Underwater explosion poses a significant threat to the structural integrity of ocean vehicles and platforms. Accurate prediction of the dynamic loads from an explosion and the resulting structural response is crucial to ensuring safety without overconservative design. When the distance between the explosive charge and the structure is relatively small (i.e., near-field explosion), the dynamics of the gaseous explosion product, i.e., the “bubble”, comes into play, rendering a multiphysics problem that features the interaction of the bubble, the surrounding liquid water, and the solid structure. The problem is highly nonlinear, as it involves shock waves, large deformation, yielding, contact, and possibly fracture. This paper investigates the two-way interaction between the cyclic expansion and collapse of an explosion bubble and the deformation of a thin-walled elastoplastic cylindrical shell in its vicinity. Intuitively, when a shock wave impinges on a thin cylindrical shell, the shell would collapse in the direction of shock propagation. However, some recent laboratory experiments have shown that under certain conditions the shell collapsed in a counter-intuitive mode in which the direction of collapse is perpendicular to that of shock propagation. In other words, the nearest point on the structural surface moved towards the explosion charge, despite being impacted by a compressive shock. This paper focuses on replicating this phenomenon through numerical simulation and elucidating the underlying mechanisms. A recently developed computational framework (“FIVER”) coupling a nonlinear finite element structural dynamics solver and a finite volume compressible fluid dynamics solver is used to complete this study. The solver utilizes an embedded boundary method to track the wetted surface of the structure (i.e. the fluid-structure interface), which is capable of handling large structural deformation and topological changes (e.g., fracture). The solver also adopts the level set method for tracking the bubble surface (i.e. the liquid-gas interface). The fluid-structure and liquid-gas interface conditions are enforced by constructing and solving one-dimensional multi-material Riemann problems, which naturally accommodates the propagation of shock waves across the interfaces. In this paper, mesh refinement study is made to examine the sensitivity of the results to various meshing parameters. The results show that the intermediate level of refinement is appropriate in terms of both the accuracy and the computation costs. Next, the deformation history of both the bubble and the structure are presented and analyzed to provide a detailed view of the counter-intuitive collapse mode mentioned above. We show that timewise, the structural collapse spans multiple cycles of bubble oscillation. Additional details about the time-histories of fluid pressure, structure displacement, and bubble size are presented to elucidate this dynamic bubble-structure interaction and the resulting structural failure.
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Effect of bubble interface position on propulsion and its control for oscillating-bubble powered microswimmer
It has been previously reported that a gaseous bubble trapped in a one-end-open tube oscillates in the presence of acoustic wave and generates strong microstreaming flows and thus a propulsion force. The propulsion highly depends on the frequency and the voltage of the external acoustic wave. This paper presents a new discovery that the direction of this propulsion is dependent on the relative location of the bubble interface. The oscillating bubble propels forward when its interface stays deep inside the tube. On the contrary, the bubble propels in a reverse direction when its interface is at the exit of the tube. Learning from this phenomenon, we developed and introduced physical structures (necks) to precisely control the location of the bubble interface. As a result, the length and interface position of the bubble is more controllable, and the bubble oscillation and propulsion becomes more predictable and consistent.
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- Award ID(s):
- 1637815
- NSF-PAR ID:
- 10076808
- Date Published:
- Journal Name:
- The 31st IEEE International Conference on Microelectromechanical Systems
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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