• 대한기계학회논문집B
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• 제23권1호
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• pp.43-57
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• 1999

The fluid flow and heat transfer in a thin liquid film are investigated numerically. The flow Is assumed to be two-dimensional laminar and surface tension is considered. The most important characteristics of this flow is the existence of a hydraulic jump through which the flow undergoes very sharp and discontinuous change. Arbitrary Lagrangian-Eulerian(ALE) method is used to describe moving free boundary and a modified SIMPLE algorithm based on streamline upwind Petrov-Galerkin(SUPG) finite element method is used for time marching iterative solution. The numerical results obtained by solving unsteady full Navier-Stokes equations are presented for planar and radial flows subject to constant wall temperature or constant wall heat flux, and compared with available experimental data. It Is discussed systematically how the inlet Reynolds and Froude numbers and surface tension affect the formation of a hydraulic jump. In particular, the effect of temperature dependent fluid properties is also discussed.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2001년도 ICCAS
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• pp.180.2-180
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• 2001

In the hot rolling process, the RF AGC (Roll Force Auto Gauge Control) is used to control the roll gap to reduce the variation of rolling force caused by the roll eccentricity and the variation of material thickness. However the effect of the roll eccentricity cannot be distinguished. To eliminate the effect of the roll eccentricity, the roll eccentricity estimation is needed to supplement some drawbacks of RF AGC. In this paper, an ALE(Adaptive Line Enhancer) that extracts the rolling force variation due to the roll eccentricity is suggested. We also provide an algorithm that enhances the convergence time of roll eccentricity estimation. The performance improvement of the Suggested algorithm is shown via simulations.

• 대한기계학회논문집B
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• 제21권11호
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• pp.1538-1551
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• 1997

Kinetic energy conservation for fixed and moving grids is examined in time-accurate finite element computation of fully unsteady inviscid flows. As numerical algorithms, fractional step method (FSM) and modified SIMPLE are used. To simulate the flow in moving grid system, arbitrary Lagrangian-Eulerian (ALE) method is adopted. In the present study, the energy conserving time integration rule for finite element algorithm is proposed and discussed schematically. It is shown that the discretization by Crank-Nicolson in time and Galerkin (central difference) in space must be used to ensure energy conservation. The developed code has been tested for a standing vortex in fixed or moving grid system, sloshing in a tank and propagation of a solitary wave, and has been shown to be a completely energy conserving algorithm.

• Journal of Mechanical Science and Technology
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• 제16권5호
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• pp.683-695
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• 2002

The objective of the present study is to analyze the fluid flow with moving boundary using a finite element method. The algorithm uses a fractional step approach that can be used to solve low-speed flow with large density changes due to intense temperature gradients. The explicit Lax-Wendroff scheme is applied to nonlinear convective terms in the momentum equations to prevent checkerboard pressure oscillations. The ALE (Arbitrary Lagrangian Eulerian) method is adopted for moving grids. The numerical algorithm in the present study is validated for two-dimensional unsteady flow in a driven cavity and a natural convection problem. To extend the present numerical method to engine simulations, a piston-driven intake flow with moving boundary is also simulated. The density, temperature and axial velocity profiles are calculated for the three-dimensional unsteady piston-driven intake flow with density changes due to high inlet fluid temperatures using the present algorithm. The calculated results are in good agreement with other numerical and experimental ones.

• 한국항공우주학회지
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• 제34권8호
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• pp.47-54
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• 2006

본 연구에서는 Lagrangian 단계와 Remap 단계로 이루어진 Two-step Eulerian 기법에 적용되는 수치기법에 대해 살펴보고, 이를 구현하였다. 요소 값은 donor cell 과 van Leer 기법으로 이류처리 하였고, 절점 값은 Simplifed ALE [SALE] 기법으로 이류처리 하였으며, 재료 경계면은 Simple Line Interface Calculation [SLIC] 기법으로 결정하였다. 또한, 프로그램 구현 과정과 Lagrangian 단계와 Remap 단계의 연결 시 주의 깊게 고려해야할 사항들에 대해 자세히 기술하였다. 본 연구를 통해 구현된 Two-step Eulerian 코드의 검증을 위해, 순수 Lagrangian 기법, 그리고 상용코드의 결과와 비교하여 해석 결과의 정확성을 검증하였다.

• 한국전산유체공학회지
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• 제5권1호
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• pp.1-7
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• 2000

In general, FDM(finite difference method) and FVM(finite volume method) are used for analyzing the fluid flow numerically. However it is difficult to apply them to problems involving complex geometries, multi-connected domains, and complex boundary conditions. On the contrary, FEM(finite element method) with coordinates transformation for the unstructured grid is effective for the complex geometries. Most of previous studies have used commercial codes such as KIVA or STAR-CD for the flow analyses in the engine cylinder, and these codes are mostly based on the FVM. In the present study, using the FEM for three-dimensional, unsteady, and incompressible Navier-Stokes equation, the velocity and pressure fields in the engine cylinder have been numerically analyzed. As a numerical algorithm, 4-step time-splitting method is used and ALE(arbitrary Lagrangian Eulerian) method is adopted for moving grids. In the Piston-Cylinder, the calculated results show good agreement in comparison with those by the FVM and the experimental results by the LDA.

• 대한조선학회논문집
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• 제47권5호
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• pp.681-688
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• 2010

During certification of freefall lifeboats, it is necessary to estimate the injury potential of the impact loads exerted on the occupants during water entry. This paper focused on the numerical simulation to predict the acceleration response during the impact of freefall lifeboats on the water using FSI(Fluid-Structure Interaction) analysis technique of LS-DYNA code. FSI problems could be conveniently simulated by the overlapping capability using Arbitrary Lagrangian Eulerian(ALE) formulation and Euler-Lagrange coupling algorithm of LS-DYNA code. Through this study, it could be found that simulation results were in relatively good agreement with experimental ones in the acceleration peak values, and that the loading conditions were very sensitive to the acceleration responses by the experimental and simulation results.

• 한국음향학회지
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• 제29권1호
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• pp.10-17
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• 2010

수중에서 소나를 이용하여 표적을 탐지하고자 할 때 자함에서 발생되는 소음을 감소시켜 표적의 탐지성능을 향상시키는 것은 매우 중요한 일이다. 본 논문에서는 수상함에서 선체고정형소나(HMS)를 사용하는 경우 두 가지 운영모드에 대하여 자함의 소음감소 성능을 분석하였다. 운영자모드에서는 ALE(Adaptive Line Enhancer)기법을 적용하여 자함신호의 광대역 성분을 감소하므로 토널 성분의 탐지성능을 향상하였으며, 자동모드에서는 주 입력신호와 상관관계를 가진 기준 입력신호를 선정하여 조향 방위로 유입되는 잡음신호를 제거하였다. 적응필터를 설계하기 위하여 NLMS(Normalized LMS)알고리즘을 이용하였으며 실제 해상실험 데이터를 이용하여 시뮬레이션을 수행하므로 제안한 기법의 성능을 확인하였다.

• 한국해양환경ㆍ에너지학회지
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• 제10권4호
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• pp.211-217
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• 2007

새로운 공격 무기들의 등장과 적과의 전투환경 변화로 현대의 함정설계에 있어 생존성의 향상은 가장 중요한 요소가 되었으며, 특히 적에게 쉽게 노출되는 수상함에 있어서는 생존성의 취약성에 대비한 감소대책이 보다 강조되고 있다. 생존성을 고려한 함정설계를 위하여 우선 적절한 공격 시나리오를 설정하고 이에 따라 폭발해석을 수행하여야 한다. 폭발은 함의 국부 손상 및 대변형 손상을 야기시키며 이 때 손상된 함정에 대한 적절한 생존성 평가가 중요하다. 본 연구에서는 구조-유체 연성기법 중 하나인 ALE기법을 적용하여 폭발해석을 수행하고 함정의 붕괴거동을 조사하였으며 이 손상된 함정에 대하여 정량적으로 생존시간을 계산할 수 있는 간략계산법을 제시하였다.

• 한국전산유체공학회지
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• 제4권2호
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• pp.39-46
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• 1999

The FVM(Finite Volume Method) have been used mainly for the flow analyses in the piston-cylinder. The objective of the present study is to analyze numerically the piston-driven intake flows using the FEM(Finite Element Method). The FEM algorithm used in this study is 4-step time-splitting method which requires much less execution time and computer storage than the velocity-pressure integrated method and the penalty method. And the explicit Lax-Wendroff scheme is applied to nonlinear convective term in the momentum equations to prevent checkerboard pressure oscillations. Also, the ALE(arbitrary Lagrangian Eulerian) method is adopted for the moving grids. The calculated results show good agreement in comparison with those by the FVM and the experimental results by the LDA.