Relevance of pressure field accuracy for nonlinear Froude–Krylov force calculations for wave energy devices

Abstract

Due to their computational convenience, linear mathematical models for wave energy converters are usually employed. Including nonlinearities may improve the accuracy of the results, but often at the price of an additional computational and complexity burden, which can be justified only if nonlinearities are significant. One of the sources of nonlinearity in fluid–body interactions is the wave field itself. Different wave models exist, among which are linear Airy’s theory, Wheeler’s stretching approach, the nonlinear Rienecker–Fenton method, and higher order spectral methods, all of which achieve a different compromise of accuracy and complexity. The impact of the accuracy of such wave theories strongly depends on the specific device (operating principle, power production region or survivability mode), and installation site (water depth, occurrences of each sea state in the scatter diagram of the installation site). This paper evaluates the performance of different wave field representations, firstly in absolute terms and, secondly, in relation to the associated computation of nonlinear Froude–Krylov forces for different wave energy devices, in regular and irregular sea states. It is shown that Wheeler’s stretching offers a good accuracy/complexity compromise for WECs operating in the power production region.