Study on Floating Attenuator Wave Energy Devices

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In this paper the theory of optimal control is developed in a form in which non absorbing modes of motion may be included in any system. The theory is developed for wave energy absorption by phase controlled systems and ones where only a simple resistive damping may be applied. The theory is applied to two attenuators based on the Kaimei (an attenuator) concept. Firstly, a system of vertically oscillating pistons are considered which is intended to model a device with bottom opening oscillating water columns, and secondly horizontally moving pistons are considered. The latter system is analogous to a device containing side opening oscillating water columns. Results are shown for both devices when constrained so that only the column motions are possible and for the case where the systems float freely. In addition, power extraction systems corresponding to phase control and resistive damping alone are considered. The conclusions from the study are unexpected in that floating attenuators perform better than fixed ones. Less surprising is the fact that phase controlled systems are considerably more effective than simple damped ones. Overall the results supported a bottom opening floating attenuator to be superior to other configurations although to what extent this conclusion is dependent upon the actual device geometries chosen is difficult to deduce.
社団法人日本船舶海洋工学会の論文