H型断面气动自激力非线性特性和流场演化机理研究

Due to its convenience in manufacture and installation, H-shape section is frequently used in the flexible members of long-span bridges; however, H-shape members are prone to wind-induced transverse galloping and soft flutter in a large range of wind attack angles because of aerodynamic unfavorable characteristics and have suffered from numerous reported damages in many hangers of steel arch bridges and members of truss bridges at home and abroad, therefore, it is still an open issue in wind engineering to establish a theoretical model to predict the wind-induced vibration of flexible H-shape members with acceptable accuracy. In this study, H sections with typical aspect ratios will be adopted as research objects to investigate the underlying aerodynamic mechanism of soft-galloping and soft-flutter during vibration onset and suppression by typical aerodynamic countermeasures using the integrate technique of aerodynamic static force measurement of sectional model, spring-suspended sectional model free vibration and CFD simulation. Afterwards, the influence of free stream turbulence and coupling effect of along-wind vibration on soft-galloping and soft-flutter will be investigated. On this basis, an analytical theory will be built for the nonlinear and unsteady self-excited vibration of H-shape sections in large range of attack angles, which will be validated by aeroelastic model tests of flexible hangers. The research results of this proposed project will have comprehensive theoretical significance and application prospect.

大跨度桥梁柔性构件为了便于制造和安装，经常采用气动性能较差的H型断面，在大风攻角范围内极易发生横风向软驰振或扭转软颤振，国内外多座钢拱桥和桁架桥均报道了H型吊杆/桁杆的风致破坏事故，因此，建立能够准确预测H型柔性构件风致振动的理论模型仍然是风工程届悬而未决的课题。本项目选取典型宽高比的H型断面，采用节段模型静止测力、弹簧悬挂节段模型测振试验、CFD数值分析相结合的方法，研究软驰振/软颤振起振过程及典型抑振措施的内在气动机理，探讨顺风向自由度耦合效应和来流紊流对软驰振和软颤振的影响规律，以此为基础，尝试建立H型断面大攻角自激振动的非线性非定常分析理论，并通过柔性吊杆的气弹模型试验验证该理论的适用性。研究成果具有重要的理论意义和广泛的应用前景。

H型断面是桥梁工程常见的一种钝体断面，其气动外形较差，容易发生风致振动。近年来，多座钢桥的H型柔性构件发生了风致破坏事故，目前对H型断面风致振动特性认识不足，特别是大攻角、来流紊流和多自由耦合振动特性的研究匮乏，传统分析理论也难以满足实际工程的需求。.为此，本项目从典型宽高比（1.9、2.4和4.88）H型断面入手，建立了柔性钝体构件非线性风致分析理论。首先，研发了适用于大攻角的三自由度耦合振动装置，实现了H型断面在任意攻角下大振幅自由振动模拟。随后，测量了典型宽高比H型断面的气动力特性；通过节段模型和气弹模型试验，研究了H型断面在大攻角状态下的风致振动响应特性，揭示了来流紊流、宽高比、质量-阻尼参数对风致振动的影响规律。然后，基于CFD分析和节段模型测压试验，获得了H型断面流场绕流的特征和抑制风致振动的气动方案。最后，提出了适用于软驰振的非定常气动升力模型，适用于软颤振的弯扭耦合非线性自激力模型，以及涡振Griffin图快速识别算法和非线性涡激力模型，在此基础上，建立了柔性构件非线性风致振动的多模态耦合分析理论。.研究结果表明：来流紊流很可能降低H型断面的颤振稳定性，颤振形态由均匀流场的软颤振转变为紊流风场的硬颤振；来流紊流有助于削弱涡振稳定振幅，但降低了中小宽高比H型断面驰振稳定性；H型断面软驰振表现出强轴-弱轴耦合特性，耦合系数随风速增加变化不大；软颤振表现出弱轴-扭转耦合特性，耦合程度随着宽高比和风速的增大而增大。软驰振和软颤振的自限幅特性主要由气动阻尼随振幅变化导致的。.本项目建立了非线性风致分析理论经验证也适用于其他钝体断面，所研发的试验装置可以广泛应用在输电线缆、高层建筑等细长结构的抗风研究，因而，具有推广应用价值。.研究结果表明：来流紊流很可能降低H型断面的颤振稳定性，颤振形态由均匀流场的软颤振转变为紊流风场的硬颤振；来流紊流有助于削弱涡振稳定振幅，但降低了中小宽高比H型断面驰振稳定性；H型断面软驰振表现出强轴-弱轴耦合特性，耦合系数随风速增加变化不大；软颤振表现出弱轴-扭转耦合特性，耦合程度随着宽高比和风速的增大而增大。软驰振和软颤振的自限幅特性主要由气动阻尼随振幅变化导致的。.本项目建立了非线性风致分析理论经验证也适用于其他钝体断面，所研发的试验装置可以广泛应用在输电线缆、高层建筑等细长结构的抗风研究。