Tudor S., Gheorghe G., Odobescu G., Stammers C.W.

The paper presents the analytical model, numerical simulation and experimental results for a semi-active vibration isolation system with magnetoreological fluid dampers for large machinery rotating at high speed. As in this case the isolator is usually low tuned, resonance is encountered during transient regimes to attain operating speed or full stop. For the small scale model employed, the relative long run down time interval encountered in the case of large rotating machines was obtained by using a frequency converter and a PLC. The instantaneous rotational speed or the foundation displacement are used as control variable to modulate the magnetic field applied to the damper fluid according to the frequency response of the oscillating system consisting of machine body, foundation block and suspension device. Also, an electronic circuit is developed for implementation of balance logic control strategy. The principle of the control method is to provide larger damping forces as the machine passes through resonance frequencies and very low ones at nominal frequency or to cancel as much as possible the transmitted force in both transitory and stationary operating conditions. It is shown that a better trade-off between force transmissibility and amplitude amplification factors can be achieved by using these semi-active control strategies.