Collaborative Optimization Of Aerospace Multi-stage Structure Considering Load Path

With the great development of China's launch vehicle design level and major national safety requirements such as manned moon landing and deep space exploration,the complexity of the launch vehicle structural system has added significantly.Due to the increasing of number of segments and parts,the structural optimization design difficulty will increase dramatically.The multi-segment structure is widely applied in the design of aerospace craft.However,several challenges such as the large-scale numerical analysis of finite element analysis model,numerous design variables in structure design optimization and heavy computational cost of the optimization process,remain to be solved.Based on the conventional design methods of stiffened shell,the entire structure is uniformly reinforced,i.e.the sensitive domain and non-sensitive region adopt the same design.It should be mentioned that this design is not conducive to the realization of structural weight reduction design because of the low material utilization in non-sensitive region.The multi-segment partition design and non-uniformly stiffener design,an significant method to enhance the level of refined design of aerospace load-carrying structure,can fully tap the structural load-carrying capacity potential.The aerospace structure booster segment is taken as the research object in this paper.And its 3D finite element model with shell element is established on the basis of ABAQUS software.The concept of generalized structural stiffness U~*is introduced and a method for extracting the main load path of 3D structure is proposed in this paper.The generalized structural stiffness nephogram of the entire structure is obtained by clamping every node in a fixed order.The entire structure is layered from top to bottom according to the element,and the main load path of the booster structure is obtained by fitting the node where the minimum generalized structure stiffness value of each layer is located.The difference between the actual load path and the ideal load path is compared by the uniformity evaluation index.The structure is partitioned reasonably by combining the structural stress analysis and topology optimization.Based on the proposed method,taking the structural mass as the constraint and the load-carrying capacity maximization as the optimization objective,Based on the surrogate model and the minimum response surface criterion,the design of oblique cone segment and the straight segment are collaboratively optimized.The results show that the optimum design of partitioned uniformly stiffened shell can improve the load-carrying capacity by 12.4%without increasing the structural weight.Furthermore,the optimization framework of non-uniformly stiffened multi-stage structure is established,based on PCHIP interpolation function and the previous optimum design,a non-uniformly stiffened shell characterization and optimization method for grid configurations is proposed.Then,the distribution of longitudinal stiffeners in each region is optimized with the overall structural weight constraint.The number of longitudinal stiffeners and the angle distribution coefficient of longitudinal stiffeners are set as variables.the structural load-carrying is set as the objective.The results indicate that the density of the stiffeners in the more sensitive regions are obviously increased and the material utilization is improved,which meet the design expectation.The results show that the optimum design of partitioned non-uniformly stiffened shell can improve the load-carrying capacity by 27.2%without increasing the structural weight.For the lofting curved surface structure segment that is widely used in aerospace structures,based on the structural load path,the design method of stiffener angle for lofting structure is proposed in this paper.Compared with the traditional orthogonal stiffener design,it can effectively restrain the local-buckling deformation of the lofted surface with much smaller thickness of stiffeners.This work has certain reference value for the design of multi-segment aerospace structures.