Airframe optimization based on structural evolution simulation by means of the GA and sequence of numerical models

Abstract

The peculiarities of aircraft structural optimization are discussed. It is shown mat structural mass is very important indicator which must be minimized for successful airframe. However the accurate optimal problem formulation and solution are possible if some of most influential parameters are defined in advance and fixed during search of structural mass minimum. Therefore to include these influential parameters in the set of design variables (DVs) more general function, relative expenses, is chosen as a goal function and structural optimization problem is formulated as a task of airframe relative expenses minimization subject to broad spectrum of constraints. Vector of design variables x is divided into three subvectors (s), (r and m). Vector (s(describes principal parameters which define aerodynamic layout, structural scheme and structural material type. Vector r consists of shape and skeleton parameters, for example position of spare in wing structure or angle of stringers orientation. Material distribution parameters like thickens or area of cross section are described in m vector. Optimization problem solution is presented as evolution of the conception, therefore the design process is an iterative one, where the sequence of models are used and values of design variables are verified. GA is used in external loop of the algorithm for search of the best set of s-type of DVs which are treated as structural genes. In inner loops the genotype string of each individual is decoded into phenotype and the embryo is developed as the sequence of numerical models. Skeleton (r-type) and muscular (m-type) parameters are optimized by ordinary methods of structural mass minimization. Conceptual design of short-range passenger aircraft is presented as a numerical test. The test demonstrates the workability of the method, algorithm and software created in this research.