Influences of initial and boundary conditions on underwater explosion bubble dynamics

Abstract

Numerical and experimental methods are combined in this paper to study the bubble dynamics generated by an underwater charge explosion with different initial charge shape, detonating styles and boundary conditions. Outdoor experiments are carried out to employ sunlight with the assistant of lamplight to get clearer pictures of bubble motion. The results show that the charge detonating stage is not finished instantly but takes some time to explode fully. The explosion begins from its detonating end and finishes at the other end, which results in its uneven distribution of initial normal velocity. So instead of following the traditional method of treating the charge explosion instantly, a real charge explosion model is built in this paper with the combination of LS-DYNA and the boundary element method (BEM). LS-DYNA is used to solve the charge initial detonation and the BEM to solve its subsequent bubble motion. The linking relationship between these two methods is modeled. The convergence study has been firstly taken with different meshes. In this paper, charges with a different slenderness ratio from 0.99 to 20 are chosen to carry out the experiments and their corresponding numerical results are put forward. It can be found in both experimental and numerical results that the initial charge shape and its detonating style would affect its following bubble dynamic behavior. When the cylindrical charge is horizontally installed and end detonated, an oblique jet leaned to the detonating end would be formed and a horizontal migration process is also observed during the whole bubble pulsating stage. The bubble dynamic behaviors near different solid boundaries are further studied and the numerical results coincide well with the experimental ones.