Comparative Study on Optimal Stiffener Placement for Curvilinearly Stiffened Panels

Abstract

Recent studies have shown that curved stiffeners offer potential for structural tailoring of metallic panels. However, the optimal placement of the stiffener curves has remained a challenge, due to both the presence ofmultiple localminima in the design space as well as the associated CPU cost to solve the problem. This paper presents two new approaches to design the stiffener curves by decomposition of the design space into size and shape variables. The approaches are built on a heuristic concept of effectiveness of a stiffener configuration, which argues that the most effective configuration will also provide the lowest optimized panel mass. The first approach estimates the best stiffener configuration, based purely on the first buckling mode of the unstiffened panel. The approach defines a heuristic metric for the effectiveness of a stiffener in increasing the buckling load capacity of a panel. The second approach uses optimization methods on both the sizing and shape variable subspaces. Mass is minimized over the sizing variable subspace, with constraint on buckling, while the buckling eigenvalue is maximized over the shape design variable subspace by varying the stiffener curves. The results are compared with optimization over a unified design space using a global optimization procedure, and it is shown that the proposedmethods lead to better designs at lower CPU cost.