• Title/Summary/Keyword: Circumferential Groove

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Internal Flow Characteristics in the Draft Tube of a Francis Turbine

  • Wei, Qingsheng;Zhu, Baoshan;Choi, Young-Do
    • Journal of Advanced Marine Engineering and Technology
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    • v.36 no.5
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    • pp.618-626
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    • 2012
  • Suppression of abnormal flow phenomena in the Francis hydro turbine is very important to improve the turbine performance. Especially, as cavitation and cavitation surge makes serious problems when the turbine is operated in the range of partial flow rate, optimum method of suppressing the abnormal flow characteristics is required necessarily. Moreover, as swirl flow in the draft tube of the Francis turbine decreases pressure at the inlet of the draft tube, suppression of the swirl flow can be an useful method of suppressing the occurrence of cavitation. In order to clarifying the possibility of suppressing the swirl flow by J-Groove in the draft tube, a series of CFD analysis has been conducted in the range of partial load, designed condition and excessive flow rate of a Francis turbine. A kind of J-Groove is designed and applied to the draft tube of the Francis hydro turbine model. The pressure contours, circumferential velocity vectors and vortex core regions in the draft tube are compared by the conditions with or without J-Groove. In addition, a group of data about the velocity in the draft is presented to show the influence of J-Groove.

Estimations of Strain-Based J-integral and CTOD for Circumferential Outer Surface Crack in the Weld of Gas Pipeline Under Axial Displacement (축방향 변위가 작용하는 가스 파이프라인 용접부에 존재하는 원주방향 외부표면균열의 변형률 기반 J-적분 및 CTOD 계산)

  • Kim, Kyoung-Min;Park, Ji-Su;Moon, Ji-Hee;Jang, Youn-Young;Park, Seung-Hyun;Huh, Nam-Su
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.16 no.1
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    • pp.100-109
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    • 2020
  • Pipelines subjected to ground movement would be easily exposed to large-scale deformation. Since such deformations may cause the pipeline failure, it is important to ensure the safety of pipelines in various operation conditions. However, crack in weld metal have been considered as one of the main causes that can deteriorate the structural integrity of the pipeline. For this reason, the structural integrity of the pipe containing the crack in the weld should be obtained. In order to assess cracked pipe, J-integral and crack-tip opening displacement(CTOD) have been applied widely as the elastic-plastic fracture mechanics parameters representing crack driving force. In this study, engineering solutions to calculate the J-integral and CTOD of pipes with a circumferential outer surface crack in the weld are proposed. For this purpose, 3-dimensional elastic-plastic finite element(FE) analyses have been performed considering the effect of overmatch and width of weld. The shape of the weld was simplified to I-groove, and axial displacement was employed as for loading condition. Based on FE results, the effects of crack size, material properties and width of weldment on J-integral and CTOD were investigated. Additionally, the J-integral and CTOD for I-groove were compared with those for V-groove to examine the effects of the weld shape, and a proportionality coefficient of J-integral and CTOD was calculated from the results of this paper.

The Effect of Oil Pressure Fluctuation on the Engine Lubrication System (엔진 윤활 시스템에서 오일 압력 변동의 영향)

  • 윤정의;전문수
    • Transactions of the Korean Society of Automotive Engineers
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    • v.10 no.3
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    • pp.44-50
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    • 2002
  • The connecting rod big-end bearing is one of the most heavily loaded components of the lubrication system of high-speed combustion engines. The supply oil flow has to pass to the main bearing and the rotating crankshaft before entering the connecting rod bearing. It is common knowledge that the centrifugal forces due to the crankshaft rotation influence the oil flow to connecting rod bearing through the oil supply bore, especially, when the oil supply system to the connecting rod bearing has a 180$^{\circ}$circumferential groove via a single drilling in the crankshaft. In this case, it should be confirmed that the groove oil pressure in the main bearing is sufficient to overcome these centrifugal forces. For the purpose, the dynamic oil pressure before entering oil supply bore to the connecting rod bearing was measured instead of averaged oil pressure in main gallery. Experimental test results show that the dynamic oil pressure in the oil groove was more useful than that of main gallery. And it was also found that the oil pressure fluctuation in the groove was sensitively affected by the reduction of the main bearing clearance.

A Study of Thermal Effects for a Half-Circumferential Grooved Journal Bearing (半圓周形 윤활홈을 갖는 저어널 베어링의 熱效果에 관한 연구)

  • Chun, Sang-Myung;Lalas, Demetrius P.
    • Tribology and Lubricants
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    • v.6 no.1
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    • pp.36-51
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    • 1990
  • A parametric study of the thermal effects of a half-circumferential grooved journal bearings under aligned and misaligned conditions has been carried out by solving numerically the coupled Reynolds and energy equation system. Five different sets of boundary conditions for the energy equation have been used which include mixing between recirculating oil and inlet oil and a contraction ratio for the cavitation region. The effects of changes of the inlet oil temperature and pressure, the wall temperature and the L/D ratio have also been examined. For the range of parameters found in internal combustion engines, the mixing effectiveness at the groove and the resulting final mixture temperature have been found to be as important as the wall temperature and the heat transfer rate. The variability of the temperature, though, has been shown to smooth out the peaks of both pressure and friction during misaligned condition Distributions of friction and pressure in the oil are also examined which may be useful in attempts to reduce friction without reducing load. Results for an axial grooved bearing are also presentsed for comparision purpose.

An Analysis of the Circumferentially Grooved Floating Ring Journal Bearing (원주방향 급유홈 프로팅링 저어널베어링의 해석)

  • 정연민;김경웅
    • Tribology and Lubricants
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    • v.7 no.2
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    • pp.75-84
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    • 1991
  • The static and dynamic performances of a floating ring journal bearing with central circumferential grooves at the inner and outer films are obtained numerically with isothermal lubrication theory. Elrod algorithm implementing Jakobsson-Floberg-Olsson cavitation boundary condition is adopted to predict cavitation regions in the inner and outer films more accurately than conventional analyses using half Sommerfeld or Reynolds conditions. The pressure drop in the circumferential groove of the inner film due to the rotation of the journal and ring is taken into account. It is shown that the lubricant supply pressure has significant influence on the load capacity and dynamic coefficients of the bearing. When the supply pressure is low and the journal speed is high, the pressure drop results in severe starvation of lubricant in the inner film and varies the overall performance of the bearing remarkably.

Recent Research and Development on Aerosol Cyclones-Review

  • Lee, K.W.;Kim, H.T.
    • Journal of Korean Society for Atmospheric Environment
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    • v.16 no.E
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    • pp.59-68
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    • 2000
  • In this paper Various aerosol cyclones that are developed recently form Kwangju Institute of Science and Technology(KJIST) for increasing collection efficiency or for decreasing pressure drop are reviewed. For the first time, new sets of experimental data are reported on the particle collection efficiency of cyclones with modified surface bodies namely, spiral guide body, circumferential groove body, and vertical groove body. Multi-cylinder cyclones by adding one or two additional cylindrical walls into the conventional cyclone are also described. Ad an attempt to increase the collection efficiency of small particles, electrocyclone using an externally applied electric field was designed and operated. In addition, factors affecting the cyclone performance were studied including flowrate, body and outlet sizes, cyclone dust outlet, and gas property.

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A Study on Mechanical Properties of Fillet Weldment in Pipeline Repair Welding Using Sleeve (슬리브덮개를 이용한 배관 보수용접시 필릿용접부의 기계적특성에 관한 연구)

  • 김영표;김형식;김우식;홍성호
    • Journal of Welding and Joining
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    • v.14 no.5
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    • pp.49-58
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    • 1996
  • In Korea Gas Corporation, as one of the pipeline repairing methods, damaged pipelines are sometimes treated with a temporally employment of split sleeve. On conducting the repair process, circumferential fillet and longitudinal groove welding usually must be included. For the case of groove welding, a considerable amount of R&D have been carried out related to property changes, while few study on the property change in fillet welding has been conducted. In this paper, so as to confirm the specification of fillet welding in terms of safety and reliability, properties changed by fillet welding were investigated for two welding processes. Qualifying tests such as reviewing macrostructure and nick-break tests were performed according to API 1104 and ASME section IX. In addition, tensile properties and hardness were evaluated according to KS B0841 and BS 4515. The fillet weld prepared by the qualified procedure showed melting depth of 0.8∼1.3mm and heat affected zone of 2.8∼3.4mm length. No crack and lack of penetration were observed. And the results of hardness and nick-break tests satisfied code requirements. The area crossed by fillet and groove welding line was found to have minimal tensile strength.

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Optimal Design of the Crank Press Main Journal Bearings (크랭크 프레스 주축 저널 베어링의 최적 설계)

  • 심현해;김창호;권오관
    • Tribology and Lubricants
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    • v.5 no.1
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    • pp.69-75
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    • 1989
  • The mobility method of dynamically loaded journal bearings was applied to optimize the lubrication of the main journal bearing of the crank press. The effects of oil viscosity, temperature bearing clearance, length, the existence of the circumferential groove, peak press force, and crank rpm were examined. From the results of the minimum film thickness and the maximum film pressure, some of the factors could be optimized, and the degrees of the beneficial and detrimental effects of the others could be estimated.

The Effect of Dimensions and Location of Oil Grooves on the Static Performance of a Cylindrical Journal Bearing (급유홈의 크기와 위치가 원통형 저널 베어링의 정적성능에 미치는 영향)

  • Son, Sang-Ik;Kim, Kyung-Woong
    • Tribology and Lubricants
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    • v.26 no.4
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    • pp.209-218
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    • 2010
  • In this study, the effect of dimensions and location of oil grooves on the static performance of a cylindrical journal bearing is analyzed numerically. Axial length, circumferential length and location of oil grooves are considered as parameters. Cavitation occurs within the diverging region of a journal bearing. The distribution of cavitation region where cavitation occurs varies with dimensions and location of oil grooves and affects the performance of a journal bearing. Elrod's cavitation algorithm which implements JFO boundary conditions based on the principle of mass conservation at the interfaces between cavitation and full film region is adopted in order to consider the effect of cavitation. The result shows that parameters, especially location of oil grooves have a great effect on the static performance of a journal bearing.

3-D Finite Element Mesh Generation of Tires Considering Detailed Tread Pattern (상세 트레드 패턴을 반영한 3차원 타이어 유한요소 격자 생성)

  • Cho, Jin-Rae;Kim, Ki-Whan;Hong, Sang-Il;Kim, Nam-Jeon;Kim, Kee-Woon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.10
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    • pp.1615-1622
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    • 2003
  • Being contacted directly with. ground, the tire tread part is in shape of complex patterns of variable ASDs(anti-skid depth) to satisfy various tire performances. However, owing to the painstaking mesh generation job and the extremely long CPU-time, conventional 3-D tire analyses have been performed by either neglecting tread pattern or modeling circumferential grooves only. As a result, such simplified analysis models lead to considerably poor numerical expectations. This paper addresses the development of a 3-D tire mesh generation considering the detailed tread pattern and shows that the contact pressure and frictional energy distribution of tires considering the detailed pattern become better than those by the simplified tire model.