Abstract
This numerical study compares the wave field generated by the spectral wave action balance code, SNL-SWAN, to the linear-wave boundary-element method (BEM) code, WAMIT. The objective of this study is to assess the performance of SNL-SWAN for modeling wave field effects produced by individual wave energy converters (WECs) and wave farms comprising multiple WECs by comparing results from SNL-SWAN with those produced by the BEM code WAMIT. BEM codes better model the physics of wave-body interactions and thus simulate a more accurate near-field wave field than spectral codes. In SNL-SWAN, the wave field’s energy extraction is modeled parametrically based on the WEC’s power curve. The comparison between SNL-SWAN and WAMIT is made over a range of incident wave conditions, including short-, medium-, and long-wavelength waves with various amounts of directional spreading, and for three WEC archetypes: a point absorber (PA), a pitching flap (PF) terminator, and a hinged raft (HR) attenuator. Individual WECs and wave farms of five WECs in various configuration were studied with qualitative comparisons made of wave height and spectra at specific locations, and quantitative comparisons of the wave fields over circular arcs around the WECs as a function of radial distance. Results from this numerical study demonstrate that in the near-field, the difference between SNL-SWAN and WAMIT is relatively large (between 20% and 50%), but in the far-field from the array the differences are minimal (between 1% and 5%). The resultant wave field generated by the two different numerical approaches is highly dependent on parameters such as: directional wave spreading, wave reflection or scattering, and the WEC’s power curve.
Highlights
As wave energy converter (WEC) technology matures from deployments of individual wave energy converters (WECs) for testing and demonstration, to wave farms consisting of multiple WECs for utility-scale power generation, it will be increasingly necessary to understand and quantify the effect of these WECs on the surrounding wave field
This paper extends previous work modeling wave field effects produced by individual WECs and multiple WEC wave farms with spectral-domain models by comparing the performance of SNL-SWAN with the linear-wave, boundary element method (BEM) code WAMIT
The wave field coefficient represents the change in wave height due to the presence of the WEC: A value of 0 means the wave field is undisturbed, which is represented by green in the plot; a positive value means wave heights are higher than they would otherwise be; and a negative value means there is a wave shadow
Summary
As wave energy converter (WEC) technology matures from deployments of individual WECs for testing and demonstration, to wave farms consisting of multiple WECs for utility-scale power generation, it will be increasingly necessary to understand and quantify the effect of these WECs on the surrounding wave field. In order for wave energy projects to be permitted, and for wave energy to be a viable part of our renewable energy portfolio, we must have numerical tools capable of modeling the effects of wave farms on their surrounding environment. Frequency-domain models include linear potential flow methods such as the boundary element method (BEM) codes WAMIT [2] and NEMOH [3]. Spectral-domain models include numerical methods based on the spectral action balance equation, such as the codes SWAN and TOMAWAC [5,6]. The rate of change of the action density is governed by the action density balance equation This equation includes wave kinematics, variations in depth and currents, sources, and sinks but is not phase resolving
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