Effects of Nonlinear Magnetic Forces on the Dynamics of Hydropower Generators with Floating Rotor Rim

Hydropower generators are normally considered rigid in rotordynamic studies; nevertheless, according to previous studies, they should be regarded as elastic, and this will affect the system's dynamics. The interaction between the magnetic flux of the stator and rotor creates attractive forces between the parts that would balance to zero at the centered position. However, asymmetries in the magnetic flux create an uneven distribution of forces that threaten the machine's life; these forces are non-linearly dependent on the gap between the rotation and stationary part of the generators, although it has been considered linear for simplification. This study focuses on how the dynamics of the rotor are affected by static eccentricity and unbalanced masses while considering nonlinear electromagnetic forces. The rotor has been modeled using curved beams and attached to the rotor-spider by connecting plates, allowing the expansion of the ring due to centrifugal and thermal loads. The electromagnetic forces are modeled as a sum of exponential functions. Bifurcation diagrams and Poincaré maps are employed to analyze the stability of the generator.