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作者： Jonsson, Eirikur University of Michigan

学位级别：Ph.D.

High-fidelity optimization of aircraft has the potential to produce more efficient designs and to further reduce the risk of late design changes. For the optimization to generate a useful design, all the relevant constraints must be considered, including flutter. This is especially important in the high-fidelity aerostructural optimization of commercial aircraft, which is likely to result in high-aspect-ratio wing designs that are prone to flutter. To address this issue, we develop a flutter constraint formulation suitable for gradient-based aerostructural optimization with accurate and efficient adjoint derivatives. This approach scales well with the number of design variables and considers both structural sizing and aerodynamic planform variables. An effective bounding curve defines the flutter-free flight envelope, prevents discontinuities in the flutter constraint, and allows for minimum flutter speed to be specified implicitly. The flutter constraint formulation utilizes an efficient non-iterative p-k method, an effective bounding curve, and an aggregation technique that results in a single constraint in the optimization problem. Accurate and efficient derivatives of the flutter constraint value with respect to structural sizing variables and aerodynamic planform variables are computed. Furthermore, to enable changes in planform, derivatives of the mode shapes are also computed efficiently. The derivatives are computed using a combination of analytic and automatic differentiation methods in reverse mode (adjoint) and rigorously validated using the complex-step method. We perform a multipoint, high-fidelity aerostructural optimization of a wing and full configuration aircraft with and without the flutter constraint, subject to stress and buckling constraints. With the flutter constraint, we obtain a stiffer, lower aspect ratio wing with stark differences in structural sizing, but without a significant reduction in objective. These results demonstrate the importa

关键词： Aeroelastic optimization flutter constraint Thesis

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Bifurcation-Diagram-Free Postflutter Response constraint for Design Optimization

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AIAA JOURNAL 2023年第8期61卷 3449-3465页

作者： Riso, Cristina Cesnik, Carlos E. S. Epureanu, Bogdan I. Georgia Inst Technol Daniel Guggenheim Sch Aerosp Engn 275 Ferst Dr Northwest Atlanta 30332 Georgia Univ Michigan Dept Aerosp Engn 1320 Beal Ave Ann Arbor MI 48109 USA Univ Michigan Dept Mech Engn 2350 Hayward St Ann Arbor MI 48109 USA

This paper introduces a new metric to constrain postflutter responses of aeroelastic systems in design optimization. The new metric aggregates the recovery rate to equilibrium for a range of operating conditions, modes, and amplitudes, resulting in a scalar constraint that does not involve the bifurcation diagram. By generalizing damping-based flutter constraints, the formulation yields mathematical properties oriented toward gradient-based optimization. The approach is demonstrated by optimizing a typical section with a subcritical bifurcation using a gradient-based algorithm and finite-difference derivatives. The postflutter response constraint suppresses self-sustained oscillations below a given flow speed while minimizing the mass penalty, which avoids a conservative solution. This constraint can help design highly efficient aeroelastic systems with feasible postflutter dynamics. Future development of adjoint derivatives will enable large-scale gradient-based optimization.

关键词： Multidisciplinary Design Optimization flutter constraint Postflutter Response constraint Bifurcation Theory Dynamic Aeroelasticity Nonlinear Aeroelasticity

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