Beat vibration mechanism of a sluice pier under high-speed flood discharge excitation

Abstract

The sluice pier prototype vibration test conducted in China Shuhe Hydropower Station shows that the vibration response of the measuring points exhibits a special form of vibration, which demonstrates intermittency and impact under high-speed flood discharge excitation. The waveform envelope increases or decreases sharply with time and shows the formation of beat vibration. Research on the mechanism of this type of vibration is rare. To analyze the characteristics and causes of the obvious beat phenomenon in the testing of the sluice pier prototype, we conduct research in the following manner. First, mathematical models of synthetic signals are built to analyze the influences of initial phase difference, frequency ratio, and amplitude ratio and determine the beat vibration formation condition. Second, the stochastic subspace identification method is used to identify the operational modal parameters (including the vibration order, frequency, damping ratio, and mode of vibration) on the basis of the measured prototype dynamic response. Last, the internal causes of the beat vibration phenomenon are analyzed based on the combination of the formation conditions of apparent beat vibration. Results show that the vibration of Shuhe sluice pier is dominated by the first two frequency components. The vibration frequency ratio is between 0.928 and 0.962 and satisfies the necessary conditions of beat vibration. The amplitude ratio is between 0.66 and 1.63 and thus makes the waveforms of beat vibration highly evident.