• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.229-232
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• 2007

하이브리드 로켓의 연소율을 높이기 위해 유동 특성을 바꾸면서 실험을 수행하였고 연소된 연료 내부 표면이 고르지 못한 것을 볼 수 있었다. 그 원인을 밝히기 위해 연료 표면을 관찰하고 유동가시화 실험을 한 결과 거친 연료 표면의 원인이 검댕 때문이고 이것은 국부적인 산화제 부족현상 때문에 발생하게 되었다는 것을 알 수 있었다. 또 연소 시 연료 전체에 발생하는 검댕의 특성은 이 현상이 하이브리드 로켓만의 독특한 특징인 분출효과 때문이라고 예측할 수 있게 해주었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.12
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• pp.59-66
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• 2006

To understand the role of helical geometry on the regression rate enhancement, two competing underlying mechanisms such as turbulence enhancement and swirling motion production were studied by numerical calculations. Experimental results showed that the enhancement of heat transfer rate has the very close relation to the increase in regression rate even though the percentage of increase in heat transfer rate is different from that in regression rate. This discrepancy is presumably due to the change of turbulent flow feature caused by so-called "blowing mass flux" from the fuel surface. In this regard, the results of RANS calculation show that the blowing velocity is responsible for the reduction of the swirl generation and the increase in the turbulent kinetic energy. And the dominancy of one of the mechanisms causes the increase in the regression rate. Meanwhile, the increase in turbulent kinetic energy due to the mixing of blowing flow and free stream flow does not contribute for the enhancement of the heat transfer rate to the surface because the blowing flow pushes boundary layer away from the solid surface.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.6
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• pp.1282-1291
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• 1989

본 연구에서는 이러한 연구의 시작단계로 노즐내의 열 경계층 방정식을 정리하고 압축성 와점도모델을 도입하여 유한 차분법을 이용한 전산프로그램을 작성 하였다. 한편 실제로 추진모테에서는 고온 고속의 열기류가 분출되기 때문에 추진 하고 있는 동안 노즐벽을 형성하고 있는 내열재가 심하게 손상되어 표면의 상태가 매우 거칠게 된다. 더구나 경우에 따라서는 내열재가 용발(ablation)하게 된다. 이러한 상태를 감안하여 마찰계수와 열전달 계수를 합리적으로 추정해야만 노즐의 설계와 주변장치를 합리적으로 수행할 수 있다. 따라서 본 연구에는 주로 경계층 내의 압력구배, 압축성의 효과, 물성치의 변화를 고려한 기존 난류모델에 근거하여 프로그램을 작성하고, 이것을 토대로 노즐표면 조도의 영향 및 분출(blowing)의 영 향을 중점적으로 고려하여 그 특성을 연구하였다. 노즐벽에서 분출을 고려한 이유는 표면이 용발할 때 표면의 온도가 거의 일정하게 유지된 상태로 노즐표면이 화학작용을 수반하면서 가스화됨을 초보적으로 고려해보기 위함이다.

• The Journal of the Petrological Society of Korea
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• v.11 no.2
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• pp.74-89
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• 2002

Rock units, relating with the Guamsan caldera, are composed of Guamsan Tuff and rhyolitic intrusions. The Guamsan Tuff consists almost entirely of ash-flow tuffs with some volcanic breccias and fallout tuffs. The volcanic breccia comprises block and ash-flow breccias of near-vent facies and caldera-collapse breccia near the ring fracture. The lower ash-flow tuffs are of an expanded pyroclastic flow phase from the pyroclastic flow-forming eruption with an ash-cloud fall phase of the fallout tuffs on the flow units, but the upper ones are of a non-expanded ash-flow phase from the boiling-over eruption. The rhyolitic intrusions are divided into intracaldera intrusions and ring dikes that are subdivided into inner, intermediate and outer dikes. We compile the volcanic processes along a single cycle of cadela development from the eruptive phases in the Guamsan area. The explosive eruptions began with block and ash-flow phases from collapse of glowing lava dome caused by Pelean eruption, progressed through expanded pyroclastic flow phases and ash-cloud fallout phases during high column collapse of pyroclastic flow-forming eruption from a single central vent. This was followed by non-expanded ash-flow phases due to boiling-over eruption from multiple ring fissure vents. The caldera collapse induced the translation into ring-fissure vents from a single central vent in the earlier eruption. After the boiling-over eruption, there followed an effusive phase in which rhyolitic magma was injected and erupted to be progressively emplaced as small plugs/dikes and ring dikes with many lava domes on the surface. Finally rhyodacitic magma was on emplaced as a series of dikes along the junction of both outer and intermediate dikes on the southwestern side of the caldela.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.4
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• pp.327-334
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• 1994

The manifold designates a pipe system discharging or absorbing water through multiple holes installed along the finite length of the pipe. The proper design of the manifold requires the pre-analysis of the hydraulic characteristics such as system head and flow rate. head loss and hole discharges, etc. On the contrary to the general pipe systems. the head loss along the pipe is hardly quantified in an explicit way since it is complicately varied by the size and arrangement of the holes. In the present study, both energy and continuity equations are employed to analyze the hydraulic characteristics, constituting nonlinear simultaneous equations which are solved by Newton method. In addition, a hydraulic experiment utilizing the manifold system equipped with an automatically controlled valve is performed to reproduce model tide. The result shows that the manifold system can be effectively used in a tidal basin where water flow should be maintained uniformly over the basin width.

• Proceeding of EDISON Challenge
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• 2016.11a
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• pp.71-73
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• 2016

기존 우산의 단점을 보완한 발명품, 공기우산이 개발되었다. 하지만 공기우산의 단점인 짧은 사용시간을 보완하기 위해 강우량에 따라 적절하게 공기 분사압을 변화시키는 것뿐만 아니라 공기우산의 사용인원의 조절을 위해 압력비와 분사구 형태에 따른 우산의 효과를 알아보는 것이 실 사용에 중요한 요소일 것이다. 이에따라 본 연구에서는 우산 앞 부분의 분출구 형상과 자유류와의 분사 압력비에 따른 자유류의 방어 능력을 확인해 보았다. 평면 분사구에서 압력비가 1.3, 1.5인 구간에서는 우산의 효과를 나타낼 수 없었고 압력비가 1.5인 구간부터 삼각형 분사구와 육각형 분사구에서 우산의 형태가 나타남을 알 수 있었다. 압력비가 2.0인 구간에서 육각형 분사구의 경우 통상적인 우산의 형상을 보이기 시작하는 것을 알 수 있다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.210-213
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• 2010

Recent experimental data shows that the noticeable feature of irregular roughened spots on the fuel surface occurs during the combustion test. The generation of these unexpected patterns is likely to be resulted from the disturbed boundary layer due caused by wall blowing which is intended to simulate the process of fuel vaporization. LES without chemical reaction was conducted to investigate the flow characteristics at the near-fuel surface and the behavior of turbulent structures which is evolved by the wall blowing at the Reynolds number of 23,000. Cylindrical geometry was considered to get the most reality of the calculation results because real hybrid rocket motor is circular grain configuration. It was shown that the wall blowing pushed turbulent structures upwards making them tilted and this skewed displacement, in effect, left the foot prints of the structures on the surface. This change of kinematics may explain the formation of irregular isolated spots on the fuel surface observed in the experiment.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.05a
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• pp.219-220
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• 2016

The behavior of fire plumes has not yet been clearly identified for cases where sidewalls are installed near an opening in an unconfined space. In this research, we aim to quantitatively identify the effects on fire spread when sidewalls are located on both sides of an opening. Specifically, we focus on the effects on the fire plume of the relation between the location of sidewalls and the opening, and carry out a scale-model experiment to devise a flame height model and to evaluate the temperature distribution along the central axis of the flame.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.3
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• pp.569-577
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• 1992

The effect of combustion promotion in a constant volume combustion chamber with sub- chamber located in the vicinity of spark plug, was analyzed for variables such as sub- chamber volume and diameter of orifice, and was also compared and evaluated with that of the chamber with sub-chamber which spark plug was located in the sub-chamber. Consequently, it was shown that decrease of duration of combustion in the latter case was larger than in the former case, but comparing by rate of overall combustion promotion that duration of combustion and pressure were both considered, the optimum configuration factor and the effect of combustion promotion were almost same in both cases.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2008.11a
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• pp.49-54
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• 2008

나노결정입자와 일반 입자를 이용하여 $60cm{\times}60cm{\times}180cm$의 밀폐 공간에서 연기제거 성능을 평가해보았다. MgO, $CeO_2$, $Al_2O_3$, ZnO, $TiO_2$등의 나노결정입자와 $NaHCO_3$ 등의 일반입자를 사용하였다. 실험은 입자를 30초, 1분, 2분 간격으로 연기에 분사하여 시간에 따른 연기 제거 성능을 관찰해 보았고, 아울러 3, $6\;kgf/cm^2$등의 입자 분사 압력 변화에 따른 연기 제거 성능도 평가해 보았다. 평가 결과, $TiO_2{\fallingdotseq}MgO$ > ZnO > $CeO_2$ > $NaHCO_3$ > $Al_2O_3$의 순으로 연기 제거 성능이 우수하였다. MgO와 $TiO_2$를 분사한 경우 자연스럽게 연기가 제거 되는 속도보다 약 10배 정도로 빠르게 연기가 제거되었다. 분사압력이 $6\;kgf/cm^2$에서 $3\;kgf/cm^2$로 감소하면, 입자가 연기와 부딪히는 힘이 약하고 분출양이 작아서 연기 제거 성능도 아울러 감소한 것으로 판단된다. 연기 제거 성능은 입자의 특성, 분출 압력, 분출 양, 분사 노즐의 크기 등에 영향을 받는다. 따라서 효과적인 연기제거를 위해서는 이러한 조건을 최적화하는 것이 중요하다. 본 연구는 이러한 연기 제거 입자가 실제 화재에 적용하는 것을 최종적 목표로 한다.