Modeling and experiments of linear and nonlinear dynamics of a flexible multi-bearing rotor

A new flexible multi-bearing rotor rig was recently developed in the Rotor Dynamic Laboratory at Case Western Reserve University to incorporate simultaneous multiple fault detection scenarios for vibration monitoring and diagnostic purposes. Modeling and experiments of linear and nonlinear dynamics on this versatile test rig are presented in this work. The main objective of thesis research is to further ongoing research in developing model-based observers for fault detection and diagnosis in rotating machinery. To achieve the objective in this research work a new design was made and added to the test rig. The devised rig will be used for testing purposes in a monitoring and diagnosis system for rotating machinery. The test rig has two controllable balancers that are assembled on rotor shaft, a journal bearing or rub impact device at the center, and ball bearings at both ends of the shaft. A 12-degree-of-freedom (DOF) linear model was developed for this test rig. The nonlinearity of this system occurs in either the journal bearing fluid-film force or the rub impact forces (normal and friction forces). The journal bearing fluid-film force requires solutions of the Reynolds lubrication equation. A closed form solution approximation for the pressure distribution was derived. The normal force in the rub impact is assumed to depend exponentially on the distortion of the surface during contact (Hertzian Contact). A nonlinear hysteresis loop was tested experimentally and simulated computationally. As bearing static load is increased, the instability threshold speed occurs at progressively higher rotor speeds. In addition, rub impact was examined experimentally and computationally. The occurrence and severity of the rub impact between the rotor (shaft) and the stator (bearing) is dependent on the mass unbalance of each balancer and the rotational (operating) speed. Good agreements were found between experimental and simulation results for both journal bearing (linear and nonlinear model) and rubs impact tests.