Wake Interference Effect And Aerodynamic Measures Of Tandem Double Cables

As the key component of long-span bridge structure,there are often multiple cables arranged adjacently in practical engineering,such as cable-stayed bridge cables,suspension bridge slings and suspension bridge tandem double main cable.When the two structures are arranged in tandem in the fluid,the downstream structure is significantly affected by the wake of the upstream structure.At present,the sectional model wind tunnel test is the main means to study the aerodynamic interference of the cable structure.It is often limited by objective conditions such as wind tunnel size and test wind speed.The test is often carried out with a smaller scale model,resulting in a series of test parameters including Reynolds number.There are differences with the actual bridge situation,which may lead to deviations between the wind tunnel test results and the actual situation.At the same time,the research mainly uses free vibration to study the wake interference effect,and lacks the exploration and research on the wake interference effect under various forced motion forms.In order to study the difference caused by the scale model of wind tunnel test and explore the wake interference effect under forced vibration,the influence of Reynolds number on the wake interference effect of the segment model is studied by changing the scale ratio of the model.Combined with the forced vibration test,the wake interference effect under various amplitude and frequency conversion motions is analyzed,and finally the vibration reduction effect of various aerodynamic measures on the structure is compared.The main work and conclusions of this paper are as follows:(1)Based on the similarity theory and similarity criterion of segment model,the main influencing factors affecting the wake interference test of rigid segment model of main cable are summarized and analyzed.The finite element modeling and dynamic calculation are completed and the design parameters of segment model are determined.The wind tunnel test conditions,data acquisition system,forced vibration device and the identification principle and method of nonlinear characteristics of elastic suspension system are introduced,and the nonlinear characteristics of elastic suspension system in this paper are tested.(2)The free vibration test of tandem cylinders was carried out in subcritical,critical and supercritical Reynolds number ranges.The difference of test results in different Reynolds number ranges was explored,and the influence of three-dimensional effect of airflow under wind yaw angle on the test was considered.The results show that the critical wind speed of the downstream cylinder is the lowest at the critical Reynolds number,and the subcritical Reynolds number is the highest.At the same time,the center distance between the cylinders corresponding to the vibration is the smallest at the supercritical Reynolds number and the largest at the subcritical Reynolds number.The structural vibration response is the smallest under the sub-critical state.the potential vibration risk of the upstream cylinder in the critical Reynolds number range will lead to the wake galloping divergence of the downstream cylinder.In the supercritical Reynolds number range,the upstream and downstream cylinders are significantly affected by the wind yaw angle.The downstream cylinder will experience a continuous wake vortex-galloping phenomenon at multiple center distances,or promote a more severe large-scale vibration phenomenon of the whole structure.(3)The forced vibration device is used to analyze the forced vibration of the tandem cylinder,and the aerodynamic interference effects of the upstream cylinder static,amplitude and variable frequency motion on the downstream cylinder are studied respectively.The analysis results show that there are strong and weak coupling modes between tandem cylinders,and different coupling modes appear alternately with the change of Reynolds number.The process of strong coupling to weak coupling is reversible,and there is also a process of direct transition from weak coupling mode to complete coupling mode.The large amplitude vibration of the downstream cylinder occurs when the upstream forced vibration f_f/f_n is 1-1.13.The amplitude gradually decreases with the increase and decrease of the forced vibration frequency.There is a significant locking relationship between the crosswind vibration frequency and the forced vibration frequency of the upstream structure.The phase difference decreases first and then increases with the increase of the vibration frequency,especially in the process of f_f/f_n from 1-1.1.The motion trajectory under the action of wake interference will present various forms.(4)The aerodynamic control measures of tandem cylinders are assembled,and the wind tunnel tests of aerodynamic vibration reduction of tandem main cables under free vibration and forced vibration are carried out respectively.The results show that the winding spiral line and the added surface roughness will not increase the amplitude of the upstream cylinder in the subcritical Reynolds number test,and the vibration reduction effect on the downstream cylinder is significant.However,there is a potential risk of wake-induced vibration in the supercritical Reynolds number test.At the same time,the maintenance lane of the main cable in the bridge state is considered to be a more unfavorable aerodynamic shape,which will cause a significant reduction in the starting wind speed of wake galloping.