Dynamic Response Analysis of an Unbalanced and Misaligned Rotor Supported on Active Magnetic Bearings and Touchdown Bearings

Abstract

This paper investigates a study of the simultaneous interaction between active magnetic bearing (AMB) and touchdown bearing (TDB) in an unbalanced and misaligned rotor system. Numerous practical importance of the working together of both bearings in high-speed rotating machinery, such as the turbines and pumps, can be explained by examining two cases depending upon the types of touchdown bearings. The first case is to consider a faulty rotor supported by active magnetic bearings and conventional touchdown bearings (rolling element bearings) as backup support, in which AMB is active but conventional touchdown bearing is inactive during operation. The second case is considering foil bearings as touchdown bearings, in which AMB and foil bearing both are in action during operation. The hydrodynamic principle of air in foil bearing while rotation of the rotor causes to make it in working condition. Mathematical modelling of the unbalanced and misaligned rigid rotor with a disc at middle supported on both bearings has been done for this investigation purpose. Misalignment has been considered between the rigid rotor and active magnetic bearings. The dynamic equations of motion are developed to numerically generate rotor displacement and current responses of the system. It has been found that simultaneous working of AMB and foil touchdown bearings helps in suppressing the vibration response of the rotor system, increasing the reliability of the machine and making more energy efficiently. It is also observed that current consumption is less in the second case than the first.