| Abstract: | The problem of how to extract energy from ocean waves is discussed by analysing theoretically the hydrodynamic properties of a few ideal devices, involving vertical energy absorbing plates. the aim is to find a mechanism with high ideal efficiency, but still simple enough, such that its realization in practice can be economically feasible. The most promising device involves one or more vertical elastic plates situated in the water perpendicular to the incoming waves. About a quarter of a wavelength after the (first) plate there is a stiff vertical construction extending sufficiently deep in the water such that it is rather immobile. It serves as a reflector of the waves. the elastic plate is set in oscillation by the wave motion and this motion is used to extract the energy by applying a braking force. the optimal force field is discussed in some detail, and it is shown that not much of the optimal efficiency is lost by letting the force field simply be proportional to the velocity. the device is also shown to be sensitive to a fairly broad spectrum of wavelengths, and this spectrum can be broadened by adding more swinging plates. In this way efficiencies of 80-100 per cent are attained in theory over a wavelength spectrum extending over an order of magnitude. |
