Master of Science in Mechanical Engineering (MSME)


Mechanical Engineering

Document Type



A journal bearing is used to support radial loads under high speed operating conditions. In a journal bearing, pressure or hydrodynamic lift is generated in the thin lubricant oil film that separates the shaft and the bushing, thus preventing metal-to-metal contact. Some journal-bearing configurations are susceptible to large-amplitude, lateral vibrations due to a “self-excited instability” known as oil whirl. In order to investigate the effects of lubricant viscosity on oil whirl, a simplified Thermohydrodynamic analysis (THD) analysis of a plain cylindrical journal bearing system has been developed. The “classical” form of the Reynolds equation coupled with simplified, first-order energy equations are solved in an approximate fashion by assuming a parabolic pressure distribution in axial direction. THD design charts for the rapid evaluation of dynamic coefficients and the threshold speed are developed to investigate the effects of temperature on oil whirl instability. A non-linear transient stability analysis is also presented. This investigation reveals that the inlet viscosity has a pronounced influence on the bearing dynamic coefficients of the lubricating oil film. This investigation also reveals that it is possible to stabilize a journal bearing either by heating the oil or by cooling the oil depending upon the operating region.



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Committee Chair

Michael M. Khonsari