Effect of random roundness error on the stability of a hydrodynamic journal bearing system part I: Theoretical study

From a manufacturing viewpoint, the profile of a journal out-of-roundness is random. In order to be closer to the engineering practice, the study presents a dynamic modelling, analysis and calculating method for the hydrodynamic journal bearing system considering random roundness error. The random character of manufacturing errors is presented by Monte Carlo method in the analysis to establish the relationship between the level of journal roundness error and the system stability characteristics. The results of theoretical analysis show that the effect on the stability of the hydrodynamic journal bearing system is minimal when the grade of journal roundness error P is below 9; when P？>？9, the journal out-of-roundness promotes the system stability. However, the increase in the random roundness error will generate high-frequency vibrations and aggravate the system vibration. Besides, the journal random out-of-roundness has a minimal effect on the system stability when the eccentricity is between 0.5 and 0.6 or the Sommerfeld number is between 0.05 and 0.1, which suggests that the system should be operated within this region to minimise the effect of journal out-of-roundness