• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.433-436
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• 2009

This study is concerned with an effect of frictional condition in a forward/backward combined extrusion process. Generally, the material flow of the billet is influenced by the corners of the die cavity, the ratio in reduction in area, and thickness ratio of backward can thickness to forward can thickness. In addition, the frictional condition in contact area between the billet and the punch/die also affect the material flow. This paper investigated the effect of frictional condition for variable friction factors. The FEM simulation has been carried out in order to examine the effect of frictional condition. Deformation patterns and flow characteristics were examined in terms of design parameters such as extruded length ratio etc. Die pressure exerted on the die-workpiece interface is calculated by the simulation results and analyzed for safe tooling. Therefore the numerical simulation works provide a combined extrusion process of stable cold forging process planning to avoid the severe damage on the tool.

• 대한기계학회논문집
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• 제18권11호
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• pp.3039-3045
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• 1994

The k-$\varepsilon$ turbulence models by Launder et al.(1977, LPS) and Leschziner and Rodi(1981, LR) are modified to account for the secondary straining effect with having a generality in the present paper. The modified models are obtained by replacing the gradient Richardson number used to account for the secondary straining effect in the original models by a new parameter with a tensor-invariant correction form. These two modified models are used to predict the turbulent flow over a backward-facing step. In contrast to both standard and modified LR models, the modified LPS model is found to predict the reattachment point fairy well, as well as mean velocity, wall static pressure, turbulent kinetic energy and Reynolds shear stress in the recirculating region.

• ETRI Journal
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• 제27권2호
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• pp.206-218
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• 2005

We measure and compare externalities of IT and R&D capital stocks in different Korean industry sectors using inter-industry input-output tables of 1985, 1990, 1995 and 2000. We also compute the multiplier effects that relate to the directions of future economic effects. The key findings are as follows. First, we observed continuous capital deepening in all nine industries over the period of 1985 to 2000. Second, the backward multipliers of IT capital were the highest in the manufacturing industry. As for inter-industry externalities, the indirect backward multipliers, which exclude intra-industry backward multiplier effects within the industry, were also the highest in the manufacturing industry. Third, the forward multiplier effects of IT capital stock were the most substantial in the construction industry during the 1980s and in the manufacturing industry thereafter. Finally, using the transition multiplier matrix reflecting the backward effects of the two capitals in the past, the economic backward effects, especially the external economic effects, are predicted to increase through 2010 among all industries. The above findings suggest that, in order to maximize the forward and backward effects of the ever-increasing IT capital, we need to formulate an industry policy reducing the cost of capital accumulation in the manufacturing industry through improvement in productivity of the IT industry.

• 대한지구과학교육학회지
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• 제11권2호
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• pp.90-106
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• 2018

이 연구에서는 초등 과학과 수업에서 과정 중심 평가가 반영된 백워드 설계가 과학 학업성취도 및 과학 학습 동기에 미치는 효과를 확인하고자 하였다. 학습자의 성장과 발달을 지원하는 과정 중심 평가와 학습자의 온전한 이해를 추구하는 백워드 설계는 과학 학습에 큰 도움을 줄 수 있다. 연구 결과는 다음과 같다. 첫째, '지구와 달의 운동' 단원을 중심으로 과정 중심평가가 반영된 백워드 설계를 실시하였고, 성취기준도달에 도움이 되는 다양한 과정 중심 평가를 반영하였다. 둘째, 실험집단 학생들은 과학학업 성취도 검사와 과학학습 동기 검사에서 통계적으로 유의미한 차이를 나타냈다. 과학 교과의 특성을 반영한 과정 중심 평가가 백워드 설계와 연계되어 학교 현장에서 의미 있게 활용되길 기대한다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2010년도 추계학술대회 논문집
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• pp.783-784
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• 2010

• 한국정밀공학회지
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• 제22권3호
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• pp.86-92
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• 2005

In this paper a forward-backward can extrusion process are analyzed by using rigid-plastic FEM simulation. FEM simulation is conducted to investigate forming characteristics such as deformation modes fur different process parameters. Design parameters such as thickness ratio, punch angle, friction factor and diameter ratio are selected to study the effect of them on the pattern of material flow. The analysis is focused mainly on the influences of the design factors on deformation pattern in terms of forming load, extruded length ratio and volume ratio. It is known for the simulation that the forming load, the length ratio and the volume ratio increase as the thickness ratio (TR), the wall thickness in forward direction to that in backward direction, decreases. The various punch angles have slight influence on the forming load. length ratio and volume ratio. However friction factor have little effect on the forming characteristics such as the forming load, volume ratio and so on. In addition the forming load increases as diameter ratio (DR), the outer diameter of a can in forward direction to that in backward direction, increases. Furthermore the extruded length ratio is lowest with a certain value of DR=0.85 among diameter ratios. Pressure distribution exerted on the die-material interface is illustrated schematically.

• 대한기계학회논문집
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• 제19권9호
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• pp.2328-2341
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• 1995

An experimental study on the flow over the axisymmetric backward-facing step was carried out. The purposes of the present study are to investigate the effect of the free stream turbulence intensity on the reattachment length and to understand the turbulence structure of the recirculating flows. Local mean and fluctuating velocity components were measured in the separated and reattaching axisymmetric turbulent boundary layer over the wall of convex cylinder placed in a water tunnel by using 2-color 4-beam fiber optics laser Doppler velocimetry. As the free stream turbulence intensity increased, the reattachment length became shorter due to the enhanced mixing in the separated shear layer. It was also observed that the reverse flow velocity and turbulent kinetic energy increase with increasing free stream turbulence intensity. Spectral data and flow visualization showed that low-frequency motions occur in the separated flow behind a backward-facing step. These motions have a significant effect on the time-averaged turbulence data.

• 자원ㆍ환경경제연구
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• 제18권4호
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• pp.637-652
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• 2009

본 연구는 지난 1995년부터 2007년 동안에 우리나라 제조업에서 산업별 에너지 소비가 해당 산업과 다른 산업에 어느 정도의 에너지 소비를 유도했는지에 대한 실증분석을 실시하였다. 본 연구에서 실시한 분석결과를 종합하면 다음과 같다. 첫째, 우리나라 제조업에서 에너지 소비가 이루어짐에 따라서 에너지 소비량을 증대시키는 총 산업연관효과는 감소하는 구조변동을 보였다. 이러한 산업구조적 변화는 산업별로 에너지소비의 전방효과 및 후방효과에서 유사한 결과를 나타내었다. 둘째, 우리나라 9개 산업 중에서 광물 및 금속관련 산업과 화학산업에서 해당 산업과 다른 산업들의 에너지 소비를 증대시키는 후방유발효과가 가장 크게 나타났다. 그러나 에너지 소비의 유발효과를 나타내는 간접후방효과는 1995년에는 화학 및 금속산업에서보다 다른 산업에서 상대적으로 크게 나타났으나 2007년에는 동일 산업에서 나타났다. 셋째, 에너지가 체화된 산업별 생산물의 활용 정도를 나타내는 전방효과의 경우에도 광물처리 및 금속산업과 화학산업이 가장 크게 나타났다. 후방효과와 달리 에너지 소비의 유발효과를 나타내는 간접전방효과는 전 기간 동안 화학 및 금속산업이 다른 산업에서 상대적으로 크게 나타났다. 본 실증분석결과로 볼 때, 2000년대부터 친환경산업육성정책의 정책효과는 우리나라 산업구조를 급격하게 에너지 절감형 구조로 전환시키고 있음을 보여준다.

• 대한기계학회논문집
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• 제19권4호
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• pp.1102-1115
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• 1995

An experimental study on the flow over the axisymmetric backward-facing step was carried out. The purpose of the present study is to investigate the effect of the boundary layer thickness at the separation point on the reattachment length and to understand the structure of the recirculating flows. Local mean and fluctuating velocity components were measured in the separating and reattaching axisymmetric turbulent boundary layer over the wall of convex cylinder placed in a water tunnel by using 2-color 4-beam fiber optics laser Doppler velocimetry. The study demonstrated that the reattachment length increases with increasing boundary layer thickness. It was also observed that the reverse flow velocity and turbulent kinetic energy decrease with an increase in the momentum thickness at the separation point. The measured velocity field suggests that the boundary layer thickness at the separation can affect definitely on the formation of corner eddy.

• 대한기계학회논문집
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• 제18권9호
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• pp.2463-2476
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• 1994

Local mean fluctuating velocity components were measured in the separating and reattaching axisymmetrc region of turbulent boundary layer over the wall of convex cylinders placed in a water tunnel by using 2-color 4-beam fiber optics laser Doppler velocimetry. Measurements were made with three different diameters of cylinders with four different diameters of cylinders with four different diameter of the obstructions. The range of Reynolds number based on step height was between 5,000 to 25,200. The study demonstrates that the reattachment length decreases with decreasing cylinder radius and is always shorter than that for the two-dimensional backward-facing step flow at the condition of the same step height. It was also observed that the turbulent kinetic energy in the recirculating region increases with an increases in the radius of convex curvature. The measured velocity field suggests that the transverse curvature can effect definitely the formation of corner eddy.