Wind Induced Buffeting Characteristics And MTMD Control Method Of Long-span Cantilevered Sightseeing Platform

This paper based on the engineering background of a long-span cantilever landscape platform adopts the time-domain analysis method of buffeting response to model and analyze the structure by finite element analysis software ANSYS and uses the improved harmonic synthesis method to simulate the fluctuating wind field to calculate the three-dimensional buffeting response of the structure.The statistical characteristics of various responses（buffeting displacement,buffeting stress,cable force）under different angles of attack and wind deflection are concluded,and the influence of resonance components on wind-induced buffeting response is evaluated.At the same time,the buffeting response analysis of Guanshan corridor bridge establishes the goal of MTMD vibration reduction control.MTMD parameters are optimized by using H₂method in robust control theory,which has achieved a better effect of suppressing bridge buffeting.It mainly includes the following contents:1.The time-domain expression formula of self-excited force with higher accuracy in bridge engineering is obtained.The steps and theoretical basis of bridge buffeting time domain analysis are introduced,and the buffeting force time domain calculation formula studied in this paper is given.2.This paper expounds the basic theory of computational fluid dynamics（CFD）,uses Fluent software to conduct two-dimensional and three-dimensional unsteady numerical simulation of Guanshan covered bridge,and conducts rigid body force measurement wind tunnel test,obtains the aerodynamic coefficient of the section and the surrounding flow field information,finds that there are multiple main vortices around the section of Guanshan covered bridge,and the resistance,lift and lifting moment coefficients of the section of the covered bridge are larger than those of the general streamlined box girder.With the change of wind deflection angle,the site model has a more obvious influence on the wind field of the whole force measuring model.The three component coefficients obtained from the rigid body force measuring wind tunnel test are closer to the three-dimensional CFD calculation results.3.The finite element analysis software ANSYS is used to model the structure and conduct modal analysis.The improved harmonic synthesis method is used to simulate the fluctuating wind field at the bridge site considering the space-time correlation.The three-dimensional buffeting response of Guanshan Langqiao viewing platform under the fluctuating wind field is calculated.The statistical characteristics of various responses（buffeting displacement,buffeting stress,cable force）are obtained.It is found that the angle of attack has a significant impact on the buffeting displacement and internal force of the structure.Cable forces may be reduced to zero during buffeting,which may cause instantaneous failure of cable support to the girder.However,the probability of cable force failure during bridge buffeting is not large and the load of the girder can still be borne by the adjacent cables after failure.The maximum displacement of the node considering the resonance response can reach 3 times of the background response,and the maximum internal force of the node can reach 2.2 times of the background response,which will greatly overestimate the ultimate bearing capacity of the structure,therefore,the influence of resonance response must be taken into account in the design to ensure safety.4.The system equation of bridge structure with MTMD under buffeting force load is derived.The layout of MTMD is determined based on wavelet transform theory.MTMD parameter optimization and control effect based on H₂method are analyzed through numerical simulation.The results show that H₂optimization scheme can effectively suppress buffeting displacement of the bridge.The vibration suppression effect of MTMD controlling bridge multi order buffeting is better than that of MTMD controlling bridge single order buffeting response,and the stroke of the inertia mass of each TMD is less than the single order buffeting response of the bridge controlled by MTMD.