Browsing by Author "Demenkov, M. N. (Max)"

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    Computation of controllability regions for unstable aircraft dynamics.
    (American Institute Aeronautics and Astronautics, 2004-01-01) Goman, M. (Mikhail G.); Demenkov, M. N. (Max)
    An active control approach to air vehicle design can significantly expand the flight envelope and improve vehicle performance characteristics. In some cases it can be attained by implementing the aerodynamically unstable configuration or expanding operation at flight regimes with dynamic instability, which are then purposely stabilized by the flight control system. An important issue in stabilization of unstable dynamics is connected with the size of the controllability region, which is the set of all states of the aircraft dynamics that can be stabilized by some realizable control action. This region is bounded because of nonlinear actuator constraints, and its size can be considered as a measure for allowable level of external disturbances. In this paper an algorithm based on convex optimization technique is proposed for computation of the controllability region of an unstable linear system under amplitude and rate control constraints. Examples of the controllability region analysis for an aeroservoelastic airfoil system and unstable aircraft dynamics are presented to illustrate the capabilities of the proposed algorithm.
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    Effect of Control Constraints on Active Stabilization of Flutter Instability
    (Cambridge Scientific Publishers Ltd, 2009) Vikhorev, K.; Demenkov, M. N. (Max); Goman, M. (Mikhail G.)
    The effect of amplitude and rate control constraints in active flutter suppression was analysed for a number of different linear and nonlinear control laws considering mathematical model of two degree-of freedom aeroelastic airfoil system with trailing and leading edge flaps. The LQR control law providing maximum region of attraction for the linearized system under amplitude control constraints was investigated taking into account a structural nonlinearity and actuator rate constraints. The region of attraction of a stabilized equilibrium was used as a metric to identify a set of linear control laws providing practically global stabilization of flutter instability with account of structural nonlinearities and rate control constraints. The eigenstructure assignment method was implemented for control law design considering trailing edge flap or a combination of leading and trailing edge flaps.
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    From local to global stabilizability of aeroelastic oscillations.
    (IEEE, 2009) Demenkov, M. N. (Max)
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    Multiple Attractor Dynamics in Active Flutter Suppression Problem
    (Cambridge Scientific Publishers Ltd, 2009) Goman, M. (Mikhail G.); Demenkov, M. N. (Max)
    An active stabilization of flutter instability was investigated using mathematical model for two degree-of freedom aeroelastic airfoil system with trailing and leading edge flaps. A number of control laws based on LQR, linear eigenstructure assignment and nonlinear dynamic inversion methods have been analysed. The open-loop aeroelastic airfoil system following the onset of linear flutter instability exhibits limit cycle oscillations due to nonlinearities in the torsional and/or bending stiffness. The dynamic properties of the closed-loop system were investigated using a systematic search method for all possible equilibrium solutions and the continuation of limit cycles by application of the numerical continuation package MATCONT. A computational analysis revealed that multiple attractors can coexist in the closed-loop system. These multiple attractors include a stabilized equilibrium, transformed open-loop limit cycle oscillations with large amplitude and asymmetrical equilibria or asymmetrical oscillations with small amplitude, induced by feedback control law. The size of region of attraction of a stabilized equilibrium depends on the size of unstable saddle-type limit cycle and may be dramatically reduced due to onset of additional asymmetrical equilibrium solutions. The computational analysis showed that for a global stabilization of flutter instability a designed control law should annihilate or destabilize the open-loop limit cycle and prevent the onset of asymmetrical equilibria.
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    Stabilization of unstable aircraft dynamics under control constraints.
    (CRC Press, 2004-04) Goman, M. (Mikhail G.); Demenkov, M. N. (Max)
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    Suppressing aeroelastic vibrations via stability region maximization and numerical continuation techniques
    (2009-09) Demenkov, M. N. (Max); Goman, M. (Mikhail G.)
    An active flutter suppression using linear sub-optimal control scheme is investigated for a 2dof airfoil system with nonlinear torsional stiffness and limited deflection amplitude of its single actuator. The suppression of limit cycle oscillations in the nonlinear closed-loop system is achieved through maximization of the stability region of its linearized system. The critical value of the control input amplitude is determined via numerical continuation of closed-loop limit cycle. At this value, the cycle experiences saddle-node bifurcation and disappears, satisfying the necessary condition for the global stability in the closed-loop system.