Experimental investigation of the entrapped air on the hydroelasticity induced by liquid slamming under shallow-water condition

Abstract The liquid impact induced by slamming in the membrane-type tank is an important issue for the design of Floating Liquefied Natural Gas (FLNG) facilities. The free surface entrapping air may easily happen under shallow-water condition in the tank, which could result in structural local failure. Studying the effect of entrapped air on slamming load is essential to understand the air-free surface-elastic structure interaction. Thus, a series of experiments are designed and conducted in an elastic rectangular tank under shallow-water condition. The evolution of free surface and the development of entrapped air are analyzed quantitatively. Furthermore, both impact load and structural response are measured and studied in the spatial and temporal distribution under shallow-water condition. The results show that the air cavity plays a cushion role between free surface and elastic wall. Therefore, the impact mode is changed from liquid-direct impact to liquid-indirect impact. The existence of the air cavity leads to a significant reduction of the maximum slamming load and structural response but an increase in the pressure impulse in spatial distribution. It is suggested to consider the effect of the entrapped air on the determination of the slamming load for the design of super-large LNG tanks in the offshore engineering.