| With the gradual consumption of traditional energy and the enhancement of awareness of carbon emissions,the development of renewable energy has been paid more and more attention by countries all over the world.the capture of low-speed ocean current energy or river energy based on vortex-induced vibration has become a new choice for the use of clean renewable energy.In this paper,aiming at the rigid cylinder as the energy capture structure,the three-dimensional vortex-induced vibration of the energy capture structure in the low speed flow environment is simulated by the fluid-solid coupling numerical method,and the energy capture and energy capture efficiency of the energy capture structure are analyzed in the range of resonance reduction velocity(U_r=2～12).In order to obtain the effect of three-dimensional wake on the capture energy of energy trapping structure,the relationship between capture energy and wake dissipation under different vibration branches is explored.The entropy generation theory and wake characteristics are used to capture the energy loss source and distribution of the trapping structure wake vortex.In view of the low energy conversion efficiency of single cylindrical vortex-induced vibration energy capture device,genetic algorithm is used to optimize the array arrangement of multi-cylinder vortex-induced vibration energy capture device to improve the power generation efficiency of the array device.The main research includes the following areas:(1)Three-dimensional wake analysis of vortex-induced vibration energy capture device for a single cylinder.The self-defined function(UDF)method is used to simulate the bi-directional fluid-solid coupling of cylindrical vortex-induced vibration.the results show that the amplitude and frequency response of vortex-induced vibration is close to the experimental results under the three-dimensional effect,and the directional vortex of the trapping structure wake has a stronger control effect on the directional vortex with the increase of the reduced velocity.With the increase of the amplitude,the transverse width of the shedding vortex in the wake area will become larger,and the wake vortex model will change from the 2S mode of the initial branch to the 2P and P+T mode of the upper branch,enter the lower branch and develop into the P+S model.In this process,the tip effect of the wake becomes more and more obvious in the three-dimensional state.(2)In the energy capture analysis of three-dimensional cylindrical vortex-induced vibration,the energy loss is analyzed based on the entropy production theory,and the energy dissipation trend of the energy capture structure is accurately captured.The results show that with the increase of reduction rate,the maximum energy capture efficiency of the energy conversion device reaches 30.5%when U_r=6is in the upper branch.The viscous entropy production mainly occurs on the cylinder surface,and the turbulent entropy occurs in the wake region with large dissipation rate.with the increase of captured hydrokinetic energy,the viscous entropy loss on the cylinder surface and the turbulent entropy production loss around the cylinder and in the wake region also increases.the viscous entropy production loss on the surface of the energy trapping structure and the turbulent entropy production loss in the wake region are the main reasons for the decrease of energy capture efficiency.(3)Optimization of array arrangement of multi-cylinder vortex-induced vibration energy capture device.The mathematical model of optimal arrangement of multi-cylindrical array aiming at energy capture is adopted for the first time,and the model is calculated and analyzed by genetic algorithm.The results show that genetic algorithm can effectively optimize the arrangement of multi-cylindrical energy capture device array.The optimized arrangement enhances the interaction between the devices in the array,and significantly improves the power generation efficiency of the multi-cylindrical vortex-induced vibration energy capture device array. |
