Effects of friction between an overhung multiple-rotor and stator on nonlinear motion

This study investigates the effects of impacts and friction between an overhung multi-rotor system and a stator on nonlinear dynamic behavior, including rotor-stator bouncing in the rotating frame, internal resonance between forward and backward modes (which are commensurate in the rotating frame), and dry friction-induced backward whirling motion. While previous studies have explored rotor-stator impacts in four-degree-of-freedom (4-DOF) systems, they have not accounted for friction studied. Therefore, this work focuses on the influence of friction in a 4-DOF model. Chaotic motions are observed for the first time for current system, which hasn’t been reported before. The equations of motion for the overhung coupled rotor system are derived using the Lagrangian method. A smoothed friction model is introduced to simulate Coulomb friction, and a parametric study is conducted on friction and eccentricity to explore the system responses. Three types of motion are observed: rotor-stator bouncing, stiffened backward whirling, and internal resonance-induced bouncing using bifurcation diagrams, orbit plots, Poincaré maps, and spectral intensity plots. Results show that for low eccentricity, rotor-stator bouncing occurs in the primary resonance region as friction increases, while stiffened backward whirling with higher radial displacements emerges above the primary resonance, and radial displacement increases with rotational speed. For moderate eccentricity, the system exhibits both rotor-stator bouncing and stiffened backward whirling. For high eccentricity and low friction, internal resonance between forward and backward modes is observed in the rotating frame, whereas at high friction, the system exhibits backward whirling motion with increased radial displacement. In addition, chaotic motions are observed with the increasing friction. These findings provide important insights for diagnosing rotor-stator rubbing phenomena in 4-DOF systems.