The Performance Research On The Oscillating Float Type Wave Energy Converter

With the increasingly serious effect of energy crisis, it focuses people's attention to the use of new energy sources, ocean energy contains a huge of renewable energy,wave energy is one of the most abundant in ocean resource and there are lots researches on the wave energy converter types. There are a variety of types of wave energy converters(WEC) device worldwide, and a portion of the device has reached the commercialization stage, and this paper is the study of direct-drive oscillation float type wave energy converter. By establishing WEC motion equations in the frequency domain and introducing the concept of energy capture width, the paper analysis the influence of different factors on the capture width of WEC; combined with the china actual sea conditions,the thesis calculates the energy absorption of WEC using time domain analysis method.Firstly, based on the linear potential theory, assuming the power take off system(PTO) model is linear, the motion equation of WEC is established in the frequency domain. The thesis considers the float motion in heave and surge direction, and deduce the relationship between the capture width and the float 's movement. The thesis considers three shapes of float influence on the capture width of WEC, analysis the effect of damping elasticity and pretension coefficient to the power absorption of WEC. Studies have shown that: the capture width of WEC presents increasing and later decreasing trend with the increase of damping coefficient, decreases with the increase of elasticity and pretension coefficient.Secondly, in order to consider the influence of nonlinear factor to the WEC's capture width, the thesis further analysis the WEC characteristics by time domain model. It introduces the approximate solution of state space equation in time domain convolution,and the results are compared to frequency domain,which verify the correctness of the algorithm. Take the nonlinear damping influence on the power absorbed power of WEC into account, and the results show that when the nonlinear damping coefficient changes nearly at optimal damping, there are little effect on power absorption. Consider the sea states of china's coastal and select three typical operating conditions, the thesis optimizes the performance of WEC by taking the float type characteristics in to account and determine the optimal size and damping of WEC.At last, for considering the actual application form of WEC in the project, the thesis gets reference from the Swedish WEC test and calculates the power absorbed at different nonlinear damping. Numerical results are coincided with the test and the correctness of the model calculation is verified.