• 터널과지하공간
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• 제11권3호
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• pp.257-269
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• 2001

지하 500 m의 화강암반내 단층지역에 위치한 지하 방사성폐기물 처분장의 구조거동을 이해하기 위하여 수치 해석을 수행하였다. 해석에는 2차원 해석코드인 UDEC을 사용하였다. 해석모델은 화강암반, 처분공내의 압축 벤토나이트로 둘러싸인 PWR 사용후 핵연료 처분용기 및 처분동굴내에 채워진 혼합 벤토나이트를 포함한다. 한 개의 단층이 처분동굴의 지붕과 벽이 만나는 지점을 33, 45, 및 $58^{\circ}$의 각도로 관통하는 세가지 다른 경우게 대한 구조거동을 비교, 분석하였다. 그리고 $45^{\circ}$단층의 경우에 대해서는 수리역학적, 열역학적, 및 열수리역학적 상호작용 거동을 해석하고 비교, 분석하였다. PWR 사용후 핵연료내의 방사성 물질로부터 나오는 시간의존 방사성 붕괴열에 의한 영향을 해석하였다. 지하수위는 지표면 아래 10 m로 가정하였고, 지하수해석은 정류 알고리즘을 사용하였다.

• Journal of Biosystems Engineering
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• 제25권3호
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• pp.213-220
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• 2000

Grafting of fruit-bearing vegetables has been widely used to increase the resistance to soil-borne diseases, to increase the tolerance to low temperature or to soil salinity, to increase the plant vigor, and to extend the duration of economic harvest time. After grafting, it is important to control the environment around grafted seedlings for the robust joining of a scion and rootstock. Usually the shading materials and plastic films are used to keep the high relative humidity and low light intensity in greenhouse or tunnel. It is quite difficult to optimally control the environment for healing and acclimation of grafted seedlings under natural light. So the farmers or growers rely on their experience for the production of grafted seedling with high quality. If artificial light is used as a lighting source for graft-taking of grafted seedlings, the light intensity and photoperiod can be easily controlled. The purpose of this study was to develop a prototype system for the graft-taking enhancement of grafted seedlings using artificial lighting and to investigate the effect of air current speed on the distribution of air temperature and relative humidity in a graft-taking enhancement system. A prototype graft-taking system was consisted by polyurethane panels, air-conditioning unit, system controller and lighting unit. Three band fluorescent lamps (FL20SEX-D/18, Kumho Electric, Inc.) were used as a lighting source. Anemometer (Climomaster 6521, KANOMAX), T-type thermocouples and humidity sensors (CHS-UPS, TDK) were used to measure the air current speed, air temperature and relative humidity in a graft-taking system. In this system, air flow acted as a driving force for the diffusion of heat and water vapor. Air current speed, air temperature and relative humidity controlled by a programmable logic controller (UP750, Yokogawa Electric Co) and an inverter (MOSCON-G3, SAMSUNG) had an even distribution. Distribution of air temperature and relative humidity in a graft-taking enhancement system was fairly affected by air current speed. Air current speed higher than 0.1m/s was required to obtain the even distribution of environmental factors in this system. At low air current speed of 0.1m/s, the evapotranspiration rate of grafted seedlings would be suppressed and thus graft-taking would be enhanced. This system could be used to investigate the effects of air temperature, relative humidity, air current speed and light intensity on the evaportranspiration rate of grafted seedlings.

• 터널과지하공간
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• 제23권3호
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• pp.169-179
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• 2013

치밀 또는 셰일가스층과 같은 비전통 저류층에서 물성을 구할 때 기존의 전통 가스정 시험법을 적용하면 올바른 결과값을 얻을 수 없다. 일반적으로 셰일가스 저류층에서는 지층의 저투과성으로 인해 유동 속도가 느려 방사형 유동 구간이 나타나기까지의 시간이 매우 오래 걸리며 수압파쇄 후에는 방사형 유동 구간이 전혀 나타나지 않을 수도 있다. 이로 인해 시험 비용이 많이 들 뿐만 아니라 결과값의 정확도 또한 매우 낮다. 이러한 이유로 셰일가스 저류층 물성 분석법으로 DFIT(diagnostic fracture injection test)이 새롭게 주목받고 있다. 수압파쇄 전에 수행되는 DFIT은 셰일가스의 중요성이 커져감에 따라 저류층의 물성을 얻기 위한 가장 실용적인 방법 중의 하나로 알려져 있다. DFIT 데이터를 분석하는 방법에는 여러 가지가 있으며 한 가지 방법으로는 데이터를 잘못 분석할 수 있기 때문에 다양한 방법을 통해서 종합적으로 물성을 분석하는 것이 매우 중요하다. 본 연구에서는 이러한 다양한 DFIT 분석법들에 대해 설명하고 이를 통해 3개 저류층의 DFIT 데이터에서 여러 가지 분석법들이 어떻게 적용되는지 비교, 분석하여 정확한 저류층 물성을 얻고자 하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.671-679
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• 2008

The effect of Pre-cooled Turbojet Engine installation and nozzle exhaust jet on Hypersonic Turbojet EXperimental aircraft(HYTEX aircraft) were investigated by three-dimensional numerical analyses to obtain aerodynamic characteristics of the aircraft during its in-flight condition. First, simulations of wind tunnel experiment using small scale model of the aircraft with and without the rectangular duct reproducing engine was performed at M=5.1 condition in order to validate the calculation code. Here, good agreements with experimental data were obtained regarding centerline wall pressures on the aircraft and aerodynamic coefficients of forces and moments acting on the aircraft. Next, full scale integrated analysis of the aircraft and the engine were conducted for flight Mach numbers of M=5.0, 4.0, 3.5, 3.0, and 2.0. Increasing the angle of attack $\alpha$ of the aircraft in M=5.0 flight increased the mass flow rate of the air captured at the intake due to pre-compression effect of the nose shockwave, also increasing the thrust obtained at the engine plug nozzle. Sufficient thrust for acceleration were obtained at $\alpha=3$ and 5 degrees. Increase of flight Mach number at $\alpha=0$ degrees resulted in decrease of mass flow rate captured at the engine intake, and thus decrease in thrust at the nozzle. The thrust was sufficient for acceleration at M=3.5 and lower cases. Lift force on the aircraft was increased by the integration of engine on the aircraft for all varying angles of attack or flight Mach numbers. However, the slope of lift increase when increasing flight Mach number showed decrease as flight Mach number reach to M=5.0, due to the separation shockwave at the upper surface of the aircraft. Pitch moment of the aircraft was not affected by the installation of the engines for all angles of attack at M=5.0 condition. In low Mach number cases at $\alpha=0$ degrees, installation of the engines increased the pitch moment compared to no engine configuration. Installation of the engines increased the frictional drag on the aircraft, and its percentage to the total drag ranged between 30-50% for varying angle of attack in M=5.0 flight.

• 터널과지하공간
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• 제30권6호
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• pp.573-590
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• 2020

본 논문에서는 국제공동연구인 DECOVALEX-2023 프로젝트 Task G의 연구 현황과 현재까지 수행된 benchmark 해석 결과를 소개하였다. Task G의 명칭은 'Safety ImplicAtions of Fluid Flow, Shear, Thermal and Reaction Processes within Crystalline Rock Fracture NETworks(SAFENET)'로, 결정질 암반 내 균열의 생성과 성장 메커니즘 및 균열에서 발생하는 열-수리-역학적 복합거동을 해석하기 위한 수치해석기법을 개발하는 데에 목표가 있다. Task G의 첫 번째 연구 테마는 결정질 암석 내 단일 균열의 역학적 거동에 대한 해석해(analytical solution)를 바탕으로 각 연구팀의 수치모델링기법을 개발 및 검증하는 Benchmark 해석이다. 본 연구에서는 3차원 입자기반 개별요소모델을 이용하여 단일 균열을 포함한 암석의 역학적 거동 특성을 모델링하고자 하였다. 이 모델에서는 상호독립적으로 거동하는 개별입자의 집합체를 통해 암석의 구조적 특징을 모사하고, 입자와 입자간 접촉에서 발생하는 역학적 거동을 개별요소해석모델인 3DEC을 통해 계산하게 된다. 해석 결과, 도메인의 경계응력으로 인해 균열에 유도되는 수직응력과 전단응력 수준은 변위 구속과 응력 재배치로 인해 이론적인 수치보다 낮게 나타났다. 그러나 수치모델에서 계산된 수직변위와 전단변위는 실제 균열의 유도 응력을 통해 추정된 해석해와 비교할 때 상당히 유사한 결과를 보였으며 균열의 응력-변위 관계를 합리적으로 재현할 수 있음을 확인하였다. 본 연구의 해석모델은 Task G에 참여하는 국외 연구팀들과의 의견 교류와 워크숍을 통해 지속적으로 개선하는 한편, 향후 다양한 조건의 실내시험에 적용하여 타당성을 검증할 예정이다.

• 지적과 국토정보
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• 제51권2호
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• pp.5-20
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• 2021

지하공간통합지도는 2014년도에 전국적으로 발생했던 싱크홀을 계기로 15종의 지하정보를 통합한 국가공간정보로서, 2015년부터 지속적으로 구축되고 있다. 그러나 최근까지도 온수관 파열, 통신구 화재, 지반 침하 등과 같은 지하공간에서의 재난·재해가 지속적으로 발생함에 따라 지하정보의 품질 향상에 대한 요구가 증대되고 있는 실정이다. 이에 본 논문에서는 지하공간통합지도 데이터의 품질 향상을 위한 방안을 마련하고자 하였다. 특히 지하공간통합지도를 통해 관리되는 15종의 지하정보 중 신규 구축 비중이 가장 높은 지하시설물(구조물형) 데이터의 품질검증 개선 방안을 제시하였다. 대부분 육안검수로 진행되고 있는 현재의 검수 방식을 개선하기 위해 품질검사 기준을 좀 더 구체화·세분화하고자 하였다. 이를 위해 현재 품질요소, 세부요소, 세세부요소, 품질검사 기준으로 구성된 검사항목에 품질검사 방법, 품질검사 규칙, Flow Diagram, 해결 가능 오류 유형 항목을 추가하여 속성정보 뿐 아니라 도형정보까지 소프트웨어로 자동검수하기 위한 알고리즘을 개발하였다.

• Wind and Structures
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• 제34권1호
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• pp.127-136
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• 2022

In this work a multi-fidelity non-intrusive polynomial chaos (MF-NIPC) has been applied to a structural wind engineering problem in architectural design for the first time. In architectural design it is important to design structures that are safe in a range of wind directions and speeds. For this reason, the computational models used to design buildings and bridges must account for the uncertainties associated with the interaction between the structure and wind. In order to use the numerical simulations for the design, the numerical models must be validated by experi-mental data, and uncertainties contained in the experiments should also be taken into account. Uncertainty Quantifi-cation has been increasingly used for CFD simulations to consider such uncertainties. Typically, CFD simulations are computationally expensive, motivating the increased interest in multi-fidelity methods due to their ability to lev-erage limited data sets of high-fidelity data with evaluations of more computationally inexpensive models. Previous-ly, the multi-fidelity framework has been applied to CFD simulations for the purposes of optimization, rather than for the statistical assessment of candidate design. In this paper MF-NIPC method is applied to flow around a rectan-gular 5:1 cylinder, which has been thoroughly investigated for architectural design. The purpose of UQ is validation of numerical simulation results with experimental data, therefore the radius of curvature of the rectangular cylinder corners and the angle of attack are considered to be random variables, which are known to contain uncertainties when wind tunnel tests are carried out. Computational Fluid Dynamics (CFD) simulations are solved by a solver that employs the Finite Element Method (FEM) for two turbulence modeling approaches of the incompressible Navier-Stokes equations: Unsteady Reynolds Averaged Navier Stokes (URANS) and the Large Eddy simulation (LES). The results of the uncertainty analysis with CFD are compared to experimental data in terms of time-averaged pressure coefficients and bulk parameters. In addition, the accuracy and efficiency of the multi-fidelity framework is demonstrated through a comparison with the results of the high-fidelity model.

• 터널과지하공간
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• 제33권5호
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• pp.399-413
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• 2023

본 연구에서는 TOUGH-FLAC 연동해석 기법을 사용하여 장기분지 유망 저장소 부지에서의 CO₂ 주입을 수치적으로 모델링하고, 주변 지층과 단층에 야기되는 수리-역학적 안정성을 검토하였다. 대상부지의 현장조사와 3D 지질모델을 기반으로 3년간 32,850톤의 CO₂ 주입을 가정하여 시뮬레이션을 수행하였다. 저류층의 투수계수에 따른 CO₂ 플럼의 유동 경로를 분석한 결과, 투수계수를 10^-14 m²로 가정한 경우 방사형 유동을 보이며 2년 9개월 경과 시 단층에 도달하는 것으로 나타났다. 투수계수를 10^-13 m²로 가정한 경우에는 저류층을 따라 서쪽 방향의 유동이 우세하게 나타났으며 단층 방향으로의 유동은 거의 발생하지 않았다. 주입공 주변의 압력 변화는 3년 동안 0.6 MPa 이하로, 지층 및 단층의 역학적 안정성에 미치는 영향은 미미한 것으로 분석되었다.

• Journal of Cardiovascular Imaging
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• 제30권2호
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• pp.99-108
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• 2022

BACKGROUND: Adding pulsation to the Fontan circulation might change the fate of patients palliated by this procedure. Our aim was to compare the pulsatility index (PI) of the pulmonary artery (PA) between the various modifications of Fontan palliation. METHODS: Doppler-derived PI was measured in PA branches of a cohort of 28 patients palliated by 6 modifications of Fontan procedure. A group of normal individuals was included for comparison. RESULTS: Atriopulmonary connection (APC) group had the highest PA branches PI and statistically was close to the PI of the normal individuals (right pulmonary artery [RPA] PI of 1.58 vs. 1.63; p = 0.99 and left pulmonary artery [LPA] PI of 1.54 vs. 1.68; p = 0.46, respectively). The lowest PA branches PI was seen in the group of extracardiac total cavopulmonary connection (RPA PI of 0.62 and LPA PI of 0.65). Other 4 modifications including the extracardiac conduit with oversewn pulmonary valve, extracardiac conduit with preserved adjusted antegrade flow, extracardiac conduit from inferior vena cava onto the rudimentary right ventricle and lateral tunnel had a mean "RPA and LPA" PI of "1.19 and 1.17", "1.16 and 1.11", "1.13 and 1.11", "0.82 and 0.84", respectively. The modified Dunnett's post hoc test has shown a significant statistical decline in PI of all modifications compared to the normal individuals except for the APC group. CONCLUSIONS: Fontan palliated patients in different groups of surgical modification showed a spectrum of Doppler-derived PI with the highest amounts belong to the groups of pulsatile Fontan.

• 설비공학논문집
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• 제20권12호
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• pp.844-861
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• 2008

The papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during the year of 2007 have been reviewed. Focus has been put on current status of research in the aspect of heating, cooling, ventilation, sanitation and building environments. The conclusions are as follows. (1) The research trends of fluid engineering have been surveyed as groups of general fluid flow, fluid machinery and piping, etc. New research topics include micro nano fluid, micropump and fuel cell. Traditional CFD was still popular and widely used in research and development. Studies about fans and pumps were performed in the field of fluid machinery. Characteristics of flow and fin shape optimization are studied in the field of piping system. (2) The research works on heat transfer have been reviewed in the field of heat transfer characteristics, heat exchangers, and desiccant cooling systems. The research on heat transfer characteristics includes thermal transport in pulse tubes, high temperature superconductors, ground heat exchangers, fuel cell stacks and ice slurry systems. For the heat 'exchangers, the research on pin-tube heat exchanger, plate heat exchanger, condensers and gas coolers has been cordially implemented. The research works on heat transfer augmenting tubes have been also reported. For the desiccant cooling systems, the studies on the design and operating conditions for desiccant rotors as well as performance index are noticeable. (3) In the field of refrigeration, many papers were presented on the air conditioning system using CO2 as a refrigerant. The issues on the two-stage compression, the oil selection, and the appropriate oil charge were treated. The subjects of alternative refrigerants were also studied steadily. Hydrocarbons, DME and their mixtures were considered and various heat transfer correlations were proposed. (4) Research papers have been reviewed in the field of building facilities by grouping into the researches on heat and cold sources, air conditioning and air cleaning, ventilation and fire research including tunnel ventilation, flow control of piping system, and sound research with drain system. Main focuses have been addressed to the promotion of efficient or effective use of energy, which helps to save energy and results in reduced environmental pollution and operating cost. (5) Studies were mostly focused on analyzing the indoor environment in various spaces like cars, old tombs, machine rooms, and etc. in an architectural environmental field. Moreover, subjects of various fields such as the evaluation of noise, thermal environment, indoor air quality and development of energy analysis program were researched by various methods of survey, simulation, and field experiment.