• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.4
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• pp.145-151
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• 2005

The synthetic breaking test method was developed to evaluate the breaking performance of ultra high-voltage circuit breaker and made up of two independent circuits; current source circuit and voltage source circuit. In application of this test method, it is necessary to extend the arc of the test breaker. So, the new re-ignition system using VTGS (Vacuum Triggered Gap-Switch) was constructed to improve the efficiency and reliability of this test. In this re-ignition system, VTGS operates in high vacuum state of $5{\time}10^{17}$torr and control system consists of the triggering device and the air M-G (Motor-Generator). This re-ignition system showed the operating characteristics, such as delay time ($t_d$) and jitter time ($t_j$ not exceeding 5us and 1us respectively, and had the operating voltage of $25\~150kVdc$ at the gap distance of 24mm.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1661-1665
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• 2004

Hard disk drives (HDD) in computer are used extensively as data storage capacity. The trend in the computer industry to produce smaller disk drives rotating at higher speeds requires an improved understanding of fluid motion in the space between disks. Laser sheet and digital camera was used for 2-dimensional visualization of the unsteady flow between co-rotating disks in air with a cylindrical enclosure (or shroud). Geometric parameters are gap height (H) between disks, and gap distance (G) between disk tip and shroud. The lobe-structured boundary between inner region and outer region was detected by inserted particles, and the number of dominant vortices was determined clearly It is found from flow visualization that the number of vortex cells can be correlated with Reynolds number based on H which is defined as $Re_H={\Omega}RH/v$ ranging from $7.96{\times}10^2$ to $1.43{\times}10^4$, and decreases as the disk speed increases. The lobe pattern by vortex cells is changed to a circular pattern for the wide gap than narrow one.

• Journal of Communications and Networks
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• v.13 no.5
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• pp.494-498
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• 2011

Satellite digital multimedia broadcasting (S-DMB) systems use gap fillers (GFs) to provide wireless multimedia services to non-line-of-sight locations. GFs act as repeaters, and S-DMB systems require GF networks in order to guarantee mobile reception. Each GF covers a cell or sector. In order to provide contiguous coverage of an area comprising two or more cells or sectors, multiple GFs are needed. However, when multiple GFs are situated close to each other, interference is likely to occur. As a result, in this study, we have investigated system-level environments for planning the design of interference-free GF networks in S-DMB systems. Our investigations revealed that S-DMB services are unavailable because of quality deterioration caused by interference when the delay attributable to a GF and the satellite signals exceeds ${\pm}$256 chips and the distance between the GF and its reception terminal is greater than 4.6 km. On the basis of this analysis, we conducted a field test that confirmed that the above-mentioned time delay can be controlled in such a way as to ensure high quality S-DMB services.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1413-1416
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• 1995

Plasma Display(PDP) was successfully demonstrated on 30-60inch display panel. Research for mass production is also been accelerating. The basic study of PDP are mainly focused on understanding of micro discharge in each cell In this paper, DC PDP with Ag electrode is made and the discharge charcateristics in micro gap is studied with the variation of the distance of electrode gap and the pressure in discharge cell.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.04a
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• pp.453-458
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• 2004

A capacitate sensor is a proper device for measuring high small displacement. General design parameters and procedure are discussed and a test sensor was built to have a measuring range of 100$\mu\textrm{m}$ and a sensitivity about 30nm. This sensor has too opposing electrode of comparably large area and has nominal gap distance about 150$\mu\textrm{m}$. So as to achieve a nano order displacement sensitivity, both sensor and target system have to be considered. This is important for the sensitivity can be achieved by minimizing a system total noise level in electronic type sensor application. Typical performance of the developed sensor is demonstrated in precision moving stage having 0.1$\mu\textrm{m}$ moving resolution.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.92-97
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• 2009

The performance of cooling fan is affected by many peripheral parts, such as radiator, condenser, engine block and etc. Higher power has been requested in more confined automobile engine room. Thus, cooling performance becomes very important to remove the heat generated from the automobile engine more efficiently. In this paper, the performance of cooling fan including effects of engine block is investigated by using a fan tester based on the ASHRAE and the AMCA standards. A flow rate - gap distance curves and a flow rate - engine block constant curves are obtained from this study.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 1998.04a
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• pp.36-47
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• 1998

The test transimissionof DGPS correction data has been carried out since early 1996. The data has been sent from marine radiobeacon station at Changgi Gap Ligthouse. It was the first test brosdcast of DGPS correction data based on midium frequency of marine radiobeacon where transmission power and rate are 300W and 100bps respectively. However, there has not been any scientific study on the characteristic of the accuracy of a marine DGPS/radiobeacon. Accordingly. this paper investigates the accuracy of the system, which is currently operating in 310KHz. As a result , planned 8 reference station and coverage verified that the differential positioning accuray using themarine radiobeacon is sufficient to ensure the safetyof marine activities around the coast of Korea(position error of distance 107NM at reference station was about10m(drms)).

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.3
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• pp.429-436
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• 2003

The electrical discharge machining(EDM) with Si electrode instead of Gr or Cu electrode. made enormous effects on the surface. machining time, anti-caustic workpiece surface and so on In this paper. we experimented on the inter-role distance during discharge the electrical phenomenon of inter-pole, the distribution of discharge point. the distribution of off load time. etc., using Si electrode Cu electrode and Gr electrode under the same machining condition. As a result of a large quantity generated exclusive powders. the performance of the EDM using Si electrode. compared with EDM using others. is improved. We show that the quantities of those make far pole-gap discharge and discharge scatter under stable machining status possible.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.125-131
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• 2000

The local heat/mass transfer coefficients for arrays of impinging circular air jets on a plane surface are determined by means of the naphthalene sublimation method. Spent fluid makes a crossflow in the confined space. The crossflow reduces heat/mass transfer at the small gap distance between the jet plate and impingement surface because of reentrainment of the spent fluid. The present study suggests a new exhaust system having effusion holes in the impinging jet plate. The spent air flow out after impingement just through effusion holes located in the upper plate. This system increases heat/mass transfer coefficients and uniformity for small gap distances$(H/d{\leq}2)$

• 한국연소학회:학술대회논문집
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• 2002.11a
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• pp.141-148
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• 2002

Experimental investigation of the interaction between dual spray formed by swirl type injector was conducted. Experimental parameter was fuel temperature, varied in the range from $-20^{\circ}C$ to $120^{\circ}C$. Measuring parameter were vertical distance from injector tip to patternator and gap between injectors. Volumetric distiribution and SMD were measured for the various combination of parameters. The results of present study show that the arithmetic sum of each of spray is not equal to dual spray, but it is equal above specific fuel temperature. As the increases of fuel temperature, SMD decreases and becomes more uniform. As the increases of gap between injectors, fuel volume and SMD at collision area increases, but penetrated fuel decreases.