The implosion of cylindrical shell structures in a high-pressure water environment

Abstract

The implosion of cylindrical shell structures in a highpressure water environment is studied experimentally. The shell structures are made from thin-walled aluminium and brass tubes with circular cross sections and internal clearance-fit aluminium end caps. The structures are filled with air at atmospheric pressure. The implosions are created in a high-pressure tank with a nominal internal diameter of 1.77 m by raising the ambient water pressure slowly to a value, P c , just above the elastic stability limit of each shell structure. The implosion events are photographed with a high-speed digital movie camera, and the pressure waves are measured simultaneously with an array of underwater blast sensors. For the models with larger values of length-to-diameter ratio, L/D 0 , the tubes flatten during implosion with a two-lobe (mode 2) cross-sectional shape. In these cases, it is found that the pressure wave records scale primarily with P c and the time scale R i √ ρ/P c (where R i is the internal radius of the tube and ρ is the density of water), whereas the details of the structural design produce only secondary effects. In cases with smaller values of L/D 0 , the models implode with higher-mode cross-sectional shapes. Pressure signals are compared for various mode-number implosions of models with the same available energy, P c V, where V is the internal air-filled volume of the model. It is found that the pressure records scale well temporally with the time scale R i √ ρ/P c , but that the shape and amplitudes of the pressure records are strongly affected by the mode number.

Mitigation of pressure pulses from implosion of hollow composite cylinders

“…This method of temporal scaling has been used successfully for the implosion of metallic cylinders in recent work. 10 In the plots in Figure 3, t¯=0ms represents the moment of wall contact.

Figure 3.Local pressure histories measured at midspan, normalized by collapse pressure, plotted against dimensionless time for exterior coated specimens.

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“…studied the free-field implosion of aluminum and brass tubes with varying geometries, to examine the effect of collapse mode on the emitted pressure pulse. 10…”

Computational analysis of bubble–structure interactions in near-field underwater explosion

“…While most research on submarines is classified, several applicable papers have been published regarding the collapse of cylindrical tubes under hydrostatic loading, shock-induced loading, and the combined loading of both these conditions. Ikeda presented a study that discussed how the length/diameter ratio influenced the mode of collapse of a cylindrical shell and found that models with a larger length/diameter ratio collapsed in mode 2, whereas models with a smaller ratio collapsed in a higher mode [16]. Kyriakides et al also performed multiple investigations on how imperfections and characteristics of the geometry of a cylindrical shell would influence collapse, including studies on denting [17], localization of collapse on finite-length shells [18], and the collapse of long cylindrical shells under the combined loads of external hydrostatic pressure and bending [19].…”

“…Even an ovality of 1% can have a significant impact on the critical pressure of a cylindrical shell, potentially reducing the collapse pressure of a thick-walled pipeline by over 25% [23]. An ovality of 10% would have even more drastic influence on the critical pressure of a cylinder, reducing it to 50% that of a cylindrical shell that had no ovality [16].…”

Study of dynamic underwater implosion mechanics using digital image correlation

“…Ikeda et al [9] reported that, during an implosion process, the structure becomes so weak that the influence of the structural details on the pressure waves can be neglected and the structure behaves similarly to a bubble of low-pressure gas. Hence, the pressure wave records and the time primarily scale with the critical collapse pressure and the time period of the equivalent size bubble oscillations, respectively.…”