Date of Award
2026
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Mechanical Engineering and Applied Mechanics
Department
Mechanical, Industrial and Systems Engineering
First Advisor
Arun Shukla
Abstract
As humans continue to rapidly advance undersea systems, the risk of catastrophic events of these undersea systems must be investigated and understood with the same rigor. Underwater structures including pipelines, autonomous underwater vehicles (AUVs) and deep-sea submersibles are constantly exposed to high pressure along with cyclic loading cycles. These structures support a range of military and commercial activities including submarine and antisubmarine warfare, oceanographic surveying, inspection and repair of cables, pipelines, marine salvage, exploration, and exploitation of ocean resources, along with recreational or tourist operations. When the high pressure at depth surpasses the critical threshold for a given structure, the potential to experience catastrophic collapse, known as implosion, is likely. This implosion event consists of a rapid inward collapse of the structure, generating strong propagating pressure waves capable of damaging nearby structures.
In many undersea systems, multiple implodable volumes are placed in close proximity, wherein failure of a single component can trigger cascading implosions in neighboring structures, in what is called sympathetic implosion. While underwater implosion has been studied for over a century, pressure mitigation remains comparatively underexplored, despite the significant economic and human losses associated with catastrophic implosion failures, many being due to sympathetic implosion. To date, all implosion mitigation strategies reported in the literature rely on direct modification of the implodable structure to increase structural durability and mitigate emitted pressure, including coatings, weldments, fillers, and stiffeners. No mitigation concepts have been developed that act externally without contacting or altering the primary structure.
The objective of this work is to develop and experimentally validate the first class of non-contact implosion mitigation devices for cylindrical structures. These devices mitigate emitted pressure and increase collapse capacity without mechanical contact prior to instability or modification of the implodable volume. Such non-contact mitigation concepts enable cost-effective after-production installation, impose no reduction in flow capacity since the internal cross-sectional area of the implodable volume is preserved, and allow modular deployment, such that for military or commercial applications requiring relocation or reuse, the device may be readily removed or reinstalled as needed.
Therefore, a fundamental experimental investigation is conducted to characterize underwater implosion and evaluate mitigation performance using three external non-contact devices: (a) a sacrificial perforated shroud placed concentric to the implodable volume, (b) submerged plates and mesh screens positioned adjacent to the implodable volume to alter pressure transmission and flow interaction, and (c) externally fitted non-contact metallic rings designed to modify the collapse mode shape and collapse capacity. In addition to investigating the mechanics of these non-contact mitigation concepts in isolated configurations, this work presents the first experimental study of sympathetic implosion of three ductile metallic cylindrical shells. The three non-contact mitigation devices are incorporated into the sympathetic implosion configuration to evaluate their effectiveness in preventing collapse of adjacent structures.
Chapter 1 provides a thorough review of the state of the art of underwater implosion across experimental, numerical, and analytical domains. This review covers the advancements and shortcomings of existing underwater implosion research. The study begins with the foundational work on the buckling theory of spherical and cylindrical shells, followed by the experimental and computational methodologies used in underwater implosion research. This review then examines the collapse mechanics of implodable volumes under external hydrostatic pressure, with foci on the effects of varying geometry and material. Next, UNDEX initiated implosion, sympathetic structures, partially confined, and fully confined environments are explored. Finally, existing methods to increase collapse capacity and mitigate emitted pressure, including internal and external coatings, ring stiffeners, foam fillers, buckle arrestors, and grooves are investigated.
Chapter 2 introduces the first novel non-contact pressure mitigation device, a sacrificial confining shroud. This study experimentally explores the effectivity of a thin-walled metallic shroud with several small perforations along its length placed concentric to a sealed implodable volume. Eight unique shroud configurations are tested, each varying in perforation density and orientation. This study reveals through high-speed photography, 3D Digital Image Correlation (DIC), and dynamic pressure transducers, that shrouds mitigate the entire emitted pressure history up to 90% when compared to a non-shrouded baseline. Two regimes of shroud behavior are observed and discussed. Limited visibility of the implodable volume during collapse necessitated the work presented in the following chapter.
Chapter 3 presents an experimental investigation of underwater implosion pressure pulse mitigation utilizing a transparent cylindrical polycarbonate shroud held concentric around an implodable volume. The authors provide a comprehensive analysis of implodable volume collapse mechanics simultaneously with the evolution of the shroud deformation. High-speed imaging with a high-contrast random speckle pattern applied to one half of the shroud lengthwise and the opposing half of the implodable volume is employed such that the 3D Digital Image Correlation (DIC) technique could be applied to both shells, simultaneously. This work investigates the effects of perforation area, intershroudal volume, and shroud stiffness on the effectiveness of a shroud for pressure mitigation. This chapter presents a predictive model for emitted specific impulse and develops non-dimensional parameters to represent the two regimes of shroud behavior first discussed in Chapter 2.
Chapter 4 experimentally explores the second implosion pressure mitigation device, submerged screens and plates, placed adjacent to an implodable cylindrical shell. This study examines the influence of plate type, perforation density, and standoff distance on the transmitted pressure history and collapse dynamics of the implodable volume. Experiments were conducted using solid plates, perforated plates, and mesh screens, with pressure sensors mounted on both sides of the plate to quantify pressure transmission and asymmetry. Results demonstrate minimal change in the transmitted pressure across the tested screen or plate configurations. However, when comparing the implodable volumes with a screen or plate nearby to the baseline case, the collapse shape transitions from a classical mode-2 to an asymmetric c-shaped collapse, associated with reductions in the peak pressure amplitude. These observations motivate the investigation of c-shaped collapse mechanics and their mitigation potential presented in the following chapter.
Chapter 5 presents an experimental and numerical investigation of the third mitigation device: external metallic non-contact rings. Despite the extensive work performed on internal and external rings, existing studies have exclusively involved contact-based rings, with most efforts directed towards buckle arrestors in underwater pipelines. Consequently, the potential of non-contact devices that increase collapse capacity while mitigating the emitted pressure signature remains largely unexplored. The objective of this work is threefold. First, a novel external ring device designed to mitigate the emitted pressure signature is developed and experimentally investigated, showing an increasingly c-shape collapse with decreasing ring diameter and reduction in peak overpressure and emitted impulse up to 60% when compared to a non-ring baseline. Second, an equation to predict the buckling pressure of the implodable volume with an external ring is developed. And third, complimentary numerical simulations performed using a coupled Arbitrary Lagrangian-Eulerian (ALE) formulation in LS-DYNA are conducted to understand the impact of fluid flow and collapse shape on the emitted pressure signature. The proposed external ring configurations are significantly lower in profile than shrouds and screens, offering potential cost, mass, and spatial advantages for future applications involving UUVs and deep-sea submersible designs.
Chapter 6 integrates the mitigation devices developed in the preceding chapters by examining their performance in multi-structure underwater implosion scenarios. The focus of this chapter is the characterization and mitigation of sympathetic implosion of ductile, metallic cylindrical shells, where failure of the primary shell induces subsequent collapse of neighboring structures. Three identical thin-walled aluminum tubes were arranged in parallel to experimentally quantify how the critical distance between tubes and their collapse direction affects cascading failure. Baseline sympathetic implosion experiments establish the critical distance governing secondary and tertiary collapse and characterize the causation of this collapse. The effects of the three external non-contact mitigation devices - shrouds, screens, and external rings - are then investigated by incorporating the devices into the sympathetic implosion arrangement.
Chapter 7 provides a short summary and future scope of work based on this dissertation. The proposed future research directions build directly upon the findings of this thesis and introduce several original concepts and ideas developed through this work to both further advance implosion mitigation strategies and the knowledge of undersea systems.
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Recommended Citation
Reilly, Victoria, "NOVEL STRATEGIES FOR MITIGATING ENERGY RELEASED FROM UNDERWATER IMPLOSION OF CYLINDRICAL SHELLS" (2026). Open Access Dissertations. Paper 4566.
https://digitalcommons.uri.edu/oa_diss/4566