The The finite element models were updated and refined, using physical parameters, to increase correlation with the measured modal data. Excellent agreement, within an average 1.59/; to 2.9%, was obtained between the predicted and measured modal frequencies of the stringer, frame and dome components. The predictions for the modal frequencies &the assembled component Configurations I through V were within an average 2.9% and 9.1%. Finite element modal analyses were performed fbr comparison with 3 psi and 6 psi internal pressurization conditions in Configuration VI. The modal fi'eqnencies were predicted by" applying differential stiNless to the elements with pressure loading and creating reth_ced matrices for beam elements with offisets inside external superelements. The average disagreement between the measured and predicted diffi_rences tbr the 0 psi and 6 psi internal pressure conditions was less than 0.5%. Comparablygood agreement was obtained tbr the diftbrences between the 0 psi and 3 psi measured and predicted internal pressure conditions.
A procedure to design a structure for minimum sensitivity to uncertainties in problem parameters is described. The approach is to directly minimize the sensitivity derivatives of the optimum design with respect to fixed design parameters using a nested optimization procedure. The procedure is demonstrated for the design of a bimetallic beam for minimum weight with insensitivity to uncertainties in structural properties. The beam is modeled with finite elements based on two dimensional beam analysis. A sequential quadratic programming procedure used as the optimizer supplies the Lagrange multipliers that are used to calculate the optimum sensitivity derivatives. The procedure is validated by comparing the optimization results to parametric studies. 14. SUBJECT TERMS Optimization Robust design Design for uncertainty 17. SECURrrY CLASSIFICATION OF REPORT Unclassified NSN 7540-01-280-5500 Optimum sensitivity Uncertainties 18. SECURITY CLASSIFICATION OF THIS PAGE Unclassified lg. SECU RITY CLASSIFICATION OF ABSTRACT Unclassified 15. NUMBER OF PAGES 9
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