• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.1
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• pp.61-69
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• 2004

This paper describes numerical efforts to characterize the flame-holding and air-fuel mixing process of model SCRamjet engine combustor, where a hydrogen jet injected into a supersonic cross flow and in a cavity Combustion phenomena in a model SCRamjet engine, which has been experimentally studied at University of Queensland and Australian National University using a free-piston shock tunnel, was observed around separation region of upstream of the normal injector and inside of cavity. The results show that the separation region and cavity generates several recirculation zones, which increase the fuel-air mixing. Self ignition occurs in the separation-freestream and cavity-freestream interface.

• Journal of the Korean Vacuum Society
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• v.17 no.5
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• pp.408-418
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• 2008

The rectangular resonant cavity was designed and characterized as a microwave plasma source for focused ion beam. The optimum cavity was calculated analytically and analyzed in detail by using HFSS(High Frequency Structure Simulator). Since the resonant cavity can be affected by the permittivity of quartz chamber and plasma, the cavity is designed to be changeable in one direction. By observing the microwave input power at which the breakdown begins, the optimum cavity length for breakdown is measured and compared with the calculated one, showing in good agreement with the optimum length reduced by 10cm according to the permittivity change in the presence of quartz chamber. The shape of breakdown power curve as a function of pressure appears to be similar to Paschen-curve. After breakdown, plasma densities increase with microwave power and the reduced effective permittivity in the cavity with plasma results in larger optimum length. However, it is not possible to optimize the cavity condition for high density plasmas with increased input power, because too high input power causes expansion of density cutoff region where microwave cannot penetrate. For more accurate microwave cavity design to generate high density plasma, plasma column inside and outside the density cutoff region needs to be treated as a conductor or dielectric.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.5 s.120
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• pp.496-502
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• 2007

In this paper, a slotted waveguide feeder for the electric field uniformity in multi-mode cavity is designed and fabricated. In case of the conventional feeder, a mode stirrer or a turntable is used for improving electric field uniformity in the multi-mode cavity. The proposed feeder has four slots, which have uniform radiation characteristic, on broad wall and shorted terminations at both ends. The electric field uniformity is simulated by CST's MWS(Microwave Studio) for the conventional and proposed feeders, respectively. The fabricated feeder shows the return loss of less than -20 dB at 2.45 GHz. To verify the validity of our proposal, the temperature distribution of the water samples in the multi- mode cavity is observed after a few minutes' heating. The proposed feeder is confirmed to have much better field uniformity in the multi-mode cavity than the conventional feeder.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.281-284
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• 2008

The flow of combustor in scramjet engine is supersonic speed. So residence time and mixing ratio are very important factors for efficient combustion. This study used open cavity on fuel/air mixing model and laser schlieren was carried out to investigate flow characteristics around a jet orifice and a cavity. A source of illumination has 10 ns endurance time so it can observe unsteady flow characteristics efficiently. Pressure was measured by varying momentum flux ratio. And the change of critical ignition point was observed to change of momentum flux ratio.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.4
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• pp.9-15
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• 2009

The flow of combustor in scramjet engine has supersonic speed so that the residence time and mixing ratio are very important factors for the efficient combustion. This study used open cavity(L/D=4.8) as a fuel/air mixing model. Laser schlieren visualization and pressure measurement were carried out to observe the flow characteristics around a jet orifice and a cavity at the time of fuel injection. As a result of 10ns laser schlieren, unsteady flow which was around the cavity could be observed effectively. Pressure was measured that momentum flux ratio(J) was changed. And the change of critical ignition point could be observed by the momentum flux ratio changed.

• Journal of the Korean earth science society
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• v.27 no.5
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• pp.539-547
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• 2006

The activity of the seismic wave propagation around the cavity is investigated for the exact inversion of the crosshole tomography data, in order to understand the possibility of the existence inside the underground cavity. It is found that the adequate frequency range for the tunnel investigation is about 2 kHz to 5 kHz, and the grid space should be set up to 1/10 of the wavelength. The propagation of the seismic wave near the cavity may go through or detour the cavity according to the seismic velocity inside the cavity. The detouring wave propagates with the seismic velocity of mother rock in spite of the velocity of inside of the cavity. The smaller the velocity difference is between the mother rock and cavity, the more frequent penetration of the seismic wave through the cavity appears.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.1062-1066
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• 2004

암반 내에 공동을 굴착하여 LPG 혹은 원유를 저장하는 경우 공동에서의 지하수 유입량은 공동상부의 수압과 공동내의 가스압과의 관계를 파악할 수 있는 정량적인 지표가 된다. 공동내의 유입량은 되도록 일정하게 유지되는 것이 굴착등의 시공단계와 공동 운영 및 유지관리면에서 유리하며, 유입량의 급증 혹은 급감이 일어나는 경우는 그 원인을 조기에 규명하여야 한다. 이를 위해서는 지하수위, 가스저장압, 수막공 주입압 등에 따른 공동주변의 유동장 해석, 공동내로의 지하수 유입량 해석을 실시해야 한다. 지하저장공동의 유입량 해석에 있어서는 공동의 정확한 형상을 반영하기 위해서 유한요소법이 보편적으로 사유되어 왔으나 한번 설정한 유한요소망으로부터 공동의 설계요소를 변경하는 작업은 수원하지 않아 설계전단계에서 공동 및 수막 시설의 다양한 배치에 따른 모의를 수행하는데는 다소 무리가 있다. 이러한 불편함은 경계부의 형상과 조건만으로 내부점에서의 미지변수 계산을 효과적으로 수행할 수 있는 경계요소법을 도입함으로써 극복할 수 있다. 따라서 본 연구에서는 지하공동으로 배수되는 유입량 산정을 위해 경계요소법을 근간으로 한 2차원 지하수 흐름모형을 구성하였고, 이를 지하저장공동이 위치한 A기지에 적용하여 상부경계조건인 지하수위의 변화, 수막공 주입압 등에 따른 공동내의 유입량과 공동저장압과의 관계를 정량적으로 분석하였다. 분석 결과를 지하저장공동의 운영 및 유지관리에 활용될 수 있도록 수식화하여 제시하였다.

• Journal of the Korean Institute of Gas
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• v.20 no.5
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• pp.89-95
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• 2016

Keeping the gas pipelines in the common utility tunnel is useful because it has a lower risk of corrosion than conventional burial, and can prevent from excavating construction. But, explosions in common utility tunnels can cause greater damage from the blast overpressure compared to outdoor explosions, due to nature of the confined environment. Despite this fact, however, research on common utility tunnels has been limited to fire hazard and little has been studied on the dangers of explosions. This study developed scenarios of methane gas explosion caused by gas leak from gas piping within the common utility tunnel followed by unknown ignition; the study then calculated the extent of the impact of the explosion on the facilities above, and suggested the needs for designing additional safety measures. Two scenarios were selected per operating condition of safety devices and the consequence analysis was carried out with FLACS, one of the CFD tools for explosion simulation. The overpressures for all scenarios are substantial enough to completely destroy most of the buildings. In addition, we have provided additional measures to secure safety especially reducing incident frequency.

• Fire Science and Engineering
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• v.23 no.4
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• pp.104-111
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• 2009

To research about the fire spread in Korean apartment house, a full-scale fire test in a four-story apartment was executed. The fire started at the third floor, and originated from overheated cooking oil in the kitchen. The apartment included all combustibles in general house. Through measuring temperature, measuring the concentration of oxygen and observing, we investigated the fire spread inside the apartment house. As a result, we got the data of the time needed for the initiation of fire, the time for fire to spread into each area in the house, and the time required until flash-over was seen. Also we grasped the understanding of the fire spread to the upper floor.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.2
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• pp.1-11
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• 2021

The cavity inside the combustor increases the mixing efficiency of fuel and air by inducing a oscillation of the flow and the recirculation area with a low speed, and enables continuous combustion by maintaining the flame. In this study, the characteristics of the internal flow by change in the shape parameters of the cavity were analyzed through experiments and two-dimensional computational analysis. It was observed that the flow in the supersonic combustor was greatly influenced by various shape parameters of cavity besides L/D. Even with the same L/D, it was confirmed that the flow type varies depending on the depth of the cavity, either open or closed type, and the aft ramp angle of the cavity and the height of the combustor also affect the flow characteristics. As a result, the change in the shape parameters of the cavity had a great influence on the total pressure loss.