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STAGS model of general buckling of a ring and stringer stiffened axially compressed cylindrical shell previously optimized by PANDA2

This and the next 10 slides are concerned with buckling of an axially compressed, imperfect, internal T-ring- and external T-stringer-stiffened, optimized cylindrical shell.

These 11 slides are from the paper: David Bushnell, "Optimization of an axially compressed ring and stringer stiffened cylindrical shell with a general buckling modal imperfection", AIAA 48th Structures, Structural Dynamics, and Materials Conference, Paper no. AIAA-2007-2216, 2007.

In the next several slides this paper is referred to as "2007 paper by Bushnell" or "2007 Bushnell paper".

This slide shows the critical general buckling mode shape obtained from a STAGS model of an optimized axially compressed cylindrical shell with external T-shaped stringers and internal T-shaped rings. (The optimized design was obtained by Bushnell's computer program, PANDA2.)

This general buckling mode shape can be used as an initial imperfection in a subsequent STAGS execution with use of the same finite element model for static nonlinear equilibrium with step-wise increasing applied uniform axial load, Nx.

As the axial compression Nx increases the imperfect shell bends, giving rise to the following two effects:

1. stresses are redistributed over the skin and stiffeners, affecting the local buckling behavior and maximum stresses in the skin, in the rings, and in the stringers, and

2. where there exist inward lobes of the buckling modal imperfection pattern, which is amplified by the compressive loading, there exist locally flattened areas where the effective circumferential radius of curvature of the imperfect shell exceeds the nominal radius of the perfect cylindrical shell, causing a reduction in the general buckling load of the imperfect shell compared with that of the perfect shell.

Both of these effects are included in an approximate manner by PANDA2. The STAGS model shown here is used in order to verify the optimum design obtained by PANDA2.

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