Experimental Study on Shallow Water Sloshing

Abstract

Sloshing of liquid in a partially filled container, subjected to higher amplitude of dynamic load, is a complex phenomenon. In shallow water conditions, the natural frequency of sloshing depends on the amplitude of excitation. Sloshing frequency tends to change with increase in amplitude of excitation. The change in natural frequency is critical if we use the sloshing tank as a passive damping device, such as Tuned Liquid Damper (TLD) for offshore structures or onshore structures. A small change in sloshing frequency in TLD may affect the structural vibration control significantly. Therefore, it is essential to comprehend the natural frequency of shallow water sloshing. Experimental study is one of the best ways to understand the physical insights of change in sloshing frequency. Experimental studies are conducted to study the jump in sloshing frequency at different excitation amplitudes. Several rectangular tanks (1163, 1064, 951, and 844 mm) under different water depths (60, 50, and 40 mm) are taken for the study to generalize the results. The liquid tank is mounted on a uni-directional horizontal shake table, which is subjected to simple harmonic motion. The amplitude of excitation varied from 5 to 50 mm. A single capacitance-type wave probe is used at the end of the tank wall to measure the wave surface elevation. The wave elevation increases as the excitation frequency reaches toward the natural frequency of sloshing. The measured liquid sloshing frequency, at the resonance condition, is considered as actual sloshing frequency of liquid in tank. This sloshing frequency changes with the amplitude of excitation and shows the sudden jump in frequency from a particular amplitude of excitation. The objective of this paper is to generalize the relation between the jump frequency ratio (ratio of jump frequency to linear frequency) and the non-dimensional amplitude of excitation.