Surface bulk cavity formation on flat isotropic plates subjected to near-field underwater explosions

Abstract

The formation of surface bulk cavities on isotropic flat plates due to the detonation of a near-field underwater explosive (UNDEX) has been computationally investigated. Experiments were performed in an air-backed condition for polycarbonate plates of 6.35 mm thickness, and 12.70 mm thickness, as well as steel plates 12.70 mm in thickness. Moreover, three distances between the explosive and targets were selected. Numerical simulations were performed with the fully coupled Eulerian–Lagrangian fluid structure interaction code Dynamic System Mechanics Advanced Simulation (DYSMAS). Initially, the numerical simulations were validated with the experimental data. Once validated, the numerical simulations were utilized to explore a wide range of structures and standoff distances. Results show that a surface bulk cavity forms on the plate when the centerpoint out of plane velocity of the plate reaches its maximum magnitude while the plate displaces towards the UNDEX gas bubble. Moreover, plates with equal flexural stiffness attained comparable maximum surface bulk cavity volumes. Additionally, the maximum surface bulk cavity volume exponentially decreases as the plate’s flexural stiffness increases. The maximum volume attained by the UNDEX gas bubble is directly related to the timing in which the surface bulk cavity begins to form on the plate. This timing is related to the plate’s flexural stiffness, as well as the plate’s natural frequency. The loading on the plate resulting from the collapse of the surface bulk cavity and the UNDEX gas bubble are influenced by the plate’s flexural stiffness.