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A Novel Optimization Strategy for Composite Beam Type Landing Gear for Light Aircraft

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A Novel Optimization Strategy for Composite Beam Type Landing Gear for Light Aircraft.
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    A novel optimization strategy for composite beam type landing gear for light aircraft  Edwin Spencer * United Technologies Aerospace Systems 850 Lagoon Drive Chula Vista Ca. 91910 Abstract Composite beam type landing gear have applications in small light aircraft. A novel optimization strategy using Nastran finite element models and sol 200 (optimization solution sequence) is presented in this paper. The analysis criteria are to meet stiffness strength and weight requirements for multiple landing load cases. The optimization analysis strategy is a novel two stage approach. In the first stage a shape optimization is carried out on a tapered rectangular hollow cross section beam finite element model . Each beam element had 8 design variables: height, width, cap thickness and web thickness at each end of the beam. The design constraints for the optimization analysis is a specified vertical deflection at the wheel attachment to meet landing energy absorption criteria and stresses below allowable for all elements for all load cases. The optimum cross-sections from the beam analysis are used to create a 3D composite shell finite element model with multiple ply lay-up property regions for the second stage of the optimization analysis. In the second stage a ply thickness optimization analysis was carried out on the 3D composite shell finite element model. The design variables are the thicknesses of zero degree, + / - 45 degree and 90 degree plies for the various property regions. The objective function for both shape optimization and ply thickness optimization was to minimize weight. *Currently employed at UTAS, work for this paper was carried out while the author was formerly employed at MSC Software .    Introduction Landing gear for small light aircraft need to satisfy minimum weight criteria, strength criteria with adequate margin of safety against failure and a precisely tuned stiffness or deflection on landing to absorb the landing energy. Laminate composite structures are ideal for this application because the material system can be tailored to meet the specific requirements in a very predictable manner. To design the landing gear structure to meet these requirements manually by trial and error will be very labor intensive and extremely time consuming. Finite element laminate composite analysis coupled with optimization techniques offer a robust and efficient methodology to design a beam type landing gear. Optimization Concept A novel two stage optimization strategy using Nastran finite element models and Sol 200 optimization solution sequence has been devised which can be used to design any generic beam type landing gear for multiple landing load cases. In the first stage the landing gear structure is modeled with tapered rectangular hollow cross section beam elements (see Figure 1). Each beam has 8 design variables : height, width , cap thickness and web thickness at each end of the beam which are initially set to nominal values and a shape optimization is carried out whereby the cross sectional shape can change span-wise as shown on Figure 2 which is a 3D rendering of the optimized beam structure. The optimum cross-sections from the beam analysis (Figure 2) are used to create a 3D composite shell finite element model with multiple ply lay-up property regions (Figure 3 and Figure 4) for the second stage of the optimization analysis. In the second stage a ply thickness optimization analysis was carried out on the 3D composite shell finite element model. The design variables are the thicknesses of zero degree, + / - 45 degree and 90 degree plies for the various property regions. The objective function for both shape optimization and ply thickness optimization was to minimize weight.    Figure 1  –  Tapered Rectangular Hollow Cross Section Shape Optimization Beam Model    Figure 2  –  3D Rendering of Shape Optimized Beam Model

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Jul 24, 2017
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