Optimal design of imperfect, anisotropic, ring-stiffened cylinders under combined loads

Abstract

Development of an algorithm to perform the optimal sizing of buckling resistant, imperfect, anisotropic ringstiffened cylinders subjected to axial compression, torsion, and internal pressure is presented. An axisymmetric, geometrically nonlinear prebuckling equilibrium configuration is assumed and both stress and stability constraints are considered. The enforcement of stability constraints is treated in a way that does not require any eigenva]ue analysis. Case studies performed using a combination of penalty function and feasible direction optimization methods indicate that the presence of the axisymmetric initial imperfection in the cylinder wall can significantly affect the optimal designs. Weight savings associated ~vith the addition of two rings to the unstiffened cylinder and/or the addition of internal pressure is substantial when torsion makes up a significant fraction of the combined load state.

Local behavior of discretely stiffened composite plates and cylindrical shells

“…This peak strain is about 3 times more than the corresponding strain of the unstiffened cylindrical panel at this location. This phenomenon of pillowing or bulging of the shell skin under pressure load resulting in localized regions of high strains near the stiffeners has also been reported in References [25][26][27]. However, note that far from the mid-point where there is a marked inflection point for the unstiffened case, the stiffeners tend to smoothen out the peak in circumferential strains.…”