Theoretical and experimental study on the trans-critical vibration reduction of flexible shafts by multi-gap limiting ring device considering rub-impact and dry friction

Abstract The flexible shafts in aviation equipment experience severe vibration upon exceeding the critical speed, causing severe damage to the equipment. To address this issue, a novel technique for vibration reduction using a multi-gap limiting ring device is proposed. The coupled effects of rub-impact, dry friction, and limiting are considered in a dynamic model for a multi-gap limiting ring device, and then the dynamic equation for the bending-torsional coupling of the flexible shaft with the limiting ring device is derived. Furthermore, the reverse whirl instability behavior of the shaft and the effect of various parameters on the damper performance are analyzed using a hybrid numerical method. Finally, experiments are conducted to verify the accuracy of the theoretical method. The findings show that the critical speed of the shaft rises due to the increased stiffness from the rub-impact between the limiting ring device and the shaft. The rub-impact point simultaneously causes bending-torsional coupling, which leads to torsional vibration of the shaft. Moreover, the rubbing gap, friction coefficient, preload force, and dry friction gap have a considerable impact on the limiting ring device's ability to reduce vibration. A poor choice of parameters can result in malfunctioning of the limiting ring device. Overall, this study can serve as an effective theoretical guide for the vibration reduction of flexible shafts.