• 한국화재소방학회논문지
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• 제32권4호
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• pp.35-41
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• 2018

본 연구는 고온조건하에서 소방용 보호복 착용시 주기적 작업과 작업강도가 신체에 미치는 영향을 연구하여 소방공무원의 건강과 안전을 위한 기초자료 구축을 목적으로 한다. 소방전공 대학생(9명)을 대상으로 소방용 보호장구를 착장한 경우, 실험온도 WBGT $30^{\circ}C$에서 작업강도(3, 9 METs)와 주기적 작업(실험 15분, 휴식 15분, 실험 15분) 따른 비교실험을 수행하였다. 실험결과, 작업강도가 3 METs에서 9 METs로 증가함에 따라 실험기간동안 평균피부온도차(33.3%), 고막온도차(242.9%), 심박수(36.2%), 호흡수(53.9%), 운동자각도(81.6%), 온냉감(20.8%), 체중감소(60.0%), 혈당(-4.4%), 젖산(41.7%)가 통계적으로 유의하게 높게 나타났다. 이상의 결과 고온조건하에서 소방용 보호복 착용시 주기적 작업과 작업강도가 신체에 미치는 영향이 매우 크게 나타나는 것으로 판단된다.

• 한국기계가공학회지
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• 제16권4호
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• pp.38-45
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• 2017

A finite element analysis-based approach which investigates the causes of the breakdown in the outer ring of the choke at hot rod rolling mill is presented. Two-dimensional drawings of the whole vertical-type mill stand are transformed into three-dimensional CAD models. Non-linear elasto-plastic deformation analysis of material at the roll gap is performed for computing roll force and torque of the work roll. Then, the reaction forces of the bearing rings together with a set of roller bearings that support the work roll are obtained by means of rigid body motion analysis. Finally, stress behaviors in the bearing rings together with a set of roller bearings that support the work roll are investigated by linear elastic analysis. Results reveal that stress at the contact area between the outer ring and roller bearing is extraordinary high when an internal gap between an external surface of the outer ring and the internal surface of the chock due to wear of the inside of the chock occurs.

• 한국산업보건학회지
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• 제11권1호
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• pp.48-55
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• 2001

The purpose of this study was to evaluate the analytical accuracy and precision of microwave oven digestion/atomi absorption spectrophotometry (AAS) for analyzing airborne chromium collected on mixed cellulose ester membrane (M filter from the work environment, and to compare the accuracy and the precision with those of the National Institute for Occupational Safety and Health (NIOSH) Method #7024 hot plate digestion/AAS method. For this study, field air sample pairs were collected from a electroplating process, and spiked samples in a laboratory were prepared and using these samples. Two digestion methods were comp; and evaluated in terms of recovery rate and bias as indices of accuracy and coefficient of variation as a index of precision. The results and conclusions are as follows. In spiked samples, the accuracies (% mean recoveries) of hot plate/AAS and microwave oven/AAS method were 97.19%, 97.1%, respectively, and the precisions (pooled respectively, and the precisions (pooled coefficient of variance, $CV_{pooled}$) 6.93% and 3.88%, respectively. The biases of hot plate ani microwave oven methods were 4.56 - 14.7% and 2.22 - 7.42% respectively. There was no statistically significant difference between hot plate and microwave oven methods recovery rates of spiked samples (p>0,05). Also, no statistically significant difference was shown among the concentrations of air samples determined by two method (p>0.05). In conclusion, microwave oven/AAS method h excellent accuracy and precision, and advantages such as time-saving and simple procedure in comparison with the classical NIOSH method. Therefore, this method can be use widely to analyze airborne chromium collected on MCE filter from the work environments.

• 한국추진공학회지
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• 제14권5호
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• pp.24-31
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• 2010

충돌형 분사기가 장착된 모델 연소실에서 연소장 수치 해석을 이용하여 연소 안정성을 평가하였다. 충돌형 분사기로는 F(fuel)-O(oxidizer)-O-F형 분사기를 채택하였다. 본 연구에서는 연료와 산화제의 제트 혼합과정이 지배적이라는 가정하에 순간 화학 반응 모델을 채택하여 수치해석을 수행하였다. 선행 연구를 통해 제안된 방법론을 토대로 모델 연소실 형상이 설계되고 연소실 작동 조건이 결정되었다. 본 연구에서 제시한 방법을 토대로 얻은 연소 안정성 경계는 공기 분사 음향 실험과 연소 실험결과와 정성적으로 잘 일치하였다. 연료와 산화제의 분사와 혼합이 연소 불안정 유발에 지배적인 경우, 본 연구에서 제안된 수치해석 기법을 이용하여 효과적으로 분사기의 연소 안정성을 평가할 수 있다.

• 자원리싸이클링
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• 제12권4호
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• pp.58-64
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• 2003

폐자동차 shredder line에서 발생한 ASR 재질을 사용하여 가열성형법으로 RDF 시편을 제조하기 위한 실험을 수행하였다. 성형 실험은 ASR 재질 가운데 플라스틱, 섬유 및 스폰지의 3종을 선택하고 이들을 미리 크기 10mm 이하로 절단하여 사용하였으며, 성형용 mold는 직경 40, 60 및 80mm의 3종류를 사용하였다. 실험결과 가열온도, 가열시간 및 재질 혼합비가 RDF 성형에 중요한 변수로 나타났으며, 가열온도가 높을수록 또한 스폰지 함량이 낮을수록 성형상태는 양호하였다. RDF 시편의 성형밀도는 성형조건에 따라 0.5∼0.9gr/ml 의 범위인 것으로 확인되었으며, 스폰지 혼합비율이 클수록 성형밀도는 낮았다. RDF 성형시편의 파괴강도는 대체로 0.8∼3.0MPa의 값을 보였으며, 성형밀도가 증가할수록 강도가 향상되었다. 한편, 가열온도가 높을수록 ASR 재질의 용융부위가 늘어나 성형밀도가 증가하며, 이에 따라 RDF 시편의 파괴강도는 상대적으로 높아지는 것으로 나타났다.

• Journal of Communications and Networks
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• 제6권3호
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• pp.216-225
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• 2004

In a cellular network, if there are too many data users in a cell, data may suffer long delay, and system's quality-of-service (QoS) will degrade. Some traditional schemes such as dynamic channel-allocation scheme (DCA) will assign more channels to hot (or overloaded) cells through a central control system (CC) and the throughput increase will be upper bounded by the number of new channels assigned to the cell. In mobile-assisted data forwarding (MADF), we add an ad-hoc overlay to the fixed cellular infrastructure and special channels-called forwarding channels- are used to connect mobile units in a hot cell and its surrounding cold cells without going through the hot cell's base station. Thus, mobile units in a hot cell can forward data to other cold cells to achieve load balancing. Most of the forwarding-channel management work in MADF is done by mobile units themselves in order to relieve the load from the CC. The traffic increase in a certain cell will not be upper bounded by the number of forwarding channels. It can be more if the users in hot cell are significantly far away from one another and these users can use the same forwarding channels to forward data to different cold neighboring cells without interference. We find that, in a system using MADF, under a certain delay requirement, the throughput in a certain cell or for the whole net-work can be greatly improved.

• Journal of Advanced Marine Engineering and Technology
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• 제38권9호
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• pp.1021-1026
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• 2014

본 논문에서는 hot-gas를 이용한 다양한 바이패스 제어 방식 중에서 증발기 흡입부 방식에 대해 각각의 성능에 영향을 미치는 외기온도, 출수온도, 과열 및 과냉도 등에 대해서 알아보았다. 그 주요 결과를 요약하면 다음과 같다. 우선, 증발기 흡입부로 hot-gas를 바이패스 하였을 경우에 냉동장치의 성능은 외기온도, 출수온도, 과열 및 과냉도 등에 영향을 받는 것을 알 수 있었다. 따라서 이러한 변수에 대한 최적화를 통해 본 냉동장치의 기초 설계 자료를 제공할 수 있다. 그리고 증발기 흡입부 hot-gas 바이패스 방식의 운전특성을 고찰하여 본 논문에서 제안하는 냉동장치에 대한 적용 가능성을 확인할 수 있었다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.87-90
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• 2008

Since fastener bolt for airplane require high specific strength and corrosion resistance, Ti-6Al-4V alloy is widely used. However, the Ti-6Al-4V bolt is generally manufactured by cutting and rolling because of their poor workability. The aim of present work is to develop hot forming technology for high strength Ti-6Al-4V. Various heat-treatments were applied to specimen in order to increase hot-workability and prevent galling with die Multiple forging were simulated with FE code to determine optimum process parameters including specimen temperature, strain rate, local strain, and thermal shrinkage. Forged samples were heat-treated again to increase their mechanical properties.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.184-187
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• 2003

The simulation program is developed to get the target strip crown of high strength steel in the continuous hot strip rolling. The developed program consists of several sub-program, which contains work roll shifting pattern, roll wear profile, roll thermal expanded profile and strip profile. Also, the variation of strip profile is investigated according to roll deflection and flattening. The results are compared with the values observed from the actual hot rolling of high strength steel. And effect of bender force on the strip profile is studied. The strip crown is shown to decrease with increasing bender force.

• 한국분말재료학회지
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• 제3권4호
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• pp.253-259
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• 1996

The efficiency of thermoelectric devices for different applications is known to depend on the thermoelectric effectiveness of the material which tends to grow with the increase of its chemical homogeneity. Thus an important goal for thermal devices is to obtain chemically homogeneous solid solutions. In this work, the new process with rapid solidification (melt spinning method) followed by hot pressing was investigated to produce homogeneous material. Characteristics of the material were examined with HRD, SEM, EPMA-line scan and bending test. Property variations of the materials were investigated as a function of variables, such as dopant ${CdCl}_{2}$ quantity and hot pressing temperature. Quenched ribbons are very brittle and consist of homogeneous $Bi_2Te_3$, ${Bi}_{2}{Se}_{3}$ solid solutions. When the process parameters were optimized, the maximum figure of merit was 2.038$\times$$10^{-3}K^{-4}. The bending strength of the material hot pressed at 50$0^{\circ}C$ was 8.2 kgf/${mm}^2$.