气液耦合系统中固有频率的实验研究

Abstract

The wave impact phenomenon widely exists in nature, ocean and aerospace engineering. When the wave impacts on the large-scale structure, the violent free surface may break and the wave tip entraps the air. As a consequence, wave impact with gas-entrapment may cause localized and large load, which may lead to structural failure. During the slamming process, the influence of gas on the natural modes of the free surface has not been systematically reported. A series of experiments were designed and conducted to study the influences of 2 different ullage space pressures on the natural frequencies and damping ratios of gas-liquid coupled systems. High-speed cameras were employed to record the free-surface vibration. Furthermore, the surface wave height was extracted with a self-made image-processing software. The results show that, the sloshing energy mainly concentrates on the lowest natural frequency of the free surface under a low ullage space pressure; while the sloshing energy mainly concentrates on the 2nd natural frequency of the free surface under a high ullage space pressure. As the ullage space pressure of the sloshing tank increases, the dominant natural frequency of the free surface will increase, while the corresponding damping ratio will decrease. Therefore, the gas compressibility is an important factor for the sloshing issue in the tank.