NEW STRUCTURAL DESIGN OF SPHERICAL PRESSURE HULL FOR DEEP-SEA SUBMERSIBLES:A MULTILAYER AND PRESSURE REDISTRIBUTION APPROACH

The pressure hull is the most important key structure to a deep-sea submersible, whose safety and overall performance depend on the integrity of the pressure hull. The current single shell design of the pressure hull is reviewed and a new design based on the multilayer and pressure redistribution mechanism is also proposed in this study. The design is inspired by two deep-sea animals of sperm whale and nautilus. The two mechanisms, the multilayer structure of sperm whale and the shell substructure divided by the septa of nautilus, are synthesized in the design to improve the pressurebearing capacity of the hull. Compared with the one layer structure of the pressure hull, the new design increases both the structural strength and buckling load. Furthermore, the new design can also significantly improve the overall performance of the deep-sea submersible by enlarging the hull volume, enhancing its reliability and lessening the technical challenges of fabricating ultra-thick shell structure. Because the truss structure is introduced in the new shell design, which effectively divides a spherical shell into several substructures of cylindrical shell, a formula is strictly derived to evaluate the truss effect on the buckling load bearing capability of a cylindrical shell. The difference between the newly derived formula and the formula of the Taylor basin, which is summarized from the experimental data and widely used as a standard for the current design of submersible shell, is only 6%. Furthermore, this new derivation also lays a solid theoretical foundation for our new shell design.