• Composites Research
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• v.16 no.3
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• pp.1-8
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• 2003

Densification occurs by the inelastic flow of the matrix materials during the consolidation processes at high temperature for MMCs, and the results depend on many process conditions such as applied pressure, temperature and volume fraction of fiber and matrix materials. This is particularly important in titanium matrix composites since material failure may occur by either the applied conditions or microstructural parameters through the processes, and thus a generic model based on micro-mechanical approaches enabling the evolution of density over time to be predicted has been developed. The mode developed is then implemented into FEM so that practical process simulation has been carried out. Further the experimental investigation of the consolidation behavior of SiC/Ti-6Al-4V composites using vacuum hot pressing has been performed, and the results obtained are compared with the model predictions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.5
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• pp.60-67
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• 2019

In general, a reinforced concrete slabs are known to have a high fire resistance performance due to thermal properties of concrete materials. However, according to previous research, the thermal behavior of voided slabs is reported to be different from that of conventional RC solid slabs, and the differences seem to be caused by the air layer formed inside the voided slab. Therefore, it is difficult to estimate the temperature distribution of the voided slab under fire by using the existing methods that do not take into account the air layer inside the voided slab. In this study, a numerical analysis model was proposed to estimate the temperature distribution of voided slabs under fire, and evaluated. Heat transfer of slabs under fire is generally caused by conduction, convection and radiation, and time-dependent temperature changes of slab can be determined considering these phenomena. This study proposed a numerical method to estimate the temperature distribution of voided slabs under fire based on a finite difference method in which a cross-section of the slab is divided into a number of layers. This method is also developed to allow consideration of heat transfer through convection and radiation in air layer inside of slabs. In addition, the proposed model was also validated by comparison with the experimental results, and the results showed that the proposed model appropriately predicts the temperature distribution of voided slabs under fire.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.193-193
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• 2011

본 연구에서는 산불발생인자들에 대한 정보를 각각의 요인별로 집적화하고 체계화시킴으로써 산불예방활동의 기초자료로 활용할 뿐만 아니라 산불발생 시, 산불의 거동을 예측하기 위한 자료로 활용하고자 하였다. 발생인자는 크게 연료 및 기상조건 관련 인자와 열적특성 관련 인자로 분류하고 연료 및 기상조건 관련 인자는 수종별, 부위별, 지역별, 고도별, 월별 산림연료들의 구성 요인들에 대해서 분석하였다. 수종별로는 생강나무, 초피나무, 조록싸리, 산초, 개암, 청미래, 고추나무, 철쭉, 조릿대, 털진달래 등 관목류 10개 수종과 김의털, 방아풀, 주름조개풀, 칡, 엉겅퀴 등 초본류 5개 수종 그리고 소나무, 잣나무, 리기다소나무, 해송, 구상나무, 주목 등 6개의 침엽수 및 굴참나무, 떡갈나무, 신갈나무, 갈참나무, 졸참나무, 상수리, 산개벚나무, 고채목, 개서어나무, 굴거리나무, 서어나무, 산벚나무, 때죽나무, 당단풍나무, 단풍나무 등 15개의 활엽수로 구성된 교목류를 대상으로 분석하였다. 부위별로는 생엽, 낙엽, 가지, 수피, 솔방울 등으로 구분하여 분석을 수행했으며, 지역별 구성은 강원(삼척/태백산), 경북(응봉산), 경기(용문산), 충북(월악산), 충남(계룡산), 전북(덕유산), 전남(월출산), 부산(금정산), 제주(한라산) 등 9개 지역을 대상으로 선정하였다. 고도별로는 강원도에 소재하고 있는 태백산을 중심으로 소나무와 신갈나무 생엽을 대상으로 900m, 1000m, 1100m, 1200m, 1300m, 1400m, 1500m 고도를 선정하여 분석을 수행하였다. 월별 분석데이터는 소나무 생엽의 경우, 2008년 6월부터 2010년 11월까지 매월 분석을 수행하였으며, 굴참나무 생엽의 경우에는 2008년부터 2010년까지 매년 6월부터 10월까지 생엽을 채취할 수 있는 기간 동안 분석을 수행하였다. 또한, 열적특성 관련 인자로는 착화특성(무염착화온도, 발염착화시간, 소염시간, 화염지속시간), 발열특성(총열방출량, 평균열방출률), 발연특성(총연기방출량, 최대연기밀도, 최대밀도시간) 등을 고찰하였다. 이와 같은 결과들은 산불발생인자 DB구축으로 부터 산불발생 위험도 및 동태예측의 기본 자료로 활용할 수 있을 뿐만 아니라 지역별 연료별 산림연료의 열적특성 DB로 부터 산불발생시 산불 위험도에 대한 기술정립과 응용성을 향상시킬 수 있을 것으로 사료된다. 이외에도 산림연료 종류별 열적특성을 결과를 토대로 문화재보존지역과 같이 문화적 가치가 높은 시설이나 주유소, 가스 충전소 등의 위험 시설에 대한 효과적인 보호를 위한 대처 방안을 사전에 준비할 수 있어 산불 피해에 대한 국민의 불안감을 줄일 수 있을 것으로 생각된다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.367-372
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• 2006

When we design a linear motor, the thermal behavior investigation is one of great important considerations with respect to uniform thrust force and thermal deformation of a linear motor. In this study, we conduct the research for the structural design of the linear motor for LMTT(Linear Motor-based Transfer Technology) which is the next generation of container horizontal transfer system in order to automate a container terminal. After the dimensions of main parts for a linear motor were set up, we carried out the thermal-structural analysis of the linear motor considering the thermal analysis of the stator module.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.325-335
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• 2010

A new geothermal energy source obtained from a tunnel structure has been studied in this paper. The geothermal energy is extracted through a textile-type ground heat exchanger named "Energy Textile" that is installed between a shotcrete layer and a guided drainage geotexitle. A test bed was constructed in an abandoned railway tunnel to verify the geothermal heat exchanger system performed by the energy textile. To evaluate the applicability of the energy textile, we measured the thermal conductivity of shotcrete and lining samples which were prepared in accordance with a common mixture design. An overall performance of the energy textile installed in the test bed was evaluated by carrying out a series of in-situ thermal response test. In addition, a 3-D finite volume analysis (FLUENT) was adopted to simulate the operation of the ground heat exchanger being encased in the energy textile with the consideration of the effect of the shotcrete and lining thermal conductivity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1410-1417
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• 1999

A thorough understanding of the transient behavior during start-up is essential in the design and operation of the heat recovery steam generator(HRSG). During this period of time, material that is exposed to high temperature and experiences a large temperature variation is subject to high thermal stress. In this work, a transient formulation of the HRSG is constructed including the estimation of the thermal stress and fatigue of the drum wall. Start-up behavior of a single-pressure HRSG is analyzed and the effect of bypassing part of the gas turbine exhaust flow on the thermal stress evolution is examined. It is found that the modulation of the gas flow rate using a bypass damper is very useful in view of reducing the thermal stress of the drum and ensuring the fatigue lifetime.

• Proceedings of the KWS Conference
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• 2007.11a
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• pp.215-217
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• 2007

철계 피삭재 가공 시 적용되는 cBN(cubic Boron-Nitride)의 경우 열적/구조적 안정성으로 인해 융착 시 계면에서 화학적 결합이 어려워, 지립이 단일층으로 형성되어야 하는 융착 공구의 경우 적용되질 못하고 있다. 이러한 문제를 해결하기 위해 세라믹과의 젖음성이 우수한 Ti 성분이 포함된 67Ag+28Cu+5Ti(wt.%) 조성의 합금분말을 이용하여 cBN을 접합을 하였으며, 이때 융착조건은 진공 분위기($6{\times}10^{-6}$Torr), $900^{\circ}C$ 온도에서 5분간 유지하여 융착을 실시하였다. 본 연구의 주목적은 Ti 합금화 된 Ag계 합금분말 및 cBN의 융착 계면에서의 융착 계면거동해석을 통한 건전한 접합공정을 찾는데 있다. 이에 온도 $900^{\circ}C$, 유지시간 5분에서 건전한 융착층을 형성함을 알 수 있었다. 또한 결합력 측정기를 이용하여 결합력을 측정한 결과 diamond와 융착하였을 때가 123N, cBN을 융착하였을 때 107N으로써, cBN 융착이 diamond 융착의 87%정도의 결합력을 보임을 알 수 있었다. 한편 cBN과 Ag-Cu-Ti계 브레이징 필러의 계면에서의 미세조직 및 화학반응의 메커니즘은 SEM, EDS를 이용하여 분석하였다.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.6
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• pp.126-132
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• 2011

Fatigue cracks of the turbocharger are often observed for high performance engines under thermal shock tests. Maximum exhaust gas temperature of recently developed gasoline engines could reach approximately $950^{\circ}C$. It's very important to estimate transient temperature histories during thermal shock cycles to predict the stress and the fatigue life of the turbocharger. With these temperature profiles, temperature-dependent material properties and boundary conditions, we could identify critical locations by the application of finite element simulation technologies. In this paper, we applied the reliable analysis approach to the actual turbocharger to predict the weak locations due to the repetitions of plastic strains and compared the results with the crack locations under physical engine test.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.399-404
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• 2010

Test results including the variation of propellant-inlet pressure, pulsed thrust, and environment vacuum with the accompanying thermal responses are presented for the pulse-mode operation of a set of monopropellant hydrazine thrusters producing $0.95lb_f$ of nominal steady-state thrust at an inlet pressure of 350 psia. The test data are reduced into the impulse bit, specific impulse, and force centroid that are the factors typically characterizing pulse-mode performance of small rocket engines. With a scrutiny to the performance parameters, their comparison to the reference criteria of 1 lbf standard monopropellant rocket engine are successfully made.

• Journal of the Korean institute of surface engineering
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• v.48 no.1
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• pp.23-26
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• 2015

What causes the transformation of a solar cell is the behavior difference of thermal expansion occurred between the substrate and the layer of semiconductor used in the solar cell. Therefore, the substrate has to possess a behavior of thermal expansion that is similar with that of semiconductor layer. This study employed electroforming to manufacture Fe-Ni alloy materials of different compositions. To verify the result from a finite element analysis, a two-dimensional Mo substrate was calculated and its verification experiment was conducted. The absolute values from the finite element analysis of Mo/substrate structure and its verification experiment showed a difference. However, the size of residual stress of individual substrate compositions had a similar tendency. Two-dimensional CIGS/Mo/$SiO_2$/substrate was modeled. Looking into the residual stress of CIGS layer occurred while the temperature declined from $550^{\circ}C$ to room temperature, the smallest residual stress was found with the use of Fe-52 wt%Ni substrate material.