The transverse vibrations of flexible rotors can be reduced to safe levels by radial control forces at an intermediate span position, applied by a suitable actuator. One versatile control strategy applies forces proportional to displacement and velocity, with coefficients dependent on the rotational speed. This control can be realized with an electromagnetic bearing under microprocessor control. Suitable microprocessor software is described, to implement the required real-time computation of the control forces. Experimental results obtained from a test rig are compared with theoretical predictions. There are advantages in allowing the stiffness coefficient to become negative, provided that positive damping is simultaneously applied.

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