• 설비공학논문집
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• 제17권9호
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• pp.789-798
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• 2005

This paper is a numerical study concerning how the interactions between a pair of the vortices effect flow field and heat transfer. The flow field (common flow down) behind a vortex generator is modeled by the information that is available from studies on a half-delta winglet. Also, the energy equation and the Reynolds-averaged Wavier-Stokes equation for three-dimensional turbulent flows, together with a two-layer turbulence model to resolve the near-wall flow, are solved by the method of AF-ADI. The present results predict that the boundary layer is thinned in the regions where the secondary flow is directed toward the wall and thickened where it Is directed away from the wall. Although some discrepancies are observed near the center of the vortex core, the overall performance of the computational model is found to be satisfactory.

• 열처리공학회지
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• 제18권6호
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• pp.355-361
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• 2005

In this study, the effects of the maximum undeformed chip thickness on grinding characteristics of hardened steel in down-grinding have been investigated. The meaured grinding forces become larger as the workpiece velocity increases. The specific energy, e decreases as the maximum undeformed chip thickness increase. When the maximum undeformed chip thickness is the same, the specific energy, e decreases as the grain size increases.

• 한국태양에너지학회 논문집
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• 제25권4호
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• pp.133-139
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• 2005

In this paper, the ventilation performance of suspended particulates in indoor side was investigated by step-down method. Experiments were performed in function of mechanical ventilation types and locations of supply and extract air. The type 2 ventilation system shows the highest removal characteristics rather than other 2 types. It means that the displacement ventilation has also good decay rates of concentration compared to mixing ventilation.

• 조명전기설비학회논문지
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• 제25권10호
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• pp.28-37
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• 2011

Though Korea has introduced CBP(Cost Based pool) power trading system since 2001, long-term Generation system planning has been executed by government for Cost minimization every 2 years. Until currently the model which is used for Generation system planning and best-mix only considers cost minimization and total yearly or quarterly electricity demand every year. In a view point of one day power supply operation, technical characteristics, like the ramp up/down rate of total generation system, minimum up/down time and GFRQ(Governor Free Response Quantity), are very important. this paper analyzes Optimal Fuel-Mix for 2022 Korea generation system satisfying these constraints of each fuel type and considering pump storage plants, construction cost and $CO_2$ emission charge Using MILP(Mixed Integer Linear Programming) method. Also the sensitivity analysis which follows in future power industry environmental change accomplished.

• 한국공작기계학회논문집
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• 제12권6호
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• pp.1-7
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• 2003

The experimental research was conducted to find an end mill with an ideal helix angle, which has a superior anti-vibration effect and a low machining tolerance. A conventional endmill which all low blades are $30^{\circ}$ helix angles and a different helix angle endmill which the opposite two blades are $30^{\circ}$ and the other opposites are different helix angles were studied. The cutting farce, machining tolerance and surface roughness were obtained. The AE signals appeared to have low values in up-milling rather than in down-milling. These are also appeared to have low values at low spindle revolutions rates. The cutting force values of Fxy and Fxyz were found to be increased according to the value of helix angle. In up-milling, it was difficult to find a definite tendency in machining tolerance, but in down-milling machining tolerance of the different helix angle end mill was found to be lower than that of the convention end mill. There is a definite tendency that the surface roughness gets better as the RPM increases. In down-milling, Type A($25^{\circ}$＋$30^{\circ}$) appeared to bring the most satisfactory result.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2003년도 춘계학술대회 논문집
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• pp.196-201
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• 2003

The experimental research was conducted to find an end mill with an ideal helix angle, which has a superior anti-vibration effect and a low machining-tolerance. A conventional endmill which all four blades are $30^\circ$ helix angles and a different helix angle endmill which the opposite two blades are $30^\circ$ and the other opposites are different helix angles were studied. The cutting force, machining tolerance and surface roughness were obtained. The AE signals appeared to have low values in up-milling rather than in down-milling. These are also appeared to have low values at low spindle revolutions rates. The cutting force values of Fxy and Fxyz were found to be increased according to the value of helix angle. In up-milling, it was difficult to find a definite tendency in machining tolerance, but in down-milling, machining tolerance of the different helix angle end mill was found to be lower than that of the convention end mill. There is a definite tendency that the surface roughness gets better as the RPM increases. In down-milling, Type $A(25^\circ+30^\circ)$ appeared to bring the most satisfactory result.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(5)
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• pp.85-88
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• 2000

This paper describes a Band-Selective Charge-Pump PLL(CPPLL) for clock recovery and clock generator. The proposed PLL satisfies fast acquisition time and low jitter characteristics simultaneously by reducing initial frequency error. The acquisition time of the designed Band-Selective CPPLL can be decreased down to 55% of a conventional CPPLL.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 추계 학술대회논문집
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• pp.101-104
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• 2004

CFD simulation is peformed for 2D and 3D frisbees flying at 10m/s. For convenience of simulation, rotation of 3D model is not considered. CFD results show that pitching moment makes the nose down and holes at the leading and trailing edges improve the lift characteristics of the frisbee.

• 한국전자파학회논문지
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• 제8권3호
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• pp.243-253
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• 1997

차량과 같은 지상 이동체 통신에서는 안테나에 도래하는 입사전파가 안테나의 수직평변면에 대해서 약 $60^{\circ}$ 정도 의 낮은 입사각을 가지므로 이를 효과적으로 수신할 수 있는 평면형 안테나를 제작하고 그 특성을 고찰하였다. 유전체 덮개층 효과를 이용한 설계를 하여 안테나의 기판층을 포함한 평면에서의 방사계가 영이 되지 않도록 함으로써 이러한 안테나의 설계가 가능하다. 주파수 1.2 GHz에서 70 MHz 정도의 대역폭을 갖고 저각도 입사전파를 수신할 수 있는 소형 마이크로스트립 안테나를 구현하였다.

• 한국전자파학회논문지
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• 제13권8호
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• pp.764-768
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• 2002

본 논문에서는 (주)타키오닉스의 SiGe HBT 공정을 이용하여 double balanced Gilbert cell down conversion MMIC mixer를 구현한 결과를 제시하고, 이를 통해 RFIC 설계용 SiGe HBT 파운드리의 정확성과 신뢰성을 평가하였다. 제작된 Mixer는 3 V 동작 전압에서 10 mA의 전류를 소모하며, 2 GHz의 주파수 대역에서 17 dB의 Conversion Gain과 9.8 dB NF, -4.2 dBm Output 1 dB Compression Point, -27 dEc의 RF-IF Isolation의 특성을 나타내었으며 우수한 50 $\Omega$ 입. 출력 정합 특성을 갖는다. 시뮬레이션 결과와 측정결과는 거의 유사한 특성을 가지며, 이를 통해 SiGe HBT 모델 라이브러리의 정확성과 공정의 재현성을 검증할 수 있었다.