Study On The Methods To Improve The Efficiency Of Active Resonance Wave Energy Converter

In order to address the contradiction between energy consumption and the growing demand for energy,we need to adjust the energy structure and develop new energy industries.As a form of new energy,wave energy has large reserves and high flow density.Therefore,the development and utilization of wave energy is strongly concerned.Various kinds of wave energy use schemes have been proposed,but they have failed to achieve large-scale commercialization.Efficiency is the leading cause of this situation.The phenomenon of high efficiency of wave energy system in resonant state is confirmed by experiments and theories.Based on the resonant thought of the wave energy system,professor Cai Yuan-qi of Wuhan University has proposed an Active Resonance Wave Energy Conversion Technology(ARWECT).By adjusting the dynamic characteristics of the wave energy converter,the wave energy system's self-oscillation frequency is consistent with the wave frequency,so that the wave energy system can enter the resonance state.According to the control model,the dynamic characteristics of Active Resonant Wave Energy Converter(ARWEC)are studied,and the influence of the additional weight's height on the dynamic characteristics is analyzed.Using the numerical simulation experiment to study the capture ability of ARWEC.In addition,the influence factors of efficiency and the mechanism of energy conversion are analyzed.The main results are as follows:(1)The change of the additional weight's height can affect the stiffness and vibration mode without changing the size of the device and the depth of the draft.When the weight is placed in a certain position,the stiffness and vibration mode of the wave energy device can be singular and the normal operation of the device is affected.This position is associated with wave frequency.The higher the wave frequency,the lower the position.Therefore,in order to effectively expand the applicable scope of the wave cycle,we need to properly set the additional weight's height based on the usual wave cycle.(2)The current design of the experimental prototype is smaller,and its characteristics are similar to the Oscillating Water Converter(OWC).The motion and torque of the pitching direction have changed greatly during the adjustment of the additional weight's height.As the height of the additional weight drops,the phase of force and velocity response on pitching direction are adjusted.Their phase is gradually reversed to the same direction.(3)By reducing the height of the additional weigh and increasing the rotational inertia of the floating body part can effectively reduce the pitching angle and enhance the device's ability to resist capsizing,at the same time provide conditions to increase efficiency.(4)Reducing the PTO damping of the device can effectively increase the amplitude of the pendulum and improve the energy captured by the pendulum.But as the damping is reduced,the vibration amplitude and radiation ability of floating body part increase accordingly.The efficiency does not vary with the PTO damping monotonically,so the trap can have the best PTO damping.Therefore,the PTO damping has the optimal value.(5)Increasing the weight of the pendulum and the length of the swing arm can greatly improve the efficiency of the device,but also increase the non-linearity of the wave energy system.When the non-linearity is strong,the capture and extraction of energy is still relatively stable.Therefore,ARWEC has strong robustness.The results of numerical simulation experiment show that the efficiency of the prototype machine can be improved effectively by adjusting the design parameters of the prototype.The maximum wave conversion efficiency of the prototype is 32.7%.If we continue to optimize the design parameters of the prototype,we will further improve the efficiency.The ARWECT is an efficient wave energy utilization technology.