• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.1253-1257
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• 2010

그라우팅은 건설공사에서 지반의 갈라진 틈이나 공동, 공극 등에 적절한 충전재를 압력을 이용하여 주입하는 것으로, 굴착공사 시 누수방지와 불안정한 지반의 보강을 위하여 광범위하게 사용되고 있다. 가장 많이 사용되고 있는 그라우팅 주입재의 재료로는 물유리계를 주재료로 사용하는 약액주입공법이 많이 사용되어지고 있다. 기존의 물유리계 재료를 사용할 경우 발생하는 용출현상 및 강도저하를 보완하기 위하여 가소성을 부과한 무기질계 재료ECG(Eco Clean Grouting)를 사용하여, 강도 및 내구성이 우수하고 주입재의 용출 현상이 발생하지 않아 환경오염 문제가 거의 없는 영구적인 차수 및 보강에 적합한지와 친환경적 특성을 확인한다. 본 연구는 가소성 무기질계 재료인 ECG(Eco Clean Grouting)재료를 사용하여 현재 많이 사용되는 재료인 물유리계 재료로 일축압축강도, 체적변화, 내구성 평가, 투수시험, 어독성 시험, 용탈시험등을 수행하여 비교 분석 하였다. 일축압축 시험결과 재령 28일 강도는 ECG가 물유리재료에 비해 크게 발현되었고, 내화학성시험 결과 ECG의 길이변화율이 거의 없는 것으로 내화학성에서 강점을 보였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.6
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• pp.25-30
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• 2010

Dual throat nozzle(DTN) is recently attracting much attention as a new concept of the thrust vectoring technique. This DTN is designed with two throats, an upstream minimum and a downstream minimum at the nozzle exit, with a cavity in between the upstream throat and exit. In the present study, a computational work has been carried out to analyze the performance of a dual throat nozzle(DTN) at various mass flow rate of secondary flow and nozzle pressure ratios(NPR). Two-dimensional, steady, compressible Navier-Stokes equations were solved using a fully implicit finite volume scheme. The present computational results were validated with some experimental data available. Based upon the present results, The control effectiveness of thrust-vector is discussed in terms of the thrust coefficient and the discharge coefficient.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.7
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• pp.634-642
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• 2011

A numerical analysis of steady/unsteady flow applying cavitation model and moving mesh method was carried out in order to analyze flow and response characteristics inside the pilot valve which controls the flight actuator system. The flow of the valve was assessed according to operation temperature and time. This research has found that valve characteristics became stable at above a specific temperature and the cavitation affected valve's performance. Internal pressure and response characteristics of the valve were analyzed and flow characteristics of steady and developed unsteady flow were confirmed to be matched each other.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.5
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• pp.1-7
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• 2010

Dual throat nozzle(DTN) is recently attracting much attention as a new concept of the thrust vectoring technique. This DTN is designed with two throats, an upstream minimum and a downstream minimum at the nozzle exit, with a cavity in between the upstream throat and exit. In the present study, a computational work has been carried out to analyze a fundamental performance of a dual throat nozzle(DTN) at various nozzle pressure ratios(NPR) and throat area ratios. Two-dimensional, axisymmetric, steady, compressible Navier-Stokes equations were solved using a fully implicit finite volume scheme. NPR was varied in the range of NPR from 2.0 to 10.0, at different throat area ratios. The present computational results were validated with some experimental data available. Based upon the present results, the performance of DTN is discussed in terms of the discharge coefficient and thrust efficiency.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.843-846
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• 2004

Cavity tone is generated due to the feedback between flow and acoustic wave. It is recognized that the period is determined by the time required for the flow convection in one direction, the time required for the acoustic propagation in the other direction and the time for phase shift depending on the flows and mode. Most of the phenomena have been investigated by experiments and a simple but fundamental theory. But the cause of the phase shift and the correctness of the theory have not been clearly explained so far. In this paper, the phenomena are calculated numerically to obtain detail information of flow and acoustic wave to explain the mechanism including the phase. High order high resolution scheme of optimized high order compact is used to resolve the small acoustic quantities and large flow quantities at the same time. The data are reduced using cross correlation function in space and time and cross spectral density function which has phase information. Abrupt change in pressure near corner in cavity is observed and is relate to phase variation. The time required for the feedback between the flow and acoustic wave is calculated after the numerical simulation f3r various modes. The periods based on the time calculated using the above method and direct observation from the acoustic waves generated and propagated in the numerical simulation are compared. It is found that no phase shift is required if we examine the time required carefully. Rossiter's formula for the cavity tone used for quick estimation needs to be modified far some modes.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.1
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• pp.116-124
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• 2002

The bubble model by Keller and Prosperetti is adapted to solve the nonlinear oscillation of a gas bubble. This formulation leads to accurate results since it introduces the energy equation instead of the polytropic assumption for the bubble interior. The numerical method used in this study is stable enough to handle large amplitude of bubble oscillation. The numerical results show some interesting nonlinear phenomena fur the bubble oscillator. The excitation changes the natural frequency of the bubble and makes some harmonic resonances at $f/f_0=1/2, 1/3$ and so on. The natural frequency of a bubble oscillator decreases compared with the linear case result, which means that the nonlinear bubble oscillation system is a "softening"system. In addition, the frequency response curve jumps up or down at a certain frequency. It is also found that there exist multi-valued regions in the frequency response curve depending on the initial conditions of bubble. The dependency of the bubble motion on the initial condition can generate extremely large pressure and temperature which might be the cause of the acoustic cavitation and the sonoluminescence.inescence.

• Proceedings of the Korea Contents Association Conference
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• 2013.05a
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• pp.371-372
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• 2013

먹거리 안전에 대한 우려가 커져가면서, 무엇을 먹을 것인지 식료품을 어떻게 구매할 것인지에 대한 소비자들의 관심이 증가하고 있다. 미국에서 2000년 중반부터 생겨난 신조어인 '로카보어 (locavore)'는 이와 같은 현상을 반영한 것이다. 이 용어는 지역이라는 의미의 '로컬(local)'과 먹는다는 뜻의 'vore'에서 파생된 것으로서 '지역에서 생산된 음식을 먹는 사람'이라는 의미를 가지고 있다. 건강에 좋은 음식을 소비하기 위한 적절한 장치로 로카보어 운동은 여러 가지 방식으로 음식 공급 체계를 유지할 수 있다. 농촌경제는 이어지는 FTA체결 등 시장 개방의 압력으로 인해 쇠퇴 일로에 있다. 이와 같은 관점에서 보면 지금은 지역농업을 살리기 위한 보다 효과적이고 실질적인 대응책을 개발할 시점이다. 따라서 로카보어 운동을 활성화함으로써 농촌 공동체는 사회적 결속을 강화할 수 있을 뿐만 아니라 지역경제 활성화를 꾀할 수 있다. 이 연구에서는 경기도 포천을 로카보어 운동의 한국형 모델로 선정하였다. 이는 포천이 서울과 근접해 있으며 관광객들이 자주 찾는 관광콘텐츠가 지역에 산재해 있을 뿐만 아니라 도 농복합도시로서 다수의 농장과 경작지로 구성되어있기 때문에 인근 대도시의 농축산물 수요를 충족할 수 있는 충분한 농축산물 산지라는 것이 장점이다. 이러한 측면에서 포천은 품질 좋은 지역의 농축산물의 공급처로서 '농축산 플랫폼(agro-platform)'의 구축을 체계화함으로써, 한국형 로카보어 운동의 중추적인 역할을 할 수 있을 것이다.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2003.11a
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• pp.48-53
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• 2003

The high temperature melting test for nonflammable wastes using a plasma torch was conducted. The AP-200L hollow cathode type plasma torch was installed at the pilot plasma melting furnace in NETEC. The surrogates were prepared to simulate concrete, soil and their mixture with steel. The experimental conditions such as feeding rate, the distance between melts surface and torch nozzle, torch rotation speed, gas flow rate and pressure in the furnace were decided. Basic parameters such as temperatures of cooling waters, off-gas and torch power were measured. The vitrified samples were analyzed by SEM/EDS.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.889-894
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• 2008

Exhaust system used in toilet and cooking place of high riser public house is roof fan of two basic types : natural roof ventilator and natural/forced roof ventilator. Natural/forced roof ventilator has a motor in the rotary shaft. There are many high riser public house in Korea. These buildings were not viewed as being major contributors to exhaust pollutants producted in indoor. It was because many engineers thought that exhaust in high riser building depend on stack effect. This study investigates on stack pressure determined by exterior pressure and the difference pressure control in exhaust stack used in high riser public house. This paper focuses mainly on the effect of the time interval for power supply of motor installed in roof fan with function of natural wind velocity and of exhaust air volume of toilet. It is observed there are higher exhaust efficiency than the existing natural roof ventilator.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.6
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• pp.91-102
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• 2017

The early basic studies on RDE has been surveyed in the previous paper. Recently active researches are carrying on for the application to the power plant and aerospace propulsion systems. Collaboration researches are going on for the application of RDE for the gas turbine, liquid rocket and combined cycle engines in many countries. Following the previous Part 1 paper, present paper is intended to provide the comprehensive survey of recent worldwide efforts on the realistic application of RDE.