conversion characteristics, and has the flexibility to be applied to any emerging WEC design.
This study develops and implements two novel candidate high-fidelity representations of a Backwards Bent Duct Buoy Oscillating Water Column (BBDB) WEC within a Simulating WAves Nearshore (SWAN) coastal model. Each candidate representation is developed by post-processing time series data generated from a time domain numerical simulation to form a meta-model, referred to as an obstacle case, consistent with the SWAN governing equations and discretization scheme. The study is executed within the framework of SNL-SWAN – a modified version of SWAN that includes a WEC obstacle case that is built on the established concept of using SWAN's transmission coefficient to emulate the wave-WEC interactions. The two new WEC obstacle cases build on SNL-SWAN by considering the WEC's intercepted power, the rate of energy extraction from the waves, instead of the captured power, the rate of energy conversion by the power-take-off. The two new candidates differ in their level of spectral resolution: one homogenizes the intercepted power across the frequency domain while the other attempts to spectrally resolve the energy transfer mechanisms.
The two new candidate obstacle cases were compared by considering up to 5 BBDB devices subject to irregular wave conditions. For an individual device, a region of significantly perturbed wave heights, referred to as a wake, stretched 200 m in the lee of the WEC, with the maximum impact on wave heights seen 50 m behind the device. The wake behind five devices is largely dependent on the device spacing. The five unit WEC array only presented decreases of wave height between 0.2 and 0.7 m 200 m behind the last device in the array. A five unit WEC array model showed that estimates of individual WEC power performance was reduced by 2.3% and 6.0% when implementing the two new obstacle cases.