Designing implodable underwater systems to minimize implosion pulse severity

Underwater implosion is the rapid and catastrophic collapse of a pressure vessel subjected to external pressure, resulting in a very short but high-pressure pulse in the surrounding water that can potentially damage adjacent structures or personnel. Any system with an internal pressure below external pressure is susceptible to implosion. The pressure pulse from a single implosion has been known to trigger subsequent sympathetic implosions. This work investigates methods of reducing the implosion pulse severity for unstiffened metallic cylindrical pressure vessels. The implosion pulse energy is proportional to the maximum system kinetic energy developed during collapse. It can be reduced by (1) increasing the plastic energy dissipated by the collapsing structure, or (2) increasing the energy required to compress the internal gas. Plastic energy dissipation is increased by triggering higher buckling modes through introduction of geometric imperfections. Numerical simulations show that this technique can reduce implosion pulse energy for a sample cylinder by up to 33%, while reducing the buckling strength of the cylinder by only 0.5%. The energy required for gas compression can be increased by initially pressurizing the interior of the implodable. The benefit from this technique is bounded by other limitations on internal pressure, such as equipment and human survivability. A slight increase in gas compression energy is also realized by substituting a noble gas for air. These techniques can be applied, singly or in combination, to any implodable design to significantly reduce the pulse severity and minimize the risk of sympathetic implosions.