• Title/Summary/Keyword: spatial differencing method

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A Hybrid Spatial Differencing Scheme for Discrete Ordinates Method in 2D Rectangular Enclosures (2차원 사각 밀폐 공간에서의 구분 종좌표법을 위한 하이브리드 공간 차분법)

  • Kim, Il-Kyoung;Kim, Woo-Seung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.1
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    • pp.104-113
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    • 1999
  • A hybrid spatial differencing scheme for the discrete ordinates method is proposed to predict radiative heat transfer in two-dimensional rectangular enclosures. Since this scheme takes the advantages of the diamond scheme and step scheme and includes the characteristics of medium, more accurate and stable results can be obtained. In its development several spatial differencing schemes are examined to address the effect of numerical smearing (or false scattering). Predictions from the proposed hybrid scheme are compared to those of other schemes for transparent, purely absorbing, purely scattering, or absorbing-emitting-isotropically scattering media. It is found that the proposed scheme predicts stable and less smeared results than others.

A Decorrelation Technique for Direction-of-Arrival Estimation of Coherent Signals (Coherent 신호의 입사방향 추정을 위한 상관관계 제거 기법)

  • Park, Geun-Ho;Shin, Jong-Woo;Kim, Hyoung-Nam
    • Journal of the Institute of Electronics and Information Engineers
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    • v.53 no.8
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    • pp.95-104
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    • 2016
  • Subspace-based direction-of-arrival (DOA) estimation algorithms have a difficulty in dealing with coherent signals caused by multi-path environment. As one of attempts to solve this problem, a spatial differencing method is known to be useful for not only estimating DOAs of the coherent signals but also improving the number of resolvable wavefronts even more than the number of antenna elements. However, since the conventional spatial differencing method uses only the partial statistics of the observed data, this method suffers from the performance degradation in estimation accuracy caused by the residual correlation between the uncorrelated signals. To cope with this problem, in this paper, a generalized spatial differencing method is proposed. Unlike the conventional method, the proposed method utilizes the entire statistics of the received signals. Therefore, the additional performance enhancement in both estimation accuracy and the number of resolvable wavefronts can be achieved. The performance analyses with computer simulations show that the proposed method outperforms the conventional method in terms of the estimation accuracy and the number of resolvable wavefronts.

A Study on Turbulent Flow Fields around Ships (선체주위 난류유동장의 해석에 관한 연구)

  • Lee S. H.;Park J. J.
    • Journal of computational fluids engineering
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    • v.1 no.1
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    • pp.64-70
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    • 1996
  • Three dimensional turbulent flow fields around ships are simulated by a numerical method. Reynolds Averaged Navier-Stokes equations are used where Reynolds stresses are approximated by Baldwin-Lomax and Sub-Grid Scale(SGS) turbulence models. Body-fitted coordinate system is introduced to conform three dimensional ship geometries. The governing equations are discretized by a finite volume method. Temporal derivatives are approximated by the forward differencing and the convection terms are approximated by the QUICK or Kawamura scheme. The 2nd-order centered differencing is used for other spatial derivatives. Pressure and velocity fields are simultaneously iterated by the Highly Simplified Marker-And-Cell method. To verify the numerical method and turbulence models, flow fields around ships are simulated and compared to the experiments.

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A Study on Turbulent Flow Fields around Ships (선체주위 난류유동장의 해석에 관한 연구)

  • Park J. J.;Lee S. H.
    • 한국전산유체공학회:학술대회논문집
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    • 1995.10a
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    • pp.148-153
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    • 1995
  • Three dimensional turbulent flow fields around ships are simulated by a numerical method. Reynolds Averaged Navier-Stokes equations are used where Reynolds stresses are approximated by Baldwin-Lomax and Sub-Grid Scale(SGS) turbulence models. Body-fitted coordinate system is introduced to conform three dimensional ship geometries. The governing equations are discretized by a finite volume method. Temporal derivatives are approximated by the forward differencing and the convection terms are approximated by the QUICK or Kawamura scheme. The 2nd-order centered differencing is used for other spatial derivatives. Pressure and velocity fields are simultaneously iterated by the Highly Simplified Marker-And-Cell method. To verity the numerical method and turbulence models, flow fields around ships are simulated and compared to the experiments.

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Numerical Simulation for Transonic Wing-Body Configuration using CFD (CFD를 이용한 천음속 날개-동체 형상 해석)

  • Kim, Younghwa;Kang, Eunji;Ahn, Hyokeun
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.45 no.3
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    • pp.233-240
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    • 2017
  • The flowfield around transonic wing-body configuration was simulated using in-house CFD code and compared with the experimental data to understand the influence of several features of CFD(Computational Fluid Dynamics) ; grid dependency, turbulence models, spatial discretization, and viscosity. The wing-body configuration consists of a simple planform RAE Wing 'A' with an RAE 101 airfoil section and an axisymmetric body. The in-house CFD code is a compressible Euler/Navier-Stokes solver based on unstructured grid. For the turbulence model, the $k-{\omega}$ model, the Spalart-Allmaras model, and the $k-{\omega}$ SST model were applied. For the spatial discretization method, the central differencing scheme with Jameson's artificial viscosity and Roe's upwind differencing scheme were applied. The results calculated were generally in good agreement with experimental data. However, it was shown that the pressure distribution and shock-wave position were slightly affected by the turbulence models and the spatial discretization methods. It was known that the turbulent viscous effect should be considered in order to predict the accurate shock wave position.

An Adequate Band Selection for Vegetation Index of CASI-1500 Airborne Hyperspectral Imagery Using Image Differencing and Spectral Derivative (차연산과 분광미분을 이용한 항공 초분광영상의 식생지수 산출 적절밴드 선택)

  • Kim, Tae-Woo;We, Gwang-Jae;Suh, Yong-Cheol
    • Journal of the Korean Association of Geographic Information Studies
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    • v.16 no.4
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    • pp.16-28
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    • 2013
  • Recently the various applications and spectral indices development of airborne hyperspectral imagery(A-HSI) has been increased. Especially the vegetation indices (VIs) were used to verify stress and vigor of vegetation. The VIs needs two or more spectral bands selectively to calculate as NIR(near infrared) and red wavelength. The A-HIS has specific band characteristics as narrow, continues and many. The A-HIS has narrow, continues and many specific band characteristics. That could be make it confuse which of bands could be explained for appropriate vegetation characteristics. If the A-HIS bands is not the same the wavelength with VIs' development band setting, then it need a selection adequate for spectral characteristics of target vegetation. Therefore we set 4 substitute bands for NIR and red wavelength respectively and calculated two VIs combined with substitute bands such as NDVI(normalized difference vegetation index) and MSRI(modified simple ratio index). To consider the variation of each VIs, we adapted the image differencing method of change detection technique. Also, we used spectral derivative to identify appropriate bands for spectral characteristics of digital forest cover type map. The result of adequate bands for two VIs selected red #3 as 680.2nm and NIR #2 as 801.7nm. This wavelength was good for any forest type in low variations.

Effectiveness of the Discrete Elements Method for the Slab-Geometry Neutron Transport Equation (1차원 평판에서 Discrete Elements Method의 정확도에 대한 연구)

  • Na, Byung-Chan;Kim, ong-Kyung
    • Nuclear Engineering and Technology
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    • v.22 no.2
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    • pp.151-158
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    • 1990
  • The new discrete elements method (DEM) is applied to the one-group neutron transport equation in one-dimensional slab geometry. The fixed source and the criticality problems are treated and three spatial differencing schemes (the DD, the SC, -and the LC schemes) are tested to determine the most computationally efficient in the DEM. In all cases, the accuracy of the results obtained from the DEM shows an improvement over that obtained from the standard discrete ordinates calculations. And the LC scheme gives the most accurate results in the DEM.

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Parallelization of an Unstructured Implicit Euler Solver (내재적 방법을 이용한 비정렬 유동해석 기법의 병렬화)

  • Kim J. S.;Kang H. J.;Park Y. M.;Kwon O. J.
    • Journal of computational fluids engineering
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    • v.5 no.2
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    • pp.20-27
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    • 2000
  • An unstructured implicit Euler solver is parallelized on a Cray T3E. Spatial discretization is accomplished by a cell-centered finite volume formulation using an upwind flux differencing. Time is advanced by the Gauss-Seidel implicit scheme. Domain decomposition is accomplished by using the k-way n-partitioning method developed by Karypis. In order to analyze the parallel performance of the solver, flows over a 2-D NACA 0012 airfoil and 3-D F-5 wing were investigated.

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Parallelization of an Unstructured Implicit Euler Solver (내재적 방법을 이용한 비정렬 유동해석 기법의 병렬화)

  • Kim J. S.;Kang H. J.;Park Y. M.;Kwon O. J.
    • 한국전산유체공학회:학술대회논문집
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    • 1999.11a
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    • pp.193-200
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    • 1999
  • An unstructured implicit Euler solver is parallelized on a Cray T3E. Spatial discretization is accomplished by a cell-centered finite volume formulation using an unpwind flux differencing. Time is advanced by the Gauss-Seidel implicit scheme. Domain decomposition is accomplished by using the k-way N-partitioning method developed by Karypis. In order to analyze the parallel performance of the solver, flows over a 2-D NACA 0012 airfoil and a 3-D F-5 wing were investigated.

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A Study on the Numerical Analysis of the Viscous Flow for a Full Ship Model (비대선 모형에 대한 점성유동의 수치해석연구)

  • 박명규;강국진
    • Journal of the Korean Institute of Navigation
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    • v.19 no.2
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    • pp.13-22
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    • 1995
  • This paper presents the numerical analysis results of the viscous flow for a full ship model. The mass and momentum conservation equations are used for governing equations, and the flow field is discretized by the Finite-Volume Method for the numerical calculation. An algebraic grid and elliptic grid generation techniques are adopted for generation of the body-fitted coordinates system, which is suitable to ship's hull forms. Time-marching procedure is used to solve the three-dimensional unsteady problem, where the convection terms are approximated by the QUICK scheme and the 2nd-order central differencing scheme is used for other spatial derivatives. A Sub-Grid Scale turbulence model is used to approximate the turbulence, and the wall function is used at the body surface. Pressure and velocity fields are calculated by the simultaneous iteration method. Numerical calculations were accomplished for the Crude Oil Tanker(DWT 95,000tons, Cb=0.805) model. Calculation results are compared to the experimental results and show good agreements.

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