Comparative study of physics-based and CAD-based multi-body dynamic models for a coupled gear Pair–Bearing transmission system under fault conditions

Reliable fault diagnosis in rotating machinery demands accurate prediction of their condition before failure occurs. Model-based diagnosis of faults in rotating machinery is an effective method to overcome the high cost of experimental investigation. This work develops and validates experimentally two complementary dynamic models of a coupled bearing–gear pair transmission system: a 15-degrees-of-freedom physics-based model formulated in MATLAB/Simulink, which captures nonlinear bearing contact and time-varying gear mesh stiffness, and a high-fidelity CAD-based multi-body model built in MSC ADAMS to closely replicate the physical configuration. Defects are intentionally introduced into the bearing subsystem in both simulations and a machine-fault simulator. Responses of the systems acquired in the load zone are processed using short-time synchronous averaging (related to fault characteristics time) to suppress non-synchronous disturbances (not related to faulty conditions), followed by envelope analysis to extract bearing characteristic frequencies. A comparative evaluation (qualitative and quantitative) across different faulty conditions of the system’s bearing demonstrates strong agreement between the simulated and experimental fault signatures. The study confirms that both models serve as effective virtual platforms, significantly reducing reliance on time-consuming, costly experimental campaigns and enabling the scalable development of condition-monitoring strategies for rotating machinery.