دانلود رایگان مقاله انگلیسی تجزیه و تحلیل دمپر ستون مایع میزان شده - الزویر 2018

ABSTRACT

Broadband environmental excitations from wind, ocean wave and earthquakes are especially dangerous for flexible tall structures such as wind turbines, towers or cable-stayed bridges. Liquid Dampers have been studied for almost thirty years in terms of their capability for suppression of vibration in such structures. The work presented in this paper focuses on the Tuned Liquid Column Damper, both open and sealed, and the identification of its time-varying properties of nonlinear damping, frequency and air pressure identification. Experimental tests are conducted on a full scale model of the damper which is subjected to both white noise and harmonic excitation by means of a hydraulic shaker. Exponential decay of the displacement of the liquid column was measured and analysed. The identification procedure was conducted step-wise, first, mode separation with the use of Continuous Wavelet Transform was carried out and then identification of the instantaneous damping ratio for the first mode of vibration was performed. Results indicate that the damping ratio is nonlinear, timevarying and depends on the level of vibration. The air pressure data in the sealed TLCD was also recorded and analysed to reveal the nonlinear nature of the pressure change and the presence of higher odd harmonics.

Conclusions

The dynamics of a TLCD was investigated. The major focus was on identification of frequency of the oscillating liquid column, nonlinear damping estimation and air pressure characterization. The response of the first vibration mode associated with the – liquid column of the TLCD was considered to obtain the dynamic equation of motion with a quadratic damping model. The air pressure above the water level in case of a sealed TLCD was also modelled to reveal its nonlinear nature. Experimental study was performed to identify and validate the proposed models. The experimental results show that the proposed quadratic damping model can be used to describe the dissipative behaviour associated with the first vibration mode of the analysed TLCD. The time-varying damping was effectively identified using the combined envelope analysis, curve fitting and logarithmic decrement. Further, in case of the sealed TLCD, the air pressure above the liquid level can be modelled using the constant pressure-volume polytropic relation. This model leads to a nonlinear behaviour of the pressure change and indicates the presence of higher odd harmonics. The experimental work and timefrequency analysis of the air pressure confirmed the nonlinear behaviour predicted by the model.