• Journal of computational fluids engineering
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• v.1 no.1
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• pp.123-141
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• 1996

In this paper the upwind flux difference splitting Navier-Stokes method has been applied to study the perfect gas and the equilibrium chemically reacting hypersonic flow over an axisymmetric sphere-cone(5°) geometry. The effective gamma(γ), enthalpy to internal energy ratio was used to couple chemistry with the fluid mechanics for equilibrium chemically reacting air. The test case condition was at altitude(30km) and Mach number(15). The equilibrium shock thickness over the blunt body region was much thinner than that of perfect gas shock. The pressure difference between perfect gas and equilibrium gas was about 3 ∼ 5 percent. The heat transfer coefficient were also calculated. The results were compared with VSL results in order to validate the current numerical analysis. The results from current method were compared well VSL results ; however, not well at near nose. The proper boundary condition and grid system will be studied to improve the solution quality.

• 한국전산유체공학회:학술대회논문집
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• 1995.10a
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• pp.203-212
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• 1995

In this paper the upwind flux difference splitting Navier-Stokes method has been applied to study the perfect gas and the equilibrium chemically reacting hypersonic flow over an axisymmetric sphere-cone($5^{\circ}$) geometry. The effective gamma($\bar{r}$), enthalpy to internal energy ratio was used to couple chemistry with the fluid mechanics for equilibrium chemically reacting air. The test case condition was at altitude(30Km) and Mach number(15). The equilibrium shock thickness over the blunt body region was much thinner than that of perfect gas shock. The pressure difference between perfect gas and equilibrium gas was about $3\sim5$ percent. The skin friction coefficient and heat transfer coefficient were also calculated.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.459-464
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• 2001

The main object of this study is to develop a reliable FEM simulation technique for the analysis of Steel D&I Can bodymaking process using ABAQUS software. The body making process includes drawing, redrawing, 3 step ironing, doming. The newly developed FEM code in this research is based on the previous research achievement of POSCO for the drawing, redrawing and ironing process. The analysis is performed using two dimensional axisymmetric elements to analyze the punch force, the height of can, the distribution of residual stress and strain. The effect of blank thickness, gap of ironing die is also analyzed.

• Journal of Mechanical Science and Technology
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• v.16 no.11
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• pp.1448-1456
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• 2002

The present study addresses the flow characteristics involved in the self-induced oscillations of the underexpanded jet impinging upon a cylindrical body. Both experiment and computational analysis are carried out to elucidate the shock motions of the self-induced oscillations and to find the associated major flow factors. The underexpanded sonic jet is made from a nozzle and a cylindrical body is placed downstream to simulate the impinging jet upon an obstacle. The computational analysis using TVD scheme is applied to solve the axisymmetric, unsteady, inviscid governing equations. A Schlieren system is employed to visualize the self-induced oscillations generated in flow field. The data of the shock motions are obtained from a high-speed video system. The detailed characteristics of the Mach disk oscillations and the resulting pressure variations are expatiated using the time dependent data of the Mach disk positions. The mechanisms of the self-induced oscillations are discussed in details based upon the experimental and computational results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.5
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• pp.1613-1623
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• 1996

In this paper, two discretization methods, hybrid and QUICK, are tested for the Navier-Stokes equations written in general nonorthogonal body fitted coordinates. Comparison is made by calculating two laminar flows at low Reynolds numbers of 10 - 100. One is a two-dimensional channel of gradually expanding cross section and the other is an axisymmetric flow through a circular tube having a circular constriction. Results show that the QUICK scheme results in a numerical solution more accurate than that of hybrid. The QUICK scheme also shows faster convergence for both test cases. As the number of grid points increases, all numerical solutions converge with more oscillation. The number of grid points in the y-direction(cross stream direction) is also shown to play a significant role in the approximation of convection term within separated flow zone.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.1
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• pp.1-8
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• 1996

A potential-based panel method has been developed for numerical computation of wave resistance on a hybrid hydrofoil. Hybrid hydrofoil is composed of a main body, two struts and two hydrofoils. The main body, which is assumed to be an axisymmetric body for the present analysis, is normally used to support displacement of a body with its buoyancy. Normal dipoles and the sources are distributed on the body(main body, struts, hydrofoils) and the sources are distributed on the free surface. Linearized free surface and the radiation conditions are satisfied using the fourth order finite difference operator and the semi-linear pressure Kutta condition is used for the numerical computation of the hydrofoils. Poisson type free surface condition has been used for the numerical computation and hyperboloidal panel method has been used for better numerical accuracy. To verify this numeric method, model tests are performed in circulation water channel. From the comparison of experimental results with numeric ones, the present method can be used as a useful tool for the design of high speed vessels.

• 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.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.3
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• pp.252-264
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• 2018

The calculation of steady-state cavitating flows around Supercavitating Underwater Bodies (SUB's), which consist of a circular disk head (cavitator), a conical fore-body, a cylindrical middle-body and either a boat-tail or a flare-tail, are carried out. To calculate the axisymmetric cavitating flow, used is a commercial computational fluid dynamics code based on the finite volume method, Fluent. From the analysis of numerical results, the cavity and drag, affected by the fore-body and tail of the SUB's, are investigated. Firstly, the effect of the fore-body shape is investigated with the same disk cavitator and a cylindrical rear-body of fixed diameter. Then with the same cavitator and a fixed fore-body, the effect of the rear-body shape is investigated. Before the cavity generated by the cavitator covers the slant of fore-bodies sufficiently, the larger the cone angle of the fore-body(i.e., the shorter the slant length), the larger the drag and the slower the development of cavity. After the cavity covers the fore-body completely so that the pressure drag component of the body is vanished, the characteristics of drag-velocity curves are identical. Also, as the tail angle is bigger, the cavity generated by the cavitator is suppressed further and the drag becomes larger. The peak of the drag appears for the flare-tail, i.e., when the tail angle is positive(+). On the contrary, the trough of the drag appears for the boat-tail, i.e., when the tail angle is negative(-). When the tail angle is 5 degrees, the peak of the drag appears at the body speed of 80m/s and the value of the drag is 43% larger than that at the design speed of 100m/s. When the tail angle is -5 degrees, the trough of the total drag appears at 75m/s and that drag is 30% smaller than that of the cavitator, which means the rest of the body has a negative drag.

• The Journal of Korean Academy of Prosthodontics
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• v.38 no.3
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• pp.348-357
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• 2000

The purpose of this study is to examine the effect of partial osseointegration situation on bone loading patterns around two different free-standing screw shaped implants (Nobel Biocare, Gothenburg, Sweden and Degussa-Huls, Hanau, German). Two dimensional axisymmetric Finite element models of two implants(10mm length and 4mm diameter) were created according to different bone quantity, quality and osseointegration ratio in maxilla and mandible bone. At the same time uni-cortical and hi-cortical fixation were analyzed. Generally, full bond case showed less stress than partial bond case in overall area and mandibular model showed less amount of stress than that of maxilla model. Maximum stress of the Branemark implant is higher than that of ANKYLOS regardless of bonding ratio at crestal and apex region. However, more stress concentration was noted in ANKYLOS implant at screw body area especially in mandible. The effect of bicortical fixation on crestal bone stress reduction is dramatical in mandible however, there was no significant effect in maxillary case. The effect of partial bond on stress distribution was more significant at screw body and apex region than in crestal region. Partial bond cases demonstrated greater stress accumulation in trabecular bone than cortical bone. It is concluded that the more accurate model of implant and bone which affects stress and strain distribution is needed to mimic in vivo behavior of implants.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.293-298
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• 2005

We calculate the coordinates of an axisymmetric nozzle with a central body. This nozzle ensures a transonic flow with a plane sound surface, which is orthogonal to the symmetry axis and has a wall kink at the sonic point, The Chaplygin transformation in the subsonic part of the flow leads the Dirichlet problem for a system of nonlinear equations. The definition domain of the solution in the velocity-hodograph plane is taken as a rectangle. This enables one to obtain the nozzle with a monotonic distribution of velocity along its subsonic part. In the nonlinear differential equation, the linear Chaplygin operator for plane flows is separated, which allows the iterative calculation of the solution. The supersonic part of the nozzle is calculated under the assumption that the flow at the nozzle exit is uniform and parallel to the symmetry axis; i.e., the supersonic jet outflows to the submerged space with the same pressure. The calculation is performed by the characteristic method. The exact solution of Tricomi equation for near-sonic flows with the straight sonic line is used to 'move away' the sound plane. The velocity distribution alone the supersonic part of the nozzle is also monotonic, which ensures the absence of the boundary-layer separation and, therefore, the adequacy of the ideal-gas model. calculations show that the flow in the supersonic part of the nozzle is continuous (compression shocks are absent)