Analysis On Fluid Dynamic And Modal Of Large Underwater Air Storage Container

With the change of energy structure,renewable energy is playing an unprecedented important role.However,the inherent "intermittent","random" and "low energy density"characteristics of renewable energy greatly hinder its efficient and reliable utilization.There is a serious imbalance between the fluctuating power generated by renewable energy and the fluctuating power load.Energy storage technology is one of the most effective ways to solve this imbalance problem.Underwater compressed air energy storage technology is a large-scale renewable energy storage technology suitable for construction in coastal areas,islands,marine platforms and other areas.By storing compressed air in the underwater container,the pressure of sea water can be used to ensure that the pressure in the container is relatively constant,but Under the influence of complex current,it is necessary to carry out hydrodynamic analysis and modal analysis to ensure the safety and reliability of the container.The main research contents of this paper are as follows:1.In the marine environment,the structure failure of container is easily caused by the influence of current(1)Based on the CFD method and previous experimental results,the accuracy and applicability of LES and k-? SST Turbulence model,parameter setting and solution setting are verified to ensure the high reliability of numerical simulation results.Compared with the experimental results,LES method shows better simulation accuracy in general,and the calculation results of convection field shape and velocity are more accurate.Therefore,LES method is selected for numerical simulation of container.(2)By controlling the variables,the models of spherical top and flat top were established.Based on the LES method,the effects of different end shapes of container on the flow field were studied.The research contents include the influence characteristics of the end shapes of cylinder with the AR7 and underwater container.The results show that the spherical top structure of the container can restrain the backflow near the top of it,avoid the formation and disturbance of velocity concentration and small vortices near the end,and can effectively use the downwash flow to disturb the regular formation and fall off of the lateral vortices,but it should be avoided to be installed in the soft area of the seabed so as not to change the installatio n position of the container due to the impact of the downwash flow on the sediment.(3)Based on the LES method,the numerical simulation of the flow around the container in the marine environment with different velocity is carried out.Through the monitoring of the time average velocity components,velocity vector,vorticity and other physical quantities in each direction of the convection field,the flow pattern characteristics and change rules of the wake flow field after the container is passed are compared and analyzed.The analysis results show that the characteristics of the flow field formed after passing through the container are similar,and the value of the characteristic velocity is related to the range of the special watershed and the current velocity with different velocity.The vortex formed around the flow has obvious three-dimensional structure characteristics,including the vortex gradually twisted to the bottom near the leeward side of the container and the vortex symmetrically distributed in the flow field near the leeward side.The vortex formed laterally begins to fall off near the center 2 times of the diameter of the container,and changes in lift coefficient,velocity vector and vorticity in the cross flow direction The results show that the period of vortex shedding is about 100s,which will cause low-frequency disturbance to the container.(4)This paper studies the characteristics of the fluid forces on the container in different marine environments.Through the comparative analysis of the lift and drag coefficients and their variation rules under various working conditions,the lift and drag coefficients of the container are 0.60 and 0.45 respectively,which can be used to calculate the fluid forces on the container in the marine environment with different velocity.(5)The material,pipeline structure and wall thickness are taken as variables to carry out the modal analysis of the container.In the low-order mode,the main deformation area of the container is at the top,the shape variable is in the range 1.9?3.6mm,in the high-order mode,the deformation position is at the side waist of the container,and the shape variable is in the range2.7?5.0mm.The natural frequencies of containers with different materials vary greatly from 30Hz to 50Hzs and the natural.frequencies are 32Hz after pipeline optimization.The natural frequencies of containers with different wall thickness vary little,and the vibration frequencies of each stage are far greater than the vortex shedding frequency,so the risk of vortex induced vibration is low.With the increase of wall thickness,the maximum shape variable decreases,and the natural frequency increases with the increase of wall thickness,which shows that the stronger the overall structural strength of the container,the smaller the shape variable of free vibration,and the higher the natural frequency.The obtained results clearly describe the basic hydrodynamic and structural characteristics of the underwater container in the complex marine environment,which can provide a theoretical basis for the design and optimization of the container.