• Elastomers and Composites
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• 제51권4호
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• pp.301-307
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• 2016

Additive manufacturing (AM), so called 3D Printing is a new manufacturing process and is getting attraction from many industries. There are several methods of 3D printing. Among them fused deposition modeling (FDM) type is most widely used by reason of cheap maintenance, easy operation and variety of polymeric materials. Articles manufactured by 3D printing have weak deposition strength compared with conventionally manufactured products. Deposition strength of FDM type 3D printed article is highly dependent of deposition temperature. Subsequently the nozzle temperature in the FDM type 3D printing is very important and it is controlled by heat source in the 3D printer. Nozzle is connected with heat block and barrel, and heat block contains heat source. Nozzle becomes hot through heat conduction from heat source. Nozzle temperature has been predicted for various thermal boundary conditions by computer simulation and compared with experimental measurement. Nozzle temperature highly depends upon thermal conductivities of heat block and nozzle. Simulation results are good agreement with experiment.

• 에너지공학
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• 제8권2호
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• pp.224-232
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• 1999

캡슐형 잠열재를 이용한 열저장 시스템은 바닥 난방 및 건물 난방에서 매우 효과적인 시스템이다. 이러한 시스템 개발에 필수적인 요소가 열유동 매체가 순환하는 파이프 주변의 캡슐내 온도 분포와 열유동 매체의 유량 등이다. 그러므로 본 연구에서는 3차원 비정상 상태에서 Navier-Stokes 방정식, 난류모델을 비롯한 스칼라 보존 방정식을 적용하여 캡슐 블록의 온도 분포 및 파이프 내의 유동장 해석을 수행하였다. 또한 본 연구와 같이 계산 영역이 특별한 기하학적 현상을 형상(circle+square)인 문제 해결하는데 적용할 수 있는 새로운 격자 생성 기술(MBFGE/CCM)을 개발하였다. 격자계는 파이프에서 원형 격자를 이용하였고, 캡슐 블록에서 사각 격자를 이용하여 다중격자와 미세격자를 결합하여 사용하였다. 본 연구의 목적은 컴퓨터를 이용한 수치해석적 방법을 미세 캡슐을 이용한 축열보드에 적용하여 2종류의 열경계 상태에 대하여 속도와 온도분포를 계산하여 비교분석을 하는 것이다. 온도는 축열 보드의 한 쪽면은 대류면이고 다른 한쪽면은 단열면인 경우(Case 2)보다 양면 모두 단열인 경우(Case 1)일 때 더 높게 상승하였다. 온수 파이프 중심선인 Y=0 에 가까운 영역에서 Case 1과 Case 2사이에 축열 보드 내에서 온도 차이는 확연하게 나타났다. 향후 수치해석의 정확도를 높이고 축열 보드의 열전달 현상을 보다 정확히 계산하기 위해서는 위치 및 시간에 따른 정밀한 온도 측정값이 필요하고 특히 잠열재인 미세 캡슐이 상변화를 하므로 온도 변화에 따른 물질의 비열(C$_{p}$)과 열전달율(λ)을 고려한 방정식이 요구된다.

• 한국전산유체공학회지
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• 제16권3호
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• pp.95-103
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• 2011

In the block type VHTR core, there are inevitable gaps among core blocks for the installation and refueling of the fuel blocks. These gaps are called bypass gap and the bypass flow is defined as a coolant flows through the bypass gap. Distribution of core bypass flow varies according to the reactor operation since the graphite core blocks are deformed by the fast neutron irradiation and thermal expansion. Furthermore, the cross-flow through an interfacial gap between the stacked blocks causes flow mixing between the coolant holes and bypass gap, so that complicated flow distribution occurs in the core. Since the bypass flow affects core thermal margin and reactor efficiency, accurate prediction and evaluation of the core bypass flow are very important. In this regard, experimental and computational studies were carried out to evaluate the core bypass flow distribution. A multi-block experimental apparatus was constructed to measure flow and pressure distribution. Multi-block effect such as cross flow phenomenon was investigated in the experiment. The experimental data were used to validate a CFD model foranalysis of bypass flow characteristics in detail.

• Steel and Composite Structures
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• 제52권4호
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• pp.435-450
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• 2024

The geometry change of railway tracks significantly influences the safety and ride comfort of high-speed trains. This paper presents an analytical method to map the thermal deformations of a long-span arch bridge to the geometry of CRTS Type I double-block ballastless tracks for high-speed railways. A mechanical model of the bridge-track coupled system was developed to derive analytical formulae of the deformations of the track. The analytical formulae explicitly consider the mechanical properties of the bridge-track coupled system and the temperature profile. A three-dimensional finite element model was established to evaluate the predictions obtained from the analytical formulae. The results show that the analytical formulae provide accurate predictions of the track deformations caused by the thermal deformations of bridges. This research will promote the design, evaluation, and operation of high-speed railway bridges for improved safety and ride comfort in engineering practices.

• 한국수산과학회지
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• 제33권4호
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• pp.325-330
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• 2000

갈조류의 주성분인 alginate는 다양한 생리적 기능을 가지고 있으나, 고점성과 난용성으로 인하여 식품에의 광범위한 이용에 제한을 받고 있는 실정이다. Alginate가 가지고 있는 고유의 생리적 기능성을 유지 향상시키면서 점성을 줄이고 용해도를 높혀서 alginate의 이용성을 확대할 목적으로 가열에 의한 저분자화를 시도하였다. 즉, 평균분자량이 약 10,000 (HAG-10), 50,000 (HAG-50) 및 100,000 (HAG-100) 정도의 alginate를 제조하여 각 저분자 atginate의 물리${\cdot}$화학적 특성 변화를 검토하였다. 가열에 의한 점도와 평균분자량은 가열시간이 경과할수록 급격히 저하하였으며, 점도와 평균분자량사이에는 서로 밀접한 상관관계 ($r^2=0.955$)를 나타내었다. 가열에 의한 alginate의 block조성비 및 M/G 비율은 가열시간이 경과함에 따라 MM-block은 변화가 없었으나 GG-block은 급격히 저하하였다. 그리고, MG-block은 오히려 완만히 증가하였으며 M/G 비율은 급격히 증가하는 경향을 보였다. 분자량의 감소에 따른 alginate의 분자구조의 변화를 $FT-IR, ^1H-NMR$ 및 $^(13)C-NMR$로 측정한 결과, 가열에 의해 alginate가 저분자화되어도 분자구조의 특징적인 변화는 관찰할 수 없었다.

• 한국철도학회논문집
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• 제5권3호
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• pp.167-173
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• 2002

The influence of thermal stress at tread breaking in Korean High Speed Train wheel was investigated using the coupled thermal-mechanical analysis technique. The mechanical load or wheel-rail contract load and braking load were considered during FEM analysis. During the stop braking, the effect of mechanical stress on the combined stress is relatively larger than that of thermal stress in the rim of wheel. However, the effect of thermal stress is relatively larger than that of mechanical stress in the plate of wheel. When 300% of the block force was applied, the maximum von Mises stress of 61.0 MPa was found at the outside plate around 400 mm far away from the wheel center.

• Journal of Advanced Marine Engineering and Technology
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• 제28권1호
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• pp.46-55
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• 2004

Thermal characteristics of the various cooling methods in electronic equipment are studied numerically. A common chip cooling system is modeled as a parallel channel with protruding heat sources. A two-dimensional model has been developed for the numerical analysis of compressible. viscous. laminar flow. and conjugate heat transfer between parallel plates with uniform block heat sources. The finite volume method is used to solve this problem. The assembly consists of two channels formed by two covers and one printed circuit board that is assumed to have three uniform heat source blocks. Various cooling methods are considered to find out the efficient cooling method in a given geometry and heat sources. The velocity and the temperature fields. the local temperature distribution along the surface of blocks. and the maximum temperature in each block are obtained. The results are compared to examine the thermal characteristics of the different cooling methods both quantitatively and qualitatively.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.966-970
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• 2011

The thermo-mechanical interaction between brake block and wheel tread during braking has been found to cause thermal crack on the wheel tread. Due to thermal expansion of the rim material, the thermal cracks will protrude from the wheel tread and be more exposed to wear during the wheel/block contact than the rest of the tread surface. The wheel rim is in residual compression stress when is new. After service running, the region in the tread has reversed to tension. This condition can lead to the formation and growth of thermal cracks in the rim which can ultimately lead to premature failure of wheel. In the present paper, the thermal cracks of railway wheel, one of severe damages on the wheel tread, were evaluated to understand the safety of railway wheel in running condition. The residual stresses for damaged wheel which are applied to tread brake are investigated. Mainly X-ray diffusion method is used. Under the condition of concurrent loading of continuous rolling contact with rails and cyclic frictional heat from brake blocks, the reduction of residual stress is found to correlate well with the thermal crack initiation.

• The Korean Journal of Pain
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• 제7권2호
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• pp.258-262
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• 1994

Thermography is a non-invasive, comfortable, diagnostic technique to monitor successful sympathetic block. We observed abnormal thermal distribution during disease state and then followed with thermography on the process of treatment with stellate ganglion block.

• 공업화학
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• 제4권2호
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• pp.349-357
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• 1993

Hydroxy-difunctional polyarylate(PAR) 올리고머와 toluene diisocyanate를 반응시켜 합성한 고분자 활성체를 사용하여 ${\varepsilon}$-caprolactam을 음이온 중합하여 다양한 블록길이의 PAR-nylon 6 블록공중합체들을 합성하였다. 합성한 블록공중합체들의 열적성질을 differential scanning calorimeter(d.s.c.)로 측정한 결과, 블록공중합체를 구성하는 PAR 블록과 nylon 6 블록은 부분적 상용성을 가졌으며, 그 정도는 블록의 길이가 짧을수록 컸다. PAR-nylon 6 블록공중합체와 PAR 혹은 nylon 6 homopolymer와의 이원블렌드에서 PAR homopolymer와 PAR 블록, nylon 6 homopolymer와 nylon 6 블록 사이의 분자수준의 섞임을 시사하는 거동을 d.s.c.로 관찰할 수 있었다.