• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.4
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• pp.50-56
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• 2001

The present study is an experimental work of the soni $c^ersonic air ejector-diffuser system. The pressure-time dependence in the secondary chamber of this ejector system is measured to investigate the steady operation of the ejector system. Six different primary nozzles of two sonic nozzles, two supersonic nozzles, petal nozzle, and lobed nozzle are employed to drive the ejector system at the conditions of different operating pressure ratios. Static pressures on the ejector-diffuser walls are to analyze the complicated flows occurring inside the system. The volume of the secondary chamber is changed to investigate the effect on the steady operation. the results obtained show that the volume of the secondary chamber does not affect the steady operation of the ejector-diffuser system but the time-dependent pressure in the secondary chamber is a strong function of the volume of the secondary chamber.er.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.6
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• pp.479-487
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• 2015

In a reflected shock tunnel, stagnation conditions of a nozzle are determined by the flow behind a reflected shock. When calculating the flow behind the reflected shock, unlike a shock tube, the flow leakage through the nozzle is to be considered. The analytical studies were done to find out the characteristics of the stagnation conditions of the nozzle with various nozzle throat size. Experiments and numerical simulations were also carried out for further understanding of the flow leakage effects. It was found that the nozzle stagnation pressure was diminished by the increase of the size of the nozzle throat. It was also found that the steady pressure in the stagnation were maintained well at the area ratio of the driven tube to the nozzle throat is 4.5.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.1
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• pp.1-12
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• 1998

Industrial ejector system is a facility to transport, to compress or to pump out a low pressure secondary flow by using a high pressure primary flow. An advantage of the ejector system is in its geometrical simplicity, not having any moving part, compared with other fluid machinery. Most of the previous works have been performed experimentally and analytically. The obtained data. are too insufficient to improve our current understanding on the detailed flow field inside the ejector. In order to provide more comprehensive data on this ejector flow field, two-dimensional computations using Reynolds-averaged Navier-Stokes equations were performed for a very wide range of operating pressure ratio of the supersonic ejector with a secondary throat. The current results showed that the supersonic ejector system has an optimum pressure ratio for the secondary flow total pressure to be minimized. The numerical results clearly revealed the shock system, shock/boundary layer interaction, and secondary flow entrainment inside the supersonic ejector.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.4
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• pp.26-35
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• 2000

This paper depicts the computational results for the axisymmetric subsonic/sonic ejector systems with a second throat. The numerical simulations are based on a fully implicit finite volume scheme of the compressible Reynolds-Averaged Navier-Stokes equations in a domain that extends from the stagnation chamber to the ejector diffuser exit. In order to obtain practical design factors for the subsonic/sonic ejector systems which are applicable to industrial vacuum pumps, the ejector throat area, the mixing section configuration, and the ejector throat length are changed in computations. For the subsonic/sonic ejector systems operating in the range of low operation pressure ratios, the effects of the design factors on the vacuum performance of the secondary chamber are discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.04a
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• pp.298-304
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• 1995

유동이 있는 경우 발생하는 소음에 대한 실험적 연구는 풍동과 무향실이 결합된 음향풍동에서 수행될 수 있다. 이러한 음향풍동은 팬, 수축부, 수집부, 확산부 그리고 무향실에 주의해서 설계되어야 하고 특히 각 부분에서 발생할 수 있는 이차소음을 최소화하도록 설계되어야 한다. 최종적으로 소음기와 흡음재를 이용해서 팬소음과 이차소음의 전파를 줄인다. 본 음향풍동은 개방형 흡입식(open suction type)으로 시험부에서 유속 62.8m/s, 난류강도 0.1%이하, 배경소음 50-55dB 이하로 설계되었다. 이러한 조건을 만족시키기 위하여 하니콤과 6장의 스크린이 있는 정체실과, 21:1의 수축비를 갖는 수축부를 이용하여 난류강도를 낮추고, 흡음재와 90도 각도의 모서리 그리고 공명형과 소산형 소음기로 소음의 전파를 줄였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.3
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• pp.1-8
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• 2015

A ground hot-firing test(HFT) was accomplished to draw a correlation between the pressure oscillation intensity of combustion chamber and thrust response characteristics in a 70 N-class hydrazine thruster which has been developed recently. Monopropellant grade hydrazine was adopted as a propellant for the HFT, and combustion-chamber characteristic length, propellant injection pressure were applied as test parameters. It was confirmed that the decrease of thrust-chamber diameter and injection pressure augmented the pressure oscillation of stagnation chamber in the test condition specified, and the oscillation hampered the pulse response performance of test models.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.19 no.1
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• pp.58-70
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• 2020

Detour behavior on the expressway means that the driver uses the local road by passing the part of the expressway which is stagnant at the time of the traffic demand such as holidays. Since the detour rate was estimated through the survey at toll gate in the past, there was a difficulty in estimating the actual detour rate due to the small sample of the survey. In this study, we use DSRC-based route travel data to conduct empirical studies on detour patterns such as the estimation of actual detour rate, the improvement of travel time using detour road, and the correlation between traffic conditions on the expressway and detour rate. On the day of Chuseok and the day before Chuseok, the analysis of Giheung-DongtanIC→OsanIC and Seopyeongtaek IC→Walgott JC showed that the use of detour roads increased gradually during the congestion of the main line and travel time reduced when using detour roads, However, when the traffic congestion of the main line is not severe, the travel time increases when using the detour roads. The correlation between the traffic condition of the expressway and the actual detour rate has a negative correlation, which is consistent with the congestion pattern of the main line. The results of this study can be used to overcome limitations of detour pattern research based on surveys in the past and to establish a detour strategy for expressway sections where traffic demand is concentrated.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10a
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• pp.206-211
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• 1992

A mathematical model of the blow-down type wind tunnel is developed in order to design the controller which controls the stagnation pressure being used to obtain the setpoint Mach Number. The motion of compressible fluids in the tunnel is modeled using the one-dimensional gasdynamics. The time responses of the wind tunnel states, such as pressures, mass flow rates, and valve open area, are investigated by digital computer simulation. By the simulation study it is shown that the real blow-down wind tunnel can be simulated by the obtained mathematical model.

• SUVANNABHUMI
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• v.3 no.2
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• pp.79-123
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• 2011

문화정체성은 실로 구성적 성격을 지닌 개념으로, 문화정체성의 구성은 상황 (그리고 역사)과 상념 사이에서 발생하는 역동적인 상호작용의 결과에서 비롯된다. "다약인"이라는 개념의 형성 및 구성에 있어서도 서로 다른 다양한 힘이 작용해왔다. 식민 지배기에 탐험가들과 학자들은 서구적 방식으로 "다약인"의 구성을 구체화시켰고, 이것은 해방 이후 인도네시아 국가의 향방에 순차적으로 영향을 끼쳤다. 다약인 정체성의 구성과 그 동인에 관한 논의는 머리사냥, 긴 형태의 가옥들, 종교 등과 같이 다약인을 그려내는 특정한 이미지에 다만 집중하고, 다약을 그려내는 이러한 이미지들이 오늘날 다약인 정체성과 어떠한 연관성을 지니는가에 관한 논의이다. 과거 머리사냥 풍습에 관해서도 다약인에게 있어서 머리사냥의 의미와 관례를 충분히 설명할 수 있는 분석이 현재 전무하다. 다약인 사회의 또 다른 주요 특징은 독특한 주거양식에서 찾을 수 있다. 주거양식은 대부분의 문헌에서 추정해온 것처럼 독특한 것이 아니라 오늘날에 이르기까지 다약인은 껜야인처럼 종종 연립가옥(라민)을 그들의 중심문화로 여긴다. 깔리만딴 동부에 위치한 롱메카에서 문화와 청년축제가 개최되었는데 이 축제의 전체 진행은 자문화의 재건과 밀접하게 연관되어있다. 2006년에 끄라얀에서 개최된 이와 유사한 한 문화축제는 페뭉 에라우 펜제라니(Pemung Erau Pengerani)라고 불린다. 종교 역시 다약인의 인류학적 설명에 있어서 주요 특징으로, 다약인은 보르네오에 거주하는 비(非)무슬림교도들로 정의된다. 과거에는 거의 대부분의 사람들이 정령신앙을 숭배했으나, 다약인들 사이에서 기독교로의 대규모 개종이 일어나면서 다약인은 기독교도와 일반적으로 동일시되었다. 깔리만딴 지역의 무슬림은 다약인이 될 수 없다는 게 일반적인 생각이다. 실로 다약인이 된다는 것은 수많은 힘들의 집합체로부터 그 구성이 이루어진다는 것을 의미한다.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.6
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• pp.19-26
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• 2014

A ground hot-firing test (HFT) was carried out to make a close examination into the pressure instability for the 70 N-class hydrazine thruster under development. Monopropellant grade hydrazine was adopted as a propellant for the HFT, and catalyst-bed was filled with $Ir/Al_2O_3$ catalyst. In order to investigate the effects of thrust-chamber diameter on combustion stability, evaluation tests for the development models were performed on three kinds of lower thrust chambers having the length-to-diameter ratio (L/D) of 1.03, 1.13, and 1.26. As results, it was found that low frequency instability (~ 50 Hz) was inherent in the models, and in addition, increase of the L/D and decrease of the operating pressure led to an amplification of pressure oscillation in the test condition specified.