• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.759-764
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• 2000

In this study, the confined laminar flow around a square cylinder, which ejects a either on the front face or on the rear face, is numerically simulated. In each case, three ratios of jet velocity to the fixed upstream velocity are considered. In all cases of the rear fuel jet, the high mass-fraction region is formed along the streamlines from the jet exit. In case of front jet, drag is significantly decreased when the jet velocity ratio is greater than 1. The results obtained exhibit flow and scalar-mixing characteristics encountered in a planar combustor

• 한국결정학회지
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• 제5권2호
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• pp.93-99
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• 1994

K2O/3MOOS/0.SBB03 융제를 사용하여 TSSG 법으로 육성한 Md:Yal3(BO3)4 (NYAB) 단결정의 결정외형 및 표면형상을 연구하였다. <100>과 <120> 종자정을 사용한 경우는 서로 다른 크기의 프리즘 면들과 (101) 면들이 발달하였고 <001> 종자정을 사용하였을 때는 (001) 면이 함께 발달하였다. 종자정의 방향이 <100>또는 <120> 일때 프리즘 면 위에 성장구룽이 많이 형성되었으나, <001> 일때는 이웃하는 (101) 면에 평행한 줄무늬가 형성 되었다. (101) 면은 이차원 핵생성에 의한 성장이 지배적이고, <001> 종지정을 사용할 때 발달하는 (001) 면은 나선형 전위에 의한 성장이 지배적이었다. 종자정의 방향은 성장외형을 변화시키고 성장외형과 결정의 질을 결정하는 중요한 성장변수로 작용하였다.

• 한국산업보건학회지
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• 제11권1호
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• pp.34-41
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• 2001

Passive samplers have been used for personal, indoor, and outdoor air monitoring of VOCs at ppb concentrations in community and office environments. The path length of modified passive sampler was shortened, so it was intended to increase an uptake rate. The performance of the modified 3M 3500 organic vapor monitor(OVM) as a tool for assessing exposures to toxic air pollutants in nonoccupational community environments was evaluated using combined controlled test atmospheres of six selected target volatile organic compounds(VOCs): benzene, methyl tert-butyl ether(MTBE), chloroform, 1,4-dichlorobenzene, tetrachloroethylene, and toluene. The experiments were conducted by exposing the dosimeters to concentrations of $50{\sim}100{\mu}g/m^3$ on six face velocity(0.00, 0.02, 0.06, 0.12, 0.20, 0.30 m/sec) for 24 hours. If the uptake rate was increased, that means that we could use the passive sampler more effectively. The uptake rates were increased linearly according to reduce the path length. Although the diffusion path length was shortened, the change of uptake rate was within ${\pm}25%$ of theoretical value, indicating that the modified passive sampler(TM) can be effectively used over the range of concentrations and environmental conditions tested with a 24-h sampling period if the face velocities were over 0.12 m/s for 6 components of VOCs. But when the face velocities were less than 0.12 m/s, uptake rates were reduced more than expected values. So, the passive sampler with the shortened path length should be used at indoor or outdoor environment where the face velocity should be over about 0.10 m/s. If the path length was shortened more, the uptake rate was more effected by starvation.

• 대한기계학회논문집A
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• 제20권1호
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• pp.222-231
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• 1996

Temperature distribution on the flank face in orthogonal turning with cutting tool of high speed steel is studied by using a finite element method and experiments. Experiments are carried out to verify the validity of the temperature measurement by using a thermoelectric couple junciton imbedded in a cutting tool of high speed steel. Good agreement is obtained between the analytical results and the experimental ones for the temperature distributions on flank face of cutting tool with igh speed steel. The analytical results show that the temperature on the top flank face of a tool is higher because of the difference of the friction velocity on each face of the tool.

• Journal of Advanced Marine Engineering and Technology
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• 제19권1호
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• pp.45-53
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• 1995

Temperature distribution on flank face in orthogonal turning with cutting tool of high speed steel is studied by using a finite element method and experiments. Experiments are carried out to verify the validity of the temperature measurement by using a thermoelectric couple junction imbedded in a cutting tool of high speed steel. Good agreement is obtained between the analytical results and the experimental ones for the temperature distributions on flank face of cutting tool with high speed steel. The analytical results show that the temperature on the top flank face of a tool is higher because of the difference of the friction velocity on each face of the tool.

• 콘크리트학회논문집
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• 제28권4호
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• pp.455-462
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• 2016

본 실험적 연구는 고속 비상체 충돌 시 UHPC 외장재의 내충격성을 파악하는데 그 목적이 있다. 이 연구에서는 두께를 주요 변수로 UHPC과 화강암 패널 실험체에 고속충격을 가하여 실험체의 성능을 비교하였으며, 배면의 변형률을 기록하였다. UHPC는 외관이 우수하였으며, 내충격성도 화강암에 비해 우수하여 외장재로 사용하기에 적당하다고 판단된다. 비상체가 시험체에 충돌한 후 압축파가 배면에 도달하고 그 후 자유단 지점을 중심으로 인장파가 발생하여서 배면파괴를 일으킨 것으로 사료된다. 이러한 배면파괴 발생 메커니즘은 변형률 기록이 압축파구간, 보합구간, 인장구간으로 나누어지는 것을 통해 알 수 있다. 관통파괴 형태를 살펴보면 고속 충돌 시 전단력이 배면에 작용하여 파괴가 발생되는 shear plug 현상이 나타난 것으로 판단된다. 즉 충격하중에 대하여 배면의 파괴는 전단력과 인장응력에 의해 동시에 영향을 끼쳐 발생한 것으로 사료된다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.78-82
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• 2001

Impact behaviors of Aluminum Honeycombs Sandwich Panel(AHSP) by drop weight test were investigated. Two types of specimens with 1/2" and 1/4" cell size were tested by two impactors which are weight of $5.25\textrm{kg}_{\textrm{f}}$ and $11.9\textrm{kg}_{\textrm{f}}$. Parametric studies were achieved including the impactor weight and impact sites which consist face, long-edge, short-edge, and point of the specimen. Face one of impact sites was the strongest and short-edge one of impact sites was the weakest. The damaged area of AHSP was enlarged with the increase of impactor weight that is equal to impact energy. After 3 point bending test, fracture modes of AHSP were analyzed with AE counts. Lower facesheet was fractured in the long-edge direction and then separated between facesheet and core. In the short-edge direction after core wrinkled, lower facesheet tear occurred. Impact behavior by FE analysis were increased localized damage in fast velocity because the faster velocity of the impact was, the smaller the stress of core was. Consequently, impactor weight had an effect on widely damaged area, while the impact velocity was caused on the localized damaged area.aged area.

• Nuclear Engineering and Technology
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• 제16권1호
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• pp.29-35
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• 1984

유리섬유 여과포에 의한 0.1~0.45$\mu\textrm{m}$ 크기의 DOP 부유입자의 제거효율시험을 1~10cm/sec의 유속범위에서 수행하였다. 섬유여과포에 의한 미세입자의 여과는 여과속도에 의하여 결정되는데, 최소제거 효율을 나타내는 DOP 입자의 크기는 여과속도가 증가함에 따라 감소한다. Kuwabara Cell Model과 Von Mises Transformation을 사용하여 유리섬유 여과포내에서 화산에 의한 입자 제거효율을 수치해석적으로 전개하여 구하였으며, 이 계산치는 실험치와 잘 일치하였다. 본 실험의 결과는 여과포의 입자제거효율을 예측하고 최적 운전조건을 추구하는데 기여할 수 있을 것이다.

• 한국산업보건학회지
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• 제29권2호
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• pp.208-216
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• 2019

Objective: The aim of this study is to control residual chemicals or by-products generated in chambers during preventive maintenance (PM) in the semiconductor manufacturing industry. We designed local exhaust ventilation using computational fluid dynamics (CFD). Methods: The air flow characteristics and capture efficiency between rectangular and slot hoods were compared numerically. The software Fluent 18.1 was used to estimate uniform velocity distribution and capture efficiency for contaminants. A metal from group 15 in the periodic table was released at the bottom of the chamber to simulate emissions. Results: The slot hood had a higher capture efficiency than a rectangular hood under the same conditions because the slot hood provided uniform air flow and higher face velocity. Also, there was no rotating swirl in the plenum for slot, that is why slot had better efficiency than rectangular even though they had similar face velocity. With less than 10 slots, the capture efficiencies for contaminants were nearly 95%. The optimum conditions for a hood to achieve high efficiency was 8 to 10 slots and a face velocity over 1 m/s. Conclusions: Well-designed ventilation systems must consider both efficiency and convenience. For this study, a slot hood that had high capture efficiency and no work disturbance was designed. This will contribute to protection of the worker's health in a PM area and other areas as well. Also, this study confirms the possibility of the application CFD in the semiconductor fabrication industry.

• 대한기계학회논문집B
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• 제41권3호
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• pp.191-197
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• 2017

본 연구는 Weis-Fogh형 수차모델의 비정상 유동장을 PIV를 이용해 가시화한 것이다. 실험은 비교적 효율이 높은 날개의 열림각 ${\alpha}=40^{\circ}$ 및 날개의 이동 속도에 대한 일정류의 속도비 U/V=1.5~2.5 범위 내에서 진행했다. 유동장은 각 실험 파라메터에 대해 열리는 과정, 병진운동의 과정 및 닫히는 과정으로 나누어 고찰되었으며, 그 결과를 요약하면 다음과 같다. 열리는 과정에서는 날개와 벽 사이에 유체가 흡입되며, 그 유입속도는 열림각이 클수록, 속도비가 클수록 증가했다. 병진운동의 과정에서 날개 압력면의 유체는 날개의 이동방향으로 움직였으며, 배면에서의 경계층의 두께는 속도비 2.0일 때 가장 작았다. 닫히는 과정에서는 날개와 벽 사이에서 유체가 분출되며, 그 분출속도는 열림각이 작을수록 증가했지만, 속도비와는 관계가 없었다.