圆截面高柔结构不稳定涡振机理及响应评估研究

High flexible structures with circular section are frequently damaged by violent vortex-induced vibration (VIV) or resonance. Existing studies on the mechanism of unstable VIV, the level of VIV response, as well as equivalent load evaluation method are still insufficient and not thorough. The proposed project will employ three kinds of wind tunnel test, i.e., pressure measuring test by rigidity model, MDOF aero-elastic model test, and continuous housing aero-elastic model test. The rigidity model test will be used to simulate Reynolds number effect. The simulation method will then be applied to aero-elastic model test. The VIV displacement and wind pressure of aero-elastic model test will be measured simultaneously. The aerodynamic stiffness will be determined through the wind pressure of VIV and the system vibration frequency respectively. On the basis of vortex-induced vibration characteristic of VIV response and the relationship between wind pressures and displacement response, the reason for unstable vortex-induced vibration will be revealed. Subsequently, the mechanism of vortex-induced resonance excitation and the unstable mechanism of high flexible chimney will be investigated. Finally a semi-theoretical evaluation model of resonance response considering the aerodynamics stiffness and the instability of vortex-induced vibration will be established. And the method for calculating equivalent wind load of vortex-induced vibration will be proposed based on the model. This study will provide reference for the wind design of similar structures, such as chemical tower, TV tower with circular section, and solar energy chimney.

圆截面高柔结构因大幅涡振而发生破坏的案例屡见不鲜。既有研究对此类结构的涡振不稳定机制和负气动刚度的认识存在不足，可能使设计风荷载偏于危险。本申请项目以典型圆截面高柔结构（烟囱）为对象，进行刚性测压模型、多自由度气弹模型和连续壳体气弹模型相结合的风洞试验。通过刚性模型试验实现雷诺数效应模拟，将模拟方法应用于气弹模型。对气弹模型涡振位移和风压进行同步测量，通过涡振过程中涡脱频率和体系振动频率的关系来对比分析气动刚度的变化规律。结合非线性随机振动理论，基于气弹模型涡振响应特点及风压与位移响应互制关系的分析，揭示涡振不稳定性的根本原因。进而研究高柔烟囱在湍流场中涡激共振的激发机制和不稳定机制，及发生共振后的响应水平。最终提出兼顾气动刚度和涡振不稳定性的共振响应评估模型，在此基础上建立涡振等效风荷载计算方法。该研究可为此类结构(普通排气烟囱、天阳能烟囱、电视塔、化工塔)的抗风设计提供参考。

圆截面高柔结构的涡振不稳定机制和负气动刚度是影响涡激振动结果的重要因素。项目通过调查分析、风洞试验和理论研究的到了一些有价值的成果。主要包括：分析了几乎所有见诸报道高烟囱破坏实例，得到了宏观的规律性结论，可为相关设计、施工和研究人员提供参考。研发了一种采用“开模、灌胶、再拆模”方式制作连续壳体气弹模型的方法，可以较好地模拟圆截面高柔结构的涡激振动情况，并将该方法成功应用到实际工程的抗风设计中，可为此类实际工程气弹模型风洞试验提供指导。分析了圆截面高柔结构的既有实测数据和风洞试验模拟结果，证实了升力系数、斯托罗哈数等参数是决定圆截面细柔结构涡振水平的关键参数，指出了不模拟这些关键参数的雷诺数效应将对圆截面高柔结构涡激振动风洞试验造成的重大影响，为后续研究指明了方向。进行了大量刚性模型测压试验，研究了粗糙条对圆截面模型雷诺数效应的影响。基于高层建筑气弹模型试验结果，分析了漩涡脱落与结构频率关系、振动功率谱带宽、涡振响应峰因子和竖向风压相关性等因素与共振不稳定的关联性，提出了涡激共振判别标准及共振发生的概率模型。上述研究成果为圆截面高柔结构的涡激共振评估研究提供了很好的铺垫。