Keywords: flexible wing, wingbox optimization, surrogate model, NACA profiles.

This paper presents a two-step approach that was adopted in a collaborative multi-disciplinary work named OSYCAF for wing-box design optimization. This approach encompasses: 1) the initialization of a full parametric PCL flexible wing optimization with analytical design, and 2) the comparison of the sol200 optimization (mass of the wing) with a simple surrogate model (also known as a reduced order model as a result of the quadratic form in the regression). The main objective is to optimise the global structure weight while respecting all structural criteria and constraints [1], and using the spars and skin thickness as design variables. It is shown that after the optimization the importance of upper and lower skins is minimised and almost all effort is concentrated on spars, especially the rear spar. It is also shown that the strain criterion is stronger than the stress one, which considers shear and buckling deformations as the critical design points, although fatigue is also relevant when designing the lower wing-box skin. It is shown that the results obtained for the local optimisation of several considered NACA-4 profiles by using an automated process. This strategy is developed such that an association with an aerodynamic approach using CFD and composite materials [2,3,4] would make it possible to create a variation of the required profile to construct the real wing that, when deformed, would assume its best shape in terms of aerodynamics, still respecting all structural constraints and minimum weight possible.

Comparison of this result with the previous upper skin response surface has shown that this one has lower relative errors. This indicates that the choice of the design space directly affects the quality of the solutions, and that, for this case, it is better to separate into two design spaces and build up two surrogate models for the upper skin.

1

E. Roux, "Modèle de Masse Voilure Avions de transport civil pour une approche analytique de la Dynamique du Vol", Institut Supérieur de l'Aéronautique et de l'Espace - Supaero & ONERA, 2006.

2

F. Luraghi, "Surrogate-Based Shape Optimization of Fiber Paths in Tow-Steered Laminates for Maximum Buckling Load", 16th International Conference on Composite Structures, Porto, Portugal, 28-30 June 2011.

3

N. Bartoli, D. Bettebghor, F. Luraghi, M. Samuelides, "Surrogate Model-Based Design Optimization of Composite Panels for Aeronautical Applications", 15th Austrian-French-German Conference on Optimization, Toulouse, France, 19-23 September 2011.

4

F. Luraghi, "Efficient Design Optimization of Tow-Placed Panels for Enhanced Load-Carrying Capabilities by Adaptive Metamodeling", 53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, Honolulu, HW, 23-26 April 2012.

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