• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.33-36
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• 2007

We performed a discharge analysis on ac plasma display panel through the numerical simulation of the EF (Energy Fluid) model using the electron's energy equation. When it is compared to the results of commonly used LFA (Local Field Approximation) model, there is a clear difference in the spatiotemporal distribution of Xe excited species. In particular, the experimentally observed striation phenomena in the anode region could be observed in EF model and the occurrence of the striation was attributed to the ionization and excitation instability due to the streaming electrons in the anode region plasma.

• Korean Journal of Crystallography
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• v.3 no.2
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• pp.72-84
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• 1992

The investigation has been carried out for purification, single crystal growth mechanism and convective phenomena in EBFZM of Nb metal. It is found that the EBFZM refined effectively oxygen and nitrogen, the interstitial impurities in Nb, but carbon was increased slightly by backstream of diffusion pump oil. The mechanism of single crystal growth associated with the second recrystallieation in Nb was suggested from the relationship between texture of starting materials and the crystal growth in EBFZM. It was observed from the investigation of convection phenomena in molten zone that the Marangoni convection was dominant in molten zone, which caused the striation in Nb and increased the purification effect of oxygen and nitrogen.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.256-261
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• 2007

The purpose of this study is to investigate the effect of shot peening on the fatigue strength and fatigue life of two kinds of aluminum alloys. The fatigue strength behavior of aluminum alloys were estimated by the stress ratio and shot velocities. The fatigue life and strength increased with increasing the test shot velocity. However, at the shot velocity range between 50m/s and 70m/s, the compressive residual stress phenomena were observed in test conditions of different shot velocity. The optimal shot velocity is acquired by considering the peak values of the compressive residual stress, dislocations, brittle striation, slip, and fisheye on the fracture surface of test specimen. It was observed from the SEM observation on the deformed specimen that the brittle striation, fisheye were showed in the intergranular fracture structure boundaries at the this velocities. Therefore, fatigue strength and fatigue life would be considered that shot velocity has close relationship with the compressive residual stress.

• Korean Journal of Materials Research
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• v.22 no.12
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• pp.711-716
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• 2012

Tungsten bronze structure $Sr_{1-x}Ba_xNb_2O_6$ (SBN) single crystals were grown primarily using the Czochralski method, in which several difficulties were encountered: striation formation and diameter control. Striation formation occurred mainly because of crystal rotation in an asymmetric thermal field and unsteady melt convection driven by thermal buoyancy forces. To optimize the growth conditions, bulk SBN crystals were grown in a furnace with resistance heating elements. The zone of $O_2$ atmosphere for crystal growth is 9.0 cm and the difference of temperature between the melt and the top is $70^{\circ}C$. According to the growth conditions of the rotation rate, grown SBN became either polycrystalline or composed of single crystals. In the case of as-grown $Sr_{1-x}Ba_xNb_2O_6$ (x = 0.4; 60SBN) single crystals, the color of the crystals was transparent yellowish and the growth axis was the c-axis. The facets of the crystals were of various shapes. The length and diameter of the single crystals was 50~70 mm and 5~10 mm, respectively. Tungsten bronze SBN growth is affected by the temperature profile and the atmosphere of the growing zone. The thermal expansion coefficients on heating and on cooling of the grown SBN single crystals were not matched. These coefficients were thought to influence the phase transition phenomena of SBN.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.2
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• pp.76-85
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• 1993

In order to predict the free surface signature of turbulent ship wakes two things are essential; a basic understanding of the mechanism of turbulent vortical flow/free surface interactions and a mathematical model to accurately predict the signature. The goal of the study described here is both to supplement experimental work to obtain basic understanding, as well as to condense this understanding in a model(or models) that captures the essential phenomena and thus allows predictions. To do so we followed two main paths guided by experimental observations. One is full simulations of the flow using the clavier-Stokes equations. The other is a vortex modeling, where the vortical structures of the flows are approximated by idealized structures, an the interaction assumed to be essentially inviscid. These approaches complement each other. Full simulations are only applicable to small scale phenomena, where the system is simple, and the Reynolds number is low. The vortex modeling, on the other hand, cannot represent essentially viscous aspects of the problem such as the effect of contamination gradient. Obviously, the modeling is what may eventually lead to a prediction method; the full simulations-too limited to mimic all but the simplest circumstances-are to aid and support the construction of realistic models. We address two-dimensional aspects of the vortex/free surface interaction first. Secondly we obtain some basic understanding of the interaction process through an experiment and then talk about several three-dimensional problems hoping to develop a successful prediction model.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.06a
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• pp.197-201
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• 1997

The momentum, heat and mass trasfer phenomena in the silicon melt of the Czochralki crystal growth system are calculated using a three dimensional numerical simulation thechnique. Even though axisymmetrical boundary conditions are imposed to all calculations in a 3cm diameter crucible, several types of non-axisymmetric profiles of velocities, temperature and oxygen concentration appeared in the melt. Because of the non-axisymmetric profiles of velocities, temperature and oxygen concentration appeared in the melt. Because of the non-axisymmetric profiles and rotations of fluid induced by the crucible rotation, temperatures and oxygen concentrations in the silicon melt fluctuate. The rotating velocity of the profile is calculated from the phase shift of the data of temperature or oxygen at two different points which have same radius from center but 90 degree angular difference. From this calculation, it is found that the rotating veolocity of the oxygen and temperature is different from the crucible rotation rates. Therefore the frequencies of the oscillating temperature and oxygen concentrations are not same to the frequencies of the crucible rotations. Futhermore, the components of the frequencies of the temperature and oxygen concentration at the same point are not same. The fluctuation behaviors of the temperature or oxygen themselves are also different when the points are different. The calculation show that the temperature and the oxygen concentration near the interface also fluctuate. The results suggest that the striation pattern found in the grown silicon single crystals may ben generated by the oxygen concentration and the temperature oscillations of the melt occurred near the interface.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06a
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• pp.522-522
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• 1996

An investigation of the effects of transverse magnetic field and Peltier effect on melt convection and macrosegregation in vertical Bridgman crystal grosth of Te doped InSb was been carried out by means of microstructure observation, Hall measurement, electrical resistivity measurement and X-ray analysis. Before the experiments, Interface stability, convective instability and suppression of convection by magnetic field were calculated theoretically. After doping 1018, 1019 cm-3 Te in InSb, the temperature of Bridgman furnace was set up at $650^{\circ}C$. The samples were grown in I.D. 11mm, 100mm high quartz tube. The velocity of growth was about 2${\mu}{\textrm}{m}$/sec. In order to obtain the suppression of convection by magnetic field in the middle of growth, 2-4KG magnetic field was set on the melt. For searching of the shape of solid-liquid interface and the actual velocity of crystal growth, let 2A current flow from solid to liquid for 1second every 50seconds repeatedly (Peltier effect). The grown InSb was polycrystal, and each grain was very sharp. There was no much difference between the sample with and without magnetic field at a point of view of microstructure. For the sample with Peltier effect, the Peltier marks(striation) were observed regularly as expected. Through these marks, it was found that the solid-liquid interface was flat and the actual growth velocity was about 1-2${\mu}{\textrm}{m}$/sec. On the ground of theoretical calculation, there is thermosolutal convection in the Te doped InSb melt without magnetic field in this growth condition. and if there is more than 1KG magnetic field, the convection is suppressed. Through this experiments, the effective distribution coefficients, koff, were 0.35 in the case of no magnetic field, and 0.45 when the magnetic field is 2KG, 0.7 at 4KG. It was found that the more magnetic field was applied, the more convection was suppressed. But there was some difference between the theoretical calculation and the experiment, the cause of the difference was thought due to the use of some approximated values in theoretical calculation. In addition to these results, the sample with Peltier effect showed unexpected result about the Te distribution in InSb. It looked like no convection and no macrosegregation. It was thought that the unexpected behavior was due to Peltier mark. that is, when the strong current flew the growing sample, the mark was formed by catching Te. As a result of the phenomena, the more Te containing thin layer was made. The layer ruled the Hall measurement. The values of resistivity and mobility of these samples were just a little than those of other reference. It was thought that the reason of this result was that these samples were due to polycrystal, that is, grain boundaries had an influence on this result.