• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제51권5호
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• pp.242-248
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• 2002

It is important to develop new effective technologies to increase the interruption capacity and to reduce the size of a UB(Gas Circuit Breakers). Major design parameters such as nozzle geometries and interrupting chamber dimensions affect the cooling of the arc and the breaking performance. But it is not easy to test real GCB model in practice as in theory. Therefore, a simulation tool based on a computational fluid dynamics(CFD) algorithm has been developed to facilitate an optimization of the interrupter. Special attention has been paid to the supersonic flow phenomena between contacts and the observation of hat-gas flow for estimating the breaking performance. However, there are many difficult problems in calculating the flow characteristics in a GCB such as shock wave and complex geometries, which may be either static or in relative motion. Although a number of mesh generation techniques are now available, the generation of meshes around complicated, multi-component geometries like a GCB is still a tedious and difficult task for the computational fluid dynamics. This paper presents the CFD program using CFB-CAD integration technique based on Cartesian cut-cell method, which could reduce researcher's efforts to generate the mesh and achieve the accurate representation of the geometry designed by a CAD tools.

• 한국유체기계학회 논문집
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• 제16권5호
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• pp.5-10
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• 2013

The regenerative pump is a kind of turbomachine which is capable of developing high pressure rise at relatively lower flow rates compared to the centrifugal and axial pumps. Although the efficiency of regenerative pumps is much lower than other turbomachines, still they have been widely used in many industrial applications for working at low specific speeds. There are some theoretical models to analysis the pump performance, however, the effect of the blade angle on the pump performance has not been covered in any model to date. In the present study, experimental study on the regenerative pump performance according to the impeller blade angle and its shape has been carried out. The straight radial blades with forward, backward and chevron blades which have inclined angles of $15^{\circ}$, $30^{\circ}$ and $45^{\circ}$ were tested. The pump performance characteristics as the pressure head, efficiency were obtained depending on the flow rate for every impeller, and their results, expressed in appropriate non-dimensional coefficients, were compared and analysed in detail. From the experimental results, it was found that the pressure head and the efficiency depend strongly on the blade angles as well as the blade type. These experimental data has made it possible to better understand the effects of the blade angle on the pump performance, and widen the applicability of the current performance analysis and design models with including the effect of blade angles.

• International Journal of Fluid Machinery and Systems
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• 제4권2호
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• pp.271-288
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• 2011

The mathematical modelling of screw compressor processes and its implementation in their design began about 30 years ago with the publication of several pioneering papers on this topic, mainly at Purdue Compressor Conferences. This led to the gradual introduction of computer aided design, which, in turn, resulted in huge improvements in these machines, especially in oil-flooded air compressors, where the market is very competitive. A review of progress in such methods is presented in this paper together with their application in successful compressor designs. As a result of their introduction, even small details are now considered significant in efforts to improve performance and reduce costs. Despite this, there are still possibilities to introduce new methods and procedures for improved rotor profiles, design optimisation for each specified duty and specialized compressor design, all of which can lead to a better product and new areas of application. A review of methods and procedures which lead to modern screw compressor practice is presented in this paper. This paper is intended to give a cross section through activities being done in mathematical modelling of screw compressor process through last five decades. It is expected to serve as a basis for further contributions in the area and as a challenge to the forthcoming generations of scientists and engineers to concentrate their efforts in finding future and more extended approaches and submit their contributions.

• 한국지반공학회논문집
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• 제27권9호
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• pp.77-86
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• 2011

지반 물질의 열전도도는 경험식이 제안하는 단위 중량, 간극률 등의 영향 인자 이외에도 하중조건에 따라 크게 좌우된다. 본 논문에서는 개별요소법에 의해 생성된 입자상 지반재료의 열 전달 특성을 열 네트워크 모델로 해석하여 하중이 열전도도에 미치는 영향을 평가하였다. 하중의 변화에 의한 개별 입자들간의 접촉수 및 간극률, 간극수의 전도도에 따른 열전도도를 산출하여 영향 요소들간의 관계를 분석하였다. 전도도의 변화 양상은 전단강성도 분석과 유사하게 열전달 방향 및 하중 크기에 따른 멱함수 형태로 회귀분석이 가능하였다. 해석 결과 하중에 따른 입자간 접촉 면적의 증가 및 간극수의 전도도가 전체 입자상 물질의 열 흐름에 큰 영향을 미침을 알 수 있었다. 열전도도의 이방성은 하중 방향에 의해 좌우되며 입자 스케일에서의 매커니즘이 열 흐름을 좌우하는 중요한 인자임을 보였다.

• Nuclear Engineering and Technology
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• 제38권2호
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• pp.147-154
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• 2006

Thermal fatigue of the coolant circuits of PWR plants is a major issue for nuclear safety. The problem is especially accute in mixing zones, like T-junctions, where large differences in water temperature between the two inlets and high levels of turbulence can lead to large temperature fluctuations at the wall. Until recently, studies on the matter had been tackled at EDF using steady methods: the fluid flow was solved with a CFD code using an averaged turbulence model, which led to the knowledge of the mean temperature and temperature variance at each point of the wall. But, being based on averaged quantities, this method could not reproduce the unsteady and 3D effects of the problem, like phase lag in temperature oscillations between two points, which can generate important stresses. Benefiting from advances in computer power and turbulence modelling, a new methodology is now applied, that allows to take these effects into account. The CFD tool Code_Saturne, developped at EDF, is used to solve the fluid flow using an unsteady L.E.S. approach. It is coupled with the thermal code Syrthes, which propagates the temperature fluctuations into the wall thickness. The instantaneous temperature field inside the wall can then be extracted and used for structure mechanics computations (mainly with EDF thermomechanics tool Code_Aster). The purpose of this paper is to present the application of this methodology to the simulation of a straight T-junction mock-up, similar to the Residual Heat Remover (RHR) junction found in N4 type PWR nuclear plants, and designed to study thermal striping and cracks propagation. The results are generally in good agreement with the measurements; yet, in certain areas of the flow, progress is still needed in L.E.S. modelling and in the treatment of instantaneous heat transfer at the wall.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.353-362
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• 2009

In the process of turbine modernizations, the investigation of the influences of water passage roughness on radial flow machine performance is crucial and validates the efficiency step up between reduced scale model and prototype. This study presents the specific losses per component of a Francis turbine, which are estimated by CFD simulation. Simulations are performed for different water passage surface roughness heights, which represents the equivalent sand grain roughness height. As a result, the boundary layer logarithmic velocity profile still exists for rough walls, but moves closer to the wall. Consequently, the wall friction depends not only on roughness height but also on its shape and distribution. The specific losses are determined by CFD numerical simulations for each component of the prototype, taking into account its own specific sand grain roughness height. The model efficiency step up between reduced scale model and prototype value is finally computed by the assessment of specific losses on prototype and by evaluating specific losses for a reduced scale model with smooth walls. Furthermore, surveys of rough walls of each component were performed during the geometry recovery on the prototype and comparisons are made with experimental data from the EPFL Laboratory for Hydraulic Machines reduced scale model measurements. This study underlines that if rough walls are considered, the CFD approach estimates well the local friction loss coefficient. It is clear that by considering sand grain roughness heights in CFD simulations, its forms a significant part of the global performance estimation. The availability of the efficiency field measurements provides an unique opportunity to assess the CFD method in view of a systematic approach for turbine modernization step up evaluation. Moreover, this paper states that CFD is a very promising tool for future evaluation of turbine performance transposition from the scale model to the prototype.

• Pediatric Infection and Vaccine
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• 제13권2호
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• pp.174-179
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• 2006

국내에서는 아직도 소아연령에서 결핵 감염이 적지 않게 존재하기 때문에 폐외 결핵 환자가 발생될 위험도 지속적으로 존재한다. 이런 측면에서 폐외 결핵의 하나인 골관절 결핵은 매우 드물기는 하나, 관절염을 주소로 내원한 환자의 원인으로 고려해 볼만하다. 나이 어린 소아에서는 증상과 징후가 비특이적이기 때문에 오진이나 진단 지연이 우려되므로, 항생제 치료에 잘 반응하지 않는 관절염 환자에서는 결핵성 골관절염에 대한 진단과 치료를 시도하는 것이 중요하다.

• 한국자동차공학회논문집
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• 제16권6호
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• pp.74-80
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• 2008

A combustion of CAI engine is purely dominated by fuel chemical reactions. In order to simulate the combustion of CAI engine, it should be considered the effect of fuel components and chemical kinetics. So it needs enormous computational power. To overcome this problem reduced problem of needing massive computational power, chemical kinetic mechanism and multi-zone method is proposed here in this paper. A reduced chemical kinetic mechanism for a gasoline surrogate was used in this study for a CAI combustion. This gasoline surrogate was modeled as a blend of iso-octane, n-heptane, and toluene. For the analysis of CAI combustion, a multi-zone method as combustion model for a CAI engine was developed and incorporated into the computational fluid dynamics code, STAR-CD, for computing efficiency. This coupled multi-zone model can calculate 3 dimensional computational fluid dynamics and multi-zoned chemical reaction simultaneously in one time step. In other words, every computational cell interacts with the adjacent cells during the chemical reaction process. It can enhance the reality of multi-zone model. A greatly time-saving and yet still relatively accurate CAI combustion simulation model based on the above mentioned two efficient methodologies, is thus proposed.

• 한국수정란이식학회지
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• 제24권4호
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• pp.259-263
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• 2009

Salivary lipocalin (SAL1) is a member of the lipocalin protein family that has a property to associate with many lipophilic molecules and was identified as pheromone-binding protein in pigs. Our previous study has shown that SAL1 is expressed in the uterine endometrium in a cell type- and implantation stage-specific manner and secreted into the uterine lumen in pigs. However, function of SAL1 in the uterus during pregnancy in pigs is still not known. To understand physiological function of SAL1 in the uterine endometrium during pregnancy in pigs, it needs to elucidate the ligand(s) for SAL1. Thus, to identify the ligand for SAL1 in the porcine uterus, we collected uterine luminal fluid from pigs on day 12 of pregnancy by flushing with PBS. Proteins from the uterine luminal fluid were separated by ion exchange chromatography and gel filtration. Fractions containing SAL1 protein were pooled and concentrated. Immunoblot analysis confirmed successful purification of SAL1. Then, we extracted lipids from the purified SAL1 protein and analyzed the lipids by liquid chromatography-mass spectrometry, and predicted to be steroid hormones and prostaglandins as SAL1 ligands. Results in this study showed that SAL1 protein in the uterine secretions has a small lipophilic molecule as a natural ligand. Further characterization of ligand extracted from purified SAL1 will be useful for understanding physiological function of SAL1 during pregnancy and its application to increase the pregnancy rate in pigs.

• 한국해양공학회지
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• 제33권4호
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• pp.313-321
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• 2019

The prediction of the hydrodynamic performance of a planing hull vessel is an important and challenging topic for computational fluid dynamic (CFD) applications to naval hydrodynamics. In this paper, the resistance and planing attitude analysis for a Fridsma hull, which is a prismatic planing hull, in still water are numerically studied using OpenFOAM. OpenFOAM is an open source code package based on C++ libraries and the finite volume method (FVM) for the discretization of the RANS equation. The volume of fluid method (VOF) is used to capture the water-air interface and the SST ${\kappa}-{\omega}$ model is used for the turbulence simulation. The overset mesh method is used to capture the large motion of the hull at higher speeds. Before the extensive analysis, uncertainty analyses using various time steps and grid sizes were performed for one ship speed case of Fn = 1.19. The results of the present study are compared with those of a model test, other CFD research, and Savitsky's empirical formula. The results of the present study, following the trend of other CFD results, slightly over predict the resistance and under predict the sinkage and, more significantly, the trim.