A novel dynamic model for magnetorheological dampers with multiscale insights into field-responsive yield transitions

Magnetorheological (MR) dampers provide tunable stiffness and damping properties for adaptive rotor systems, yet the underlying rheological transitions governing their performance remain insufficiently characterized. This work introduces a novel dynamic model of an MR damper based on a smooth-transition constitutive equation, accurately capturing progressive yielding and re-yielding behavior of MR fluids under coupled axial-circumferential shear. The model is consistently validated through theoretical analysis and targeted MR-damper rotor experiments, demonstrating reliable predictive capability at both local and system levels. High-resolution simulations reveal that increasing magnetic field strength can induce a topological transformation of the oil-film pressure-field distribution, where broad shear plateaus evolve into localized high-pressure peaks driven by yield-surface contraction and migration. This reconfiguration alters the phase relationship between load and motion, giving rise to a previously unreported non-monotonic damping response as rotor eccentricity grows. At large eccentricities, shear-rate dominance diminishes the relative contribution of field-dependent yield stress, triggering a saturation regime that limits further controllability. These findings provide multiscale insights that connect film-scale yield evolution and flow-field reorganization to the macroscopic dynamic characteristics of MR dampers, offering critical design guidance for smart MR-fluid-based damping systems.