• Journal of the Korean Society of Propulsion Engineers
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• v.26 no.1
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• pp.47-59
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• 2022

Four swirl coaxial injectors with different recess lengths were manufactured using an additive manufacturing method. Single-injection and bi-injection cold-flow experiments were performed using water and air as simulated propellants in an atmospheric pressure environment. According to the recess length and propellant flow conditions, the injection pressure drop and discharge coefficient were investigated, and the breakup length and spray angle were measured using an image processing technique. In the bi-injection pressure drop and discharge coefficient results, the liquid-side injector was not affected by the recess. For the gas-side injector, however, the injection pressure drop increased and the discharge coefficient decreased as the recess length increased. The breakup length in the single-injection increased with the increase of the recess, but decreased in the bi-injection.

• Communications for Statistical Applications and Methods
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• v.5 no.3
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• pp.623-632
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• 1998

이원혼합모형에서 고정효과의 추정가능한 함수에 대한 신뢰구간을 구하는 경우에 어떤 분산성분추정량을 선택하는 것이 가장 바람직한가를 모의실험을 통하여 살펴본다 혼합모형에서는 t-분포와 일반화최소제곱추정량을 사용하여 신뢰구간을 구할 수 있는데, 일반적으로 분산성분을 알 수 없기 때문에 분산성분을 반드시 추정하여야만 한다. 이 경우 분산성분의 추정량으로 가장 많이 사용되는 추정량들인 Henderson의 방법 III 추정량, 사전추측값이 1인 MINQUE 추정량, MLE(최우추정량), REMLE(제한최우추정량)를 이용하여 분산행렬을 추정하고, 신뢰구간의 포함범위확률과 평균길이를 모의실험을 통하여 살펴본다. 모의실험의 결과는 4가지 추정량 모두 비슷한 신뢰구간의 포함범위확률과 평균길이를 갖는 것으로 판명되었다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.42-42
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• 2003

Ni/Si 기판상에 CH$_4$, H$_2$, $N_2$의 혼합기체를 사용하여 $700^{\circ}C$에서 5분 동안 MPECVD법으로 탄소나노튜브 성장시켰다. 이 과정에서 CH$_4$, H$_2$에 대한 $N_2$의 유량비를 여러 가지 값으로 변화시켜 그 성장 양상을 살펴보았다. 혼합기체 내 질소의 함량에 따라 나노튜브의 성장길이와 quality가 달라짐을 SEM과 Raman spectroscopy 측정을 통하여 확인하였다. 나노튜브의 성장 시 혼합기체 내 주입하는 질소량에 의해 나노튜브의 성장길이가 변화됨을 SEM을 통해 관찰할 수 있었고 혼합기체 내 질소의 비율이 커질수록 carbonaceous particle 등의 감소로 인한 나노 튜브의 quality가 향상됨을 Raman spectra를 통해 확인할 수 있었다. 또한 TEM과 SEM 관찰을 통해 성장된 탄소나노튜브가 대나무(bamboo) 구조를 가진 수직 배향된 다중벽 탄소나노튜브임을 확인하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.5
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• pp.2610-2616
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• 2014

An ejector is a kind of pump which is using pressure energy of high pressure fluid. This study aims to investigate performance influencing according to change the ejector mixing section shape using CFD simulation by Finite Volume Method. Optimum conditions were suggested 3 kind of variable such as nozzle diameter, nozzle length, distance from nozzle tip to the diffuser inlet. The results, It was confirmed that the diameter of the nozzle was the greatest effect in performance of the ejector. The diameter of the nozzle get smaller, mixing ratio was increased. On the other hand, nozzle length, distance from nozzle tip to the diffuser inlet had little effect on performance. It was proposed specific Mixing section, Nozzel diameter 23.8mm using the Artificial Neural Network.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.445-449
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• 2005

The mixed acoustic-convective mode combustion instability and the possibility of combustion control using a loudspeaker to these instabilities were studied. By changing inlet velocity, combustor length and equivalence ratio, the dynamic pressure signals and the flame structures were simultaneously taken. The results showed that as the combustor length increased and the inlet velocity decreased, the instability frequency decreased and the maximum power spectral densities of the dynamic pressures generally decreased. The instability frequency could be affected by an equivalence ratio over the operating conditions. From the data of close-loop control, as the loudspeaker may work out-of-phase with the natural instability, the optimum time-delay controller was confirmed to be able to reduce the vortex shedding from the mixed acoustic-convective mode combustion instability.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.74-77
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• 2011

A mixing characteristics on recess length change of Gas-centered swirl coaxial injector using high-performance staged combustion rocket engine carry out study through CFD(Computational fluid dynamics). propellant phase that combined gas-liquid simulate gas-gas. In order to measure spreading angle, velocity distribution to injector exit and spray structure of propellant analyzed. Axial velocity increase by increasing recess length, but tangential velocity decrease. The result confirmed qualitative characteristics that the spreading angle decreases.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.2
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• pp.62-69
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• 2003

Swirl injectors have the advantage of stable combustion, high efficiency, and insensibility to variable O/F ratio. Recess length is the length from outer orifice tip to inner orifice tip. It is the very important variable of performance of swirl type injector Recess length have influence on collision, mixing, spray, and combustion of propellants. This study investigated on the engine performance with the change of recess length through CFD, cold flow test, and combustion test. In result, we could confirm the change of engine performance with the change of recess length. And we found that performance forecast process through CFD, cold flow test is the right process through combustion test.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.75-81
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• 2003

To investigate the reinforcing effect of subsurface layers of marine dredged clay(DMC) mixed with the micro-fiber(MF), a series of laboratory tests were performed on the DMC specimens with and without MF through uniaxial and triaxial compression tests. For the test programme, the elapsed time after dredging of marine clay, mixing rate and length of MF, and curing time of the composite were chosen as the important factors affecting the strength behaviour. The strength of the DMC mixed with MF and waste lime(WL) used for the admixture was found to be enhanced with the increasing content and length of MF, and with decreasing water content of DMC. MF and WL were applied as materials for trafficability improvement of the very soft reclaimed ground by DMC.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.1
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• pp.24-33
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• 2020

In this study, model combustion tests were conducted to investigate the combustion instability characteristics of swirl coaxial injectors for a liquid rocket engine. To examine the effects of the combustion chamber resonant frequency and the injector mixing conditions, pressure fluctuations in the combustion chamber were measured by changing the combustion chamber length, injector recess length, and propellant mixture ratio. From the test results, the variation in the pressure fluctuations for each experimental condition was confirmed and the combustion stability was evaluated by stability mapping. It was found that the longitudinal mode and Kelvin-Helmholtz instabilities occurred due to the change in the combustion chamber and recess lengths.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.30-30
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• 2009

GTA 용접에서 용입, 용접부의 크기와 형상이 형성되는 아크 물리학적 현상을 이해함에 있어서 에너지 분포특성은 매우 중요한 인자이다. GTA 용접에서 아크 길이의 변화와 사용된 실드 가스 종류에 따라 음극인 텅스텐 전극 팁의 아크 루트 직경에 큰 변화를 주며, 양극인 모재 쪽의 에너지 분포에 영향을 미치며 된다. 기존의 연구자들은 저전류나 중전류 영역의 GTA 용접에서 텅스텐 전극의 선단각과 용입 형태와 의 관계를 plasma 기류 등에 의해 고찰하거나, 최대 아크압력에 미치는 전극형상의 영향에 대하여 연구하였다. 용접부에 작용하는 아크 압력의 분포는 결국 운동 에너지의 분포이다. 기존의 연구자들에 비하여 보다 간편한 실험을 통하여 양극 모재위의 아크 압력에 의한 에너지 분포특성을 규명하는 연구가 필요하다. 본 연구의 목적은 GTA 용접의 용접전류 100A~200A 영역에서 아크 길이 변화와 Ar 가스에 $H_2$ 혼합에 따른 측정된 아크 압력으로부터 기존연구자들의 아크 물리학적 결과들을 활용하여 양극 모재 위에 작용하는 전류밀도 분포를 유도하는 것이다. GTA 용접에서 아크 길이의 변화와 Ar 가스에 $H_2$ 혼합은 아크 압력분포에 큰 영향을 미치며, 이에 따라 에너지 분포특성에 많은 영향을 미친다. 아크 길이가 증가함에 따라 Ar가스와 $H_2$ 혼합가스의 에너지 분포는 감소하였고, Ar가스에 $H_2$ 혼합에 의해 아크 에너지가 증가하여 용입형상에 큰 영향을 미칠 것으로 판단된다. 이에 대한 연구는 향후 GTA 용접 응용분야 확대 적용될 것이며, 아크 물리학 연구에 기초적이고 아주 중요한 과학적인 자료가 될 것으로 판단된다.