Rotor systems supported by the radial active magnetic bearings (AMBs) are considered in thispaper. If dynamic characteristics of the rotor systems are examined numerically by the finite elementmethod, it is necessary to determine forces in the bearings. Considering supporting by the AMBs, ashaft levitates in an air gap between the rotor and the stator part. Forces of magnetic levitation arecaused by the electromagnetic field in the bearing. Electromagnetic forces in AMB are determined bytwo methods. One is based upon the principle of virtual work and the other one upon the Maxwellstress tensor. The forces computations are provided for three-dimensional and two-dimensional finiteelement models of the radial AMB. One-dimensional approximation of the magnetic circuit isprovided as well. Rates of convergence, efficiencies and accuracies of the electromagnetic forcescomputations are evaluated from several points of view. These are compared also with used type ofmaterial model, methods of the forces calculation and size of AMB model meshes.
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