• The KSFM Journal of Fluid Machinery
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• v.11 no.6
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• pp.46-53
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• 2008

Flow structures in an axial compressor with a non-uniform tip clearance were predicted by solving a simple prediction method. For more reliable prediction at the off-design condition, off-design flow characteristics such as loss and flow blockage were incorporated in the model. The predicted results showed that flow field near the design condition is largely dependent on the local tip clearance effect. However overall flow field characteristics are totally reversed at off-design condition, especially at the high flow coefficient. The tip clearance effect decreases, while the local loss and flow blockage make a complicated effect on the compressor flow field. The resultant fluid induced Alford's force has a negative value near the design condition and it reverses its sign as the flow coefficient increases and shows a very steep increase as the flow coefficient increases.

• Bulletin of the Korean Mathematical Society
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• v.51 no.4
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• pp.1087-1100
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• 2014

We present an accurate and efficient numerical method for solving the Black-Scholes equation. The method uses an adaptive grid technique which is based on a far-field boundary position and the Peclet condition. We present the algorithm for the automatic adaptive grid generation: First, we determine a priori suitable far-field boundary location using the mathematical model parameters. Second, generate the uniform fine grid around the non-smooth point of the payoff and a non-uniform grid in the remaining regions. Numerical tests are presented to demonstrate the accuracy and efficiency of the proposed method. The results show that the computational time is reduced substantially with the accuracy being maintained.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.171-174
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• 2006

When two particles close to each other are in electrophoretic motion, each particle is under the influence of the non-uniform electric field generated by the other particle. Two particles may attract or repel each other due to the dielectric force depending on their positions in the non-uniform electric field. It is shown analytically that two adjusting rigid particles can form an aggregate due to the dielectric interaction. To verify the validity of the theoretical prediction, an experiment is carried out by using a microchannel. In the experiment, AC electric field is used to eliminate cumbersome electroosmotic flow. The experimental result shows that the particles form a chain-like structure, which is typically observed in electro-rheological fluid, due to the dielectric interaction.

• Journal of the Korean Vacuum Society
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• v.7 no.s1
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• pp.7-14
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• 1998

Details are given of an study of the characteristics of field-induced electron emission from hydrogen-free high $sp^3$ content(>90%) amorphous diamond (a-D) film deposited on heavily doped ($\rho$<0.01 $\Omega\cdot\textrm{cm}$) n-type monocrystalline Si(111) substrate. It is demonstrated that a-D film has excellent electron field emission properties. Emission current can reach 0.9 $\mu$A at applied field as low as 1 V/$\mu\textrm{m}$, and emission current density can be obtained about several mA/$\textrm{cm}^2$. The emission current is stable when the beginning current is at 50 $\mu$A within 72 hours. Uniform fluorescence display of electron emission from whole face of the a-D film under the electric field of 10~20 V/$\mu\textrm{m}$ was also observed. It can be considered that the contribution of excellent electron emission property results from its smooth, uniform, amorphous surface and high $sp^3$ content of the a-D films.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.9
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• pp.136-141
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• 2010

In this paper, after the third electrode type oxidant generator which could format non-uniform electric field in water had been manufactured and installed, by direct electrolysis, the effects of the hydrogen potential and oxidation reduction potential characteristics attendant upon electric field change on a higher concentration oxidant generation characteristics were investigated. Consequently, as the third electrode was installed in the middle of two slit electrodes and the polarity of applied power was changed, it was observed that the third electrode system with the positive electrode can generate a higher concentration oxidant, hydrogen potential and oxidation reduction potential as compared with that of the negative electrode. It is because the positive electrode was bombarded mostly energetic electrons and the negative electrode was bombarded mainly by less energetic positive ions.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.450-450
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• 2010

Recently, field emission emitters made by carbon nanotubes(CNTs) and ink-jet method have been extensively studied due to their low cost, little limitation of size and a high resolution. When CNT emitters are operated, a few highly protruded ones generate most of the emission currents that cause spatial nonuniformity. In this study, we applied selective oxidation to solve this problem on ink-jet printed CNT emitters. Consequently, O2 exposures to field emitting CNT arrays give rise to a permanent damage selectively on the highly emitting CNTs. In spite of turn-on field increase, emission images was showed remarkably uniform after oxygen trimming.

• Journal of Mechanical Science and Technology
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• v.20 no.8
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• pp.1302-1308
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• 2006

The unsteady Hartmann flow of an electrically conducting, viscous, incompressible fluid bounded by two parallel non-conducting porous plates is studied with heat transfer taking the Hall effect into consideration. An external uniform magnetic field and a uniform suction and injection are applied perpendicular to the plates while the fluid motion is subjected to an exponential decaying pressure gradient. The two plates are kept at different but constant temperatures while the Joule and viscous dissipations are included in the energy equation. The effect of the ion slip and the uniform suction and injection on both the velocity and temperature distributions is examined.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.5
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• pp.596-608
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• 2018

The present study aims to assess test uncertainty assessment method of nominal wake field measurement by a Stereoscopic Particle Image Velocimetry (SPIV) system in a towing tank. The systematic uncertainty of the SPIV system was estimated from repeated uniform flow measurements. In the uniform flow measurement case, time interval between image frames and uniform flow speed were varied to examine the effects of particle displacement and flow around the SPIV system on the systematic standard uncertainty. The random standard uncertainty was assessed by repeating nominal wake field measurements and the estimated random standard uncertainty was compared with that of laser Doppler velocimetry. The test uncertainty assessment method was applied to nominal wake measurement tests of a very large crude oil carrier model ship. The nominal wake measurement results were compared with existing experimental database by other measurement methods, with its assessed uncertainty.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.5
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• pp.411-414
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• 2009

It has been investigated for the film uniformity and deposition rate of a-C:H films on glass substrate and polymeric materials in the presence of the modulated crossed magnetic field. We used Plasma CVD, i.e, using a crossed electromagnetic field, for uniform depositing thin film. The optimum discharge condition has been discussed for the gas pressure, the magnetic flux density and the distance between substrate and electrodes, As a result, it is found that the optimum discharge conditions are $CH_4$ concentration $CH_4$=10 %, modulated magnetic flux density B=48 Gauss, pressure P=100 mTorr, discharge power supply voltage V=l kV under these experimental conditions. By using these experimental condition, it is possible to prepare the most uniform film extends over about 160 mm of the film width. In this study, we deposited a-C:H thin film on glass substrate, and have a plan that using this condition, study depositing a-C:H thin film on polymeric substrate in next studies.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.9
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• pp.683-694
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• 2008

The performance and durability of Polymer Electrolyte Fuel Cells (PEFCs) are strongly influenced by the uniformity of current density, temperature, species distributions inside a cell In order to obtain uniform distributions in them, the optimal design of flowfield must be a key factor. In this paper, the numerical study of land/channel flowfield optimizations is performed, using a multi-dimensional, multi-phase, non-isothermal PEFC model. Numerical simulations reveal more uniform current density and HFR(High Frequency Resistance) distributions and thus better PEFC performance with narrower land/channel width where the less severe oxygen depletion effect near the land region and more uniform contact resistance variation along the in-plane direction are achieved. The present study elucidates detailed effects of land/channel width and assist in identifying optimal flow-field design strategies for the operation of PEFCs.