• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.8
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• pp.1087-1096
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• 2001

The dynamic structures of unsteady CH$_4$/Air jet diffusion flame with a flame-vortex interaction were numerically investigated. A timed-dependent, axisymmetric computational model and a low mach number approximation were employed in the present calculation. A two-step global reaction mechanism which considers 6 species, was used to calculate the reaction rates. The predicted results including the gravitational effect show that the large outer vortices and the small inner vortices can be well simulated without any additional disturbances near nozzle tip. It was found that the temperature and species concentrations have deviated values even for the same mixture fraction in the flame-vortex interaction region. It was also shown that the flame surface is not deformed by the inner vortex in upstream region, while in downstream region, the flame surface is compressed or stretched by the outer vortex roll-up. The present unsteady jet flame configuration accompanying a flame-vortex interaction is expected to give good implications for the unsteady structures of turbulent flames.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.951-955
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• 2001

The experimental comparison between bonded and unbonded types stem-cement interface was carried out on axisymmetric stem-cement-aluminum model of the femoral component of a total hip replacement. Human femur was modeled in non-tapered and tapered($7.5^{\circ}$) aluminum hollow cylinders to emulate the diaphyseal and metaphyseal segments of the femur. For unbonded type, we tested stems with three different taper angles($5^{\circ},\;7.5^{\circ},\;10^{\circ}$). In every case, the cement-aluminum interface was designed to endure 8MPa shear strength. (a measured value at cement-bone interface) We tested aluminum models under axial loading for both cases. As an experimental result, it was found that unbonded stem sustained more axial load as bonded stem in both cases, diaphyseal and metaphyseal models. The unbonded types failed in cement mantle under axial compressive load, while the bonded ones failed in shear at cement-aluminum interface. These results suggest that a polished stem will sustain much higher axial load than a roughened stem. And a polished stem will make more stable cement-bone interface that may promote better osteosythesis around the stem.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.459-464
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• 2000

In order to investigate the effectiveness of an orifice system in producing pressure drops and the effect of compressibility on the Pressure drop, computations using the mass-averaged implicit Wavier-Stokes equations were applied to the axisymmetric pipe flows with the operating pressure ratio from 1.5 to 20.0. The standard k-e turbulence model was employed to close the governing equations. Numerical calculations were carried out for some combinations of the multiple orifice configurations. The present CFD data showed that the orifice systems, which have been applied to incompressible flow regime to date, can not be used for the hint operating Pressure ratio flows. The orifice interval did not strongly affect the total pressure drop but the orifice area ratio more than 2.5 led to high pressure drops. The total pressure drop rapidly increased in the range of the operating pressure ratio from 1.5 to 4.0, but it did not depend on the operating pressure ratio over 4.0.

• Proceedings of the KIEE Conference
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• 1999.11b
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• pp.21-23
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• 1999

In this paper, the analysis of the electric field in the chamber of high voltage $SF_6$ GCB(Gas Circuit Breaker) is presented by using C-1 FEM. For this purpose, pre-processing program and post-processing program were developed for axisymmetirc 3 dimensional analysis and the electric field in cylindric chamber was analyzed. Important problem is that electric analysis must be considered coronal due to break-down of $SF_6$ when it is cutted off. To solve this problem, a procedure is needed to verify that the solution of Poisson's equation for scalar potential satisfy charge continuos condition because of using first order element os not satisfy the electric continuous condition, C-1 FEM is introduce to obtain electirc potential and electric field at the same time. Analysis of the distribution of electric field on model was done. It is confirmed that the developed program in this paper applicable to design and to analyze of characteristics in total program as electric characteristics analysis routine.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.4
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• pp.318-330
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• 2011

This paper investigates the convergence characteristics of the modified artificial compressibility method proposed by Turkel. In particular, a focus is mode on the convergence characteristics due to variation of the preconditioning factor (${\alpha}_u$) and the artificial compressibility (${\beta}$) in conjunction with an upwind method. For the investigations, a code using the modified artificial compressibility is developed. The code solves the axisymmetric incompressible Reynolds averaged Navier-Stokes equations. The cell-centered finite volume method is used in conjunction with Roe's approximate Riemann solver for the inviscid flux, and the central difference discretization is used for the viscous flux. Time marching is accomplished by the approximated factorization-alternate direction implicit method. In addition, Menter's k-${\omega}$ shear stress transport turbulence model is adopted for analysis of turbulent flows. Inviscid, laminar, and turbulent flows are solved to investigate the accuracy of solutions and convergence behavior in the modified artificial compressibility method. The possible reason for loss of robustness of the modified artificial compressibility method with ${\alpha}_u$ >1.0 is given.

• Journal of Welding and Joining
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• v.29 no.2
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• pp.64-71
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• 2011

In this paper, crack propagation analyses in the inner diameter (ID) repair weld of the dissimilar metal weldment of a nozzle were performed using a finite element alternating method (FEAM). To calculate the theoretical solution for the crack tip stress intensity factor, a weak type singular integral equation consisted of crack surface traction and dislocation density function was constructed and solved in conjunction with the FEAM. A two-dimensional axisymmetric finite element nozzle model was prepared and ID repair welding was simulated. An initial crack, 10% depth of weld thickness, was assumed and crack propagation trajectory from the initial crack to the 75% depth of thickness was calculated using the FEAM. Crack growth versus time curve was also calculated and compared with the curves obtained from ASME code method. With the method constructed in this paper, crack propagation trajectory and crack growth time were calculated automatically and effectively.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.678-681
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• 2010

In the present work, a numerical study is conducted to investigate the effect of the transient nozzle pressure ratio (NPR) on the flow fields inside the nozzle. The unsteady, compressible, axisymmetric, Navier-Stocks equations with SST $k-{\omega}$ turbulence model are solved using a fully implicit finite volume scheme. In order to simulate the start-up and shut-down processes of the engine, NPR is varied from 2.0 to 10.0. It is observed that the interaction patterns and the hysteresis phenomenon strongly depend on the time variation of NPR, leading to significantly different characteristics in the lateral forces.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.2
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• pp.7-14
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• 2003

Computational work using the axisymmetric, compressible, Navier-Stokes Equations is carried out to predict the discharge coefficient of mass flow through a micro-critical nozzle. Several kinds of turbulence models and wall functions are employed to validate the computational predictions. The computed results are compared with the previous experimented ones. The present computations predict the experimental discharge coefficients with a reasonable accuracy. It is found that the standard $\kappa$-$\varepsilon$turbulence model with the standard wall function gives a best prediction of the discharge coefficients. The displacement thickness of the nozzle wall boundary layer is evaluated at the nozzle throat and is well compared to a prediction obtained by an empirical equation. The resulting displacement thickness of the wall boundary layer is about 2% to 0.6% of the diameter of the nozzle throat for the Reynolds numbers of 2000 to 20000.

• Journal of the Semiconductor & Display Technology
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• v.18 no.3
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• pp.12-18
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• 2019

The protective double layer polymer coatings on silica optical fibers are realized by wet-on-wet liquid coating process and they play an important role in final quality of mass produced optical fibers. This numerical study aims to analyze the effects of secondary coating die design parameters by employing two dimensional axisymmetric model of coating cup and coating die geometry and computational fluid dynamics simulations which include temperature dependent viscosity of polymer coating liquids and viscous dissipation heating. Under high speed fiber drawing conditions and pressurized coating liquid supply, the effects of converging die angle are investigated in order to appreciate the change of coating liquid flow patterns such as flow recirculation zone near coating die as well as primary and secondary coating layer thicknesses. The auxiliary coating die to converging coating die is also tested and the results find that this concept is advantageous in achieving stable double layer coatings on silica glass fiber.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.4
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• pp.16-23
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• 2008

Theoretical and numerical approaches were conducted in order to study supersonic exhaust diffusers to simulate high altitude performance of rockets on the ground. A physical model of concern includes a rocket motor, vacuum chamber, and diffuser, which have axisymmetric configurations. An analysis was conducted to investigate operation characteristics of supersonic exhaust diffusers from a flow-development point of view. Emphasis was placed on theoretical formulation to predict the starting pressure of diffusers, the effect of the vacuum chamber size, and the minimum starting pressure of the rocket motor to start the diffuser.