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The modelling of ocean waves is an integral part of coastal and offshore engineering. Both theoretical and experimental modelling methods are available and are commonly used in support of each other. In particular, due to the difficulty in measuring the velocity throughout the water column, the wave kinematics are often derived, by means of wave theory, from a measurement of the free surface elevation. However, wave theory is often based upon idealistic conditions, such as infinite spatial domains and time lengths. The question therefore arises, how well are the wave kinematics in an experimental wave tank described by wave theory? The present paper compares theoretical solutions against experimental data, for the free surface elevation and the velocity throughout the water column, to assess the ability of Stokes’ wave theory to describe the kinematics of regular waves in a short, physical, wave flume. Experimentally, the free surface elevation is measured with a set of resistive wave probes, while wave kinematic data is acquired with particle image velocimetry (PIV). For this study, ten different regular waves, of varying steepness, are generated in a 35 m long and 0.7 m deep wave flume. The theoretical solutions are computed based on Stokes 2 nd order wave theory. The presented results show error values of the order of 10–20%, indicating validity of the employed wave theory as a function of the reflection coefficient achieved in the physical wave flume. These result highlight the potential inaccuracies incurred in any wave tank if the wave theory is used to derive the kinematics from the free surface elevation without having detailed knowledge of the reflection characteristics at the point of interest in the tank.

For the research and development (R&D) of wave energy converters (WECs), numerical wave tanks (NWTs) provide an excellent numerical tool, enabling a cost-effective testbed for WEC experimentation, analysis and optimisation. Different methods for simulating the fluid dynamics and fluid structure interaction (FSI) within the NWT have been developed over the years, with increasing levels of fidelity, and associated computational expense. In the past, the high computational requirements largely precluded Computational Fluid Dynamics (CFD) from being applied to WEC analysis. However, the continual improvement and availability of high performance computing has led to the steady increase of CFD-based NWTs (CNWT) for WEC experiments. No attempt has yet been undertaken to comprehensively review CNWT approaches for WECs. This paper fills this gap and presents a thorough review of high-fidelity numerical modelling of WECs using CNWTs. In addition to collating the published literature, this review tries to make a step towards a best practice guideline for the applications of CFD in the field of wave energy.

Performing rigorous technical and commercial assessment of wave energy converters (WECs) numerically, before engaging in expensive wave tank and open ocean tests, is vital for the economically successful development of prototypes. To that end, this paper presents a high-fidelity wave-to-wire simulation platform (the HiFiWEC), where a Computational Fluid Dynamics (CFD)-based numerical wave tank is coupled to a high-fidelity power take-off (PTO) model, which enables assessment of WEC performance with greater accuracy than with previous wave-to-wire approaches. A test case, simulating the performance of a heaving point absorber type WEC in realistic conditions, is presented and compared against traditional lower fidelity modelling methods. The WEC response is evaluated with a number of different approaches, including different techniques to model hydrodynamic wave-structure interactions and the power take-off system, and the benefits of the HiFiWEC are highlighted. The results highlight that excessive simplifications in the modelling of the PTO system can lead to significant overestimation in generated energy output, with relative deviations ( ∊ ) of up to 150% compared to the HiFiWEC. In addition, uncertainty in viscous drag parameters added to hydrodynamic models based on boundary element method solvers, reinforce the necessity of CFD-based models for applications where high-fidelity is essential. Finally, it is demonstrated that minor/insignificant inaccuracies in the hydrodynamic model ( ∊ = 0.5 % ) can result in significant differences in the estimation of the final energy generation ( ∊ = 7 % ), highlighting the need for a coupled high-fidelity platform.

The modelling approach presented in this chapter is that of system identification, where models are determined from input/output data measured from the system under study. Models identified from recorded wave energy converter (WEC) data can accurately describe WEC behaviour, provided the data is of a sufficiently high quality. The chapter details generating data for the system identification process and outlines the requirements of the data to ensure representative models are obtained. Different parametric model structures are presented, along with identification algorithms to determine the optimum parameter values for the models. A number of case studies illustrating the use of system identification to obtain numerical models of WECs are given.