This paper describes both the development of a new low-cost optimization method for the optimal design of laminated composite structures, and a result of applying this method to the minimum weight design of a hat-stiffened composite panel subject to a buckling constraint. The new method is based on two levels of optimization. In the low level optimization, the fractal branch and bound method is used for a stacking sequence optimization. In the high level optimization, the particle swarm optimization technique is used for optimizing configurations of the hat-stiffened panel. Moreover, a Kriging-based response surface is used to find the global optimum, and not just to approximate an objective function value. For this purpose, we use the 'expected improvement' (EI) criterion defined in the Kriging model. The validity of the proposed method is examined and the results show that the method provides valuable solutions with good precision and a low computational cost.
Stiffened composite panels are often used as structural components in aircraft in order to avoid buckling. It is well known that stacking sequence optimizations are indispensable for laminated composite structures. Stiffened composite panels usually have more than two stacking sequences because they consist of a panel skin laminate and stiffener laminates. This means that the stacking sequences need to be jointly optimized to achieve structural optimization of the stiffened composite panel. The authors have proposed a new stacking sequence optimization method, called the fractal branch and bound method, for optimizing a single laminate. In the present study, the fractal branch and bound method is extended to optimizing multiple stacking sequences. The extended method is applied for obtaining two optimal stacking sequences for the maximization of the buckling load of a hat-stiffened composite panel. The improved method successfully provides two optimal stacking sequences determined in a short period of time.
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