• Journal of the Korean Solar Energy Society
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• v.30 no.1
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• pp.34-41
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• 2010

Gas hydrates are solid solutions when water molecules are linked through hydrogen bonding and create host lattice cavities that can enclose many kinds of guest(gas) molecules. There are plenty of methane(gas) hydrate in the earth and distributed widely at offshore and permafrost. Several schemes, to produce methane hydrates, have been studied. In this study, depressurization method has been utilized for the numerical model due to it's simplicity and effectiveness. IMPES method has been used for numerical analysis to get the saturation and velocity profile of each phase and pressure profile, velocity of dissociation front progress and the quantity of produced gas. The values calculated for the sample length of 10m, show that methane hydrates has been dissolved completely in approximately 223 minutes and the velocity of dissociation front progress is 3.95㎝ per minute. The volume ratio of the produced gas in the porous media is found to be about 50%. Analysing the saturation profile and the velocity profile from the numerical results, the permeability of each phase in porous media is considered to be the most important factor in the two phase flow propagation. Consequently, permeability strongly influences the productivity of gas in porous media for methane hydrates.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.11 s.176
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• pp.64-71
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• 2005

In order to measure surface roughness profile, stylus type equipments are commonly used, but the stylus keeps contact with surface and damages specimens by its tip pressure. Therefore, optics based measurement systems are developed, and light phase interferometer, which is based on light interference phenomenon, is the most noticeable research. However, light interference based measurements require translation mechanisms of nano-meter order in order to generate phase differences or multiple focusing, thus the systems cannot satisfy the industrial need of on-the-machine and in-process measurement to achieve factory automation and productive enhancement. In this research, we focused light reflectance phenomenon rather than the light interference, because reflectance based method do not need translation mechanisms. However, the method cannot direct]y measure surface roughness profile, because reflected light consists of several components and thus it cannot supply surface height information with its original form. In order to overcome the demerit, we newly proposed an image processing based algorithm, which can separate reflected light components and conduct parameterization and reconstruction process with respect to surface height information, and then confirmed the reliability of proposed algorithm by experiment.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.2
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• pp.296-303
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• 1987

The composite gear which is composed of involute curve and circular arc has been studied. In the vicinity of pitch point, its profile is an involute curve, and in the dedenum, a circular arc. The curve in the dedendum is generated by the circular arc of the mating gear. Though the available range between minimum and maximum radius of circular arc can be given by existing tooth profile equation, there was no formulation which relates design parameters to the desired radius. It is attempted to get the formula for the radius of circular arc as a function of design parameters, such as unwounded angle, number of teeth, module, and pressure angle. The radius of circular arc, the chordal tooth thickness at working root circle, nominal bending stress, Hertz stress and contact ratio obtained from derived formula are compared with those of the existing design criteria. And these are compared with those of involute gear.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.17 no.4
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• pp.382-394
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• 1988

Dynamic characteristics of thermally-forced stratification process in a square enclosure with a linear temperature profile at the side walls have been investigated through flow visualization experiment and numerical analysis. The experiment was performed on air with the Rayleigh numbers of order $10^5$. A particle tracer method is used for the flow visualization and to obtain a sudden linear temperature profile at the side walls copper blocks which already have a linear temperature profile are come into contact with the thin copper plates of the test section. Immediately a meridional circulation is developed and heat transfer takes place from the wall to the interior region by circulation of fluid and finally a thermal stratification is achieved. In the numerical study, QUICK scheme for convective terms, SIMPLE algorithm for pressure correction, and the implicit method for the time marching are adopted for the integration of conservation equations. Comparison of flow visualization and numerical results shows that the developing flow patterns are very similar in dynamic nature even though there is a time lag due to the inevitable time delay in setting up a linear temperature profile. For high Rayleigh numbers, the oscillatory motion is likely to take place and stratified region is extended. However, initial temperature adjustment process is much slower than that for low Rayleigh numbers.

• Computers and Concrete
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• v.17 no.2
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• pp.189-199
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• 2016

Chloride penetration is considered as a most crucial factor for the determination of the service life of concrete. A lot of experimental tools for the chloride penetration into concrete have been developed, however, the mechanism was based on only diffusion, although permeability is also main driving forces for the chloride penetration. Permeation reacts on submerged concrete impacting for short to long term durability while capillary suction occurs on only dried concrete for very early time. Furthermore, hydrostatic pressure increases in proportional to measured depth from the surface of water because of the increasing weight of water exerting downward force from above. It is thought, therefore, that the water pressure has a great influence on the chloride penetration and thereby on the service life of marine concrete. In this study, new experiment is designed to examine the effect of water pressure on chloride penetration in concrete quantitatively. As an experiment result, pressure leaded a quick chlorides penetration by a certain depth, while diffusion induced chlorides to penetrate inward slowly. Therefore, it was concluded that chloride should penetrates significantly by water pressure and the phenomena should be accelerated for concrete exposed to deep sea. The research is expected as a framework to define the service life of submerged concrete with water pressure and compute water permeability coefficient of cementitious materials.

• Journal of the Korean Society of Combustion
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• v.16 no.3
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• pp.33-40
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• 2011

Combustion experiments were conducted at three different fuels ($CH_4$, $C_2H_4$ and $C_3H_8$) to investigate the effects of combustor pressure (30 ~ -30 kPa) on combustion charateristics and reaction zone structure. Regardless of the fuels, emission index of CO (EICO) increased with decreasing combustor pressure, and EICO of $C_2H_4$ was mostly affected by changing combustor pressure at subatmospheric pressure. In order to observe reaction zone, $OH^*$, $CH^*$ and ${C_2}^*$ chemiluminescence intensity were measured. The sequence of the chemiluminescence intensity peak position was affected by chemical characteristics of fuels rather than changing combustor pressure. The emission zone thickness of $C_2H_4$ and $C_3H_8$, defined by the full width at half maximum (FWHM) of $CH^*$ intensity profile, were increased with decreasing combustor pressure. however, the thickness of $C_2H_4$ exhibited the opposite tendency due to the characteristics of the fuel as the bond structure.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.1
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• pp.154-159
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• 2011

The effect of the ignition delay time gap is newly studied. The operational characteristics of the linked two pyrotechnic thrusters are affected by the time gap. Although two thrusters are simultaneously ignited, the time at which the pressure starts to rise in each thruster may not be synchronized. The characteristic of the system with the time gap is compared with that of the fully synchronized system without any time gap. Depending upon the magnitude of the time gap, the pressure-time profile and the ballistic performance are different. When two pyrotechnic thrusters have a time gap, the peak pressure of one thruster(in which the pressure is built up earlier) is increased and the other is decreased. As the time gap is increased, the peak pressure is converged into the maximum pressure. This maximum pressure can be obtained when only one thruster is activated. Because the maximum pressure is bounded, it is predicted that there isn't any catastrophic failures in the considered system. When the time gap is relatively small, the impulse of the combined force acting on the moving body is almost maintained. But the ballistic performance of the system with a large time gap should be carefully estimated because the reduction of the ballistic performance should not be easily neglected.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.285-286
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• 2002

The lubricating characteristics of negative pressure slider were performed by using divergence formulation method with the coordinate transformation method. This method makes it possible to deal with an arbitrary configuration of a lubricated surface. The pressure profile of the slider is calculated. These results are compared to that from direct numerical method. The steady-state, including minimum film thickness, pitching and rolling angle are calculated by multi-dimensional Newton-Rapson method. The stiffness and damping characteristics are also calculated.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.482-483
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• 2009

In chemical mechanical planarization (CMP) process, the uniformity of stress acting on wafer surface is a key factor for uniform material removal of thin film especially in the oxide CMP. In this paper, we analyze the stress on the contact region between wafer and pad with finite-element analysis (FEA). The setting pressure acting on wafer back side was $500g/cm^2$ and the retainer pressure was changed from 300 to $700g/cm^2$. The polishing test is also done with the same conditions. The material removal rate profiles well-matched with stress distribution.

• IE interfaces
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• v.15 no.4
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• pp.432-438
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• 2002

When the trailing edge and leading edge of an airfoil contour of high pressure compressor blades are measured, there exists a measurement error due to the size of the probe stylus ball diameter. In the paper an experimental study is provided to determine the optimum diameter of the probe stylus in inspecting the airfoil of the high pressure compressor blade. The measurement and analysis procedure suggested in this paper will be helpful to those who are involved in measuring and inspecting various types of blades.