Browsing by Author "Barker, Jeffrey M."

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    Comparing Linear Parameter-Varying Gain-Scheduled Control Techniques for Active Flutter Suppression
    (American Institute of Aeronautics and Astronautics, 2000) Barker, Jeffrey M.; Balas, Gary J.
    Two linear parameter-varying gain-scheduled controllers for active flutter suppression of the NASA Langley Research Center’s Benchmark Active Control Technology (BACT) wing section are presented and compared to a previously presented gain-scheduled controller. The BACT wing section changes significantly as a function of Mach and dynamic pressure. The two linear parameter-varying (LPV) gain-scheduled controllers incorporate these changes as well as bounds on the rate of change of Mach and dynamic pressure. The inclusion of rate bounds in the design process allows for improved performance over a larger range of operating conditions than previously achieved by a linear fractional transformation gain-scheduled controller. The LPV controllers differ in that one primarily reduces coupling between the trailing-edge flap and the pitch and plunge modes, whereas the second optimizes wind gust attenuation. Closed-loop stability and improved performance are demonstrated via time simulations in which both Mach and dynamic pressure are allowed to vary in the presence of a Dryden wind-gust disturbance.
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    Comparison of μ- and H2-Synthesis Controllers on an Experimental Typical Section
    (American Institute of Aeronautics and Astronautics, 1999) Vipperman, Jeffrey S.; Barker, Jeffrey M.; Clark, Robert L.; Balas, Gary J.
    An experimental comparison of H2 - and μ-synthesized flutter suppression control systems was performed. A simple parametric uncertainty can be used to track changes in system dynamics as a function of dynamic pressure. The control system was implemented experimentally on a NACA 0012 test model of a typical section mounted in a low-speed wind tunnel. The pitching angle, flap angle, and plunge deflection of the airfoil were measured with sensors and fed back through the control compensator to generate a single control signal commanding the trailing-edge flap of the airfoil. The model of the aeroelastic system, including the dynamics of the sensors and actuators in the bandwidth of interest, was obtained using system identification techniques. For comparison purposes, an H2 control system with standard linear quadratic Gaussian weightings also was designed and implemented. When compared to the H2 control system, the μ-synthesis controller provided better disturbance rejection in the bandwidth of the unsteady aeroelastic dynamics. In addition, the μ controller required less control energy than the H2 control system. The final advantage of μ-synthesis is the ability to design an aggressive μ control system that is stabilizing across the range of operating dynamic pressures.
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    Gain-Scheduled Linear Fractional Control for Active Flutter Suppression
    (American Institute of Aeronautics and Astronautics, 1999) Barker, Jeffrey M.; Balas, Gary J.; Blue, Paul A.
    A gain-scheduled controller for active flutter suppression of the NASA Langley Research Center’s Benchmark Active Controls Technology wing section is presented. The wing section changes significantly as a function of Mach and dynamic pressure and is modeled as a linear system whose parameters depend in a linear fractional manner on Mach and dynamic pressure. The resulting gain-scheduled controller also depends in a linear fractional manner on Mach and dynamic pressure. Stability of the closed-loop system over a wide range of Mach and dynamic pressure is demonstrated. Closed-loop stability is demonstrated via time simulations in which both Mach and dynamic pressure are allowed to vary in the presence of input disturbances. The linear fractional gain-scheduled controller and an optimized linear controller (designed for comparison) both achieve closed-loop stability, but the gain-scheduled controller outperforms the linear controller throughout the operating region.