Further analysis of change in nearshore wave climate due to an offshore wave farm: An enhanced case study for the Wave Hub site

This paper addresses the use of numerical wave models for assessing the impact of offshore wave farms on the nearshore wave climate. Previous studies have investigated the effect of energy extraction by wave energy devices through the use of spectral models such as SWAN, representing a wave farm as one or more barriers within the model domain and applying a constant wave energy transmission percentage across the whole wave spectrum incident at the barrier. However, this is an unrealistic representation of the behaviour of real wave energy converters. These will exhibit frequency-dependent energy absorption characteristics that will correspond to the spectral response of the device, and may reflect its ability to be tuned to extract energy at particular frequencies. This study describes a modification of the SWAN source code to enable frequency-dependent wave energy transmission through a barrier. A detailed analysis of the wave climate at the Wave Hub wave farm site is also presented, with a particular focus on the occurrence of bimodal sea states. The modified SWAN code is used to assess how impact predictions for typically occurring sea states may differ when using frequency-dependent rather than constant wave energy transmission, with reference to a previous study using the unmodified code (Millar, Smith and Reeve, 2007 [1]). The results illustrate the dependence of the magnitude of the impact on both the response function of the devices and the spectral sea state in which they are operating.