• Nuclear Engineering and Technology
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• 제32권2호
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• pp.169-179
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• 2000

A detailed numerical analysis of the evolution of thermal stratification in a curved piping system in a nuclear power plant is performed. A finite volume based thermal-hydraulic computer code has been developed employing a body-fitted, non-orthogonal curvilinear coordinate for this purpose. The cell-centered, non-staggered grid arrangement is adopted and the resulting checkerboard pressure oscillation is prevented by the application of momentum interpolation method. The SIMPLE algorithm is employed for the pressure and velocity coupling, and the convection terms are approximated by a higher-order bounded scheme. The thermal-hydraulic computer code developed in the present study has been applied to the analysis of thermal stratification in a curved duct and some of the predicted results are compared with the available experimental data. It is shown that the predicted results agree fairly well with the experimental measurements and the transient formation of thermal stratification in a curved duct is also well predicted.

• 한국CDE학회논문집
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• 제10권5호
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• pp.314-327
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• 2005

This paper describes the volumetric data modeling and analysis methods that employ volumetric NURBS or VNURBS that represents heterogeneous objects or fields in multidimensional space. For volumetric data modeling, we formulate the construction algorithms involving the scattered data approximation and the curvilinear grid data interpolation. And then the computational algorithms are presented for the geometric and mathematical analysis of the volume data set with the VNURBS model. Finally, we apply the modeling and analysis methods to various field applications including grid generation, flow visualization, implicit surface modeling, and image morphing. Those application examples verify the usefulness and extensibility of our VNUBRS representation in the context of volume modeling and analysis.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
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• pp.163-169
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• 1999

The numerical procedure has been developed for simulating incompressible viscous flow around a turbine stage with rotor-stator interaction. This study solves 2-D unsteady incompressible Navier-Stokes equations on a non-orthogonal curvilinear coordinate system. The Marker-and-Cell concept is applied to efficiently solve continuity equation. To impose an accurate boundary condition, O-H multiblocked grid system is generated. O-type grid and H-type grid is generated near and outer rotor-stator The cubic-spline interpolation is applied to handle a relative motion of a rotor to the stator. Turbulent flows have been modeled by the Baldwin- Lomax turbulent model. To validate present procedure, the time averaged pressure coefficients around the rotor and stator are compared with experiment and a good agreement obtained.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.900-907
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• 2000

The three-dimensional turbulent flow in curved pipes susceptible to flow-accelerated corrosion has been analyzed numerically to predict the pressure and shear stress distributions on the inner surface of the pipes. The analysis employs the body-fitted non-orthogonal curvilinear coordinate system and a standard $ {\kappa}-{\varepsilon}$ turbulence model with wall function method. The finite volume method is used to discretize the governing equations. The convection term is approximated by a high-resolution and bounded discretization scheme. The cell-centered, non-staggered grid arrangement is adopted and the resulting checkerboard pressure oscillation is prevented by the application of a modified version of momentum interpolation scheme. The SIMPLE algorithm is employed for the pressure and velocity coupling. The numerical calculations have been performed for two curved pipes with different bend angles and curvature radii, and discussions have been made on the distributions of the primary and secondary flow velocities, pressure and shear stress on the inner surface of the pipe to examine applicability of the present analysis method. As the result it is seen that the method is effective to predict the susceptible systems or their local areas where the fluid velocity or local turbulence is so high that the structural integrity can be threatened by wall thinning degradation due to flow-accelerated corrosion.

• 한국전산유체공학회지
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• 제7권1호
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• pp.10-19
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• 2002

The non-staggered(collocated) grid approach in which all the solution variables are located at the centers of control volumes is very popular for incompressible flow analyses because of its numerical efficiency on the curvilinear or unstructured grids. Rhie and Chow's paper is the first in using non-staggered grid method for SIMPLE algorithm, where pressure weighted interpolation was used to prevent decoupling of pressure and velocity. But it has been known that this non-staggered grid method has stability problems when pressure fields are nonlinear like in natural convection flows. Also Rhie-Chow scheme generates large numerical diffusion near curved walls. The cause of these unwanted problems is too large pressure damping term compared to the magnitude of face velocity. In this study the magnitude of pressure damping term of Rhie-Chow's method is limited to 1∼10% of face velocity to prevent physically unreasonable solutions. The wall pressure extrapolation which is necessary for cell-centered FVM is another source of numerical errors. Some methods are applied in a unstructured FV solver and analyzed in view of numerical accuracy. Here, two natural convection problems are solved to check the effect of the Rhie-Chow's method on numerical stability. And numerical diffusion from Rhie-Chow's method is studied by solving the inviscid flow around a circular cylinder.

• 대한기계학회논문집
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• 제17권10호
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• pp.2535-2542
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• 1993

Two-noded curved beam elements, CMLC (field-consistent membrane and linear curvature) and IMLC(field-inconsistent membrane and linear curvature) are developed on the basis of Timoshenko's beam theory and curvilinear coordinate. The curved beam element is developed by the separation of the radial deflection into the bending deflection. In the CMLC element, field-consistent axial strain interpolation is adapted for removing the membrane locking. The CMLC element shows the rapid and stable convergence on the wide range of curved beam radius to thickness. The field-consistent axial strain and the separation of radial deformation produces the most efficient linear element possible.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 A
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• pp.146-148
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• 1998

For the shape design of electromagnetic devices using the FEM, the choice of design parameters influence to the success of the optimization process. If the design parameter distribution has a one to one corespondence with finite element model, we can encounter not only serious accuracy problem but also obtain a zigzag shape along the interface. The nodes between those design parameters can be parameterized by interpolating using one among many interpolation methods. The conventional parameterization of design parameters has a limit of application for shape, because design parameters and movable nodes are linearly intepolated. In this paper, using the B-spline curve that use to present any interfaces in computer graphics, the curvilinear parameterization between design parameters and node points is compared with the linear parameterization.

• 대한조선학회논문집
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• 제29권3호
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• pp.59-70
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• 1992

2차원 비압축성, 정상, 층류 Navier-Stokes 방정식을 일반 곡선 좌표계에서 계산하기 위한 유한체적법을 개발하였다. 수치해석은 정규 격자구조를 채택하였으며, 이때 압력의 불안정한 거동은 모멘텀 보간법에 의하여 제거하였다. NACA0012 날개 단면 주위의 유동을 개발된 컴퓨터 프로그램으로 계산한 결과들은 실험 및 다른 계산결과와 잘 일치하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.474-481
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• 2001

This paper addresses a numerical method for predicting transient temperature distributions in the wall of a curved pipe subjected to internally thermal stratification flow. A simple and convenient numerical method of treating the unsteady conjugate heat transfer in the non-orthogonal coordinate systems is presented. The proposed method is implemented in a finite volume thermal-hydraulic computer code based on a cell-centered, non-staggered grid arrangement, the SIMPLEC algorithm, a higher-order bounded convection scheme, and the modified version of momentum interpolation method. Calculations are performed for the transient evolution of thermal stratification in two curved pipes, where the one has thick wall and the other has so thin wall that its presence can be negligible in the heat transfer analysis. The predicted results show that the thermally stratified flow and transient conjugate heat transfer in a curved pipe with a finite wall thickness can be satisfactorily analyzed by the present numerical method, and that the neglect of wall thickness in the prediction of pipe wall temperature distributions can provide unacceptably distorted results.

• 한국수자원학회논문집
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• 제50권7호
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• pp.455-465
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• 2017

2차원 유속장(flow field)은 하천흐름의 특성을 이해하기 위한 중요한 수리학적 자료 중 하나로서, 수공구조물 위치선정 및 설계, 하천에서의 이송-확산 예측, 하천의 수리학적 거동을 예측하기 위한 중요한 기본 자료로 사용된다. 지금까지 이러한 하천흐름 특성을 예측하기 위해 제한적인 현장조건과 적절한 계측방법, 계측기기의 기술적 한계로 인해 현장실험 보다는 다양한 수치모형을 이용하여 왔다. 하지만 최근에는 계측기기의 발달로 과거보다 정확하고 정밀한 현장계측이 가능하여 졌으며, 현장 계측자료의 질적이고 양적인 수요를 만족시키고 있다. 대표적으로 초음파도플러유속계(ADCPs; Acoustic Doppler Current Profilers)는 유량을 정확하게 측정하는 것으로 유명하며, 2차원 뿐만 아니라 3차원 유속장 등 자세한 유속자료를 제공한다. 하지만 이러한 측정 능력에도 불구하고, ADCP를 활용한 유속 측정은 주로 횡단면 측정을 기본으로 수행하기 때문에, 수치모형의 결과와 같이 높은 밀도의 유속장을 얻기 위해서 공간보간기법이 활용되고 있다. 하지만 만곡이 존재하는 자연하천은 하도형상에 따라 유속이 지속적으로 변화하기 때문에 일반적인 공간보간기법을 적용하기 어렵다. 즉, 자연하천의 만곡에 따른 비등방성을 고려하지 않는다면, 역거리가중법(IDW)과 크리깅(Kriging)과 같은 일반적인 공간보간기법으로는 잘못된 결과를 초래할 수 있다. 본 연구에서는 이러한 문제점을 해결하고자 만곡이 존재하는 사행하천을 대상으로 방향성을 고려하기 위한 곡선좌표계와 비등방성을 고려하기 위한 비등방적 참조범위를 적용한 공간보간기법을 개발하였다. 본 연구에서 제시한 기법을 한국건설기술연구원 하천실험센터에 존재하는 3개의 사행수로가 포함된 실규모의 실험수로를 대상으로 적용한 결과, 평균제곱근오차와 상관계수는 기존의 공간보간기법과 비교하여 각각 41.5% 감소, 40.0%가 증가하여 정확성과 상관성이 개선되었다.