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This paper details a numerical study of the dynamic stability of a cylindrical shell structure under combined hydrostatic and dynamic pressure loading within a tubular environment as compared to the traditional loading of hydrostatic pressure alone. Simulations are executed using a coupled Eulerian-Lagrangian scheme, within the dynamic system mechanics advanced simulation (DYSMAS) code, to explicitly model the (1) structural response of a single unstiffened cylindrical shell to dynamic pressure loading and (2) the fluid flow field within the surrounding environment due to the shock and the shell structural response. Simulations involve a non-pressure-compensated aluminum 6061-T6 cylindrical structure with a length-to-diameter ratio, L/D, equal to 9.6. This structure is 31.8 mm (1.25-in) in outer diameter and is concentrically and longitudinally centered within the outer tube, which has an inner diameter of 177.8 mm (7.00-in) and total internal length of 2.13 m (84-in). Simulations are run at four hydrostatic tank pressures, which are categorized by percentage of measured critical collapse pressure, Pc, of the shell structure: 66% Pc, 80% Pc, 85% Pc, and 90%Pc. For each case, the shell structure is subjected to shock loading created by the detonation of a commercial blasting cap at a given standoff to the structure within the confining tube. Simulated pressure histories are compared to experimental pressure data at gage locations. The simulations and corresponding experiments produce the same overall result for three of four cases (i.e., survive: 66%Pc or implode: 85%Pc and 90%Pc). For the 80%Pc case, the overall result differs between simulation and experiment in that the specimen in the experiment survives but the simulated cylinder implodes. However, the discrepancy between the overall experimental result and corresponding simulation is not deemed a failure for the 80%Pc case; instead, this signifies a transitional case for the dynamic stability of the shell structure (i.e., collapse is sensitive to small deviations from assumed conditions in this regime). [ABSTRACT FROM AUTHOR]

Energy-based metrics are developed and applied to a numerical test case of implosion of an underwater pressure vessel. The energy metrics provide estimates of the initial energy in the system (potential energy), the energy released into the fluid as a pressure pulse, the energy absorbed by the imploding structure, and the energy absorbed by air trapped within the imploding structure. The primary test case considered is the implosion of an aluminum cylinder [diameter: 2.54 cm (1 in.), length: 27.46 cm (10.81 in.)] that collapses flat in a mode-2 shape with minimal fracture. The test case indicates that the structure absorbs the majority (92%) of the initial energy in the system. Consequently, the energy emitted as a pressure pulse into the fluid is a small fraction, approximately 5%, of the initial energy. The energy absorbed by the structure and the energy emitted into the fluid are calculated for additional simulations of underwater pressure vessel implosions. For all cases investigated, there is minimal fracture in the collapse, the structure absorbs more than 80% of the initial energy of the system, and the released pressure pulse carries away less than 6% of the initial energy. [ABSTRACT FROM AUTHOR]

Abstract: Validation and application examples are presented for a beam-column element that uses bounding surface plasticity models to characterize the effects of blast-induced damage in structures with steel wide-flange members. Element formulation and implementation within the nonlinear explicit dynamic finite element code CU-BAMM appears in the companion paper . The current paper details the creation of a library of bounding surfaces for various wide-flange members and explosive scenarios, and library integration with the code. A validation example shows favorable agreement between CU-BAMM simulation results and results obtained from a high-resolution model for prediction of the post-blast collapse load for an A-frame system. [Copyright &y& Elsevier]

Abstract: A beam-column element is formulated and implemented within a nonlinear explicit dynamic finite element code for simulating explosive effects in steel skeletal structures composed of wide-flange members. Blast damage is encapsulated by a bounding surface plasticity model in stress-resultant space. Bounding surfaces are formed by fitting numerical failure data to a basis of real-valued spherical harmonics: the data are obtained through numerical experiments in which a shell element-based model of a member is exposed to a blast and then statically loaded to failure for various combinations of proportional moment-thrust loading. Code validation and examples are presented in a companion paper . [Copyright &y& Elsevier]

The current research presents a detailed methodology for generating air blast loading for use within a finite element context. Parameters describing blast overpressure loading on a structure are drawn from open literature sources and incorporated within a blast load generation computer code developed for this research. This open literature approach lends transparency to the details of the blast load modeling, as compared with many commonly used approaches to blast load generation, for which the details are not publicly available. As a demonstration, the load generation code is used with the finite element software LS-DYNA to simulate the response of a steel plate and girder subjected to explosions modeled using these parameters as well as blast parameters from other sources. [ABSTRACT FROM AUTHOR]