• Nuclear Engineering and Technology
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• 제22권1호
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• pp.66-74
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• 1990

원자력 7, 8호기에 장전된 17$\times$17 최적 핵연료집합체의 열수력학적 특성을 원자력 5, 6호기에 장전된 17$\times$17표준 핵연료집합체와 비교하여 분석하였다. 분석된 열수력학적 특성은 정상상태와 과도출력상태에서의 최소 DNBR, 연료봉 중심온도, 출구 기포율등이며, 아울러 연료봉의 중심이 용융되는 국부선출력과 원자로 운전변수들에 대한 DNBR 민감도 계수도 계산하였다. 사용된 코드는 COBRA-IV-I이며, 임계열속 계산에는 R형 그리드에 대해 수정된 W-3 상관식을, 기포율계산에는 drift-flux model을 이용하였다. 계산결과, DNB가 발생할 확률은 최적 핵연료집합체가 더 높았으나, 연료봉의 중심이 용융되는 국부선출력은 표준 핵연료집합체와 거의 동일한 것으로 나타났다.

• 한국정보과학회논문지:시스템및이론
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• 제33권10호
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• pp.768-776
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• 2006

연결 정보가 없는 포인트 데이타가 주어졌을 때, 본 논문은 MLS(moving least-squares) 근사화 기법을 이용하여 포인트 데이타에 대해 근사화된 표면을 생성한다. 근사화된 표면에서의 각 포인트에 대해 지역적인 곡률과 곡률 미분 값을 측정 한 후, 딜러니 삼각화(Delaunay tessellation)를 통해 이웃간의 정보를 생성하게 되고, 연결된 포인트들 간의 제로-클로싱(zero-crossing)을 측정하여 특징 포인트들을 추출하고, 곡률 방향으로 추출 된 포인트들을 연결한다. 본 방법은 기존의 메쉬 데이타에서 특징 선을 찾는 방법과 비슷한 복잡도를 갖는다. 몇 개의 포인트-샘플 된 모델에 대해 특징 선 추출을 수행하며, 곡률의 크기에 따라 특징선의 두께를 조절하고 포인트-스플릿팅 방법에 의해 렌더링 한다.

• 한국주조공학회지
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• 제38권1호
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• pp.16-26
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• 2018

In this study, the effects of the pouring temperature, preheating temperature, surface condition and fraction of the wear resistant part on the production of duo-castings were investigated using a high Cr white cast iron with excellent abrasion resistance and a low Cr alloy steel with good toughness. The constituent materials of the duo-castings were designed to have high hardness, fracture toughness and abrasive wear resistance for the replacement of high Mn alloy steels with low abrasive wear resistance. In particular, the amount of abrasive wear of 17% Cr white cast iron was about 1/20 of that of high Mn alloy steel. There was an intermediate area of about 3mm due to local melting at the bonding interface of the duo-castings. These intermediate regions were different from those of the constituent materials in chemical composition and microstructure. This region led to fracture within the wear resistant part rather than at the bonding interface in the bending strength test. The bending fracture strengths were 516-824 MPa, which were equivalent to the bending proof strength of high Mn steel. The effects of various casting conditions on the duo-cast behavior were studied by simple pouring of low Cr alloy steel melt, but the results proved practically impossible to manufacture duo-castings with a sound bonding interface. However, the external heating method was suitable for the production of duo-castings with a sound bonding interface.

• 패션비즈니스
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• 제1권3호
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• pp.35-44
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• 1997

The purpose of this study is to the processes and quality of local women's apparel production using the stretch fabric and to address the problems related to production in order to provide useful data for producing competitive apparels. The result of the survey can be summarized as follows; 1. Results of surveying the process for raw materials and notions indicated that most of the workers were ignorant of the properties of stretch fabrics. And most factories were stacking the stretch fabrics across improperly, while being aware of the properties of the fabrics through their experiences or in-company test. 2. The major problem involving spreading fabrics was the uneven tension, followed by static electricity, overlap and warp twist. The problems involving the cutting work were melting of the fabric by cutter and difference of size between upper and lower parts. 3. Most of the businesses were not tempering the fabric before and after its linking works due to lack of working space, short delivery time, ignorance and etc. The majority of the sample businesses were operating their cutters at the speed of 3,000 rpm or higher, which suggests a poor technological guidance.

• International Journal of Automotive Technology
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• 제6권5호
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• pp.445-451
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• 2005

Most of the pollutants from passenger cars are emitted during the cold-transient phase of the FTP-75 test. In order to reduce the exhaust emissions during the cold-transient period, it is essential to warm up the catalyst as fast as possible after the engine starts, and the Unburned Exhaust Gas Ignition (UEGI) technology was developed through our previous studies to help close-coupled catalytic converters (CCC) reach the light-off temperature within a few seconds after cold-start. The UEGI system operates by igniting the unburned exhaust mixture by glow plugs installed upstream of the catalyst. The flame generates a high amount of heat, and if the heat is concentrated on a specific area of monolith surface, then thermal crack or failure of the monolith could occur. Therefore, it is very important to monitor the temperature distribution in the CCC during the UEGI operation, so the local temperatures in the monolith were measured using thermocouples. Experimental results showed that the temperature of CCC rises faster with the UEGI technology, and the CCC reaches the light-off temperature earlier than the baseline case. Under the conditions tested, the light-off time of the baseline case was 62 seconds, compared with 33 seconds for the UEGI case. The peak temperature is well under the thermal melting condition, and temperature distribution is not so severe as to consider thermal stress. It is noted that the UEGI technology is an effective method to warm up the catalyst with a small amount of thermal stress during the cold start period.

• Journal of Welding and Joining
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• 제20권1호
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• pp.34-40
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• 2002

The laser strengthening of $35kgf/\textrm{mm}^2$ grade steel sheet is investigated by using $CO_2$ laser beam irradiation. The increase of tensile strength is dominated by the number of fully penetrated melting lines. Also, the optimal laser irradiation pattern is obtained by 3-point bending test. Local laser strengthening clay be effective for the weight reduction of automobile components where the tailored welded blank can not be applied.

• 한국레이저가공학회지
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• 제18권1호
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• pp.12-17
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• 2015

This work performed numerical analysis of electromagnetic field and thermal phenomena occurring in femtosecond laser irradiation of silver nanowires. The local electric field enhancement was computed to calculate the optical energy dissipation as a Joule heating source and the thermal transport was analysed based on the two-temperature model (TTM). Electron temperature increased up to 1000K after 50fs and its spatial distribution became homogeneous after 80fs at the fluence of 100mJ/cm2. The result of this work is expected to contribute to revealing the photothermal effects on silver nanowires induced by femtosecond laser irradiation. Although the highest increase of lattice temperature was substantially below the melting point of silver, the experimental results showed resolidification and fragmentation of the silver nanowire into nanoparticles, which cannot be explained by the photothermal mechanism. Further studies are thus needed to clarify the physical mechanisms.

• 대한원격탐사학회지
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• 제37권1호
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• pp.1-11
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• 2021

This study measures the change of ice flow velocity of David Glacier, one of the fast-moving glaciers in East Antarctica that drains through Drygalski Ice Tongue. In order to effectively observe the rapid flow velocity, we applied the offset tracking technique to Sentinel-1A SAR images obtained from 2016 to 2020 with 36-day temporal baseline. The resulting velocity maps were averaged and the two relatively fast points (A1 and A2) were selected for further time-series analysis. The flow velocity increased during the Antarctic summer (around December to March) over the four years' observation period probably due to the ice surface melting and reduced friction on the ice bottom. Bedmap2 showed that the fast flow velocities at A1 and A2 are associated with a sharp decrease in the ice surface and bottom elevation so that ice volumetric cross-section narrows down and the crevasses are being created on the ice surface. The local maxima in standard deviation of ice velocity, S1 and S2, showed random temporal fluctuation due to the rotational ice swirls causing error in offset tracking method. It is suggested that more robust offset tracking method is necessary to incorporate rotational motion.

• 한국주조공학회지
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• 제43권2호
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• pp.55-63
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• 2023

Due to the importance of the surface on the final slab quality, it is essential to maintain a smooth segment roll surface that is in touch with the thin solid shell during solidification. In this paper, the surface of the used continuous casting guide roll was analyzed to realize the mechanism of its surface deterioration. Surface analysis has revealed severe corrosion at two distinct areas leading to deep roughness occurring on the guide roll. Firstly, the severe corrosion follows prior austenite grain boundary due to exposure with acidic environment. Also, in heat affected zone (HAZ) where two cladding beads overlap, more severe corrosion takes place. The overheat input results in local ferritization without full melting which increases retained δ-ferrite content almost 10 times higher than surrounding area. Corrosion was observed to happen at the δ-γ interface where Cr depletion takes place.

• 보존과학회지
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• 제26권1호
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• pp.1-12
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• 2010

초 록 부여 쌍북리 유적에서 출토된 백제시대 도가니는 유리와 금속의 용융에 사용했던 것으로서, 기질은 대체로 경질이며 담갈색, 회청색 및 회갈색의 색조를 보인다. 태토에는 다량의 석영과 파쇄된 토기가 혼입되어 있으며, 외부에는 정선된 석영입자를 도포하여 도가니에 내화성을 부여하였다. 이 도가니는 운모류의 분해와 뮬라이트의 형성 및 장석류의 관찰여부로 볼 때, 공통적으로 $1,000^{\circ}C$ 이상의 소성을 경험한 것으로 판단되며 일부 도가니는 $1,100^{\circ}C$ 이상에서 열적 변화가 수반된 것으로 사료된다. 그러나 검출된 광물상의 특성을 고려할 때 소성 및 용융시 최대 상한 온도는 $1,200^{\circ}C$를 넘지 않았을 것으로 판단된다. 전암대자율 측정과 지구화학적 특성 분석에서 도가니 시료는 크게 두 그룹으로 분류되었으며, 이는 적어도 두 종류 이상의 성인이 다른 태토로 제작되었음을 지시한다. 그러나 도가니의 태토와 유적을 구성하는 토양의 풍화정도가 유사하고 주성분원소의 분포 또한 대체로 동일한 것으로 보아 유적이 위치한 이 일대의 충적층은 두 암종의 풍화산물이 혼재할 가능성이 매우 높다. 따라서 도가니를 구성하는 태토는 모암이 다른 쌍북리 일대의 풍화토로 구성되었던 것으로 판단된다.