Theoretical study of bubble pulsation characteristics in underwater contact explosions

Contact explosion is an important condition in the damage and protection of underwater structures, and the pulsating bubbles generated by explosive underwater explosion are an important damage source. At present, the research on underwater explosion bubbles mainly focuses on the pulsating characteristics of spherical bubbles under free-field and typical boundary conditions, while there is limited research on non-spherical bubbles under contact explosion conditions. This study systematically investigates the pulsation characteristics of underwater contact explosion bubbles through theoretical modeling, numerical simulations, and experiments. To address the theoretical gap in contact explosion dynamics, a hemispherical bubble dynamics model under rigid wall contact conditions is established based on incompressible and inviscid fluid assumptions. By comparing with the spherical bubble pulsation model in an incompressible flow field, quantitative relationships between parameters such as the maximum bubble radius, initial radius, pulsation period, in the two models were obtained. Theoretical analysis reveals that the maximum radius, initial radius, and pulsation period of contact explosion bubbles are 1.26 (theoretical scaling factor) times those of free-field conditions. An error analysis of the aforementioned conclusions was performed, accounting for fluid compressibility, unstable bubble deformation, and energy dissipation induced by bubble-rigid wall interactions. Numerical simulations using LS-DYNA for 0.3 g TNT underwater explosions demonstrate that the maximum radius and pulsation period under contact explosion conditions are 1.22 and 1.20 times those of free-field results, respectively, with simulation errors below 10% compared to theoretical predictions. Experimental validation in a water tank shows that the maximum radius and period of contact explosion bubbles are 1.10 and 1.06 times those of free-field conditions. During the experiments, plate vibrations were observed upon explosion, which significantly contributed to experimental errors. This work addresses the theoretical gap in contact explosion bubble dynamics, enhances the understanding of boundary effects in underwater explosion phenomena, and provides a theoretical foundation for damage assessment in underwater contact explosions.