Estimation of the underwater implosion pulse from cylindrical metal shells

Abstract

Underwater implosion, the rapid and catastrophic collapse of a structure caused by hydrostatic pressure, generates a short-duration, high-pressure pulse in the surrounding water that is potentially damaging to adjacent structures or personnel. This paper presents a method to estimate the energy in the pressure pulse as the difference between the known total potential energy and energy lost by plastic deformation. The implosion pulse energy is proportional to the maximum system kinetic energy developed during collapse. The pulse was approximated by considering only the first phase of collapse (up to the instant of first contact), because the maximum kinetic energy occurs very near that instant. The plastic energy dissipated by the structure during the initial phase of implosion was evaluated analytically, using the principle of virtual velocities. The solution for energy dissipation agreed with numerical simulation within 1% at the end of the initial collapse phase. It was found that for a representative aluminum cylinder, the implosion pulse represents only 15% of the total available energy.