Abstract.Recent experiments involving near-contact underwater explosions on air-backed plates suggest the following failure mode categories: (1) holing and petaling, (2) complete or partial edge tearing due to shock only, (3) complete or partial edge tearing due to shock and bubble collapse, and (4) large deformation without rupture. Finite-element analysis was used to further investigate the detailed response and failure of the plates, and determine the limit between center plate holing and edge failure. When compared with experimental results, finite-elements showed good agreement with the failure modes of the plates and reasonable agreement with the experimental deformations. It was found that the linear interaction criteria (LIC) failure between plastic strain and through-thickness shear stress produced results closer to experiments than the quadratic interaction criteria (QIC). For the 18 gauge specimens it was found that the through-thickness shear dominated the failure initiation for very close proximity charges, with the direct strain becoming dominant as the standoff was increased. For the thinner 20 and 22 gauge plates the direct strain was always found to be the dominant factor in the failure criteria.
The study describes recent simulation results for underwater explosions in close-proximity to rigid targets. Simulations are performed using Chinook, an Eulerian computational fluid dynamics (CFD) code. Predicted target loadings are compared with measurements taken from a series of experiments conducted under an international collaboration between Canada, The Netherlands, and Sweden. The simulations of the rigid target tests focused on the modelling of gas bubble collapse and water jetting behaviour. Both two-dimensional and three-dimensional simulations were performed. It was found that the two-dimensional analyses produced good bubble periods and reasonable impulse loading compared to experimental data. The time of arrival of the bubble collapse and water jetting were found to be very mesh dependent and refining the mesh did not always produce better results. The two-dimensional approach provides a good initial understanding of the problem for a reasonable computational effort. The three-dimensional simulations were found to produce improved impulse predictions. The numerical gas bubble radii time histories are also compared to empirical time histories.
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