• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2568-2573
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• 2008

A drop impact on the liquid film/pool generates several phenomena such as the drop floating, bouncing, formation of vortex ring, jetting, bubble entrapment and splashing. These phenomena depend on the impact velocity, the drop size, the drop properties and the liquid film/pool thickness. These parameters can be summarized by four main dimensionless parameters; Weber number, Ohnesorge number, Froude number and non-dimensional film/pool thickness. In the present study, the phenomena of the splashing and bubble entrapment due to the drop impact on the liquid film/pool were numerically investigated by using a Level Set method for the sharp interface tracking of two distinct phases. After the drop impact, the splashing phenomena with the crown formation and spreading were predicted. Under the specific conditions, the bubble entrapment at the base of the collapsing cavity due to the drop impact was also observed. The numerical results were compared to the available experimental data showing good agreements.

• 한국세라믹학회지
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• 제25권1호
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• pp.78-82
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• 1988

Good quality LiNbO3 single crystals which can be applied to SAW devices, were grown by Czochralski method. It was observed that the gas-bubbles were concentrated in ring shape at the outer part of grown crystals, and this anomaly was illustrated by modeling the mechanism of gas-bubble entrapment according to the melt flow pattern in the crucible. And this mechanism was also encertained by observation of solid-liquid interface shape of grown crystals. The optimal condition for good quality crystals was known that the solid-liquid interface shape was slightly concave.

• 한국해양공학회지
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• 제30권1호
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• pp.44-50
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• 2016

An experimental study was performed to investigate the behavior of green water on a structure with a rectangular cross section under wave conditions, along with the flow characteristics in bubbly water flow. An experiment was conducted in a two-dimensional wave flume using an acrylic model (1/125) of FPSO BW Pioneer operating in the Gulf of Mexico under its design wave condition. The occurrence of green water, including its development, in front of the model was captured using a high-speed Charge Coupled Device (CCD) camera with the shadowgraph technique. Using consecutive images, the generation procedure for green water on the model was divided into five phases: flip through, air entrapment, wave run-up, wave overturning, and water shipping. In addition, the distinct water elevations of the green water were defined as the height of flip through, height of splashing jet, and height of freeboard exceedance, and showed a linear relationship with the incoming wave height.

• 한국결정학회지
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• 제6권2호
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• pp.141-157
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• 1995

직경자동제어장치를 이용한 초크라스키법에 의해 대형 TeO2 단결정을 공기 중에서 성장시켰다. 온도구배를 가능한 한 적게 한 성장조건 하에서 단결정과 도가니의 직경비율을 60-70% 범위에서 양질의 단결정 성장이 가능하였다. 이 때 결정의 품질을 좌우하는 주요 요인은 인상 및 회전 속도였다. 무색 투명한 고품질 단결정을 육성하기 위한 인상속도는 1.2mm/hr 이하였고, 고액계면은 10-23 rpm 이하일 때 볼록하였으며, 25 rpm 이상일 때 오목하였다. 단결정의 성장은 {110} 방향의 종자결정을 사용하였다. 용융체 내의 백금 함량이 증가하면 조성적 과냉이 발생하여, 성장되는 결정 내에 기포가 포획되므로 성장된 단결정의 질이 저하된다. 적외선 측정결과 파수 2,000cm-1 이상에서 완전 투명하였고, 전위밀도를 측정 결과 직경자동제어를 이용한 경우 3×103/cm2 - 2×104/cm2로 양호하였으며 수동성장인 경우도 결정과 도가니의 직경비율이 40-45%의 범위에서는 매우 양호하였다. 또한 포유물 등 불순물에 혼입 원인에 대하여 논하였다.