• Proceedings of the Korean Nuclear Society Conference
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• 2002.05a
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• pp.315.2-315
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• 2002

• Proceedings of the Korean Nuclear Society Conference
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• 2002.05a
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• pp.259.2-259
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• 2002

• Proceedings of the Korean Nuclear Society Conference
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• 2002.10a
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• pp.395.2-395
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• 2002

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.3
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• pp.235-242
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• 2014

To investigate pressure distributions on the shaft surface of the air bearing, the commercial CFD software was employed to study three different nozzle geometries to improve the nozzle performance: general drill-shaped, matched cube-shaped and trimmed exit nozzles. Under the influence of stagnation point, the maximum pressure was observed at the center of shaft surface for all cases. Owing to the blocking effect of a fine gap between the shaft surface and the nozzle exit, the drill-shaped nozzle has the rapid local pressure increase near the nozzle exit corner, generating the ring vortex in the radial direction within pressure ratio of 6.92, and its pressure becomes negative in a certain range of downstream. In comparison, the contoured nozzle showed a local pressure increase in the measured range of pressure ratios, but a negative pressure appeared within the pressure ratio of about 10. The trimmed nozzle was seemed to extend the high pressure zone near the stagnation point in the radial direction substantially, and no negative pressure was appeared in the whole range. Based on these observations, it is found that trimming nozzle exit becomes more effective for improving the performance than modifying the nozzle inside contour.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.8
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• pp.599-606
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• 2019

The pulse gun device is designed to identify the transverse pressure wave propagation/damping mechanism into the combustion flow field and in the combustion chamber according to the arrangement of multiple injectors. The manufactured pulse gun was tested to verify operability at the target combustion pressure and control of the pressure wave intensity. Gas nitrogen was used to pressurize the high-pressure tube and an OHP film of $100{\mu}m$ thickness was used for the diaphragm. To check the speed and intensity of the pressure waves, the dynamic and static pressure were measured using the pressure transducer. The performance test confirmed that the manufactured pulse gun can generate pressure waves with transverse characteristics that can be controled for strength depending on the supply pressure.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.24-31
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• 2002

The effects of vortex generators, in the form of small delta-shaped tabs or thin tapes at an axi-symmetric supersonic nozzle exit, on the characteristics of supersonic jet flowfields are investigated by Schlieren images and Pitot-tube measurements. Small tabs as small as 1 % of the nozzle exit area can introduce streamwise vortices and produce a significant effect on the jet flowfield downstream of the nozzle. The effect is stronger for the cases of under-expanded jet than over- and perfect-expanded cases, introducing a larger flow entrainment. The effects of the angle of tabs with respect to the flow direction are also investigated, and for over-expanded jet cases, it is found that the tabs bended toward upstream can weaken the interaction strength and remove the Mach disc in the jet flowfield. Introduction of small proturbances inside the nozzle surface by attachment of thin tapes is also found to change the pressure distribution in the circumferential direction of the flowfield. Its effect is also found to be dependent on the jet expansion ratio.

• Journal of Korea Water Resources Association
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• v.44 no.3
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• pp.189-198
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• 2011

The aim of this study is to compare k-$\varepsilon$ and k-$\omega$ closures under the condition of oscillatory layer flow at high Reynolds number. A one dimensional vertical model incorporated with flow momentum equations and turbulence models (k-$\varepsilon$ and k-$\omega$) is applied to the laboratory measurements in the turbulent oscillatory boundary layer. The numerical simulation reveals that both turbulence models calculate similar velocity profiles and turbulent kinetic energy (TKE). In addition, both deliver high accuracy under the condition of negligible spanwise pressure gradient. Therefore, it is recommended in this study to use k-$\varepsilon$ closure, of which numerical coefficients have been calibrated from many studies, for the cases of straight channel, estuary, and coastal environment where the spanwise pressure gradient is not significant.

• Elastomers and Composites
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• v.38 no.4
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• pp.295-302
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• 2003

The amount of shrinkage of injection molded parts is different from operational conditions of injection molding such as injection temperature, injection pressure and mold temperature, and mold design such as gate size. It also varies depending on the presence of crystalline structure in resins. In this study, part shrinkage was investigated for various operational conditions and resins. Poly(butylene terephthalate) (PBT) for crystalline polymer, and polycarbonate (PC) and poly(methyl methacrylate) (PMMA) for amorphous polymers were used. Crystall me polymer showed higher part shrinkage by about three times than that of amorphous polymers. Part shrinkage increased as melt and molt temperatures increased, and injection pressure decreased. Part shrinkage decreased as gate size increased since the pressure delivery is mush easier for larger gate sizes. Part shrinkage at the position close to the gate was larger than that or the position far from gate. This phenomenon might be occur by difference of residual stress.

• Proceedings of the KAIS Fall Conference
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• 2009.12a
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• pp.152-155
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• 2009

본 논문에서는 Manta 형상 무인잠수정의 자유항주모델을 설계하였고 이를 이용하여 제어실험을 실시하였다. 제작된 MUUTV모형은 직진방향으로 1개의 추진기를 가지고 있으며, 승강타와 방향타를 이용하여 수심 및 방향 제어를 실시하게된다. MUUTV는 수심제어시 사용되는 수심을 측정하기 위한 압력센서, 방향제어를 위해 방향각 측정을 위한 마그네틱 컴파스가 설치되어있으며, 잠수정의 전체적인 운용을 위한 Windows XP기반의 소형 On-board PC104가 장착되어있다. 시뮬레이션에 사용된 6자유도 운동모델은 PMM실험과 이론적 추정을 통해 얻어진 유체동역학계수와 파라미터를 이용하여 구성된다. 잠수정의 운동성능과 제어응답을 비교하기 위해 PID, 슬라이딩모드, 퍼지, 제어기가 설계되었으며, 이를 통해 제어 성능을 비교하고자 하였다. 또한 제작된 모델을 이용하여 수심 및 방향제어 실험을 수조에서 실시하였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2017.04a
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• pp.436-438
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• 2017

자본주의의 꽃인 주식시장은 파생시장에 의해 영향을 받고 있으며, 파생시장은 지수옵션 상품에 의해 영향을 받고 있다. 최근 들어 시스템 트레이딩에 대한 관심이 점점 더해가고 있으며 투자자에게 컴퓨터 시스템과 매매 전략에 대한 이해를 요구하고 있다. 지수옵션 시장은 만기일을 기준으로 마치 파도와 같이 순간순간 살아 움직이고 있다. 옵션에 대한 효과적인 관점은 투자자에게 확률 높은 매력적인 전략을 제공하며 옵션의 움직임을 전체적으로 해석할 수 있게 한다, 그리고 궁극적으로 옵션가의 예측을 가능하게 한다. 행사가와 방향성에 의한 개별 옵션은 함수로 해석될 수 있다. 다양한 입력값에 의해 가격이라는 하나의 출력값이 결정되는 구조이다. 입력값에는 지수, 시간, 거래량 의 세가지 카테고리로 이루어진다. 이중 거래량은 예측이 가능한데, 개별 옵션이 아닌 앙상불의 경우 출력값으로 처리될 수 있다. 하지만 앙상불 옵션에서 개별 옵션가는 경직성을 가지게 되어 예상가의 차이에 의한 압력이 발생하게 된다. 이 압력은 이후의 지수변화에 핵심적인 에너지로 작용할 수 있다. 압력의 측정은 다양한 방법이 있을 수 있는데, 본 논문에서는 뉴로-퍼지 시스템을 이용한 예측값과의 차이를 측정하여 계산하였다. 일단 학습된 뉴로-퍼지 시스템은 가격을 예측하게 되며, 실제 가격과의 괴리는 압력으로 해석할 수 있다.