Multi objective optimization of orthogonally stiffened cylindrical shells using optimality criteria method

A multi objective optimality criteria (OC) is used to obtain optimum design of metal cylindrical shells under combined external loading. The objectives are to maximize the axial and hoop stiffness and minimize the mass of stiffened cylinders subject to the constraints including functions of weight and buckling load in such a way that the stiffened shell has no increase in the weight and no decrease in the buckling load with respect to the initial unstiffened shell. The optimization process contains six design variables including shell thickness, number of circular ring stiffeners, number of longitudinal stringer stiffeners, height of ring stiffeners, width of ring stiffeners, and longitudinal stiffeners eccentricity from shell's centerline. In analytical solution, the Rayleigh–Ritz energy procedure is applied and the ring stiffeners are treated as discrete elements. The shapes of the ring and stringer stiffeners are assumed as rectangular and Z, respectively. The shell is subjected to the uniform axial and non-constant external pressure, simultaneously. The longitudinal stringers are placed in equal spacing, whereas, the rings can be placed in unequal space due to non-constant of external pressure over the cylinder length. The results show that the iteration numbers depends on the ring stiffener space states.