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This and the next several slides are from the 2010 GENOPT paper, "Use of GENOPT and BIGBOSOR4 to optimize weld lands in axially compressed stiffened cylindrical shells and evaluation of the optimized designs by STAGS" by David Bushnell and Robert P. Thornburgh, AIAA 51st Structures, Structural Dynamics, and Materials Conference, 2010, AIAA Paper 2010-2927, referred to as "2010 GENOPT paper" in the next several slides.
ABSTRACT from the 2010 GENOPT paper:
BIGBOSOR4 is used in an optimization loop in which the dimensions of a typical axially oriented weld land and the cross-section dimensions of reinforcing Tee-shaped stringers along the two straight edges (generators) of the weld land are decision variables.
The optimization is carried out in a GENOPT context. Any number of equally spaced identical T-stiffened weld lands in a 360-degree cylindrical shell can be accommodated.
The weld lands are embedded in an internally stiffened "acreage" cylindrical shell that has been previously optimized by PANDA2. The previously optimized "acreage" cylindrical shell has internal "acreage" stringers and internal "acreage" rings with rectangular cross sections.
The spacings, heights, and thicknesses of the internal "acreage" stiffeners are not decision variables for the optimization problem in which the weld land and its reinforcing edge T-stringers are optimized.
The design constraints for the cylindrical shell with the T-stiffened weld lands are: 1. general buckling, 2. inter-ring buckling, and 3. stress.
The prebuckled state is assumed to be uniform end shortening, with the membrane axial compression in each segment of the structure proportional to the axial membrane stiffness of that segment. The prebuckled state is assumed to be a membrane state: no prebuckling bending. The entire shell structure is fabricated of the same material.
In the model for general buckling the previously optimized "acreage" rings and stringers are smeared out and the cylindrical shell is simply supported at its ends.
In the model for inter-ring buckling adjacent "acreage" rings are replaced by simple supports, that is, a length of shell equal to the ring spacing is analyzed, and the previously optimized "acreage" stringers are smeared out.
The maximum stress in the weld-land-edge-stringer region is computed as if there were no prebuckling bending (membrane compression only).
The cylindrical shell is modeled as a 180-degree segment of a huge torus, with symmetry conditions applied along the generators at zero and at 180 degrees.
In the GENOPT examples studied here there are three identical T-stiffened weld lands spaced at 120-degree intervals.
The adequacy of the optimized "acreage" cylindrical shell with and without the optimized T-stiffened weld lands is evaluated with various STAGS finite element models. There is good agreement between predictions from the GENOPT/BIGBOSOR4 model and the various STAGS models.
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