• Tribology and Lubricants
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• v.37 no.4
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• pp.117-124
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• 2021

In this study, we perform a 3D CFD conjugate analysis according to the shape of the foil ramp of the air foil thrust bearing, analyze the flow characteristics inside the bearing, and compare the results corresponding to the two shapes. Air has a lower viscosity than lubricating oil. Therefore, the thrust runner of the bearing must rotate at high speed to support the load. The gap between thrust runner and foil is significantly smaller than that of the oil bearing. Hence, it is crucial to analyze the complex flow characteristics inside the bearing to predict the complex flow inside the bearing and performance of the bearing. In addition, flow characteristics may appear differently depending on the ramp shape of the bearing foil, which may affect bearing performance. In this study, we numerically analyze the main flow path of air flowing into the bearing and the secondary flow path used for cooling the bearing using the commercial CFD software ANSYS CFX and compare the flow characteristics for straight and curved foil ramp shapes. Notably, there is a difference in the speed of the flowing air according to the shape of the ramp, which affects the bearing performance.

• Tribology and Lubricants
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• v.40 no.1
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• pp.17-23
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• 2024

This study analyzes the thermal effects on the performance of an air foil thrust bearing (AFTB) using COMSOL Multiphysics to approximate actual bearing behavior under real conditions. An AFTB is a sliding-thrust bearing that uses air as a lubricant to support the axial load. The AFTB consists of top and bump foils and supports the rotating disk through the hydrodynamic pressure generated by the wedge effect from the inclined surface of the top foil and the elastic deformation of the bump foils, similar to a spring. The use of air as a lubricant has some advantages such as low friction loss and less heat generation, enabling air bearings to be widely used in high-speed rotating systems. However, even in AFTB, the effects of energy loss due to viscosity at high speeds, interface frictional heat, and thermal deformation of the foil caused by temperature increase cannot be ignored. Foil deformation derived from the thermal effect influences the minimum decay in film thickness and enhances the film pressure. For these reasons, performance analyses of isothermal AFTBs have shown few discrepancies with real bearing behavior. To account for this phenomenon, a thermal-fluid-structure analysis is conducted to describe the combined mechanics. Results show that the load capacity under the thermal effect is slightly higher than that obtained from isothermal analysis. In addition, the push and pull effects on the top foil and bump foil-free edges can be simulated. The differences between the isothermal and thermal behaviors are discussed.

• Tribology and Lubricants
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• v.19 no.3
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• pp.123-132
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• 2003

The effect of surface texture on elastohydrodynamic lubrication (EHL) point contact of a ball Joint mechanism in small reciprocating compressors is studied numerically by using multigrid method. Pressure and film thickness profiles have been calculated for surface roughness with waviness of different orientations and transverse ridge and dent at minimum and maximum Hoes M parameter conditions. The influence of the amplitude and the wavelength of the surface roughness was also studied. Results show that the oblique waviness with orientation angle of 30$^{\circ}$generates the smallest minimum film thickness as compared with those of longitudinal, transverse, and other oblique roughness. The influence of transverse waviness on the minimum film thickness is smaller than for the longitudinal waviness case.

• Tribology and Lubricants
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• v.20 no.5
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• pp.225-230
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• 2004

Most studies of elsatohydrodynamic lubrication are oriented only to the measurement of film thickness itself with optical interferometer. In order to exactly investigate the tribological characteristics of a certain lubricant, it is also important to get the information of traction behaviors as well. In this work, we developed a device for measuring the friction force of ehl contact condition as well as the film thickness. To verify the validity of the measuring system, the friction forces and film thicknesses under ehl condition are simultaneously measured with the variations of additive ratios of viscosity index improvers which cause non-linear tendencies of film thickness to contact velocity.

• Tribology and Lubricants
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• v.25 no.5
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• pp.342-347
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• 2009

This paper presents EHL analysis for rough surfaces with directional roughness. Three different types of surfaces with pure longitudinal roughness, pure transversal roughness and isotropic roughness are generated. For the surfaces with longitudinal and transversal roughness, two cases are analyzed; one is a case of asperity peak on a spherical contact center, the other one is of valley on a spherical contact center. As a results, the surface with pure transversal roughness gives higher pressure and smaller minimum film thickness than the surface with pure longitudinal roughness, and the surface with isotropic roughness has similar EHL behavior with the surface with pure transversal roughness.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.305-310
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• 2001

Within some degree of journal misalignment, maximum pressure, maximum temperature, bearing load, friction and side leakage in high-speed journal bearing operation are examined under the condition of variable density and specific heat. The results are compared with the calculation results under the conditions of constant density and specific heat, and variable density and constant specific heat. It is found that the effects of variable density and specific heat on shaft misalignment are significant in determining the load capacity of a journal bearing operating at high speed.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.287-292
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• 2001

Under the condition of variable density and specific heat, maximum pressure, maximum temperature, bearing load, friction and side leakage in high-speed journal bearing operation are examined. The results are compared with the calculation results under the conditions of constant density and specific heat, and variable density and constant specific heat. It is found that the condition of variable density and specific heat play important roles in determining friction and load of journal bearing at high speed operation.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.5
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• pp.66-74
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• 1998

The operating torque and tribological characteristics of a cam/tappet system of an I.C. engine have an important effect on the engine efficiency. More power is lost for higher operation torque which is affected by the friction of a cam/tappet system. In this work experimental investigation of the torque behavior of a cam/tappet system was conducted to get tribological characteristics. Specifically, the torque was measured with respect to oil temperature and camshaft speed. The torque decreased with increasing camshaft speed because of decreasing friction coefficient but was hardly affected by the oil temperature. Also, the torque was the largest near the cam nose region.

• Tribology and Lubricants
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• v.26 no.1
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• pp.1-6
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• 2010

In the last decade, laser surface texturing (LST) has emerged as a viable option of surface engineering. Many problems related with mechanical components such as thrust bearings, mechanical face seals and piston rings, etc, LST result in significant improvement in load capacity, wear resistance and reduction in friction force. It is mainly experimentally reported the micro-dimpled bearing surfaces can reduce friction force, however, precise theoretical results are not presented until now. In this paper, a commercial computational fluid dynamics(CFD) code, FLUENT is used to investigate the lubrication characteristics of a parallel thrust bearing having 3-dimensional micro-dimple. The results show that the pressure, velocity and density distributions are highly affected by the location and number of dimple. The numerical method and results can be use in design of optimum dimple characteristics, and further researches are required.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1996.10a
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• pp.168-175
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• 1996

This paper reports on theoretical study of the pressure overshoot in the delivery ports and pressure rising within balanced type vane pump. Pressure overshoot occur due to the accelerated fluid through the notch, so, result in pressure ripple, flow ripple, and noise. For calculating the pressure rising and fluctuations of pressure, we have modeled mathematically used continuity equation based on compressibility and momentum equation considered fluid inertia in the notch, and analyzed simultaneously. As a results of analysis, we have found oscillation of pressure and compression chamber pressure depend on the rotational speeds, bulk modulus of working fluid, notches, number of vane and camring. Using the model, notches have been shown to be important design factor in relaxing the rapid pressure rising and reducing the amplitudes of pressure overshoot.