Ultimate Load-Carrying Capacity Analysis of a Deep-Submersible Pressure Hull Based on Patran/Nastran

The load-bearing performance of a pressure hull is one of the key factors controlling the operational depth and safety of deep-submersible vehicles. In this paper, a titanium-alloy spherical-cylindrical pressure hull reinforced with external T-shaped stiffeners was investigated under external hydrostatic pressure. A finite element model was developed in Patran, and both linear eigenvalue buckling analysis and nonlinear post-buckling analysis were carried out with Nastran. The eigenvalue analysis was used to identify the initial buckling characteristics, while the first buckling mode was introduced into the nonlinear model as an initial geometric imperfection. The ultimate critical pressure was then obtained by using the Riks arc-length method. The effects of stiffener size and stiffener number were examined in detail. The results indicate that enlarging the T-section stiffeners can significantly improve the buckling resistance of the hull, but the improvement becomes much smaller after the stiffener dimensions reach a relatively high level. Among the geometric parameters studied, the web height shows the most obvious influence on the ultimate pressure, whereas the flange width has a limited effect. Increasing the number of stiffeners also improves the structural stability, but excessive stiffeners may cause additional weight and manufacturing cost. Considering structural performance and engineering economy together, the pressure hull with four stiffeners is selected as a reasonable configuration. For this design, the nonlinear ultimate critical pressure is 20.29 MPa, which corresponds to an approximate limiting diving depth of 2029 m. The study can provide a reference for the design and assessment of titanium-alloy pressure hulls used in deep-sea vehicles and subsea engineering equipment.