Examples on increased-order aeroservoelastic modeling

Abstract

Aeroservoelastic loads calculations usually rely on linear analyses that use implicit structural models (Finite Elements Method) and frequency domain unsteady aerodynamics (Doublet Lattice Method). The hypotheses that underpin this methodology impose some limitations that may be overcome in some cases of interest. This paper details some of these cases, examples in which Increase Order Modeling has been used in aeroservoelastic and structural dynamic problems to include effects that are generally not taken into account in standard linear analyses. Increase order modeling is based on the hypothesis that the problem is mainly linear and that non-linear effects are known and concentrated. The linear part is solved in the frequency domain and convolution integrals are used to account for non-linear effects. During the last years, this methodology has been included as the standard tool at the Structural Dynamics and Aeroelasticity department of Airbus Defence and Space, allowing for tackling different problems. The first type of problems are linked to overcoming limitations imposed by the unsteady aerodynamics hypotheses; these include: taking into account aerodynamic forces dependent of in-plane motions, accounting for in-plane aerodynamic forces and considering the change in direction of aerodynamic forces during the analyses. The second group take into account non-linear effects, as the inclusion of non-linear Flight Control System for gust response calculation. Also structural non-linearities, such as actuator freeplay, contacts that change boundary conditions, and the rupture of structural elements have been implemented in dynamic problems in which frequency domain unsteady aerodynamic is considered. The Increased Order Modeling tool has been designed to fit seamlessly with the standard aeroservoelastic loads calculation methodology and models.