Abstract:
Buckling strength of shell structures under compression significantly drops if cutouts exist. In order to compensate this, these structures are reinforced with stiffeners. In this thesis, the objective is to optimize stiffener geometry and pattern on a cylindrical shell with two square holes to maximize the buckling load capacity without increase in weight. A finite element models is developed to evaluate the buckling load of the structure. A good correlation is observed between the nonlinear analysis results of the model and the numerical and experimental results reported in the literature. Optimization is achieved in two levels. In the first level, topography optimization is performed to obtain the optimal stiffener pattern over the shell surface based on linear eigenvalue buckling analyses. In the second level, the stiffener heights and shell thickness are optimized using a local search algorithm, Nelder-Mead. Buckling load levels are obtained by carrying out nonlinear buckling analyses in ANSYS. A PHYTON code is developed to implement the optimization method and conduct analyses in ANSYS. The results show that stiffeners need to be introduced around the cutouts and the regions near the top and bottom edges for maximum buckling load capacity. The results also reveal that stiffeners on the mid lateral surfaces of the cylinder do not make considerable contribution to buckling strength. The bucking load of the optimized stiffened geometry is 22% higher than that of the unreinforced geometry having the same weight.
