Experiment And Mechanism Research On Vortex Vibration Suppression Of Double Side Box Type Π Section

In recent years,Π section is widely used in bridge construction,especially in cable-stayed bridge.Although the Π section has the advantages of reasonable stress,convenient construction and high economy,it is also very sensitive to the wind,especially the vortex induced vibration,so it often needs some vibration suppression measures to improve its aerodynamic performance.Aerodynamic measures can change the flow field around the section by changing the section shape,so then improve the aerodynamic performance of the section at the root.A lot of expert has been researching on the aerodynamic measures of Π section,however,the aerodynamic measures are particularly sensitive to the cross-section shape,a little difference may cause dramatic changes in the vortex vibration performance.Therefore,by mastering the vibration suppression mechanism of various aerodynamic measures,the aerodynamic measures will been used better for vibration suppression control.Therefore,in this paper,based on the combination of synchronous pressure and vibration measurement and numerical wind tunnel technology,the basic vibration suppression test are studied to explain the mechanism of vortex vibration and aerodynamic measures.The main research contents include:(1)In this paper,the basic structural parameters of Π section applied in practical bridge is summarized,and the section model of Π section of typical double side box type with width to height ratio of 10:1 is designed.The results show that the section with width to height ratio of 10:1has obvious phenomenon of the vertical bending and torsional vortex induced vibration.There are two locking intervals and the Strouhal number in the first locking interval about triple the second locking interval.The vertical bending and torsional interval overlap phenomenon is obvious under high wind speed,and their vibration patterns are not independent each other under the overlapping wind speed,but the two vibration patterns not couple into a new vibration form.(2)In view of the obvious vortex induced vibration phenomenon of the section,the corresponding vibration suppression test is studied.First,by changing the mass and damping parameters,the influence of them is analyzed on the vortex response of the section.Under the same mass damping parameters,it is texted that three aerodynamic measures including inverted L-shaped flap,lower central stabilizer and fairing.It is found that the mass and damping have different effects on the vortex response of Π section.The mass can change the starting wind speed and amplitude,while the damping only affects the amplitude.The L-shaped flap has obvious effect on the vertical bending and torsion of cross section.The stabilizer can well inhibit the vertical bending vortex vibration,but intensify the torsion.The results show that the wind angle effect is obvious in the vortex vibration response of fairing suppression.At 0 ° wind attack angle,the vertical bending and torsional vortex vibration of the section are eliminated,while at + 3 ° wind attack angle,the vertical bending vortex vibration is eliminated,but the torsional vortex vibration is intensified.(3)The synchronous pressure and vibration tests are carried out on the original section,the section with the lower central stabilizer and fairing.The surface pressure distribution characteristics of Π section before and after adding aerodynamic measures are compared and analyzed.At the same time,the static flow around the original section,the section with the lower central stabilizer and fairing are analyzed by using CFD technology.It is found that the lower central stabilizer weakens the separation degree of the air flow downstream of the lower surface and suppresses the vertical bending vortex vibration.At the same time,it intensifies the correlation between the aerodynamic force of each measuring point on the upper and lower surface of the middle area of the section and the vortex induced aerodynamic force.Thus intensifies the torsional vortex vibration response.The fairing accelerates the separation of the air flow on the upper surface and the reattachment process of the lower surface.The aerodynamic force of each measuring point on the upper and lower surface are loss of correlation with vortex induced aerodynamic forces,at a result of suppressing vertical and torsional vortex vibrations.