• 한국전산유체공학회지
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• 제11권1호
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• pp.57-66
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• 2006

An optimal shape design approach is presented for a subsonic S-shaped intake using aerodynamic sensitivity analysis. Two-equation turbulence model is employed to capture strong counter vortices in the S-shaped duct more precisely. Sensitivity analysis is performed for the three-dimensional Navier-Stokes equations coupled with two-equation turbulence models using a discrete adjoint method For code validation, the result of the flow solver is compared with experiment data and other computational results of bench marking test. To study the influence oj turbulence models and grid refinement on the duct flow analysis, the results from several turbulence models are compared with one another and the minimum number of grid points, which can yield an accurate solution is investigated The adjoint variable code is validated by comparing the complex step derivative results. To realize a sufficient and flexible design space, NURBS equations are introduced as a geometric representation and a new grid modification technique, Least Square NURBS Grid Approximation is applied With the verified flow solver, the sensitivity analysis code and the geometric modification technique, the optimization of S-shaped intake is carried out and the enhancement of overall intake performance is achieved The designed S-shaped duct is tested in several off-design conditions to confirm the robustness of the current design approach. As a result, the capability and the efficiency of the present design tools are successfully demonstrated in three-dimensional highly turbulent internal flow design and off-design conditions.

• Nuclear Engineering and Technology
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• 제55권2호
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• pp.756-768
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• 2023

Neutron transport calculations are extremely challenging due to the high computational cost of large and complex problems. A multilevel octree grid algorithm (MLTG) of discrete ordinates method was developed to improve the modeling accuracy and simulation efficiency on 3-D Cartesian grids. The Balakovo-3 VVER-1000 neutron dosimetry benchmark is calculated to verify and validate this numerical technique. A simplified S₂ synthetic acceleration is used in the MLTG calculation method to improve the convergence of the source iterations. For the triangularly arranged fuel pins, we adopt a source projection algorithm to generate pin-by-pin source distributions of hexagonal assemblies. MLTG provides accurate geometric modeling and flexible fixed source description at a lower cost than traditional Cartesian grids. The total number of meshes is reduced to 1.9 million from the initial 9.5 million for the Balakovo-3 model. The numerical comparisons show that the MLTG results are in satisfactory agreement with the conventional S_N method and experimental data, within the root-mean-square errors of about 4% and 10%, respectively. Compared to uniform fine meshing, approximately 70% of the computational cost can be saved using the MLTG algorithm for the Balakovo-3 computational model.

• 한국전산유체공학회지
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• 제6권3호
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• pp.51-56
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• 2001

As IT(Information Technology) has been developing, an application engineering is advanced so quickly. Especially, CFD field that is influenced greatly by Computing Power is an outstanding example. In this paper, it says a research tendency of the KISTI Supercomputing Center that performs the CFD research based on IT. The representative researches are the National Grid Project, TeraCluster Construction and development and a supporting plan for Supercomputer users' parallelization.

• 대한기계학회논문집
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• 제17권6호
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• pp.1640-1647
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• 1993

본 연구에서는 속도-압력 연계방법으로는 SIMPLE기법을 적용하고, 비균일 격자계에서도 사용할 수 있는 QUICKER방법과 함께 HYBRID방법을 이용하여 이와 같은 물음에 대한 대답을 구하고자 하였다. 이를 위하여 수치적 실험을 위한 흐름으로 본 연구에서 선택한 정사각형 공동 흐름 (square cavity flow)은 재순환 유동의 수치 적 해법을 위한 표준유동으로 많이 사용되어 왔으며, 대한기계학회 전산유체분과에서 도 여러 수치기법을 비교평가 하기 위한 흐름으로 채택된 적이 있는 흐름이다.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2002년도 추계학술발표논문집 (상)
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• pp.233-236
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• 2002

Computational steering system은 계산 및 응용 과학자들이 컴퓨터를 이용해서 보다 효과적이고 효율적인 방법으로 시뮬레이션을 진행하고 제어하기 위해서 제안되었다. 하지만 시간이 흐를수록 시뮬레이션의 규모가 커지면서 단일 컴퓨터 시스템으로 시뮬레이션을 수행하는 것이 어렵게 되었다. 이 문제를 해결하기 위해서 최근 새로운 형태의 슈퍼컴퓨팅 환경으로 주목받기 시작한 그리드와 computational steering system을 연계하는 방법에 대한 연구가 진행되고 있다. 본 논문에서는 computational steering system의 개념과 함께 그리드에서 운용 가능한 대표적인 computational steering system을 소개하고 KISTI 슈퍼컴퓨팅센터에서 구축하고 있는 국가 그리드 기반인 N* Grid를 위한 computational steering system의 구현 방향을 제시하고자 한다.

• International Journal of Contents
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• 제6권3호
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• pp.15-18
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• 2010

Grid system is based on the Grid Security Infrastructure (GSI). GSI uses user's proxy to guarantee availability among multi-trust domains. Since grid system has been developed focusing on availability, GSI provides authentication and authorization performed by systems, but there are lacks of privacy consideration. For this reason, some researchers decide to use their own cluster system and do not want to use public grid systems. In this paper, we introduce a new privacy enhanced security mechanism for grid systems. With this mechanism, user can participate in resource allocation and authorization to user's contents more actively. This mechanism does not need to change previous middleware and minimize the computational overheads.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.86-87
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• 2003

Unstructured grid system is suitable for flows of complex geometries. For problems with moving boundary walls, the grid system must be changed and deformed with time if we use a body fitted grid system. In this paper, a new moving-grid finite-volume method on unstructured grid system is proposed and developed for unsteady compressible flows with shock waves. To assure geometric conservation laws on moving grid system, a control volume on the space-time unified domain is adopted for estimating numerical flux. The method is described and applied for two-dimensional flows.

• 한국전산유체공학회지
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• 제1권1호
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• pp.1-8
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• 1996

본 논문은 전산 유체 역학에서 필요한 3차원 다구획 격자구성 프로그램을 개발한 것이다. 유동장에 격자를 구성하는 것은 유동해석 방정식을 푸는 것 보다 일반적으로 시간이 더 소요되므로 격자구성 시간을 단축하기 위해서 사용자 편의를 도모하는 컴퓨터 화면과의 대화형 코드를 개발하였다. PIGG라고 부르는 본 격자구성 프로그램은 형상 모델링, 표면격자 구성, 유동장격자 생성, 그리고 격자의 재구성에 이르는 일련의 과정이 대화형/화면게시 형태로 수행된다. 본 PIGG를 이용하여 전통적인 전투기 형상 격자를 구성한 결과 많은 시간을 단축할 수 있었다.

• 한국전산유체공학회지
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• 제21권1호
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• pp.36-42
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• 2016

One of the obstacles on the grid generation for complex geometries with multi-block structured grids is the domain decomposition. In this paper, the domain decomposition for two-dimensional flow is studied using the flow characteristics. The potential flow equation with the source distribution on the panel surface is solved to extract the information of the flow. The current approach is applied to a two-dimensional cylinder and Bi-NACA0012 problems. The generated grids are applied to generic flow solvers and reasonable results are obtained. It can be concluded that the current methods is useful in the domain decomposition for the multi-block structured grid.

• 한국전산유체공학회지
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• 제17권1호
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• pp.70-77
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• 2012

In this paper, diagonal implicit harmonic balance method with overset grid technique is applied to analyze helicopter rotor blade flow in hover and forward flight condition. The chimera grid need interpolation time with sub-grid and background grid in moving problem such as forward flight on every time step. Present method is available enough to reduce the grid module interpolation time. In order to demonstrate present method, Caradonna & Tung's and AH-1G rotor blades are used and the results are compared to other researchers' result and experimental data.