• Journal of computational fluids engineering
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• v.8 no.2
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• pp.57-63
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• 2003

Two nonlinear κ-ε models with the wall function method are applied to the fully developed turbulent flow in a square duct. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in details both qualitatively and quantitatively with each other. A nonlinear κ-ε model with the wall function method capable of predicting accurately duct flows involving turbulence-driven secondary motion is presented in the present paper. The nonlinear κ-ε model of Shih et al.[1] adopted in a commercial code is found to be unable to predict accurately duct flows with the prediction level of secondary flows one order less than that of the experiment.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.11a
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• pp.259-262
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• 1998

PbTi $O_3$ family ceramics can be used for the piezoelectric transformer using thickness extensional vibration mode because it is a material with the large anisotropy between electromechanical coupling factors $k_{t}$ and $k_{p}$. However, PbTi $O_3$ family ceramics have a difficult poling condition on account of its large anisotrophy. In this study, the structural and piezoelectric properties of (P $b_{0.76}$ $Ca_{0.24}$)[ $Ti_{0.96}$(M $n_{1}$3/S $b_{2/3}$)$_{0.04}$] $O_3$ system ceramics were investigated as a function of poling voltage in order to find the best poling condition.ion.n.n.ion.n.

• Journal of the Earthquake Engineering Society of Korea
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• v.2 no.2
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• pp.77-85
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• 1998

Propagation of elastic surface waves in anisotropic media is considered in this study. An analytical technique is proposed to study the scattering of surface waves at the interface between two anisotropic quarter-spaces. The Green's function technique is used to derive a system of equations which can determine the scattering coefficients at the interface. A numerical study is carried out and the trade-offs between the material anisotropy and inhomogeneity are studied.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1980-1985
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• 2003

Two nonlinear ${\kappa}-{\epsilon}$ models with the wall function method are applied to the fully developed turbulent flow in a square duct. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in details both qualitatively and quantitatively with each other. A nonlinear ${\kappa}-{\epsilon}$ model with the wall function method capable of predicting accurately duct flows involving turbulence-driven secondary motion is presented in the present paper. The nonlinear ${\kappa}-{\epsilon}$ model adopted in a commercial code is found to be unable to predict accurately duct flows with the prediction level of secondary flows one order less than that of the experiment.

• Journal of computational fluids engineering
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• v.8 no.1
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• pp.23-29
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• 2003

Two nonlinear κ-ε models with the wall function method are applied to the fully developed turbulent flow in a square duct. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in details both qualitatively and quantitatively with each other. A nonlinear κ-ε model with the wall function method capable of predicting accurately duct flows involving turbulence-driven secondary motion is presented in the present paper. The nonlinear κ-ε model of Shih et al.[1] adopted in a commercial code is found to be unable to predict accurately duct flows with the prediction level of secondary flows one order less than that of the experiment.

• Transactions of Materials Processing
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• v.19 no.7
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• pp.393-398
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• 2010

This paper investigates the effect of material properties on the formability of sheet metals based on the Marciniak-Kuczynski model (M-K model). The hardening behavior of the material is modeled as the Hollomon model with the strain rate effect. The yield surfaces are constructed with Hosford79 yield function. The material properties considered in this study include the R-value, the strain hardening exponent, the strain rate hardening exponent, and the crystal structure of the material. The effect of the crystal structure on formability is roughly expressed as the change of the yield surface by varying the value of the exponent in Hosford79 yield function. Results show that the R-value affects neither the magnitude nor the shape of right hand side of forming limit diagrams (FLDs). Higher strain hardening exponent and higher strain rate hardening exponent improve the formability of sheet metals because they stabilize the forming processes.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.291-294
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• 2005

Recently, the usage of aluminum alloy is rapidly increasing in automobile industry to achieve weight reduction for fuel efficiency. However, design of forming process of aluminum is more difficult than steel because of poor formability and severe springback. Since applications of finite element analysis for the design of sheet metal forming process are actively performed, it is required to conduct proper consideration of aluminum material behavior. In this study, a plane stress yield function Yld2000(Yoon et al., 2000), proven to describe well the anisotropic behavior of aluminum alloy, is implemented for FE analysis. One element test is considered to verify the validity of implementation of Yld2000 model. In addition, cylindrical cup drawing test is performed to verify earing shape of a drawn cup.

• Transactions of Materials Processing
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• v.9 no.6
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• pp.590-597
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• 2000

A finite element formulation lot the simulation of axisymmetric sheet hydroforming is proposed, and an implicit program is coded. In order to describe normal anisotropy of steel sheet, Hill's non-quadratic yield function (Hill, 1979) is employed. Frictional contacts among sheet surface, rigid tool surface, and flexible hydrostatic pressure are considered using mesh normal vectors based on finite element of the sheet. Applied hydraulic pressure is also considered as a function of forming rate and time and treated as an external loading. The complete set of the governing relations comprising equilibrium and interfacial equations is approximately linearized for Newton-Raphson algorithm. In order to verify the validity of the developed finite element formulation, the axisymmetric bulge test is simulated. Simulation results are compared with other FEM results and experimental measurements and showed good agreements. In axisymmetric hydroforming processes of a disk cover, formability changes are observed according to the hydraulic pressure curve changes.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.41 no.5
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• pp.492-501
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• 1992

In this paper, an ion analyzer is used in conjunction with a Langmuir probe to study the chracteristics of ECR plasma such as the ion temperature, ion current density and electron temperature as the operating pressure, ${\mu}$-wave power and axial position change, Silicon etching has been performed with RF-biasing and its etching chracteristics have been discussed in terms of the ion energy distribution function. The maximum value of ion current density appears in the range of 10S0-3T mbar and the broadening of ion energy distribution function increases as pressure increases. Therefore, as pressure decreases, anisotropy increases but selectivity to photoresist decreases.

• Progress in Superconductivity
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• v.6 no.1
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• pp.1-6
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• 2004

Melt-textured YBCO in high quantity and good quality is prepared in a batch process. A mean trapped field >1. IT at 77K is achieved in batch processed material. Studying the microstructure is a necessary tool to understand the growth mechanisms and thus to opimise the material. From the growth induced structures in the material the anisotropy in growth speed is 1.37. From batch processed material function elements for different cryomagnetic applications are constructed. Motors with an output power > 200 kW at 77 K and bearings that can lift more than 200 kg were equipped with melt-textured YBCO.