| With the continuous increase of the span of the suspension bridge,its fundamental frequency is getting smaller and smaller,as well as the stiffness and damping of the structure.At the same time,the frequency distribution of the vertical modes of suspension bridge is dense,and the problem of multimode vertical vortex-induced vibration is prone to occur under frequent wind speeds.In 2020,many iconic suspension bridges such as Humen Bridge and Xihoumen Bridge experienced multi-mode vertical vortex-induced vibration.Therefore,the phenomenon of multi-mode vertical vortex-induced vibration is widely concerned.However,the commonly used aerodynamic measures and TMD are difficult to effectively control the multi-mode vertical vortexinduced vibration,so the effective control of the multi-mode vertical vortexinduced vibration is an urgent problem to be solved.In this paper,the damping and vibration reduction problem of multi-mode vertical vortexinduced vibration is studied,the control scheme using direct energy dissipation damper is proposed and the optimization problem of damper parameters is studied.A control scheme using direct energy dissipation dampers was proposed and the damper parameter optimization research was carried out.The main research contents and conclusions of this paper are as follows:(1)This paper briefly expounds the mechanical properties of suspension bridges,The development history of suspension Bridges at home and abroad,the research status of wind-induced vibration of bridge structures and the research progress of bridge vibration control measures are summarized,and the research content and technical route of this paper are proposed.(2)The problem of multi-mode vertical vortex-induced vibration of suspension bridge is briefly introduced,and the difficulties of aerodynamic measures and tuned mass dampers(TMD)scheme in controlling multi-mode vertical vortex-induced vibration of long-span suspension Bridges are analyzed,and the use of direct energy dissipation damping is proposed.Three kinds of direct energy dissipation dampers scheme are proposed,namely,the scheme of setting the damper on the outrigger of the bridge tower,the scheme of connecting the damper with diagonal braces at the lower part of the bridge tower,and the scheme of connecting the damper with the cable at the lower part of the bridge tower.(3)Numerical analysis of the vibration reduction effect and influencing parameters of the direct energy damper is carried out,and the vibration reduction effect of the three kinds of dampers are compared.Taking the Parrot Island Bridge as the research object,the finite element model of the whole bridge was established by ANSYS finite element software,and the modal analysis was carried out on the finite element model of the Parrot Island Bridge,and three kinds of damper vibration reduction schemes are simulated.Based on the complex modal analysis method,the additional damping ratio of each vertical mode of the structure is calculated by three kinds of damper arrangement,namely,the damper on the outrigger of the bridge tower,the damper connected with the diagonal braces at the lower part of the bridge tower,and the damper connected with the cable at the lower part of the bridge tower.After the analysis,it is concluded that the additional modal damping ratio increases first and then decreases with the increase of the damping coefficient for each order vertical bending mode,and each order mode has the maximum modal damping ratio and optimal damping coefficient;After the parameter analysis,it is concluded that the maximum additional modal damping ratio gradually increases and the optimal damping coefficient decreases gradually as the installation position increases gradually(but does not exceed the maximum displacement of the mode shape),and the optimal damping coefficient gradually decreases;After the parametric analysis,it is concluded that the maximum additional modal damping ratio decreases gradually with the increase of the stiffness coefficient of the vertical bending modal damping ratio of each order.Finally,several optimal parameter selection methods are given for practical engineering reference.(4)The shortcomings of traditional viscous dampers are expounded and a scheme of using eddy current dampers is proposed;COMSOL finite element software is used to simulate a tubular eddy current damper applied to the fullbridge aeroelastic model test,and the Various variables(mesh accuracy,copper magnetic gap,presence and size of magnetic tube,size of conductor tube,size of permanent magnet and pure iron,relative motion speed of permanent magnet and conductor tube,and block size of permanent magnet number)were analyzed.The eddy current damper simulated by COMSOL is processed,and a single-degree-of-freedom frame structure is designed to test the damping coefficient of the eddy current damper with different numbers of permanent magnet blocks.The test results verify the correctness of the finite element simulation.(5)Based on the full-bridge aeroelastic model of a typical single-span suspension bridge,using the small circular tube eddy current damper prototype designed and manufactured in the previous chapter,through the free vibration test and the model wind tunnel test,the additional modal damping ratio and the vibration response are reduced.The vibration rate of the two indicators was used to evaluate the control effect of the damper on the multiorder vertical vortex vibration of the suspension bridge.In the free vibration test,it is concluded that the additional damping ratio provided by the damper to the structure increases with the increase of the installation distance and the damping coefficient,and it is found that the damping ratio of the structure has nonlinear characteristics,and the damping ratio of the structure decreases with the amplitude.When the amplitude is smaller than a certain value,the damping ratio does not change;in the wind-induced vibration test,it is found that with the increase of the installation distance of the damper,the vibration reduction rate gradually increases,and the maximum vibration reduction rate for the first symmetrical vertical mode and the second antisymmetric vertical mode under test conditions 72.3% and 76%,respectively.The correctness of the finite element simulation law and the effectiveness of the direct energy dissipation damper on the multi-mode vertical vortex-induced vibration control of the suspension bridge are verified. |
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