Insight into the underwater implosion mechanisms of thin-walled metallic cylindrical shells

Underwater hollow structures are prone to implosion due to high hydrostatic pressure and structural imperfections. The implosion deformation patterns and induced shock wave impulses are quite involved, and the underlying mechanisms are still not clear. This paper presents an investigation of the implosion mechanisms of metallic cylindrical tubes. The finite element model is first established and validated by the existing experimental results. Numerical simulations are then performed for the aluminum alloy (6061-T6) cylindrical tubes with different length diameter and wall thickness. The deformation features, as well as the induced implosion shock wave characteristics, are analyzed, and the boundaries for the switch of deformation modes are derived. Furthermore, a comparison between the implosion of the cavity and that of the cylindrical shells is implemented. Results show that with the variation of geometrical dimensions, three deformation modes are developed for the cylindrical shells. The implosion shock wave pressure is non-uniformly distributed in the nearby fluid field, and the higher peak is generated in the area around the valleys of the deformed shells. The finding of this work can help understand the implosion mechanics and facilitate the design of underwater hull structures.