Dynamic response characteristics of multiplicative faults in a misaligned-bowed rotor-train system integrated with active magnetic bearings

The present study deals with the modeling and response analysis of two coupled rotor systems that are subjected to the coupling angular misalignment accompanied by the shaft bow and integrated with an active magnetic bearing (AMB). The innovative aspect of the work lies in modeling a rotor-train system in the contemporaneous presence of the residual bow and the misalignment in the shaft, which has multiplicative effect. To study the responses, a fundamental model of the rotor-AMB system has been derived. The angular misalignment introduces an additional coupling stiffness (ACS) and changes the intact stiffness. An excitation function has been chosen to model the misalignment, which gives both odd and even frequency components in the full spectrum. In the misaligned system, the presence of bow generates a multiplicative load, which also affects the multi-harmonic responses and makes it more challenging to interpret. The AMB has been used to control vibrations caused by multiplicative faults, and its adoption represents a unique approach to reduce vibrations. The present control model modulates the supply current to the AMB via PID (proportional-integral-derivative) controller. The study numerically simulates the steady-state responses and analyses the harmonic components by examining the time-domain responses, orbit, and displacement spectra. Furthermore, the study is extended to examine the responses acquired from an experimental test rig constructed in the laboratory. The angularly misaligned and residual bowed shaft responses from the test rig were captured with the help of proximity probes. Finally, the proposed model is validated by comparing the pattern of the orbit plots and full spectra obtained from the numerical simulation and experiment and are found to be consistent.