Buckling of complex toroidal shell structures

A recent innovation in the design of submersibles is the employment of a series of circular pipes to form part of the pressure hull. These pipes serve as storage for gaseous oxygen, which is mixed with fuel oil to drive a diesel engine in a closed-cycle mode. One of the structural design problems with these vessels is the calculation of the local buckling pressure of the hull and in this paper this is tackled by isolating a short section of the vessel. Two adjacent toroids were considered first, together with their connecting annular segments. Then three toroids were considered. The loading was external pressure on the external surface of the vessel plus the axial thrust caused bl, the pressure on the end closures. The stress distributions, elastic-plastic buckling pressures and mode shapes were determined using the variational finite-difference BOSOR5 program. Factors investigated for the 2-torus case were: the shape of the connecting segments, the constraint conditions at the contact point between the toroids and the influence of the yield stress. The results of the investigation showed that. (i) the local buckling pressure of the 3-torus structure was almost the same as that of the 2-torus case; and (ii) cylindrical connecting segments gave a higher buckling pressure than circular toroidal ones. A simple approximate method for calculating the local buckling pressure of the 2-torus shell structure was also checked. It turned out to be conservative, giving a buckling pressure,which was about three-quarters of the BOSOR5 value. Copyright (C) 1996 Elsevier Science Ltd.