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김정중(J.J. Kim),김형태(H.T. Kim),반석호(S.H. Van) 한국전산유체공학회 1998 한국전산유체공학회 학술대회논문집 Vol.1998 No.-
A computer code has been developed for the computation of the viscous flow around a ship model with the free surface. In this code, the incompressible Reynolds-averaged Navier-Stokes equations are solved numerically by a finite difference method which employes second-order finite differences for the spatial discretization and a four-stage Runge- Kutta scheme for the temporal integration of the governing equations. For the turbulence closure, a modified version of the Baldwin-Lomax model is exploited. The location of the free surface is determined by solving the equation of the kinematic free-surface condition using the Lax-Wendroff scheme and the boundary-fitted grid is generated at each time step so that one of the grid surfaces always coincides with the free surface. An inviscid approximation of the dynamic free-surface boundary condition is applied as the boundary conditions for the velocity and pressure on the free surface. To validate the computational method and the computer code developed in the present study, the numerical computations are carried out for both Wigley parabolic hull and Series 60 CB=0.6 ship model and the computational results are compared with the experimental data.
김정중(J.J. Kim),김형태(H. T. Kim) 한국전산유체공학회 1998 한국전산유체공학회 학술대회논문집 Vol.1998 No.-
In this paper. incompressible two-dimensional Navier-Stokes equations are numerically solved for the study of steady laminar flow around a body with the wall effect. A second-order finite difference method is used for the spatial discretization on the nonstaggered grid system and the 4-stage Runge-Kutta scheme for the numerical integration in time. The pressure field is obtained by solving the pressure-Poisson equation with the Neumann boundary condition. To investigate the wall effect. numerical computations are carried out for the NACA 0012 section at the various blockage ratios. The pressure and skin friction on the foil surface. velocity profile in its wake and drag coefficient are investigated as functions of the blockage ratio.
정규격자를 사용한 비압축성 Navier Stokes 방정식의 수치해석을 위한 압력 Poisson 방정식의 이산화
김연규(Y.G. Kim),김형태(H.T. Kim),김정중(J.J. Kim) 한국전산유체공학회 1998 한국전산유체공학회 학술대회논문집 Vol.1998 No.-
Various discretiation methods of Laplacian operator in the Pressure-Poisson equation are investigated for the solution of incompressible Navier-Stokes equations using the non-staggered grid. Laplacian operators previously proposed by other researchers are applied to a Driven-Cavity problem. The computational results are compared with those of Ghia. The results show the characteristics of the discrete Laplacian operators.
김연규(Y.G. Kim),김정중(J.J. Kim),김형태(H.T. Kim) 한국전산유체공학회 1999 한국전산유체공학회 학술대회논문집 Vol.1999 No.-
A numerical simulation method has been under development for solving turbulent flows around a ship model in maneuvering motion using the Reynolds Averaged Navier-Stokes equations. The method used second-order finite differences, collocated grids, pressure-Poisson equation and four-stage Runge-Kutta scheme as key components of the solution method. A modified Baldwin-Lomax mode! is used for the turbulence closure. This paper presents a preliminary result of the computational study on turbulent flows past a ship model in drift motion. Calculations are carried out for a Series 60 CB=0.6 ship model, for which detailed experimental data are available. The results of the present calculations are compared with the experimental data for hydrodynamic forces acting on the model as well as velocity distributions at longitudinal sections. Only fair agreements has been achieved. The computational results show the complex asymmetrical shear flow patterns including three-dimensional separations followed by formation of bilge vortices both in bow and stem regions.
김형태(H. T. Kim),김정중(J. J. Kim) 한국전산유체공학회 1997 한국전산유체공학회지 Vol.2 No.1
A FA-FD hybrid method, developed for solving three-dimensional incompressible Navier-Stokes equations, is applied to calculate three-dimensional laminar flows through a square duct with a 90˚ bend. The method discretizes the convective terms in the primaryflow direction with 3rd-order upwind finite-differences and the convective and diffusive terms in the transverse directions with the two-dimensional finite analytic method. The non-staggered grid system is used and the pressure-velocity coupling is achieved by a global iteration procedure based on the PISO algorithm. Detailed comparisons between the computed solutions and the available experimental data are given mainly for the velocity distributions at cross-sections in a 90˚ bend of a square duct with both fully developed and developing entry flows. Although the computational result shows generally a good agreement with the experimental data, there are some significant discrepancies underlining the necessity of more accurate numerical methods as well as reliable experimental data for their validation.
김원상(W.S. Kim),김영신(Y.S. Kim),김정중(J.J. Kim),강윤종(Y.J. Kang),정우창(W.C. Jung),정병창(B.C. Jeong),홍정기(J.K. Hong),서인영(I.Y. Suh) 전력전자학회 2010 전력전자학술대회 논문집 Vol.2010 No.7
본 논문은 2㎿급 풍력시스템의 이중여자유도형 발전기(DFIG)를 제어하기 위한 PCS의 전력변환장치와 주변장치 및 제어기술에 대해서 기술한다. 최근 국내 뿐만 아니라 해외 전력회사에서는 계통전원 사고 시 풍력시스템이 계통연계를 유지하면서 계통의 전력품질에 기여할 수 있는 기능(FRT)을 요구하고 있다. FRT기능 구현을 위한 H/W와 제어 시퀀스를 소개한다.