Optimization of composite stiffened panels with postbuckling constraints P. Arendsen, H.G.S.J. Thuis, J.F.M. Wiggenraad National Aerospace Laboratory NLR, P. 0. Box T/te ABSTRACT An optimization code is described which allows the design of stiffened composite panels with buckling and postbuckling constraints.The analysis makes use of a simple analysis model and an assumed simplified representation of the postbuckling behavior of the panel. The optimization strategy makes use of linking and scaling of variables, and employes an approximate model of the constraints. This selection of analysis and optimization procedures allows panel designs that are produced in seconds, using a NEC SX-3 supercomputer. The accuracy of the postbuckling analysis is demonstrated by comparison with experimental values. The optimization strategy is elucidated by discussing a solution to avoid global buckling mode jumping. INTRODUCTION Stiffened panels are important components of today's and tomorrow's composite structures for civil aircraft. Restricting the subject to the mechanical performance of light and intermediate wing and empennage panels, it is well known from experience with metal panels, that lighter panel designs may be obtained when buckling is allowed below Design Ultimate Load. Presently, the postbuckling behavior of stiffened panels made of composite material is equally well understood and predictable, as nonlinear analyses of detailed finite element models usually provide solutions that closely approximate experimental results. To incorporate desirable postbuckling characteristics of a stiffened panel already in the design phase, where many alternatives need to be evaluated, quicker, hence less complicated analysis tools are required, that can be consulted frequently during an optimization process. Such an analysis tool requires a simple model with considerably less degrees of freedom, and a simplifiedapproximation of the postbuckling behavior to avoid elaborate incremental procedures needed for nonlinear analyses. Resticting the design loads to inplane compression, and requiring the geometry to be prismatic, the model can be simplified by assuming sinusoidal displacements in the longitudinal direction, hence allowing the use of a finite strip model. The postbuckling behavior for flat stiffened panels loaded in compression can be simplified by assuming the initial postbuckling stiffness to remain unchanged when progressing into the postbuckling regime. This paper presents a description of an optimization code for the design of prismatic, stiffened panels made of composite material, loaded in compression into the postbuckling regime, named PAN OPT. The major constraints that are imposed on the Transactions on Engineering Sciences vol 4, © 1994 WIT Press, www.witpress.com, ISSN 1743-3533
Optimization of composite stiffened panels with postbuckling constraints
Jun 14, 2023
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