|Abstract:||Inspired by the shape adaption of a bird’s wing during flight, this work presents a bio-inspired wingtip concept leveraging bend-twist coupling (BTC) in composite laminates. The structural characteristics, incidence angle and dihedral angle, of a bird’s wingtip feathers, adapt and change configurations for optimal flight performance. It has been successfully shown by the author, by varying the BTC parameter, a passively adaptive BTC composite wingtip can simultaneously achieve the required bending (dihedral angle) and twist (incidence angle).
This thesis presents a design optimization framework for a composite wingtip. The BTC behavior is investigated by analytical methods, numerical modeling, and experimentation. A Laplace transform method was applied to derive the analytical Green’s functions corresponding to the bending displacement and twist. Additionally, using ANSYS APDL, a nonlinear finite element analysis (FEA) was performed. The numerical and analytical results were then compared to previously published experimental data. The analytical model matched the experimental results in the linear region of the deflection and twist response. The error in bending and twist were 6.5% and 2.5%, respectively. The FEA results compared to experimental data had an error in bending and twist of 2.9% and 5.7%, respectively, in the nonlinear region.
Next, the thesis presents a multi-objective design optimization framework using an elitist non-dominated sorting genetic algorithm (NSGA-II). The objectives of the design optimization were to determine the fiber orientation angles required to achieve the desired bending and twist deformation. The composite fiber angles were set as the design parameter, while the number of laminates and their thickness were held constant. The optimization framework was validated using published data and a problem formulation is presented to design an optimal composite wingtip. In this thesis, an optimal BTC composite wingtip was designed, manufactured and physically tested. The optimal design based on Green’s functions achieved a bending displacement and twist with an error of 10.7% and 2.0%, respectively. The formulated design framework using the analytical Green’s functions provide a time-efficient tool to design optimal composite wingtips. It was shown that BTC composite wingtips can be optimally designed to achieve passive shape adaption useful for improvements in the aerodynamic performance of aircraft systems.