Multiphysics Modelling of Segmented Passive Magnetic Bearings for a Vertical Rotor

This paper presents the segmentation and modelling of radial support magnets for a vertical rotor in a flywheel energy storage system (FESS) demonstrator, emphasizing the impact of magnetic configuration on the nonlinear rotordynamic response. A multiphysics-based model is developed to simulate the magneto-mechanical behaviour of the bearings, enabling high-fidelity prediction of stiffness and damping of supports under several operative conditions. The model incorporates field-dependent material properties, magnetic saturation, and geometric asymmetries. The case study is the current FESS demonstrator under realisation at the Politecnico di Torino in its operating conditions. Several Halbach array configurations, including segmented and continuous ring topologies, are implemented and compared in terms of their magnetic field uniformity, and resulting rotor nonlinear dynamics. Through parametric studies, optimal segmentation patterns and Halbach configurations are identified to minimize cross-coupled stiffness and enhance passive stability while maintaining high energy density. The segmentation of the radial support magnets is shown to influence static suspension properties and the nonlinear dynamic behaviour of the rotor mainly in subcritical regime.