Nonlinear hydrodynamic and real fluid effects on wave energy converters

Abstract

Ocean wave energy has been of interest since at least the mid-1970s and great advances in the understanding of the fundamental principles of wave energy extraction and converter modelling have been made using linear hydrodynamic analysis. This paper reviews efforts that have been made to use nonlinear hydrodynamics to analyse wave energy converter behaviour and performance. Both 'partially nonlinear' and fully nonlinear potential flow methods, as well as computational fluid dynamics methods solving the Navier-Stokes equations and smoothed particle hydrodynamics have been used for this purpose and are reviewed here. These more complex methods have been applied primarily to single devices, so array and mooring line interactions are not considered. While a number of studies have been performed in these areas and results are encouraging, further advances are required to give accurate prediction or reproduction of experimental results.

Linear diffraction analysis for optimisation of the three-float multi-mode wave energy converter M4 in regular waves including small arrays

“…Many devices have been considered for the conversion of ocean wave motion into electricity, see for example, the reviews of Falcão (2010), Wolgamot and FitzGerald (2015) and Babarit (2015). The wave resource is greatest offshore in deeper water and here we consider a three-float moored system with high capture width known as M4 (Stansby et al 2015a, b).…”

Peak Forces on Wave Energy Linear Generators in Tsunami and Extreme Waves

“…Computational fluid dynamics (CFD) modeling offers a complement to physical experiments, and allows the user to study specific parameters individually in predefined conditions. The turbulent flow around a WEC in high sea states can be approximated with Reynolds Average Navier-Stokes (RANS) equations together with a turbulence model [1], and the surface can be tracked with the volume of fluid (VOF) method. Several CFD models of different wave power concepts have been developed and verified in recent years [2,3].…”

A coupled hydrodynamic–structural model of the M4 wave energy converter

“…A wide range of devices has been proposed for harnessing wave energy (as reviewed for example in Loṕez et al (2013) and Babarit et al (2012)), and appropriate numerical methods for modelling and methods of benchmarking have also been subjected to extensive examination and review (e.g. Babarit et al, 2012;Wolgamot and FitzGerald, 2015). Out of these various reviews have emerged suggestions for classifying wave energy converters according to their geometric form and their principles of operation.…”

“…Widely used is the distinction between overtopping devices; terminators; attenuators; and point absorbers (e.g. Wolgamot and FitzGerald, 2015). But these authors and others have also pointed out that some of the more promising devices do not readily fit into such a scheme of classification.…”

“…It is not suggested that this would be sufficient for detailed design, particularly where extreme wave conditions must be investigated. It is expected that at that stage (as discussed for example by Wolgamot and Fitzgerald (2015)) a fully nonlinear analysis may be appropriate, including full hydrodynamic interactions and modelling the details of what may be a nonlinear control system. It may also be considered desirable then to undertake limited CFD studies to develop a much more detailed assessment of how viscous effects influence the response of the device.…”