Active Vibration Control of a Flexible Rotor Mounted on Journal Bearings

This paper presents a theoretical investigation of an active vibration control scheme for controlling transverse unbalance vibration response of a rotor shaft mounted on plain cylindrical journal bearings with electromagnetic actuators. The electromagnetic exciters/actuators are considered to be mounted on the stator at a plane, in general away from the conventional support locations, around the rotor shaft for applying suitable force of actuation over an air gap to control transverse vibration. Electromagnets used for vibration control do not levitate the rotor or facilitate the bearing action, which is provided by the journal bearings. Suitable force of actuation is achieved by varying the control current in the exciters depending upon a proportional-derivative control law applied to the distance of the rotor section fed back by pick ups with respect to the non-rotating position of the section taken as the reference. Thus control force is obtained over an air gap and the process is free from the difficulties of maintenance, wear and tear and power loss. Theoretical simulation with linearized expressions of electromagnetic force show good reduction in transverse response amplitude, appreciable postponement of instability caused by rotor internal damping and fluid film forces. Influence of the parameters of electromagnets on response and control current and optimum spatial placement of the actuator is studied with an example.