Theoretical modelling of two wave-power devices

Abstract

Many wave energy devices are currently studied. In this thesis we focus on two specific devices: the Oscillating Water Column (OWC), and the buoys. In the first part of this thesis we examine the effects of coastline geometry on the performance of an OWC. Under the assumption of inviscid irrotationnal flow, we develop a linear theory for the velocity potential for the case of a coastline of arbitrary apex angle. Scattering and radiation problems are solved separately using eigenfunctions expansions, and are then combined to study the energy extraction rate. Numerical simulations for a convex and a concave corner are considered and comparison with an OWC at the tip of a thin breakwater and on a straight coast are discussed. Assuming that the multiple-turbine system can be controlled over a wide range of frequencies, we study the effects of fixed chamber size and air compressibility on the optimal power extraction. A simpler way of optimization is then develop and we show that this simpler scheme can achieve almost as high an efficiency as the idealized many-frequency optimization. In the second part of this thesis, we first model theoretically an array of cylinders and then apply the theory developped to an array of buoys. However, numerical difficulties encountered for the array of cylinders have led to the conclusion that the theory developed is numerically inefficient, although it is accurate.