Hydrodynamic Interaction of an Offshore Floating Support Structure and Tidal Energy Converter

Sustainable energy generation through renewable sources is a rapidly expanding industry within the energy sector and as part of that the industry applies floating turbines to convert the kinetic energy into electrical energy. Moreover the maintenance cost of the floating turbine is lower compared to the fixed turbine, although the hydrodynamic interaction is not completely understood. This work, firstly studies the effect of the thrust and power generation of an horizontal axis tidal turbine under imposed surge and pitch motion. Secondly, a 2D numerical model of a floating moored platform with the turbine is used to analyse the influence of the hydrodynamic interaction between the platform and the tidal turbine in time domain. To gain understanding in the coupled dynamic system, it will be subjected to a single harmonic wave and constant current profile. Tidal turbine models are typically used from the quasi-static wind turbine models, which are known as the Actuator Disk Momentum (ADM) Model and Blade Element Momentum (BEM) model. Furthermore the quasi-static models are compared with the reproduced experimental data from existing literature. Both models are analysed at blade pitch angles (θ) of 5o, 7o and 9o. For analysing the dynamic model, the quasi-static BEM model is extended to account for the added mass effects in the axial direction of the blade. As with the most turbine system, a control system regulates the turbine to maintain the desired power output. The quasi-static BEM model as well as the dynamic BEM model is analysed from an optimal operation criteria especially for the fixed rotational speed and control rotational speed. Also the models are analysed at different oscillatory frequencies at θ = 5o, examined under the same hydrodynamic conditions. The results provide an insight into the added mass effect (force) in the axial direction on the blade and will support our understanding with this kind of phenomenon, for a rotor operating in unsteady flow. The outcomes for the thrust and power generation of the floating turbine and fixed turbine are compared at a water depth of 105 m and a single harmonic wave, with an amplitude of 1 m. The results for thrust and power extracted from the floating turbine are higher due to the relative velocity acting on each blade section. However the fixed turbine captures only the incoming wave loading whereas the floating turbine is subjected to the wave loading and the motion of the platform.Mechanical, Maritime and Materials EngineeringOffshore & Dredging Enginee