• 대한기계학회논문집A
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• 제25권4호
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• pp.748-755
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• 2001

This paper concerns rotor vibration reduction using magnetic damper system. The fuzzy control logic is utilized to fulfill desired motion. The fuzzy system structure and membership function were first determined by simulation results. The researched control logic contains two fuzzy controller : reference position variation according to the rotor whirling status and error compensation algorithm to minimize the rotor vibration due to unbalance and unstable fluid film force. The Sugeno type output membership function was utilized by several trials and optimized membership function constants were selected from experiments. The experimental results show that the proposed method effectively control and reduce the rotor vibration with fluid film bearings.

• Tribology and Lubricants
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• 제16권2호
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• pp.106-113
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• 2000

Effects of surface roughness on bearing performances are investigated numerically in this study, especially for the parallel thrust bearing. Although mating surfaces are parallel and separated by thin fluid film, the pressure distribution is formed due to asperities. Model surface is generated numerically with given autocorrelation function and some surface profile parameters. Then the average Reynolds equation is applied to predict the effects of surface roughness between hydrodynamic and mixed lubrication regimes. In this equation, flow factors are defined as correction terms to smooth out high frequency surface roughness. The correlation length is proposed to get the minimum load for the parallel thrust bearing for various sliding conditions.

• Tribology and Lubricants
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• 제24권6호
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• pp.343-348
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• 2008

In this paper, a CFD (Computational fluid dynamics) code, FLUENT is adopted to investigate accurate flow characteristics for a slipper bearing which is used swash plate type hydraulic axial piston pump. Static pressure and velocity distributions, and velocity vectors are plotted for different film thickness and slipper rotational velocity. In recess region, there exists a doughnut shaped vortex ring. The static pressure distributions are non-uniform and the flow fields are highly asymmetrical under bearing rotation. Therefore the numerical method adopted in this paper can be use in design of hydrostatic components and further studies are required.

• 한국생산제조학회지
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• 제20권1호
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• pp.96-100
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• 2011

The hydrostatic bearings have a relatively small run-out comparing to its shape error by fluid film effect in hydrostatic state as like pneumatic bearing and have a high stiffness, load capacity and damping characteristics. As there is no maintenance and semipermanent in these bearing type, it has been usually adopted as main spindle bearing for grinding machine. In this thesis, to develop hydrostatic bearing for high speed spindle, the cooler setting temperature, bearing clearance and nozzle pressure of belt-driven hydrostatic bearing are investigated. The bearing temperature is decreased, as the cooler setting temperature is lower, nozzle pressure is higher and bearing clearance is wider. The front temperature of bearing is nearly $8^{\circ}C$ higher than the rear one up to 13,000 rpm of spindle revolution. The thermal deflection of X-axis is ${\pm}16\;{\mu}m$ in range of 12,000 rpm-13,000 rpm. Therefore, it is conformed that the built-in motor hydrostatic bearing can be used to high speed spindle.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제33회 춘계학술대회 개최
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• pp.201-211
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• 2001

The influence of aerated oil on high-speed journal bearing is examined by classical thermohydrodynamic lubrication theory coupled with analytical models for viscosity and density of aerated oil in fluid-film bearing. Convection to the walls, mixing with supply oil and re-circulating oil, and some degree of journal misalignment are considered. The considered Parameters for the study of bubbly lubrication are oil aeration level, air bubble size, shaft misalignment and shaft speed. The results show that deliberate oil aeration can more clearly bring on the increasing load capacity under high-speed operation of plain journal hearing than previous normal speed operation. And the load capacity may be increased more by oil aeration under the conditions of shaft misalignment and the increasing speed.

• Tribology and Lubricants
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• 제36권4호
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• pp.193-198
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• 2020

Fluid film bearings are among the best devices used for overcoming friction and reducing wear. Surface texturing is a new surface treatment technique used for processing grooves and dimples on the lubricated surface, and it helps to minimize friction further and improve the wear resistance. In several studies, parallel surfaces, such as thrust bearings and mechanical face seals, have been investigated, but most sliding bearings have a convergent film shape. This paper presents the third part of a recent study and focuses on the effect of the groove shape on the lubrication performance of inclined slider bearings, following the two previous papers on the effects of the groove position and depth. We adopted the continuity and Navier - Stokes equations to conduct numerical analyses using FLUENT, which is a commercial computational fluid dynamics code. The groove shape adopted in the numerical analysis is rectangular and triangular, and its depth is varied. The results show that the streamlines, pressure distributions, and groove shape significantly influence the lubrication performance of the inclined slider bearing. For both shapes, the load-carrying capacity (LCC) is maximum near the groove depth, where vortices occur. In the shallow grooves, the LCC of the rectangular shape is higher, but in deeper grooves, that of the triangular shape is higher. The deeper the rectangular groove, the higher the decrease in the frictional force. The results of this study can be used as design data for various sliding bearings.

• 유공압시스템학회논문집
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• 제4권3호
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• pp.1-6
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• 2007

The leakage generated from the clearance between the cylinder bore and the piston is one of the most serious problems in the hydraulic piston pump, and it even results in terrible decrease of the volume efficiency at a great velocity and high pressure. In this paper, the lubrication characteristic of the hydrostatic slipper bearing equipped in the hydraulic piston pump has been worked out by experimentation with three model bearings of different shape. Preparatory to this, not only the three models of piston-slipper were designed, but the corresponding experimental apparatus were also manufactured. As a result, it was verified that, according to the supply pressure, the hydrostatic bearing part of the slipper is severely affected by the pocket pressure, land pressure, oil film thickness, and leakage flow.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.141-146
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• 2013

This research investigates the stability analysis for the rotating and the stationary grooved journal bearing. The dynamic coefficients of the journal bearing are calculated by using FEM and the perturbation method. When journal bearing is in whirling motion, the dynamic coefficients have time-varying components as a sine wave due to the reaction force of oil film toward the center of journal even in the steady state. The solutions for the equations of motion can be assumed as the Fourier series expansion. The equations of motion can be rewritten as the linear algebraic equations with respect to the Fourier coefficients. Then, stability of the grooved journal bearing can be calculated by Hill's infinite determinant. The periodic function of dynamic coefficients is derived using Fourier Fast Transform(FFT).The stability of journal bearing is determined as rotating speed increases and the stability of rotating grooved journal bearing is compared and discussed with the stability of stationary grooved journal bearing.

• Tribology and Lubricants
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• 제38권6호
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• pp.267-273
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• 2022

Surface texturing is the latest technology for processing grooves or dimples on the friction surface of a machine. When appropriately applied, it can reduce friction and significantly increase durability. Despite many studies over the past 20 years, most are isothermal (ISO) analyses in which the viscosity of the lubricant is constant. In practice, the viscosity changes significantly owing to the heat generated by the viscous shear of the lubricant and film-temperature boundary condition (FTBC). Although many thermohydrodynamic (THD) analyses have been performed on various sliding bearings, only few results for surface-textured bearings have been reported. This study investigates the effects of the FTBC and groove number on the THD lubrication characteristics of a surface-textured parallel thrust bearing with multiple rectangular grooves. The continuity, Navier-Stokes, and energy equations with temperature-viscosity-density relations are numerically analyzed using a commercial computational fluid dynamics code, FLUENT. The results show the pressure and temperature distributions, variations of load-carrying capacity (LCC), and friction force with four FTBCs. The FTBCs greatly influence the lubrication characteristics of surface-textured parallel thrust bearings. A groove number that maximizes the LCC exists, which depends on the FTBC. ISO analysis overestimates the LCC but underestimates friction reduction. Additional analysis of various temperature boundary conditions is required for practical applications.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1996년도 제23회 학술대회
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• pp.41-46
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• 1996

For a vertical type crankshaft-journal bearing system used in scroll compressor, nonlinear transient response analysis is applied includung nonlinear fluid film reaction forces of journal beatings. By a connected behavior analysis of crankshaft and orbiting scroll, the radial clearance of scroll wraps is calculated. Considering tangential leakage for this clearance, a coupled analysis model for leakage and dynamic behavior of the orbiting scroll is made, and analyzed by iterative calculation. By regarding clearances of main, sub bearing of crankshaft and orbiting scroll shaft bearing clearance as design parameters, the radial clearance of scroll wraps is analyzed.