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Wang Hao, Ke Shitang
Chinese Journal of Theoretical and Applied Mechanics    2019, 51 (1): 111-123.   DOI: 10.6052/0459-1879-18-125
Abstract   (206 HTML2 PDF(pc) (15937KB)(271)  

Recent study found that the time-varying characteristic of the load may have a significant effect on the vibrational strength and energy mechanism. The most important structures in fire/nuclear power plants (such as cooling towers, chimneys, etc.) are all typical rotating thin-walled structures. To reveal the vibration evolution characteristic and working mechanism of thin-walled structures in post-critical turbulent interval, the vibration responses of eight typical rotating thin-walled structures of high Reynolds number flow ($Re \ge $3.5$\times $10$^6$) are measured. Firstly, non-stationary identifications of signals with different time intervals are performed after depressing and filtering noise. The time-varying mean and extreme estimation of response are studied based on non-stationary analysis model. Besides, the frequency domain evolution characteristics are studied based on evolution spectrum method. On this basis, proportion of resonance component in wind-induced response and its effect are discussed. Then, self-resonant frequency and damping ratio of the structures are identified, and the damping mechanism of different rotating thin-walled structures is studied. The evolution characteristic and working mechanism are revealed as follows. (1) The wind-induced vibration response of the rotating thin-shell structure in post-critical turbulent interval is characterized by stable frequency evolution characteristics and non-stationary evolution characteristics in intensity aspect; (2) The wind-induced vibration problem of rotating thin-walled structures in post-critical turbulent interval should be studied as quasi-static and resonance excitation points separately. The vibration energy distributions of resonance excitation points at different regions of the cooling tower were similar, but the PSD functions of quasi-static points were dramatically different from each other; (3) Vibration energy distribution of the resonant excitation points showed a phased trend, and the proposed resonance spectral expression takes three variation stages of responses into account and achieves high prediction accuracy; (4) With the concept of equivalent damping ratio proposed in this paper, the damping ratio prediction formula is proposed. More importantly, these analysis results show that resonance effects and non-stationary effects on wind-induced effects of rotating thin-walled structures in post-critical turbulent interval are generally notable, and the irrationality of 5% damping ratio value commonly used in the current project for this type of rotating thin-walled structure has been demonstrated.

b1 b2 b3
1.705 62x10-7 -1.802 91x10-6 -10.809 71
Table 4 Fitting coefficients of power spectrum section dominated by cross term
Extracts from the Article
载荷的时变特征可能会对结构振动强度和能量作用机理产生重要影响,火/核电厂最重要的大型建筑结构均为典型的旋转薄壳结构(如冷却塔、烟囱等).为揭示后临界湍流区间内旋转薄壳结构的振动演化特征及其作用机制,实测了后临界雷诺数($Re\ge $3.5$\times $10$^{6}$)条件下8座典型旋转薄壳结构的振动响应.首先,在对实测响应进行降噪滤波处理后进行了不同时距的信号非平稳识别,基于非平稳分析模型对响应的时变均值和极值估计进行研究,并基于多尺度小波变换的演化谱方法开展了响应的频域演变特性研究.在此基础上,探讨了结构风振响应的共振分量占比及其效应,识别了结构的自振频率和阻尼比,并以结构基频为划分依据分别讨论了不同旋转薄壳结构的阻尼作用机制.研究结果表明:(1)旋转薄壳结构在后临界湍流区间内风致振动响应表现为强度非平稳、频率平稳的演化特性;(2)后临界湍流区间内的旋转薄壳结构的风振问题应区分准静力作用点与共振激发点分别进行研究,不同共振激发点的功率谱分布形式较为相近,而准静力作用点的功率谱分布规律差异较大;(3)共振激发点的振动能量分布呈现明显的分段趋势,基于本文大量实测分析结果回归得出适用于共振激发点的三阶段共振谱表达式;(4)借助本文提出的等效阻尼比概念拟合出此类结构的阻尼比预测公式,论证了目前工程中通用的5%阻尼比取值的不合理性.
表4   共振谱交叉项分量为主阶段谱表达式系数
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