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A comprehensive experimental!numerical study on the implosion of longitudinally offcentered cylindrical implodable volumes was conducted within a tubular confining space. In partic ular, the aim of this study was to examine the changes in the implosion mechanics and in the nature of pressure waves, arising from the longitudinally off-centered location of the implodable volume. Experiments were conducted with 31.8 mm outer diameter, cylindrical aluminum 606I-T6 implodable volumes placed concentrically within the confining tube. Three longitudinal offset locations were chosen within the confining tube, such that distance from the center of the implodable volume to the center of confining tube is equal to: (a) zero, (b) 317 of the half-length of confining tube (L), and (c) 5 U7. Pressure transducers mounted on the inner suiface of the confining tube were used to capture the pressure waves released during the implosion event. Computational simulations were performed using a coupled Eulerian-Lagrangian scheme to explicitly model the implosion process of the tubes along with the resulting compressible fluid flow. The experiments revealed that the longitudinal asymmetric placement of the implodable volume enhances the strength of hammer pressure waves generated during the implosion process. The off-centered location of the implodable volume causes a pressure imbalance in the entire length of the confining tube. Hence, the water particle velocity shifts toward the implodable volume producing high pressure region at the end-plate near the implodable volume, while the other end-plate experiences significantly longer cavitation due to low pressure. This far end-plate cavitation duration is also found to increase with increasing longitudinal offset, even though the total combined cavitation duration at both the end-plates is approximately same for all offset locations. With high correlation observed between the experiments and simulations, computation models were further used to correlate the longitudinal offset and the signature of pressure waves at various interpolated locations. Simulations show that there is increase in both the peak pressure and the impulse of the hammer wave with increasing longitudinal offset of the implodable volume. Simulations also show that the collapse rate of the implodable volume decreases with the increasing longitudinal offset. [ABSTRACT FROM AUTHOR]

A fundamental experimental investigation, with corresponding computational simulations, was conducted to understand the physical mechanisms of implosions of cylindrical shells occurring within a tubular confining space which has a limited potential energy reservoir. In particular, attention was focused on studying the generation of pressure waves from the implosion, the interaction of the pressure waves with the confining tube walls and end caps, and the collapse mechanisms of the implodable volume. Experiments were conducted with three implodable volume geometries which had similar critical collapse pressures. The implodable volumes were aluminum 6061-T6 cylindrical tubing and were placed concentrically within the confining tube. Pressure histories recorded along the length of the confining tube during the experiments were utilized to analytically evaluate the deformation of the implodable volume using fluid–structure coupled deformation models. Computational simulations were conducted using a coupled Eulerian–Lagrangian scheme to explicitly model the implosion process of the tubes along with the resulting compressible fluid flow. The numerical model developed in this study is shown to have high correlation with the experimental results and will serve as a predictive tool for the simulation of the implosion of different cylindrical geometries as well as various tube-in-tube implosion configurations. The experimental results show that the limited hydrostatic potential energy available in a confined environment, as compared to a free field, significantly influences the implosion process. The wall velocities of the implodable volume during the collapse, as well as the extent of the collapse progression, are largely affected by the sudden decrease in the available hydrostatic potential energy. This energy is shown to be partially transformed into elasto-plastic strain energy absorbed in the deformation of the implodable volume, as well as the kinetic energy of the water during the implosion process. Experiments also show that the extent of the collapse progression of an implodable volume can potentially be inhibited within a closed environment, which can lead to the arresting of an implosion event prior to completion for larger implodable volumes. The pressure waves generated during collapse comprise of waves emitted due to the impact of the implodable volume walls, the arrest of rushing water and contact propagation along the walls. These processes later evolve into water hammer type axial wave behavior. [ABSTRACT FROM AUTHOR]

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]