大幅振动桥梁高阶自激力及气动参数研究

Large-amplitude oscillations of the long-span bridges can result in significant higher-order self-excited forces (HOSEFs), which have important effects on the aerodynamic stability. Conventionally, forced single degree-of-freedom (DOF) vibrations of the bridge deck with large amplitudes are investigated in the wind tunnel tests. In such a case, it is difficult to examine the modal aerodynamic coupling effects and the HOSEFs feedbacks on the bridge deck motions. In this study, the numerical simulation method using the forced vibration technique is utilized. It allows to consider the large-amplitude, time-dependent amplitude harmonic motion and coupling effects. The free-vibration numerical simulation method is developed, and hence the HOSEFs feedback effects can be involved as well as the analysis of the post-flutter/galloping characteristics. A novel device, which can carry out large-amplitude free-vibration wind tunnel tests, will be developed, and a new technique for identifying the aerodynamic parameters of HOSEFs will be proposed. Furthermore, a comprehensive analysis framework of HOSEFs, nonlinear aerodynamic parameters and post-flutter /galloping, using the newly addressed methods and experimental device, will be established. Typical bridge decks (2D sectional model and 3D aeroelastic model) under various conditions of different oscillating amplitudes, reduced wind velocities, mean attack angles, and modal parameters will be investigated. The major contributions to HOSEFs will be explored based on the flow field, pressure field, and spatial vibration information obtained by using numerical simulation and wind-tunnel tests. This will be helpful to further investigate the driven and mitigation mechanisms of flutter and post-flutter/galloping. Breakthroughs on numerical simulation techniques, wind-tunnel test strategies, nonlinear aerodynamic parameter identification theory and post-flutter/galloping analytical experimental and numerical method, in the context of bridge HOSEFs, will be achieved.

大跨桥梁风致大幅振动可诱发明显高阶自激力，进而反馈影响气动稳定性。以往大幅简谐、单自由度、强迫振动风洞试验方法，难以真实模拟模态耦合效应和高阶自激力对振动反馈效应。本课题提出可实现大幅、非简谐、耦合、强迫振动数值模拟方法；发展计入自激反馈效应、分析颤振(驰振)后状态的自由振动数值模拟方法；研发可实现大幅自由振动风洞试验的新型装置；提出高阶气动参数的实用识别方法。采用新提出、发展的数值模拟方法及风洞试验装置，全面研究典型桥梁二维节段模型和三维气弹模型在不同振幅、折算风速、平均攻角、模态参数等条件下高阶自激力、非线性气动参数和颤振(驰振)后状态特性。融合数值模拟及风洞试验获得的流场、压力场、空间振动信息，研究高阶自激力主要影响因素，揭示其对颤振(驰振)的作用机制。最终在桥梁高阶自激力的数值模拟技术、风洞试验方法、非线性气动参数识别理论、颤振(驰振)后状态风洞试验和数值模拟方法等方面取得突破。

大跨桥梁风致大幅振动可诱发明显高阶自激力，进而反馈影响气动稳定性。以往大幅简谐、单自由度、强迫振动风洞试验方法，难以真实模拟模态耦合效应和高阶自激力对振动反馈效应。经过四年研究，课题组研究了气动阻力的高阶成分，揭示了高阶阻力产生机理，提出了适用于气动阻力的非线性气动力模型；研发成大振幅自由振动试验装置；发展了主梁断面大幅软颤振数值模拟程序，研究了初始攻角、阻尼比等参数对大幅软颤振特性的影响；开展了典型主梁断面大幅软颤振风洞试验，探讨了软颤振现象机理，提出了表征软颤振现象的简单多项式模型；通过时变幅值强迫振动数值模拟，研究了振幅及振幅变化率（即阻尼比）对典型主梁断面颤振导数的影响；探讨了颤振导数耦合强迫振动法识别中，静气动力、惯性力及信号长度对精度的影响，给出了合理的信号长度；提出了含有幅变颤振导数的非线性气动力模型，该模型可用于预测断面涡激振动及大幅软颤振现象；基于数值模拟研究了典型主梁断面的气动力特性，提出了改善断面气动性能的气动措施；提出了基于自由振动数值模拟的颤振导数识别方法；研究了无风环境下主梁断面大振幅条件下非线性气动阻尼及附加质量特性，提出了准确识别机械系统参数的试验方法；采用新提出、发展的数值模拟方法及风洞试验装置，全面研究典型桥梁二维节段模型在不同振幅、折算风速、平均攻角、模态参数等条件下高阶自激力、非线性气动参数和颤振后状态特性。融合数值模拟及风洞试验获得的流场、压力场、空间振动信息，研究高阶自激力主要影响因素，揭示其对颤振的作用机制。最终在桥梁高阶自激力的数值模拟技术、风洞试验方法、非线性气动参数识别理论、颤振后状态风洞试验和数值模拟方法取得了一些重要成果。