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

The implosion of cylindrical shell structures in a high-pressure 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, , 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, /, 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 and the time scale [Formula: see text] (where is the internal radius of the tube and is the density of water), whereas the details of the structural design produce only secondary effects. In cases with smaller values of /, 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, , where is the internal air-filled volume of the model. It is found that the pressure records scale well temporally with the time scale [Formula: see text], but that the shape and amplitudes of the pressure records are strongly affected by the mode number.