• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.4
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• pp.335-341
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• 2015

In this study, we analyzed a two-dimensional Stokes flow through a microchannel containing projections with constant spacing attached to each wall. The projections on the top and bottom walls were semi-circular in shape, with in-phase locations. By considering the periodicity and symmetry of the flow, the eigenfunction expansion and least squared error method were applied to determine the stream function and pressure distribution. For some typical radius and spacing values, the streamline patterns and pressure distributions in the flow field are shown, and the shear stress distributions on the boundary walls are plotted. In addition, the average pressure gradients in the microchannel are also calculated and shown with the radius and spacing of the projections. In particular, the results for the case of extremely small gaps between the projections on the top and bottom walls are in good agreement with the lubrication results.

• Journal of the KSME
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• v.33 no.12
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• pp.1063-1068
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• 1993

왕복식엔진에서 연소과정은 실린더내 유체유동에 지배되므로 최적조건의 엔진설계를 위해서는 실린더내 유체유동을 효과적으로 이용하는 것이 필요하다. 연소과정에 중요한 영향을 미치는 압축말기 연소실내 난류강도는 흡입과정시 생성된 유동의 에너지가 압축과정을 거치면서 작은 스케일의 에디(eddy)로 깨지면서 발생된다. 연소과정시 이러한 에디들은 초기화염생성을 촉진 시키고 화염전파속도를 증진시키는 역할을 함으로써 실린더내 유체유동에 대한 이해증진을위해 실린더내 평균속도 및 난류유동을 측정하는 연구들이 많이 진행되고 있다. 엔진유동은 매사이 클의 유동이 엄밀히 주기적인 운동을 하지 않고, 각 사이클의 유동이 비정상유동을 하며, 유동의 생성 및 소멸이 매우 짧은 특성을 가진다. 따라서 산란입자가 측정체적을 통과할 때 속도데이 터가 발생하는 LDV(laser Doppler velocimetry) 측정에 있어서 레이저빔의 산란광노이즈 감소와 산란입자의 효율적인 공급으로 데이터 발생률을 높이는 것이 어려운 점이다. 이 글에서는 엔진 유동의 LDV측정시 고려해야 할 문제점들, 실험장치구성, 그리고 데이터처리 방법과 주요측정 결과에 대해 본 연구팀에서 지금까지 수행한 연구결과를 토대로 하여 기술하고자 한다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.34-40
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• 2016

In ventilated seats for cars, air flow is generated by a fan and passed through a foam pad, foam filter, and seat cover. There is a significant loss of air flow in this process, and it is not easy to analyze the amount delivered to the driver. Another difficulty is the geometric complexity of the air flow passage inside the seats. In this paper, the air flow through a foam pad was analyzed. Proper modeling of the bumps in the ventilation mat was found to be important in the analysis. Air flow is lost when it passes through the porous pad foam, which was measured and used to correct the analysis results. The corrected analysis results were in a good agreement with the experimental results. The amount of air flow delivered to a driver was measured using an airflow cone. Only 35.7% of the air flow from the fan was delivered.

• Geotechnical Engineering
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• v.13 no.5
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• pp.155-168
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• 1997

The phenomena of detachment and movement of One particles are one of the important mechanisms both in geotechnical and geoenvironmental engineering. In geoenvironmental engineering, in particular, movement of fine particles may facilitate the transport of contaminants since the particle surfaces absorb contaminants before movement. Weathered granitic residual soils, which are the most abundant in Korea. contain large quantities of fine particles up to 50%. The characteristics of fine particle movement of weathered granitic residual soils are investigated in this paper. Samples are obtained from Poiiong, Shinnaedong in Seoul and Andong in Kyungpook : each of the samples represents typical residual soil types in Korea. Laboratory experiments for the three adopted soil types are performed. It is found that effluent concentration of the samples is influenced by porosity, fine particle percentage and particle size distribution. The critical velocity decreases as the fine particle percentage increases and the rate of change of erosion rate increases as the porosity increases. And well-graded samples showed less effluent concentrations compared to poorly-graded samples. The governing equation on the physical mechanism of fine particle movement and its nomerical solution scheme are suggested on the basis of the test results.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.181-186
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• 2007

Compressible flow characteristics in a butterfly valve is studied experimentally and numerically. The disk angle of the valve is changed as $0^{\circ}{\sim}30^{\circ}$. The SST model is used to represent the turbulent effect in the commercial code, CFX11. It was found that the numerical results are similar to the experimental ones, general discussions are given to the pressure distributions upon the disk angle of the valve.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.2
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• pp.124-130
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• 1999

Flow characteristics of a compressible gas flow through a rotating disc-type rotary valve are investigated experimentally under various conditions. It is known that the mass flow rate through poppet valves of 4-stroke cycle engines and through piston valves of 2-stoke cycle engines decrease with increase in engine speed. Rotary valve is one means by which air may be made to flow inter-mittently through a pipe. In this paper an exhaust system simulator of engine was used to experi-mentally analyze the decrease in flow rate at high rotation speeds and to determine what variables other than rotational speed give rise to the observed behaviour. These variables have been included in an empirical equation which is representative of the measured flow characteristics.

• Journal of Biomedical Engineering Research
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• v.21 no.5
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• pp.449-455
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• 2000

순간적으로 승모판에서 혈류가 역류하는 영역을 측정하기 위해서, PISA 방법이 자주 이용되고 있다. 이 방법은 물질보존법칙에 근거하여, 구멍을 통과하는 유체량을 isotach 표면적과 이에 대응하는 속도의 곱으로 구하는 것이다. 이러한 PISA 방법에서 사용되는 유동모델은 반구모델과 비반구모델의 형태인데, 이는 isotach 표면적이 반구이거나 비반구임을 가정하여 계산된 것이다. 이러한 isotach 모델링에서는 isotach의 높이와 폭의 결정이 유체량을 추정하는데 아주 중요한 변수가 된다. 본 연구에서는 in-vitro 칼라 도플러 영상으로부터 PISA 영역을 추정을 위하여 영역기반을 근간으로 하는 비반구모델에 대한 표면적 추정방법을 제안하였다. 이 방법의 타당성을 알아보기 위해 180개의 칼라 도플러 영상에 대해 isotach의 높이와 폭을 추정한 결과, 기존의 에지기반방법이 19개 영상에서 에러를 가지는 반면, 제안한 방법에서는 에러영상이 없음을 알 수 있었다.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.54-58
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• 2015

인간이 생활하는데 필요한 전기를 생산하는 시설 중 하나인 화력발전소의 발전수차를 냉각시키기 위하여 많은 양의 냉각수를 바다에서 취수하게 되는데, 이 과정 중에서도 특히 흡입수조(Intake Basin)에서 흡입펌프(Suction Pump)를 통과하는 단계가 매우 중요하다. 흡입수조의 형상과 펌프운용조건 등에 의하여 흡입구(Bell Mouth)에 접근하는 유동이 비대칭일 경우 흡입구 주변에서 선회류가 발생하거나 유속분포가 비균일?비대칭이 되기 쉽다. 그러면 선회류가 더욱 악화되어 볼텍스(Vortex)로 발달되면 취수 펌프에 악영향을 준다. 또한 볼텍스의 발생은 흡입수조의 형상뿐만이 아니라 낮은 수위일 경우 수면과 흡입구의 거리가 짧아지면서 자유수면볼텍스 또는 수중볼텍스가 발생할 확률이 높아지게 된다. 본 연구에서 수리모형시험을 통하여 펌프 조합 및 수위 변화에 따른 볼텍스의 발생여부를 파악하고 볼텍스 저감장치를 고안하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.4
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• pp.397-404
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• 2012

In this research, a numerical study was carried out on the mixing and flow characteristics of a vane-type static mixer for the reduction of $NO_x$ in the SCR systems from the diesel exhaust environments. The mixer was located at a distance of 57 times the pipe diameter away from the inlet. The analyses were performed by changing various parameters such as vane angles, blockage ratio, and location of the vane. Flow characteristics through the mixer were characterized by the uniformity index, swirl number, and pressure drop. The results show that uniformity index, pressure coefficient and swirl number are substantially influenced by the vane angle, blockage ratio and position of the vane of the mixer. In particular, the swirl number was increased when the vane was located near the pipe wall, or the vane angle was increased or scale was extended.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.1
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• pp.69-74
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• 2017

The validity of friction factor theory, based upon conventional-sized passages for microchannel flows, is an active area of research. The high surface to volume ratio of a microchannel offers many advantages over macroscale devices and processes. This study focused on the laminar flow (16$161{\mu}m$ to $664{\mu}m$ for single-phase liquid flow. A controllable syringe pump was used to provide flow while a differential pressure transducer was used to record the pressure drop. These results demonstrated that a 3D printer can drastically simplify custom microchannel fabrication and still support complex features, which are typically only accessible with advanced fabrication techniques.