Cantilevers find a wide range of applications in the design of scientific equipment and large-scale engineering structures such as aircraft wings. Analysis techniques based on linearization approximations are unable to capture the large amplitude oscillation behaviour of such structures and thus, necessitates development of dedicated nonlinear methods. In this work, the recent developments in the Koiter-Newton model reduction method are utilized to obtain nonlinear reduced order models (ROMs) from full finite element structural models in order to simulate large amplitude dynamics of cantilevers. The method describes a nonlinear system of governing equations comprising quadratic and cubic terms which are obtained as higher order derivatives of the in-plane strain energy. To ensure that the large rotations in cantilevers and the resultant foreshortening effect is also accounted for, a ROM updating algorithm is adopted where the ROM parameters are varied with the structural deflections. Linear eigenmodes of the structure are utilized to form the reduction subspace. To validate the methodology, the ROM solution is compared against experimental results and a convergence study is conducted to identify the number of modes needed to replicate the nonlinear response. Finally, a composite wingbox structure is considered for which time domain simulations are conducted and frequency response curves, obtained through a frequency sweep, are presented.

@en

Wing structures subjected to large deflections are prone to nonlinear load-deflection behavior. Geometric nonlinearities can arise due to the accompanying large rotations and in-plane deflections that manifest in the form of stiffening effects in the nonlinear static response. To account for these nonlinearities, reduced-order modeling techniques in combination with nonlinear finite element formulations have been previously proposed. However, these methods often have a limited range of validity due to linear eigenmode-based formulations with assumptions of small rotations. In this paper, a large deflection analysis framework based on the Koiter–Newton model reduction technique is presented. It is demonstrated that the reduced model in its basic form is ineffective for large deflection analysis. To resolve this, an incremental updating procedure is used for the reduced-order model that incorporates the necessary nonlinear effects. The model updating enables the computation of nonlinear response for a large range of deflections.

@en

This article presents the application of aeroelastic tailoring in the design of wings for a flying demonstrator, as well as the validation of the design methodology with flight test results. The investigations were performed in the FLEXOP project (Flutter Free Flight Envelope Expansion for Economical Performance Improvement), funded under the Horizon 2020 framework. This project aimed at the validation of methods and tools for active flutter control, as well as at the demonstration of the potential of passive load alleviation through composite tailoring. The technologies were to be demonstrated by the design, manufacturing and flight testing of an unmanned aerial vehicle of approximately 7 m wingspan. This article addresses the work towards the load alleviation goals. The design of the primary load-carrying wing-box in this task is performed using a joint DLR–TU Delft optimization strategy. Two sets of wings are designed in order to demonstrate the potential benefits of aeroelastic tailoring—first, a reference wing in which the laminates of the wing-box members are restricted to balanced and symmetric laminates; second, a tailored wing in which the laminates are allowed to be unbalanced, hence allowing for the shear–extension and bending–torsion couplings essential for aeroelastic tailoring. Both designs are numerically optimized, then manufactured and extensively tested to validate and improve the simulation models corresponding to the wing designs. Flight tests are performed, the results of which form the basis for the validation of the applied aeroelastic tailoring approach presented in the article.

@en

Wings of modern aircraft have to be designed to give optimal response with respect to loads, comfort and performance. An essential part of the wing development is thus a design process which can take all these aspects into consideration. In the “Adaptive Wing” work package of the CleanSky “Smart Fixed Wing Aircraft” project, a multi-fidelity wing design method using aeroelastic tailoring has been developed. In the article, the process is presented in detail. The approach is based on a parametric wing design approach. Both beam models and shell models are derived and optimized in separate optimization environments. Investigations of the use of unbalanced laminates in aeroelastic tailoring are presented, employing the optimization of lamination parameters. The applications are demonstrated on two aircraft configurations, a long range and a short range transport aircraft. Further developments presented in the article include the introduction of CFD-based aerodynamics in the tailoring process, and a process extension to assess the influence of aeroelastic tailoring on fatigue.

@en

In the work package “Adaptive Wing” in the Clean-Sky “Smart Fixed Wing Aircraft” (SFWA) project, design processes and solutions for aircraft wings have been created, giving optimal response with respect to loads, comfort and performance by the introduction of passive and active concepts. Central activity of the work was the design and optimization of adaptive wing structures, for complete wings as well as for special components. This process, often called "aeroelastic tailoring", formed the backbone of the work package. Other important contributions have encompassed the development and improve-ment of methods for loads analysis, by extending the classical linear tool set by fast non-linear approach-es. Partners from industry and research involved in the work package contribute with special expertise to the process. The paper gives an outline of the objectives and the work done in the work package, as well as an over-view of the integration of the “Adaptive Wing” activi-ties in the framework of the SFWA project.@en