• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.137-140
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• 2005

Resin transfer molding (RTM) is one of the most popular processes for producing fiber reinforced polymer composites. In the manufacture of complex thick composite structures, analysis on flow front advancement on the resin impregnating the multi-layered fiber preform is helpful for the optimization of the process. In this study, three-dimensional mold filling simulation of RTM is carried out by using CVFEM (Control Volume Finite Element Method). On the assumption of isothermal flow of Newtonian fluid, Darcy’s law and continuity equation are used as governing equations. Different permeability tensors employed in each layer are obtained by experiments. Numerically predicted flow front is compared with experimental one in order to validate the numerical results. Flow simulations are conducted in the two mold geometries, rectangular plate and hollow cylinder. Permeability tensor of each layer preform in Cartesian coordinate system is transformed to cylinder coordinates system so that the flow within the multi-layered preforms of the hollow cylinder can be calculated exactly. Our emphasis is on the three dimensional flow analysis for circular three-dimensional braided preform, which shows outstanding mechanical properties such as high impact strength and toughness compared with other conventional two-dimensional laminar-structured preforms.

• 전기화학회지
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• 제2권2호
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• pp.98-105
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• 1999

본 연구에서는 전기장에 의하여 유발되는 자연대류의 영향을 줄이기 위하여 수평 다공성 유체층에 열적 성충화를 유지하여 부력과 유체층의 안정화 효과를 체계적으로 조사하였다. 이를 위하여 수평 다공성 유체층에서 이중확산대류에 의한 물질전달 상관식을 이론적으로 유도하고, 전기화학 실험을 통하여 이론에 의한 모델을 보완하였다. 물질전달 상관식은 다공성 매질층에 대한 유동 방정식으로 Forchheimer모델을 사용하고 미세 난류 모델을 적용하여, 용질 및 열 Darcy-Rayleigh수와 Lewis 수로 유도하였다. 실험에서는 다공성매질에 포화된 황산구리황산용액내의 구리이온을 전기 화학적 방법을 통하여 확산 또는 자연대류에 의한 물질전달 실험을 수행하였다. 이론 및 실험적 해석 결과를 종합하면 다공성 매질 내에서 구리이온의 이중확산대류에 의한 물질전달 상관식은 다음과 같다. $$Sh=\frac{0.03054(Rs_D-LeRa_D)^{1/2}}{1-3.8788(Rs_D-LeRa_D)^{-1/10}}$$ 본 연구의 결과는 실험치와 잘 부합되었으며, 모델식의 원형은 열 및 물질전달계에서 자연대류의 영향을 효과적으로 제어할 수 있는 방안으로 활용될 수 있을 것이다.

• 한국농공학회지
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• 제39권2호
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• pp.62-73
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• 1997

The application of nutrients and pesticides to agricultural lands has been reported to contribute to groundwater contamination, which can be explained by preferential flow in lieu of convective-dispersive flow. An one-dimensional numerical model depicting preferential water and solute movement was modified to describe multi-layer flows. The model is based on a piecewise linear conductivity function. By combining conservation of mass and Darcy's law and using the method of characteristics a solution is obtained for water flow in which water moves at distinct velocities in different flow regions instead of an average velocity for the whole profile. The model allows transfer ofqr solutes between pore groups. The transfer is characterized by assuming mixing coefficients. The model was applied to undisturbed soil columns and an experiment site with structured sandy clay loam soil. Chloride, bromide, and 2, 4-D were used as tracers. Simulated solutes concentrations were in good agreement with the soil column data and field data in which preferential flow of solute is significant. The proposed model is capable of describing preferential solute transport under laboratory and field conditions.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 춘계학술발표대회 논문집
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• pp.184-187
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• 2003

Complete prediction of second order permeability tensor for three dimensional circular braided preform is critical to understand the resin transfer molding process of composites. The permeability can be predicted by considering resin flow through the multi-axial fiber structure. In this study, permeability tensor for a 3-D circular braided preform is calculated by solving a boundary problem of a periodic unit cell. Flow field through the unit cell is obtained by using a 3-D finite volume method (FVM) and Darcy's law is utilized to obtain permeability tensor. Flow analysis for two cases that a fiber tow is regarded as impermeable solid and permeable porous medium is carried out respectively. It is found that the flow within the intra-tow region of the braided preform is negligible if inter-tow porosity is relatively high but the flow through the tow must be considered when the porosity is low. To avoid checkerboard pressure field and improve the efficiency of numerical computation, a new interpolation function for velocity variation is proposed on the basis of analytic solutions. Permeability of the braided preform is measured through a radial flow experiment and compared with the permeability predicted numerically.

• 한국콘텐츠학회논문지
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• 제16권4호
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• pp.614-623
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• 2016

스마트워터그리드의 중요한 요소기술로써 그리드(관망)의 설계는 압력, 마찰계수, 마찰속도, 수두손실, 그리고 에너지 경사와 같은 수리학적 매개변수를 추정하는 것이 필수적이다. 특히, 그리드의 마찰속도는 에너지 경사, 마찰계수, 압력, 수두손실 등의 결합에 있어 매우 중요한 인자이다. 그러나 마찰 수두손실, 마찰속도 등 마찰인자를 정확히 산정하는 것은 매우 어려우며, 경험적 마찰 인자는 여전히 약 100년 전에 개발된 공식과 이론을 사용함으로써 산정된다. 따라서, 본 논문에서는 최대유속과 마찰속도 사이의 새로운 공식을 Darcy-Weisbach의 마찰수두 손실공식과 Schlichting 공식 사이의 적분관계 및 회귀분석을 통하여 개발하였다. 개발된 공식을 증명하기 위하여 매끄러운 관 자료가 사용되었으며 제안한 공식은 관측 자료와 비교하여 높은 정확성을 보여준다. 이 연구의 결과는 안정성 향상과 그리드 설계에 사용이 가능할 것으로 판단된다.

• 자원환경지질
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• 제29권3호
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• pp.325-333
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• 1996

폐기물 매립지 내에셔 가스 흐름을 추정하기 위하여 수치 모델을 개발하였다. 가스 흐름은 밀도에 영향 받는 밀도류이고 매립지 내의 매체는 매우 불균질하므로 단순한 수학적 해법으로 가스 흐름을 추정하기 어렵다. Darcy 방정식과 절량 보존의 법칙을 결합하고 이상 기체 방정식을 도입하여 지배방정식을 만들어지고, 이 지배방정식을 유한요소법으로 풀이하였다. 정류상태 모의의 결과는 AIRFLOW 모델에 의한 모의 결과와 일치한다. 부정류 상태 모의 결과는 질량 보존 평가와 일정 시간 후의 결과를 정류상태의 결과와 비교하여 간접적으로 결과의 신뢰성을 평가하였다. 대우건설에서 1993년에 실시한 난지도 매립지 가스 추출 시험 결과를 모델을 사용하여 분석하였다. 개발된 모델은 1994년 재단법인 한국컴퓨터 프로그램 보호회에 등록되었다.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 1993년도 Proceedings of International Conference for Agricultural Machinery and Process Engineering
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• pp.1318-1328
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• 1993

Expression of chinese cabbage was conducted in order to investigate its dewatering behavior. Chipped cabbage was packed into cylinder and pressed by piston up to the predetermined pressure on Instron-1000. The rates of dewatering were affected domintantly by the applied pressure, but not significantly by the packed amount of cabbage in the cylinder. The pressure effect was increased very abruptly at first, but the increase rate was very low at high pressure greater than 20 MPa, showing great deviation from linear dependence of flow rate on pressure in Darcy's Law. Therefore, water expression from cabbage was not Newtonian flow of water through cell wall. In fact, the squeezed water contained a lot of solid particles, showing destruction of cell wall. The content of solid particles in expressed water was only slightly lower than the dry matter content of fresh chinese cabbage, determined by drying oven method.

• Journal of Biosystems Engineering
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• 제19권1호
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• pp.3-8
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• 1994

An experiment on the expression and dewatering of chinese cabbage was conducted in order to investigate its dewatering behavior. Chopped cabbage was packed into cylinder and pressed by piston upto the predetermined pressure on Instron-1000. The rates of dewatering were affected domintantly by the applied pressure, but not significantly by the packed amount of cabbage in the cylinder. The pressure effect was increased very abruptly at first, but the increase rate was very low at high pressure greater than 20 MPa, showing great deviation from linear dependence of flow rate on pressure in Darcy's Law. Therefore, water expression from cabbage was not Newtonian flow of water through cell wall. In fact, the squeezed water contained a lot of solid particles, about 3% of solid cabbage particles, showing destruction of cell wall. It appeared that compression and dewatering of vegetable wastes in the low pressure. under 20 MPa, is more desirable for later treatment of the dewater. More researches are needed in order to develop a treatment method for the solid particles in the expressed water before an expeller treatment system can be applied to vegetable wastes.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 춘계학술대회논문집
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• pp.98-105
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• 1997

The behaviour of alloys in the semi-solid state strongly depends on the imposed stress state and on the morphology of the phase which can very from dendritic to globular. The estimation of behaviour characteristic in the compression simulation with seim-solid materials are calculated by finite element method with proposed algorithm. The proposed theoretical model and a various boundary conditions for compression process is investigated with the coupling calculation between the liquid phase flow and the solid phase deformation. The simulation process considering soldification phenomena is performed to the isothermal conditions of two dimensional problems. To analysis of compression process by using semi-solid materials, a new stress-strain relationship is described, and compression analysis is performed by viscoelastic model for the solid phase and the Darcy's law for the liquid flow. The calculated results for compression force and ram displacement will be compared to experimental data.

• 한국전산유체공학회지
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• 제21권4호
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• pp.19-27
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• 2016

The flow analyses through a porous hydraulic fractures is among the most important tasks in recently developed shale reservoirs but is rendered difficult by non-Darcy effects and geometric changes in the hydraulic fractures during production. In this study, several Computational Fluid Dynamics(CFD) models of hydraulic fractures, with a simple shape such as that of parallel plates, filled with proppants were built. Direct Numerical Simulation(DNS) analyses were then carried out to examine the flow loss characteristics of the fractures. The hydraulic diameters for the simulation models were calculated using the DNS results, and then they were compared with the results from Kozeny's definition of hydraulic diameter which is most widely used in the flow analysis field. Also, the characteristic parameters based on both hydraulic diameters were estimated for the investigation of the flow loss variation features. Consequently, it was checked in this study that the hydraulic diameter based on Kozeny's definition is not accordant to the results from the DNS analyses, and the case using the CFD results exhibits f Re robustness like general pipe flows, whereas the other case using Kozeny's definition doesn't. Ultimately, it is expected that discoveries reported in this study would help further porous flow analyses such as hydraulic fracture flows.