桥梁断面几种气动导纳模型的合理性剖析

Rationality analysis of some existing aerodynamic admittance models for bridge deck sections

首先介绍非定常运动状态下的薄机翼的升力产生机制,机翼的相对运动速度用一系列固定分布模态表达成一种级数形式的广义模式。在这些速度分布模式中包括有平动模式、转动模式以及其他高阶的非线性模式。与此相对应,机翼所受的非定常升力也可根据环量理论求解成一种广义模式。由于所有频率特性的脉动风均可采用Bessel函数展开成广义形式,因而这一类方法直接得出机翼气动导纳的表达式。目前,桥梁风致抖振计算中几种应用较广的气动导纳模型均与机翼理论有关,该文的主要目标是通过对机翼理论的回顾,剖析桥梁风工程中气动导纳模型的合理性与所存在问题的根源。分析表明,任何试图通过气动导数求出气动导纳的方法都是在逻辑上不正确的。通过气动导纳的本质特征的分析,对试验测试钝体桥梁断面气动导纳的方法提出一些建议。

This paper reviewed the thin airfoil non-stationary lift producing mechanism, where the non-uniform motion is expressed in a general form composed of a series of relative vertical velocity distribution modes. These modes, including rigid translation, rotation, and other nonlinear high-order modes, result in a general form of the non-stationary lift, according to the theory of circulation. The aerodynamic admittance formula of an airfoil can be derived directly from this general form because fluctuation wind of any frequency can be expressed in a general form by Bessel functions. Currently, most adopted aerodynamic admittance models in bridge engineering are related to airfoil theory. The main purposes of this paper are, through the review of the thin airfoil theory, to point out problems existing in these models. The analysis results indicate that, any attempt of determining the aerodynamic admittance via flutter derivatives is logically incorrect. By analyzing the substantive characteristics of aerodynamic admittances, some suggestions with respect to aerodynamic admittance experimental methods for bluff bridge sections, are presented.