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Laser Texturing한 평행 스러스트 베어링의 윤활특성 : 제1보 - 딤플깊이의 영향
박태조(Tae-Jo Park),황윤건(Yun-Geon Hwang) 한국트라이볼로지학회 2009 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.25 No.5
Laser surface texturing (LST) methods are applied recently to generate micro-dimples in machine components having parallel sliding surfaces such as thrust bearings, mechanical face seals and piston rings, etc. And it is experimentally reported by several researchers that the micro-dimpled bearing surfaces can reduce friction force. Until now, however, theoretical results for various dimple parameters are not fully presented. In this paper, a commercial computational fluid dynamics (CFD) code, FLUENT is used to investigate the effect of dimple depth on the lubrication characteristics of parallel thrust bearing. The results show that the pressure, velocity and density distributions within dimples are highly affected by dimple depths and cavitation conditions. Adoption of micro-dimple on the bearing surface can reduce the friction force highly and its levels are affected by dimple depth. The numerical methods and results can be use in design of optimum dimple characteristics to improve thrust bearing performance.
Groove 단면형상에 따른 유압 Spool Valve의 윤활해석
박태조(Tae-Jo Park),황윤건(Yun-Geon Hwang) 한국트라이볼로지학회 2009 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.25 No.1
The spools in most hydraulic spool type control valve have several circumferential grooves to prevent well known hydraulic locking problems which result in high friction force and excessive wear. In this paper, a commercial computational fluid dynamics (CFD) code, FLUENT is used to investigate the flow and lubrication characteristics of grooved hydraulic spool valve. The stream lines and pressure distributions are obtained for various groove cross sectional shapes and film thicknesses. The stream lines are highly affected by groove cross sectional shape but pressure distributions mainly depend on the film shape and its magnitude. Therefore the numerical method adopted in this paper and results can be use in designing of various grooved spool valve.
구름/스핀 운동을 하는 경우의 타원접촉 EHL 유막두께
박태조(Tae-Jo Park) 한국트라이볼로지학회 2008 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.24 No.6
In highly stressed machine elements such as angular contact ball bearings and toroidal type traction drives, the elastohydrodynamic lubrication of elliptical contacts with both rolling and spinning motion are occur. In this paper, a finite difference method with non-uniform grid systems and the Newton-Raphson method are applied to solve the problems. Pressure distributions, film contours and variations of the minimum and central film thicknesses are compared with various ellipticity parameter, dimensionless speed and load parameter. The results showed that the spinning motion has significant influence especially on the film shapes. Reduction of the minimum film thickness under spinning is remarkable whereas the central film thickness is relatively less. Especially variations of the minimum film thicknesses with rolling velocity, load and ellipticity ratio are a great different from those of pure rolling. Therefore present numerical scheme can be used in the analysis of general elliptical contact EHL problems and further studies are required.
Lundberg형 프로파일의 원통형 로울러의 탄성유체윤활 해석
박태조(Tae-Jo Park) 한국트라이볼로지학회 2013 한국윤활학회지(윤활학회지) Vol.29 No.6
The rollers and/or races in cylindrical and tapered roller bearings should be profiled to relieve high edge stress concentrations caused by their finite lengths and misalignment. In this study, a numerical analysis was performed to investigate the elastohydrodynamic lubrication (EHL) of a Lundberg profile-type cylindrical roller. A finite difference method with fully nonuniform grids and the Newton-Raphson method were used to present detailed EHL pressure distributions and film shapes, as well as the variations in the minimum and central film thicknesses with the profile modification coefficient. In the Lundberg profile, the maximum pressure and minimum film thickness always occurred near the edges. Proper modification of the Lundberg profile considerably increased the minimum film thickness.
시일과 코팅된 스틸면 사이의 구형 마멸입자에 의한 접촉응력 해석
박태조(Tae-Jo Park),유재찬(Jae-Chan Yoo),정현기(Hyun-Gi Jung),조현동(Hyun-Dong Cho) 한국트라이볼로지학회 2007 한국트라이볼로지학회 학술대회 Vol.2007 No.11
Seal is very useful mechanical component in protection of leakage of lubricant or working fluid and incoming of debris from outside. Elastomer are widely used as sealing materials and shaft surfaces are generally coated with high hardness material after heat treatment. When debris or wear particle get stuck into sealing surface, shaft surface is damaged and worn by mainly abrasive wear. In this paper, using MARC, contact analysis are conducted to show the coated shaft surface can be fatigue failed by spherical fine elastic wear particle exists between seal and coated steel shaft surface. Variations of normal contact and von-Mises stresses distributions and contact half-widths etc. with interference and coating thickness are presented. The results can be used in design of coating and choice of seal and further studies are required.
박태조,Park, Tae-Jo 한국트라이볼로지학회 2007 한국윤활학회지(윤활학회지) Vol.23 No.2
A numerical analysis of elastohydrodynamic lubrication of elliptical contacts with both rolling and spinning has been carried out. A finite difference method with non-uniform grid systems and the Newton-Raphson method are applied to solve the problems. The velocity vectors resulting from combined spinning and rolling/sliding motion lead to asymmetric pressure distributions and film shapes. Pressure distributions, film contours and variations of the minimum and central film thicknesses are compared with various spin-roll ratios. Reduction of the minimum film thickness under spinning is remarkable whereas the central film thickness is relatively less. The spin motion have large effect on variations of the minimum film thickness with load parameter which are small in pure rolling/sliding cases. Therefore present numerical scheme can be used in the analysis of general elliptical contact EHL problems and further studies are required.
Laser Texturing한 평행 스러스트 베어링의 운활특성
박태조(Tae-Jo Park) 한국트라이볼로지학회 2011 한국윤활학회지(윤활학회지) Vol.27 No.6
Laser surface texturing (LST) methods are widely applied recently to reduce friction and improve reliability of machine components such as thrust bearings, mechanical face seals and piston rings, etc. In this paper, numerical analysis is carried out to investigate the effect of number of dimples on the lubrication characteristics of parallel thrust bearing using a commercial computational fluid dynamics (CFD) code, FLUENT. Pressure distributions of present analysis are physically consistent than those obtained from numerical analysis of Reynolds equation. The overall lubrication characteristics are highly affected by number of dimples and their locations. The results can be use in design of optimum dimple characteristics to improve thrust bearing performance and further researches are required.
Laser Texturing한 평행 스러스트 베어링의 윤활특성
박태조(Tae-Jo Park) 한국트라이볼로지학회 2011 한국윤활학회지(윤활학회지) Vol.27 No.6
Laser surface texturing(LST) methods are widely applied now to reduce friction and improve reliability of machine components such as thrust bearings, mechanical face seals and piston rings, etc. In this paper, the etfect of dimple shapes on the lubrication characteristics of parallel thrust bearing are studied using a commercial computational fluid dynamics (CFD) code, FLUENT. Pressure and streamline distributions, variations of supporting load, leakage flow rate and friction torce, are compared for three different dimple sectional shapes such as circle, pyramid and rectangle type. The lubrication characteristics are highly affected by dimple shapes and number of dimples. The pyramid type dimple shape can support the highest load while the rectangle type is the best in friction reduction.
그루브가 있는 사판식 유압피스톤 펌프용 Slipper Bearing의 윤활특성
박태조(Tae-Jo Park),황윤건(Yun-Geon Hwang),김관준(Kwan-Joon Kim),손자덕(Ja-Deok Sohn) 한국트라이볼로지학회 2009 한국트라이볼로지학회 학술대회 Vol.2009 No.6
In this thesis, FLUENT is adopted to investigate accurate flow characteristics for a tilted and grooved rotating slipper bearing which is used swash plate type hydraulic axial piston pump. Static pressure and velocity distributions, and velocity vectors are plotted for different radial groove position. In case that slipper bearing is rotating, the flow fields of tilted and grooved slipper bearing are highly asymmetrical. Static pressure, bearing load, tilting moment acting on bearing and leakage flow rate are highly affected by radial groove position, rotation of slipper bearing and film thickness. Therefore the numerical method and results adopted in this paper can be use in design of swash plate type hydraulic piston pump and further studies are required.