| Energy is the material basis for human survival and development.Every major change and progress in society cannot be separated from the promotion of the energy revolution.However,with the development of the economy,energy demand continues to grow.The excessive exploitation and use of traditional fossil energy sources not only bring about energy shortages,but also bring about deteriorating environmental pollution problems.Developing clean and renewable energy has become the core of energy structure transformation.Wave energy has attracted people's attention because of its wide distribution,large reserves,high energy density and easy development.So far,thousands of wave energy technologies have been proposed,but they have not yet been commercialized.The main reason is that the low efficiency of wave energy conversion leads to the high cost of power generation,which becomes the bottleneck restricting commercialization.It has become a general consensus of researchers that resonance can improve the efficiency of wave energy conversion.Based on this,Professor Cai Yuanqi of Wuhan University has proposed active resonance C-type buoyancy pendulum wave energy generation technology,which derives three technical schemes.One of them is to design the front wave surface according to the average value of the maximum gradient direction of the incident wave potential function,and to optimize the back wave surface with minimum radiation.In this paper,the numerical simulation of the active resonance C-type buoyancy pendulum wave energy converter(hereinafter referred to as C converter)is carried out.In this paper,the momentum source term function for wave-making and waveeliminating is deduced by Z-transform.A numerical wave flume is constructed,which can generate second-order Stokes waves,irregular waves based on Jonswap wave spectrum and white noise wave spectrum.The numerical simulation shows that the numerical wave flume is stable and accurate,and the wave elimination effect is good.This paper establishes the motion equation and dynamic control equation of C converter in wave field,derives the mathematical model of controlling the natural frequency of wave energy system,puts forward the method of adjusting the natural vibration period of C converter,and verifies the correctness of the natural vibration frequency control model through numerical simulation,thus realizing real-time resonance with wave.In this paper,Newmark integral method,Newton iteration method and Fluent UDF are used to solve the motion equation of C converter on Fluent software platform.A numerical simulation platform of wave field-C converter is formed by combining the numerical wave flume technology.Using this platform,the response and energy capture efficiency of C converter in resonance and non-resonance state in second-order Stokes wave field with period of 3.0s~7.0s and wave height of 0.1m~0.8m are studied.The results show that although high-efficiency wave energy conversion can be achieved by resonance,there is still an optimal wave period;the energy capture power is proportional to wave height,but the energy capture efficiency is inversely proportional to wave height;the maximum efficiency is 62.25% and the minimum efficiency is 5.25% in the range of wave studied.The C converter studied in this paper has the best capturing capacity in the period of 3.0s~4.0s.The natural vibration period of C converter is adjusted to 4.0s.The energy capture efficiency is 24.9% in irregular waves of Jonswap wave spectrum and 9.8% in irregular waves of white noise wave spectrum.The main reason for inefficiency is that irregular waves are more dissipative in numerical wave flume.In this paper,the optimal PTO damping of C converter is studied by using the linear search method.It is found that the optimal PTO damping of C converter is consistent with that of linear system in small motion.In large motion,the optimal PTO damping derived from linear system is not the optimal PTO damping,and the system shows strong non-linear characteristics.At large amplitude,the energy capture power of the optimal PTO damper is much higher than that of the optimal PTO damper derived from the linear system.For example,when the period is 6.5s and the wave height is 0.8m,the power increase is about 48.33%.Therefore,the optimal PTO damping should be further studied for large period and high wave height.In this paper,a method of controlling PTO damping by rectangular square wave is proposed.The numerical simulation shows that this method can improve the energy capture efficiency of C converter,but it is important to ensure that the generator generates electricity at the optimal speed and improve the efficiency of the generator.In order to improve the survivability and achieve full cross-section energy capture of C converter,C converter is underwater when working.The influence of submergence depth on the response and energy capture efficiency of C converter under the condition of 3.0s~7.0s and 0.8m wave height is discussed in this paper.It is found that if the submergence depth is too large,the wave energy leakage at the top of the converter is too large,and the energy capture power will decrease;if the submergence depth is too small,the energy dissipation such as wave rollover,breakup and eddy will be caused,and the energy capture power will be greatly reduced.The optimal PTO damping of C converter under different submergence depths is searched by linear search method.The optimal submergence depth and PTO damping is found.It is found that the optimal PTO damping of C converter in the same wave field will not be changed by the submergence depth,but the energy capture power of C converter will be changed.Therefore,reasonable setting of submergence depth is very important to enhance the energy capture capacity of C converter. |
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