• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.6
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• pp.41-48
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• 2000

The Compression molding process is widely used in the automotive industry to produce parts that are large, thin, light-weight, strong and stiff. Compression molded parts are formed by squeezing a glass fiber reinforced polypropylene sheet, known a glass mat thermoplastic(GMT), between two heated cavity surfaces. In this study, the anisotropic viscosity of the Unidirectional Fiber-Reinforced Plastic Composites is measured using the parallel plastometer and the composites is treated as an incompressible Newtonian fluid. The effects of molding parameter and fiber contents ratio on longitudinal/transverse viscosity are also discussed.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.44-44
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• 2015

저수지나 하천 사면에서 발생하는 산사태와 토석류는 저수지와 하천 수체에 충격을 가한다. 이로 인해 발생하는 수면 충격파는 전파되어 반대편 제방으로 파의 처오름 또는 댐 제체위로의 물넘이로 큰 피해를 줄 수 있다. 최근 외국에서는 2차원 충격파 생성 및 전파의 기본 과정을 구명하기 위한 실험적 연구가 이뤄지고 있으며, 이들 연구들은 충격파의 발생과 전파, 사면활동 물질과 수체의 상호작용 그리고 자유 수면과 유속분표의 발달에 대한 자세한 관측 자료를 제시하고 있다. 아울러 충격파에 영향을 주는 지배 매개변수를 제시하고 있다. 하지만, 이러한 실험적 연구의 최근 진보에도 불구하고, 이들 지배 매개변수를 고려한 충격파 지배공식들은 대상 지역의 복잡한 바닥 지형이나, 평면적 지형 변화를 단순한 추정치로만 고려하게 된다. 따라서 복잡한 지형조건에서 토석류와 수체의 상호작용과 수면 충격파의 전파를 합리적으로 해석하는 데는 한계가 있다. 이 경우 수치모델링 기법을 대안으로 적용할 수 있으나, 수치모델링은 수면에서 충격파의 전파와 수중에서 토석류의 전파를 동시에 모의해야 하고, 뉴턴 유체와 비뉴턴 유체의 특성을 동시에 고려해야하므로 수치해석 연구자들에게는 하나의 큰 도전사항이다. 이 연구는 경계면 포착기법을 이용한 계산유체동력학 기법을 이용하여 사면활동과 이로 인한 정지 수역에서의 충격파의 발생 및 전파를 재현하기 위한 수치 모델링 기법을 개발하는 것이 목적이다. 사면활동과 수면의 경계면을 포착하고 위치를 정립하기 위해서 VOF (volume of fluid) 경계면 재구축 기법을 이용한다. 지배 방정식은 비압축성(incompressible) 질량 보존방정식과 나비어-스톡스(Navier-Stokes) 방정식이며, 서로 다른 유체의 상(phase)애 대한 체적분할이송방정식을 이용한다. 큰와 모의 계열의 난류 모델링 기법을 적용하여 충격파의 전파와 붕괴에 대한 난류의 영향을 고려하였다. 토석류는 비뉴턴 흐름저항 관계식을 적용하여 그 흐름특성을 재현하였다. 이들 지배방정식은 2차 정확도의 유한체적법(finite volume method)을 이용하여 해석한다. 외국의 연구자들이 관측하여 제시한 길이 11 m 그리고 폭 0.5 m의 수로에서 발생한 충격파를 수치적으로 재현하여 개발된 모형의 실제 문제에 대한 적용성을 보여준다.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.747-752
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• 2003

Many clinical studies have suggested that the blood flow in ideal geometry is involved in the development of atherosclerosis. This study simulated blood flow in the abdominal artery with real geometry to investigate MWSS(mean wall shear stress), AWSS(amplitude of wall shear stress) and OSI(oscillator shear index). The calculation grid for the real geometry was constructed by extracting the surface of arterial wall from CT(Computed Tomography) or MRI(Magnetic Resonance Imaging) sheets called as DICOM (Digital Imaging and Communications in Medicines). The calculated MWSS, AWSS and OSI are much different from those of ideal geometry calculation. The MWSS increased while the AWSS decreased. Many shear forces are related to shapes of gradient. This paper will give clinical datum where the MWSS, AWSS and OSI are strong or weak. The hemodynamic analysis based on real geometry can provide surgeons with more reliable information about the effect of blood flow.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.300-303
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• 2010

The present study investigates the flow characteristics of simulant gel propellant(carbopol 0.5%wt) in a variety of injectors. Rheological data for gel propellant has been measured and injector flow characteristics for plain-orifice, chamfered-orifice and venturi type injector have been numerically analyzed. The apparent viscosity of plain-orifice and chamfered-orifice have tendency to increase along axial direction, whereas for venturi type injector, low viscosity has been achieved in the injector flow. This phenomenon was clearly pronounced as Reynolds number is increased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.5
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• pp.1603-1612
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• 1996

The pressure loss coefficient of Newtonian and non-Newtonian fluids such as water, aqueous solutions of Carbopol-934 and Separan AP-273 and blood in the stenotic tubes are determined experimentally and numerically. The numerical analyses for flows of non-Newtonian fluids in the stenotic tubes are conducted by the finite element method. The effect of the contraction ratio and the ratio of length to diameter on the pressure drop are investigated by the experiments and numerical analysis. The pressure loss coefficients are significantly dependent upon the Reynolds number in the laminar flow regime. As Reynolds number increases, the pressure loss coefficients of both Newtonian and non-Newtonian fluids decrease in the laminar flow regime. As the ratio of length to diameter increases the maximum pressure loss coefficient increases in the laminar flow regime for both Newtonian and non-Newtonian fluids. Newtonian fuid shows the highest values of pressure loss coefficient and blood the next, followed by Carbopol solution and Separan solution in order. Experimental results are used to verify the numerical analyses for flows of Newtonian and non-Newtonian fluids. Numerical results for the maximum pressure loss coefficient in the stenotic tubes are in fairly good agreement with the experimental results. The relative differences between the numerical and experimental results of the pressure loss coefficients in the laminar flow regime range from 0.5% to 14.8%.

• Journal of Ocean Engineering and Technology
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• v.10 no.4
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• pp.118-127
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• 1996

Flow patterns of fluid flow in dividing trbe were visualized, and the energy losses due to dividing were measured in laminar dividing flow of the viscoelastic fluid and its solution in tube junctions with dividing angles of $90^{\circ}$, $60^{\circ}$, $65^{\circ}$ and $15^{\circ}$. Two separation zones were observed. swelling of the streamline to the main tube or to lateral tube was observed. The sizes of the separation zones depend on the Reynolds number, the dividing angle and the dividing flow rate. The energy loss coefficients decrease with increasing Reynolds number, but their decreasing rate decreases with increasing Reynolds number as the sizes of the separation zone increase. The effect of dividing angle on the energy loss coefficients and separation is greater for main tube than for the lateral tube.

• Journal of computational fluids engineering
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• v.19 no.4
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• pp.61-67
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• 2014

Since the most of the existing non-Newtonian models are not adequate to apply to the lattmce Boltzmann method, it is a challenging task from both the theoretical and the numerical points of view. In this research the hydro-kinetic model was modified and applied to the 3-D moving sphere in the circular channel flow and the characteristics of the shear thinning effect by the HK-model was evaluated and the condition of ${\Gamma}$ in the model was suggested for the stable simulation to generate non-trivial prediction in three dimension strong shear flows. On the wall boundaries of circular channel the curved wall surface treatment with constant velocity condition was applied and the bounceback condition was applied on the sphere wall to simulate the relative motion of the sphere. The condition is adequate at the less blockage than 0.7 but It may need to apply a multi-scale concept of grid refinement at the narrow flow region. to obtain the stable numerical results.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.10
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• pp.1146-1152
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• 2011

Ink transfer process is very important to determine quality of printed pattern, therefore its mechanism should be understood to control printing quality. Although there have been many attempts to understand ink transfer mechanism by numerical simulation and experimental studies, their model was too much simple to model realistic printing process and our understanding is not enough yet. In this paper we designed ink transfer visualization system to present flow visualization of ink transfer process for gravure offset printing. We considered rotational effect of blanket roll which is related with printing speed and used non-Newtonian fluid as working fluid such as Ag paste. For printing unit, cantilever-type blanket roll is used for convenient visualization of ink transfer. Serial images were captured continuously by using high-speed CMOS camera and long range microscope. We investigated the effects of various design parameters such as printing speed and pattern angle on the ink transfer process. We found more stretched ink filament for non-Newtonian fluid than Newtonian fluid. As increasing printing speed, length of stretched ink filament and height of break-up point are also increased. We also compared ink transfer process between CD and MD pattern and its relationship with ink transfer mechanism.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.4
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• pp.1501-1509
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• 1996

Differential pressure devices such as an orifice and Venturi are widely used in the measurement of flow rate of fluid mainly due to cost effectiveness and easy installation. In the current study, the viscoelastic effect on discharge and loss coefficients of those flow meters were investigated experimentally. Aqueous solutions of Polyacrylamide (200, 500, and 800 ppm) as viscoelastic fluids were used. Discharge coefficient of an orifice for viscoelastic fluids increased significantly up to approximately 15-20% when compared with that for water, while loss coefficient decreased up to 10-25% depending on the diameter ratio, .betha.. Also, pressure recovery for viscoelastic fluids was extended much longer than that for water. On the other hand, discharge and loss coefficients of Venturi for viscoelastic fluids were found to be strongly dependent on the Reynolds number. In both flow meters, the concentration effect for discharge and loss coefficients was not observed at more over than 200 ppm of aqueous solution. Conclusively, orifice and Venturi flow meters should be calibrated very carefully in the flow rate measurement for viscoelastic fluids.

• Journal of the Korean Society of Visualization
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• v.17 no.2
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• pp.10-16
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• 2019

Considering the role of viscosity in the hemorheology, the characteristics of non-Newtonian fluid are important in the pulsatile blood flows. Stenosis, with an abnormal narrowing of the vessel, contributes to block blood flows to downstream tissue and lead to plaque rupture. Therefore, systematic analysis of blood flow around stenosed vessels is crucial. In this study, non-Newtonian behaviors of blood analog fluids around the micro-stenosis with 60 % severity in diameter of $500{\mu}m$ was examined by using CFX under the pulsatile flow conditions with the period of 10 s. Viscosity information of two non-Newtonian fluids were obtained by fitting the value of normal blood and highly viscous blood. As the Newtonian fluid, the water at room temperature was used. During the pulsatile phase, wall shear stress (WSS) is highly oscillated. In addition, high viscous solution gives rise to increases the variation in the WSS around the micro-stenosis. Highly oscillating WSS enhance increasing tendency of plaque instability or rupture and damage of the tissue layer. These results, related to the influence on the damage to the endothelium or stenotic lesion, may help clinicians understand relevant mechanisms.