Effective Model Reduction for Magnetically Levitated Flexible Rotors Including Contact Dynamics

Reduced order models are required for controller design purposes to allow practical realization and implementation in real-time applications. In the rotor dynamics field, the controllers associated with magnetic bearings are classic examples of such a requirement. A technique is introduced to reduce the order of a finite element rotor model to one involving only the required rectilinear displacements in sensor and controller nodal planes. The reduced order model is shown to predict a number of natural frequencies and responses to step changes in unbalance with considerable accuracy. A simulation of the rotor making contact with a rigid retainer bearing is also established using a constrained Lagrangian multiplier. Again, the differences between the full and reduced order model rotor orbits are shown to be small.