Non-linear buckling analysis of imperfect thin spherical pressure hull for manned submersible

Thin spherical pressure hulls are used as a human occupancy in deep water applications. DNV and other standards specify the imperfection allowed for pressure hulls. Numerical analyses are carried out to find the buckling pressure for both perfect and imperfect thin spherical pressure hulls, considering the geometric and material non-linearities. It is observed that there is a huge variation in the elastic and inelastic buckling pressure in perfect spherical pressure hulls. Moreover, if the manufacturing imperfections are considered in the inelastic numerical analysis, still there is a reduction in the buckling pressure. Design criteria, for deep water pressure hulls, is that both buckling pressure and yield pressure must be greater than the design pressure. In the elastic analysis, if t/D > 0.006 buckling pressure is always greater than the yield pressure whereas in the inelastic analysis, the buckling pressure is falling below the yield pressure for all t/D ratios. Hence, inelastic numerical analysis with manufacturing imperfection has to considered in the design of deep water spherical pressure hulls of manned submersibles.