Most Individual Blade Control (IBC) approaches have attempted to suppress rotor vibration by actively altering the varying aerodynamic loads on the blade using techniques such as trailing edge servo-flaps or embedded piezoelectric fibers to twist the blade. Unfortunately, successful implementation of these approaches has been hindered by electromechanical limitations of piezoelectric actuators. The Smart Spring is an unique IBC approach that is designed to suppress the rotor vibration by adaptively altering the "structural impedance" at the blade root out of phase from the time varying aerodynamic forces. It overcomes many limitations associated with the capabilities of piezoelectric actuators inherent in other IBC approaches. The details of the Smart Spring concept as a class of actively Tunable Vibration Absorbers (TVA) for the rotor blade application is presented in this paper. A proof-of-concept hardware model of the Smart Spring was fabricated and a real-time adaptive control algorithm was implemented to demonstrate the concept as an actively TVA. The initial dynamic tests using a mechanical shaker achieved significant vibration suppression at harmonic peaks as well as the broadband reduction in vibration. Further testing of the hardware was conducted in a wind tunnel using a non-rotating blade to evaluate the performance of the device in a more representative rotor blade aerodynamic environment. Shaker test and wind tunnel test results verified the capability of the Smart Spring to suppress multiple harmonic components in rotor vibration through adaptive control of the structural impedance at the blade root.

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Conference 44th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference
Wickramasinghe, V.K. (Viresh K.), Zimcik, D.G. (David G.), Yong, C. (Chen), & Nitzsche, F. (2003). Smart spring - An actively tunable vibration absorber designed to control aeroelastic response. In Collection of Technical Papers - AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference (pp. 3651–3658).