• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1997년도 추계 학술대회논문집
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• pp.66-72
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• 1997

Circular-to-rectangular transition ducts are used as exhaust components of high performance fighter aircraft with vectored thrust nozzles. Three-dimensional incompressible Navier-Stokes solver is used to analyze the transition duct. Cross sections of transition duct are defined by superelliptic equation. The grid system is generated by Non-Uniform Rational B-Spline, after generating surface grid by blending the cross sections. Good agreement between the results of the computational simulation and the experimental data is observed.

• 한국전산유체공학회지
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• 제11권1호
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• pp.1-7
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• 2006

Numerical investigation of a centrifugal compressor volute having a modified straight conical duct hill been made. Three-dimensional Reynolds-Averaged Navier-Stokes equations with $k-{\varepsilon}$ turbulence equation are solved To avoid coordinate singularity at the central axis of the duct, multi-block H-type grid is generated on the circular cross-sections of the volute and stretched toward the solid wall boundary. We obtained numerical results with three different mass flow rates at the volute inlet, namely, with the inlet conditions that give small, medium and large mass flow rates at the outlet of the conical duct. Agreement with the experimental results is observed.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2001년도 춘계학술대회 논문집
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• pp.52-57
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• 2001

Laminar two-dimensional time-dependent flow past a circular cylinder is numerically investigated using direct numerical simulation for the low Reynolds number (Re=164∼280). The higher-order finite difference scheme is employed for the spatial distributions along with the second order Adams-Bashforth and the first order backward-Euler time integration. The convection term is applied by the 7th order up wind scheme and the pressure and viscosity terms are applied by the 4th order central difference. The grid system makes use of the regular grid system and it is generated by an equation. The calculated results of drag coefficients, lift coefficients, pressure distributions, and vorticity contours and other information are compared with experimental and numerical ones. These results obtained by the present DNS show good agreement with the previous studies.

• Journal of Ship and Ocean Technology
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• 제5권1호
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• pp.38-54
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• 2001

A finite difference method for calculating turbulent flow and surface wave fields around a ship model is evaluated through the comparison with the experimental data of a Series 60 $C_B$=0.6 ship model. The method solves the Reynolds-averaged Navior-Stokes Equations using the non-staggered grid system, the four-stage Runge-Kutta scheme for the temporal integration of governing equations and the Bladwin-Lomax model for the turbulence closure. The free surface waves are captured by solving the equation of the kinematic free-surface condition using the Lax-Wendroff scheme and free-surface conforming grids are generated at each time step so that one of the grid surfaces coincides always with the free surface. The computational results show an overall close agreement with the experimental data and verify that the present method can simulate well the turbulent boundary layers and wakes as well as the free-surface waves.

• 대한토목학회논문집
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• 제28권6B호
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• pp.697-707
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• 2008

격자기반 운동파 강우유출모형 KIMSTORM(grid-based KIneMatic wave STOrm Runoff Model)은 유역의 지표흐름, 지표하흐름 및 하천흐름의 시간적 변화와 공간적 분포를 모의할 수 있다. 본 모형은 유닉스 운영체제의 C++언어로 개발되었으며, 각 셀에서의 흐름을 모의하기 위하여 단방향흐름 알고리즘과 격자기반 수문학적 물수지요소를 채택하고 있으나 운영에 몇몇 제약사항이 있다. 본 연구에서는 기존모형을 개선하고자 하였으며, MS Windows 운영체제에서 실행 가능하도록 FORTRAN 90 언어를 이용하여 ModKIMSTORM을 개발하였다. 기존모형에 비해 개선된 주요사항으로, 물리적 기반의 침투기법인 GAML(Green-Ampt & Mein-Larson) 침투모형 추가, 격자 유출심과 Manning 조도계수에 의한 논에서의 지표유출 제어, 지표격자의 기저유출 요소 추가, 공간강우와 지점강우의 처리, 전 후 처리부문 개발, 5개 평가항목(피어슨의 결정계수 $R^2$, Nash & Sutcliffe 모형효율 E, 유출용적 편차 $D_v$, 첨두유출의 상대오차 $EQ_p$, 첨두시간의 절대오차 $ET_p$)을 이용한 모의결과의 자동 평가 기능을 개발하였다. 추가적으로, 모형의 계산효율을 향상시키고 지표격자의 기저유출을 하천격자로 이송하기 위하여 쉘정렬 알고리즘을 채택하였다. 모형의 입력자료는 ESRI ArcInfo W/S 또는 ArcView와 같은 GIS 소프트웨어 및 MS Excel을 이용하여 간단히 구축할 수 있으며, 모의결과의 공간적 분포를 확인할 수 있는 토양수분, 지표유출, 유출심 및 유속분포도는 BSQ, ESRI ASCII Grid, ESRI Binary Grid 및 IDRISI Raster 형식으로 출력할 수 있도록 개선하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.518-522
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• 2011

Cartesian grid system has mainly been used in the casting simulation even though it does not nicely represent sloped and curved surfaces. These distorted boundaries cause several problems. A special treatment is necessary to clear these problems. A cut cell method on Cartesian grids has been developed to simulate three-dimensional mold filling Cut cells at a cast-mold interface are generated on Cartesian grids. Governing equations were computed using volume and areas of cast at cut cells. In this paper, we propose a new method that can consider the cutting cells which are cut by casting and mold based on the patial cell treatment (PCT). This method provides a better representation of geometry surface and will be used in the computation of velocities that are defined on the cell boundaries in the Cartesian gird system. Various test examples for several casting process were computed and validated. The analysis results of more accurate fluid flow pattern and less momentum loss owing to the stepped boundaries in the Cartesian grid system were confirmed. We can know the momentum energy at the cut cell is conserved by using the cut cell method. By using the cut cell method. performance of computation gets better because of reducing the whole number of meshes.

• 항공우주기술
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• 제1권2호
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• pp.1-10
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• 2002

본 연구에서는 전진익 소형기 항공기 형상에 대한 공력해석을 수행하였다. 전진익 소형 항공기는 주익의 평면형상이 후퇴각을 가진 스트레이크(strake) 형태의 안쪽(inboard) 날개와, 전진각을 가진 바깥쪽(outboard) 날개가 결합되어 있는 형태로 구성되어 있다. 이와 같은 두개의 다른 형태의 날개 평면형상의 결합으로 킹크(kink)로 정의되는 날개의 불연속선이 존재하게 되어, 이 부분에 의한 날개 공력특성의 면밀한 분석이 요구되었다. 전진익 소형 항공기에 대한 기본적 공력계수의 산출 및 유동해석은 해석방법 간의 차이에서 기인하는 정확도를 분석하기 위해 4가지의 방법으로 계산을 수행하였다. 항공기 형상에 대한 격자생성의 용이성을 위해 중첩격자기법(Chimera grid)을 적용하였다. 본 해석을 통하여 전진익 소형기 형상에 대한 기본적인 공력계수의 도출과 함께 주익에 대한 공력특성이 분석되었다.

• 국제초고층학회논문집
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• 제8권4호
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• pp.255-264
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• 2019

This paper describes large eddy simulation of wind pressures on a square cylinder in a uniform flow and a high-rise building immersed in an atmospheric turbulent boundary layer. For the atmospheric boundary layer case, the inflow turbulence is generated by a numerical wind tunnel. In the numerical simulation, particular attention is devoted to the performance of an auto hexahedral non-structural mesh. Both simulations are performed for three grid systems: an auto hexahedral non-structured grid, a structured Cartesian grid and a non-structured triangular prism grid, and for three grid numbers. The present study shows that the auto hexahedral unstructured mesh achieves the best simulation results for wind pressures on the square cylinder and the high-rise building. When the grid number is sufficiently large, the differences among the results obtained from the three investigated grid systems are not significant. However, the advantage of the auto hexahedral unstructured mesh becomes clear when the grid number decreases, because it enables a balanced distribution of orthogonal grids. The results described in this paper demonstrate that the auto hexahedral non-structured mesh has good potential applicability to simulation of urban flows.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.791-794
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• 2002

Cavity is inevitably included in automobile vehicle configuration. The complex unsteady flow and sound waves generated by the cavity are very important issues because of the involved fluid dynamics and the practical importance in the field of aerodynamics. The LES method used is a conventional one with Smagorinsky eddy-viscosity model and the computational grid is small enough to be handled by workstation-level computers. LES can successfully simulate of cavity noise analysis.

• 한국전산유체공학회지
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• 제4권1호
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• pp.53-61
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• 1999

Two-dimensional, unsteady, incompressible and compressible Navier-Stokes codes are developed for the computation of the viscous turbulent flow over high-lift airfoils. The compressible code involves a conventional upwind-differenced scheme for the convective terms and LU-SGS scheme for temporal integration. The incompressible code with pseudo-compressibility method also adopts the same schemes as the compressible code. Three two-equation turbulence models are evaluated by computing the flow over single and multi-element airfoils. The compressible and incompressible codes are validated by predicting the flow around the RAE 2822 transonic airfoil and the NACA 4412 airfoil, respectively. In addition, both the incompressible and compressible code are used to compute the flow over the NLR 7301 airfoil with flap to study the compressible effect near the high-loaded leading edge. The grid systems are efficiently generated using Chimera overlapping grid scheme. Overall, the κ-ω SST model shows closer agreement with experiment results, especially in the prediction of adverse pressure gradient region on the suction surfaces of high-lift airfoils.