振荡浮子式波能转换装置动力输出系统特性研究

Power take-off mechanism analysis of oscillating-buoy wave energy converter

动力输出系统(Power Take-Off,PTO)作为波浪能转换装置(Wave Energy Converter,WEC)的主要构件之一,对系统运动及能量转换至关重要。首先基于势流理论,运用特征函数展开法得到圆柱形浮体所在流域的速度势函数级数表达式,进而通过边界匹配法得到作垂荡运动浮子的附加质量、阻尼系数及波浪激励力的解析表达式。针对阻尼器特性,分别研究线性和非线性PTO阻尼作用下,浮子的运动及波能转换特性,重点研究了线性PTO作用下的过阻尼问题。计算结果表明,低速度指数的PTO系统对装置运动的影响主要体现在PTO阻尼系数上,随着阻尼系数增大,波能装置的共振频率逐渐减小,但减小幅度很小;PTO系统的非线性特性并不能改变浮子的最优转换效率,但是较大的速度指数能有效改善PTO系统的阻尼容量;在较低频和较高频时,通过解析算法得到的最优PTO阻尼系数会使得装置处于过阻尼工作状态,且在低频部分需要进行最优PTO修正的最高频率和在高频部分需要进行修正的最低频率均随着半径和吃水的增大而逐渐减小。

As one of the main components,the Power Take-Off(PTO)mechanism is very important to the motion and power conversion for the Wave Energy Converter(WEC).Based upon the potential flow theory,the series expression of velocity potential function of the basin where the cylindrical floating body is located was obtained by using the eigenfunction expansion method.Then the analytical expressions of additional mass,damping coefficient and wave exciting force of the floating body were obtained by the boundary matching method.According to the characteristics of the PTO damper,the motion and wave energy conversion characteristics of the float under the linear and nonlinear PTO damping were studied respectively,and the over-damping problem under the linear PTO damping was emphatically explored.The results show that the influence of PTO system with low velocity index on the motion of the device is mainly reflected in the PTO damping coefficient.With the increase of damping coefficient,the resonance frequency of the wave energy device decreases gradually,also the decrease amplitude is very small.The nonlinear characteristics of PTO system cannot change the optimal transfer efficiency of the float,but the large velocity index can effectively improve the damping capacity of PTO system.At lower and higher frequencies,the optimal PTO damping obtained by the analytic algorithm will make the device reaching an over-damped state.The highest frequency in the low frequency part and the lowest frequency in the high frequency part which need to be modified will gradually decrease with the increase of radius and draught.