Active control of structural response has been considered to be one of the most practical and effective technologies of active vibration control of a helicopter. In this paper, the authors present a harmonic synchronous identification-updating (HSIU) method for active control of helicopter structural response driven by piezoelectric stack actuators. The identification method for the harmonic coefficients of controlled responses is established based on the recursive least-squares algorithm, whereas the updating method for the harmonic coefficients of control inputs is established using the steepest gradient based adaptive harmonic control algorithm. By using the HSIU method, an experimental control system for a free-free beam structure driven by piezoelectric stack actuators has been established. The numerical simulations for active vibration control of a simplified airframe model and the experimental investigations on active vibration control of a free-free beam structure driven by piezoelectric stack actuators have indicated that the active control of helicopter structural response by using the HSIU method combined with piezoelectric stack actuators can reduce airframe vibration levels by more than 97% for simulation excitations and more than 75% for vibration responses measured in a Z11 helicopter and enhances convergence and robustness.
The vibration of a helicopter fuselage is mainly produced by the rotor exciting loads which are three forces and three moments containing harmonics in three directions at rotor hub center, and has the characteristic of large, steady and harmonic vibration. The active control of helicopter fuselage vibration by using inertia actuator needs to pay a heavy weight cost for achieving a good control effect. In this paper, a method for multi-input multi-output multi-harmonic (MIMOMH) feed-forward adaptive control of helicopter fuselage vibration by using piezoelectric stack actuators is presented. The method is composed of the harmonic coefficients identification and the MIMOMH feed-forward adaptive filtering algorithm, and has excellent characteristics such as light weight, fast response, wide working frequency range, adaptive ability and high effect. The numerical simulations for a frame structure scaled by the Z11 helicopter fuselage floor with four actuating inputs, four vibration outputs, three rotor exciting loads and the first three harmonic frequencies contained in each exciting load were performed, indicating that the vibration levels at objective points are reduced by 99% by using the method and are much lower than the results by only controlling the first harmonic frequency. When the phases, amplitudes and frequencies of exciting loads are changed, the method demonstrates an excellent adaptability to control vibration.
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