• Tribology and Lubricants
• /
• 제19권2호
• /
• pp.85-93
• /
• 2003

In this study, a multigrid multi-integration method has been used to solve the steady-state, elastohydrodynamic lubrication (EHL) point contact problem of a ball joint mechanism used in small reciprocating compressors. Pressure and film thickness profiles have been calculated at minimum and maximum Moes M parameter conditions during one revolution of crankshaft. The effects of various lubricant viscosities, loads, ball velocities, elastic modulli, and radii of curvature on the calculated pressure distribution and film thicknesses have been investigated. The results indicate that the viscosity of lubricant, the sliding velocity of ball, and the reduced radius of curvature have considerable effects on the minimum and central film thicknesses. Solutions obtained with the multigrid analysis are compared with results calculated according to the Hamrock ＆ Dowson relations for the minimum and central film thicknesses.

• 대한지리학회지
• /
• 제49권1호
• /
• pp.32-44
• /
• 2014

본 연구에서는 중부지방의 1월 최저기온 분포 특성을 파악하고 철원의 극한 최저기온의 원인을 규명하고자 하였다. 이를 위해 중부지방 25개 관측소의 1991~2010년 1월 기온 분포 특성과 철원 기온과 춘천, 홍천, 봉화, 대관령, 원주, 제천 등 중부내륙 지역의 기온 차이를 기압배치형에 따라 분석하였다. 일평균기온과 평균 일최저기온은 철원과 해발고도가 높은 지역에서 낮게 나타나지만, $-15^{\circ}C$ 이하 일수와 같은 극한기온의 출현빈도는 철원에서 두드러졌다. 시베리아 고기압이 확장하거나 우리나라 북쪽에 이동성 고기압이 위치할 때 철원 기온이 비교지점에 비해 상대적으로 더 낮다. 이동성 고기압의 영향을 받을 때는 철원과 비교지점 간 기온 차이가 적거나, 봉화, 제천과 같은 분지의 기온이 더 낮다.

• Tribology and Lubricants
• /
• 제23권2호
• /
• pp.49-55
• /
• 2007

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.

• 한국항해항만학회:학술대회논문집
• /
• 한국항해항만학회 2007년도 추계학술대회 및 제23회 정기총회
• /
• pp.198-199
• /
• 2007

이 연구에서는 36년간(1970-2005년)의 장기 데이터를 이용하여 우리나라에 영향을 미치는 태풍의 대부분이 통과하는 남해의 해수면온도 변화와 태풍의 세기 변화와의 관계가 분석 연구되었다. 우리나라 남해의 해수면온도는 연구 기간 동안 지속적으로 상승하는 추세를 보인다. 2000년 이래 6년간(2000-2005년)의 평균 해수면온도는 16.95$^{\circ}C$로 1970년대 10년간(1970-1979년)의 평균 해수면온도 15.74$^{\circ}C$보다 1.21$^{\circ}C$나 높다. 특히, 1994년 이후 그 상승폭은 크다. 태풍의 세기는 중심기압에 의하여 나타낼 수 있다. 남해를 통과하면서 우리 나라에 영향을 미친 태풍의 최저중심기압의 변화를 살펴보면 1970년 이후 지속적으로 하강하고 있음을 알 수 있다. 2000년 이래 6년간 (2000-2005년)의 평균 최저중심기압은 983hPa로, 1970년대 10년간(1970-1979년)의 평균 최저중심기압 992hPa보다 9hPa 이나 낮다. 상관 분석에 의하여, 1970년 이후의 태풍 세기 강화는 남해 해수면온도의 상승과 관련이 있다는 사실을 알 수 있었다.

• Tribology and Lubricants
• /
• 제24권6호
• /
• pp.355-361
• /
• 2008

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.

• Tribology and Lubricants
• /
• 제19권3호
• /
• pp.123-132
• /
• 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.

• 한국공간구조학회논문집
• /
• 제18권2호
• /
• pp.59-67
• /
• 2018

Various pilotis are installed in the lower part of high rise buildings. Strong winds can generate sudden airflow around the pilotis, which can cause unexpected internal airflow changes and may cause damage to the exterior of the piloti ceiling. The present study investigates the characteristics of peak wind pressure coefficient for the design of piloti ceiling exteriors by conducting wind pressure tests on high rise buildings equipped with penetration-type and end-type pilotis in urban and suburban areas. The minimum peak wind pressure coefficient for penetration-type piloti ceilings ranges from -2.0 to -3.3. Minimum peak wind pressure coefficient in urban areas was 30% larger than in suburban areas. In end-type piloti ceilings, maximum peak wind-pressure coefficient ranges from 0.5 to 1.9, and minimum peak wind-pressure coefficient ranges from -1.3 to -3.6. With changes in building height, peak wind pressure coefficient decreases as the aspect ratio increases. Peak wind-pressure coefficient increases with taller pilotis. On the other hand, when piloti height decreases, the absolute value of the minimum peak wind pressure coefficient increases.

• Tribology and Lubricants
• /
• 제29권6호
• /
• pp.353-359
• /
• 2013

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.

• 한국연초학회지
• /
• 제27권2호
• /
• pp.163-170
• /
• 2005

A theoretical model for predicting the capability curve of cellulose acetate filter is derived. The pressure drop is expressed as a function of the filter dimensions, the tow fiber characteristics, the filter weight, the fluid flow rate, and a filter fiber factor. Where, the filter fiber factor is affected by the distribution of the tow fibers within the filter, the relative orientations of the tow fibers, and their cross-sectional shapes. The minimum and maximum fraction of solids in capability curves determined from experimental data. Also, the filter fiber factor is expressed as a function of the filter length, tow fiber length, and tow fiber diameter. Capability curves predicted by the suggested model in this work correspond well with capability curves by experimental data.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 1999년도 제29회 춘계학술대회
• /
• pp.182-188
• /
• 1999

A theoretical study of elastohydrodynamic lubrication of elliptical contacts with both rolling and spin has been carried out. A finite difference method and the Newton-Raphson method are applied to solve the problem. The velocity vectors resulting from combined spin and rolling/sliding motion lead to asymmetric pressure distributions and film shapes. Film contours and variations of the minimum and central film thicknesses are compared with various spin-roll ratios. At high spin-roll ratios the minimum film thickness is considerably reduced, whereas the central film thickness decreases less dramatically, The present numerical scheme can be used in the analysis of general elliptical contact problems.