Underwater shock and bubble interactions from twin explosive charges

The loading of a marine structure by an underwater explosion (UNDEX) has long been known to consist of two main parts: the shock from the charge detonation followed at a much later time by the strong flow and pressure waves from the collapsing detonation product bubble, Snay [1]. The shock loading from close-proximity charges is complicated by possible Mach reflection due to the interactions between the strong shocks and the structure. The loading from the bubble collapse is also complicated by the complex flow field generated by the interaction between the collapsing bubble and the rigid structure. A significant portion of the energy released by an underwater explosive displaces a large volume of water during bubble expansion and collapse, Arons et al. [2], Sternberg and Hurwitz [3]. In the presence of a nearby rigid structure, the bubble evolves into an annulus while collapsing towards the structure and produces a strong impinging jet, Klasboer et al. [4]. Measuring the near-field loading phenomenon is challenging due to both the strong shock and the high-velocity bubble jet flow. Due to the comparable shock impedances of water and a rigid structure such as a steel wall, the strong shock transmitted into the wall poses problems in embedding diagnostic gauges in the wall while decoupling them from the shock effects. In the present work, the conditions of an explosion near an infinitely-rigid wall are reproduced with two identical charges detonated simultaneously while measuring the pressure along the plane of symmetry between the charges.