Load characteristics of near-field of underwater explosion and its fluid-structure interaction

Near-field underwater explosion of the torpedo warhead is an effective way to induce damage of warship hull. However, much more attention has been paid to understand the shock-wave load and its damage mechanism instead of the complicated loads induced by the bubble dynamics. To utilize or reduce the devastating effects, the response of submerged structures due to both shock wave and loads induced by bubble dynamics, especially the reloading effect during the bubble motion, is investigated with an experimental and numerical study. The arbitrary Lagrangian-Eulerian method using LS-DYNA software is applied to simulate the entire process of close-in underwater explosion, including its interaction with free surfaces and the submerged structures. Detailed numerical simulation and analysis of near-field underwater explosion are presented. The comparison of the experimental tests is conducted to verify the results of numerical solutions. The shock-wave propagation characteristics of underwater explosions near different boundaries are simulated and compared. Especially, the unsteady cavitation just near the free surface and the structure surface is described and captured. In addition, the bubble migration in water, pressure pulse, water jet formation, and flow field velocity surrounding the bubble are examined. The proposed method, which provides the accurate results, is a relatively realistic and practical assessment tool for simulating the underwater explosions.