| The Π-shaped section has been favored by designers in the construction of large-span bridges in recent years,but the open bluff body form and the more complicated flow characteristics than the streamlined section make it often unable to meet the design requirements for aerodynamic stability.One of the main constraints is the vortex-induced vibration(VIV)problem,so appropriate vibration suppression measures need to be considered to improve this.Aerodynamic measures,as one of the VIV control technologies,improve the VIV performance of the section by optimizing the aerodynamic shape of the main beam section,which has good applicability.Commonly used aerodynamic measures include fairings,stabilizers,spoilers,deflectors,etc.Among them,systematic research on the vibration suppression effect of the inverted L-shaped deflector on the Π-shaped main girder section is relatively lacking.In order to reduce the blindness of selecting this measure in wind tunnel tests,this paper takes the Π-shaped section as the research object,and combines the synchronous vibration and pressure measurement wind tunnel test and numerical simulation methods to investigate the vibration suppression effect and mechanism of this measure.The main contents include:(1)The development history and application examples of the Π-shaped main girder section are reviewed,and the basic parameters of multiple bridge structures using this type of section are summarized.Based on this,the Π-shaped section with an aspect ratio of 10:1 is designed.The test results show that the section has significant vortex-induced vibration.Both vertical bending and torsion have vortex-locking intervals,and the high-wind speed lock-up interval has overlapped modes.(2)Aiming at the VIV phenomenon of Π-shaped section,the aerodynamic shape is optimized by setting the outer cantilever of different lengths,and the ratio of the cantilever height to the beam height is parameterized as the cantilever extension coefficient.The VIV characteristics of the Π-shaped section under different aerodynamic shapes are studied,and combined with the synchronous vibration and pressure test,the reasons for the influence of the changing aerodynamic shape on the VIV characteristics are analyzed from the perspective of surface pressure distribution.The test results show that the torsional vortex vibration response of the Π-shaped section is more sensitive to the aerodynamic shape,and its torsional amplitude is basically eliminated when the cantilever extension coefficient is greater than 1.(3)By only installing the inverted L-shaped deflector on windward side that can effectively suppress the vibration,it is found that the inverted L-shaped deflector has an effect on the VIV of the main beam mainly on the windward side,while the leeward side has little effect on the VIV response.Research on the vibration suppression effect of different sizes of the inverted L-shaped deflector shows that the horizontal width b of the inverted L-shaped deflector is [0.5D,D],and the vertical skirt length a is [0.33 D,0.5D](a and b cannot take the minimum value at the same time),which can effectively suppress vertical bending and torsional VIV.Further combining the surface pressure test and CFD numerical simulation technology,it is found that the addition of an inverted L-shaped baffle effectively weakens the flow separation between the upper and lower surfaces of the original section,reduces the pulsation value of the separation zone,reduces the periodic pressure difference between the upper and lower surfaces,and destroys the correlation between the local aerodynamic force of the section and the overall aerodynamic force,thereby suppressing the occurrence of vortex-induced vibration. |
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