The effectiveness of a disk-type magnetorheological(MR) fluid damper for attenuating rotor vibration under AC magnetic field is experimentally studied on an overhung flexible rotor with two disks. It is shown that as the frequency of AC magnetic field increases, the capability of the disk-type MR fluid damper for attenuating rotor vibration significantly reduces. There are a maximum frequency of AC magnetic field for a given magnetic field strength and a minimum strength of AC magnetic field for a given frequency of AC magnetic field. If the frequency of AC magnetic field is over the maximum frequency or the applied magnetic field strength is less than the minimum strength of AC magnetic field, the dynamic behavior of the disk-type MR fluid damper rotor system is the same as that without applied magnetic field. Even if the dynamic behaviors of a rotor on the disk-type MR fluid damper are controlled by an external AC magnetic field in some cases, nonsynchronous and amplitude-modulated phenomenon will appear in the rotor motion, the disk-type MR fluid damper cannot effectively attenuate the rotor vibration. Therefore, it is better to use the DC magnetic field to control the dynamic behaviors of the disk-type MR fluid damper for rotational machinery.
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