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This is Fig. 22 from the 1987 PANDA2 paper. This slide shows a single skin-T-stringer module:
(a) Discretized model of a tee-stiffened module with
(b) a local bifurcation buckling mode.
Model (b) is used by PANDA2 to determine local post-buckling behavior and stiffener pop-off.
Discretization of the module cross section is the same as that used in the BOSOR4 code: The "meridian" (arc length along each segment of the skin-stringer cross section) is discretized, and variation of the buckling modal displacements normal to the plane of the screen is trigonometric with m axial half-waves (strip method). The critical local buckling mode is found by searching over a range of m established by PANDA2 automatically or specified by the PANDA2 user.
Wide-column buckling, an approximate model of general instability or of inter-ring buckling if there exist rings, is obtained from the same single-module model except that the normal buckling modal displacement at the left-hand edge of the model is set equal to that at the right-hand edge of the model instead of being set equal to the negative of that at the right-hand edge of the model, as is done for local buckling.
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