• Water Engineering Research
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• 제3권1호
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• pp.9-22
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• 2002

In general, two dimensionless numbers are used in predicting the front propagation rate of density currents: the densimetric Froude number and the dimensionless front velocity. The former expresses the front speed in terms of the characteristic length and reduced gravitational acceleration. Previous papers report that the range of this dimensionless number is wide. The other is the dimensionless front velocity, which is a function of the buoyancy flux per unit width. This paper presents the state of the art review of the dimensionless numbers for the front propagation rate of density currents. Values of the densimetric Froude number are found to be consistent when the proper characteristic length is used for normalization. Then, the densimetric Froude number and the dimensionless front velocity are compared by using the experimental data of density currents over a horizontal surface.

• 한국화재소방학회논문지
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• 제15권2호
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• pp.91-95
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• 2001

복도나 터널과 같이 특정한 방향성을 가지는 공간에서는 천장아래에 형성되는 연기선단의 성상해석이 학술적인 면에서나 실용적인 면에서도 매우 중요하다. 본 연구는 2차원 축대칭 천장제트 선단의 전파속도를 모델화하기 위하여 상사해석 및 차원해석을 수행하였다. 실험에서는 질소와 헬륨의 혼합가스를 원형 천장에 노즐로 분출시켜 화재로 인한 연기를 구현하였으며 속도측정을 위하여 레이저와 고속카메라를 이용한 가시화 기법이 사용되었다.

• 수산해양기술연구
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• 제31권3호
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• pp.228-239
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• 1995

우리나라 800 ps급 쌍끌이 저인망어선에서 사용할 수 있도록 덴마크에서 이미 보편적으로 사용하고 있는 사용하고 있는 쌍끌이 중층 트롤 어구를 Tauti의 어구비교법칙과 예인수조의 크기 등을 고려하여 1/30의 크기로 축소 제작하여, 이 모형어구에 대한 기본 성능을 알아보기 위해 예인속도 0.46~1.15m/sec(실물환산 2~5k't), weight 142g(실물환산 640kg)에 Front weight 15.5~62.0g(실물환산 70~280kg) 및 양선간격 5~8m(실물환산 150~240m)의 변화에 따른 모형어구의 망고, 망폭, 예인장력, 예망수축 등을 측정 분석하여 실물로 환산한 결과를 요약하면 다음과 같다. 1. 망고는 예인속도 2k't, Front weight 280kg, 양선간격 150m 일 때 32m로 가장 높게 나타났으며, 예인속도 5k't, Front weight 70kg, 양선간격 240m 일 때 6m로 낮게 나타났다. 2. 망폭은 예인속도 5k't, Front weight 70kg, 양선간격 240m 일 때 45m로 가장 넓게 나타났으며, 예인속도 2k't, Front weight 280kg, 양선간격 150m 일 때 33m로 가장 좁게 나타났다. 3. 예인장력은 예인속도 5k't, Front weight 280kg, 양선간격 240m일 때 10,000kg로 가장 크게 나타났으며, 예인속도 2k't, Front weight 70kg, 양선간격 150m 일 때 1,600kg로 가장 작게 나타났다. 4. 어구의 예망수층은 예인속도 2k't, Front weight 280kg, 양선간격 150m 일 때 38m로 가장 깊게 나타났으며, 예인속도 5k't, Front weight 70kg, 양선간격 240m 일 때 6m로 가장 얕게 나타났다. 5. 어구의 망구면적은 예인속도 2k't, Front weight 280kg, 양선간격 180m 일 때 1,100m 상(2)로 가장 크게 나타났으며, 예인속도 5k't, Front weight 70kg, 양선간격 240m 일 때 250m 상(2)로 가장 작게 나타났다

• 한국정밀공학회지
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• 제30권12호
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• pp.1295-1301
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• 2013

The cause of flow mark defect is known as non-uniform temperature of mold surface when the flow front meets the cold cavity. The exact definition and classification of Flow mark is not clear because the mechanism of flow mark is not figured out till now. Any injection molding analysis software can not predict the flow mark phenomena. To solve weldline and flow mark defects, the gate thickness is reduced to increase the melt front velocity and the melt front velocity of the flow mark area is increased from 82.3mm/s to 104.7mm/s. In addition, the bulk temperature of the flow mark area is increased from $178.3^{\circ}C$to $215.2^{\circ}C$ by adding a cold slug well. The flow mark phenomena can be greatly reduced by increasing the flow front velocity and elevating the bulk temperature.

• 대한기계학회논문집
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• 제17권10호
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• pp.2418-2425
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• 1993

A two-dimensional transient heat transfer model for reactive gas assisted laser cutting process with a moving Gaussian heat source is developed using a numerical finite difference technique. The kerf width, melting front shape and temperature distribution were calculated by using the boundary-fitted coordinate system to handle the ejection of workpiece material and heat input from reaction and evaporation. An analytical solution for cutting front movement was adopted and numerical simulation was performed to calculate the temperature distribution and melting front thickness. To calculate the moving velocity of cutting front, the normal distribution of the cutting gas velocity was used. The kerf width was revealed to be dependent on the cutting velocity, laser power and cutting gas velocity.

• 한국생산제조학회지
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• 제20권1호
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• pp.23-27
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• 2011

This study analyzes about the variation of pressure and stream velocity according to the movement of tail wing. The pressure at the front part of airplane becomes lower than at the rear part and the stream velocity has decreased by being bumped against the wing of airplane. The pressure at the front part of rudder becomes higher than at its rear part according to the movement of rudder among the tail wings of airplane. The more stream velocity becomes decreased, the more rudder spreads out. As the tail wing of airplane folds, the pressure at its front part becomes higher. And the pressure at its rear part becomes lower than at its front part. The more tail wing of airplane folds, the more stream velocity becomes decreased.

• Journal of Advanced Marine Engineering and Technology
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• 제39권2호
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• pp.136-142
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• 2015

The shell and tube heat exchanger is an essential part of a power plant for recovering transfer heat between the feed water of a boiler and the wasted heat. The baffles are also an important element inside the heat exchanger. Internal materials influence the flow pattern in the bed. The influence of baffles in the velocity profiles was observed using a three-dimensional PIV (Particle Image Velocimetry) around baffles in a horizontal circular tube. The velocity of the particles was measured before the baffle and between them in the test tube. Results show that the velocity vectors near the front baffle flow along the vertical wall, and then concentrate on the upper opening of the front baffle. The velocity profiles circulate in the front and rear baffle. These profiles are related to the Reynolds number (Re) or the flow intensity. Velocity profiles at lower Re number showed complicated mixing to obtain the velocities and concentrate on the lower opening of the rear baffle as front wall. Numerical simulations were performed to investigate the effects of the baffle and obtain the velocity profiles between the two baffles. In this study, a commercial CFD package, Fluent 6.3.21 with the turbulent flow modeling, k-${\epsilon}$ are adopted. The path line and local axial velocities are calculated between two baffles using this program.

• 화약ㆍ발파
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• 제20권2호
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• pp.21-31
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• 2002

We did bench blasting upon the natural rock which it's uniaxial compressive strength was about $1,420~1,476kgf/\textrm{cm}^2$. This is the results we inferred after measuring, analyzing the ground vibration velocity of the front and back direction from the free face of the bench blasting. We have to induce the square and cube root scaled equation and the general equation to guarantee confidence upon the data when analyzing the measurement data of the test blasting. The variable distance is in reverse proportion to the permitted ground vibration velocity. The shorter is the exploding point to a protection structure, the bigger is the reflection that the direction of the free face experts the ground vibration velocity, The ground vibration velocity front of the free face tends become reduced about 38~46% compare with back of the free face in the range that the permitted ground vibration velocity is 2.0~5.0mm/sec. In case of 2.0mm/sec, when a protection structure is within about 95m, the max. allowable charge weight per delay on positing front of the free face can be more used about 2.61 times than that on positing back of the free face, in case of 3.0mm/sec within about 78m more about 2.38 times, in case of 5.0mm/sec within 60m more about 2.10 times. In case of 2.0~5.0mm/sec when a protection structure is within about 200m front from the free face, the max. allowable charge weight per delay can become about 1.52 times than the case on back to the free face.

• 한국공작기계학회논문집
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• 제10권2호
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• pp.64-72
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• 2001

Weld line is one of serious troubles which are observed in a plastic part manufactured by a injection molding process. This is caused by many process factors, which are molding pressure, temperature, velocity, location of a injection gate, mold geometry and material properties. investigation on the effects of these process factors to the appearance of a weld line was carried out using a finite element method. Filling and packing analyses were carried out by modifying both the configuration of the injection gates and cavity thickness. Proper locations of the injection gates could be determined by considering molding pressure, temperature, velocity and frozen layer, and whereby the weld line was controled. In order to make a weak appearance of the weld line, flow velocity and flow front in a cavity were also investigated by modifying a cavity thickness. As a result, flow front was extended around the corner in the cavity by changing the flow velocity and hence the appearance of the weld line was much weakened.

• 지질공학
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• 제21권1호
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• pp.25-34
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• 2011

본 연구에서는 도로시공을 위한 사면절개시 발생된 산사태 현장을 대상으로 강우시 침투를 고려한 사면안정해석 방법을 적용하였다. 강우시 침투를 고려한 사면안정해석법은 크게 세가지로 구분할 수 있다. 첫 번째는 지반내 습윤전선이 하강을 고려하여 해석하는 방법, 두 번째는 지반내 지하수위의 상승을 고려하여 해석하는 방법, 그리고 세 번째는 지반내 습윤전선 하강 및 지하수위 상승을 고려하여 해석하는 방법이다. Bishop의 간편법을 이용하여 해석한 결과, 강우시 습윤전선 하강으로 인한 사면안전율 감소가 지하수위 상승으로 인한 사면안전율 감소보다 빠르게 진행됨을 알 수 있다. 또한, 습윤전선 하강 및 지하수위 상승이 동시에 일어날 경우 사면안전율은 매우 급속하게 감소함을 알 수 있다. 따라서, 강우시 사면안정해석법은 지반내 지하수위 상승과 습윤전선 하강을 동시에 고려하여 해석하는 것이 보다 바람직하다.