Electromechanical Dampers for Vibration Control of Structures and Rotors

Viscoelastic and fluid film dampers are the main two categories of damping devices used for the vibration suppression in machines and mechanical structures. Although cost effective and of small size and weight, they are affected by several drawbacks: the need of elaborate tuning to compensate the effects of temperature and frequency, the ageing of the material and their passive nature that does not allow to modify their characteristics with the operating conditions. Active or semi-active electro-hydraulic systems have been developed to allow some forms of online tuning or adaptive behavior. More recently, electrorheological, (Ahn et al., 2002), (Vance & Ying, 2000) and magnetorheological (Vance & Ying, 2000) semi-active damping systems have shown attractive potentialities for the adaptation of the damping force to the operating conditions. However, electro-hydraulic, electrorheological, and magnetorheological devices cannot avoid some drawbacks related to the ageing of the fluid and to the tuning required for the compensation of the temperature and frequency effects. Electromechanical dampers seem to be a valid alternative to viscoelastic and hydraulic ones due to, among the others: a) the absence of all fatigue and tribology issues motivated by the absence of contact, b) the small sensitivity to the operating conditions, c) the wide possibility of tuning even during operation, and d) the predictability of the behavior. The attractive potentialities of electromechanical damping systems have motivated a considerable research effort during the past decade. The target applications range from the field of rotating machines to that of vehicle suspensions. Passive or semi-active eddy current dampers have a simpler architecture compared to active closed loop devices, thanks to the absence of power electronics and position sensors and are intrinsically not affected by instability problems due to the absence of a fast feedback loop. The simplified architecture guarantees more reliability and lower cost, but allows less flexibility and adaptability to the operating conditions. The working principle of eddy current dampers is based on the magnetic interaction generated by a magnetic flux linkage’s variation in a conductor (Crandall et al., 1968), (Meisel, 1984). Such a variation may be generated using two different strategies: