桥梁结构正弦激振力与阵风激振力非线性相互作用的数值研究
Numerical investigation of the nonlinear interaction between the sinusoidal motion-induced and gust-induced forces acting on bridge decks
摘要：
随着桥梁跨度的不断增大和桥面形状的复杂化，气动非线性成为大跨度桥梁设计中的一个重要问题。本文采用计算流体动力学的涡粒子法（VPM）研究了作用在桥梁上的风振力和运动力之间的非线性相互作用。这种非线性的相互作用是复杂的和棘手的传统的线性半解析模型，采用叠加原理。为了激发这种相互作用，正弦振动桥面受到正弦垂直阵风。研究了两个不同的方面：大尺度正弦垂直阵风对运动物体剪切层的影响和气动力对有效迎角的非线性依赖。对于后者，在正弦阵风和运动引起的相同有效迎角下，比较了基于线性半解析模型和CFD模型的合成气动力。该方法首先验证了平板的线性行为，然后研究了两个桥面的非线性行为。结果表明，线性叠加原理适用于剪切层失稳最小的流线型桥面。然而，该原理可能不适用于非流线型桥面，因为剪切层中存在强烈的分离涡，这会导致通过一次谐波振幅差和高阶谐波出现而表现出的气动力非线性。本研究的结果旨在提供一个复杂的非线性流固耦合发生的钝体运动和自由流阵风更深入的了解。
英文摘要：
With the increasing spans and complex deck shapes, aerodynamic nonlinearity becomes a crucial concern in the design of long-span bridges. This paper investigates the nonlinear interaction between the gust-induced and motion-induced forces acting on bridge decks using the Vortex Particle Method (VPM) as a Computational Fluid Dynamics (CFD) method. This nonlinear interaction is complex and intractable by the conventional linear semi-analytical models that employ the superposition principle. To excite such interaction, a sinusoidally oscillating bridge deck is subjected to sinusoidal vertical gusts. Two distinct aspects are studied: The influence of large-scale sinusoidal vertical gusts on the shear layer of a moving body and the nonlinear dependence of the aerodynamic forces on the effective angle of attack. For the latter, the resultant aerodynamic forces based on a linear semi-analytical and a CFD model are compared for the same effective angle of attack due to sinusoidal gust and motion. The methodology is first employed to verify the linear behavior of a flat plate and then study the nonlinear behavior of two bridge decks. The results show that the linear superposition principle holds for streamlined bridge decks with minimal shear layer instability. However, this principle may not be valid for bluff bridge decks due to strong separation vortices that dictate the shear layer, which induces nonlinearity in the aerodynamic forces manifested through amplitude difference in the first harmonic and emergence of higher-order harmonics. The outcome of this study aims to provide a deeper understanding of the complex nonlinear fluid-structure interaction occurring for bluff bodies subjected to motion and free-stream gusts.
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