超高层建筑涡激振动不稳定现象分析

An analysis on the instability of vortex induced resonance of super high-rise buildings

为了研究方截面超高层建筑涡激振动不稳定现象的特点及原因。进行了多自由度气弹模型风洞试验,对模型表面风压和模型顶部涡振位移进行了同步测量;定性分析了模型表面风压和涡振位移响应的瞬时频率及瞬时相位关系。结果表明:在共振临界风速下,涡振位移幅值并不稳定,涡振位移时程曲线表现为间歇性的"葫芦波";并且,模型表面风压频率和模型风振频率并不是一个恒定的值,二者时程的相位差一直处于波动状态,即没有构成一方"俘获"另一方的"锁定"现象;说明超高层建筑实际共振并不是理想的稳定共振,瞬时风压频率和位移频率的动态差异是涡激振动不稳定现象的直接原因。

Flexible high-rise buildings may be exposed to vortex-induced resonance if the vortex shedding frequency is close to the natural frequency of the building. Although phenomena of instability of VIR have been reported in a few references,the investigation is seldom conducted by the MDOF aero-elastic model,which is considered as an accurate experimental approach,and moreover,the mechanism of the instability VIR of high-rise buildings has not yet been investigated by the MDOF aero-elastic model. In order to investigate the instability phenomenon and its mechanism of vortex induced resonance of super high-rise buildings,a series of wind tunnel tests of multi-degree-of-freedom（ MDOF）aero-elastic models were carried out. The wind pressure on the surfaces and VIV displacement response at the top of the model were measured synchronously. The differences between frequencies as well as time history phases of wind pressure and displacement were analyzed. The wind tunnel data reveal that VIV displacement responses are not ideal harmonic vibrations,and their amplitudes are fluctuating in different extent. The envelope curve of VIV displacement amplitude is just like ＂gourd wave＂. Vortex induced resonance（ VIR） occurs only in certain periods of VIV,so VIV response is intermittent resonance,and even VIR occurs the vibration amplitude is not a stable value,then this phenomenon was named as unstable resonance. Furthermore,it shows that the vibration frequency does not lock the vortex shedding frequency completely in the VIV process. In other words,their frequency cannot maintain equality once they are equal to each other. The key factor of the instability mechanism of VIR is the periodic deviation between transient frequencies of across-wind pressure and displacement due to the negative aero-dynamic stiffness. In other words,their frequencies cannot maintain equality once they are equal to each other,which eventually leads to a transformation of VIV response among＂random＂,＂transition＂and＂resonance＂.