• 한국진공학회지
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• 제9권3호
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• pp.285-289
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• 2000

축방향의 약한 자기장(약 1∼20 gauss)으로 자화된 inductively coupled plasm의 투과깊이와 전파 상수의 특성변화를 계산하였다. 자화 플라즈마에 있어서 전자밀도의 증가로 인한 플라즈마의 투과깊이 감소와, 그와 상반되는 충돌주파수 증가로 인한 투과깊이 증가를 고려하여, 보다 균일한 플라즈마 공정을 위한 기초 자료로서 중성 입자와 전자간의 충돌주파수, 전자밀도 및 자기장의 크기와 플라즈마 투과깊이 간의 상관관계를 확인하였다. 통상적인 저압 공정 플라즈마 조건하에서, 약 4.8 gauss의 자기장이 축방향으로 인가되는 경우 cyclotron 공명에 의해 투과깊이가 최소값을 가지는 것을 재확인하였으며, 그 이상의 자기장에서는 원형 편광파의 침투깊이를 비롯한 제반 특성의 급격한 변화를 볼 수 있었다.

• Geomechanics and Engineering
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• 제11권3호
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• pp.385-400
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• 2016

Bearing capacity of open-ended piles depends largely on inner frictional resistance, which is influenced by the degree of soil plugging. While a fully-plugged open-ended pile produces a bearing capacity similar to a closed-ended pile, fully coring (or unplugged) pile produces a much smaller bearing capacity. In general, open-ended piles are driven under partially-plugged mode. The formation of soil plug may depend on many factors, including wall thickness at the pile tip (or inner pile diameter), sleeve height of the thickened wall at the pile tip and relative density. In this paper, we studied the effects of wall thickness at the pile base and sleeve height of the thickened wall at the pile tip on bearing capacity using laboratory model tests. The tests were conducted on a medium dense sandy ground. The model piles with different tip thicknesses and sleeve heights of thickened wall at the pile tip were tested. The results were also discussed using the incremental filling ratio and plug length ratio, which are generally used to describe the degree of soil plugging. The results showed that the bearing capacity increases with tip thickness. The bearing capacity of piles of smaller sleeve length (e.g., ${\leq}1D$; D is pile outer diameter) was found to be dependent on the sleeve length, while it is independent on the sleeve length of greater than a 1D length. We also found that the soil plug height is dependent on wall thickness at the pile base. The results on the incremental filling ratio revealed that the thinner walled piles produce higher degree of soil plugging at greater penetration depths. The results also revealed that the soil plug height is dependent on sleeve length of up to 2D length and independent beyond a 2D length. The piles of a smaller sleeve length (e.g., ${\leq}1D$) produce higher degree of soil plugging at shallow penetration depths while the piles of a larger sleeve length (e.g., ${\geq}2D$) produce higher degree of soil plugging at greater penetration depths.

• 한국도로학회논문집
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• 제7권4호
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• pp.203-210
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• 2005

바인더의 노화로 인한 성능변화는 침입도 또는 점도시험을 실시하여 판정하여왔다. 기존의 시험방법으로 아스팔트 바인더의 점탄성 특성과 실제거동을 평가할 수 없기 때문에 새로운 분석방법이 요구되어 왔다. 본 연구에서는 기존시험 방법을 사용하여 침입도지수와 잔류침입도를 판정하였고, 양방향 반복회전 모드와 일방향 반복회전 모드 시험을 실시하여 단기 노화된 아스팔트 바인더의 유변학적 특성을 분석하였다. 시험결과 단기 노화된 아스팔트 바인더는 시험주기(frequency) 즉, 차량속도의 변화에 따라 서로 다른 복합계수와 위상각을 나타냈으며 단기 노화 전후의 크리프 컴플라이언스 및 전단점도 시험결과에도 영향을 미치는 것으로 나타나서 포장 설계시 이러한 특성이 고려되어야 한다.

• International Journal of Fluid Machinery and Systems
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• 제10권2호
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• pp.164-175
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• 2017

Francis turbines are often operated over a wide load range due to high flexibility in electricity demand and penetration of other renewable energies. This has raised significant concerns about the existing designing criteria. Hydraulic turbines are not designed to withstand large dynamic pressure loadings on the stationary and rotating parts during such conditions. Previous investigations on transient operating conditions of turbine were mainly focused on the pressure fluctuations due to the rotor-stator interaction. This study characterizes the synchronous and asynchronous pressure and velocity fluctuations due to rotor-stator interaction and rotating vortex rope during load variation, i.e. best efficiency point to part load and vice versa. The measurements were performed on the Francis-99 test case. The repeatability of the measurements was estimated by providing similar movement to guide vanes twenty times for both load rejection and load acceptance operations. Synchronized two dimensional particle image velocimetry and pressure measurements were performed to investigate the dominant frequencies of fluctuations, vortex rope formation, and modes (rotating and plunging) of the rotating vortex rope. The time of appearance and disappearance of rotating and plunging modes of vortex rope was investigated simultaneously in the pressure and velocity data. The asynchronous mode was observed to dominate over the synchronous mode in both velocity and pressure measurements.

• Journal of Advanced Marine Engineering and Technology
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• 제37권7호
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• pp.711-717
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• 2013

Titanium (Ti) metal and its alloys are desirable materials for ship hulls and other structures because of their high strength, light weight and corrosion-resistance. And light weight and corrosion-resistant aluminum (Al) is the ideal metal for shipbuilding. The joining of Ti and Al dissimilar metals is one of the effective measures to reduce weight of the structures or to save rare metals. Ti and Al have great differences in materials properties, and intermetallic compounds such as Ti3Al, TiAl, TiAl3 are easily formed at the contacting surface between Ti and Al. Thus, welding or joining of Ti and Al is considered to be extremely difficult. However, it was clarified that ultra-high speed welding could suppress the formation of intermetallic compounds in the previous study. Results of tensile shear strength increases with an increase in the welding speed, and therefore extremely high welding speed (50m/min in this study) is good to dissimilar weldability for Ti and Al. In this study, therefore, full penetration dissimilar lap welding of Ti (upper) - Al (lower) and Al (upper) - Ti (lower) with single-mode fiber laser was tried at ultra-high welding speed, and the microstructure of the interface zones in the dissimilar Al and Ti weld beads was investigated.

• Journal of Advanced Marine Engineering and Technology
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• 제38권2호
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• pp.133-139
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• 2014

Titanium (Ti) metal and its alloys are desirable materials for ship hulls and other ocean structures because of their high strength, corrosion-resistance and light weight properties. And light weight and corrosion-resistant aluminum (Al) is the ideal metal for shipbuilding. The joining of Ti and Al dissimilar metals is one of the effective methode to reduce weight of the structures. Ti and Al have great differences in materials properties, and intermetallic compounds such as $Ti_3Al$, TiAl, $TiAl_3$ are easily formed at the contacting surface between Ti and Al. Thus, dissimilar welding and joining of Ti and Al are considered to be very difficult. However, it was clarified that ultra-high speed welding could suppress the formation of intermetallic compounds in the previous study. Results of tensile shear strength increases with an increase in the welding speed, and therefore extremely high welding speed (50 m/min) is good to dissimilar weldability for Ti and Al. In this study, therefore, full penetration dissimilar lap welding of Ti (upper) - Al (lower) and Al (upper) - Ti (lower) with single-mode fiber laser was tried at ultra-high welding speed, and the microstructure of the interface zones in the dissimilar Al and Ti weld beads was investigated.

• Imaging Science in Dentistry
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• 제32권4호
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• pp.187-194
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• 2002

Purpose: To evaluate the performance of the LOGICON Caries Detector using RVG-4 and RVG-ui sensors, by comparing results of each detector to the results of clinical and histological examinations. Materials and Methods : Pairs of extracted teeth were radiographed, and a total of 57 proximal surfaces, which included both carious and non-carious situations, were analyzed. The RVG-4 produced 8-bit images, while the RVG-ui unit produced 12-bit images, which were taken in the high sensitivity mode. The images produced by the LOGICON were evaluated by a trained observer using both automated and manual caries detection software modes. Ground sections of the teeth established the actual absence or existence of caries. Results: LOGIC ON-aided caries detection and depth discrimination of the RVG-4 and RVG-ui sensors were equally inconsistent irrespective of whether the LOGIC ON software was set to the automated or manual mode. Sensitivity ranged from 50% to 57% for caries penetration of the enamel-dentin junction. Conclusion: Care needs to be taken when using LOGIC ON in conjunction with RVG images as an adjunct for treatment planning dental caries. Even when applied by a trained observer, substantial discrepancies exist between the results of the LOGIC ON software-guided evalutations using RVG images and histologic examination.

• 한국안전학회지
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• 제18권1호
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• pp.19-27
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• 2003

This paper presented an experimental modal analysis of clamped perforated rectangular plates submerged in water. The penetration of holes in the plates had a triangular pattern with P/D (pitch to diameter) 1.750, 2.125, 2.500, 3.000 and 3.750. The natural frequencies of the perforated plates in air were obtained by the Rayleigh-Ritz method and compared with the experimental results. Good agreement was obtained between the analytical solution and experimental result. The experimental results in water showed that the mode shapes are not sensitive to the depth of submergence. The natural frequencies were shown to decrease drastically once the perforated plates come in contact with water. However, the natural frequencies decrease with the depth of submergence until a certain depth is reached, and become the asymptotic values beyond this depth of submergence. The depth of submergence did not affect the damping ratio greatly.

• 한국자동차공학회논문집
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• 제10권4호
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• pp.60-68
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• 2002

Experiments have been conducted to investigate the effects of emulsified fuels on the spray characteristics and exhaust emissions in a diesel engine. Four different fuels were examined : diesel, emulsified fuels with water contents which were varied with 13, 15, and l7wt%. Characteristics of fuel spray were measured by an optical method, PLLIF(planar liquid laser induced fluorescence). Compared to diesel fuel, emulsified fuels which had relatively high kinematic viscosity showed smaller spray angle and longer spray tip penetration. The qualitative droplet distributions of emulsified fuels showed worse atomization process than that of diesel fuel. As the water contents were increased, PM and NOx could be reduced simultaneously. It was specially noted that the emulsified fuel with l7wt% water content was found to be the best in reducing rates, NOx 30% and PM 40%.

• 해양환경안전학회지
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• 제5권1호
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• pp.1-8
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• 1999

During the last 10 years, the various type of high speed craft have been greatly developed, and since around of 1990 the large size of high speed passenger and/or cargo vessels are also introduced and took into the service in the various routes over the world. In a marine traffic way some bridge need to build across a rivers, cannals or a waterways. This one will be an obstruction and potential risk of collision in the way of high speed craft. Accordingly some of collision accident have been reported, which were caused by a lost control, wind and hydrodynamic forces, fog or human errors. In this paper a high speed craft having 40 m length is assumed to be collided with a circular type of bridge piers at right angle. The mode of deformation, penetration depth of collapse, impact forces, reduction of speed, loss of kinetic energy, and influence of scantlings, etc. have been calculated in each speed with a time variation to find a maximum values within a limit, and are graphically presented.