Design and performance evaluation of ModuleRaft wave energy converter

Abstract

This thesis presents a novel wave energy converter (WEC), referred to as the ModuleRaft WEC. The WEC consists of a floating modular flap and four rafts hinged at the main floating structure. ModuleRaft WEC is unique due to its ability to convert both wave potential energy and wave kinetic energy by utilizing the pitch motion of rafts and floating modular flap. In the first section, the conceptual design of the ModuleRaft wave energy converter is presented. The motion characteristic, performance and optimization of the ModuleRaft wave energy converter are investigated under regular wave conditions using ANSYS-AQWA. The effect of wave frequency, power take-off (PTO) damping coefficient and floating / fixed main structure on capture factor is analyzed. Results indicate that using a single point mooring (SPM) system, the ModuleRaft WEC can operate optimally by utilizing all directions wave energy. In addition, comparing WEC with and without rafts, the capture factor of the ModuleRaft WEC was larger by 13.5 % when a combination of modular flap and rafts was used rather than modular flap without rafts. Furthermore, the capture factor of the ModuleRaft WEC could be increased 44 % by having a fixed main structure instead of floating main structure. Moreover, the two influential parameters; wave frequency and PTO damping coefficient have a significant effect on the capture factor of the ModuleRaft WEC. Secondly, the performance of the ModuleRaft WEC model was evaluated by conducting the wave flume tests. The experimental tests were performed for both unidirectional regular and irregular waves. The experimental results show that the wave height, wave period, significant wave height, average wave period and PTO damping torque have a significant influence on the capture factor of the ModuleRaft wave energy converter. The capture factor of the ModuleRaft WEC which is a combination of modular flap and rafts was larger than only a modular flap without rafts by 27.7 % in regular wave conditions and 6.7 % in irregular wave conditions. It indicates that rafts play a positive role by floating and increasing the overall capture factor of the conventional floating modular flap-type wave energy converter. A systematic comparison of the numerical results (ANSYS-AQWA) with the corresponding experimental data was conducted. The overall performance tendency of the ModuleRaft WEC model based on the numerical simulation was quite similar and consistent with the experimental results. The dimensions of full-scale prototype with annual energy production of 50.4 MWh/year were presented.