• 터널과지하공간
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• 제10권4호
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• pp.516-525
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• 2000

최근, 도시 재개발과 산업설비 개·보수에 따른 노후화된 콘크리트 및 철근구조물에 대하여 환경 공해가 발생하지 않는 해체 기술 개발에 대한 요구가 급증하고 있다. 본 연구는 철근 구조물의 폭발절단 해체를 위한 성형폭약을 개발하기 위하여 폭발절단 효과에 영향을 주는 요소인 대상 구조물의 재질 및 형상, 두께와 강도 특성, 성형폭약의 형상, 폭약의 종류, 장약량, liner의 종류, stand-off distance, 성형폭약의 폭 및 너비, 기폭방법에 따른 영향과 폭발 절단시 발생되는 폭풍압에 의한 진동 및 소음의 영향 등을 검토함으로 폭발절단 최적조건을 선정하였다. 따라서, 본 연구를 통해 얻어진 폭발절단기술은 강교, 공장, 폐선박 등의 해체에도 적용될 것이다.

• 한국추진공학회지
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• 제1권2호
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• pp.32-40
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• 1997

무제트초기의 불안정성이 하류에서의 와류성장에 영향을 끼치기 때문에 와류의 조절에 의한 충돌면에의 유동 및 열전달 효과의 변화를 기대할 수 있게 된다. 따라서 본 논문에서는 FFT를 이용하므로써 제트의 와류생성과 병합의 주파수 특성을 연구하고 이에 적절한 주파수로 와류를 여기하여 자유제트의 유동특성 변화와 충돌제트의 유동 및 열전달 특성을 고찰하였다. 음향여기를 하게되면 제트주위의 와류형성을 조절할 수 있게 되는데, 자연적으로 형성되는 와류의 주파수(와류의 고유주파수)와 관련하여 여기해준 주파수성분 자체보다는 여기주파수의 부조화성분이 중요한 역할을 하게 된다. 음향여기를 통해 와류의 병합이 촉진되면 중심부에서의 난류강도가 증가하게 되고 억제하면 난류강도는 감소하게 된다. 따라서 와류병합을 촉진하면 가까운 거리에서는 높은 난류강도로 인해 정체점에서의 열전달이 증가하지만 멀어질수록 포텐션코어길이의 감소로 오히려 낮은 결과를 나타내었다. 이와 반대로 와류병합을 억제하면 중심부에서의 낮은 난류강도로 가까운 거리에서는 열전달이 감소하였으나 포텐셜코어길이가 길어지면서 먼거리에서는 열전달에 효과적이었다.

• Journal of Mechanical Science and Technology
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• 제15권12호
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• pp.1784-1793
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• 2001

The flow fields around an elliptic cylinder of axis ratio AR=2 adjacent to a free surface were investigated experimentally using a water channel. The main objective is to understand the effect of the free surface on the flow structure in the near-wake. The flow fields were measured by varying the depth of cylinder submergence, for each experimental condition, 350 velocity fields were measured using a single-frame PIV system and ensemble-averaged to obtain the spatial distribution of turbulent statics. For small submergence depths a large-scale eddy structure was observed in the near-wake, causing a reverse flow near the free surface, downstream of the cylinder. As the depth of cylinder submergence was increased, the flow speed in the gap region between the upper surface of the cylinder and the free surface increased and formed a substantial jet flow. The general flow structure of the elliptic cylinder is similar to previous results for a circular cylinder submerged near to a free surface. However, the width of the wake and the angle of downward deflection of the shear layer developed from the lower surface of the elliptic cylinder are smaller tan those for a circular cylinder.

• 동의생리병리학회지
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• 제20권2호
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• pp.365-371
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• 2006

Bee Venom aqua-acupuncture (BVA) simultaneously exerts pharmacological effects of biologically active compounds, existed in the whole bee venom, and medicinal effect of the stimulation of acupuncture points. BVA has been considered as a promising therapeutic method for treating various chronic diseases, mainly accompanying severe pain and inflammation. As a painless injection device, jet injectors have been commercially marketed for various clinical applications including insulin injection and vaccination. Among them, a pressure-driven jet injector system could be used for intradermal delivery of a variety of drugs. The aim of this study was to investigate the analgesic effects of the BVA using a needle-free injector (Biojector $2000^{\circledR}$, Bioject Inc., OR, USA), compared to the conventional BV aqua-acupuncture using a typical syringe. Adult Sprague-Dawley rats were injected with bee venom $(0.08mg/kg,\;50{\mu}l)$ using Biojector $2000^{\circledR}$ (BVA-B) or a syringe (BVA-5) into the Zusanli (ST36) acupoint, 30 minutes before plantar injection of 2% formalin. It was found that BVA-B-, or BVA-5-treated rats, compared to controls, exhibited significantly less licking behavior during the late phase in the rat formalin test, when compared to controls. During early phase, however, those effects were not significant but substantial. The analgesic effect of BVA-B was also compatible with that of the conventional BVA-5. In the immunohistochemical studies, BVA-B significantly suppressed the expression of formalin-evoked c-fos, a biomarker of neuronal activity, in the lumbar dorsal horn of the spinal cord. These results indicated that BVA-B waseffective in the modulation of pain in the rat formalin test, compared to BVA-5. Taken together, the needle-free jet injector system could be substituted for the conventional aqua- acupuncture with the advantage of little pain.

• 대한기계학회논문집B
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• 제32권7호
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• pp.504-512
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• 2008

The characteristics of nonpremixed oxy-fuel flame in a multi-jet burner were experimentally and numerically investigated. The overall flow rate of fuel and oxygen was fixed, and the oxygen feeding ratio (OFR) was varied by 0.25, 0.5, and 0.75. The results of numerical simulation were compared with the measured results which are temperature profile and direct flame observation. The probability density function (PDF) model was applied accounting to the description between turbulence and chemistry, and standard ${\kappa}-{\varepsilon}$ model was used for turbulent flow field. Equilibrium assumption is very reasonable due to fast chemistry of the oxy-fuel combustion. Thus, the equilibrium calculation based on Gibbs free energy minimization was guaranteed to generate the solution of the oxy-fuel combustion. The result was obtained by numerical simulation. The predicted radial temperature profiles were in good agreement with the measured results. The flame length was shorten and was intensified with the decrease of OFR because the mixture of fuel and oxidizer are fast mixed and burnt. The maximum temperature became lower as the OFR increased, as a consequence of large flame surface area.

• 대한기계학회논문집
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• 제18권5호
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• pp.1253-1263
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• 1994

The experimental study is carried out to identify the combustion generated noise mechanism in free turbulent jet diffusion flames. Axial mean fluctuating velocities in cold and reacting flow fields were measured using hot-wire anemometer and LDv.The overall sound pressure level and their spectral distribution in far field with and without combustion were also measured in an anechoic chamber. The axial mean velocity is 10-25% faster and turbulent intensities are about 10 to 15% smaller near active reacting zone than those in nonreacting flow fields. And sound pressure level is about 10-20% higher in reacting flow fields. It is also shown that the spectra of the combustion noise has lower frequency characteristics over a broadband spectrum. These results indicate that the combustion noise characteristics in jet diffusion flames are dominated by energy containing large scale eddies and the combusting flow field itself. Scaling laws correlating the gas velocity and heat of combustion show that the acoustic power of the combustion noise is linearly proportional to the 3.8th power of the mean axial velocity rather than 8th power in nonreacting flow fields, and the SPL increases linearly with logarithmic 1/2th power of the heat of combustion.

• 대한기계학회논문집B
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• 제20권4호
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• pp.1395-1405
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• 1996

The purpose of this experimental research is to investigate the local heat transfer characteristics in the upward free water jet impinged on a downward flat plate of uniform heat flux. The inner shape of rectangular nozzle used was sine curve type and its contraction ratio of inlet to outlet area was five. Experimental parameters considered were Reynolds number, nozzle exit-flat plate distance, and level of supplementary water. Local Nusselt number was influenced by Reynolds number, Prandtl number, supplementary water level, and distance between the nozzle exit and flat plate. Within the impingement region, the Nusselt number has a maximum value on the nozzle center axis and decreases monotonically outward from center. Outside of the impingement region, on the other hand, the Nusselt number has a secondary peak near the position where the distance from nozzle center reaches four times the nozzle width. However if nozzle exit velocity exceeds 6.2 m/s, the secondary peak appears also in the impingement region. The empirical equation for the stagnation heat transfer is a function of Prandtl, Reynolds, and axial distance from the nozzle exit. The optimum level of supplementary water to augment the heat transfer rate at stagnation point was found to be twice the nozzle width.

• 한국추진공학회지
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• 제2권3호
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• pp.10-19
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• 1998

초음속 부족팽창제트가 충돌할 때 유동장은 매우 복잡한 유동구조를 나타낸다. 본 연구에서는 음속노즐 출구 직경의 1.5배 거리에 경사각 $60^{\cire}$~$90^{\cire}$로 설치된 평판에 미치는 초음속 제트에 대해 쉴릴렌 장치를 이용하여 유동구조를 가시화 하였으며, 평판 위에 작용하는 압력분포를 측정하였고 감열지를 이용하여 평판 표면 유동을 가시화하여 기존의 연구결과와 비교하였다. 연구결과 간단한 방법으로 저마하수에서의 평판 유동을 가시화 할 수 있는 방법을 제시하고 충돌제트의 유동구조를 규명하였다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 추계학술대회
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• pp.471-473
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• 2006

An object of the present study is to provide a hollow fiber membrane humidifier capable of improving the humidification efficiency while lowering the pressure loss, and is suitably usable for PEMFC(Polymer Electrolyte Membrane Fuel Cell). The performance of PEMFC is decisively dependent on the humidity of the electrolyte membrane(fluorinated membrane) and a humidifier plays an important role in moisturizing electrolyte membrane. Especially this humidifier is adaptable for lower price to promote the commercialization of fuel cell vehicles and is passive type to be power free and to be volumetrically optimized. In this research, we propose the substitutes for the expensive fluorinated materials and the optimum dry-jet wet spinning conditions of hollow fiber membrane to get the fuel cell humidifier. In addition to that we established the standard method of evaluating the moisturizing performance of the humidifier of various materials.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
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• pp.167-170
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• 2012

Self-excitations of edge flame were studied in laminar lifted free- and coflow-jet as well as counterflow flames diluted with nitrogen and helium. The self-excitations, originated from variation of edge flame speed and found in the above-mentioned configurations, are discussed. A newly found self-excitation and flame blowout, caused by the conductive heat loss from premixed wings to trailing diffusion flame are described and characterized in laminar lifted jet flames. Some trials to distinguish Lewis-number-induced self-excitation from buoyancy-driven one with O(1.0 Hz) are introduced, and then the differences are discussed. In counterflow configuration, important role of the outermost edge flame in flame extinction is also suggested and discussed.