• 수산해양기술연구
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• 제30권2호
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• pp.109-115
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• 1994

This paper presents a new concept to reduce turbulent frictional drag by injecting micro-bubble into near the buffer layer of turbulent boundary layer on flat plate. The concentrations of micro bubble distribution in the boundary was calculater by eddy viscosity equations in the governing equations. When near region of the buffer layer of turbulent boundary layer is filled with micro-bulle of air and viscous of the region is kept low, the velocity profile in the near region should be changed substantially. Then the Reynolds stress in the region becomes less, which guide to lower velocity gradient there. It results in reduction of velocity gradient at the viscous sublayer, which gives the reduction of shear stress at the wall.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2005년도 추계 학술논문 발표대회
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• pp.25-28
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• 2005

This study investigates the field application of surface insulation curing method, which combined double layer bubble sheet(DBS) and thick-curing-material(TCM) for cold weather concreting. According to the test, deck slab, curing only upper section with DBS and TCM, does not make big different temperature history with that, curing both upper and bottom section during daily average temperature 6.5t. It is concluded that combination of DBS and TCM in only upper section can be safely cured in early period of time during cold water concreting. The field test was carried out with this favourable data. The upper deck slab was insulated by combination of DBS and TCM, and the construction was surrounded by tent. in order to protect from outside wind. The test result shows that the lowest temperature of deck slab indicated 6$ ^{circ}C $. It demonstrated that this curing method can resist early frost and save construction cost in the side of management and saving labor cost, compared with previous method. In addition, the column specimen, combined both form and bubble board, exhibited favorable temperature history, due to internal hydration heat insulation effect.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1999년도 춘계학술발표회요약집
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• pp.159-159
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• 1999

Application of the macro layer dryout model has been performed to predict CHF at inclined plates. For the identification of the detachment frequency of coalesced bubble, experiments have been performed with high-speed motion analyzer and bubble behaviors at inclined plates have been investigated. Based on the observed bubble behaviors, the detachment frequency of the coalesced bubble is measured and linear relations between detachment frequency and heat flux have been developed. In the case of 60$^{\circ}$ and 90$^{\circ}$ inclined plate, the detachment frequency decreases with the increase of heat flux. However, opposite trend has been identified in $30^{\circ}$ in-clined plate: the detachment frequency increases with the increase of heat flux. Using the cor- relation of macro layer thickness suggested by Haramura & Katto and the extrapolation of the identified linear relations, CHFs at different conditions have been predicted. According to the prediction results, CHF values are well predictable.

• Journal of Mechanical Science and Technology
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• 제17권2호
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• pp.280-287
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• 2003

The unsteady flow characteristics and the related noise of separated incompressible laminar boundary layer flows (Re$\sub$$\delta$/* = 614, 868, and 1,063) are numerically investigated. The characteristic lines of the wall pressure are examined to identify the primary noise source, related with the unsteady motion of the vortex at the reattachment point of the separation bubble. The generation and propagation of the vortex-induced noise in the separated laminar boundary layer are computed by the method of Computational Aero-Acoustics (CAA), and the effects of Reynolds number, Mach number and adverse pressure gradient strength are examined.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.300-305
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• 2001

The unsteady flow structure and the related noise generation, which are caused by the separation of a two-dimensional, incompressible, laminar boundary-layer on the flat plate under the influence of local adverse pressure gradient, are numerically examined. The characteristic lines of the wall pressure are examined to understand the unsteady behavior of vortex shedding near the reattachment point of the separation bubble. Also, the generation and propagation of the vortex-induced noise in the separated boundary-layer are calculated by the method of computational aero-acoustics (CAA), and the effects of Reynolds number, Mach number and the strength of the adverse pressure gradient on the unsteady flow and noise characteristics are examined.

• 방송공학회논문지
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• 제26권6호
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• pp.809-812
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• 2021

PCB를 코팅하는 과정에서 기포가 발생하면 회로 오작동의 원인이 되기 때문에 기포 검출은 컨포멀 코팅 검사에서 매우 중요한 작업이다. 이전 연구에서는 기포의 밝기 특성을 이용하여 기포의 후보를 추출하고, 합성곱 신경망(CNN: Convolutional Neural Networks)을 이용하여 추출된 후보를 검증하였다. 본 논문에서는 전이학습 기반의 합성곱 신경망 모델을 이용하여 기포를 검출하는 방법을 제안한다. 이를 위해 합성곱 신경망 모델로 VGGNet을 사용하고, 분류층(Classification Layer)으로 시그모이드(Sigmoid)를 적용하였으며, 마지막 합성곱층(Convolutional Layer)과 분류층을 함께 학습하는 전이학습 방법을 적용하였다. 제안하는 방법의 기포 검출 성능은 F1-score 0.9044로서 이전 연구 대비 약 0.17의 개선 효과를 나타내었다.

• 한국세라믹학회지
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• 제28권6호
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• pp.478-482
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• 1991

Numerous researchers have observed the bubble formation from C/C composite at high temperature (1300$^{\circ}C$∼1700$^{\circ}C$). According to thermodynamic calculation, the bubble can be formed at the temperatures above 1500$^{\circ}C$ in the case of SiC coated C/C composite. However, the bubble below 1500$^{\circ}C$ could not be explained. Therfore, in an effort to explain the low temperature bubble formation, the effects of inhibitors such as B, Al, Zr and Si were thermodynamically investigated along with hydrogen and water vapor impurities resolved in C/C composite and SiC coating layer.

• 한국공작기계학회논문집
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• 제16권5호
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• pp.55-62
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• 2007

With the developments in knitting, manufacturing, and polymers, coated gloves have been evolved in a way to maximize occupational safety and functionality. In this paper, we have considered the PU-coating process for the glove knitted by Dyneema to reduce the occurrence of the defects due to air bubble. This paper classifies the types of defect due to air bubble and traces their forming mechanisms. The air between coating layer of glove and mold's surface forms the defects if it is not evacuated fully in the process of submerging into water. The defects can be suppressed or avoided by forming air-evacuating path on the surface of the molds.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2016년도 춘계 학술논문 발표대회
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• pp.11-12
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• 2016

The contemporary buildings are becoming super-taller gradually as the industry evolves. Accordingly, winter concrete also became an important element for the year-round construction since shortening of a construction duration became important. Accordingly, this research team once developed a double bubble sheet as concrete cover curing compound during winter. But since there is no proper countermeasure for the exposed reinforcement bars, it is worried that the concrete can be damaged by exposed frozen reinforcement bars at a low temperature during the initial period. Therefore, in this study, it is intended to review the temperature history of the reinforcement bars depending on changes of the covering methods of the exposed reinforcement bars by using bubble sheets.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2006년도 추계 학술논문 발표대회 논문집
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• pp.87-90
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• 2006

This study investigates the temperature history of slab mock-up specimens for hot weather concreting applying various surface insulating methods, in order to improve concrete quality at hot weather condition. Test showed that the use of insulating blanket or a bubble sheet on upper section of slab prevented from abrupt increase of temperature and vaporization of moisture during early curing at hot weather circumstance. In addition, it secured higher strength at early age. Therefore it is concluded that concrete construction insulating with the bubble sheet will reduce the plastic and drying shrinkage as well as improve strength at early age, thus securing concrete duality.