• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.2
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• pp.68-77
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• 2020

The purpose of the paper is to evaluate the pore structure and mechanical properties of early frost damaged concrete using electric arc furnace slag as aggregate. From the results, when the concrete is exposed to frost damage at an early age, the peak point of pores 100 to 150 ㎛ in diameter were transferred into larger one. When the freezing duration is not exceeded 24 hours, it is possible that the pore distribution of under the 200 ㎛ is maintained and pore size of over 500 ㎛ is not formed, and, the freezing resistance of concrete using EFG could be improved. When BFS was mixed in concrete using EFG as coarse aggregate, the relative strength is higher than that of natural coarse aggregate. Meanwhile, the elastic modulus and resonance frequency did not change significantly due to the early frost damage as compared with the compressive strength. So, it is necessary to analyze the correlation between the experimental results in order to evaluate the performance degradation due to early frost damage.

• Composites Research
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• v.14 no.2
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• pp.22-32
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• 2001

Damage induced by low-velocity impact on the curved composite laminates was experimentally evaluated for CFRP cylindrical shells with the radius of curvatures of 50, 150, 300, and 500 mm. The result was then compared with that of flat laminates and with the results by nonlinear finite-element analysis. The radius of curvatures and the effective shell stiffness appeared to considerably affect the dynamic impact response of curved shells. Under the same impact energy level, the maximum contact force increased with the decreasing radius of curvatures, with reaching 1.5 times that for plates at the radius of curvature of 50 mm. Since the maximum contact farce is directly related to the impact damage, curved laminates can be more susceptible to delamination and less resistant to the low-velocity impact damage. Delamination was distributed rather evenly at each interface along the thickness direction of curved laminates on the contrary to the case of flat laminates, where delamination is typically concentrated at the interfaces away from the impact point. This implies that the effect of curvatures has to be considered for the design of a curved composite laminate.

• Journal of the Korean Electrochemical Society
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• v.11 no.1
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• pp.16-21
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• 2008

The key component of a direct methanol fuel cell (DMFC) is the membrane electrode assembly (MEA), which comprises a polymer electrolyte membrane and catalyst layers (anode and cathode electrode). Generally the catalyst layer is coated on the porous electrode supporter (e.g. carbon paper or cloth) using various coating methods such as brushing, decal transfer, spray coating and screen printing methods. However, these methods were disadvantageous in terms of the uniformity of catalyst layer thickness, catalyst loss, and coating time. In this work, we used bar-coating method which can prepare the catalyst layer with uniform thickness for MEA of DMFC. The surface and cross-section morphologies of the catalyst layers were observed by SEM. The performances and resistance of the MEAs were investigated through a single cell evaluation and impedance analyzer.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.5
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• pp.110-116
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• 2003

With the growth of aircraft performance and needs for light aircraft, the problems associated with hail impacts on aircraft during flights and grounding become and important issue. These hail encounters can cause severe damages to aircraft and result in major concerns in safety and cost. Since nearly all external components of the commercial and military aircraft-in particular, the nose section and the leading edge of the wing and tail-are subject to damages, much effort has been put into understanding of this problem. However, most of the previous studies have focused on the composite components and few results have been reported for the metallic components. In this paper, we study the ice impacts on the aluminum component with the finite element analysis method utilizing commercial non-linear dynamics solver LS-DYNA. The results are compared with the experimental data and a simple measure of the ice impact effects is proposed.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.35 no.2
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• pp.118-128
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• 1999

The shape of the net mouth in a midwater trawl gear is examined by measuring towing speed, gear resistance, the width of otter boards, net height, and so on of a full-scale gear in operation. In addition, a mathematical model is developed to predict shapes of the net mouth. In the model, shapes of head, ground, side ropes, which governs the shape of net mouth, are assumed as a catenary. The validity of the model is tested with observations. The results can be summarized as follows: 1. The warp tension and vertical opening of the gear is highly dependent to the towing speed. The depth of the gear and width of otter boards are very sensitive to the variations of the warp length. 2. The model results indicate that the wing tip of the head and side ropes is reduced and the vertical distances of the head and side ropes sagged to the back with increasing towing speed. 3. The results of comparing the measured net height with calculated side rope height were satisfying. 4. The results of analysis showed the vertical axis of the net mouth was decreased and the width of the net mouth was little changed when the towing speed increased.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.2
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• pp.174-183
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• 2006

The resistance spot-welded region in most current finite element crash models is characterized as a rigid beam at the location of the welded spot. The region is modeled to fail with a failure criterion which is a function of the axial and shear load at the rigid beam. The role of this rigid beam is simply to transfer the load across the welded components. The calculation of the load acting on the rigid beam is important to evaluate the failure of the spot-weld. In this paper, numerical simulation is carried out to evaluate the calculation of the load at the rigid beam. The load calculated from the precise finite element model of the spot-welded region considering the residual stress due to the thermal history during the spot welding procedure is regarded as the reference value and the value of the load is compared with the one obtained from the spot-welded model using the rigid beam with respect to the element size, the element shape and the number of imposed constraints. Analysis results demonstrate that the load acting on the spot-welded element is correctly calculated by the change of the element shape around the welded region and the location of welded constrains. The results provide a guideline for an accurate finite element modeling of the spot-welded region in the crash analysis of vehicles.

• Tunnel and Underground Space
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• v.11 no.1
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• pp.36-41
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• 2001

It is often said that the supply of fossil fuels in use for energy source will last only for 40 years. Futhermore, statistics shows that most of the fuels are imported from outside and that 30-40% of total cost for housing in Korea. One of those methods for reducing the energy cost for housing is to use underground space. Being used well, it may bring a considerable saving of energy since the underground space keeps its air cool in summer and warm in winter. To use underground space, we need to analyse its temperature first. For this purpose, what is generally used is the numerical analysis with the use of nodal system. That is, we can calculate a specific underground temperature with the matrix of thermal resistance after we make a nodal system. However, the existing numerical analysis programs need usually high cost and require a computer with large capacity. So they are seldom used in practice. Considering such problems, this study seeks to find a method for making the matrix of thermal resistance operatable on PC level.

• Tunnel and Underground Space
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• v.9 no.1
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• pp.20-26
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• 1999

The completion of the Bakun Diversion Tunnel is subsequently to the Main Dam construction. Therefore, the completion date is very important for the Bakun Hydroelectric Project. Generally, the tunnel lining work as a finishing phase of the tunnelling project occupies a important portion as well as an excavation and a support work of the tunnels in respect to the construction cost and period. Internal section of Bakun Diversion Tunnel is designed circular shape to reduce the roughness of the water flow with 12 meters in diameter of total length 4314.6 meters of 3 tunnels. The lining thickness is varied between 500 mm and 700 mm depending on the structural condition. From the original Tender design of the Bakun tunnels, the required quantity of steel bars was 5,985 ton designed by Reinforced Concrete (RC) through the entire tunnel linings. During the detail design stage by the consideration of the rock conditions and various load conditions, we could suggest five kinds of RC lining type including plain concrete lining type. Through the detail design modification, we could reduce the required amount of steel bars to 2,178 ton, as a half of original Bill of Quantity. Finally, this design modification give us the time and cost saving effect to catch up the construction progress in time.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.152.2-152.2
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• 2011

본 연구는 2012년 시행할 예정인 신재생에너지 공급의무화제도(RPS) 하에서 신재생에너지 전력에 대한 추가비용 발생 시 국민들이 RPS 제도의 목표 및 형태에 대하여 어떤 선호를 가지고 있으며, RPS 제도에 대한 소비자들의 만족도를 높이기 위한 개선점이 있는지 알아보고자 수행되었다. 이에 소비자 선호를 조사하는 대표적인 연구방법론인 조건부가치평가법(CVM)을 활용하여, RPS 제도 하에서 발생 가능한 소비자 선호, 구성요소 합산효과 및 지역별 선호의 차이의 3개 주제에 대한 연구를 3차례 설문을 통해 수행하였다. 해당 연구의 주요 내용을 요약하면 다음과 같다. 첫째, 우리나라 국민들의 신재생에너지 전력에 대한 WTP는 가구당 1,456~1,560원/월 수준으로 이는 우리나라 가구당 월 평균 전기요금의 약 3.7~3.5% 수준에 해당한다. 이를 토대로 추산한 신재생에너지 전력 이용에 대한 국민들의 편익은 2011년 신재생에너지 보급 관련 예산의 42.4% 정도인 것으로 나타났다. 둘째, 국민들은 에너지원의 선택에 대한 비용 차이가 있을 시에는 개별 신재생에너지원을 대체재(substitutes)로 인식하였다. 그러나 에너지원의 선택에 대한 비용 차이가 없는 경우에는 특정 신재생에너지원에 대한 선호를 보이며, 특히 태양광에 대한 선호도가 가장 높게 도출되었다. 셋째, 소비자들의 선호도에 따른 재생에너지 포트폴리오를 적용한 결과, 우리나라 국민들은 연 2,618~2,806 GWh 규모의 신재생에너지 전력을 생산하는데 소요되는 추가비용을 지불할 의사가 있는 것으로 분석되었다. 이는 2010년도 우리나라 전체 전력 수요의 0.62~0.66% 정도로 RPS에서 목표로 하는 의무비율을 이행하기에는 부족한 것으로 보인다. 넷째, 신재생에너지 전력에 대한 선호는 지역별로 다르게 나타났다. 이는 지역 간 저항응답의 비율, 재생에너지 시설 인근 경험 및 재생에너지 시설 입지에 대한 찬반의사 등의 지역별 차이에서 기인하는 것으로 분석되었다.

• Journal of the Korean Vacuum Society
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• v.8 no.1
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• pp.75-82
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• 1999

Ion energy is one of the crucial property in thin film deposition by internal ICP assisted I-PVD. As ion energy is determined by the difference between the plasma potential and the substrate bias potential, ICP excitation frequency was tested with medium frequency of 4 MHz and two types of tuning circuits, alternate and floating LC network with a biasing resistor, were tested. The results showed that plasma potential was less than 5 V in a range of Ar pressures, 5mTorr to 30 mTorr, at 4 MHz RF 600 W and 60 V of maximum RF antenna voltage was maintained either at RF input or output terminal. By proper control of RLC circuit installed after after RF antenna, 50V of RF induced voltage on RF antenna was obtained at 500W input power. The total impedance of RF antenna and plasma was around 10$\Omega$, and minimum RF voltage was obtained with a condition of lowest reactance at most 0.05$\Omega$.