• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 E
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• pp.2170-2172
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• 1999

A low energy large aperture(LELA) pulsed electron beam generator of a cold cathode type has been developed for environmental applications, for example, waste water cleaning, flue gas cleaning, and pasteurization etc. The operational principle is based on the emission of secondary electrons from cold cathode when ions in the plasma hit the cathode, which are accelerated toward exit window by the gradient of an electric potential. We have fabricated the LELA electron beam generator with the peak energy of 200keV and beam diameter of 200mm and obtained the large aperture electron beam in air. The electron beam current density has been investigated as a function of glow discharge current, accelerating voltage and radial distribution in front of the exit window foil. The plasma density and electron temperature have been measured in order to confirm the relation with the electron beam current density. We are going to upgrade the LELA electron beam generator in the electron energy, electron beam current and stability of operation for various applications.

• 한국안전학회지
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• 제14권4호
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• pp.158-167
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• 1999

In parallel flow condition, to estimate the stability of the extended embankment constructed on a permeable foundation ground, a laboratory model test was performed due to extended materials and water level increasing velocity of a flood period. A laboratory model test was peformed for different permeability coefficients ($K_1=2.0{\times}10^{-5}cm/sec,\;K_2=1.5{\times}10^{-4}cm/sec,\;K_3=2.3{\times}10^{-3}cm/sec$) using seepage. The fluctuation of water level occurring to an extended embankment was analyzed by laboratory model tests as vary the increasing velocity of water level with 0.6cm/min, 1.2cm/min, 2.4cm/min respectively. In analysis results, the increase of water level into embankment occurs rapidly because seepage water moving along with a permeable soil flow into embankment. The larger the permeability coefficient of an extended part is the longer initial seepage distance, and the exit point of downstream slope is gradually increased and then shows unstable seepage behavior as occurring partial collapse. As the increasing velocity of water level increase, the initial seepage line is formed low, and the discharge increases. Therefore, the embankment extended by a lower permeable soil than existing embankment shows stable seepage behavior because an existing embankment plays a role as filter for an extended part.

• 대한조선학회논문집
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• 제59권2호
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• pp.80-88
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• 2022

A systematic experimental study is carried out for the fire fighting monitor nozzle of 65A diameter to design and manufacture a new nozzle with better water spray performance than available domestic nozzles. The nozzle inlet pressure, flow rate and reach for the discharged water from the nozzle are measured by utilizing the experimental facility consisting of two pumps and piping system with a flow meter and pressure gauges. It was found that the baffle position and baffle head chamfering were the most sensitive design factors to be remarkably changed in the flow rate of the discharged water. Also, It was confirmed that the baffle position and the water exit area had the significant effect on the change in reach distance. The results obtained from this study are expected to be used effectively to design new nozzles with excellent spray performances and also to validate numerical analysis results for evaluating the water spray performance of fire fighting monitor nozzles.

• 한국항해항만학회지
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• 제39권1호
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• pp.77-82
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• 2015

슬래밍은 선체가 파도와 부딪히며 선수, 선미에서 강한 충격압력을 받아 급격한 진동이 발생되는 현상이다. 이러한 슬래밍은 사람에게는 승선감의 불쾌감을 주고, 선체에는 구조적인 위험을 주며 화물의 안전과도 깊은 관계가 있다. 따라서 선박 설계기준에는 슬래밍에 의한 충격압력을 충분히 고려한 구조설계를 해야 한다. 본 연구에서는 자유낙하 하는 쐐기형 구조물의 중량 및 낙하높이의 변화에 따른 슬래밍 충격 압력 및 유동장의 유동특성을 알아보고자 실험을 수행하였다. 유동장의 계측은 2-프레임 그레이레벨 상호상관 PIV기법을 이용해 접수와 이수로 구분하여 실험하였으며, 충격압력의 계측은 압력계측장비인 Dewetron System을 이용하였다. 실험에서 모델과 자유수면간 이루는 각도는 $15^{\circ}$를 적용하였으며 이때, 중량의 변화는 1.5, 1.8 및 2.0kg이고 자유낙하높이는 100, 200 및 300mm로 하여 실험하였다. 실험값을 통한 중량의 변화에 따른 충격압력은 중량의 증가하는 것에 비례하여 충격압력 또한 증가했으며, 이러한 경향은 자유낙하 높이가 높을수록 영향을 많이 받았다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제24회 춘계학술대회논문집
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• pp.237-242
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• 2005

가스터빈엔진에서 압축기가 사용하는 에너지는 터빈에서 생성하는 에너지의 $30-50\%$까지도 이르기 때문에 압축기의 일을 줄이는 연구는 가스터빈의 효율을 증가시키는 문제와 연관된 중요한 연구주제이다. 압축기의 일을 줄이는 한 가지 방법으로 압축기의 입구에 물입자를 분사하는 방법이 제안되었는데, 이 방법은 물입자가 증발하면서 압축기 출구의 온도를 낮추어서 결과적으로 압축과정에 소요되는 에너지를 줄일 수 있는 방법이다. 이전까지의 연구는 열역학적 해석에 집중하여 온도 및 일의 감소를 해석하거나, 실험에 근거하여 가스터빈의 성능변화에 집중되었다. 본 논문에서는 물분사의 영향을 마이크로터빈용 원심압축기에 적용하여 열역학적 해석 뿐 아니라 공력학적 해석을 수행하였다. 물을 분사할 경우 공기압축과정보다 임펠러 출구 유동각이 줄어들었으며, 증발율이 높을수록 유동각 감소가 증가하였고, 압력비가 낮을수록 유동각 감소가 증가하였다.

• 한국유체기계학회 논문집
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• 제11권5호
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• pp.50-56
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• 2008

Metal cutting operations involve generation of heat due to friction between the tool and the pieces. This heat needs to be carried away otherwise it creates white spots. To reduce this abnormal heat cutting fluid is used. Cutting fluid also has an important role in the lubrication of the cutting edges of machine tools and the pieces they are shaping, and in sluicing away the resulting swarf. As a cutting fluid, water is a great conductor of heat but is not stable at high temperatures, so to improve stability an emulsion type mixed fluid with water and oil is often used. It is pumped over the cutting site of cutting machines as a state of atomized water droplet coated with oil by using jet. In this paper, to develop cutting fluid supplying nozzle to obtain ultra thin oil film for coating water droplet, a numerical analysis of three dimensional mixed fluid Jet through multi-stage nozzle was carried out by using a finite volume method. Jet flow characteristics such as nozzle exit velocity, development of mixing region, re-entrance and jet intensity were analyzed. Detailed mixing process of fluids such as air, water and oil in the nozzle were also investigated. It is easy to understand complex flow pattern in multi-stage nozzle. Important flow Information for advance design of cutting fluid supplying nozzle was drawn.

• 한국환경농학회지
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• 제24권1호
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• pp.6-11
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• 2005

A prototype surface flow constructed wetland was built in the upstream area of reclaimed tidal lands to improve the water quality of Lake Sihwa by treating severely polluted stream water. In this study, a tracer test using rhodamine-WT was performed to investigate the flow characteristics and to quantify the observed hydraulic residence time (HRT) for a high-lying cell in the Banwol wetland of the Sihwa constructed wetland. The tracer test indicated that even if flow was mainly observed in the open water area of the Banwol wetland, water flowed continuously in the vegetative area and there was no dead zone. The calculated HRT (51.3 hrs), calculated by dividing the wetland volume by the wetland inflow, exceeded the observed HRT (38.7 hrs), since the short-circuiting of flux resulting from irregular topography and vegetation was not reflected in the calculated HRT. The exit tracer concentration curves were reproduced well by both the plug flow with dispersion and tanks-in-series models, indicating that the performance of the Banwol wetland can be estimated accurately using these models.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 연약지반처리위원회 학술세미나
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• pp.93-112
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• 2000

The permeability of converter slag, replacing material of sand mat on improving soft clay foundation, was evaluated in the laboratory. The effects of grain size, flow water time and aging were investigated using sea and fresh water. Converter slag being submerged with fresh water, the coefficients of permeability in A and B samples less than 10mm grain sizes were measured as 6.52${\times}$10$\^$-2/cm/sec and 5.99${\times}$10$\^$-1/cm/sec, while changed as 1.88${\times}$10$\^$-2/cm/sec, 3.86${\times}$10$\^$-1/cm/sec under sea water condition. Also, the condition of turbulent flow may exit and was experimentally identified from the relationship between hydraulic gradient and seepage velocity. After 180 days on using sea water, the coefficients of permeability of sample A and B samples decreased ten times smaller than those initial values. And after that time continually decreased as for till 360 days. The reduction of permeability coefficient was considered to influence filled with voids in high-calcium quicklime(CaO). However, in-situ coefficient of permeability was practically satisfactory.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 연약지반처리위원회 학술세미나
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• pp.12-31
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• 2000

The permeability of converter slag, replacing material of sand mat on improving soft clay foundation, was evaluated in the laboratory. The effects of grain size, flow water time and aging were investigated using sea and fresh water. Converter slag being submerged with fresh water, the coefficients of permeability in A and B samples less than 10mm grain sizes were measured as 6.52${\times}$10$\^$-2/cm/sec and 5,99${\times}$10$\^$-1/cm/sec, while changed as 1,88${\times}$10$\^$-2/cm/sec, 3.86${\times}$10$\^$-1/cm/sec under sea water condition. Also, the condition of turbulent flow may exit and was experimentally identified from the relationship between hydraulic gradient and seepage velocity. After 180 days on using sea water, the coefficients of permeability of sample A and B samples decreased ten times smaller than those initial values. And after that time continually decreased as for till 360 days. The reduction of permeability coefficient was considered to influence filled with voids in high-calcium quicklime(CaO). However, in-situ coefficient of permeability was practically satisfactory.

• Nuclear Engineering and Technology
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• 제40권2호
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• pp.117-126
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• 2008

In this paper, a new reactor core design is proposed on the basis of a mixed core concept consisting of a thermal zone and a fast zone. The geometric structure of the fuel assembly of the thermal zone is similar to that of a conventional thermal supercritical water-cooled reactor(SCWR) core with two fuel pin rows between the moderator channels. In spite of the counter-current flow mode, the co-current flow mode is used to simplify the design of the reactor core and the fuel assembly. The water temperature at the exit of the thermal zone is much lower than the water temperature at the outlet of the pressure vessel. This lower temperature reduces the maximum cladding temperature of the thermal zone. Furthermore, due to the high velocity of the fast zone, a wider lattice can be used in the fuel assembly and the nonuniformity of the local heat transfer can be minimized. This mixed core, which combines the merits of some existing thermal SCWR cores and fast SCWR cores, is proposed for further detailed analysis.