Finite element based non-linear transient analysis of active magnetic bearing turbomachinery

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Virginia Tech

The active magnetic bearing (AMB) is a relatively new technology in which the suspension forces are generated magnetically without any contact. Although there are many advantages of AMB technology over conventional bearing design, its major selling point is the claim of reduced maintenance and longer run times between mandatory shutdowns to replace worn or defective components. This claim is, however, somewhat diluted by the fact that the majority of industrial applications have relied upon anti-friction backup bearings. These backup bearings are, in the event of control system failure or limited operation during momentary overload conditions, essential for the protection of AMB rotor, stator and other stationery seals along the shaft. The increase in the number of critical path machinery using AMB technology has focused awareness and necessity for proper design of these auxiliary bearings to avoid additional unwanted down-time.

In this research, the equations of equilibrium governing the dynamic response of a rotor-bearing system were formulated and then solved using an appropriate numerical algorithm capable of analyzing this non-linear system. An efficient transient response analysis program was developed for evaluation of shock loading, blade loss and rotor drop of active magnetic bearing machinery. This program can analytically predict the path of the rotor and the instantaneous loads acting on the backup bearings during rotor drop which would help in the design of more reliable backup bearings without evaluating them experimentally. Parameter variation study was conducted analytically to observe the influence of some important factors on the dynamics of rotor drop phenomenon. The results from this program have also been compared to the experimental data obtained from the Virginia Tech Rotor Dynamics Laboratory AMB Rotor Drop Test Rig.