Novel strategy for dissipating energy released from underwater collapse of structures

An experimental study of the underwater collapse of shrouded cylindrical shells was conducted to mitigate the pressure pulses emitted. Each experiment involved a thin-walled metallic shroud with several small perforations placed concentric to a sealed implodable volume, which was brought to instability hydrostatically within a pressure vessel. High-speed stereo photography coupled with 3D digital image correlation (DIC) provided full-field displacement histories of the shroud during the event. High frequency response dynamic pressure transducers placed at several locations around the shroud captured emitted pressure histories. The effects of varying perforation densities and perforation orientation of shrouds on the pressure signatures emitted by the implosion of thin metallic cylindrical shells were experimentally investigated. The shrouds mitigated the emitted pressure history by up to 90%. Two regimes of shroud behavior were observed, one in which the implodable underpressure is equalized primarily by shroud wall deformation and one where equalization occurs through fluid ingression via the shroud perforations. The perforation density directly determined the contribution from both of those two mechanisms. Research is ongoing to understand the fluid-structure interaction between an imploding volume and a deformable confining shroud along with impulse mitigation optimization.