Design Tradeoffs for Fiber Composite Fuselages Under Dynamic Loads Using Structural Optimization

Abstract

In this paper a fuselage shell, made of fibers composite material, of a passenger aircraft is optimized to get a minimum weight. Two different structural configurations of foam-filled sandwich and stiffened shells are analyzed under the dynamic loads due to the gust. A knowledge based engineering (KBE) approach is formulized to automate the multidisciplinary optimization problem in three different layers. The first layer takes care of the optimization of full fuselage under the constraints of real and negative eigenvalues to get an asymptotically stable closed-loop system. The second layer and third layers, take care of the optimization of the several sections along the length of the fuselage and the optimization of a particular panel of a section, respectively. The constraints in the second and third layers include the critical buckling and wrinkling stresses of the panels and the sections, under bending and torsion loads. The design variables are the stacking sequence of fibers orientations, sizes and positions of the stiffeners in a panel, section length along the longitudinal axis of the fuselage, and the skin thicknesses of the panels. Finally both of the optimized designs are compared with each other in terms of minimum weight, stability and moreover in terms of manufacturing.

Multidisciplinary Design of Flexible Aircraft

“…For the turn by turn optimization of each panel, the computer program known as WISST [7] is called in each loop. Depending upon the position of a panel along the circumference of the fuselage, the loads in the 3 rd layer are converted into the load intensities of the panel under consideration [2]. Depending upon the panel type i.e.…”

“…To get the initial loads set, the input data required for the structural and aerodynamics properties of the aircraft are taken from the Reference 6. Flight conditions for symmetric flight with the dimensions of the outer geometry of the aft fuselage are given in Reference [2]. After reading the inputs DARLoads assembles all the required matrices.…”

“…In this paper we give an overview of a framework [2] that would be applicable for optimizing the flexible aircraft under dynamic loads. Section 2 starts with the discrete representation of a fully flexible aircraft.…”