Abstract
In order to study the nonlinear characteristics of self-excited aerodynamic forces of bluff body bridge section with the change of motion parameters, a numerical wind tunnel is established by the dynamic mesh technique of computational fluid dynamics (CFD). A state-by-state forced vibration method is used to identify the self-excited aerodynamic forces of single degree-of-freedom (DOF) heaving and pitching motion. Fast Fourier transform (FFT) is adopted to obtain frequency-domain data for analysis. The reliability of the obtained aerodynamic results is verified by wind tunnel tests. The results show that the high-order harmonic components are found in the self-excited aerodynamic forces of semiclosed box deck section, which are more significant in aerodynamic lift than in aerodynamic moment. The proportion of aerodynamic nonlinear components increases with amplitude. The effect of amplitude on the nonlinear components of heaving motion is generally higher than that of pitching motion, and aerodynamic moment is highly sensitive to the increase of vertical amplitude. The variation of the nonlinear components of the deck section with frequency is not a simple monotonic relationship, and there is a stationary point at 10 Hz frequency. The existence of wind attack angle makes the proportion of nonlinear components reach more than 30% and greatly increases the proportion of second harmonic. In addition, the high-order harmonic components, which are not integer multiples, are found at large amplitude and positive angle of attack.
Highlights
In recent years, with the progress of engineering technology, the bridge has developed in the direction of large span, light weight, and flexibility [1]
In 1935, for the need of studying wing flutter, eodorson and Mutchler [3] derived an analytical expression of flutter self-excited force for an ideal plate. e current bridge flutter analysis is based on the linear unsteady self-excited force model proposed by Scanlan and Tomko [4]. e self-excited force model is based on the assumption of linear and small amplitude motion and ignores the influence of bridge aerodynamic shape of the bluff body and other factors such as amplitude, frequency, and wind attack angle
Bridge deck sections are bluff bodies, and their self-excited aerodynamic forces inevitably have nonlinear characteristics [5,6,7,8,9,10]. e nonlinear effect of the self-excited force causes an oscillation phenomenon called Limit Cycle Oscillation (LCO) [5, 11, 12] with lower starting wind speed and constant amplitude oscillations range. e LCO phenomenon cannot be explained by the above classical flutter self-excited force model. e nonlinear components of self-excited aerodynamic forces of deck sections can affect the applicability of Scanlan’s linear model and possibly cause an unsafe deviation of flutter critical wind speed based on the linear theory
Summary
Received 6 October 2021; Revised 9 December 2021; Accepted 23 December 2021; Published 4 January 2022. In order to study the nonlinear characteristics of self-excited aerodynamic forces of bluff body bridge section with the change of motion parameters, a numerical wind tunnel is established by the dynamic mesh technique of computational fluid dynamics (CFD). E results show that the high-order harmonic components are found in the self-excited aerodynamic forces of semiclosed box deck section, which are more significant in aerodynamic lift than in aerodynamic moment. E effect of amplitude on the nonlinear components of heaving motion is generally higher than that of pitching motion, and aerodynamic moment is highly sensitive to the increase of vertical amplitude. E existence of wind attack angle makes the proportion of nonlinear components reach more than 30% and greatly increases the proportion of second harmonic. The high-order harmonic components, which are not integer multiples, are found at large amplitude and positive angle of attack
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