• Journal of Korean Port Research
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• v.13 no.1
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• pp.167-174
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• 1999

Numerical analysis of two-fluid flows for both water and air is carried out. Free-Surface flows with an arbitrary deformation have been simulated around two dimensional submerged hydrofoil. The computation is performed using a finite volume method with unstructured meshes and an interface capturing scheme to determine the shape of the free surface. The method uses control volumes with an arbitrary number of faces and allows cell-wise local mesh refinement. the integration in space is of second order based on midpoint rule integration and linear interpolation. The method is fully implicit and uses quadratic interpolation in time through three time levels The linear equation systems are solved by conjugate gradient type solvers and the non-linearity of equations is accounted for through picard iterations. The solution method is of pressure-correction type and solves sequentially the linearized momentum equations the continuity equation the conservation equation of one species and the equations or two turbulence quantities.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.311-314
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• 2004

The housing of the fuel injector supports the rod, the niddle valve and the solenoid. Based on the procedure of process design, in this paper, the forming operation is designed by the rigid-plastic finite element method. The metal flow during the forming of the fuel injector housing is axisymmetric until the final forming process. The response surface method has been performed to reduce the under-fill and the maximum effective strain. From the results of RSM, the second order regression model of equation is calculated by the least square method and used to determine the optimal values of design variables by simultaneously considering the responses. It is noted that upper under-fill is affected by the design variables of the $2^{nd}$ forming process and lower under-fill is affected by the design variables of the 1st forming process.

• Wind and Structures
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• v.26 no.6
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• pp.355-367
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• 2018

This paper studies the aerodynamic stability of a tensioned, geometrically nonlinear orthotropic membrane structure with hyperbolic paraboloid in sag direction. Considering flow separation, the wind field around membrane structure is simulated as the superposition of a uniform flow and a continuous vortex layer. By the potential flow theory in fluid mechanics and the thin airfoil theory in aerodynamics, aerodynamic pressure acting on membrane surface can be determined. And based on the large amplitude theory of membrane and D'Alembert's principle, interaction governing equations of wind-structure are established. Then, under the circumstance of single-mode response, the Bubnov-Galerkin approximate method is applied to transform the complicated interaction governing equations into a system of second-order nonlinear differential equation with constant coefficients. Through judging the frequency characteristic of the system characteristic equation, the critical velocity of divergence instability is determined. Different parameter analysis shows that the orthotropy, geometrical nonlinearity and scantling of structure is significant for preventing destructive aerodynamic instability in membrane structures. Compared to the model without considering flow separation, it's basically consistent about the divergence instability regularities in the flow separation model.

• Journal of Korea Water Resources Association
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• v.31 no.6
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• pp.795-806
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• 1998

Soil moisture is affected by regional climate, soil characteristics and land surface condition, etc,. Especially, the changes in land surface condition is more than other factors, which is mainly due to rapid urbanization and industrialization. This study is to evaluate how the change of land surface condition impacts on soil moisture field evolution using a simple model of soil moisture dynamics. For the quantification of soil moisture field, the first half of the paper is spared for the statistical characterization based on the first- and second-order statistics of Washita '92 and Monsoon '90 data. The second half is for evaluating the impact of land cover changes through simulation study using a model for soil moisture dynamics. The model parameters, the loss rate and the diffusion coefficient, have been estimated using the observed data statistics, where the changes of surface conditions are considered into the model by applying various parameter sets with different second-order statistics. This study is concentrated on evaluating the impact due to the changes of land surface condition variability. It is because we could easily quantify the impact of the changes of its areal mean based on the linear reservoir concept. As a result of the study, we found; (1)as the variability of land surface condition, increases, the soil moisture field dries up more easily, (2)as the variabilit y of the soil moisture field is the highest at the beginning of rainfall and decreases as time goes on to show the variability of land surface condition, (3)the diffusion effect due to surface runoff or water flow through the top soil layer is limited to a period of surface runoff and its overall impact is small compared to that of the loss rate field.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.1
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• pp.1-8
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• 2001

The computations of the turbulent flow around the ship models with the free-surface effects were carried out. Incompressible Reynolds-Averaged Navier-Stokes equations were solved by using an explicit finite-difference method with the nonstaggered grid system. The method employed second-order finite differences for the spatial discretization and a four-stage Runge-Kutta scheme for the temporal integration. For the turbulence closure, a modified Baldwin-Lomax model was exploited. The location of the free surface was determined by solving the equation of the kinematic free-surface condition using the Lax-Wendroff scheme and a free-surface conforming grid was generated at each time step so that one of the grid boundary surfaces always coincides with the free surface. An inviscid approximation of the dynamic free-surface boundary condition was applied as the boundary conditions for the velocity and pressure on the free surface. To validate the computational method developed in the present study, the computations were carried out for beth Wigley and Series 60 $C_B=0.6$ ship model and the computational results showed good agreements with the experimental data.

• Journal of computational fluids engineering
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• v.4 no.2
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• pp.57-66
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• 1999

Numerical Analysis has been done for the supersonic off-design jet flow due to the pressure difference between the jet and the ambient fluid. The difference of pressure generates an oblique shock or an expansion wave at the nozzle exit. The waves reflect repeatedly on the center axis and the sonic surface in the shear layer. The pressure difference is resolved across these reflected waves. In this paper, the axi-symmetric Navier-Stokes equation has been used with the κ-ε turbulence model. The second order TVD scheme with flux limiters, based on the flux vector split with the smooth eigenvalue split, has been used to capture internal shocks and other discontinuities. Numerical calculations have been done to analyze the off-design jet flow due to the pressure difference. The variation of pressure along the flow axis is compared with an experimental result and other numerical result. The characteristics of the interaction between the shock cell and the turbulence mixing layer have been analyzed.

• 한국전산유체공학회:학술대회논문집
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• 1999.05a
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• pp.155-161
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• 1999

The three-dimensional turbulent cascade flows with and without endwall fences are numerically investigated by solving the incompressible Navier-Stokes equations with a high-Reynolds number $k-{\varepsilon}$ turbulence closure model. A projection method based algorithm is used in the finite-volume formulation, with the second order upwind-differencing scheme for the convective terms. First, assessments on accuracy of the present method are made by comparing the static pressure distributions at the mid-span of the cascade with measured data, and also by confirming the experimental observations on the choice of an optimal fence height for the secondary flow control. In understanding the three-dimensional nature of the secondary flow in turbine cascade, the limiting streamline patterns and the static pressure contours at the suction surface of the blade as well as on the cascade endwall are employed to visualize the effectiveness of the endwall fence for the secondary flow control. Analysis on the streamwise vorticity contour maps along the cascade with the three-dimensional representation of their iso-surfaces reveals the strucuture of the complicated vortical flow in the turbine cascade with endwall fence, and also leads to an understanding on formation of the counter-rotating streamwise vortex over the endwall fence, in explaining the mechanisms of controlling the secondary flow and also for the proper selection of an optimal fence height.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.231-232
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• 2007

Nickel oxide thin films were deposited by the DC magnetron reactive sputtering process under the conditions such as various oxygen flow rates(0, 3, 6, 8, 10 sccm) with constant 33 sccm argon flow rate for the sputtering time of 40 second with the power of 0.3 kW. Sheet resistances were measured by the four point probes. In order to observe discharge voltage characteristics according to the oxygen flow rates, the sputtering processes were performed under the powers of 0.2kW and 0.3kW. The feasibility of the coating system for high quality ferromagnetic thin films was tested through the electromagnetic simulation and the thin film thickness measurement from the experiment. It was shown that a discharge voltage was decreased under the low power and low oxygen flow rate, since the oxygen was quickly saturated on nickel target surface. The sheet resistance was increased as oxygen flow rate increased. The film thickness deposited by the coating system for ferromagnetic target was improved approximately 10% in comparison with previous coating systems.

• Structural Engineering and Mechanics
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• v.37 no.4
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• pp.401-413
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• 2011

The aerodynamic stability of orthotropic tensioned membrane structures with rectangular plane is theoretically studied under the uniform ideal potential flow. The aerodynamic force acting on the membrane surface is determined by the potential flow theory in fluid mechanics and the thin airfoil theory in aerodynamics. Then, based on the large amplitude theory and the D'Alembert's principle, the interaction governing equation of wind-structure is established. Under the circumstances of single mode response, the Bubnov-Galerkin approximate method is applied to transform the complicated interaction equation into a system of second order nonlinear differential equation with constant coefficients. Through judging the stability of the system characteristic equation, the critical divergence instability wind velocity is determined. Finally, from different parametric analysis, we can conclude that it has positive significance to consider the characteristics of orthotropic and large amplitude for preventing the instability destruction of structures.

• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.160-166
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• 1998

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 pronto in its wake and drag coefficient are investigated as functions of the blockage ratio.