On the Dynamic Collapse of Cylindrical Shells Under Hydrostatic and Impulsive Pressure Loadings

Abstract

The dynamic collapse of submerged cylindrical shells subjected to lateral impulsive
pressure loads caused by underwater explosions is studied via coupled experimental and numerical
work. The parent problem of the dynamic collapse of such structures under hydrostatic pressure is also investigated. Two sets of experiments were performed. Initially, 50.6mm outside diameter aluminum tubes with diameter-to-thickness ratio of 32.3 were tested inside a pressure vessel. Hydrostatic pressure was applied quasi-statically up to the onset of collapse in order to obtain the collapse pressure of the tubes tested. Subsequently, similar tubes were tested in a 5m x 5m x 1.6m deep water tank under various explosive charges placed at different distances. Explosive charges and standoff distances were combined so as to eventually cause collapse of the specimens. In both sets of experiments, dynamic pressure and strain measurements were recorded using a fit-for-purpose data acquisition system with sampling rates of up to 1 Mega Samples/sec per channel. In parallel, finite element models were developed using commercially available software to simulate underwater explosion, pressure wave propagation, its interaction with a cylindrical shell and the subsequent onset of dynamic collapse. The surrounding fluid was modeled as an acoustic medium, the shells as J2 flow theory based materials with isotropic hardening, and proper fluid-structure interaction elements accounting for relatively small displacements of the boundary between fluid and structure were used. Finally, the physical explosion experiments were numerically reproduced with good correlation between results.