• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.04a
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• pp.190-197
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• 1998

A new bearing concept, the wave journal bearing, has been developed to improve the steady and dynamic performance of a hydrodynamic journal bearing. This concept features a wave in inner bearing surface. Not only straight but also twisted wave journal bearing are investigated numerically. The performances of straight and twisted bearings are compared to a plain journal bearing over a relatively wide range of eccentricity. The bearing load and stability characteristics are dependent on the geometric parameters such as the number of waves, the amplitude and the starting point of the wave relative to the applied load. The wave journal bearing, especially for the twisted one, offers better stability than the plain journal bearing under all eccentricity and all wave to load orientation.

• Journal of Korean Society of Forest Science
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• v.107 no.3
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• pp.287-293
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• 2018

This study was carried out to provide surface bearing capacity reinforcement of forest road by sub-base facilities based on a soft ground use of geosynthetics to prevent the damage of the road surface passing heavy logging trucks and to pass smoothly heavy truck against growing timber harvesting. The analysis of the road surface bearing capacity as progressing time and the increase of the number of passage of heavy logging trucks were conducted experimental section of forest road on the soft ground in the Forest Technology and Management Research Center. As a result, it was found that the road surface bearing capacity were stabilized at CBR of 15% or more, the effect of reinforcement by type of geosynthetics showed no significant difference after the lapse of about 1 year. After reaching the passage of 300 times for the heavy logging trucks on the sub-base construction section, the settlements was stabilized below the allowable standard of 50 mm, road surface bearing capacity also improved to more than CBR 20% and there was no significant difference in the thickness of the sub-base. However, in the section where the sub-base is not constructed, it is found that the lack of surface bearing capacity with the settlements more than the allowable standard is not possible to pass the heavy logging trucks. Therefore, in order to reinforce the road surface bearing capacity of the soft ground for the passage of the heavy logging trucks, it is necessary to construct a sub-base of at least 0.2 m when using geosynthetics.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.8
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• pp.112-118
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• 2009

A pressure rise is generated while air bearing stages are moving in high vacuum environment. This study analyzed this pressure rise phenomenon theoretically and verified it experimentally using two different kinds of stages - linear and rotary air bearing stages. Results indicate that the pressure rise was caused by additional leakage resulting from stage velocity, along with adsorption and outgassing of gas molecules from the guide rail surface. Though tilting of the stage due to acceleration and deceleration reached several micrometers, it had a negligible effect on pressure rise because the tilting time was very short. Therefore, a rotary air bearing stage showed much less pressure rise than a linear stage because the rotary stage theoretically has nothing to do with the above causes. Additional leakage caused by stage velocity was inevitable if the stage had movements, but pressure rise caused by adsorption and outgassing could be suppressed by improving the surface quality to reduce real surface area, and by coating the guide rail surface with titanium nitride (TiN) which has less adhesion probability of gas molecules. The results also indicate that the pressure rise increased when the air bearing stage operated under high vacuum conditions.

• Tribology and Lubricants
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• v.32 no.5
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• pp.147-153
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• 2016

Friction reduction between machine components is important for improving their efficiency and lifespan. In recent years, surface texturing has received considerable attention as a viable means to enhance the efficiency and tribological performance of highly sliding mechanical components such as parallel thrust bearings, mechanical face seals, and piston rings. In this study, we perform lubrication analysis to investigate the effect of dimple shapes and orientations on the lubrication characteristics of a surface textured parallel thrust bearing. Numerical analysis involves solving the continuity and Navier-Stokes equations using a commercial computational fluid dynamics (CFD) code, FLUENT. We use dimples consisting of hemispherical and different semiellipsoidal orientations for simulation. We compare pressure and streamline distributions, load capacity, friction force, and leakage flowrate for different numbers of dimples and orientations. We find that the dimple shapes, orientations, and their numbers starting from an inlet influence the lubrication characteristics. The results show that partial texturing of the bearing inlet region, and the ellipsoidal dimples with the major axis aligned along the lubricant flow direction exhibit the best lubrication characteristics in terms of higher load capacity and lower friction. The results can be used in the design of optimum dimple characteristics for parallel thrust bearings, for which further research is required.

• Journal of the Korean GEO-environmental Society
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• v.13 no.6
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• pp.5-17
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• 2012

The study of surface ground reinforcing method is supposed to be considered preferentially is not satisfied and also doesn't contemplate plastic flow because of repetitive drive of construction equipment. Also, Terzaghi's bearing-capacity equation and Yamanouchi's suggestion have been used to design the surface reinforcement, but most engineers depend on their experience and cases constructed before because of dispersed variables and inappropriate bearing-capacity factors. Hence, plate load test and repetitive plate load test were performed in the field which is reinforced with geotextile, Geogrid whose tensile strength are 200kN/m, 100kN/m and bamboo($0.4m{\times}0.4m$). The object of this study is to evaluate bearing capacity and behaviour of surface ground and to compare each reinforcement form test results. From the results bearing capacity ratio increased by a maximum of 1.5 times with bamboo reinforcement method comparing to others.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.391-392
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• 2013

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2004.11a
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• pp.171-174
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• 2004

A method of lubrication analysis of thrust bearings in scroll compressors is proposed. A thrust bearing of typical scroll compressor is analyzed to investigate effects of bearing surface deformation.

• Tribology and Lubricants
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• v.39 no.2
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• pp.81-85
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• 2023

This study presents an experimental investigation of the effects of surface roughness on gas foil thrust bearing (GFTB) performance. A high-speed motor with the maximum speed of 80 krpm rotates a thrust runner and a pneumatic cylinder applies static loads to the test GFTB. When the motor speed increases and reaches a specific speed at which a hydrodynamic film pressure generated within the gap between the thrust runner and test GFTB is enough to support the applied static load, the thrust runner lifts off from the test GFTB and the friction mechanism changes from the boundary lubrication to the hydrodynamic lubrication. The experiment shows a series of lift-off test and load-carrying capacity test for two thrust runners with different surface roughnesses. For a constant static load of 15 N, thrust runner A with its lower surface roughness exhibits a higher start-up torque but lower lift-off torque than thrust runner B with a higher surface roughness. The load capacity test at a rotor speed of 60 krpm reveals that runner A results in a higher maximum load capacity than runner B. Runner A also shows a lower drag torque, friction coefficient, and bearing temperature than runner B at constant static loads. The results imply that maintaining a consistent surface roughness for a thrust runner may improve its static GFTB performance.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.8
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• pp.715-720
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• 2014

Recently, surface texturing technologies have been widely used in lots of industries to increase the machinery efficiency. In this research, the lubrication characteristics of a crank shaft pin turner bearing with dimples were studied. When increasing the dimples, the load carrying capacity due to the increased pressure was increased because those have sealing effects. Also, the run-out error of the bearing was decreased. Therefore, it is important to consider the depth, the number and the distribution of dimples when designing the hydrostatic journal bearing.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.6
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• pp.589-601
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• 2016

The hybrid grid was adopted and numerical prediction analysis of propeller unsteady bearing force considering free surface was performed for mode and full-scale KCS hull-propeller-rudder system by employing RANS method and VOF model. In order to obtain the propeller velocity under self-propulsion point, firstly, the numerical simulation for self-propulsion test of full-scale ship is carried out. The results show that the scale effect of velocity at self-propulsion point and wake fraction is obvious. Then, the transient two-phase flow calculations are performed for model and full-scale KCS hull-propeller-rudder systems. According to the monitoring data, it is found that the propeller unsteady bearing force is fluctuating periodically over time and full-scale propeller's time-average value is smaller than model-scale's. The frequency spectrum curves are also provided after fast Fourier transform. By analyzing the frequency spectrum data, it is easy to summarize that each component of the propeller bearing force have the same fluctuation frequency and the peak in BFP is maximum. What's more, each component of full-scale bearing force's fluctuation value is bigger than model-scale's except the bending moment coefficient about the Y-axis.