• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.290-297
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• 2009

가압 경수로의 주요 기기에서 발생할 수 있는 과도 2상 유동(Two-phase flow) 현상에 대한 해석을 수행하기 위해 원자로 기기 열수력 해석 코드를 개발 중에 있다. 개발 중인 기기 열수력 해석 코드는 지배 방정식으로 Two-phase, three-field model을 사용하고 있으며, 복잡한 기하학적 형상의 원자로 기기를 모사하기 위해 비정렬 격자계(Unstructured grid)를 활용하고 있다. 수치해석 기법으로는, 원자로 계통 해석코드 RELAP5가 사용 중이며 대부분의 원자로 내 2상 유동 조건에서 안정적이며 정확하다고 알려진 Semi-implicit 방법을 적용하였다. 그러나 기존의 Semi-implicit 방법은 1차원, 엇갈림격자(Staggered grid)에 대해 개발되었기 때문에, 이를 다차원, 비정렬, 비엇갈림 격자(Non-staggered grid)에 적용하기 위해 기존의 Semi-implicit 방법을 수정하였다. 본 논문에서는 Semi-implicit 방법의 대류항을 이차정확도를 갖도록 확장하였으며, 이차정확도에 의한 수치확산의 감소를 평가하기 위해 수행된 수치시험의 결과를 기술하였다. 이차정확도 및 일차정확도로 계산된 값을 해석해 또는 격자 수렴성 시험을 통해 평가해 본 결과, 이차정확도 계산시 수치 확산의 감소 확인하였다.

• 한국안전학회지
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• 제17권3호
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• pp.50-55
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• 2002

In this numerical study, characteristics of swirl generation by the fan and selection of the location of the fan was studied theoretically by the modified TEACH code. The governing equations for the system are solved by means of the k dimensional version of the SIMPLE method and STAGGERED grid. From the present results, the optimal position of the fm is 0.625(h/H).

• 한국산업안전학회:학술대회논문집
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• 한국안전학회 2000년도 춘계 학술논문발표회 논문집
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• pp.42-46
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• 2000

In this numerical study, characteristics of swirl generation by the fan and selection of the location of the fan was studied theoretically by the PHOENICS soft ware. The governing equations for the system are solved by means of the three dimensional version of the SIMPLE algorithm and STAGGERED grid. From the present results, the optimal position of the fan is 0.625($\ell$/L). Here we can survey the big swirl near the fan.

• Journal of Ship and Ocean Technology
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• 제7권4호
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• pp.32-40
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• 2003

Numerical simulation code is developed to study the formation of liquid drops from a nozzle into another quiescent liquid. The Navier-Stokes equations for two immiscible, incompressible, Newtonian fluids are solved on a fixed, staggered grid of cylindrical axisymmetric coordinates. Interfacial motion is captured using a Front-Tracking Method. The time variation of interfacial shape simulated by the code is in excellent agreement with experiments. Simulation results show that the viscosity ratio affects the size of the satellite drops.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 춘계 학술발표회논문집
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• pp.50-58
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• 2003

We have developed a locally variable time-step scheme matching with discontinuous grids in the flute-difference method for the efficient simulation of seismic wave propagation. The first-order velocity-stress formulations are used to obtain the spatial derivatives using finite-difference operators on a staggered grid. A three-times coarser grid in the high-velocity region compared with the grid in the low-velocity region is used to avoid spatial oversampling. Temporal steps corresponding to the spatial sampling ratio between both regions are determined based on proper stability criteria. The wavefield in the margin of the region with smaller time-step are linearly interpolated in time using the values calculated in the region with larger one. The accuracy of the proposed scheme is tested through comparisons with analytic solutions and conventional finite-difference scheme with constant grid spacing and time step. The use of the locally variable time-step scheme with discontinuous grids results in remarkable saving of the computation time and memory requirement with dependency of the efficiency on the simulation model. This implies that ground motion for a realistic velocity structures including near-surface sediments can be modeled to high frequency (several Hz) without requiring severe computer memory

• 대한조선학회논문집
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• 제50권2호
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• pp.79-87
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• 2013

In this paper, an Euler equation solver based on a Cartesian-grid method and non-uniform staggered grid system is applied to predict the ship motion response and added resistance in waves. Water, air, and solid domains are identified by a volume-fraction function for each phase and in each cell. For capturing the interface between air and water, the tangent of hyperbola for interface capturing (THINC) scheme is used with a weighed line interface calculation (WLIC) method. The volume fraction of solid body embedded in a Cartesian-grid system is calculated by a level-set based algorithm, and the body boundary condition is imposed by volume weighted formula. Added resistance is calculated by direct pressure integration on the ship surface. Numerical simulations for a Wigley III hull and an S175 containership in regular waves have been carried out to validate the newly developed code, and the ship motion responses and added resistances are compared with experimental data. For S175 containership, grid convergence test has been conducted to investigate the sensitivity of grid spacing on the motion responses and added resistances.

• 대한기계학회논문집B
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• 제22권1호
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• pp.122-130
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• 1998

The present work analyzes the pressure drop and heat transfer characteristics of the plate heat exchanger with staggered dimples. The flow is assumed to be constant property, three dimensional and laminar. A thermal boundary condition is uniform wall temperature and it is assumed that the flow is periodically fully developed. Elliptic grid generation is used for proper modelling of the internal tube geometry with dimples. Computations have been carried out for a variety of geometric parameters, Reynolds number, and Prandtl number. The friction factor ratio and the ratio of a module average Nusselt number are presented for the cases considered in this study. It is found that the distance between dimples has a substantial effect on the pressure drop and heat transfer.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.211-217
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• 2009

The numerical program has been developed for the purpose of the complicate geometries application using CIP method. The non-staggered, non-orthogonal, and unstructured grid system can be also used for the various geometries in the program. For validating CIP solver, the lid-driven cavity flow and solitary wave propagation flow are carried out. Test results show a good agreement with the verified results. The dynamic solver was used for the behavior of moving body. Interface process between the two solvers is introduced. The research was performed on the flow problem around torpedo and log and the flow problem in a tank in order to analyze the three phase flow problem Although the comparison to the verified results was not quantitatively performed, the trend of the results was reasonable.

• 한국전산유체공학회지
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• 제13권3호
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• pp.51-61
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• 2008

The SMAC (Simplified Marker And Cell) algorithm is extended for an application to thermal non-equilibrium two-phase flows in light water nuclear reactors (LWRs). A two-fluid three-field model is adopted and a multi-dimensional unstructured grid is used for complicated geometries. The phase change and the time derivative terms appearing in the continuity equations are implemented implicitly in a pressure correction equation. The energy equations are decoupled from the momentum equations for faster convergence. The verification of the present numerical method was carried out against a set of test problems which includes the single and the two-phase flows. The results are also compared to those of the semi-implicit ICE method, where the energy equations are coupled with the momentum equation for pressure correction.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제20권1호
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• pp.37-50
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• 2016

A large eddy simulation (LES) of a turbulent channel flow is performed by using the third order low-storage Runge-Kutta method in time and second order finite difference formulation in space with staggered grid at a Reynolds number, $Re_{\tau}=590$ based on the channel half width, ${\delta}$ and wall shear velocity, $u_{\tau}$. To reduce the calculation cost of LES, algebraic wall model (AWM) is applied to approximate the near-wall region. The computation is performed in a domain of $2{\pi}{\delta}{\times}2{\delta}{\times}{\pi}{\delta}$ with $32{\times}20{\times}32$ grid points. Standard Smagorinsky model is used for subgrid-scale (SGS) modeling. Essential turbulence statistics of the flow field are computed and compared with Direct Numerical Simulation (DNS) data and LES data using no wall model. Agreements as well as discrepancies are discussed. The flow structures in the computed flow field have also been discussed and compared with LES data using no wall model.