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6 - Wave-Energy Absorption by Oscillating Bodies
Published online by Cambridge University Press: 14 May 2010
Summary
This chapter starts with a consideration of absorption as a destructive interference between an incident wave and a radiated wave. Then absorption by a body oscillating in one mode only is described in some detail. The optimum motion for maximising the absorbed power is a particular subject of interest. The last part of the chapter concerns absorption by a group of bodies oscillating in several degrees of freedom, and an explanation is given of why radiation-resistance matrices may be singular.
The large-scale utilisation of ocean-wave energy is still in a rather premature state of technological development. A review of the present state of the art is given by the ECOR Working Group on Wave Energy Conversion. Some shorter reviews described the state approximately a decade ago. The theory of waveenergy absorption was reviewed in 1981 by Evans.
Absorption Considered as Wave Interference
A body oscillating in water will produce waves. A big body and a small body may produce equally large waves, provided the smaller body oscillates with larger amplitude. This may be utilised for the purpose of wave-energy conversion, for instance by a small floating body heaving in response to an incident wave, particularly if it can be arranged that the body oscillates with a larger amplitude than the wave amplitude.
Generally it can be said that a good wave absorber must be a good wavemaker. Hence, in order to absorb wave energy it is necessary to displace water in an oscillatory manner and with correct phase (timing). Absorbing wave energy for conversion means that energy has to be removed from the waves.
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- Ocean Waves and Oscillating SystemsLinear Interactions Including Wave-Energy Extraction, pp. 196 - 224Publisher: Cambridge University PressPrint publication year: 2002
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