A Review of Numerical Modelling of Wave Energy Converter Arrays

Abstract

Large-scale commercial exploitation of wave energy is certain to require the deployment of wave energy converters (WECs) in arrays, creating ‘WEC farms’. An understanding of the hydrodynamic interactions in such arrays is essential for determining optimum layouts of WECs, as well as calculating the area of ocean that the farms will require. It is equally important to consider the potential impact of wave farms on the local and distal wave climates and coastal processes; a poor understanding of the resulting environmental impact may hamper progress, as it would make planning consents more difficult to obtain. It is therefore clear that an understanding the interactions between WECs within a farm is vital for the continued development of the wave energy industry. To support WEC farm design, a range of different numerical models have been developed, with both wave phase-resolving and wave phase-averaging models now available. Phase-resolving methods are primarily based on potential flow models and include semi-analytical techniques, boundary element methods and methods involving the mild-slope equations. Phase-averaging methods are all based around spectral wave models, with supra-grid and sub-grid wave farm models available as alternative implementations. The aims, underlying principles, strengths, weaknesses and obtained results of the main numerical methods currently used for modelling wave energy converter arrays are described in this paper, using a common framework. This allows a qualitative comparative analysis of the different methods to be performed at the end of the paper. This includes consideration of the conditions under which the models may be applied, the output of the models and the relationship between array size and computational effort. Guidance for developers is also presented on the most suitable numerical method to use for given aspects of WEC farm design. For instance, certain models are more suitable for studying near-field effects, whilst others are preferable for investigating far-field effects of the WEC farms. Furthermore, the analysis presented in this paper identifies areas in which the numerical modelling of WEC arrays is relatively weak and thus highlights those in which future developments are required.

Benchmark Modeling of the Near-Field and Far-Field Wave Effects of Wave Energy Arrays

“…Experimental data presented here was provided by Porter, and details on the data analysis can be found in his Masters thesis [31] In Sec. 4.1, modeling of the wave field around a generic WEC produced interesting information about wave field characteristics including parabolic standing wave formations, wave shadows, and modification of the offshore and lee wave spectra. The data from the WEC Array tests provides a valuable resource for validating the existence of these wave field patterns.…”

“…The goal is replicate the incident wave data in the experiments as close as possible so that model results may be compared to experimental results. Here we model a frequency sweep of regular waves, and unidirectional wave spectra measured from the seven sea states listed in table 4. All of the incident spectra in this analysis are from unidirectional waves, so the directional spreading must be minimized.…”

“…Note that the response curves are quite similar except for some deviation between roughly 1.3 to 1.7 s. As the response in simulated real seas is expected to be more representative of open ocean conditions than regular waves, it is the spectral RCW that was used to parameterize the wave propagation models discussed in 3.3 and 3. 4. Rather than complicate things with multiple RCW curves, it was decided to use the mean spectral RCW curve to represent the WEC response in all conditions.…”

“…A great variety of computational methods exist for modeling wave energy converter arrays, and an excellent review and comparison is given by Folley et al [4]. Herein, the focus is linear wave theory, which because of its relative simplicity has historically been the dominant theoretical framework for studying WEC arrays.…”

“…Unless otherwise specified for the remainder of Sec. 4.1, all quantities shall be the nondimensional quantities and the word "nondimensional" shall be left out. Power absorption by the WEC shall occur through a linear power take-off (PTO) damping,…”