山区大攻角复杂来流作用下大跨度悬索桥颤振机理及优化研究

With the increasing spans being employed, flutter stability of long-span suspension bridges gradually becomes the controlling factor of structural safety. Considering the characteristics of the non-stationary and non-uniform complex inflow with large angles of attack, the effects on the flutter performance and the corresponding mechanism of long-span suspension bridges are analyzed by using theoretical analysis and wind tunnel tests. Based on the flutter mechanism, the optimization for flutter performance is further studied. At first, referring the references and summarizing the existing flutter methods, the flutter analysis method of bridges under the complex inflow is established to analyze the effects of large angles of attack, non-stationary and non-uniform inflows on the flutter response and study the changes in flutter performance and mechanism by multivariate analysis. Subsequently, according to the limitations of wind tunnel tests, improved measures are applied to simulate the non-stationary and non-uniform inflows, and the flutter performance of bridges under the complex inflow is further measured, which can be used for verifying the results obtained by the theoretical analysis. Finally, after determining the flutter mechanism of long-span suspension bridges under the complex inflow with large angles of attack, the countermeasures which can improve the flutter stability of bridges are put forward from the structural and the aerodynamic optimization perspectives, respectively, and their mechanism on the vibration inhibition is also determined. The research results of this project have a widely application prospect, which can provide guidance and reference for the practical engineering.

随着悬索桥跨度的增大，颤振稳定性已逐渐成为了结构安全的控制性因素。本项目针对山区来流的大攻角、非平稳、非均匀的特性，结合理论分析和风洞试验，分析复杂来流对大跨度悬索桥颤振性能及机理的影响，并基于颤振机理进行优化研究。首先，充分查阅相关文献，总结已有的颤振分析方法，建立复杂来流作用下桥梁颤振的计算分析方法，用以分析大攻角、非平稳、非均匀来流对桥梁颤振响应的影响，研究各种因素联合作用下桥梁颤振性能及机理的变化。然后，针对风洞试验的局限性进行改进，实现非平稳、非均匀来流风的模拟，测试复杂来流作用下桥梁的颤振性能，对理论研究的结论进行验证。最后，在明确大攻角复杂来流作用下大跨度悬索桥的颤振机理的基础上，分别从结构优化和气动优化两个方面研究提高结构颤振稳定性的优化措施，并明确优化措施的抑振机理。本项目研究成果具有较广泛的应用前景，对实际工程有指导或借鉴意义。

西部复杂山区峰峦起伏剧烈，河道深切蜿蜒，来流风受山体遮挡易出现绕流情况，导致桥址区风场时空分布呈现竖向大攻角、水平大偏角、空间非均匀、时序非平稳四大显著特征，对大跨度桥梁的颤振性能及驱动机理产生显著的影响。本项目结合CFD模拟、风洞试验，针对山区大攻角复杂来流作用下大跨度悬索桥颤振性能开展研究，建立了相应的桥梁颤振性能分析模型，克服了常规分析方法的局限性。发现和分析了大攻角来流下颤振驱动机理的变化，并以此建立了不同于常规来流情况的优化对策，指导了西部山区桥梁的气动优化选型。当风攻角较小时，可改善加劲梁断面的流线体特性，加强桥梁颤振失稳时竖弯模态和扭转模态之间的耦合，以此提高桥梁的颤振稳定性；当风攻角较大或加劲梁断面已经出现钝体特性时，迎风侧漩涡的形成及其向背风侧的移动成为了驱动扭转颤振失稳的重要原因，这时需要设置合理的措施以干扰漩涡生成、扰流漩涡结构、阻碍漩涡移动。在空间非均匀来流下，提出了考虑实桥非均匀来流影响的桥梁静风稳定性分析方法和颤振稳定性分析方法，明确了不同类型非均匀来流的影响机制和桥梁风致响应的非线性特征；在时序非平稳来流下，建立了CFD和CSD流固耦合的颤振分析模型，明确了波动非平稳来流和突变非平稳来流对桥梁颤振性能的影响机制。随着西部大开发新格局的形成和“一带一路”倡议的深入实施，越来越多的大跨度桥梁需跨越西部复杂山区，相关成果将进一步得到直接或间接应用。