Investigation On Hydrodynamic Performance Of A Heave Oscillating Buoy Wave Energy Converter

With the increasingly growing contradiction between the growing emergy demanding and increasingly exhausted traditional energy sources, people turn their eyes to ocean wave energy,which contains enormous energy. Although researching and developing on wave energy started relatively late, compared to other renewable resources, now a variety of different principles of wave energy conversion device have been put forward after the efforts of researchers, and some of them have got the engineering application. The key to the wave energy utilization technology lies in the design of the wave energy converter. The research object of this thesis is a heave oscillating bouy wave energy converter, and it transforms from wave energy to electrial energy using the direct drive linear power generation by a heaving buoy. Through frequency domain analysis and time domain simulation to explore the infulence of different control strategies and shape paremeters on the hydrodynamic performance, and wave energy capture characteristics of wave energy converter.Firstly, set up the frequency motion equation of the divice and obtain the freqency response function, which considers the direct drive heave oscillating buoy wave energy converter by using the frequency domain analysis method. The time average power and wave energy capture width under both regular wave and irregular wave have been deduced. Then four different linear PTO force control method have been introduced and discussed in detail, which use causal optimal control in regular wave and causal sub-optimal control in irregular wave.Secondly, a state space model has been adopted to repalce the convoluttion item in motion equatuon, and time domain simulation is implemented by Matlab Simulink, where the movement charecteristics and time-varying absorebed power of buoy under different control strategies have been explored. The accuracy of the state space model is verified by comparing with frequency domain results, and the mechanisms of the four linear PTO force control emthod have been further studied.Thirdly, the influence of nonlinear latching control method on the device has been studied based on time-domain simulation model, the result shows that latching control can increase the velocity of WEC so that enhance the the wave absorption, also no reactive power can be produced under latching control. However, a short-term energy storage device is needed since the energy output under latching control is discontinuous, which means that it is difficult to achieve in a direct drive system. Moreover, in order to match the actual situation, end-stop systems have been introduced to ressrict the maximum displacement of buoy, the results show that the end-stop systems can control the dislacement amplitude of device perfectly, but a huge PTO force is required when complex conjudge control is taken.Finally, basing on the frequency domain analysis method, the influence of different masses,radiuses,cone angles and shapes to the hydrodynamic parameters and wave absorption efficiency of WEC under real control have been discussed on the premise of the feasibility and economy, which provides the reference basis to the shape selection of WEC.