

EVOLUTION CHARACTERISTIC AND WORKING MECHANISM ANALYSIS OF ROTATING THINWALLED STRUCTURES IN POSTCRITICAL TURBULENT INTERVAL BASED ON FIELD MEASUREMENT
Chinese Journal of Theoretical and Applied Mechanics
2019, 51 (1):
111123.
DOI: 10.6052/0459187918125
Recent study found that the timevarying 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 thinwalled structures. To reveal the vibration evolution characteristic and working mechanism of thinwalled structures in postcritical turbulent interval, the vibration responses of eight typical rotating thinwalled structures of high Reynolds number flow ($Re \ge $3.5$\times $10$^6$) are measured. Firstly, nonstationary identifications of signals with different time intervals are performed after depressing and filtering noise. The timevarying mean and extreme estimation of response are studied based on nonstationary analysis model. Besides, the frequency domain evolution characteristics are studied based on evolution spectrum method. On this basis, proportion of resonance component in windinduced response and its effect are discussed. Then, selfresonant frequency and damping ratio of the structures are identified, and the damping mechanism of different rotating thinwalled structures is studied. The evolution characteristic and working mechanism are revealed as follows. (1) The windinduced vibration response of the rotating thinshell structure in postcritical turbulent interval is characterized by stable frequency evolution characteristics and nonstationary evolution characteristics in intensity aspect; (2) The windinduced vibration problem of rotating thinwalled structures in postcritical turbulent interval should be studied as quasistatic 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 quasistatic 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 nonstationary effects on windinduced effects of rotating thinwalled structures in postcritical turbulent interval are generally notable, and the irrationality of 5% damping ratio value commonly used in the current project for this type of rotating thinwalled structure has been demonstrated.
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