Analysis of simultaneous rotordynamic faults using coupled mechanical face seal vibration
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Rotating machines are inherently vulnerable to many different faults; detecting these faults in real time can reduce costs and improve safety. A prerequisite for a successful condition monitoring system is an accurate characterization of the system and associated faults. Furthermore, the pursuit to increase efficiency has heightened susceptibility to coexisting fault situations; comprehensive condition monitoring systems should consider the possibility of multiple simultaneous faults. Previous studies have primarily considered the rotor and associated triboelements (e.g., mechanical face seals) as separate machine components. This work hypothesizes that rotor vibration transmitted to the mechanical face seal could serve as a convenient surrogate for analyzing rotor fault signatures. A comprehensive dynamic model is developed to study the dynamics of a mechanical face seal with two flexibly mounted elements, including axial, eccentric, and angular degrees-of-freedom. In addition, and for the first time, the model developed herein includes coupled rotordynamics, inertial maneuver loads, and transient dynamic excitation (i.e., start-up and shut-down). The faults investigated here include intermittent rotor-housing contact, a breathing shaft crack, and seal face contact. A novel model for intermittent contact is developed using a realistic surface roughness model founded on elastoplastic asperity contact. Exhaustive simulation is then used to identify and characterize hallmark dynamic fault signatures. Finally, the multiple fault scenario is studied using a synthesis of stationary and non-stationary signal processing techniques.