A study on the pressure vessel design, structural analysis and pressure test of a 6000 m depth-rated unmanned underwater vehicle

Abstract

MOERI-KORDI (Maritime and Ocean Engineering Research Institute—Korea Ocean Research and Development Institute) has conducted the development of an unmanned underwater vehicle (UUV) for 6000 m deep-sea exploration, which was completed in 2006. Several pressure vessels were mounted on the UUV frame for loading electric and electronic equipment. The pressure vessels were constructed with titanium alloy Ti–6Al–4V for two main cylindrical canisters and with aluminium alloy Al6061–T6 for several hemispherical housings of electric motor drivers, respectively. This article presents the design process of the pressure vessels and experimental results acquired by high-pressure tests, which were conducted with the cooperation between MOERI-KRISO and Japan Agency for Marine-Earth Science and Technology (JAMSTEC). The pressure vessels were designed on the basis of the buckling analysis as well as structural yielding analysis, and checked the safety by the finite-element analysis (FEA) and analytical (empirical) formula. Moreover, by structural reliability analysis, the cylindrical part and the end plates of the main pressure vessels made of Ti–6Al–4V were designed with a safety of 99.98% under circumstance of 75 MPa. The pressure housings made of Al6061–T6 were also designed by the same procedure. Pressure test was performed with the large high-pressure environment simulation unit of JAMSTEC. The pressure vessels made of the titanium–aluminium alloy were safe even when they were under pressure of 75.46 MPa. Test results show that there are less than 5% difference between the FEA and the high-pressure tests. In this research, the pressure test was conducted up to 75 MPa, which corresponds with a safety factor of 1.25. Even though this is lower than the usual safety factor of 1.5–2.5, this study shows that the pressure vessels are safe if we consider the reliability analysis.