Numerical Simulation Of Underwater Explosion Based On Level Set Method

Underwater explosion is a complex physical and chemical process with huge energy transforming. Its destructive force is the most threat to naval ships. Evidently, extensive research on the damage effects of a ship arising from underwater explosion is of great importance in improving the survivability and battle capacity of the ship.Underwater explosion physical process is usually divided into three sequences: charge detonation, shock wave spread and bubble oscillation. The study of shock wave process and shock wave & structures interaction is always a key issue. However, people pay more attention to the far field. Due to the difficulties of experiments and numerical simulations, there are few papers concerned about shock wave over near field. For example, the empirical formulas of Cole and Zamyshlyayev concerning pressure and impulse are all for far field. However, the shock wave characters of near field, especially in the range of six charge radius, are crucial to understand the process of underwater explosion shock wave in the whole field.In this thesis, Level Set method is adopted to 1D symmetric model of underwater explosion and shock wave near field characters are examined extensively, and then this method is extended to 2D plane field. In detail, the Level Set method is used to capture the interface and the high-resolution Total Variation Diminishing (TVD) is adopted to solve the Euler equations for inviscid and compressible fluid. Main work includes:(1) 1D symmetric model is studied by Level Set method, and the near field characters of shock wave are examined extensively.(2) Theoretical and empirical results are compared with numerical results, which match closely. As a part of the present work, the influence of grid size on the convergence of results is also studied. Finally, approximate formulas about peak pressure, specific impulse and decline constant are obtained by curve fitting.(3) The Level Set method is extended to the 2D Euler equation system. The interaction of shock wave and the free surface is studied in this part. Also, through the numerical simulation, the second shock wave is founded in the bubble which is accordance with the experiments.