Research On Hydrodynamic Characteristics And Energy Capture Effects Of Energy Capture Devices Under Free Surfac

In most sea areas of the world,the flow velocity is concentrated at 0.4m/s-1.5m/s,and the flow velocity is low,so the conventional underwater turbine generator can’t extract the energy in the low-speed water flow,so it is a new choice to drive the low-speed water flow to capture energy based on vortex-induced vibration.At present,most scholars focus on the study of vortex-induced vibration energy capture in single-phase low-speed current environment,ignoring the influence of different arrangement depths under free surface on energy capture structure in actual current environment.In this paper,the vortex-induced vibration of a single cylinder and rigid coupled columns with different arrangement depth ratios is studied,and the influence of free surface on the hydrodynamic characteristics and energy harvesting of energy harvesting devices is discussed.The research results and work are as follows:(1)A two-way fluid-solid coupled vortex-induced vibration numerical model based on UDF is established,and a multiphase flow(VOF)model is added to realize high-precision and high-efficiency numerical simulation of vortex-induced vibration of free surface.The motion law and energy harvesting characteristics of the energy harvesting device under the free surface are obtained.(2)The vortex-induced vibration response and hydrodynamic characteristics of single cylindrical energy-harvesting structures with different arrangement depth ratios under free surface are studied.The amplitude ratio and frequency ratio under different arrangement depth ratios are compared,and the flow field characteristics of low arrangement depth ratio and high arrangement depth ratio are analyzed.The results show that the maximum amplitude ratio and response range of vortex-induced vibration response of a single cylinder with low arrangement depth ratio are smaller than those with high arrangement depth ratio.At the same time,it is found that the smaller the layout depth ratio is,the greater the influence of free surface is.(3)The shedding vortex coupling between columns with rigid coupling column group structure is stronger,and the energy harvesting effect is better than that of single columns with equal volume.The results show that the maximum amplitude ratio of rigid coupled columns is higher than that of single cylinder,and the deviation degree of structural frequency ratio of columns with reduction speed is smaller than that of single cylinder,and the response range is wider than that of single cylinder.The shedding vortex coupling between columns with rigid coupling column group structure is stronger,and the energy harvesting effect is better than that of single columns with equal volume.(4)The optimal layout depth ratio of rigid coupled columns on free surface is studied.By analyzing the hydrodynamic characteristics and energy capture results of rigid coupled column group structures with different arrangement depth ratios,it is found that the structural response and energy capture are obviously affected by free surface deformation at low arrangement depth ratios,and the vortex-induced vibration response and energy capture are consistent with those in single-phase flow when the arrangement depth ratio S~*≥5.