• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.781-785
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• 2003

This work presents a numerical analysis of two-phase natural circulation flow in reactor cavity under external vessel cooling. Steady, incompressible, three-dimensional Reynolds-averaged Navier-Stokes equations for multiphase flows with zero equation turbulence model are solved to predict the shear key effect on the circulation rate of cooling water and the distribution of void fraction according to the different mass flow of inlet air. Results show that shear key has a positive effect on the circulation rate of cooling water and induce a local increase of void fraction below the shear key, but not remarkably.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1998년도 춘계학술발표회논문집(1)
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• pp.553-558
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• 1998

The calibrating method for an electrochemical Probe, neglecting the effect of the normal velocity on the mass transport, can cause large errors when applied to the measurement of wall shear rates in thin wavy flow with large amplitude waves. An extended calibrating method is developed to consider the contributions of the normal velocity. The inclusion of the turbulence-induced normal velocity term is found to have a negligible effect on the mass transfer coefficient. The contribution wave-induced normal velocity can be classified on the dimensionless parameter V. If V above a critical value of V, $V_{crit}$, the effects of the wave-induced normal velocity become larger with an increase in V. IF V its effects negligible for V < $V_{crit}$. The unknown shear rate is numerically determined by solving the 2-D mass transport equation inversely. The president inverse method can predict the unknown shear rate more accurately in thin wavy flow with large amplitude waves than the previous method.

• 한국안전학회지
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• 제3권1호
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• pp.15-19
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• 1988

The falling ball viscometer has been widely used for measuring the viscosity of the Newtonian fluids because of its simple theory and low cost. The use of the falling ball viscometer for measuring the non-Newtonian viscosity has been of interest to rheologists for some years. The analysis of the experimental results in a falling ball viscometer rest on Stokes law which yields the terminal velocity for a sphere moving through an infinite medium of fluids. An attempt to use the falling ball viscometer to measure the non-Newtonian viscosity in the intermediate shear rate ranEe was sucessfully accomplished by combining the direct experimental obserbations with a simple analytical model for the average shear-stress and shear rate at, the surface of a sphere. In the experiments with highly viscoelastic polyacrylamide solutions the terminal velocity was observed to be dependent on the time interval between the dropping of successive balls. The time-dependent phenomenon was used to determine characteristic diffusion times of the concentrated solutions of polyacrylamide.

• EDISON SW 활용 경진대회 논문집
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• 제2회(2013년)
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• pp.403-408
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• 2013

본 논문은 EDISON_CFD를 이용하여 관상동맥 분지관에서 점도에 따른 유체의 유동현상에 관하여 연구를 하였다. 뉴턴유체인 물의 점성계수 일때와 비뉴턴유체인 혈액의 Carreau model에서의 영전단율 점성계수(${\eta}_0$)와 무한전단율 점성계수(${\eta}_{\infty}$)일 때의 유동현상을 살펴보았다. 그 결과 점도가 증가할수록 재순환 영역에서 유체의 속도가 감소하였고 CF 및 CP값이 감소하는 구간의 수가 증가하여 벽면의 저전단응력으로 인해 생기는 재순환영역의 수가 증가하는 것으로 나타났다.

• Korea-Australia Rheology Journal
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• 제17권4호
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• pp.149-156
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• 2005

A simple constitutive model for viscoelastic suspensions is discussed in this paper. The model can be used to predict the rheological properties (relative viscosity and all stresses) for viscoelastic suspensions in shear and elongational flow, and the constitutive equations combine a 'viscoelastic' behaviour component and a 'Newtonian' behaviour component. As expected, the model gives a prediction of positive first normal stress difference and negative second normal stress difference; the dimensionless first normal stress difference strongly depends on the shear rate and decreases with the volume fraction of solid phase, but the dimensionless second normal stress difference (in magnitude) is nearly independent of the shear rate and increases with the volume fraction. The relative viscosities and all the stresses have been tested against available experimental measurements.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.39-42
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• 2005

For mass production, usually injection mold has multi-cavity which is filled through geometrical balanced runner system. Despite geometrical balanced runner system, filling imbalances between cavity to cavity have always been observed. These filling imbalances are one of the most significant factors to affect quality of plastic parts when molding plastic parts in multi-cavity injection mold. Filling imbalances are results from non-symmetrical shear rate distribution within melt as it flows through the runner system. It has been possible to decrease filling imbalance by optimizing processing conditions, but it has not completely eliminated this phenomenon during injection molding processing. This paper presents a solution of these filling imbalances through using 'runner core pin'. The runner core pin which is developed in this study creates a symmetrical shear distribution within runner. As a result of using runner core pin, a remarkable improvement in reducing filling imbalance was confirmed.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 금형가공,미세가공,플라스틱가공 공동 심포지엄
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• pp.13-16
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• 2005

For mass production, usually injection mold has multi-cavity which is filled through geometrical balanced runner system. Despite geometrical balanced runner system, filling imbalances between cavity to cavity have always been observed. These filing imbalances are one of the most significant factors to affect quality of plastic parts when molding plastic parts in multi-cavity injection mold. Filling imbalances are results from non-symmetrical shear rate distribution within melt as it flows through the runner system. It has been possible to decrease filling imbalance by optimizing processing conditions, but it has not completely eliminated this phenomenon during injection molding processing. This paper presents a solution of these filling imbalances through using 'runner core pin'. The runner core pin which is developed in this study creates a symmetrical shear distribution within runner. As a result of using runner core pin, a remarkable improvement in reducing filling imbalance was confirmed.

• 유변학
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• 제11권1호
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• pp.1-8
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• 1999

본 논문은 높은 압력차의 유동모드 하에서의 정상전단거동을 고찰하였다. ER유체 조성에 사용된 비전도성 용매는 10cS의 점도를 갖는 트랜스포머 오일이 사용되었으며, 전도성 입자의 중량비를 20 wt%와 30 wt%로 조절하여 입자 중량비에 대한 영향을 고찰하였다. 두 가지로 조성된 수계 ER유체를 ERF 1과 ERF 2로 칭하였으며, 성능 비교를 위하여 외국의 우수하다고 알려진 비수계 ER유체인 ERF 3를 사용한 실험도 실시하였다. 높은 압력차의 유동모드를 발생시키기 위해, 양방향 유압 실린더를 이용하여 고압의 질소 가스로 작동되는 실험 장치를 자체 제작하였다. 전극 앞에 장착된 압력 센서를 통해 전극 양단의 압력차를 구하고, 실린더 로드에 부착된 변위센서로부터 측정한 피스톤 속도를 유량 계산의 기초 자료로 사용하였다. 유동모드에 대한 유체역학적 해석을 통해 유도된 수식을 인용했으며, 위의 기초 자료와 수식을 이용하여 유동모드형 응용 장치에 적용하기 위한 전단변형률에 대한 전단응력의 결과를 도출하였다.

• 터널과지하공간
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• 제26권1호
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• pp.12-23
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• 2016

향후 국내에서 수행될 이산화탄소 지중저장 프로젝트의 성공적인 수행을 위해서는 현장 지질조건에 최적화된 주입 조건을 설계하는 것이 중요하다. 따라서 본 연구에서는 주입량 및 주입온도 등의 주입조건이 격리저장시스템의 역학적 안정성에 미치는 영향을 열-수리-역학 연계해석기법의 하나인 TOUGH-FLAC 해석기법을 이용하여 평가하였다. 저장시스템의 역학적 안정성은 기존 균열의 전단미끄러짐 발생가능성을 활동마찰각 및 응력원을 이용하여 분석하였다. 이산화탄소의 주입온도가 저류층의 초기온도보다 낮은 저온주입의 조건에도 열응력으로 인한 인장균열은 발생하지 않는 것으로 파악되었으나, 저류층에서 전단미끄러짐이 발생하는 결과를 보였다. 단위시간당 이산화탄소 주입량을 변화시킨 시나리오 해석에서는 단계별로 주입량을 감소시키는 주입시나리오에서 기존 균열들의 전단미끄러짐 발생 가능성이 가장 낮은 것으로 평가되었다.

• Structural Engineering and Mechanics
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• 제64권4호
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• pp.461-472
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• 2017

The dynamic tests of recycled aggregate concrete (RAC) are carried out, the rate-dependent mechanical models of RAC are proposed. The dynamic mechanical behaviors of RAC frame structure are investigated by adopting the numerical simulation method of the finite element. It is indicated that the lateral stiffness and the hysteresis loops of RAC frame structure obtained from the numerical simulation agree well with the test results, more so for the numerical simulation which is considered the strain rate effect than for the numerical simulation with strain rate excluded. The natural vibration frequency and the lateral stiffness increase with the increase of the strain rate. The dynamic model of the lateral stiffness is proposed, which is reasonably applied to describe the effect of the strain rate on the lateral stiffness of RAC frame structure. The effect of the strain rate on the structural deformation and capacity of RAC is analyzed. The analyses show that the inter-story drift decreases with the increase of the strain rate. However, with the increasing strain rate, the structural capacity increases. The dynamic models of the base shear coefficient and the overturning moment of RAC frame structure are developed. The dynamic models are important and can be used to evaluate the strength deterioration of RAC structure under dynamic loading.