• 한국수자원학회논문집
• /
• 제48권12호
• /
• pp.1023-1035
• /
• 2015

본 연구에서는 해수-담수-해안대수층의 비선형 상호작용을 직접 해석할 있는 PBM(Porous Body Model) 기반의 3차원 N-S Solver인 LES-WASS-3D ver 2.0을 적용하며, 해안대수층의 해수침투모의를 수행하였다. 이와 같은 N-S Solver를 적용한 해안대수층의 해수침투모의는 국내 최초 수행되는 것일 뿐만 아니라, 국외적으로도 찾아보기 어려운 새로운 수치해석방법이라고 할 수 있다. 먼저 적용하는 수치모델을 검증하기 위하여 해안대수층의 해수-담수 경계면에 관한 수리모형실험결과와 비교 검토하여 수치모델의 타당성 및 유효성을 확인하였다. 그리고 해수위 및 지하수위 변화를 고려한 해안대수층 내의 해수침투모의를 수행하여 해수위-지하수위 차와 해수위의 비(${\Delta}h/h$)의 증가에 따른 해안대수층 내의 유동장 그리고 해수-담수 경계면 분포 특성에 관하여 논의하였다. 또한 기존의 비확산 수치모델에서 도출할 수 없었던, ${\Delta}h/h$에 따른 해안대수층 내의 연직 염분농도로 부터 해수침투 특성을 파악하였으며, 최종적으로 지표화 할 수 있는 ${\Delta}h/h$가 해안대수층 내의 해수침투거리에 미치는 영향에 대하여 분석하였다. 이 결과로부터 ${\Delta}h/h$가 작을수록 해안대수층 내의 해수침투가 약해지는 메커니즘을 이해할 수 있었다.

• 소성∙가공
• /
• 제9권3호
• /
• pp.233-241
• /
• 2000

It is well known that the quality and efficiency of the design of metal forming processes can be significantly improved with the aid of effective numerical simulations. In the present study, a two-and three-dimensional finite element simulation system, CAMP form, was developed for the analysis of metal forming processes in the PC environment. It is composed of a solver based on the thermo-rigid-viscoplastic approach and graphic user interface (GUI) based pre-and post-processors to be used for the effective description of forming conditions and graphic display of simulation results, respectively. In particular, in the case of CAMPform 2D (two-dimensional), as the solver contains an automatic remeshing module which determines the deformation step when remeshing is required and reconstructs the new mesh system, it is possible to carry out simulations automatically without any user intervention. Also, the forming analysis considers ductile fracture of the workpiece and wear of dies for better usage of the system. In the case of CAMPform 3D, general three-dimensional problems that involve complex die geometries and require remeshing can be analyzed, but full automation of simulations has yet to be achieved. In this paper, the overall structure and computational background of CAMPform will be briefly explained and analysis results of several forming processes will be shown. From the current results, it is construed that CAMPform can be used in providing useful information to assist the design of forming processes.

• 한국정보처리학회논문지
• /
• 제7권1호
• /
• pp.57-64
• /
• 2000

본 논문에서는 MPI 기반이 성층${\cdot}$회전 난류 시뮬레이션을 위한 LES코드의 기법에 대해 연구하며 그 결과를 실험한다. 본 논문에서는 병렬화 기법을 위해서 순차 LES코드에 내재되어 있는 Tridiagonal solver의 제거를 통한 병렬화의 성능 향상과 포아선 방정식의 병렬화를 위한 영역 분할 방법을 소개한다. 또한 본 논문에서 연구되어진 병렬 LES 코드를 슈퍼컴퓨터에서 다양한 영역 분할에 대한 실험을 수행하며 그 결과에 대해 나타낸다. 실험 환경은 CRAY-T3E에서 수행하였으며, 다양한 영역 분할에 대해 프로세서의 개수를 변화시키며 수행속도와 그에 따른 속도의 향상을 측정하였다. 그 결과 단일 프로세서에서 순차 LES를 수행하는 것보다 병렬 LES코드에서 최고 16배에 해당되는 속도의 향상의 결과를 얻을 수 있었다.

• 한국전산유체공학회지
• /
• 제13권2호
• /
• pp.27-41
• /
• 2008

An unstructured hybrid mesh flow solver has been developed for the simulation of three-dimensional steady and unsteady incompressible flow fields. The incompressible Navier-Stokes equations with an artificial compressibility method were discretized by using a node-based finite-volume method. For the unsteady time-accurate computation, a dual-time stepping method was adopted to satisfy a divergence-free flow field at each physical time step. An implicit time integration method with local time stepping was implemented to accelerate the convergence in the pseudo-time sub-iteration procedure. The one-equation Spalart-Allmaras turbulence model has been adopted to solve high-Reynolds number flow fields. The flow solver was parallelized to minimize the CPU time and to overcome the computational overhead. This method has been applied to calculate steady and unsteady flow fields around submarine configurations and a 3-D infinite cylinder. Validations were made by comparing the predicted results with those of experiments or other numerical results. It was demonstrated that the present method is efficient and robust for the prediction of steady and unsteady incompressible flow fields.

• International Journal of Aeronautical and Space Sciences
• /
• 제12권2호
• /
• pp.190-199
• /
• 2011

Unsteady flow simulations of complete helicopter configurations were conducted, and the flow fields and the aerodynamic interferences between the main rotor, fuselage, and tail rotor were investigated. For these simulations, a three-dimensional flow solver based on unstructured meshes was used, coupled with an overset mesh technique to handle relative motion among those components. To validate the flow solver, calculations were made for a UH-60A complete helicopter configuration at high-speed and low-speed forward flight conditions, and the unsteady airloads on the main rotor blade were compared to available flight test data and other calculated results. The results showed that the fuselage changed the rotor inflow distribution in the main rotor blade airloads. Such unsteady vibratory airloads were produced on the fuselage, which were nearly in-phase with the blade passage over the fuselage. The flow solver was then applied to the simulation of a generic complete helicopter configuration at various flight conditions, and the results were compared with those of the CAMRAD-II comprehensive analysis code. It was found that the main rotor blades strongly interact with a pair of disk-vortices at the outer edge of the rotor disk plane, which leads to high pulse airloads on the blade, and these airloads behave differently depending on the specific flight condition.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 1999년도 추계 학술대회논문집
• /
• pp.167-173
• /
• 1999

An Euler-based CFD tool has been developed for the performance evaluation of a thrust reverser mounted on a high bypass ratio turbofan engine. The computational domain surrounded by the ground and non-reflection boundary includes the whole nacelle configuration with a deployed thrust reverser. The numerical algorithm is based on the modified Godunovs scheme to allow the second order accuracy in both space and time. The grid system is generated by using eleven multi-blocks, of which the total cell number is 148,400. The thrust reverser is modeled as if it locates at the nacelle simply in all circumferential direction. The existence of a fan and an OGV(Outlet Guide Vane) is simulated by adopting the actuator disk concept, in which predetermined radial distributions of stagnation pressure ratio and adiabatic efficiency coefficient are used for the rotor type disk, and stagnation pressure losses and flow outlet angles for the stator type disk. All boundary conditions including the fan and OGV simulation are treated by Riemann solver. The developed solver is applied to a turbofan engine with a bypass ratio of about 5.7 and the diameter of the fan cowl of 83 inch. The computational results show that the Euler-based inviscid method is very useful and economical to evaluate the performance of thrust reversers.

• Advances in aircraft and spacecraft science
• /
• 제3권2호
• /
• pp.149-170
• /
• 2016

Multi-Disciplinary Optimization (MDO) is widely used to handle the advanced design in several engineering applications. Such applications are commonly simulation-based, in order to capture the physics of the phenomena under study. This framework demands fast optimization algorithms as well as trustworthy numerical analyses, and a synergic integration between the two is required to obtain an efficient design process. In order to meet these needs, an adaptive Computational Fluid Dynamics (CFD) solver and a fast optimization algorithm have been developed and combined by the authors. The CFD solver is based on a high-order discontinuous Galerkin discretization while the optimization algorithm is a high-performance version of the Artificial Bee Colony method. In this work, they are used to address a typical aero-mechanical problem encountered in turbomachinery design. Interesting achievements in the considered test case are illustrated, highlighting the potential applicability of the proposed approach to other engineering problems.

• 대한기계학회논문집B
• /
• 제33권2호
• /
• pp.69-78
• /
• 2009

Cavitating flow simulation is of practical importance for many hydraulic engineering systems, such as pump, turbine, nozzle, injector, etc. In the present work, a solver for cavitating flow has been developed and applied to simulate the flows past axisymmetric cylinders. Governing equations are the two-phase Navier-Stokes equations, comprised of continuity equation of liquid and vapor phase. The momentum equation is in the mixture phase. The solver employed an implicit, dual time, preconditioned algorithm in curvilinear coordinates. Computations were carried out for three axisymmetric cylinders: hemispherical, ogive, and caliber-0 forebody shape. Then, the present calculations were compared with experiments and other numerical results to validate the present solver. Also, the code has shown its capability to accurately simulate the re-entrant jet phenomena and ventilated cavitation. Hence, it has been found that the present numerical code has successfully accounted for cavitating flows past axisymmetric cylinders.

• 한국항공우주학회지
• /
• 제37권10호
• /
• pp.947-954
• /
• 2009

본 연구에서는 다화학종 희박유동의 해석을 위해, GH(Generalized Hydrodynamic) 방정식을 기반으로 한 축대칭 유동 해석이 가능한 다화학종 GH 수치해석 기법을 전산유체역학 수치해석자로서 개발하였다. 최초로 구현된 다화학종 GH 수치기법은 축대칭 형상의 물체 주위의 극초음속 희박유동을 대상으로 하여, DSMC(Direct Simulation Monte Carlo) 및 N-S(Navier-Stokes) 방정식의 결과와의 비교를 통해 정확도를 검증하고자 하였다. GH 해석자의 정확도 향상을 위해 고체 벽면에서의 여러 가지 slip-wall 경계조건을 적용하고 각각의 결과를 비교하였다. 또한, 높은 Knudsen 수의 1차원 수직 충격파 구조 문제를 통해 GH 방정식의 엔트로피 특성 및 정확성을 고찰하였다.

• 한국시뮬레이션학회:학술대회논문집
• /
• 한국시뮬레이션학회 2004년도 춘계학술대회 논문집
• /
• pp.136-140
• /
• 2004

A power-plant simulation tool has been developed for training the plant operators and testing a plant control system. The simulation tool is composed of a graphic editor, a component model builder and a system simulation solver. Such new programing techniques as object-oriented modeling and GUI(Graphical User Interface) are employed in developing the simulation tool. The graphic editor is based on the OpenGL library for effective implementation of GUI while the component model builder is based on object-oriented programming for efficient generalization of component models. The developed tool has been verified through the simulation of a real power plant.