Boundary element study of wave impact on a vertical wall with air entrapment

Effect of the air entrapped between an overturning wave and a vertical wall plays an essential role in the physical process of wave impact. However, due to complexity of both the physical phenomena and numerical techniques, conventional simulations with boundary element method (BEM) can only deal with the wave overturning stage, and calculations have to be terminated before the wave front impacts on the wall. This study aims to achieve the complete process simulation of wave impact with air entrapment using BEM. The key idea is to introduce a multi-scale algorithm with the help of a stretched coordinate system for the local impact zone. Interesting phenomena are observed indicating effects of the entrapped air on wave impact dynamics. In particular, free inner jets are found to form periodically inside the entrapped air cavity. The free jet has the trend to lead to the division of the cavity, indicating an initial bubble generation during wave impact. Effects of the air pressure on the impact process with air entrapment are also studied, where an analytical deduction based on the conservation law of conservation is used to explain the findings.