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

Structural analysis of spherical pressure hull viewport for manned submersibles using biological growth method

<p>Manned submersibles are important platforms for exploration and research under the oceans. One of the most important components of the manned submersible is the viewport, which develops high stresses due to the nature of its design. The basic dimensions of the viewport window and its flange are determined using ASME PVHO-1. Analysis of the viewport for given basic dimensions, shows that the corners of the low-pressure face of the viewport window and the notch regions of the flange are subjected to high stresses. Using the fillet radius method at the notch region results in stress reduction by 64%. The biological growth method helps in getting the naturally optimised shape at the corner. The use of the biological growth method for structural shape modification reduces the stress acting on the acrylic viewport by 71%. The same method applied to the flange notch region reduces its sharpness and the stress there by a considerable amount. This also helps in increasing the number of cycles of operation.</p