• 한국유체기계학회 논문집
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• 제10권6호
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• pp.17-23
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• 2007

In the present work, flow analysis has been performed in the steam turbine bypass control valve (single-path type) for two different cases i.e., case with steam only and case with both steam and water. The numerical analysis is performed by solving three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations. The shear stress transport (SST) model and $k-{\varepsilon}$ model are used to each different case as turbulence closure. Symmetry condition is applied at the mid plane of the valve while adiabatic condition is used at the outer wall of the cage. Grid independency test is performed to find the optimal number of grid points. The pressure and temperature distributions on the outer wall of the cage are analyzed. The mass flow rate at maximum plug opening condition is compared with the designed mass flow rate. The numerical analysis of multiphase mixing flow(liquid and vapor) is also performed to inspect liquid-vapor volume fraction of bypass valve. The result of volume fraction is useful to estimate both the safety and confidence of valve design.

• International Journal of Automotive Technology
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• 제8권2호
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• pp.165-177
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• 2007

Predictions of diesel particulate filtration are typically made by modeling of a particle collection, and providing particle trapping levels in terms of a pressure drop. In the present study, a series of single channel diesel particulate filter (DPF) experiments are conducted, the pressure traces are inversely analyzed and essential filtration parameters are deducted for model closure. A DPF filtration model is formulated with a non-linear description of soot cake regression. Dependence of soot cake porosity, packing density, permeability, and soot density in filter walls on convective-diffusive particle transportation is examined. Sensitivity analysis was conducted on model parameters, relevant to the mode of transition. Soot cake porosity and soot packing density show low degrees of dispersion with respect to the Peclet number and have asymptotes at 0.97 and $70\;kg/m^3$, respectively, at high Peclet number. Soot density in the filter wall, which is inversely proportional to filter wall Peclet number, controls the filtration mode transition but exerts no influence on termination pressure drop. The percolation constant greatly alters the extent of pressure drop, but is insensitive to volumetric flow rate or temperature of exhaust gas at fixed operation mode.

• 대한기계학회논문집
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• 제13권5호
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• pp.962-978
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• 1989

본 연구에서는 저자들이 이미 발표한 난류 화염에서의 매연 농도 분포 해석을 포함한 화염 구조 및 복사 열전달의 해석에 대한 연구와 관련하여, 난류 화염에서의 생성된 매연 입자의 재연소 속도에 관한 새로운 모델을 제시한다.구체적인 방법 으로, 난류 화염에 대한 난류 지배 방정식의 매듭(closure) 문제로서 문제가 되고 있는 난류 모델과 반응 속도 모델에 대해서는 비교적 잘 정립되어 있다고 할 수 있는 축대칭 분류 유동을 선택하여, 난류 모델과 난류 연소 속도 모델을 고정하고, 난류 화염에서의 매연 생성 및 연소 모델을 검토하였다.

• 대한화상학회지
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• 제23권2호
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• pp.60-63
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• 2020

A 72-year-old man with diabetes, who underwent moxibustion, developed a foot wound but did not receive proper treatment. Examination showed a soft tissue defect (6×6 cm) on the dorsal aspect of the right foot with involvement of the first and second toes along with some phalangeal bone loss. The wound was treated with a skin graft and healed without complications. The right calf showed a raw surface (4×3 cm), which underwent epithelialization after conservative treatment. We observed four focal necrotic lesions (1.5×1.5 cm) on the right lower leg and anterior chest, which served as indicators of moxibustion, and debridement and primary closure were performed. Moxibustion is increasingly used as a therapeutic option; however, statistical data describing its adverse effects are limited. Moxibustion significantly increases skin temperature and can cause burn injuries. It is important to prevent moxibustion-induced adverse effects and avoid severe complications, particularly in patients with diabetes.

• 한국항만학회지
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• 제11권2호
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• pp.241-255
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• 1997

한국의 부산에 위치한 감천만에서의 해수유동을 파악하기 위하여 3차원 유동모델을 사용하여 계산을 하고 그 결과를 관측치와 비교하였다. 모델은 개방경계에서의 조직, 바람, 화력발전소에서의 온배수에 의해 힘을 받아 해수유동을 재현한다. 난류 혼합계수는 $\kappa-\varepsilon$난류클로즈 모델의 의해 계산하였다. 수온, 염분, 해조류를 현장관측하여 관측자료와 모델결과를 비교하였다. 소용돌이 형태의 흐름이 현장관측자료와 모델결과에서 관측되었는데 이는 약한 조류와 풍성류, 온배수의 상호작용에 의해 형성된 것으로 분석되어진다. 표층과 저층의 흐름은 서로 연관되어 있는데 즉, 표층의 흐름이 강해지는 저츠으이 흐름이 약해지고 반대의 경우도 성립한다.

• 터널과지하공간
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• 제9권1호
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• pp.1-11
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• 1999

열-수리-역학적 상호작용을 해석하기 위한 유한요소 코드가 개발되었다. 이 코드는 Noorishad(1984)에 의해 제시된 유한요소 수식화에 기초하였으며, 절리 거동은 Goodman 의 절리 구성 모델로 모사되었다. 개발된 코드가 각각 절리가 있거나 없는 두가지 종류의 수갱 모델에 대한 T-H-M 상호작용 해석에 적용되었다. 절 리가 없는 모델에 대해서, 수갱벽면으로부터 바깥 방향으로 온도 증가가 뚜렷이 나타났다. 절 리가 있는 모델에 대해서, 절리의 닫힘이 열팽창에 의해 생겼으며, 물이 암석기질보다 낮은 열 전도도와 높은 비열용량을 보이기 때문에 절리를 따라 온도 분포가 상대적으로 낮게 나타났다. 또한 절리 내에서의 열 유동의 영향이 암반내에서의 수리유동의 영향보다 더 크다고 결론내릴 수 있다.

• 방사성폐기물학회지
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• 제2권4호
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• pp.253-262
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• 2004

Construction of tunnels in a deep crystalline host rock for a potential High-Level Radioactive Waste(HLW) repository inevitably generates an excavation disturbed zone (EDZ). There have been a series of debates on whether a permeability in an EDZ increases or not and what would be the maximum depth of an EDZ. Recent studies show mixed opinions on permeability. However, there has been an international consensus on the thickness of an EDZ; 30 cm for TBM and 1 meter for controlled blast. One of the impacts of an EDZ is on determining the distance between adjacent deposition holes. The void gap by the excavation hinders relaxation of temperature profiles so that the current Korean reference designing distance between holes should be stretched out more to keep the maximum temperature in a buffer region below 100 degrees Celsius. The other impact of an EDZ is on the long-term post closure radiological safety. To estimate the impact, the reference scenario, the well scenario, is chosen. Released nuclides diffuse through a bentonite buffer region experiencing strong sorption and reach a fracture surrounded by a porous medium. Inside a fractured porous region, radionuclides migrate by advection and dispersion with matrix diffusion into a porous medium. Finally, they reach a well assumed to be a source of potable water for local residents. The annual individual dose is assessed on this well scenario to find out the significance of an EDZ. A profound sensitivity study was performed, but all results show that the impact is negligible. Even though the role of an EDZ turns out to be limited on overall safety assessment, still it is worthwhile to study the chemical role of an EDZ, such as a potential source for natural colloids, potential sealing of an open fracture by fine clay particles generated by the process of an EDZ, and alteration of a sorption mechanism by an EDZ in the future.

• 광물과 암석
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• 제36권3호
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• pp.199-212
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• 2023

확산은 지구물질은 물론 운석과 같은 우주물질의 원소 및 동위원소 연구에서 매우 유용하게 활용될 수 있다. 고온의 태양계 성운에서 일어난 확산과 상대적으로 저온의 소행성에서 일어난 열수 변질 과정에서의 확산 양상은 다르기 때문에 광물에 기록된 원소 및 동위원소 확산에 대한 모델 수립은 초기 태양계 진화를 이해하는데 있어 특히 중요하다. 광물 입자 경계를 따라 일어나는 빠른 입계 확산은 닫힌계에서 구성 광물간 원소 또는 동위원소의 교환을 수치 모델화하는데 유용하며, 본 연구에서는 유한차분법을 이용하였다. 수립된 빠른 입계 확산 수치 모델은 1) CH 콘드라이트의 아메바 형태 감람석 집합체(amoeboid olivine aggregate; AOA)내 사장석의 마그네슘-26(²⁶Mg) 동위원소 조성 변화와 2) CO 콘드라이트의 콘드률, AOA, 기질 구성 광물간 Fe-Mg 상호 확산에 적용되었다. 빠른 입계 확산을 통해 광물 결정의 표면에서는 평형상태에 도달할 수 있다는 가정에 기반해서 평형상태 동위원소 질량 분배(equilibrium isotopic fractionation)와 평형상태 원소 분배(equilibrium partitioning)도 수치 모델에 포함하였다. 모델을 통해 닫힌계를 구성하는 구성 광물간 원소 또는 동위원소의 교환과 확산으로 실제 운석에서 관찰된 원소 및 동위원소 조성 분포를 설명할 수 있음을 보였다. 또한 암석을 구성하는 광물이 여러 종류일 경우에 폐쇄 온도는 확산이 가장 느린 광물종에 의해서만 결정되는 것이 아니라 전체 광물들의 함량비에도 크게 영향을 받는다는 것을 확인할 수 있었다.

• 폴리머
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• 제25권6호
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• pp.796-802
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• 2001

나프탈렌을 측쇄로 갖는 새로운 폴리벤즈이미다졸 단량체을 합성하고, 이 단량체를 친핵치환반응에 의해 중합하였다. 4-Methoxy-N-naphthyl-1,2-phenylenediamine과 4-fluoro-benzoyl chloride의 반응으로 N-(4-fluorobenzoyl)-4-methoxy-N'-naphthyl-1,2-phenyl-enediamine이 합성되었고 이로부터 고리화반응 및 demethylation에 의해 단량체인 2-(4-fluoro-benzoyl)-5-hydroxy-1-naphthylbenzimidazole이 얻어졌다. 중합반응은 potassium carbonate를 함유하는 N-cyclohexyl-2-pyrrolidinone (CHP)에서 행해졌다. 생성된 폴리벤즈이미다졸은 N-methyl-2-pyrrolidinone (NMP)에 용해되었고 0.38 dL/g (NMP at $30^{\circ}C$)의 대수 점도를 가졌다. 유리전이온도($T_g$)는 $270^{\circ}C$였고 열중량분석에서 5% 중량감소를 보이는 온도는 질소분위기에서는 $550^{\circ}C$, 공기중에서는 $540^{\circ}C$였다.

• Journal of Chest Surgery
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• 제26권3호
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• pp.180-185
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• 1993

From February 1982 to December 1991, 49 neonates and 105 infants in less than 3 months of age underwent open heart surgery in Seoul National University Hospital. There were 98 males and 56 females, and their mean ages were 16 days in neonatal group and 67 days in early infant group. Their body weight and height were less than 3 percentile of normal developmental pattern. In order of decreasing incidence, the corrected conditions included Transposition of great arteries with or without ventricular septal defect [43], isolated ventricular septal defect [34], Total anomalous pulmonary venous return [21], Pulmonary atresia with intact ventricular septum [9] and others [47]. Various corrective or palliative procedures were performed on these patients; Arterial switch operation [36], patch closure for ventricular septal defect [34], Repair of total anomalous pulmonary venous return [21], RVOT reconstruction for congenital anomalies with compromised right ventricular outflow tract [17]. Profound hypothermia and circulatory arrest were used in 94 patients [ 61% ]: 42 patients [ 85.7% ] for neonatal group and 52 patients [ 49.5% ] for early infant group. The durations of circulatory interruption were within the safe margin according to the corresponding body temperature in most cases [ 84% ]. The hospital mortality was 36.4% ; 44.9% in neonatal group and 32.4% in infant group 1 to 3 months of age. The mortality was higher in cyanotic patients [ 46.6% ], in those who underwent palliative procedures [ 57.8% ], in patients whose circulatory arrest time was longer than safe periods [ 60% 0] and in patients who had long periods of cardiopulmonary bypss and aortic crossclamping. In conclusion, there has been increasing incidence of open heart surgery in neonates and early infants in recent years and the technique of deep hypothermia and circulatory arrest was applied in most of these patients, and the mortality was higher in cyanotic neonates who underwent palliative procedures and who had long cardiopulmonary bypass , aortic cross-clamping and circulatory arrest.