1,720,965 research outputs found
A study on nonlinear frequency response analysis of hydrodynamic journal bearings with external disturbances
No full textThe 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 ran ge 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.Science and Technology Policy Institute(STEPI)(98-I-03-030
Acoustical properties of hydrodynamic journal bearings
No full textResults 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. (C) 2002 Elsevier Science Ltd. All rights reserved.Science & Technology Policy Institute(STEPI)(98-I-03-030
A study of the dynamic characteristics of synchronously controlled hydrodynamic journal bearings
No full textIn 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. (C) 2002 Elsevier Science Ltd. All rights reserved.Science & Technology Policy Institute(STEPI)(98-I-03-030
Noise and Vibration Characteristics of Externally Pressurized Slot-Restricted Air Journal Bearings
No full textEffects of design parameters on the noise of rotor-bearing systems
No full textThe purpose of the present paper is to investigate the effects of design parameters on the noise produced by rotor-bearing systems supported by oil lubricated journal bearings. To do this, the effects of radial clearance and the width of the bearing, lubricant viscosity, and mass eccentricity of the rotor on the noise of the bearing are investigated, and the numerical results are presented through the graph of the A-weighted sound pressure level of the bearing for various rotational speeds of the rotor. The results show that the A-weighted sound pressure level of the bearing is markedly influenced by the mass eccentricity of the rotor and the radial clearance and the width of the bearing. High viscosity of the lubricant slightly decreases the noise of the bearing, but its effect is relatively low at high speed. The results of the paper could aid in the design of low-noise rotor-bearing systems supported by oil lubricated journal bearings. (C) 2004 Published by Elsevier Ltd.The Ministry of Commerce, Industry and Energy(A03-A07-2207-01
A noise analysis of cylindrical roller bearings operating under zero external load
No full textThe 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 anti 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.The Brain Korea 21 project in 200
A study on the sound of roller bearings operating under radial load
No full textThe purpose of the paper is to numerically investigate the sound characteristics of roller bearings operating under radial load. For the sake of simplifying the analysis, it was assumed that the roller bearings are infinitely long, a noise source due to pressure fluctuation of oil film is taken as a line noise source, and acoustic energy losses in the bearing are neglected. To obtain sound characteristics of the bearing, the rolling contact load and the sound pressure level distributions were calculated for various operating conditions, and the results were compared with each other. How much the bearing noise can be affected by the design parameters, such as radial clearance of the bearing, viscosity of lubricant, and the number of rollers was also investigated. The results and discussions of the present paper could aid in the design of low-noise roller bearings and to solve the noise problems related to such bearings. (c) 2006 Elsevier Ltd. All rights reserved
Noise analysis of oil-lubricated journal bearings
No full textThe 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.Ministry of Commerce, Industry and Energy (A03-A07-2207-01
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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