Study On Suppressing Vortex Induced Vibration Of Cross And Inclined Steel Pipe Members Of Rransmission Towers

In recent years,China’s ultra-high voltage grid has been developed rapidly,and as an important part of the new infrastructure,it is leading the growth of the new economy High and New Technology Projects.Due to the huge structure of the UHV transmission tower lines,in order to reduce the weight of the tower,give full play to the material properties and improve the load-bearing capacity requirements.The steel pipe members with round cross-section are gradually replacing the angle steel members and have been used in large quantities.However,due to the obtuse characteristics of the round cross-section,vortices are formed in the tail flow,and the frequency of shedding of these vortices is similar to that of the self-vibrating round pipe.When the frequencies are close together,they cause vortex vibration.The prolonged existence of Vortex Induced Vibration causes fatigue damage to the round tube nodes,which leads to structural damage.Therefore,reducing the duration and intensity of the vortex vibration becomes an urgent problem to be solved.Vortex vibration control is mainly divided into two categories:active control and passive control,and the passive control is the main research direction of this paper.In this paper,the study is first carried out using a combination of numerical simulation(CFD)and wind tunnel scaling model experiments to discuss a variety of vibration suppressing measures.These measures are divided into the following areas,The numerical simulations first take the calculation accuracy and computational efficiency as the consideration,determine the calculation grid,time step,turbulence model and other pre-conditions;discuss the flow characteristics of the fixed cylinder,and compare with the classical experimental data of the predecessors;simulate the Vortex Induced Vibration of the single cylinder,analyze the vibration mechanism;change the structural mass ratio and damping ratio of the single cylinder,and compare the simulation results with the predecessors,and further discuss the applicability of the improved Griffin formula proposed by the predecessors.Two perturbation measures are considered based on the simulation of single-cylindrical Vortex Induced Vibrations,firstly,the simulation of a single-cylindrical additional circular projection at a corner.(See Fig.3.1 and Fig.3.17 for corner definitions).The passive control measures of the Vortex Induced Vibration of the plate are considered;the simulation of the passive control of the Vortex Induced Vibration of the plate with the length of 0.25D,0.5D,0.75D,1D(D represents the cylindrical diameter)attached at the location is carried out.D,0.5D,0.75D,1D(D stands for cylindrical diameter)and other lengths of plate in Reynolds number 4162～10077 to analyze the suppressing mechanism as well as the flow field characteristics;for the same Reynolds number,a0.5D long simulated The damping effect of the plates atα(28)0 30、60、90、、120 is analyzed for its suppressing mechanism and flow characteristics.On the basis of numerical simulation,this paper carries out an experimental study of wind tunnel in a shrunken steel pipe model.Two mass damping parameters were tested,two length to slenderness ratios of circular pipe vibration,and the experimental results were compared with the simulation;the surface winding of the circular pipe was tested.The vibration response of a single helix,changing the diameter of the helix as well as the pitch of the helix did not achieve the suppressing effect,and in some conditions there were vibration enhancement;tested the arrangement of one-way plate in the center of circular pipe tail flow and found that it can achieve the vibration suppressing effect.Parameter analysis of the arrangement width and length of the one-way plates in the center of the round tube;study of the one-way plates along the cylindrical Uniform arrangement of the development direction,changing the corner,testing ofα(28)0 60、90、three conditionsConsidering the limitations of the previous suppressing measures,an cross-shaped plates arrangement is adopted.Firstly,the cross-shaped plates is arranged in the center of the round tube to test the effect of its arrangement width,and it is found that the cross-shaped plates is the same as the unidirectional plates.Most vibration is suppressed at 12D.Then,test the arrangement of cross-shaped plates diffusing outward from the center,arranged in two sizes W=1D、L_P=0.5D,W=2D、L_P=0.5D(W,plates length,L_P,plates length)of the cross-shaped plates suppressing effect,yielding a The optimal arrangement spacing of the omni-directional plates with dimensions W=1D and L_P=0.5D is 3D,while the best arrangement spacing of the cross-shaped plates with W=2D and L_P=0.5D is 4D.