• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1992년도 제15회 학술강연회초록집
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• pp.66-70
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• 1992

고전적 동수압유체윤활이론은 유막 내의 점성을 일정하다고 가정한다. 유막의 전개방향이나 유막두께방향으로의 온도변화를 결정하는 데 이론적으로나 실험적으로 어려움이 있으므로 이 간소화는 베어링설계에 널리 사용되었다. 그러나 많은 실험적 관찰은 등점성 동수압유체윤활이론은 유막내의 온도상승이나 하중지지용량의 감소를 설명하지 못함을 입증하였다. Fogg는 평행한 추력베어링이 하중을 지지할 수 있음을 발견하였으며 이 fogg의 효과는 동수압 유체윤활이론의 예측과 반대되는 것이고 Thermal wedge라는 개념으로 설명되었다. Hunter와 Zienkiewicz는 유막내에서의 에너지 균형에 관한 이론적 연구를 소개하였고, 온도효과와 이로 인한 유막두께 방향의 점도 변화는 무시될 수 없다는 결론을 내렸다. 본 해석에서는 압력분포를 근사해법으로 구하여, 선지지되는 2차원 틸팅패드 트러스트베어링에서 패드의 탄성 변형을 고려한 열유체윤활해석과 고려하지 않은 얼유체윤활 해석의 결과를 서로 비교함으로서 패드의 변형이 유막의 압력장과 온도장에 미치는 영향과 패드두께의 변화가 유막의 온도장과 압력장에 미치는 영향을 고찰하고자 한다.

• 한국자동차공학회논문집
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• 제20권1호
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• pp.131-140
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• 2012

In this study, using the governing equation for thermohydrodyamic lubrication involving the homogeneous mixture of incompressible fluid derived by based on the principle of continuum mechanics, it is discussed the effects of water within engine oil on the performance of high speed journal bearing of a turbocharger. The governing equations are the general equations being able to be applied on the mixture of Newtonian fluid and non- Newtonian fluid. Here, the fluid viscosity index, n of power-law non-Newtonian fluid is supposed to be 1 for the application of the journal bearing in a turbocharger lubricated with the mixture of two Newtonian fluid, for example, water within engine oil. The results related with the bearing performance are shown that the bearing friction is to decrease and the side leakage and bearing load increase as increasing the water content in an engine oil.

• Tribology and Lubricants
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• 제27권2호
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• pp.77-87
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• 2011

In this study, using the governing equation for thermohydrodyamic lubrication involving the homogeneous mixture of incompressible fluid derived by based on the principle of continuum mechanics, it is discussed the effects of water within turbine oil on the performance of high speed journal bearing of a steam turbine shipping engine. The governing equation is the general equation being able to be applied on the mixture of Newtonian fluid and non-Newtonian fluid. Here, the fluid viscosity index, n of power-law non-Newtonian fluid is supposed to be 1 for the application of the journal bearing in a steam turbine shipping engine lubricated with the mixture of two Newtonian fluid, for example, water within turbine oil. The results related with the bearing performance are showed.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1987년도 제5회 학술강연회초록집
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• pp.57-60
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• 1987

근래에 들어 축의 고속회전이 요구되고 윤활제로 물이나 액체금속과 같은 동점성계수가 낮은 윤활제가 사용됨에 따라 베어링내의 유동은 층류상태를 벗어난 난류상태에 이르고 있다. 이와같이 고속에서 사용되는 저어널베어링에서의 윤활제의 유동은 더욱 복잡하게 되어 이들에 대한 정확한 특성을 예측하기 위한 연구가 필요하게 되었다. 최근에는 열유체윤활에 대한 연구가 행하여지고 있으나 저어널베어링의 온도특성에 대한 실험적 연구는 부족한 상태이다. 그리고 저어널의 하중을 지지하는 유막내의 압력에 대한 실험을 보면 거의 베어링면에서 국부적으로 측정하므로 유막에서 발생하는 압력의 분포를 정확히 알기는 어렵다. 본 연구에서는 저어널의 중앙단면에 압력계를 부착하여 연속적인 압력분포를 측정하고 베어링내면의 온도분포를 측정하며 편심율과 위상각, 배유량을 측정하여 저어널베어링의 성능특성을 예측하기 위한 실험자료를 제공하는 것을 목적으로 한다.

• Tribology and Lubricants
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• 제27권4호
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• pp.183-192
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• 2011

In this study, using the governing equations for thermohydrodyamic lubrication involving the homogeneous mixture of incompressible fluid derived by based on the principle of continuum mechanics, it is discussed the effects of water dispersed within engine oil on the performance of high speed journal bearing of a turbocharger. The governing equations are the general equations being able to be applied on the mixture of Newtonian fluid and non-Newtonian fluid. Here, the fluid viscosity index, n of power-law non-Newtonian fluid is supposed to be 1 for the application of the journal bearing on a turbocharger lubricated with the mixture of two Newtonian fluids, water dispersed within engine oil. The results related with the bearing performance are showed that the friction force and bearing load capacity decrease as increasing the volume percent of water.

• Tribology and Lubricants
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• 제30권5호
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• pp.303-310
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• 2014

In order to reduce friction and improve reliability, researchers have applied various surface texturing methods to highly sliding machine elements such as mechanical seals and piston rings. Despite extensive theoretical research on surface texturing, previous numerical results are only applicable to isothermal and iso-viscous conditions. Because the lubricant flow pattern of textured bearing surfaces is much more complicated than that for non-textured bearings, the Navier?Stokes equation is more suitable than the Reynolds equation for the former. This study carries out a thermohydrodynamic (THD) lubrication analysis to investigate the lubrication characteristics of a single micro-dimpled parallel thrust bearing cell. The analysis involves using the continuity, Navier?Stokes, energy, temperature?viscosity relation, and heat conduction equations with the commercial computational fluid dynamics (CFD) code FLUENT. This study discretizes these equations using the finite volume method and solves them using the SIMPLE algorithm. The results include finding the streamlines, pressure and temperature distributions, and variations in the friction force and leakage for various dimple radii and depths. Increasing the dimple radius and decreasing the depth causes a recirculation flow to form because of a strong vortex, and the oil temperature greatly increases compared with the non-textured case. The present numerical scheme and results are applicable to THD analysis of various surface-textured sliding bearings and can lead to further study.

• Tribology and Lubricants
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• 제33권6호
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• pp.288-295
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• 2017

In order to improve the efficiency and reliability of the machine, the friction should be minimized. The most widely used method to minimize friction is to maintain the fluid lubrication state. However, we can reduce friction only up to a certain limit because of viscosity. As a result of several recent studies, surface texturing has significantly reduced the friction in highly sliding machine elements, such as mechanical seals and thrust bearings. Thus far, theoretical studies have mainly focused on isothermal/iso-viscous conditions and have not taken into account the heat generation, caused by high viscous shear, and the temperature conditions on the bearing surface. In this study, we investigate the effect of dimple depth and film-temperature boundary conditions on the thermohydrodynamic (THD) lubrication of textured parallel slider bearings. We analyzed the continuity equation, the Navier-Stokes equation, the energy equation, and the temperature-viscosity and temperature-density relations using a computational fluid dynamics (CFD) code, FLUENT. We compare the temperature and pressure distributions at various dimple depths. The increase in oil temperature caused by viscous shear was higher in the dimple than in the bearing outlet because of the action of the strong vortex generated in the dimple. The lubrication characteristics significantly change with variations in the dimple depths and film-temperature boundary conditions. We can use the current results as basic data for optimum surface texturing; however, further studies are required for various temperature boundary conditions.

• Tribology and Lubricants
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• 제39권1호
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• pp.21-27
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• 2023

Surface texturing is widely applied to friction surfaces of various machine elements. Most of the theoretical studies have focused on isothermal (ISO) analyses which consider constant lubricant viscosity. However, there have been limited studies on the effect of oil temperature increase owing to viscous shear. Following the first part of the present study that investigated the effects of film-temperature boundary condition (FTBC) and groove number on the thermohydrodynamic (THD) lubrication characteristics of a surface-textured parallel thrust bearing with multiple rectangular grooves, this study focuses on the effect of groove depths. Current study numerically analyzes the continuity, Navier-Stokes, and energy equations with temperature-viscosity-density relations using a commercial computational fluid dynamics (CFD) software, FLUENT. The results of variation in temperature, velocity, and pressure distributions as well as load-carrying capacity (LCC) and friction force indicate that groove depth and FTBC significantly influence the temperature distribution and pressure generation. The LCC is maximum near the groove depth at which the vortex starts, smaller than the ISO result. For intense grooves, the LCC of THD may be larger than that from ISO. The frictional force decreases as the groove becomes deeper, and decreases more significantly in the case of THD. The study shows that groove depth significantly influences the THD lubrication characteristics of surface-textured parallel thrust bearings.

• 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.

• Tribology and Lubricants
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• 제28권2호
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• pp.81-92
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• 2012

To product multi-grade oil like engine oil, a sort of mineral base oil is mixed with a fundamental additive liquid package and a polymer liquid as viscosity index improver in order to improve the lubricating property of oil. That is, engine oil is the mixture of more than two fluids. In this paper, it will be systematically organized the governing equation describing non-Newtonian thermo-hydrodynamic lubrication related with the mixture of incompressible fluids based on the principle of continuum mechanics. Then, in order to find how the thermal analysis effect on the bearing performance lubricated with the mixture of multi-fluids, it will be compared to the performances between the mixture of each liquid to be blended and multi-grade engine oil as a single fluid in a high speed journal bearing. It is found that, in the case of lower viscosity oil, the difference of pressure distribution between the above two cases turns out to be existed, even if the load capacity is same level.