Robust Control Design for the Higher Harmonic Vibration Reduction of a Nonlinear Aeroservoelastic Rotor

Abstract

In this study, we present an improved linear quadratic closed-loop rotor vibration controller that uses a steady-state Kalman filter and an augmented integral controller to improve the traditional T-matrix-based rotor vibration controller. The proposed linearized vibration controller features closed-loop stability more rigorously than the conventional algebraic T-matrix-based controller. A relative multi-loop stability margin analysis was performed and examined using a nonlinear aeroservoelastic rotor software-in-the-loop simulation. The rotor aeroservoelastic simulation was performed using the multi-body dynamic analysis software DYMORE, equipped with a new improved inflow model employing multiple trailer time-marching free-vortex wakes. A linear time periodic representation of the rotor was identified from the exponentially modulated periodic response obtained using a recursive Fourier series filter. We found that the proposed linear controller showed improved numerical phase-margin prediction accuracy compared with the T-matrix-based method. Finally, the trade-off between the rotor vibratory load reduction performance and closed-loop stability was evaluated and discussed. We found that the proposed controller asymptotically reduced the N/rev vibratory loads that were included in the Kalman filter, and the amount of load reduction was similar to that predicted from the LTP rotor harmonic system.

Keywords

• Active vibration control
• helicopters
• linear quadratic Gaussian control
• multi-loop closed-loop stability
• nonlinear aeroservoelastic rotor simulation