Robust Aeroelastic Control of Very Flexible Wings using Intrinsic Models

Abstract

This paper explores the robust control of large flexible wings when their dynamics are written in terms of intrinsic variables, that is, velocities and stress resultants. Assuming 2-D strip theory for the aerodynamics, the resulting nonlinear aeroelastic equations of motion are written in modal coordinates. It is seen that a system which experiences large displacements can nonetheless be accurately described by a system with only weak nonlinear couplings in this description of the wing dynamics. As result, a linear robust controller acting on a control surface is able to effectively provide gust load alleviation and flutter suppression even when the wing structure undergoes large deformations. This is numerically demonstrated on various representative test cases.

Nonlinear Model Reduction for Aeroelastic Control of Flexible Aircraft Described by Large Finite-Element Models

“…Following Wang et al, 11 the terms N a (q)q, η 1 (q)λ and L(q)λ can be approximated as quadratic equations that assume v ∞ varies only slowly with time, with a minor impact in modelling accuracy.…”

“…The control system in this work will focus on dynamic stabilisastion of an unstable airframe and can be similarly applied to gust load alleviation as demonstrated in a previous work. 11 The disturbance will be assumed to be external gust loads (modelled as a prescribed distributed force), and the control input would be flap deflections at particular spanwise locations. To synthesise the H ∞ control system, define first the system state as…”

“…10 The coefficients of the resulting nonlinear structural dynamics equations in modal coordinates were then identified in the static condensation of the original 3-D model. With regards to aeroelastic analysis based on this intrisic description, we have also recently shown 11 that, under the assumption of attached flow conditions, H ∞ controllers based on the linearization of the intrinsic equations, still have excellent performance in situations with significant geometrically-nonlinear effects. Extending that work, this paper will describe and validate the full process of model reduction from a large complex aeroelastic model of the full vehicle, which is assumed to come from an off-the-shelf industrial aeroelastic analysis tool (e.g.…”

An Adaptive Aeroelastic Control Approach using Non Linear Reduced Order Models

“…In a displacement-based formulation, dominant nonlinearities arising from large deformations are cubic terms, as opposed to an intrinsic description where they appear up to second order. 22 The nonlinear beam code was coupled with strip aerodynamics using the description above. The motion of each structural node is described by 6 degrees-of-freedom.…”