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See:
http://pellegrino.caltech.edu/imperfection_shells.html
From:
Ning, X., and Pellegrino, S. (2013). “Imperfection-Insensitive Axially Loaded Cylindrical Shells”. 54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, 8 - 11 April 2013, Boston, Massachusetts. See also, International Journal of Solids and Structures, xxx (2015) xxx-xxx (13 pages, in press).
Ning and Pellegrino write:
In this research, we have designed symmetry-breaking wavy cylindrical shells that avoid imperfection sensitivity. Their cross-section is formulated by NURBS interpolation on control points whose positions are optimized by evolutionary algorithms. Both perfect and imperfect structures are used to evaluate the value of objective function in our optimization. This is fundamentally different from conventional structural optimization in which usually only perfect structures are considered.
We have applied our approach to both isotropic and orthotropic shells and have also constructed optimized composite wavy shells and measured their imperfections and experimental buckling loads. Through these experiments we have confirmed that optimally designed wavy shells are imperfection-insensitive. We have studied the mass efficiency of these new shells and found them to be more efficient than even a perfect circular cylindrical shell and most stiffened cylindrical shells.
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