An on-line natural frequency estimation method and an adaptivevibration control of composite beams are investigated. Oncedelaminations occur in the composite structures, dynamiccharacteristics of the structures are changed including the decreasesof natural frequencies due to the defected stiffness. In this paper,a real-time frequency estimation method is proposed to detectfrequency shifts of the specimen. In addition, an on-line adaptivecontroller, named Adaptive Positive Position Feedback (APPF), issuggested. Glass/Epoxy composite beams with delaminations atdifferent locations are manufactured and surface bonded piezoceramicactuator is used as an actuator. It is found that the estimatedfrequencies converge to real ones, and successful multi-modevibration suppression is achieved using the proposed on-line adaptivecontroller.
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