Abstract
Wave energy converters absorb wave power by mechanical damping for conversion into electricity and multi-float systems may have high capture widths. The kinetic energy of the floats causes waves to be radiated, generating radiation damping. The total wave power absorbed is thus due to mechanical and radiation damping. A floating offshore wind turbine platform also responds dynamically and damping plates are generally employed on semi-submersible configurations to reduce motion, generating substantial drag which absorbs additional wave power. Total wave power absorption is analysed here by linear wave diffraction–radiation–drag models for a multi-float wave energy converter and an idealised wind turbine platform, with response and mechanical power in the wave energy case compared with wave basin experiments, including some directional spread wave cases, and accelerations compared in the wind platform case. The total power absorption defined by capture width is input into a far field array model with directional wave spreading. Wave power transmission due a typical wind turbine array is only reduced slightly (less than 5% for a 10 × 10 platform array) but may be reduced significantly by rows of wave energy converters (by up to about 50%).
Highlights
Floating platforms for offshore renewable energy are becoming established for wind energy and are in early stage development for wave energy
The capture width for average mechanical power absorbed normalised by the device width is shown in Fig. 8 and the model generally underestimates, by up to 35% near the maximum while agreement is close for longer waves (Tp > 1.4 s); differences are discussed further in Sect
The total capture width due to mechanical and radiated power absorbed is estimated from the model and shown to be at least twice the mechanical power
Summary
Floating platforms for offshore renewable energy are becoming established for wind energy and are in early stage development for wave energy. We consider here total wave power absorption by platforms necessary to determine wave fields due to arrays, comprising wind or wave farms. Offshore wind farms are expanding rapidly in many parts of the world. Most platforms to date (2021) have fixed foundations of monopile or jacket structure form, suitable for relatively shallow water, less than about 30 m deep. Floating foundations or platforms are required for deeper water, markedly increasing the available energy resource. Offshore wind speeds are higher and less intermittent
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