The Implosion of Cylindrical Shell Structures in a High-Pressure Water Environment*

The implosion of gas-filled cylindrical shell structures was studied experimentally in a nearly spherical tank with a nominal internal diameter of 1.77 m. Models were made from two brass tubes with diameters of 1.67 cm and 2.54 cm ($D)$ and wall thicknesses of 0.34 mm. The models were sealed with end caps and the lengths of the models were chosen to achieve the same internal volume ($V)$ and implosion pressure ($P_{a})$, and, therefore, the same available energy ($P_{a}V)$. Underwater blast sensors recorded dynamic pressure waves at 13 positions in the tank and a high-speed movie camera recorded the implosions. For both models, $P_{a}$ was about 31.5 bar, while the small- and large-diameter cylinders imploded with mode two and three cross-sectional shapes, respectively. The dynamic pressure signals decrease when the implosion begins and then reach a sharp positive peak when the walls of the cylinder collide. The implosion times (\textit{$\Delta $t}) when divided by the time scale for the implosion of a bubble ($T_{b}$ = 0.5D(\textit{ $\rho $ /P}$_{a})^{0.5}$ where \textit{$\rho $} is the water density) for the small- and large-diameter models were similar, 1.57 and 1.66, respectively. However, the dimensionless peak pressures ($P_{max}$/($P_{a}-P_{atm}))$ were quite different, 0.345 and 0.166, respectively, for these models.