Byoung-Hoo Rho

A study of the dynamic characteristics of synchronously controlled hydrodynamic journal bearings

Abstract In this paper, synchronous control of bearing is employed through a control algorithm for an actively controlled hydrodynamic journal bearing in order to suppress whirl instability and to reduce the unbalance response of a rotor-bearing system. Furthermore, a cavitation algorithm, implementing the Jakobsson–Floberg–Olsson boundary condition, is adopted to predict cavitation regions in a fluid film more accurately than the conventional analysis, which uses the Reynolds condition. The unbalance responses and stability characteristics of the rotor-bearing system are investigated for various control gains and phase differences between the bearing and journal motion. It is shown that the unbalance responses of the system can be greatly decreased by synchronous control of the bearing. There is an optimum phase difference, which gives the minimum unbalance response of the system at given operating conditions. It is also found that the stability threshold of the system can be greatly increased by synchronous control of the journal bearing.

Acoustical properties of hydrodynamic journal bearings

Abstract Results of theoretical investigations on acoustical properties of hydrodynamic journal bearings are presented. Nonlinear analysis including rotor imbalance is performed for a rotor-bearing system in order to obtain acoustical properties of the bearing. Furthermore, a cavitation algorithm, implementing the Jakobsson–Floberg–Olsson boundary condition, is adopted to predict cavitation regions in a fluid film. Acoustical properties are investigated through frequency analysis of pressure fluctuation calculated from the nonlinear analysis. Results show that the acoustical frequency spectra of the fluid film are pure tone spectra, containing the frequency of the shaft rotation and its super-harmonics. The analysis also shows that super-harmonics are predominant at the neighborhood of the fluid film reformation and rupture regions.

Noise analysis of oil-lubricated journal bearings

Abstract The objective of the paper is to provide a procedure for calculating the noise of oil-lubricated journal bearings. In order to obtain acoustical properties of the bearing, a non-linear analysis including rotor imbalance is performed for a rotor-bearing system. Sound pressure levels of the bearing are obtained through frequency analysis of pressure fluctuations calculated from the non-linear analysis using a transmission theory of plane waves. Results show that the sound pressure level of the bearing increases with the rotational speed of the rotor, although the whirl amplitude of the rotor is decreased at high speed. The noise-estimating procedure presented in the paper could be an aid in the evaluation and understanding of acoustical properties of oil-lubricated journal bearings.

A study on nonlinear frequency response analysis of hydrodynamic journal bearings with external disturbances

The nonlinear vibration characteristics of hydrodynamic journal bearings with a circumferential groove are analyzed numerically in case that external sinusoidal disturbances are given to the rotor-bearing system. The cavitation algorithm implementing the Jakobsson-Floberg-Olsson boundary condition is adopted to predict cavitation regions in the fluid film. The comparison of the steady state journal orbits using linear dynamic coefficients with the transient motion calculated from nonlinear analysis is performed. The frequency response functions obtained by linear and nonlinear analysis are also presented. When an external sinusoidal disturbance is applied to the bearing, the range of the full film region varies periodically and it becomes smaller than that of static equilibrium state. The difference between linear and nonlinear analysis increases as the excitation amplitude or the frequency of the external disturbance increases. Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in San Francisco, CA October 21–24, 2001

A Noise Analysis of Cylindrical Roller Bearings Operating Under Zero External Load

The purpose of this article is to numerically investigate one source of acoustic noise in roller bearings, that which results from the motion of the rollers in the bearing under zero external load. For the sake of simplification, it was assumed that the cylindrical roller bearings are infinitely long. Furthermore, the effects of the following on the noise of the bearing were also examined: the radial clearance of the bearing, the viscosity of the lubricant, and the number of rollers. The results of the study show that the fundamental frequency of the noise components of the cylindrical roller bearing corresponds to the multiplication of the number of rollers and the whirling frequency of the roller center. The acoustical frequency spectra of the cylindrical roller bearing are pure tone spectra, containing the fundamental frequency of the roller bearing and its superharmonics. The factors that decrease the sound pressure level of a cylindrical roller bearing include low lubricant viscosity, high radial clearance, and a reduced number of rollers. The results and discussions of the present article could aid in the design of low-noise cylindrical roller bearings.

Prediction of Noise and Vibration Characteristics of Externally Pressurized Air Journal Bearings with a Circular Slot Restrictor

The purpose of this paper is to investigate the noise and vibration characteristics of externally pressurized air journal bearings with a circular slot restrictor. To do this, the nonlinear transient analysis including rotor imbalance was performed for a rotor-bearing system. The effects of radial clearance and the length of the bearing and mass eccentricity of the rotor on the noise and vibration characteristics of the bearing are also examined. The results show that the noise and vibration of the rotor-bearing system first increase up to critical speed of the system, and then decrease up to instability threshold speed of the system as the rotational speed of the rotor increases, and the noise of the bearing is markedly influenced by the mass eccentricity of the rotor and the radial clearance and the length of the bearing.