Keywords: worn bearings, wear identification, rotor bearing system, continuous system, non-linear system, external excitation.

In the current work, a rotor-bearing system, comprised of a step rotor and two worn fluid film bearings, is simulated using a new approach, in order to develop criteria which can identify wear present in bearings, through the analysis of the extracted time histories of the rotor response. Several similar approaches for non-linear rotor bearing systems have been tested in recent years, including rigid or elastic shafts combined with resilient bearings [1,2,3,4,5,6]. However, papers on similar aspects of combining a continuous shaft with worn journal bearings are few [7]. In this work, a continuous rotor, modeled using the Rayleigh equations of motion [8], is mounted using specific boundary conditions for non-linear finite worn fluid film bearings. The lubricant forces are evaluated using the finite difference method. Wear defect in the bearings is introduced using the Dufrane model [9,10] as an additional fluid film thickness in the worn circumferential area of the bearing.

The analysis is mainly focused on the time-frequency decomposition of the extracted time histories of the rotor's virtual start-up and also of steady-speed operation, combined with the introduction of an external excitation force. In both cases, the presence of the sub-synchronous response components is observed, and as the wear depth becomes greater, this response is amplified.

The concept of suitable external excitation can be applied in real machines rotating at constant rotational speed, in order to estimate the magnitude of the study for the case of resonance. Several cases of variable wear depths and system properties are studied in order to investigate the possibility of identifying the wear extension, judged to be at least of 20% of the radial clearance.

1

Jei Y.J, Lee C.W., "Modal characteristics of asymmetrical rotor-bearing systems", J. of Sound and Vibration, 162, 209-229, 1993. doi:10.1006/jsvi.1993.1114

2

Adams M.L., "Non-linear dynamics of flexible multi-bearing rotors", J. of sound and vibration, 71, 129-144, 1980. doi:10.1016/0022-460X(80)90413-7

3

Hong S.W., Kim J.W., "Modal analysis of multi-Span Timoshenko beams connected or supported by resilient joints with damping", J. of sound and vibration, 227, 787-806, 1999. doi:10.1006/jsvi.1999.2385

4

Hong S.W., Park J.H., "Dynamic analysis of multi-stepped, distributed parameter rotor-bearing systems", J. of sound and vibration, 227, 769-785, 1999. doi:10.1006/jsvi.1999.2384

5

Shen G., Xiao Z., Zhang W., Zheng T., "Non-linear behavior analysis of a rotor supported on fluid-film bearings", J. of Vibration and Acoustics, 128, 35-40, 2006. doi:10.1115/1.2149394

6

JianPing J., Guang M., Yi S., SongBo X., "On the non-linear dynamic behavior of a rotor-bearing system", J. of Sound and Vibration, 274, 1031-1044, 2004. doi:10.1016/S0022-460X(03)00663-1

7

Kumar A., Mishra S.S., "Stability of a rigid rotor in turbulent hydrodynamic worn journal bearings", Wear, 193, 25-30, 1996. doi:10.1016/0043-1648(95)06654-3

8

Jun O.S., Kim J.O., "Free Bending Vibrations of a Multi Step Rotor", J. of Sound and Vibration, 224, 625-642, 1999. doi:10.1006/jsvi.1999.2206

9

Dufrane K.F., Kannel J.W., McCloskey T.H., "Wear of steam turbine journal bearings at low operating speeds", J. of Lubrication Technology, 105, 313-317, 1983.

10

Fillon M., Bouyer J., "Thermo hydrodynamic analysis of a worn plain journal bearing", Tribology International, 37, 129-136, 2004. doi:10.1016/S0301-679X(03)00051-3

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