Active Flutter Suppression Of A Two-Dimensional Airfoil Using Ultrasonic Motor

This dissertation presents how to use the ultrasonic motor as an actuator to suppress the flutter of a two-dimensional airfoil section with a control surface. The ultrasonic motor, which features simple structure, high torque at low speed, small size, low weight and no electromagnetic contamination, is a promising actuator for the flutter suppression of small aircraft. The dissertation presents the combined theoretical, numerical and experimental studies on the experimental modeling of the actuator, the design of test rig and control system, the modeling of two-dimensional airfoil aeroelastic system, the control design of active flutter suppression, and the effect of group delay in the digital filter on the stability of aeroelastic closed-loop system. The main contributions of the dissertation are as follows.In Chapter 2, the dissertation demonstrates the design of an airfoil model with a control surface driven by an ultrasonic motor as the actuator first, and then presents the experimental modeling of the actuator. The ultrasonic motor is controlled by an independent control circuit, which receives rotate angle commands from an upper computer and drives the ultrasonic motor to reach the rotation angle of the control surface. For the actuator and control surface, a dynamic model of single degree of freedom is constructed so that the design of control law can be greatly simplified. The parameters of the actuator model are estimated via the tests under sweep sinusoidal excitation. The effectiveness of the model is validated through wind tunnel tests.Chapter 3 presents the design of the test rig and the measurement/control system software. The test rig includes the airfoil model, the accompanied sensors, the actuator and the protecting mechanism. There exists remarkable dry friction along the guide rail, which makes the system damping very complex, even though the track is well lubricated. Therefore, the experimental modeling is made to estimate the structural parameters of the test rig.In Chapter 4, the aeroelastic model of the whole test rig is first established by using Jones's approximation of Theodorsen's unsteady aerodynamics load. Then, the numerical simulations and wind tunnel experiments for the sub-optimal flutter suppression of the airfoil model are presented. The numerical simulations agree well with the wind the tunnel experiments, and the critical speed is increased by 13.4%. Chapter 5 presents the robust flutter suppression of the airfoil. Both H∞controller andμsynthesis are designed when the damping uncertainties in plunge...