This study presents an unscented Kalman filter (UKF) approach for identification of linear or nonlinear flutter derivatives (FDs) of bridge decks from free vibration or buffeting response time history. The nonlinear F...
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This study presents an unscented Kalman filter (UKF) approach for identification of linear or nonlinear flutter derivatives (FDs) of bridge decks from free vibration or buffeting response time history. The nonlinear FDs, which are dependent on torsional vibration amplitude, are represented in polynomial functions of torsional displacement. The augmented state variables of the two degrees of freedom (2DOF) bridge deck system, which include bridge deck motions and unknown FDs, are estimated simultaneously with the UKF approach based on response measurement data. Firstly, the steady-state vortex-induced vibration and flutter of a streamlined bridge deck section are used to illustrate the performance of UKF approach in extracting nonlinear FDs. The equivalent linear FDs are also identified from the same response data which reveals the deficiency of the linear model. Secondly, the stochastic buffeting responses of the bridge deck contributed from two modal responses with linear FDs are generated, and the performance of UKF approach with unknown excitations is examined. It is pointed out that the buffeting response must be separated into two modal response components, such that the unknown buffeting force excitations identification of FDs.
This study presents a multimode coupled nonlinearflutter analysis method for long-span bridges with consideration of vibration-amplitude-dependent flutterderivatives. By converting the equation of motion into a comp...
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This study presents a multimode coupled nonlinearflutter analysis method for long-span bridges with consideration of vibration-amplitude-dependent flutterderivatives. By converting the equation of motion into a complex eigenvalue problem, a double layer iterative method (DLIM) is proposed to determine the real iterative frequency as well as the participation of each structural mode shape to the flutter response for a given wind speed and vibration amplitude. The accuracy of the proposed scheme is cross-validated with a classical bimodal analysis method. Two suspension bridges, characterized by a soft type and a hard type nonlinearflutter, respectively, are used to examine the performance of the proposed method. Modal properties (i.e., damping ratio and frequency), as functions of wind speed and vibration amplitude, can be estimated such that the nonlinearflutter response including the critical wind speed and vibration amplitude can be accurately quantified. At last, the coupling effect among different structural modes and its further influence on the genesis and evolution of the nonlinearflutter are also discussed. (c) 2021 Elsevier Ltd. All rights reserved.
The nonlinearflutter of a narrow railway truss girder are studied through free vibration and forced vibration wind tunnel tests. Four functions are used to fit the structural amplitude-varying damping ratio under no ...
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The nonlinearflutter of a narrow railway truss girder are studied through free vibration and forced vibration wind tunnel tests. Four functions are used to fit the structural amplitude-varying damping ratio under no wind condition, and the fourth-order polynomial has higher goodness-of-fit. The narrow truss girder shows nonlinearflutter of a velocity-restricted type without amplitude hysteresis. At large angles of attack (AoA), the vertical participation and the AoA have little effect on the onset wind speed and amplitude. While at medium AoAs, even a low vertical participation level will increase the onset wind speed and decrease the amplitude. At small AoAs, there is no vibration observed. The flutter derivative A2* is positive only in the limited reduced wind speed and amplitude range. The nonlinearity of self-excited lifting moment is higher only in the limited reduced wind speed and amplitude range, while that of self-excited lift is weaker and becomes stronger with the increasing amplitude and reduced wind speed. The negative aerodynamic damping is mainly provided by the flutter derivative A2* at small or large AoAs. Generally, the nonlinearflutter response is mainly controlled by the first-order component of the self-excited force, and the influence of high-order components can be ignored.
The flutter performance of a streamlined box girder under different external excitations is experimentally examined in this study using a free-vibration wind tunnel test of a section model. The dependence of the criti...
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The flutter performance of a streamlined box girder under different external excitations is experimentally examined in this study using a free-vibration wind tunnel test of a section model. The dependence of the critical wind speed on the initial torsional amplitude is observed in the test. The nonlinear flutter derivatives as functions of the reduced wind speed and vibration amplitude are then identified using a forced-vibration wind tunnel test. The results reveal the close relationship of the torsional-motion-related flutterderivatives with the nonlinearity emerged in the flutter of the girder. The mechanisms leading to the dependence of the flutter response and critical wind speed on initial conditions is investigated through a flutter analysis in which the modal properties are expressed as functions of the wind speed and amplitude. The results indicate that the uncoupled aerodynamic negative damping plays an important role in weakening the flutter performance of the girder. Finally, the influences of the modal coupling effect and the spanwise variation of the self-excited forces (or equivalently, the flutterderivatives) on the modal properties and the flutter performance of a full bridge are discussed. The results show that the modal frequency of the full bridge is mainly affected by the spanwise variation of the nonlinear flutter derivatives, while the modal damping ratio (or equivalently, the critical wind speed) is affected by both the spanwise variation of the nonlinear flutter derivatives and the mode coupling effect.
This paper presents a comprehensive study of nonlinearflutter characteristics of a bridge deck section through free vibration wind tunnel testing and theoretical analysis. The section model is spring-supported in a s...
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This paper presents a comprehensive study of nonlinearflutter characteristics of a bridge deck section through free vibration wind tunnel testing and theoretical analysis. The section model is spring-supported in a single degree of freedom (SDOF) in torsion and 2DOFs in both vertical direction and torsion, respectively. The amplitude-dependent aerodynamic damping and other response characteristics are determined through use of Hilbert Transform of response time histories at different wind speed of smooth flow. An approach is proposed to extract flutterderivatives as nonlinear functions of amplitude of torsional motion at various reduced wind speeds. The flutterderivatives are then used to estimate the nonlinearflutter response of bridge section and a prototype suspension bridge with a main span length of 1700 m. The results showed that the magnitude of negative aerodynamic damping increases with increasing wind speed but decreases with vibration amplitude. The flutter of this bridge example is initialed from torsion but the coupled vertical motion further generates negative damping, thus reduces the flutter onset wind speed and increase the vibration amplitude. The estimation using three-dimensional bridge model with coupled vertical and torsional modal responses leads to increase in flutter onset wind speed and decrease in flutter amplitude as compared to section model estimation.
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