Study On Aerodynamic Performance And Vortex-induced Vibration Control Of Long-span Suspension Bridge With Separated Double Box Girder Based On CFD

With the increase of the span of suspension bridge,the structure presents the characteristics of small stiffness and low damping,and the problem of wind-induced vibration becomes prominent.As one of the common sections of suspension bridge,the separated double box section has the advantage of effectively improving the flutter performance of the bridge under the condition of high wind speed.However,due to the existence of the central slot,the flow field around the cross-section becomes very complex,which is easy to deteriorate the vortex vibration performance of the bridge under the condition of specific wind speed.based on computational fluid dynamics software Fluent,a large-span suspension bridge is used as the support of the project,and the following research work is carried out :1.The two-dimensional flow field model of the bridge section is established,the three-component force coefficient of the bridge under the static wind is extracted and compared with the test results,and the accuracy of the numerical simulation results is determined.Then,the Reynolds number effect of the three-component force is studied,and the variation law of aerodynamic parameters with Reynolds number is obtained.After that,the influence of the central slot ventilation rate,the height width ratio of the single width box section and the style of the outer wind fairing on the three-component force coefficient of the section is studied,and the law of the aerodynamic parameters changing with various structural parameters is obtained.The main conclusions are as follows:(1)Under the condition of low Reynolds number,the three-component force coefficient is more susceptible to the change of Reynolds number,and the drag coefficient is more sensitive to the Reynolds number than the lift coefficient and torque coefficient;(2)The drag coefficient and lift coefficient of the section increase with the increase of section slotting rate,but the influence of section slotting rate on moment coefficient is not obvious;(3)When H/B≈0.3,the drag coefficient of the section is basically at the minimum value,and the lift coefficient decreases with the increase of H/B,and the change rule of the moment coefficient is opposite to the lift coefficient;(4)Reducing the angle of the wind fairing can reduce the drag coefficient and lift coefficient of the section.2.By combining computational fluid dynamics with Newmark-β method of structural dynamics,the numerical simulation of vortex-induced vibration(VIV)of the separated double box section suspension bridge is carried out.The VIV of the section is calculated and analyzed under specific attack angles and wind speed conditions.From the point of view of the vorticity cloud chart of the flow field,the reason of VIV of the separated double box section is analyzed.The main conclusions are as follows:(1)When the wind angle of attack is 0°,VIV is less likely to occur on the section;(2)The vortex shedding occurs at the central slot and the upper and lower edge of the downstream section,which results in the cross-section vortex induced vibration.3.Based on computational fluid dynamics and Newmark-β method,the control effect of vertical and horizontal stabilizing plates on VIV of cross-section is studied.The VIV of the separated double box section with a stable plate is calculated and analyzed.Compared with the results of the VIV of the prototype section,the control effect of the vibration control measures on the VIV is analyzed.Based on the lift load time history curve and the vorticity cloud chart of the flow field,the vibration control mechanism of the stabilizing plate is analyzed.The main conclusions are as follows:(1)Among the three sections with vertical stabilizing plates,Section with the minimum height of the stabilizing plate has the best control effect on vortex induced vibration,and there is no obvious vortex induced vibration in all working conditions;(2)Among the three sections with transverse stabilizing plates,The section of the upper and lower sides with the stabilizing plates has the best control effect on the vortex induced vibration,and there is no obvious vortex induced vibration in all working conditions;(3)Reasonable aerodynamic measures can effectively limit the generation of vortices,avoid the periodic change of lift load with time,and greatly reduce the lift amplitude on the section.4.Based on the computational fluid dynamics and Newmark-β method,the control effect of the wind fairing structure in the central slot of the section on the VIV of the section is studied.Through the calculation and analysis of VIV of different types of inner air fairings,the design scheme with better control effect of VIV under different wind speed and attack angle is obtained.Then,the mechanism of controlling VIV is analyzed based on the lift load time history curve and vorticity cloud chart.The main conclusions are as follows:(1)The vortex induced vibration is very sensitive to the position and angle of the inner wind fairing of the cross section.According to the different angle of the wind fairing,the control effect of the fairing on the VIV is very different;(2)The two sections with smaller wind fairing angle have the best control effect on VIV,and only slight VIV appears in some conditions.(3)The reasonable inner wind fairing can effectively optimize the force on the section and avoid the vortex shedding.