• Computers and Concrete
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• 제31권6호
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• pp.485-499
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• 2023

Both damage and unsaturated conditions accelerate the transport of erosive media inside concrete. However, their combined effects have not been fully investigated. A multiscale mortar model using representative volume elements is developed, capturing the number and distribution in each phase. Afterwards, mortar damage microstructure evolution is simulated in the tensile process. Finally, the unsaturated mortar transport is predicted and analysed. The results indicate that damage significantly affects the diffusion process in the early stage, while the transport performance is weakened due to the obstruction of the nontransport phase in the later stage. The higher the saturation and the more connected pores, the faster the diffusion rate of chloride ions. Chloride ions spread around the cracks in a tree-like manner along. The model can very well predict the chloride ion transport performance of unsaturated and damaged mortar.

• 에너지공학
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• 제17권4호
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• pp.233-240
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• 2008

최근 새로운 2계 자기 수반형(self-adjoint) 중성자 수송 방정식으로 기존의 우성 및 기성 수송 방정식 외에 SAAF(Self-Adjoint Angular Flux) 수송 방정식이 소개되어, 이에 대한 적절한 경계조건, 수치해법, 정확도 등에 관한 논의가 활발히 진행되고 있다. 본 연구에서는 SAAF 수송 방정식의 수학적, 물리적 의미를 고찰하고 기존의 우성 및 기성 수송 방정식과의 연관성을 명확히 하였으며, Boltzmann 수송 방정식의 1계 차분식에서 2계의 SAAF 수송 방정식의 차분식을 유도하는 방법을 확산 가속법(diffusion synthetic acceleration method)과 함께 소개하였다. 유도된 SAAF 차분법이 계산 효율성과 수송해의 정확도를 증가시킴을 수치결과로 확인하였다.

• 한국전산유체공학회지
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• 제19권1호
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• pp.15-20
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• 2014

Accurate simulation of free-surface wave flows around a ship is very important for better hull-form design. In this paper, a computational fluid dynamics (CFD) code, termed SNUFOAM, which is based on the open source libraries, OpenFOAM, was developed to predict the wave patterns around a ship. Additional anti-diffusion source term for minimizing a numerical diffusion, which was caused by convection differencing scheme, was considered in the volume-fraction transport equation. The influence of the anti-diffusion source term was tested by applying it to free-surface wave flow around the Wigley model ship. In results, the band width of the volume fraction contours between 0.1 to 0.9 at the hull surface was narrowed by considering the anti-diffusion term.

• Fisheries and Aquatic Sciences
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• 제7권2호
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• pp.90-95
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• 2004

An analytical model for predicting the convection-diffusion of solute dumped in a homogeneous open sea of constant water depth has been developed in a time-integral form. The model incorporates spatially uniform, uni-directional, mean and oscillatory currents for horizontal convection, the settling velocity for the vertical convection, and the anisotropic turbulent diffusion. Two transformations were introduced to reduce the convection-diffusion equation to the Fickian type diffusion equation, and then the Galerkin method was then applied via the expansion of eigenfunctions over the water column derived from the Sturm-Liouville problem. A series of calculations has been performed to demonstrate the applicability of the model.

• Archives of Pharmacal Research
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• 제11권2호
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• pp.81-86
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• 1988

The transfer of cupric sulfate across the rat small intestine in vitro was studied by perfusion method using the segments of everted rat small intestine. Copper transport was approximately propotional to the metal concentration in the mucosal solution and no difference was observed in the metal transport among rat duodenum, jejunum and ileum. It was suggested from these results that copper transport across the rat small intestine would occur by passive diffusion. The effect of various chelating agents on copper transport across the rat small intestine n vitro and its uptake by the intestine were also studied. Copper transport was greatly enhanced in the presence of EDTA and NTA. Copper uptake decreased to a greater extent in the presence of EPTA and NTA.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.311-312
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• 2010

The fabricated photovoltaic cells based on PIN heterojunctions, in this study, have a structure of ITO/poly(3, 4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS)/donor/donor:C60(10nm)/C60(35nm)/2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline(8nm)/Al(100nm). The thicknesses of an active layer(donor:C60), an electron transport layer(C60), and hole/exciton blocking layer(BCP) were fixed in the organic photovoltaic cells. We investigated the performance characteristics of the PIN organic photovoltaic cells with copper phthalocyanine(CuPc), tetracene and pentacene as a hole transport layer. Discussion on the photovoltaic cells with CuPc, tetracene and pentacene as a hole transport layer is focussed on the dependency of the power conversion efficiency on the deposition rate and thickness of hole transport layer. The device performance characteristics are elucidated from open-circuit-voltage(Voc), short-circuit-current(Jsc), fill factor(FF), and power conversion efficiency($\eta$). As the deposition rate of donor is reduced, the power conversion efficiency is enhanced by increased short-circuit-current(Jsc). The CuPc-based PIN photovoltaic cell has the limited dependency of power conversion efficiency on the thickness of hole transport layer because of relatively short exciton diffusion length. The photovoltaic cell using tetracene as a hole transport layer, which has relatively long diffusion length, has low efficiency. The maximum power conversion efficiencies of CuPc, tetracene, and pentacene-based photovoltaic cells with optimized deposition rate and thickness of hole transport layer have been achieved to 1.63%, 1.33% and 2.15%, respectively. The photovoltaic cell using pentacene as a hole transport layer showed the highest efficiency because of dramatically enhanced Jsc due to long diffusion length and strong thickness dependence.

• Computers and Concrete
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• 제11권3호
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• pp.201-222
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• 2013

A comprehensive simulation model for the transport process of fully coupled moisture and multi-species in non-saturated concrete structures is proposed. The governing equations of moisture and ion diffusion are formulated based on Fick's law and the Nernst-Planck equation, respectively. The governing equations are modified by explicitly including the coupling terms corresponding to the coupled mechanisms. The ionic interaction-induced electrostatic potential is described by electroneutrality condition. The model takes into account the two-way coupled effect of moisture diffusion and ion transport in concrete. The coupling parameters are evaluated based on the available experimental data and incorporated in the governing equations. Differing from previous researches, the material parameters related to moisture diffusion and ion transport in concrete are considered not to be constant numbers and characterized by the material models that account for the concrete mix design parameters and age of concrete. Then, the material models are included in the numerical analysis and the governing equations are solved by using finite element method. The numerical results obtained from the present model agree very well with available test data. Thus, the model can predict satisfactorily the ingress of deicing salts into non-saturated concrete.

• Nuclear Engineering and Technology
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• 제45권6호
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• pp.707-720
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• 2013

We analyze piecewise homogenization with flux-weighted cross sections and preservation of averaged currents at the boundary of the homogenized domain. Introduction of a set of flux discontinuity ratios (FDR) that preserve reference interface currents leads to preservation of averaged region reaction rates and fluxes. We consider the class of numerical discretizations with one degree of freedom per volume and per surface and prove that when the homogenization and computing meshes are equal there is a unique solution for the FDRs which exactly preserve interface currents. For diffusion submeshing we introduce a Jacobian-Free Newton-Krylov method and for all cases considered obtain an 'exact' numerical solution (eight digits for the interface currents). The homogenization is completed by extending the familiar full assembly homogenization via flux discontinuity factors to the sides of regions laying on the boundary of the piecewise homogenized domain. Finally, for the familiar nodal discretization we numerically find that the FDRs obtained with no submesh (nearly at no cost) can be effectively used for whole-core diffusion calculations with submesh. This is not the case, however, for cell-centered finite differences.

• Korean Chemical Engineering Research
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• 제57권3호
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• pp.338-343
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• 2019

고분자전해질 연료전지에서 전해질막의 물이동과 함수율은 고분자막의 성능에 많은 영향을 미친다. 본 연구에서는 간단한 방법에 의해 물이동에 관한 고분자막의 물성(전기삼투계수, 물 확산계수)을 측정하고 이들을 이용해 막을 통한 물의 이동량과 이온전도도를 모델식에 의해 모사한 후 실험값과 비교하였다. 물이동의 구동력은 전기삼투와 확산만이 라고 본 1차원 정상상태 지배방정식을 매트랩으로 수치해석하였다. $144{\mu}m$ 두께의 고분자막의 전기삼투계수를 수소펌핑셀에서 구한 결과 1.11을 얻었다. 물확산계수를 상대습도의 함수로 나타냈고 물확산에 대한 활성화에너지는 $2,889kJ/mol{\cdot}K$였다. 이들 계수를 적용해 모사한 물이동량과 이온전도도 결과는 실험값과 잘 일치함을 보였다.

• 멤브레인
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• 제8권3호
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• pp.148-156
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• 1998

이온교환막을 이용하는 확산투석은 농도차가 구동력인 막공정으로서 철강 산업, 금속 제련 산업, 전기 도금 산업 등으로부터 발생되어지는 폐산으로부터 염산 및 기타 산들을 회수하는데 사용된다. 이론적으로는 초기산 농도가 증가함에 따라 구동력인 농도차가 커지므로 선형적으로 산의 투과속도가 증가하게 된다. 그러나 염산의 경우 약 3 N 이상의 고농도 범위에서는 투과속도 증가율이 농도차가 커짐에 따라 감소하였다. 본 연구에서는 막흡수 실험과 확산투석조 실험을 통해 염산을 회수하기 위한 확산투석에 산의 농도가 미치는 영향과 농도 범위에 따른 음이온 교환막 내부에서의 산의 이동 기작을 고찰하였다. 실험 결과 저농도(<2 N)산의 경우에는 산의 분자확산, 그리고 고농도 (>2 N)산의 경우에는 수소이온 투과현상 (proton leakage)이 막에서의 지배적인 이동 기작임을 알 수 있었다. 또한 고농도 범위에서는 삼투압에 의한 물분자의 이동과 막의 탈수현상이 수소이온의 이동을 방해하므로 막에서의 산 플럭스 증가율이 감소하였다.