Optimum Morphing Shape Design for Morphing Wing with Corrugated Structure Using RBF Network

Abstract

The morphing wing changes the geometrical shape seamlessly and continuously to improve the aerodynamic performance. Several studies have been conducted with variety of approaches. This study focuses on obtaining the optimum airfoil shape to maximize the lift-to-drag ratio or the maximum lift coefficient for the morphing wing using the corrugated flexible structures arranged in the rear side of the airfoil developed by one of the authors. The corrugated structure is connected to the upper skin to bend the airfoil as a morphing flap. During the morphing, the upper skin length is unchanged, but, on the other hand, the lower skin length is shorten. This airfoil morphing shape is mod-eled by using non-uniform rational basis spline (NURBS) curves with considering the above curve length condition, where the NURBS passing points are adopted as design variables. For numerical efficient optimization , sequential approximate optimization method using radial basis function (RBF) network is adopted. During the optimization, a design candidate will have an irrational wavy shape that brings an ill condition to the aerodynamic analysis, where the two-dimensional panel method is adopted as the aerodynamic analysis. To avoid the aerodynamic analysis for the violated design, the concept of tabu search is introduced to the RBF network. That is, if a violated wavy design candidate is selected during the optimization, the design is added to the tabu list without performing aerodynamic analysis. That is, the RBF network learning makes the searching region enclosed into the feasible design space and then the optimum design found rationally. The idea of the tabu search is also adopted to find the feasible initial design candidates. Through numerical examples, the validity of the proposed optimization method is demonstrated. Then, the optimum morphing wing shape is discussed.