Active Flutter Suppression For Multiple-actuated-wing Based On A New Method Of Uncertainty Modeling

Active flutter suppression has been developed as a new aeroelastic technology over the past decades. The implementation of this technology profits from the development and successful application of classical and modern control theory. With the program of the Active Flexible Wing(AFW) proposed, aeroelastic effect has been exploited, rather than avoided, through the use of active control technology. It is expected that these vehicles will be highly flexible, achieve weight saving, enlarge the flight envelope, and improve the maneuver ability. The program will provide key technology for the next-generation flight vehicles.The major research object of this dissertation is a small aspect ratio Multiple-Actuated-Wing(MAW) wind tunnel model with leading- and trailing-edge outboard control surfaces. The dissertation presents the combined theoretical, numerical and experimental studies on the flutter suppression for the MAW model. Firstly, the controllers for actively flutter suppression are designed. Secondly, digital control systems are constructed by using a Digital Signal Processor(DSP) and an AD5435 real-time simulator, respectively. Finally, a number of wind tunnel tests are implemented based on the control systems. The main contributions of the dissertation can be summarized as follows:1. A new scheme is proposed to model the parametric uncertainties in an aeroelastic system. The dimension of the resulting uncertainty model is very high through the traditional method. The reason of high dimension is that the perturbed system matrix includes repeated and coupled terms. Compared with the traditional method, the new scheme is based on a signal transformation so as to eliminate the repeated modeling and decouple the coupled uncertainty terms. As a result, the dimension of the mathematical model of the uncertainties can be greatly reduced. Thus, the robust flutter controller can be designed easily via the new scheme.2. The dynamic equation of a two-dimensional wing-store aero-servo-elastic system with leadingand trailing-edge control surfaces is established, firstly. The aerodynamic forces of the wing section and the store are computed via the doublet lattice approach and slender-body aerodynamic theory, respectively. To illustrate the procedure of proposed method, the wing-store aero-servo-elastic equation with flow speed uncertainties is modeled by using the proposed uncertainty scheme, secondly. The correctness of the proposed uncertainty scheme is verified through the open-loop analysis. Finally, numerical results indicate that, with the proposed scheme, the robust flutter control law is efficient and the flutter boundary of the aeroelastic system can be greatly expanded.3. The ultrasonic motor is used to suppress the flutter instability of the MAW model for the first time. The digital control system with the help of DSP is constructed to verify the controller. The angle tracking of leading- and trailing-edge motors is realized through the analog output of the DSP. Based on a second-order transfer function of ultrasonic motor, the aero-servo-elastic equation for the three-dimensional MAW model is established with an additional output equation. A Multiple-Input and Multiple-Output(MIMO) feedback controller for active flutter suppression of the MAW model is designed. As the first attempt, the conventional LQG controller is tested in the wind tunnel. However, the wind tunnel tests illustrate that the LQG-controlled MAW model has no guaranteed stability margins. To compensate the time delay, hence, a time-delay filter is added to the LQG controller. Then, a number of wind tunnel tests are implemented based on the time-delay feedback controller. The experimental results show that the present time-delay feedback controller can expand the flutter boundary of the MAW model from 34.5 m/s to 37 m/s.4. Based on the real time simulator, a digital control system for flutter suppression is constructed. An incremental PID controller with feedforward compensation is proposed, so as to realize the angle tracking of leading-and trailing-edge DC motors. The mathematical expression of the MAW aero-servo-elastic system with airspeed and air density uncertainties is modeled via the proposed uncertainty scheme. Both Single-Input and Single-Output(SISO) and MIMO controllers are designed via the theory of robust control to suppress the flutter instability of the MAW model. Then, a number of wind tunnel tests are implemented based on μ controllers. The experimental results show that, SISO μ controller can expand the flutter boundary of the MAW model from 36.5 m/s to 39 m/s. Meanwhile, MIMO μ controller can suppress the flutter instability of the MAW model from 36.5 m/s to 38 m/s. Compared with LQG controller, μ controller can suppress the flutter effectively without time delay compensation. This shows that the μ controller has better robust performance.