Sascha Dähne

Structural Optimization of Composite Wings in an automated Multi-Disciplinary Environment

This paper presents a structure design and optimization module, developed for the application inside multi-disciplinary optimization process chains. The loads necessary for sizing and optimization are calculated in CFD or aeroelastic calculations and applied on a Finite Element Model that represents all primary structural elements of a wing. The FE model is created automatically from a parametric geometry description. The deformations and inner loads of the wingbox are calculated via linear static FE calculations; geometry and loads are provided to an external sizing tool. Each component has a set of design variables with discrete design points which are permutated to get the component’s design candidates. A set of failure criteria is used to size the structure which can be made of composites or metal. The methodology is applied to the optimization of a forward swept composite for a short range aircraft and a design study comparing different stringer types and their influence on mass and structural deformation of the wing is performed.

Gradient Based Structural Optimization of a Stringer Stiffened Composite Wing Box with Variable Stringer Orientation

The structural optimization plays a key role in multidisciplinary optimization. The proof of structural integrity is a prerequisite for the performance assessment of a wing design. In addition, the modification of the structural design allows changing the bend-twist coupling properties in a beneficial way for overall cruise performance. Due to the high number of design variables affecting the mass and stiffness of a wing box, a gradient based process is established. It meets the needs of fast convergence and enables the coupling with aerodynamic analyses that provide gradients as well. A well suited parametrization of the design variables is necessary, especially for composite materials. Therefore, lamination parameters are used, which are proven to be suitable for gradient based optimization. In order to consider stiffening structures (i.e. stringer on the wing cover), a smeared stiffener approach is used. With this approach, it is not necessary to model the stringer explicitly in the Finite Element model. The influence of different stringer shapes and their orientation can be evaluated with the method suggested in this paper. In order to reduce calculation time, the numerical model is evaluated using analytic formulations for global and local stability as well as strength. The two approaches, smearing the stiffeners or explicitly modeling stiffeners, are validated by comparison of global deformations. The optimization process is applied to a representative wing box loaded with an eccentric load. The influence of different stringer orientations on the structural deformation is examined in conjunction with the optimization of lamination parameters.

Automated Structural Design of Composite Forward Swept Wings

This article describes the structural design process within a multidisciplinary environment. A forward swept wing configuration is considered where static divergence has to be avoided by using anisotropic properties of stiffened panels made of CFRP (carbon fibre reinforced plastic). The structural design includes parametric model generation and automated sizing of composite wings. An analytical formulation of stiffened panels is used to investigate different stiffener concepts, where fast analytical failure criteria are applied. The goal is to minimize weight and provide accurate deformations for a coupled process. A parametric study shows the flexibility of the approach as well as the validity of the design concept and the approach for bend twist coupling. Furthermore, the influence of neglecting the load redistribution due to the wings deformation on the wing mass is shown.