OPTIMAL-DESIGN OF IMPERFECT, ANISOTROPIC, RING-STIFFENED CYLINDERS UNDER COMBINED LOADS

Development of an algorithm to perform the optimal sizing of buckling resistant, imperfect, anisotropic ring-stiffened cylinders subjected t o axial compression, torsion, and internal pressure is presented. An a xisymmetric, geometrically nonlinear prebuckling equilibrium configura tion is assumed and both stress and stability constraints are consider ed. The enforcement of stability constraints is treated in a way that does not require any eigenvalue analysis. Case studies performed using a combination of penalty function and feasible direction optimization methods indicate that the presence of the axisymmetric initial imperf ection in the cylinder wall can significantly affect the optimal desig ns. Weight savings associated with the addition of two rings to the un stiffened cylinder and/or the addition of internal pressure is substan tial when torsion makes up a significant fraction of the combined load state.