封闭式单向张拉膜结构气弹失稳机理研究

在均匀流场中进行了封闭式单向张拉膜结构气弹模型风洞试验，考察了膜预张力和来流风速对结构振幅、振动模态和总阻尼比的影响，以及膜面位移与膜上方流场的频谱相关性，分析了封闭式膜结构的气弹失稳机理，给出了气弹失稳无量纲临界风速。研究结果表明：低风速下(无量纲风速小于1.2时),流场中的旋涡主频远低于结构基频，结构以受迫振动为主；随着风速增大，流场中出现与结构2阶反对称模态频率接近的旋涡，导致结构发生以2阶模态大幅振动为特征的涡激共振，且在无量纲风速不小于1.2 的风速范围内出现振动锁定现象，结构总阻尼比迅速衰减接近0。由此可认为，封闭式膜结构的气弹失稳由涡激共振引起，结构振幅的突然增大、主导振动模态的突然改变以及总阻尼比的突然减小为其主要特征；气弹失稳无量纲临界风速约为1.2。

Research on aeroelastic instability mechanism of closed-type one-way tensioned membrane

A closed-type one-way tensioned membrane was tested in uniform flow to study the aeroelastic instability mechanism of membrane structures. The influence of the pretension and coming flow velocity on the structural amplitude, vibration mode, and total damping ratio and the correlation relation between the displacement and flow velocity above the roof were studied. The non-dimensional critical wind velocity was proposed at last. The results indicate that the frequencies of the vortex observed above the roof are much lower than the frequencies of the structure and the vibration of the roof is a kind of forced vibration at lower wind speeds when u/(fL)＜1.2, where u is the on-coming flow velocity, f is the vibration frequency of the 2nd mode and L is the span of the roof;with the increase of the wind speed, a vortex whose frequency is close to the anti-symmetric 2nd mode of the structure occurred and lead to the vortex induced resonance which is characteristic by the large amplitude vibration of 2nd mode. Lock in phenomenon occurs when u/(fL)≥1.2 and the total damping ratio of the structure decreases dramatically and reaches nearly zero. As a result, the aero-elastic instability of the closed-type membrane structure is caused by the vortex-induced resonance and this kind of instability is characterized by a sudden increase of the amplitude, a sudden change of the dominant vibration mode and a sudden decrease of the structure total damping ratio. The non-dimensional critical wind velocity is about 1.2.