• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.2
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• pp.25-31
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• 2004

This paper describes a new vibration-suppression technique for flexible cantilevered structures by using a pipe containing an internal flow. The stability and dynamic response are analyzed based on the finite element method. The flutter limit and optimum stabilizing fluid velocity are determined in root locus diagrams. The impulse responses of the system are studied by the mode superposition method to observe the damping rate of the motion. The stabilizing effect of an internal flow is demonstrated by impulse responses of the structures with and without an material damping. It is found that the response of the pipe with flow of liquid has a larger effect of, stabilizing than that with flow of gas.

• Journal of the KSME
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• v.56 no.9
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• pp.54-57
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• 2016

로켓연소기는 수백 개의 분사기로 구성된 연소실에서 연소반응이 발생하게 된다. 이때 구조적인 특성으로 난류유동, 밀도, 온도 등의 변화가 매우 불균일한 3차원적인 분포를 가지게 된다. 이러한 불균일한 분포에 의해 발생되는 압력의 시간변화가 연소기의 고유진동수와 일치될 경우 공진이 발생하게 되어 폭발이 발생하게 된다. 이러한 현상을 연소불안정이라 하고 이글에서는 관련된 연구의 동향을 소개하고자 한다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.7
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• pp.567-574
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• 2018

Swirl injection induces not only the increase in fuel regression rate but also the reduction of combustion pressure oscillation. This acts, in turn, to stabilize combustion process. Thus, this study primarily focuses on the change in flow structure in the main chamber by swirl injection. Then examining the change in flow structure was done to understand the physical process for stabilizing combustion. In the results, the application of swirl injection could suppress the generation of p' and q' in 500Hz band and could shift the phase difference and cross correlation. Further investigations with combustion visualization also show that the development of helical motion near surface region affects the small-sized vortex generation and shedding yielding combustion stabilization eventually.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.11a
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• pp.15-15
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• 2000

두 개의 사각형 유입구가 $90^{\cire}$의 각도를 이루고 있는 액체 램제트 엔진의 연소실 형상을 최적화하기 위해서 수조를 이용한 연소실 유동 계측 실험을 수행하였다. 공기 유입구의 연소실 유입 각도는 $30^{\cire}$, $45^{\cire}$ 및 $60^{\cire}$인 세 가지 형상의 연소실 모형을 제작하였으며, 각각의 유입 각도에 대하여 연소실 재순환 영역의 크기를 5가지로 변화시킬 수 있도록 모형을 제작하였다. 그리고 연소실의 배면은 돔의 형태로 하여 재순환이 잘 이루어지도록 모형을 제작하였으며, 유입구에서 연소실로 들어가는 유동의 안정화를 위해 안내깃을 세 개 설치하여 실험하였다.(중략)

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.554-557
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• 2008

In this study, two types of central flow distributor designs are presented and compared to obtain the optimal compact design which has the least flow resistance and the uniform flow distribution in a vehicular fuel cell stack. For effective and reliable prediction on the thermo-flow characteristics of the reactants flow over the entire fuel cell stack domain, open channel flow in the bipolar plates of the power generating cells were simulated by applying a simplified flow resistance model with an empirical porous concept. A number of case studies were performed to figure out an optimal configuration of a central flow distributor device in terms of the time-dependent thermo-flow behavior and load-dependent flow distribution. The results showed that the stable and load-independent thermo-flow uniformity is very design specific, which is closely associated with the design of central manifolding devices in order to achieve the enhanced volumetric power density and the reliable long-lasting operating of fuel cells.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.82-85
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• 2008

A Helmholtz resonator is applied to control high frequency combustion instability in liquid rocket engine. Damping characteristics of the Helmholtz resonator are investigated by the flow characteristic and its design. To simulate combustion instability, resonance in a test section(with fixed volume) is made by a pressure pulsator, and then damping characteristics are investigated. Its orifice length and diameter are selected as the design parameters and flow rates are varied to reveal the effect on damping characteristics. The experimental results show that a Helmholtz resonator is also working with flows. When length and diameter of an orifice are small, the tuning frequency increases as the flow velocity increases.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.6
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• pp.11-18
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• 2014

The combustion flowfield at the near-injector region of a 50 N scale $N_2O/C_2H_5OH$ thruster was visualized using shadowgraph technique. The explosive ignition was occurred at the design spray condition, and the expanding combustion gas quenched the flame immediately. Approximately after 83 ms from the initial ignition, the propellant spray was re-ignited, and the flame was stabilized after 23 ms elapsed. In the increased oxidizer flow rate condition, the transient pressure at the moment of ignition was smoother than explosive ignition, and the blow down phenomenon was not appeared in the same operating sequence. In addition, the flame was stabilized within 17 ms, and it is caused by improved propellants mixing before ignition.

• Tunnel and Underground Space
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• v.19 no.3
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• pp.248-260
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• 2009

With regard to oversea mineral resources development, recent trend has been changed from a simple capital investment to a direct development of the resources. In relation to the stability of a slope in large open-pit coal mine, groundwater system was investigated and the validity of horizontal drainage hole was evaluated in Pasir coal mine, Indonesia. In this work, various field tests were carried out for a characterization of groundwater system, which included in-situ permeability measurement, tracer test and monitoring of groundwater levels. Especially, the influence of SM river on the characteristics of the groundwater flow system was mainly inspected. For the permeability measurement, Guelph permeameter was employed, and was found that sandstone was more permeable than mudstone and coal seam. From a comparison of lithological structure and the results of groundwater level monitoring, sandstone and thin coal seam with fractures were found to be a main channel for groundwater flow. In the results of tracer tests, the effect of SM river on the groundwater system depends on the geological structure of its base. To identify the effect of horizontal drainage holes, 2-D groundwater modeling was performed. Four different cases were tested, which are different from the length of drainage hole and the existence of pond on top of the slope. To enhance the drainage effect and slope stability, the drainage hole should be drilled to the depth of coal seam layer, which provides a main pathway of groundwater flow and embedded by sandstone. For this purpose, correct identification of surrounding geology should be preceded.

• KDI Journal of Economic Policy
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• v.21 no.3_4
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• pp.63-104
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• 1999

본 연구는 외환위기 발생 이후 취해진 고금리정책이 이후의 환율안정에 기여하였는가를 살펴보고 있다. 완전 변동환율제도로 이행된 1997년 12월 이후의 일별자료를 대상으로 표준적인 시계열모형을 사용하여 분석한 주요 결과는 금리상승이 환율의 평가절상을 유도하였다는 것이다. 축약형모형(reduced form regression)에서 나타난 환율의 금리에 대한 탄력성은, 부도율과 같은 위험(risk)변수를 통제한 단순회귀방정식뿐 아니라 VAR모형에서도 1을 소폭 상회하는 정도의 추정치를 얻을 수 있었다. 이러한 결과는 비록 외환위기 이후 환율안정화의 가장 큰 원동력이 외환유동성의 회복이었음에도 불구하고, 외환유동성이 회복될 때까지 단기적으로는 고금리정책이 환율안정화를 위하여 부분적으로 기여하였음을 시사한다고 할 수 있을 것이다.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2003.05a
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• pp.513-516
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• 2003

가스터빈 복합발전은 우리나라 총 발전설비 용량의 약 25%를 차지하고 있다. 따라서 이들 가스터빈의 안정적인 운전을 위한 연소관리기술의 개발이 필요하며, 특히 발전설비의 대기오염물 배출기준이 점차 강화됨에 따라 가스터빈의 저NOx 연소 운영기술의 확보가 필수적이다. 국내에는 서인천복합, 신인천복합, 울산복합 및 보령복합 발전소 등에 건식 저 NOx 연소기가 설치되어 운영 중에 있으며 신규 건설중인 복합발전소에는 모두 이들이 설치될 예정이다.(중략)