826. Minimum Weight Analysis of Fuselage Frames

Paper

Abstract

An automatic, iterative method is presented for obtaining the minimum weight design of a structure which supports given loads and whose design requirements such as stresses, deflections, and geometric constraints are satisfied throughout the structure to prescribed limits. It is assumed that the design parameters are known, that a continuous weight function can be constructed, and that a program exists for calculating the output stresses or deflections at selected points on the structure. The design variables are varied automatically and simultaneously in a calculated direction for minimum weight until a fully stressed design is obtained. The rate of convergence is dependent on the initial guesses of the input variables, on the dimensionality of the problem (total number of free variables) and on the complexity and behavior of the structure. Particular attention is devoted to an illustrative example involving the design of a fuselage frame under assumed design criteria and under multiple loading conditions. It is found that the method can effect an appreciable weight saving and is especially applicable to trade-off and sensitivity studies.