• Journal of Advanced Marine Engineering and Technology
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• 제32권8호
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• pp.1240-1247
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• 2008

Leakage trouble on the sea water pipeline in engine room is often resulted from a localized corrosion due to severe corrosive environment caused by both high speed and high pressure of sea water flowing through the inner pipe. In addition, when the ship is in stand-by or emergency condition, underwater welding to control the leakage of sea water from a hole of its pipe is very important in an industrial safety point of view. In this study possibility of underwater welding to control leakage of sea water and corrosion property of its welding zone were investigated with the electrochemical methods by parameters of welding methods and welding electrodes when underwater welding is achieved with a such case that sea water is being leaked out with a height at 50mm from a hole of $2.5mm{\emptyset}$ of test pipe. Corrosion resistance of weld metal zone is better than the base metal and its hardness is higher than that of the base metal. However corrosion potential of weld metal zone showed a negative value than that of the base metal, therefore weld metal zone is preferentially corroded rather than the base metal by performance of galvanic cell due to difference of corrosion potential between weld metal zone and base metal. Eventually it is suggested that leakage of sea water is successfully controlled by underwater welding,

• KIEAE Journal
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• 제16권3호
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• pp.95-101
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• 2016

Purpose: Recently, high-rise buildings are popular in korea due to high rate of land usage and cost performance in urban area. However, high-rise building causes several problems such as safety issues, cooling/heating load, stack effect, disaster prevention etc. The stack effect is one of the representative problems. Even though there are many researches on stack effect, there are few studies on design guideline considering local condition. Method: This study focuses on the change of pressure distribution according to the design factors which affects the airflow in high-rise residential buildings by simulation analysis. In this study, city, building floor, stairwell door leakage area, elevator door leakage area and changes of layout were considered ad the design factor. Result: The simulation results indicate that building height and ambient air temperature are significant design factor for stack effect.

• 대한기계학회논문집B
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• 제27권3호
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• pp.389-397
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• 2003

Effect of tip leakage flow on through flow and performance of a centrifugal compressor impeller was numerically studied using CFX-TASC flow. Seven different tip clearances were used to consider the influence of tip clearance on performance. Secondary flow and loss factor were evaluated to understand the loss mechanism inside the impeller due to tip leakage flow. The calculated results were circumferentially averaged along the passage and at the impeller exit for quantitative discussion. Tip clearance effect on Performance could be decomposed into inviscid and viscous components using one dimensional equation. The inviscid component is related with the specific work reduction and the viscous component is related with the additional entropy generation. Two components affected Performance equally. while efficiency drop was mainly influenced by viscous loss. Performance and efficiency drop due to tip clearance were proportional to the ratio of tip clearance to exit blade height. A simple model suggested in the present study predict performance and efficiency drop quite successfully.

• 한국전산유체공학회지
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• 제18권1호
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• pp.7-12
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• 2013

This paper presents a numerical investigation of the influences of various non-uniform tip clearances on the performance and flow field in a centrifugal compressor. Numerical simulations were conducted for three centrifugal compressor impellers in which the tip clearance height varied linearly from the leading edge to the trailing edge. The numerical result was compared with the experimental data for validation. Although the performance improved for low tip clearances, a smaller tip clearance at the trailing edge reduced the overall tip leakage flow more effectively than a smaller tip clearance at the leading edge. Therefore, a smaller tip clearance at the trailing edge lowered the mixing loss caused by interactions between the tip leakage flow and the main passage flow.

• 한국재료학회지
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• 제13권1호
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• pp.11-17
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• 2003

DC characteristics of recessed gate 4H-SiC MESFET were investigated using the device/circuit simulation tool, PISCES. Results of theoretical calculation were compared with the experimental data for the extraction of modeling parameters which were implemented for the prediction of DC and gate leakage characteristics at high temperatures. The current-voltage analysis using a fixed mobility model revealed that the short channel effect is influenced by the defects in SiC. The incomplete ionization models are found out significant physical models for an accurate prediction of SiC device performance. Gate leakage is shown to increase with the device operation temperatures and to decrease with the Schottky barrier height of gate metal.

• 전기학회논문지
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• 제65권10호
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• pp.1697-1701
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• 2016

The leakage conduction and critical voltage characteristic of ZnO ceramic were investigated as a function of $Sb_2O_3$ concentration. Leakage conduction in the ohmic region increased with increasing $Sb_2O_3$ concentration and was attributed to the potential barrier height. The nonlinear coefficient increased with an increasing amount of $Sb_2O_3$. It was found that increases in the apparent critical voltages were associated with the lowered donor concentration in the grain boundary of between two ZnO grains. And the decrease of donor concentration on doping with $Sb_2O_3$ additive was attributed to the lowered capacitance in the grain boundary layer.

• 반도체디스플레이기술학회지
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• 제4권3호
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• pp.5-9
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• 2005

The bonding structure of organic materials such as fluorinated amorphous carbon films was classified into two types due to the chemical shifts. The electrical properties of fluorinated amorphous carbon films also showed very different effect of two types notwithstanding a very little difference. Fluorinated amorphous carbon films with the cross-link break-age structure existed large leakage current resulting from effect of the electron tunneling. Increasing the cation due to the electron-deficient group increased the barrier height of the films with the cross-link amorphous structure, therefore the electric characteristic of the final materials with low dielectric constant was also improved. The lowest dielectric constant is 2.3 at the sample with the cross-link amorphous structure.

• 대한기계학회논문집B
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• 제30권3호
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• pp.230-237
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• 2006

Flows in the cavity with pump out vane are calculated using the CFX-Tascflow CFD code. flow calculations are performed for different values of vane height, numbers, leakage flow rate, and rotational speed. The flow is very complex and three dimensional with strong vortex and leakage flow over the vane. The variations of pressure coefficient and K-factor with these parameters and resulting effects on the thrust and torque are studied. The present study contributes to showing the capability of flow simulation of back cavity with pump-out vane. The calculated results are good enough to be used back cavity design.

• 한국가스학회지
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• 제11권4호
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• pp.79-84
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• 2007

LPG 용기에 장착된 네크링의 암나사와 개폐밸브의 수나사 사이에서 발생되는 접촉법선응력과 von Mises 응력을 유한요소법으로 해석하여 밸브나사의 체결안전성에 관련된 강도 및 가스누출 안전성에 대해 고찰하였다. LPG 봄베의 가스충전압력 $8{\sim}9kg/cm^2$은 밸브와 LP가스 용기의 체결작용과 밀봉작용을 담당하는 나사부에 가압된다. 나사 선단부에서 발생한 스크래치 마모나 칩핑 손상은 나사의 접촉높이를 실질적으로 낮추게 되어 나선부의 강도를 떨어뜨리고, LP가스의 누설을 조장하게 된다. 체결 나선부의 손상은 밸브 나사부의 이빨 강도를 약화시키고, LP가스의 누출에 영향을 미친다. FEM 해석결과에 의하면, 나사 선단부의 마모 및 칩핑에 의한 높이 손상은 이론적으로 볼 때 LP가스의 누출과 밸브의 강도에 영향을 미치지 못하는 것으로 나타났다. 그러나 황동밸브 나사 높이의 손상정도가 밸브의 임계강도를 넘어서게 되면, 나사는 밸브와 LP가스 봄베를 더 이상 체결하지 못하게 되어 압력용기는 갑자기 파손될 수도 있다.

• 한국재료학회지
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• 제13권4호
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• pp.233-238
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• 2003

Ferromagnetic tunnel junctions, Ta/Cu/Ta/NiFe/Cu/$Mn_{75}$ $Ir_{25}$ $Co_{70}$ $Fe_{30}$/Al-oxide, were fabricated by do magnetron sputtering and plasma oxidation process. The effect of annealing temperature on the local transport properties of the ferromagnetic tunnel junctions was studied using contact-mode Atomic Force Microscopy (AFM). The current images reflected the distribution of the barrier height determined by local I-V analysis. The contrast of the current image became more homogeneous and smooth after annealing at $280^{\circ}C$. And the average barrier height $\phi_{ave}$ increased and its standard deviation $\sigma_{\phi}$ X decreased. For the cases of the annealing temperature more than $300^{\circ}C$, the contrast of the current image became large again. And the average barrier height $\phi_{ave}$ decreased and its standard deviation $\sigma_{\phi}$ increased. Also, the current histogram had a long tail in the high current region and became asymmetric. This result means the generation of the leakage current that is resulted from the local generation of a low barrier height region. In order to obtain the high tunnel magnetoresistance(TMR) ratio, the increase of the average barrier height and the decrease of the barrier height fluctuation must be strictly controlled.led.