• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.118-120
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• 2003

The behavior of viscous fingerings caused by an external force is investigated by using a two­phase lattice Boltzmann method. The effects of the modified capillary number, the viscosity contrast, and the modified Darcy-Rayleigh number on the instability of interfaces are found. The calculated wave numbers are in good agreement with the theoretical ones in the range of wave numbers smaller than 10, but the calculated ones tend to become smaller than the theoretical ones in higher wave numbers.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제11권1호
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• pp.95-105
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• 2007

A mathematical modeling for the drying process of hygroscopic porous media, such as wood, has been developed in the past decades. The governing equations for wood drying consist of three conservation equations with respect to the three state variables, moisture content, temperature and air density. They are involving simultaneous, highly coupled heat and mass transfer phenomena. In recent, the equations were extended to account for material heterogeneity through the density of the wood and via the density variation of the material process, capillary pressure, absolute permeability, bound water diffusivity and effective thermal conductivity. In this paper, we investigate the drying behavior for the three primary variables of the drying process in terms of control volume finite element method to the heterogeneous transport model on one-dimensional grid.

• 설비공학논문집
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• 제25권2호
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• pp.64-69
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• 2013

The structure of pore network of gas diffusion layers (GDLs) in PEMFCs plays a critical role in determining the transport phenomena of reaction gas as well as generated water. In addition, the interactive characteristics between water and surface of pore are no less important than the structural characteristics of pore network. In this study, porometric investigation is conducted for two kinds of GDL using method of standard porosimetry which enable to distinguish hydrophobic pores from hydrophilic pores of GDLs. The porosity of TGPH-120 decreases by 6% by adding 30 wt.% of PTFE, but the porosity of hydrophilic pores decreases by 12%. The relation of $p_c-S_{nw}$ varies with the addition of PTFE, especially at low $p_c$.

• 한국세라믹학회지
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• 제37권11호
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• pp.1071-1077
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• 2000

표면 윤활층을 가진 나노 알루미나를 진공중에서 가압성형함으로써 결함발생없이 높은 충전압력을 가할 수 있었으며, 높은 밀도, 미세기공, 좁은 기공경 분포를 가지는 성형체를 제조할 수 있었다. 윤활제의 화학 및 기계적 특성에 의하여 변하는 모세관 현상을 조정함으로써 충전효율을 증대하고 결함발생을 억제할 수 있다. 나노분말의 소결에서도 성형 미세구조의 균일도가 치밀화 거동에 여전히 지배적인 역할을 하였다.

• 대한기계학회논문집B
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• 제20권6호
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• pp.1948-1958
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• 1996

Experimental and theoretical studies on the air-assist coaxial atomizer have been continuously carried out for a long time. But now the importance of the theoretical study is tending to increase as with the development of computer. This study is concerned to the spray modelization, especially, the instability of the liquid jet surrounded by the air stream which flows with high velocity. To study the phenomena of the break up, we used the linear theory based on the classical Kelvin-Helmholtz theory for capillary wave at a simple interface and we investigated the variation of liquid core radius. As a result, we obtained that the drop diameter and the variation of the liquid core radius predicted by using our model are reasonable.

• 한국안광학회지
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• 제10권3호
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• pp.173-184
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• 2005

각막과 콘택트렌즈 사이의 눈물 층에는 모세관 작용에 따른 장력이 발생하고, 순목 결과 렌즈가 평형위치에서 벗어나게 되면 렌즈의 상/하 또는 좌/우의 눈물 층의 간격이 변하며 이 간격 변화에 의해 복원력이 발생한다. 이 복원력과 눈물 층의 정성 저항력에 의해 렌즈는 진폭이 감소하는 진동을 하면서 평형위치로 복귀하게 된다. 순목 시 안검작용에 의해 렌즈가 일정한 위치로 편위 되었다고 설정할 때 순목 종료 후 매 순간 렌즈의 위치를 예측할 수 있는 미분방정식과 그 수치계산 프로그램 모델을 수립하였다. 이 컴퓨터 모델을 사용하여 렌즈의 BC, 직경, 초기 위치, 무게 등이 감쇄진동에 미치는 영향을 모사하였다. 순목 후 렌즈의 평형 위치로의 귀환은 순목 시간이 적절한 경우에는 순목 종료 직후의 렌즈 위치 및 직경에 그다지 영향을 받지 않고 빠르게 이루어지지만 렌즈의 BC가 지나치게 크거나, 무게가 큰 경우에는 렌즈 진동이 급격히 느려지기 때문에 평형 위치로 되돌아오는데 시간이 많이 걸리게 될 것이다.

• 한국수산과학회지
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• 제36권3호
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• pp.283-289
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• 2003

The effect on kidney, gill, and hepatopancreas of juvenile olive flounder, Paralichthys olivaceus were investigated by histological method under limit concentration of effulent of PCBs for 60 days. The free surface of epithelial cell layer in the renal tubules of kidney showed a strong positive reaction in alcian blue during all exposure period. There were also observed swelling of hemocyte in glomerulus and macrophage. At 60 days after exposure, epithelium of the renal tubules was fused and some of organism $(20\%)$ showed damage of glomerulus and eosinophlic cell in epithelium of the renal tubules. The phenomena such as the activation and increase of the chloride cell, and swelling of hemocyte in the capillary of gill were observed during all exposure period. At 60 days after exposure, swelling of the gill filament and mucous cell appeared in gill and some of organism $(30\%)$ showed swelling of the gill lamellar. Swelling of hemocyte in the capillary of hepatopancreas was observed and the free surface of epithelial layer of the bile duct showed positive reaction in alcian blue during all exposure period. Degenerated zymogen in the pancreas and swelling of the hepatocyte were occurred at 60 days after exposure.

• 대한기계학회논문집B
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• 제41권8호
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• pp.531-536
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• 2017

최근들어 고체 표면의 젖음성을 향상시키기 위해 표면에 나노/마이크로 기술을 적용하는 연구가 진행되고 있다. 이러한 연구를 통하여 나노 구조가 표면 젖음성을 향상 시킬 수 있고, 액체 퍼짐은 실 모세관(Capillary wicking)에 의해 형성된다는 것을 확인하였다. 그러나 대부분의 연구는 나노 구조의 작은 스케일때문에 분석하는데 어려움이 있어서 퍼짐현상을 정성적으로 분석하고 있다. 본 연구에서는 마이크로/나노/마이크로-나노 구조를 갖는 실리콘 표면에서의 액적 계면 거동을 정량적으로 분석하였으며, 계면의 거동은 방사광 X선 영상법으로 직접 측면가시화를 진행하였다. 그 결과 모든 구조 표면에서 퍼짐 현상이 발생하였고, 액체 계면의 거동이 서로 다르게 나타났다. 마이크로구조의 경우 일정한 액막 두께를 유지하며 퍼졌고, 나노구조는 완만한 경사를 갖는 것으로 나타났다. 마이크로-나노 구조의 경우 두 가지가 결합된 형태의 퍼짐현상을 보였다. 또한 액체의 퍼짐은 마이크로-나노 구조에서 가장 증진됨을 확인하였다.

• Ocean and Polar Research
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• 제31권1호
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• pp.111-119
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• 2009

Biogenic surface films, which are often present in coastal areas, may enhance the signatures of hydrodynamic processes in microwave, optical, and infrared imagery. We analyzed ERS-1/2 Synthetic Aperture Radar (SAR) and Envisat Advanced Synthetic Aperture Radar (ASAR) images taken over the Japan/East Sea (JES). We focused on the appearance of the contrast SAR signatures, particularly the dark features of different scales caused by various oceanic and atmospheric phenomena. Spiral eddies of different scales were detected through surface film patterns both near the coast and in the open regions of the JES in warm and cold seasons. During field experiments carried out at the Pacific Oceanological Institute (POI) Marine Station 'Cape Shults' in Peter the Great Bay, the sea surface roughness characteristics were measured during the day and night using a developed polarization spectrophotometer and various digital cameras and systems of floats. The velocity of natural and artificial slicks was estimated using video and ADCP time series of tracers deployed on the sea surface. The slopes of gravity-capillary wave power spectra varied between .4 and .5. Surface currents in the natural and artificial slicks increased with the distance from the coast, varying between 4 and 40 cm/s. The contrast of biogenic and anthropogenic slicks detected on vertical and horizontal polarization images against the background varied over a wide range. SAR images and ancillary satellite and field data were processed and analyzed using specialized GIS for marine coastal areas.

• 설비공학논문집
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• 제2권1호
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• pp.37-48
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• 1990

The drag and heat transfer reduction phenomena and degradation effects of drag reducing polymer solutions which are known as the viscoelastic fluids are investigated experimentally for the turbulent circular tube flows. Two stainless steel tubes are used for the experimental flow loops. Aqueous solutions of Polyacrylamide Separan AP-273 with concentrations from 300 to 1000 wppm are used as working fluids. Flow loops are set up to measure the friction factors and heat transfer coefficients of test tubes in the once-through system and the recirculating flow system. Test tubes are heated by power supply directly to apply constant heat flux boundary conditions on the wall. Capillary tube viscometer and falling ball viscometer are used to measure the viscous characteristics of fluids and the characteristic relaxation time of a fluid is determined by the Powell-Eyring model. The order of magnidude of the thermal entrance length of a drag reducing polymer solution is close to the order of magnitude of the laminar entrance length of Newtonian fluids. Dimensionless heat transfer coefficients of the viscoelastic non-Newtonian fluids may be represented as a function of flow behavior index n and newly defined viscoelastic Graetz number. As degradation continues viscosity and the characteristic relaxation time of the testing fluids decrease and heat transfer coefficients increase. The characteristic relaxation time is used to define the Weissenberg number and variations of friction factors and heat transfer coefficients due to degradation are presented in terms of the Weissenberg number.