Tuneable Vibration Absorber For Multi Modal Control Of Lightly Damped Structures

This paper presents the design of an experimental multi modal vibration absorber for controlling the transverse vibration of a lightly damped panel. Traditionally, when multiple modes of a structure need to be controlled many absorbers are scattered on the structure, each tuned to control a specific structural mode. However the use of multiple units increases the added weight to the structure and requires complex tuning process, which therefore raise the cost of the control treatment. In this paper an integrated vibration absorber able to incorporate in one unit the effect of two traditional single axis absorbers is proposed. The absorber consists of a beam with a cylindrical inertial mass mounted at the centre. The connection between the mass and the beam is realised through flexible fins that allow rotational vibrations of the mass around the beam but do not allow relative displacement. When the two ends of the beam are attached to a structure, the flexural vibration of the beam-mass system produces a transverse control force on the structure while the rotational vibration of the inertial mass generates a control moment. These two actions can be used to control the response of two resonant modes of a structure by tuning the two resonances of the device to match those of the modes under control. The flexural resonance of the beam-mass system is tuned by varying the axial tension of the beam using a piezoelectric stack transducer while the rotational resonance of the device is regulated by varying the tension on capacitors whose plates are mounting on the beam and on the rotating mass respectively.