• Journal of Welding and Joining
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• 제26권4호
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• pp.85-91
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• 2008

The grooving corrosion is caused mainly by the different microstructures between the matrix and weld which is formed during the rapid heating and cooling cycle in welding. By this localized corrosion reaction of pipes, it evolves economic problems such as the early damage of industrial facilities and pipe lines of apartment, and water pollution. So lots of researches were carried out already about grooving corrosion mechanism of ERW carbon steel pipe but there is seldom study for water hammer happened by fluid phenomenon and corrosion rate by flow velocity. In this study, the analysis based on hydrodynamic and fracture mechanics was carried out. ANSYS, FLUENT and STAR-CD were used for confirmation of flow phenomenon and stress on the pipe. As the results, fatigue failure is able to be happened by water hammer and grooving corrosion rate is increased cause by turbulent. Grooving corrosion is happened on the pipe, then friction loss of fluid is occurred from corroded part. Erosion can be happened enough in corroded region of microscopic size that wear "V" form. Also pipe is able to be damaged by water hammer effects because of corroded region is general acting as a notch effects. Corrosion depth was more than half of total thickness, it can be damaged from water hammer pressure.

• Nuclear Engineering and Technology
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• 제24권3호
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• pp.274-284
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• 1992

가압경수로 최적 열수력 분석용 전산코드인 CATHRE의 모델 평가를 위하여 가압경수로의 가상 냉각재 상실사고시 원자로 용기내의 유동현상을 모의한 1/15축소의 CREARE 실험을 모의 계산하였다. 이 실험에서 주요변수들은 비상노심 탱각재 주입량과 아냉정도 그리고 계통압력 및 노심에서 발생되는 증기유량이지만. 본 연구에서는 우선 Downcomer에서 역방향유동의 정성적 분석에 촛점을 맞추었다. 모의 계산 결과와 실험 결과를 비교할 때 정량적인 값 뿐 아니라 변화의 경향에서도 차이가 나타난 것은 주로 적절하지 못한 일부의 수치해석 모델과 상간의 계면마찰 때문으로 판단된다. 따라서 매개변수적 민감도 분석을 통하여 CATHARE 전산코드의‘VOLUME’에 접한 접합점에서 운동량 보존방정식의 상세연구 혹은 다차원 분석을 통해서 이 경우의 물리적 현상을 보다 현실적으로 나타낼 수 있다는 결론을 얻었다.

• 대한기계학회논문집B
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• 제24권7호
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• pp.957-966
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• 2000

The effect of rotation on the discharge coefficient of orifices with various length-to-diameter ratios and two different inlet corner radii was studied. Length-to-diameter ratios of the orifices range from 0.2 to 10, while the inlet shapes are square edged, or round edges of radius-to-diameter ratio of 0.5. From the experiment, we found that rotational discharge coefficient and Rotation number, when based on ideal exit velocity of the orifice considering momentum transfer from the rotor, describe the effect of rotation very well. In this study, the discharge coefficients of rotating orifices are shown to behave similar to those of the well-known non-rotating orifices. For both rotating and non-rotating orifices, the discharge coefficients increase with the length-to-diameter ratio until a maximum is reached. The flow reattachments in the relatively short orifices are responsible for the increase. The coefficient then decreases with the length-to-diameter ratio due to the friction loss along the orifice bore. The length-to-diameter ratio that yields maximum discharge coefficient, however, increases with the Rotation number because the increased flow-approaching angle requires larger length-to-diameter ratio for complete reattachment. The length-to-diameter ratio for complete reattachment is shorter for round edged orifices than that of square edged orifices by about a unit length-to-diameter ratio.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2465-2470
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• 2008

A new surface shape of an internal cooling passage which largely reduces the pressure drop and enhances the surface heat transfer is proposed in the present study. The surface shape of the cooling passage is consisted of the concave dimple and the riblet inside the dimple which is protruded along the stream-wise direction. Direct Numerical Simulation (DNS) for the fully developed turbulent flow and thermal fields in the cooling passage is conducted. The Numerical simulations for the 5 different surface shapes are conducted at the Reynolds number of 2800 based on the mean bulk velocity and channel height and Prandtl number of 0.71. The driving pressure gradient is adjusted to keep a constant mass flow rate in the x direction. The thermo-aerodynamic performance for the 5 different cases used in the present study was assessed in terms of the drag, Nusselt number, Fanning friction factor, Volume and Area goodness factor in the cooling passage. The value of maximum ratio of drag reduction is -22.86 [%], and the value of maximum ratio of Nusselt number augmentation is 7.05 [%] when the riblet angle is $60^{\circ}$ (Case5). The remarkable point is that the ratio of Nusselt number augmentation has the positive value for the surface shapes which have over $45^{\circ}$ of the riblet angle. The maximum Volume and Area goodness factor are obtained when the riblet angle is $60^{\circ}$ (Case5).

• 설비공학논문집
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• 제15권8호
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• pp.630-640
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• 2003

As tunnel ventilation has recently been playing a major role in the tunnel construction and maintenance, longitudinal ventilation systems with jet fans have been utilized a great deal because they are economical and effective. However, due to the length of tunnels and heavy traffic, it is hard to take the field measurements. In this study, therefore, the computer simulation and the model experiment of producing a wind tunnel were carried out simultaneously and the results were compared. The ultimate objective of this research was to interpret the air flow pattern inside the tunnel with a jet-fan was set up, and to offer the useful data for jet-fan installation and operation. The experiment was carried out with varying the jet-fan diameters, location of installation, the discharge velocity. Result showed that as the initial static pressure came up with the negative pressure, the tunnel air flowed into the inside of tunnel from outside due to the entrainment-effect and the backflow-phenomenon by separation-effect was observed in the lower half part of the tunnel. As the jet-fan was getting closer to the tunnel wall, the entrainment-effect caused by the interaction with the wall was increased; however, the mixing distance and irregular flow section became longer, and also the air pressure loss generated by wall friction was large.

• 한국터널지하공간학회 논문집
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• 제15권3호
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• pp.301-310
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• 2013

현재 도로터널에는 화재시 임계풍속을 유지할 수 있도록 제트팬을 설치하고 있으며, 제트팬 댓수는 임계풍속을 유지하기 위한 유동저항, 자연풍에 의한 환기저항, 열부력에 의한 환기저항을 고려하여 산정한다. 그러나, 국내의 경우, 제트팬 댓수 산정시 열부력은 고려하지 않고 있는 실정이다. 이에 본 연구에서는 열부력이 제트팬 댓수에 미치는 영향을 검토하기 위해서 터널연장(500, 750, 1000, 1500, 2000, 3500 m) 및 경사도(-1.0, -1.5, -2.0%)를 변수로 하여 화재성장곡선에 따른 비정상상태의 수치 시뮬레이션을 수행하였으며, 열기류의 평균온도 및 열부력에 의한 압력손실을 검토하여 열부력이 제트팬 댓수에 미치는 영향을 검토하였다. 이에 본 연구에서는 화재로 인한 열부력을 고려하는 경우에 제트팬 댓수의 증가가 필요하며, 특히, 설계화재강도를 100 MW로 하는 경우에는 본 해석조건의 모든 범위에서 열부력에 의한 압력손실이 차량저항에 의한 압력손실의 최대치보다 증가하며, 현행설계기준을 적용하는 경우보다. 최소 2~11대의 제트팬 대수의 증가가 필요한 것으로 분석되었다. 따라서 제연용 제트팬 용량 산정시 열부력에 대한 고려가 반드시 필요한 것으로 나타났다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.530-533
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• 2010

This paper presents numerical analysis and design optimization of various turbine blade cooling techniques with three-dimensional Reynolds-averaged Navier-Stokes(RANS) analysis. The fluid flow and heat transfer have been performed using ANSYS-CFX 11.0. A fan-shaped hole for film-cooling has been carried out to improve film-cooling effectiveness with the radial basis neural network method. The injection angle of hole, lateral expansion angle of hole and ratio of length-to-diameter of the hole are chosen as design variables and spatially averaged film-cooling effectiveness is considered as an objective function which is to be maximized. The impingement jet cooling has been performed to investigate heat transfer characteristic with geometry variables. Distance between jet nozzle exit and impingement plate, inclination of nozzle and aspect ratio of nozzle hole are considered as geometry variables. The area averaged Nusselt number is evaluated each geometry variables. A rotating rectangular channel with staggered array pin-fins has been investigated to increase heat transfer performance ad to decrease friction loss using KRG modeling. Two non-dimensional variables, the ratio of the eight diameter of the pin-fins and ratio of the spacing between the pin-fins to diameter of the pin-fins selected as design variables. A rotating rectangular channel with staggered dimples on opposite walls are formulated numerically to enhance heat transfer performance. The ratio of the dimple depth and dimple diameter are selected as geometry variables.

• Nuclear Engineering and Technology
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• 제24권3호
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• pp.263-273
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• 1992

핵연료 집합체의 속도분포, 압력강하는 열수력 설계와 안전해석에 중요하다. 본 실험적 연구의 목적은 봉다발 지지 격자 하류에서의 수력학적 혼합을 고찰하는데 있다. 이 연구에서 가압경수로형 5X5 봉다발 부수로의 상세한 수력학적 특성들을 1차익 He-Ne LDV를 이용하여 측정하였다. 축방향 유속, 난류강도와 압력강하를 주로 측정하였고 LDV의 정렬을 조정하여 측방향의 유속, 난류강도, Reynolds 전단응력 등도 역시 측정하였다. 봉다발의 마찰계수와 지지 격자의 손실계수는 측정된 압력 강하로부터 평가하였다. 서로 다른 종류의 지지 격자의 수력학적 혼합성능을 이웃하는 부수로 간에서의 난류 횡류 혼합률을 예측함으로써 고찰할 수 있었다.

• 한국화재소방학회논문지
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• 제25권4호
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• pp.89-93
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• 2011

(초)고층건축물에서 승강로가 연기 확산의 주요 통로였기 때문에 승강기를 통해 피난하는 것은 권장되지 않았다. 하지만 북미에서는 승강로를 연기로부터 방호하기 위해, 승강로를 가압하는 방식을 사용하여 왔다. 이번 시험은 실제로 승강로 급기가압 방식을 이용해서 연기 전파를 차단할 수 있는지와 피난수단으로 승강기를 사용할 수 있는지를 검증하기 위해 고층 아파트에서 실시되었다. 시험 결과 승강로가압은 공기의 이동에 의한 마찰손실이 작았기 때문에 150 CMM의 풍량에서 승강장과 세대 사이에 50 Pa의 차압을 전층에 고르게 형성시켰다. 또한 1개층 세대 문과 승강기 문이 동시에 개방되었을 때, 180 CMM의 풍량으로 연기의 역류를 차단할 수 있는 방연풍속을 형성하였다. 그리고 승강로가압은 모든 문이 닫힌 상태에서 차압유지에 필요한 풍량과 1개층이 개방되었을 때 방연풍속을 유지하는데 필요한 풍량의 차가 작아서 과압의 우려가 낮을 것으로 예상되었다. 따라서 이번 시험을 통해 고층아파트의 화재 시에 승강로가압을 적용하면 일반인과 피난약자의 피난수단으로 승강기를 사용할 수 있음을 확인하였다.

• Tribology and Lubricants
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• 제32권3호
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• pp.101-105
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• 2016

Trap effect of groove is evaluated in a lubricating system using computational fluid dynamics (CFD) analysis. The simulation is based on the standard k-ε turbulence model and the discrete phase model (DPM) using a commercial CFD code FLUENT. The simulation results are also capable of showing the particle trajectories in flow field. Computational domain is meshed using the GAMBIT pre-processor. The various grooves are applied in order to improve lubrication characteristics such as reduction of friction loss, increase in load carrying capacity, and trapping of the wear particles. Trap effect of groove is investigated with variations in cross-sectional shape and Reynolds number in this research. Various cross-sectional shapes of groove (rectangular, triangle, U shaped, trapezoid, elliptical shapes) are considered to evaluate the trap effect in simplified two-dimensional sliding bearing. The particles are assumed to steel, and defined a single particle injection condition in various positions. The “reflect” boundary condition for discrete phase is applied to the wall boundary, and the “escape” boundary condition to “pressure inlet” and “pressure outlet” conditions. The streamlines are compared with particles trajectories in the groove. From the results of numerical analysis in the study, it is found that the cross-sectional shapes favorable to the creation of vortex and small eddy current are effective in terms of particle trapping effect. Moreover, it is found that the Reynolds number has a strong influence on the pattern of vortex or small eddy current in the groove, and that the pattern of the vortex or small eddy current affects the trap effect of the groove.