Experimental research on internal solitary waves interacting with moored floating structures

Abstract

The motion response and mooring tension of a floating structure model under the action of internal solitary waves (ISWs) is investigated experimentally. Because the scales of the ISWs and model are very small, a new experimental system is proposed to measure the minute mooring tension and minute motion response variation. Particle image velocimetry technology is used to record the velocity field wave and the wave form of the ISW. Fiber Bragg grating is used to simulate the mooring line and measure the mooring tension. The motion response of the model is recorded using a charge-coupled device camera. In this experiment, 25 operating conditions are set to study the motion response and mooring tension response under different water thickness ratios and ISW amplitudes. The results demonstrate that the mooring tensions of the models vary considerably when an ISW propagates to the models. The maximum mooring tension variation was almost 40% of the pre-tension. The variation in amplitude of the mooring tension increases with an increase in the ISW amplitude. The non-dimensional mooring tension ΔF/F0 increases to 0.39 (on average) when the wave amplitude increases by 0.1 m. The pitch motion, heave motion, and surge motion of the model vary significantly as the ISW propagates. In most cases, the response amplitude increases with an increase in the ISW amplitude. However, the ISW amplitude is not the only factor related to the response; the water thickness ratio of the upper and lower layers and the model size are also important factors influencing the model response.