Analysis of Combined Effects of Couple Stress and Roughness on the Hydrodynamic Performance of the Journal Bearing
| Autor: | Hsiu-Lu Chiang, 江新祿 |
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| Rok vydání: | 2003 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 91 According to the Stokes microcontinuum theorem and the Christensen’s stochastic model, the main objective of this paper is to theoretically predict the combined influences of couple stresses and surface roughness on the lubrication performance of journal-bearing systems. To take account of both the presence of surface roughness of bearings and the couple stress effect due to the lubricant containing the polar suspensions, the generalized stochastic non-Newtonian Reynolds-type equation is derived and applied to evaluate the equilibrium solution of a short journal bearing. By using the linear theory, the eight oil-film stiffness and damping coefficients as well as the vibration stability boundary were determined. According to the results obtained, the combined effects of couple stress and surface roughness on the characteristics of journal-bearing systems are apparently and can not be negligible. Comparing to the Newtonian-lubricant smooth-bearing case, the couple stress effects can raise the film pressure of the lubricant fluid, improve the load-carrying capacity and reduce the friction parameter, especially at high eccentricity ratio. The surface roughness effect is dominant in long bearing approximation and the influence of transverse or longitudinal roughness to the journal bearing is in reversed trend. In general, the critical value of length—to— diameter ratio is 1.1. As for the linear stability analysis of short journal-bearing system, the presence of couple stress together with the longitudinal roughness provides an increase in the values of stiffness coefficients KXX, KXY and KYX as well as the damping coefficient CXX. In addition, this couple stress results in a higher stability threshold speed. Whereas, when compared to the smooth bearing lubricated with couple stress fluid, a decrease in the threshold speed is found in the case of transverse roughness. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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