Active Flutter Suppression Using Multi-Input/Multi-Output Adaptive Least Mean Square Control


The feasibility of an adaptive feedforward multi-input/multi-output (MIMO) controller for active flutter suppression has been investigated in this study. An unswept flexible wing structure is modeled by a multi-degree-of-freedom finite element representation with beam elements for bending and rod elements for torsion. Control action is provided by one or more flaps attached to the trailing edge of the wing and extending along a fraction of the wingspan. Time-domain unsteady aerodynamics have been used to generate the air forces acting on the wing model. The adaptive feedforward MIMO controller has been designed based on the filtered-X least mean square (LMS) algorithm. The controller structure includes an on-line adaptive system identification that provides the LMS controller with a reasonably accurate model of the plant. The controller is capable of tracking time-varying parameters in the plant and providing effective control. The wing model in closed loop exhibits highly damped responses at airspeeds where the open-loop responses are destructive. Simulations with the flexible wing model in a time-varying airstream show a 53% increase over its corresponding open-loop flutter airspeed. The ability of the MIMO LMS controller to suppress instabilities in a wing with abruptly changing parameters (sudden onset of flutter caused by the release of stores) has also been studied. In the examples studied, it is found that adaptation is rapid enough to successfully control flutter at accelerations in the airstream of up to 9 ft/s2. An increase in the number of flaps provides an enhancement in the overall control authority, but results in a decrease in the convergence speed of the controller, resulting in downgraded performance. The optimum number of control flaps for the model studied is found to be four, extending along 40% of the wingspan from the tip.


Mechanical and Aerospace Engineering

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Article - Journal

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© 1997 American Institute of Aeronautics and Astronautics (AIAA), All rights reserved.