Dry friction induced steady state backward whirling vibration of rotating drillstring

In this paper a numerical simulation has been carried out to study the backward whirling vibration of rotating drillstring. It becomes clear that once backward whirl is initiated, the whirling frequency and its amplitude are heavily dependent on the rotation speed, the eigenfrequency, the clearance and the formation stiffness. It also appears that the friction coefficient, which is responsible for the initiation of backward whirl, does not affect the whirl frequency and amplitude. The steady state backward whirl amplitude increases with the rotation speed but the whirl frequency is limited by the eigenfrequency of the joint drillstring-formation system.