| The development and utilization of new renewable energy is a hot topic in the world.As one of the abundant new energy sources in China,ocean current energy has high research value for its development and utilization.Based on the phenomenon of flow-induced vibration,the technology of using ocean current energy to generate electricity is a relatively new power generation technology,which is more suitable for use in small velocity sea areas than other technologies.However,for the deep sea with very low flow velocity,it is necessary to find a suitable vibrator section shape for flow-induced vibration power generation at very low flow velocity.In this thesis,a non-circular cross-section Elli-circ oscillator with two cross-sections is proposed,and its flow-induced vibration characteristics are studied.On this basis,the influence of different parameters on its energy capture characteristics is explored.The main contents and conclusions of this thesis are as follows:Firstly,this thesis introduces the related theory of vortex,and discusses the mechanism of wake vortex change in the process of flow-induced vibration in detail from three aspects:vortex and vorticity,wake shedding principle and vortex intensity-fluid equation.The numerical calculation method and flow-induced vibration parameters involved in numerical simulation are discussed.The force analysis of the physical model is carried out,and the energy conversion model is derived.Secondly,the numerical calculation model of Elli-circ oscillator with cylindrical and non-circular cross-section is constructed,and the independence of grid independence,time step independence and numerical model is verified.The three-dimensional numerical model is numerically simulated.The results are analyzed from three aspects:amplitude-frequency response,displacement time history curve and wake vortex shape.The flow-induced vibration characteristics of Elli-circ oscillator under different mass ratios,different radius ratios and different flow velocities are analyzed and discussed.The results show that the flow-induced vibration response of the vibrator is greatly affected by the radius ratio.The peak amplitude decreases gradually with the increase of the radius ratio,the optimal reduced velocity range corresponding to the peak becomes smaller,and the frequency increases gradually with the increase of the radius ratio.The Elli-circ oscillator has good vibration stability.The wake vortex morphology is affected by the radius ratio,mass ratio and reduced velocity.The mass ratio affects the wake vortex distribution,the reduced velocity affects the wake vortex strength,and the radius ratio affects the wake width.Finally,the energy capture power and energy conversion efficiency of the non-circular cross-section Elli-circ oscillator are compared and analyzed in detail.The results show that when the reduced velocity Ur<5,the energy conversion efficiency of the Elli-circ cross-section oscillator is the best among the elliptical,Elli-circ cross-section and circular cross-section oscillators,indicating that the Elli-circ cross-section oscillator is more suitable for power generation in extremely low flow rate sea areas.The energy harvesting power of the Elli-circ cross-section oscillator decreases with the increase of the radius ratio,and the energy harvesting power of the semi-elliptical semi-circular oscillator with mass ratio m~*=1.182 is higher.The energy conversion efficiency curve increases first and then decreases with the increase of the reduced velocity.As the radius ratio increases,the reduced velocity corresponding to the maximum energy conversion efficiency gradually decreases,and the optimal reduced velocity is mainly concentrated in the range of Ur∈(4.3,5.7). |
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