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The present manuscript deals with the problem of rotor-stator rubbing. Due to performance increase in rotating machinery, rubbing processes happen more frequently. These are very complicated mechanisms that lead to high impact loads, vibrations and instability. The authors propose a control technique by using an active auxiliary bearing to overcome the problem of rubbing. The control concept enables a transition of the rotor towards a contact situation (with an auxiliary bearing) without rebounding and loss of contact. To investigate the practical feasibility of this approach, numerical simulation has been used to show that using this control concept the impulse (and contact force respectively) can be significantly decreased. Experiments to validate the theoretical findings are already in progress and will be published soon.

A framework for the development of a feedback controller for an active auxiliary bearing is presented. In a new approach, a dry bushing type auxiliary bearing is attached to the foundation via two unidirectional actuators. The control force is applied indirectly using the active auxiliary bearing only in case of rubbing. A simulation for the elastic rotor and the auxiliary bearing including the non-smooth nonlinear dynamics of the rubbing contact is used to develop the feedback controller. A robust two-phase control strategy has been developed which stabilizes the rotor system in case of rubbing and effectively avoids "backward whirling". Experimental studies have been carried out at a rotor test rig. The experiments show the outstanding success of the strategy. In case of rubbing, the contact forces are reduced up to 85%.

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Auxiliary bearings are used in many rotor systems, e.g. those with active magnetic bearings. In a case of a contact with the auxiliary bearing, high impact forces and wear are possible. Therefore the auxiliary bearings have to be replaced after a certain number of contact events. This is very costly and often needs complete dismantling of the rotor system. In this paper a concept for model based condition monitoring of an auxiliary bearing is developed. The rotor system is modeled in a multibody simulation environment, including the contact to the auxiliary bearing and various fault parameters. After contact (drop or bouncing contact) occurs in the real rotor system, an identification algorithm analyses the measuremental data of the contact event and determines the fault which occurred. Based on the results of the identification algorithm, an optimization tool aligns the rotor simulation with the measurement by varying the fault parameters. After the alignment of the simulation, the simulation results are evaluated. The contact forces are evaluated against location on the surface of the auxiliary bearing and are stored. This procedure is performed after each contact event. Hence, a weighting of the load over the surface of the auxiliary bearing is gained. Depending on the material and structure, these data can be used for a life-time estimation of the auxiliary bearing. Using an active magnetic bearing test facility, the monitoring system has been successfully tested.