Magnetorheologic (MR) fluids react to the magnetic fields undergoing changes in their mechanical characteristic, viscosity in particular. Due to this characteristic, MR fluids have been used to attenuate the vibration of rotors. In this paper, assuming the Bingham model, the Reynolds equations for the MR fluid in squeeze film dampers are used to obtain related hydrodynamic forces. By applying the finite element method, an unbalanced flexible rotor is modelled and the dynamic behaviour of rotor in the presence of MR fluid is simulated and studied. Primarily, simulation is carried out with empty squeeze film damper with no fluid inside the gap in order to investigate how much the system damping is influenced by the magnetic force. By increasing the current, the small damping is added to the system and its effect can be noticed by the reduction of the resonant peak, but the magnetic field does not modify significantly the behaviour of the rotor damper. Then, the squeeze film damper filled up the gap with the MR fluid. By increasing the magnetic field, the system becomes stiffer until dampers become rigid. Simulation results indicate that the vibration amplitude of the rotor corresponding to the first critical speed is considerably reduced. In order to improve the performance of the system, the behaviour of the rotor system for different kinds of MR fluids is studied. Finally, using an on-off control, the vibration within a range of working speeds is attenuated.
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