Optimization of Cylindrical Stiffened Shells in Large Launch Vehicles Considering Manufacturing Tolerance

To improve the reliability and safety of cylindrical stiffened shells in large launch vehicles under the influence of manufacturing tolerance, the optimization of cylindrical stiffened shells is carried out considering manufacturing tolerance. The collapse mechanism of the cylindrical stiffened shells is investigated. The influences of the buckling modes and key parameters of stringers on the load-carrying capacity of cylindrical stiffened shells are also analyzed and summarized, which overturns the traditional design concept of enhancing the bending stiffness of the stringers. A parallel sequential approximate optimization incorporating an exploration strategy and an exploitation strategy is proposed, which improves the computational efficiency of the post-buckling optimization of cylindrical stiffened shells and obtains an optimum structural with a reduction of 482 kg compared with the initial design. Furthermore, a novel optimization method considering manufacturing tolerance for cylindrical stiffened shells is proposed based on the sequential approximate optimization method and the maximum manufacturing error analysis, which significantly reduces the probability of the premature failure of the optimized structure under the influence of manufacturing tolerance and enhances the reliability and safety of the cylindrical stiffened shells. Some conclusions can be drawn from the results. The flexural-torsional coupling buckling of stringers becomes the main factor of the collapse of the cylindrical stiffened shells. What's more, the load-carrying efficiency of the cylindrical stiffened shells can be elevated by reducing the width-thickness of the flange plate and increasing the height-thickness of the web without local instability. Finally, the optimized structure obtained under the consideration of manufacturing tolerance has a thicker flange plate and its load-carrying performance is more reliable under the influence of the manufacturing tolerance, indicating the effectiveness of the proposed optimization method.