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.

膜式储罐中的撞击引起的液体冲击是浮式液化天然气（FLNG）设施设计的重要问题。在浅水条件下，罐中的自由表面夹带的空气很容易发生，这可能导致结构局部损坏。研究夹带空气对冲击载荷的影响对于理解无空气的表面弹性结构的相互作用是必不可少的。因此，设计了一系列实验，并在浅水条件下的弹性矩形水箱中进行了实验。定量分析了自由表面的演变和截留的空气的发展。此外，在浅水条件下，在空间和时间分布上对冲击载荷和结构响应进行了测量和研究。结果表明，气孔在自由表面与弹性壁之间起缓冲作用。因此，冲击方式从液体直接冲击改变为液体间接冲击。空气腔的存在导致最大冲击载荷和结构响应的显着降低，但空间分布中的压力脉冲增大。对于海上工程中的超大型液化天然气储罐的设计，建议考虑夹带空气对确定砰击载荷的影响。