• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.5
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• pp.339-347
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• 2022

The post chamber in hybrid rocket is installed to induce additional increase in combustion enthalpy by allowing continuous burning of the liquefied fuels. When paraffin wax fuel is used, unsteady pressure oscillations are observed only at the beginning of combustion. This study intends to investigate the effect of additional combustion of liquefied fuel droplets on the occurrence of unsteady pressure fluctuations. For this, the combustion in post-chamber was visualized and image analysis using POD(Proper Orthogonal Decomposition) technique was performed. In addition, the hypothesis was proposed on the occurrence of unsteady pressure oscillations by identifying the modes including the behavior of droplets through mode reconstruction. Conducting a series of combustion tests, the amount of liquefied fuel flowing into the post chamber and the generation of fuel droplets were controlled. Also, the changes in frequency characteristic of unsteady pressure oscillation were monitored. As a result, the unsteady pressure oscillations observed in paraffin wax combustion were the result of additional combustion of fuel droplets generated in the post chamber.

• Aerospace Engineering and Technology
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• v.2 no.2
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• pp.133-141
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• 2003

When superplastic forming process is employed in manufacturing spherical pressure vessel, the thickness and spherical profile are not constant and varies during the forming process. In the current study, theoretical analysis for the prediction of thickness change was carried out under the consideration of membrane theory which has been employed in Kuglov et. al.'s study. Then the thickness of initial blank to obtain the required thickness at the final forming step, the time vs. pressure profile which yields uniform deformation in blank, and the thickness distribution according to the position at each forming step have been determined. The employed model and the developed analytical code were verified throughout comparing the theoretical predictions at each forming stage with the experimental results shown in literature.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.87-90
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• 2003

It has been well known that the major feature of compressible flow fields might be different depending on their formation processes. The objectives of the present study is to investigates the effect of jet development on the time history of supersonic jet flow field, accompanying nonequilibrium condensation. Especially, the behaviors of Mach disk diameter and location in a supersonic moist air jet are presented in terms of nozzle pressure ratio and initial relative humidity. The relative humidity of moist air is controlled at the nozzle supply, and the nozzle pressure ratio is varied to obtain the moderately underexpanded flows at the exit of the nozzle, installed in an indraft wind tunnel. It is found that at the same pressure ratio the Mach disk diameter increases with the initial relative humidity, while moves further upstream. Furthermore, the values of Mach disk diameter and location for increasing pressure ratio show larger than those for increasing.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2002.02a
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• pp.383-388
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• 2002

본 연구에서 구성한 바이오필터 시스템은 암모니아 가스를 대상으로 여러 조건에서 성능을 구명하였으며, 필터 설계시 중요 인자인 송풍량, 온도, 함수율, 압력강하, 체류시간들간의 관계를 구명하였다. 필터 내부의 온도 변화는 체류시간 및 압력손실에 거의 영향을 주지 않았으며, 함수율의 변화가 체류시간과 압력손실에 미치는 영향은 함수율 값이 증가할수록 체류시간은 감소했으며 반대로 압력손실은 증가하는 결과를 보였다. 이는 필터 내부의 공극률 변화로 생긴 결과라 판단된다. 송풍량은 바이오필터 효율에 절대적으로 영향을 미치며 송풍량이 증가할수록 체류시간은 감소하며 초기 제거율도 떨어진다. 미생물의 투입 여부에 따른 제거율은 미생물 접종을 하지 않은 경우 초기 흡착에 의한 영향으로 제거율이 높다가 시간이 지남에 따라 차츰 낮아져 90% 이하로 떨어지는 경향을 보였고, 균주를 접종한 경우에 있어서는 시운전 기간 동안 거의 100% 가까운 제거 성능을 보였다. 본 연구는 실험실에서 암모니아 가스만을 대상을 하여 실험하였다. 따라서 실제 축사에서 발생하는 다양한 성분의 악취와 농도에 대한 성능 검증과 개선에 대한 연구가 보다 장기간에 걸쳐 이루어져야 할 것이다. 또한 소요되는 에너지와 운전비용의 절감 등의 유지관리, 바이오필터와 타 방식과의 조합, 그리고 다양한 전처리 방식의 개발 등 여러 측면에서 바이오필터 성능 개선에 대한 연구가 병행되어야 할 것으로 판단된다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.11a
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• pp.8-8
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• 2000

하이드라진 단기액체엔진을 장착하고 궤도에서 임무를 수행하고 있는 다목적실용 위성 추진시스템 궤도비행 초기운용 자료에 근거하여 추진제 소모율을 산정 한다. 추진시스템은 위성의 궤도각과 비행고도 조정을 위한 속도증분($\Delta$V) 및 자세제어를 위한 추력을 발생시킨다. 단기액체 추진시스템에서 추진제 소모량은 추력기 밸브의 개폐시간에 비례하고 추력 생성 효율은 추진제의 연소기 유입압력에 종속한다. 일정질량의 가압 기체 압력에 의해 연료를 공급하는 추진시스템에서 잔류 추진제 량의 감소는 연소기 유입압력의 감소를 유발하고 추진기관의 효율을 저하시키는 요인으로 작용하여 임무말기로 진행함에 따라 동일한 운동량 생성에 보다 많은 연료소모가 이루어진다.(중략)

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.124.1-124.1
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• 2011

저온 고압의 환경에서 안정한 하이드레이트 함유 퇴적물 연구를 위하여 현장의 압력을 유지하여 코어를 회수할 수 있는 압력 코어러 (Pressure Corer)가 개발된 이후로 다양한 방법으로 압력코어를 이용한 연구가 진행되어 왔다. 하이드레이트의 안정영역 특성상 일반 코어러 샘플에서는 하이드레이트 함유 퇴적물의 회수가 용이하지 않았던 이유로 압력코어샘플응 이용한 현장 하이드레이트 함유 퇴적물의 연구는 필수적이다. 초기 단계에서는 압력코어를 이용한 비파괴 검사와 단순 감압 시험이 이루어졌다. 비파괴 검사를 통하여서는 X-ray 단면, 감마 밀도 (gamma density), 음파 속도 등이 측정 되었으며 감암 시험을 통하여서는 시료 내 하이드레이트 함유량을 산정하였다. 감압 후 다양한 지화학 분석이 후행되었다. 가스 하이드레이트 함유 퇴적물의 물성과 생산 거동이 점차 부각됨에 따라 압력코어 시료를 순간 감압하여 액체 질소에 보관하였다가 압밀시험, 삼축 압축 시험 등 물성 시험이 수행되었으며 수행 동안 X-ray 단면, 비저항, 음파 속도 등의 물성측정이 이루어졌다. 또한 액체 질소 보관 시료를 이용하여 감압법, 열염수 주입법, 열자극 법 등을 적용하여 생산 실험을 수행하기도 하였다. 이후에 압력코어 시료 절단 및 이동 시스템이 개발됨에 따라 보다 다양하고 많은 연구자 들이 압력코어 시료를 이용할 수 있게 되었으며 물성 연구뿐만 아니라 미생물 연구에 까지 압력코어 시료가 사용되게 되었다. 최근에는 절단 시료를 이용한 생산 실험 연구 또한 진행되었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.9
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• pp.5763-5768
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• 2015

A relief valve is a mechanical element to keep safety by controlling high pressure. Usually, the high pressure is relieved by using the spring force and letting the fluid to flow from another way out of system. When its normal pressure is reached, the relief valve can return to initial state. The relief valve should be designed for smooth operation and should satisfy the structural safety requirement under operating condition. The commercial software ANSYS/WORKBENCH is utilized for flow and structural analysis. Very high pressure may cause structural problem due to severe stress. The study suggests the design satisfying the structural design requirement

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.3
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• pp.258-263
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• 2012

In this paper the Chemical Propulsion Subsystem of COMS is briefly explained and some telemetries acquired by a series operations of CPS during the Launch and Early Operation Phase of COMS are presented. The pressure and temperature of pressurant tank telemetries are compared with the results of the developed computer program. The changes in pressure are due to the two major phases. The first one is the initialization phases of CPS composed of the venting phase to vent the helium gas in the pipe network from the downstream of the propellant tanks to the thrusters for safety, the priming phase to fill the vented pipe network with oxidizer and fuel respectively and then the pressurization phase to pressurize the ullage of propellant tank to regulated pressure. And the other is the apogee engine firings in which COMS CPS is in the orbit raising phase to use helium as a pressurant to keep the pressure of propellant tank as the liquid apogee engine get fired until COMS reached to the target orbit. This program can be applicable to prepare basis design data of the next Geostationary Satellite CPS.

• Journal of the Korean Ceramic Society
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• v.42 no.1
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• pp.22-27
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• 2005

The preparation of B4C by SHS in $B_{2}O_{3}-Mg-C$ system was investigated in this study. In the preparation of B4C, the effect on reactivity and reaction products of the initial pressure of inert gas in reactor, the content of Mg and C in mixture was investigated. The minimum initial pressure of inert gas in reactor for SHS reaction in this system was 25 atm, and as the pressure increased, the concentration of unreacted Mg decreased and combustion temperature increased. At the initial inert gas pressure in reactor of 25 atm, the optimum composition for the preparation of pure B4C was $2B_{2}O_{3}+6.3Mg +0.94C$. The B4C synthesized in this condition had an irregular shape and the particle size of $1\~3{\mu}m$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.5
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• pp.385-390
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• 2015

The flow characteristics in micro shock tube are investigated experimentally. Studies were carried out using a stainless steel micro shock tube. Shock and expansion wave was measured using 8 pressure sensors. The initial pressure ratio was varied from 4.3 to 30.5, and the diameter of tube was also changed from 3mm to 6mm. Diaphragm conditions were varied using two types of diaphragms. The results obtained show that the shock strength in the tube becomes stronger for an increase in the initial pressure ratio and diameter of tube. For the thinner diaphragm, the highest shock strength was found among varied diaphragm condition. Shock attenuation was highly influenced by the diameter of tube.