• 한국수자원학회논문집
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• 제56권spc1호
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• pp.1059-1069
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• 2023

댐붕괴흐름은 댐이 갑자기 붕괴하여 제어가 어려운 상태의 고속흐름이 방출되는 현상이다. 이 연구에서는 3차원의 댐붕괴흐름을 모의하기 위해 OpenFOAM을 사용하여 층류 및 난류 모델을 적용하고 그 결과를 비교하였다. 난류 모의를 위해 레이놀즈 평균 나비에-스토크스 (Reynolds-Averaged Navier-Stokes) 모델, 구체적으로 k-ε 모델을 사용하였다. 수리모형실험과 함께 수정된 다층 블록 장애물 시나리오를 대상으로 두 가지 모델을 평가하였다. 두 모델 모두 댐붕괴흐름을 효과적으로 재현하였으며, 난류 모델은 흐름의 변동성을 감소시키는 역할을 보여줬다. 그러나 난류 모델에서의 과도한 에너지소산은 수위를 과소 평가하게 하는 것으로 나타났다. 수치기법 및 격자 해상도를 개선하여 적용한 결과 흐름재현성이 향상되었는데 이는 특히 구조물 근처의 난류흐름에서 두드러졌다. 모델 안정성의 경우 난류모델의 사용여부보다는 수치기법 및 격자 해상도의 개선에 더 크게 영향을 받았다. k-ε 모델에 내재된 시간평균처리의 특성은 불연속성과 불안정성이 두드러진 댐붕괴흐름을 재현하는 데 한계가 있음을 나타냈다. RANS 모델을 포함한 난류모의는 방대한 계산자원이 필요하지만, 층류 모델과 비교하여 성능 향상이 제한적이었다. 댐붕괴흐름을 정확히 재현하기 위해 LES (Large Eddy Simulation) 및 DNS (Direct Numerical Simulation)과 같은 고급 난류 모델의 사용이 권장되며, 이를 위해서는 미세한 공간 및 시간 스케일의 구성이 필수적이다. 이 연구를 통해 댐붕괴흐름을 모의할 때 기본적으로 사용할 수 있는 주요 접근법과 적용가능성을 측정하였으며, 구조물 근처에서 난류흐름에 대한 정확한 표현의 중요성을 강조할 수 있었다.

• 터널과지하공간
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• 제5권1호
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• pp.1-10
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• 1995

The behavior of a jointed rock mass depends mainly on the geometrical and mechanical properties of joints. The failure mode of a rock mass and kinematics of rock blocks are governed by the orientation, spacing, and persistence of joints. The mechanical properties such as dilation angle, shear strength, maximum closure, strength of asperities and friction coeffiient play important roles on the stability and deformation of the rock mass. The normal and shear behaviour of a joint are coupled due to dilation, and the joint deformation depends also on the boundary conditions such as stiffness conditons. In this paper, the joint constitutive law including the dilatant behaviour of a joint is numerically modelled using the edge-to-edge contact logic in distinct element method. Also, presented is the method to quantify the input parameters used in the joint law. The results from uniaxial compression and direct shear tests using the numeical model of the single joint were compared to the analytic results from them. The boundary effect on the behaviour of a joint is verified by comparing the results of direct shear test under constant stress boundary condition with those under constant stiffness boundary condition. The numerical model developed is applied to a complex jointed rock mass to examine its performance and to evaluate the effect of joint dilation on tunnel stability.

• Nuclear Engineering and Technology
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• 제37권6호
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• pp.511-524
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• 2005

Thermalhydraulic reactor simulation of tomorrow will require a new generation of codes combining at least three scales, the CFD scale in open medium, the component scale and the system scale. DNS will be used as a support for modelling more macroscopic models. NEPTUNE is such a new generation multi-scale platform developed jointly by CEA-DEN and EDF-R&D and also supported by IRSN and FRAMATOME-ANP. The major steps towards the next generation lie in new physical models and improved numerical methods. This paper presents the advances obtained so far in physical modelling for each scale. Macroscopic models of system and component scales include multi-field modelling, transport of interfacial area, and turbulence modelling. Two-phase CFD or CMFD was first applied to boiling bubbly flow for departure from nucleate boiling investigations and to stratified flow for pressurised thermal shock investigations. The main challenges of the project are presented, some selected results are shown for each scale, and the perspectives for future are also drawn. Direct Numerical Simulation tools with Interface Tracking Techniques are also developed for even smaller scale investigations leading to a better understanding of basic physical processes and allowing the development of closure relations for macroscopic and CFD models.

• 대한기계학회논문집
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• 제19권4호
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• pp.908-917
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• 1995

The constant .DELTA.K fatigue tests are performed in SS41 and its weldments to investigate crack opening behavior and fatigue crack propagation behavior at each parts of weldment and its boundary layer. The weldments were annealed after welding for the purpose of relieving residual stress. Every weldments has notch at weld metal zone, and fatigue crack propagates from weld metal zone to vase metal zone perpendicular to weld line. The Laser ISDG method is used in order to determine the crack opening ratio, this method is more precise than indirect measurement method, and faster and easier than other direct measurement method.

• Journal of Chest Surgery
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• 제18권3호
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• pp.391-397
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• 1985

Ebstein`s anomaly is a rare congenital cardiac malformation and characterized by downward displacement of an abnormal tricuspid valve cusps. But until now, the ideal surgical correction is still controversial. We present a case of Ebstein`s anomaly experienced lately. The patient was 13 year old girl with the complaints of dyspnea on exertion, fatigability and cyanosis. Echocardiography revealed downward displacement of septal leaflet of tricuspid valve and atrialized right ventricle. Cardiac catheterization and cineangiography revealed ASD and large right atrium. During operation, the atrialized right ventricle was plicated and tricuspid annuloplasty was done. And the two secundum type ASD`s were closed by direct suture closure. The patient`s postoperative course was uneventful and discharged on the 24th postoperative days.

• Journal of Chest Surgery
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• 제24권2호
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• pp.135-142
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• 1991

From January 1980 to December 1989, thirteen patients underwent operation for ventricular septal defect associated with aortic insufficiency in Kyungpook national university hospital. Ten male and three female patients ranged in age from 3 years to 25 years, with an average age of 11.5 years. Aortic cusp prolapse was found in eight cases[61.5%]. The aortic regurgitation was classified by Sellers` method with grade I in 2 cases, grade II in 9 cases, and grade III in 2 cases. Direct suture or patch repair of ventricular septal defect was performed through the right ventricle. Eight cases were treated only by closure of VSD, 3 cases by plication, but two of the letter were reoperated due to the persistent of aortic regurgitation and fungal endocarditis respectively. Aortic valve replacement were performed in 2 cases at the first operation. There was only one late death[7.7%], which was caused by postoperative fungal endocarditis. Follow-up for twelve patients except one death were followed up for 3 months to six years after operation. Residual aortic regurgitation was noted in six cases[46.2%], but the postoperative course of them were uneventful.

• Journal of Chest Surgery
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• 제20권1호
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• pp.101-105
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• 1987

A clinical evaluation was performed on 17 cases of the cardiac and great vessel injuries above the subclavian vessel at the Department of Thoracic and Cardiovascular Surgery, Chungnam National University Hospital from April, 1980 to September, 1986. The results were as follows: 1. Sex distribution were 13 cases in male and 4 cases in female. In age range, second and third decades occupied in about 65% of total cases. 2. Modes of injury were penetrating wound is 14 cases and nonpenetrating wound in 3 cases. The stab wounds by knife were most frequent. 3. Time interval from injury to operation was mean 103 minutes. 4. Surgical approaches were performed with thoracotomy in 9 cases, median sternotomy in 3 cases and direct incision above the wound. 5. Sites of injury were heart in 10 cases and great vessel in 7 cases. The right ventricular injury was most common as 7 cases. 6. Operative procedures were performed with simple closure, vascular graft anastomosis and ligation. There was no postoperative death.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2001년도 춘계 학술대회논문집
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• pp.51-59
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• 2001

An evaluation of one zero-equation and two one-equation eddy viscosity-transport turbulence closure models as implemented CFDS(Characteristic Flux Difference Splitting ) code is presented herein. Comparisons of Baldwin-Lomax model as zero-equation and Baldwin-Barth and Spalart-Allmaras model as one-equation are presented for three test cases, first inlvolving the 3 dimensional supersonic flow at M=1.98 over tangent ogive cylinder, second involving the 2 dimensional transonic flow at M=0.79 over RAE 2822 airfoil, third involving the 3 dimensional transonic flow at M=0.84 over ONERA M6 wing. The numerical results of CFDS code will also examined through direct comparison with experimental data.

• Journal of Chest Surgery
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• 제20권2호
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• pp.416-422
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• 1987

Anomalous origin of a pulmonary artery from the ascending aorta is a rare congenital cardiovascular anomaly which usually involves the right pulmonary artery. For operative reconstruction, the surgical technique of choice used to be a direct end-to-side anastomosis of the ectopic pulmonary artery to the main pulmonary artery. A case of right pulmonary artery arising from the ascending aorta associated with a contralateral patent ductus arteriosus is presented, with description of a new modified surgical technique. The operation was done on cardiopulmonary bypass with deep hypothermia. After closure of PDA, a side-to-side anastomosis between the RPA and MPA, roofed with Gore-Tex patch, was established. The postoperative course was excellent, and the postoperative angiography revealed complete anatomic correction.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.363-366
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• 2005

When widening or repairing concrete deck slab, there is a joint inevitably. However, joining-construction method have following problem, that is the additional stress in existing part of bridge resulting from the specific process of joining-construction and the difference of amount of shrinkage between new and existing bridge. On this study, compared shrinkage stress of the direct joining construction method with the indirect joining construction method, and concluded the proper substitution rate of expansion cement. The rate of replacement was proper at $10\%$. but more than $15\%$, concrete had excessive expansion and weeker compressive strength. The time of placing closure concrete, considering the shinkage stresses and creep, was suitable in $45\~60$ days after placing the new concrete deck slab.