Modifications to PANDA2 are described which overcome some of the difficulties associated with the determination of a global optimum design in the presence of an initial general buckling modal imperfection. Minimum-weight designs are determined for this shell with an initial imperfection in the form of the critical general buckling mode. The maximum allowable stress is set very high so that stress constraints do not affect the evolution of the global optimum design in this example. Numerical results pertain to a metallic cylindrical shell with external T-shaped stringers and external T-shaped rings subjected to combined axial compression, external pressure and in-plane shear (torque).
Details are given on how PANDA2 determines the effect of an initial buckling modal imperfection on the load bearing capability of a ring and stringer stiffened cylindrical shell. PANDA2 is described with emphasis on the many different stress and buckling constraints that can affect the evolution of a design during optimization cycles, on the way that imperfections are treated, on certain difficulties that imperfections may cause during optimization cycles, and on difficulties encountered during attempts to evaluate optimum designs with the use of the STAGS general purpose finite element program. Some difficulties encountered during this project are described.īushnell, David and Rankin, Charles C., (Lockheed Martin Advanced Technology Center, Palo Alto, California, USA), “Difficulties in Optimization of Imperfect Stiffened Cylindrical Shells”, AIAA 47th Structures, Structural Dynamics and Materials Conference, AIAA-2006-1943, 2006ĪBSTRACT: The PANDA2 computer program generates minimum-weight designs of ring and stringer stiffened flat or cylindrical composite panels subjected to multiple sets of load combinations. The behavior of shells with an initial imperfection in the form of a general buckling mode of the imperfect shell is described from a physical point of view. Many STAGS models of optimized shells and subdomains of shells with Blade, Zee, and Tee stiffening are generated and explored, both with respect to linear bifurcation buckling and nonlinear collapse. In STAGSUNIT the edge conditions are formulated so that STAGS models of subdomains of a long cylindrical shell with many stiffeners can be constructed that do not have artificial prebuckling stress concentrations near the edges that might significantly affect predictions of bifurcation buckling and nonlinear collapse of the subdomain. A new PANDA2 processor called STAGSUNIT automatically generates STAGS input files for cylindrical panels and shells with both stringers and rings that have various open cross sections such as Blades, Zees, Jays, Tees and Is.
The good agreement between PANDA2 and STAGS predictions for the nonlinear collapse of imperfect stiffened shells justifies the use of PANDA2 for preliminary design.
#Its shell does not crack crossword code#
Bushnell, David and Rankin, Charles C., (Lockheed Martin Advanced Technology Center, Palo Alto, California, USA), “Optimiztion of perfect and imperfect ring and stringer stiffened cylindrical shells with PANDA2 and evaluation of the optimum designs with STAGS”, AIAA 43rd Structures, Structural Dynamics and Materials Conference, AIAA-2002-1408, 2002ĪBSTRACT: Ring and stringer stiffened perfect and imperfect angle-ply cylindrical shells under combined axial compression and in-plane shear are optimized with a program called PANDA2 for the minimum weight design of stiffened panels, and the optimum designs are then evaluated with use of a general purpose finite element code called STAGS.
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