| Περίληψη: | The resilient and flourishing air travel demand is expected to pose severe environmental threats in the foreseeable future, stressing the need for novel, more sustainable and efficient airframe designs. Towards the realization of this goal, the introduction of high-aspect ratio wing configurations offers enhanced aerodynamic efficiency through induced drag reduction mechanisms, with further performance gains, mainly in terms of structural mass, being attainable via composite materials airframes. Nevertheless, such configurations are prone to undesired phenomena such as geometric nonlinearities and aeroelastic couplings due to elevated flexibility, rendering the design and optimization of such airframes extremely intricate and often prohibitive in terms of computational cost. Low-fidelity tools, often preferred on the early design stages, accelerate the design process, albeit suffering from reduced accuracy and ability to capture higher-order phenomena. Contrastingly, high-fidelity computational methods incur excessive computational cost and are therefore utilized at the latter, detailed design stages. There arises, therefore, on one hand the need for the development of more efficient, rapid yet accurate low-fidelity numerical tools as well as for a combination of the various fidelities involved in the design process in a cost-effective manner, aiming at driving the design towards optimal configurations without significant performance losses. In our approach, a novel optimization framework, utilizing low-cost numerical tools for sizing contemporary composite materials aircraft wings subject to stiffness, strength and dynamic aeroelastic constraints for the conceptual design stage is initially provided. The structural representation of the numerical model is based on the well-established equivalent-plate methodology, capable of reducing the size and computational cost of the associated problem. An equivalent-plate model of a modern transport aircraft wing is developed and compared to its equivalent 3D Finite Element Method model. Results, by means of natural frequencies and modes, indicate excellent accordance between the numerical models. An efficient optimization framework is then presented, with the ply thicknesses of a baseline lay-up being assigned as design variables. The developed framework succeeds to guide the mass of the wing to a minimum while satisfying the constraints under a critical loading scenario. Optimal lay-ups for the skins, spar webs and ribs as well as spar and rib caps dimensions are obtained. The presented optimization framework, exhibiting high accuracy and efficiency, constitutes a robust numerical tool for the early design stages of composite aircraft wings. Moving on, variable fidelity aerodynamic, structural as well as fluid-structure interaction analyses are conducted in order to shed light on their effect on the structural response of a high-aspect ratio composite materials reference wing. A multi-fidelity optimization framework, combining low and high-fidelity tools in a sequential manner, is then proposed, aiming at attaining a minimum mass configuration subject to multidisciplinary design constraints. Optimal lay-ups for all of the components are obtained. The panel buckling phenomenon was deemed critical to the particular design. As demonstrated, reasonable mass reduction was obtained for a future aircraft wing configuration. Furthermore, a surrogate-based optimization framework is also constructed, aiming on the one hand to explore possible mass gains through inclusion of the static aeroelastic response, while reducing the computational cost. Convergence plots as well as the thickness distribution for each component of the wing are presented. As a conclusion, the findings of this thesis are summarized along with suggestions for future work.
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