Aerodynamic Load And Nonlinear Aerodynamic Parameter Identification For A Rectangular Cross Section Model In Wind Induced Vibration

Large vortex-induced resonance occurs when a blunt body is placed in a wind field,excessive amplitude will cause fatigue even securty problems to the structure.As the long-span flexible Bridges,especially suspension Bridges,become gentler and gentler,the vortex-induced resonance phenomenon becomes more prominent,which hinder the development of bridge span.Therefore,it has become a concern of scholars to further understand the internal mechanism of vortex-induced resonance,including identifying the variation process of various parameters during the occur rence of vortex-induced resonance and analyzing its influence.In this paper,only the vertical vibration of a rectangular sectional model is taken as the background.Research has been conducted on the identification of aerodynamic forces and corresponding system parameters,mainly including the following aspects:(1)The current researches status of vortex-induced resonance parameter identification is introduced.Fristly,the paper introduces the basic parameters of vortex-vibration structure including stiffness,damping and aerodynamic force.Then,it introduces the main existing parameters identification methods in vortex-vibration.Also,the research status of structural nonlinear aerodynamic force is introduced.(2)The vortex-vibration tests of rectangular section with different conditions is carried on wind engineering research center of Hunan University HD-2 large-scale boundary layer wind tunnel.The vortex-vibration law of the structure under different conditions is obtained.Moreover,under windless condition,the relation between the damping and the vibration amplitude is further analyzed with system free dcresed curve.(3)On the basis of EKF-UI method,the identification method of system parameters under vertical vortexes is improved.Numerical a nalysis is used to analyze the applicability of EKF-UI method to the vortex-vibration parameter identification of single-degree-of-freedom system(SDOF),which improved the disadvantage that the existing EKF-UI method could not be applied to SDOF systems.M oreover,it is extended to the identification of aerodynamic force in nonlinear vortexed-induced vibration,which solves the problem that it is difficult to identify aerodynamic force by conventional methods.(4)The real time stiffness and damping under different experimental conditions are identified.Firstly,the influence of aerodynamic stiffness and damping on the original stiffness and damping are introduced.The improved EKF-UI method is applied to the identification of various parameters such as the stiffness and damping under different experimental conditions.The results of parameters under different turbulence and the initial damping operating conditions are compared.(5)The characteristics of nonlinear aerodynamic force of the structure under large vortex-induced resonance are analyzed.Based on large vortex-induced resonance vibration can be analogy in harmonic vibration,high-order nonlinear aerodynamic force can be carried out by the first order harmonic motion synthesis.By adjusting the order of nonlinear aerodynamic parameter,the nonlinear aerodynamic force on aerodynamic force can be identified,and the pure aerodynamic force of structure is obtained.(6)The structural frequency and variation at the end of vortex-induced vibration are studied in detail.The mechanism of how the system jumps out of the lock-in state around the critical wind speed is meticulously discussed.