• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1649-1651
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• 2001

The effect of ribbed spacers having metallic particle attached to the post-type spacer on dielectric breakdown phenomena has been investigated using electric field analysis for imaginary streamer process and a breakdown experiment. It was described that the electric field analysis and the dielectric breakdown test were performed on the case that the particle was attached to the various position of the ribbed spacer having various shapes. As a result, the breakdown voltage of the spacer with two ribs was highest, and it was varied by the length and the thickness of the rib. Especially, in case of the rib with round edge, the breakdown voltage was higher than that with rectangular edge, which complied with the result through the field analysis.

• Journal of Mechanical Science and Technology
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• v.16 no.3
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• pp.395-402
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• 2002

This paper shows how to formulate the transient analysis of 2-dimensional Hagen-Poiseuille flow using smoothed particle hydrodynamics (SPH). Treatments of viscosity, particle approximation and boundary conditions are explained. Numerical tests are calculated to examine effects caused by the number of particles, the number of particles per smoothing length, artificial viscosity and time increments for 2-dimensional Hagen-Poiseuille flow. Artificial viscosity for reducing the numerical instability directly affects the velocity of the flow, though effects of the other parameters do not produce as much effect as artificial viscosity. Numerical solutions using SPH show close agreement with the exact ones for the model flow, but SPH parameter must be chosen carefully Numerical solutions indicate that SPH is also an effective method for the analysis of 2-dimensional Hagen-Poiseuille flow.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.3
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• pp.255-264
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• 2015

Wind load and flow field of a drillship with respect to various super structures were experimentally investigated in KARI 1m-wide wind tunnel with an atmospheric boundary layer simulation. Six-component external balance and Particle image velocimetry technique were used to measure wind load and velocity vectors in the flow-field around the model respectively. The experimental model was an imaginary shaped drillship with an approximated model which has 1/640 scale compared with recent typical drillships. The test Reynolds number based on the overall length was about 1.5×10⁶. It was found that dominant factors influencing on ship wind load are cabin shape and cabin height. Round cabin has smaller axial wind load and narrow boundary layer around the ship than rectangular one, but its yawing moment at certain angles becomes higher. Low cabin height also show positive effects on axial wind load too. Hull shape and forecastle shape show relatively small influences on wind loads except for slight changes around ±45° wind directions.

• New Physics: Sae Mulli
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• v.68 no.11
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• pp.1225-1230
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• 2018

Schwinger pair production of electrons and positrons in a strong electric field is a prediction of nonperturbative quantum field theory, in which the out-vacuum is superposed of multi-particle states of the in-vacuum. Solving the Dirac or Klein-Gordon equation in the background field, though a linear wave equation, and finding the pair-production rate is a difficult or nontrivial job. The phase-integral method has recently been introduced to compute the pair production in space-dependent electric fields, and a complex analysis method has been employed to calculate the pair production in time-dependent electric fields. In this paper, we apply the complex analysis method to a Sauter-type electric field and other hyperbolic-type electric fields that vanish in the past and future and show that the Stokes phenomena in pair production occur when the time-dependent frequency for a given momentum has finite simple poles (polons) with pure imaginary residues.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05b
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• pp.75-81
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• 2003

This study evaporates ZnO layer thickness differently with RF sputtering method on Si Wafer(n-100). This study is performed to examine the characteristics of photon energy and dielectric loss according to the thickness of ZnO and increase the reliability and reproduction of ZnO thin film. It is confirmed that the variation of electric Permittivity by frequency is resulted from the formation of particles within thin film, the particle size and the polarization on grain boundary. Peak of electric Permittivity value of thin film has slower and less value in early low wavelength by the coulomb force involved in carrier combination according to the increase of frequency. Reversal of electric Permittivity values is induced by dipole polarization shown in the dielectric of thin film. Complex electric constant $({\varepsilon}_1{\varepsilon}_2)$ has larger peak values as it’s thickness is thinner and then it is larger according to the increase of frequency. Electric Permittivity by photon energy has large value in imaginary number and is reduced exponentially by the increase of carrier density according to that of photon energy.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.08a
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• pp.73-79
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• 2002

This study evaporates ZnO layer thickness' differently with RF sputtering method on Si Wafer(n-100). This study is performed to examine the characteristics of photon energy and dielectric loss according to the thickness of ZnO and increase the reliability and reproduction of ZnO thin film. It is confirmed that the variation of electric Permittivity by frequency is resulted from the formation of particles within thin film, the particle size and the polarization on grain boundary. Peak of electric Permittivity value of thin film has slower and less value in early low wavelength by the coulomb force involved in carrier combination according to the increase of frequency. Reversal of electric Permittivity values is induced by dipole polarization shown in the dielectric of thin film. Complex electric constant $({\varepsilon}_1,{\varepsilon}_2)$ has larger peak values as it's thickness is thinner and then it is larger according to the increase of frequency. Electric Permittivity by photon energy has large value in imaginary number and is reduced exponentially by the increase of carrier density according to that of photon energy.

• Asian Journal of Atmospheric Environment
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• v.6 no.4
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• pp.304-313
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• 2012

In this study, the ${\AA}$ngstrom exponent for polydispersed aerosol during dynamic processes was investigated. Log-normal aerosol size distribution was assumed, and a sensitivity analysis of the ${\AA}$ngstrom exponent with regards the coagulation and condensation process was performed. The ${\AA}$ngstrom exponent is expected to decrease because of the particle growth due to coagulation and condensation. However, it is difficult to quantify the degree of change. In order to understand quantitatively the change in the ${\AA}$ngstrom exponent during coagulation and condensation, different real and imaginary parts of the refractive index were considered. The results show that the ${\AA}$ngstrom exponent is sensitive to changes in size distribution and refractive index. The total number concentration decreases and the geometric mean diameter of aerosols increase during coagulation. On the while, the geometric standard deviation approaches monodispersed size distribution during the condensation process, and this change in size distribution affects the ${\AA}$ngstrom exponent. The degree of change in the ${\AA}$ngstrom exponent depends on the refractive index and initial size distribution, and the size parameter changes with the ${\AA}$ngstrom exponent for a given refractive index or chemical composition; this indicates that the size distribution plays an important role in determining the ${\AA}$ngstrom exponent as well as the chemical composition. Subsequently, this study shows how the ${\AA}$ngstrom exponent changes quantitatively during the aerosol dynamics processes for a log-normal aerosol size distribution for different refractive indices; the results showed good agreement with the results for simple analytic size distribution solutions.