Intelligent optimum design of large-scale gradual-stiffness stiffened panels via multi-level dimension reduction.

Grid-stiffened structures have excellent performance, such as high specific stiffness and strength, and are widely used as critical load-bearing structures in aerospace equipment, including launch vehicles and spacecraft. It is now a well-established fact that curvilinearly stiffened panels with curved stiffener paths and varying stiffness distributions significantly improve load-bearing efficiency. However, existing methods are usually designed based on two clusters of approximately orthogonal stiffeners, which may limit the design flexibility and load-carrying potential of such structures. In the proposed design method, various complex variations of curved stiffener layouts can be characterized with a simple set of variables by establishing a database of stiffener unit cells and feature dimension reduction, as well as using coordinate transformation and monotonicity preserving interpolation methods for geometric dimension reduction, respectively, which allows simultaneous selection of basic stiffener unit cells and adjustment of stiffener paths. Based on the structure characterization with high design flexibility, the hyperparameter dimension reduction of the Kriging model is introduced, thereby forming an optimization framework through multi-level dimension reduction, while ensuring the efficiency of the optimization process. Moreover, an accurate geometric modeling based on NURBS is proposed to meet the needs of designing stiffened structures on various types of complex surfaces. In two typical aerospace cases, the developed structural concept and design method can improve structural performance by over 80 % compared to initial design schemes with straight stiffeners and constant stiffness. The results demonstrate that both the developed structural concept and design methodology effectively enhance the upper performance design limit of stiffened structures. These findings are practically significant for the application of advanced lightweight thin-walled structures in aerospace equipment. [ABSTRACT FROM AUTHOR]