Hydrodynamic Modelling of Wave Power using Electrical Equivalent Circuit Theory

Abstract: Ocean wave energy can be harnessed and converted into electric energy nowadays. This provides a possibility for populations that live on islands or along coastlines to utilize the renewable and safe power produced by ocean waves. Point absorbing wave energy converter (WEC) is one example of such devices for electrical power production from ocean waves. It is composed of a floating buoy on the water surface, and a linear generator that sits on seabed and is connected with the buoy via a line. Electricity is generated when the buoy moves up and down in the waves.The geometry and dimensions of the floating buoy have dominant influences on the energy absorption. This thesis introduces an equivalent electric circuit for modelling the  hydrodynamic interaction between the wave and a cylindrical buoy. The model allows a rapid assessment of the velocity, force in the connection line and output power, by which the system design and optimization can be performed faster and easier.The electric circuit model is based on the WEC's dynamic force analysis, and the electric components' parameters are determined from analytical approximations of the hydrodynamic coefficients. The simulation results of the equivalent circuit for one typical wave climate in Lysekil has been presented, and the results indicate a good fitting with former experimental results.The thesis also includes a hydrodynamic study for a torus shaped buoy, which aims at  applying a theoretical background for a force measurement experiment. A comparison has been conducted between the torus buoy and two similar cylindrical buoys. Preliminary WAMIT simulation results demonstrate that the force in the connection line will be 5% bigger by using the torus buoy. It is also found that the torus buoy is advantageous for its larger excitation force and smaller added mass. A brief introduction of the 500kN force measurement system and the communication test have been introduced as well.