Optimum Design of Stiffened Panels With Substiffeners

Abstract

The capability of the computer program PANDA2 to generate minimum-weight designs of stiffened panels and cylindrical shells is enhanced to permit the adding of substiffeners with rectangular cross sections between adjacent major stringers and rings. As a result many new buckling margins exist that govern buckling over various domains and subdomains of the doubly stiffened panel or shell. These generally influence the evolution of the design during optimization cycles. The substiffeners may be stringers and/or rings or may form an isogrid pattern. The effects of local, interring , and general buckling modal imperfections can be accounted for during optimization. Perfect and imperfect cylindrical shells with external T-shaped stringers and T-shaped rings and with and without substringers and subrings and under combined axial compression, external pressure, and in-plane shear are optimized by multiple executions of a "global" optimizer called SUPEROPT. It is found that from the point of view of minimum weight there is little advantage of adding substiffeners. However, with substiffeners present the major stringers and rings are spaced farther apart at the optimum design than is so when there are no substiffeners. The weight of a cylindrical shell with substiffeners is much less sensitive to the spacing of the major T-shaped stringers than is the case for a cylindrical shell without substiffeners. The optimum designs obtained by PANDA2 are evaluated by comparisons with buckling loads obtained from a general-purpose finite element program called STAGS. Predictions from STAGS agree well with those from PANDA2.

Stiffened panel stability behaviour and performance gains with plate prismatic sub-stiffening

“…Considering static strength, Bushnell and Rankin [10] demonstrated that including small substiffeners between the conventional primary stiffeners can, 'not only lead to an increased buckling resistance, but more importantly to a much more robust optimum in terms of stiffener pitch'. Murphy et al [3] experimentally and computationally examined plate substiffening, demonstrating potential combined performance gains for both initial plate buckling and panel post-buckling collapse.…”

Non-prismatic sub-stiffening for stiffened panel plates—Stability behaviour and performance gains

“…What is more, Bushnell and Rankin [3] demonstrated that including small sub-stiffeners between the conventional primary stiffeners 'can not only lead to an increased buckling resistance, but more importantly to a much more robust optimum in terms of stiffener pitch'. Additionally, the damage tolerance characteristics of stiffener panel structures may be improved by the addition of plate element features designed to retard fatigue crack growth [4][5][6][7].…”

Aerospace Stiffened Panel Initial Sizing With Novel Skin Sub-Stiffening Features

“…Considering static strength, numerous plate [9][10][11]18 and panel studies [12][13][14][15][16][17][19][20][21] have demonstrated that non-uniform skin thickness can be used to tailor local stability behaviour. Quinn et al 14 experimentally and computationally demonstrates that the introduction of prismatic unflanged blade sub-stiffeners within panel skin bays (see Figure 1) can significantly modify initial stability behaviour and improve both the initial buckling, and post buckling collapse performance, thus using sub-stiffeners as panel "buckling containment features".…”