考虑耦合气动力和非线性气动力的桥梁颤振分析方法研究

Flutter is a governing of wind-resistant design of long-span bridges. As a bridge girder is bluff body essentially, it's aerodynamic force is not only dependent to the motions, but also is nonlinear to some extent. A new flutter analysis method is need to be developed which match to the characteristics of aerodynamics of bridge girders. The research consist of three work stages. Firstly, the characteristics of aerodynamic force and flow field of typical girders will be obtained by forced vibration tests，CFD simulation and PIV technique for flow visualization and quantification, under different reduced velocities and different coupled motions (phase angle and amplitude and amplitude ratio). Secondly, regarding to coupled aerodynamics and nonlinear aerodynamics, put forward a new flutter analysis method of bridges based on given-value searching in a 3D or 4D space, by complex eigenvalue solution for linear flutter and by numerical solution for nonlinear flutter respectively. Finally, the validity and accuracy of the new method should be verified by section model flutter wind tunnel tests, and the improvement could be proposed through a series of refine force vibration tests. The quantification of the effect of coupled aerodynamics and nonlinear aerodynamics on flutter performance of typical bridge girders will be carried out in the end. The research can reveal the characteristics and the transformation law of bridge girder aerodynamics varying with motion status, and extend the theory of wind-resistant design of bridges. It will be of great importance and significance in both theory and practice.

颤振是大跨度桥梁抗风设计中的控制因素。本质为钝体的桥梁断面，在弯扭耦合运动下的气动力非独立于运动状态，且存在一定程度的非线性效应。为了提出贴合于桥梁断面气动力特性的颤振分析方法，项目研究将开展三个阶段的工作。首先，通过强迫振动风洞试验，结合CFD数值模拟和PIV流场显示和量化技术，获得典型桥梁断面在不同折算风速、不同耦合运动状态（相位差、振幅和振幅比）条件下的气动力和绕流场的变化特征和规律；第二，考虑气动力的耦合效应和非线性效应，沿用线性颤振的复特征值解法并采用非线性颤振的数值解法，提出基于三维或四维空间特定值搜索的桥梁颤振计算新方法。最后，通过节段模型颤振试验验证算法的有效性和准确性，借助细化测力试验对算法加以改进，并量化气动力耦合效应和非线性效应对典型桥梁断面颤振性能的影响。项目研究可获得气动力和对应流场随运动变化的特征和规律，丰富现有大跨度桥梁的颤振计算理论，具有重要的理论和现实意义。

以大跨度桥梁的颤振后研究为背景，在已有单自由度条件下（不计入耦合气动力）的非线性颤振计算方法的基础上，利用自研的大振幅强迫振动设备和大振幅自由振动装置，系统研究了典型桥梁断面在弯扭耦合条件下的非线性气动力特性，并在此基础上提出了计入气动力非线性效应（包含基波分量的非线性特性和高次谐波分量的非线性效应）的耦合颤振计算方法，为大跨度和超大跨度桥梁的非线性颤振计算和设计提供了必要的理论支撑。开展的工作和取得的成果有：（1）开展了流线型箱梁在大振幅运动下的强迫振动试验，利用POD分解获得了非线性气动力特性，提出了以扭转角为10度作为是否计入高次谐波分量影响的分界点；（2）建立了考虑耦合效应和非线性效应的气动力模型，通过气动力做功等效原理，提出了气动参数识别方法；（3）提出了计入高次谐波分量影响的耦合颤振时程计算方法，并通过自由振动风洞试验进行了验证；（4）开展了桁架梁和流线型箱梁在10°扭转振幅内的自由振动颤振后试验，获得两类梁型随振幅和折算风速变化的软颤振特性；（5）提出了随振幅变化的气动阻尼以及颤振导数的识别方法，量化了传统颤振导数随振幅和折算风速的非线性变化；（6）基于耦合颤振闭合解理论，提出了考虑自激气动力振幅依存性(基波分量随振幅的变化，无高次谐波分量)的非线性颤振计算方法，并通过自由振动风洞试验进行了验证。

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