• Tunnel and Underground Space
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• v.20 no.6
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• pp.465-474
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• 2010

Although the number of medium-length road tunnels, less than 1 km in length, has increased recently more than 30 percent each year, their ventilation and fire safety system design guidelines have not been established yet. The guidelines for long tunnel design are adopted even for the medium-length road tunnels. Therefore the necessity is brought up to optimize the ventilation and fire safety systems based on their own design guidelines. This study aims at determining the optimal start time of jet fan in case of 20 MW fires by analyzing smoke backlayering range, temperature distribution, range of poor visibility, evacuation time and critical velocity. The CFD study results are expected to contribute to propose the optimal fan operation mode.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.6
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• pp.27-36
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• 1995

This paper covers algorithms to determine a machine assignment strategy to locations on a single straight track by minimizing the total backtrack distance. Three different algorithms ar presented: an efficient heuristic procedure, the branch-and-bound algorithm, and the nerual network approach. Simulation results show that the proposed algorithms have potential power to design an on-line optimizer.

• Pediatric Gastroenterology, Hepatology & Nutrition
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• v.4 no.2
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• pp.133-141
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• 2001

Purpose: Gastroesophageal reflux (GER) has been found to be the causative factors of apnea, stridor, feeding intolerance, poor weight gain, and sudden infants death syndrome (SIDS) in infants. GER is a well-described in infants and children, but only scant mention of the premature infants with GER can be found in the literature. Methods: Esophageal pH was measured during 24 hour in 21 healthy preterm infants, using a silicone microelectrode with an external reference electrode connected to a portable recorder. The mean age of the patients was $29{\pm}8$ days, mean gestational age was $30^{+5}{\pm}2^{+0}$ weeks, mean birth weight was $1,468{\pm}329$ g, mean postconceptional age was $34^{+6}{\pm}1^{+4}$ weeks and mean weight was $1,750{\pm}329$ g. We evaluated the following reflux parameters; number of acid reflux, number of long acid reflux, longest acid reflux minutes, and reflux index. Results: Pathologic GER was detected in 12 (57%) subjects and most interesting parameters are reflux index and number of episodes with a pH<4 during 24 hour (high correlation with postprandial reflux index). Reflux was not correlated to gestational age, birth weight, age, postconceptional age, weight, sex and medication of the theophylline. Conclusion: Gastroesophageal reflux is common in preterm infants, but it is usually not apparent, even with severe reflux.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.1
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• pp.95-108
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• 2022

The increase in the use time of tunnel users due to the lengthening of the road tunnel may increase the evacuation time in case of fire, resulting in a large number of casualties. In order to reduce the casualties caused by fire, the "Road Tunnel Design Manual, Part 6 Tunnel" and "Road Tunnel Disaster Prevention Facility Installation and Management Guidelines" stipulate that ventilation facilities should be installed along with the extension of the tunnel. The ventilation system design factor considers the wind speed of the external natural wind to be at least 2.5 m/s, and it is applied upward according to the characteristics of the tunnel. As a result of analyzing the five-minute average wind speed data in the Daegwallyeong region for the past 6 years, it was analyzed that 15.8% of the windy days were winds of 10 m/s or more, and the maximum was 20 m/s. Therefore, in this study, when a fire occurs in a tunnel, the pattern of natural wind flowing into the tunnel and the backlayering distance of the tunnel fire smoke according to the maximum wind speed were analyzed. As a result, it was analyzed that a backflow of up to 490 m occurs when a gust of 20 m/s blows.

• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.2
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• pp.129-139
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• 2004

The several assumptions and design parameters to determine the ventilation rate in tunnel ventilation system were examined. In longitudinal ventilating tunnel, the ventilation rate has been determined by the critical velocity above which the smoke propagation to the upstream of ventilating air is prevented. Based upon the examination of assumptions and experimental results, we suggested the improved method to determine the critical velocity. In transverse ventilating tunnel, we found that the ventilation rate has been determined in accordance with the custom rather than fire-smoke dynamics such as the critical velocity in the longitudinal ventilating tunnel. It is because the ventilation rate in the transverse ventilation system has been determined by considering only the ventilation of contaminant by vehicle. To improve the ventilation design parameters based upon the fire-smoke dynamics, we conducted model tunnel fire experiments. From the experimental results, smoke propagating distance and smoke filling were suggested as the design parameter to determine the ventilation rate in transverse ventilating tunnel. And tunnels in Europe designed by the custom is found to have the dangerous nature in view of fire safety.

• Fire Science and Engineering
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• v.22 no.1
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• pp.16-23
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• 2008

In this research, the visualization experiment for a scaling tunnel was conducted to establish the optimum fire protection system in tunnel fires. In order to find the optimal operating condition of jet fan with the fire, the characteristics of smoke propagation was considered to find the optimal operating condition of jet fan at the time of tunnel fire, the concentration of smoke was measured experimentally for various jet fan position and it's operating condition. As a result, when jet fan in the vicinity of fire operates at the upstream, the back-layering of the smoke should be considered with separation distance from the fire source. The distance between the jet fan and the fire should be longer than 50 m. On the other hand, when the vicinity jet fan operates at the downstream, the back-layering of smoke does not occur, but stratification is not maintained because the smoke dispersion occurs at the downstream due to the operation of the jet fan.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.449-449
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• 2023

유량은 도섭법, 보트법, 횡측선법, 교량법 및 부자법 등 다양한 방법으로 측정되는데, 이들 측정방법 모두 많은 수의 관측자를 필요로 한다. 이들은 하천에 직접 들어가서 측정하거나, 인공구조물인 교량과 재방에서 측정되는데, 도섭법, 보트법, 횡측선법이 전자이며, 고수위 및 고유속으로 하천에 들어가지 못하는 경우에는 교량법 및 부자법을 사용하여 유량을 측정한다. 최근 지구 온난화로 따른 이상 기후가 빈번히 발생하고 있으며, 이로 인한 많은 피해가 발생하고 있어, 하천 수위, 유속 모니터링에 대한 중요성이 더 커지고 있다. 2022년 1월부터 시행 중인 「중대재해처벌법」으로 집중호우 및 일몰 이후에는 안전상의 문제로 유량측정이 어려운 상황으로 필요한 시기에 유량 데이터를 확보에 제약이 있다. 이에 관측자 없이도 유량을 측정할 수 있는 방법을 이용하여 중대 재해의 위험성을 해소하고자 하였다. 유량측정 방법으로 설치 회수가 용이한 비접촉 방식에서 영상표면유속측정 방식과 레이더(전자파)표면 유속측정 방식 중, 집중호우 및 태풍 발생 중 가시성이 확보되지 않아도 측정이 가능한 레이더(전자파) 표면유속계를 이용한 다측점 유량측정 방법을 개발하였다. 비접촉 다측점 유량측정시스템 Master 1대에 8대의 Slave를 연결할 수 있어 총 9개의 측선을 측정할 수 있게 개발하였다. 특히, 하천 및 수로 등의 표면 유속을 비접촉으로 측정하고 하천 단면을 이용하여 유량측정이 가능한 장비로 별도의 수중 및 수상 주조물 작업이 필요 없고 장비의 손상 및 유실 가능성이 거의 없고 역류 상태에서도 측정이 가능하다. 유속은 24GHz의 레이더 주파수를 송수신하여 도플러 변이를 이용하여 측정하였고, 수위는 80GHz의 레이더 주파수를 사용하여 왕복 시간을 거리로 환산하여 측정하였다. 유량은 각각의 유속계에 단면을 입력해 놓으면 유속분포법, 중간단면적법 및 지표유속법을 적용하여, 각각의 측선에 대한유량과 총 유량을 산출하였다. 그 결과, 기존 방식 대비 상당한 개선 효과를 확인하였고, 향후 환경부 등 중앙부처의 수문조사 사업에서 그 역할이 기대된다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.6
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• pp.373-381
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• 2016

In this study, we investigate the characteristics of the drag reduction of a circular cylinder having a detached splitter plate at the wake side. We measure the fluid force on a circular cylinder and visualize the field using particle image velocimetry (PIV) with a high Reynolds number, Re = 10,000. The experimental paraeters used were the width ratios (H/B = 0.5~1.5) of splitters to the prism width and the gap ratios (G/B = 0~2) between the prism and the splitter plate. The drag-reduction rate of the circular cylinder increased with H/B in the case of the same G/B, and it increased and then decreased with G/B in the case of the same H/B. The vortices of the opposite direction on the upper and lower sides of the detached splitter plate were generated by installing the plate. Reverse flow was caused by the vortices at the wake region of the circular cylinder, and the drag of the circular cylinder was decreased by the reverse flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.7
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• pp.2386-2396
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• 1996

A numerical simulation has been performed for isothermal and reacting flows in an exisymmetric, bluff-body research combustor. The present formulation is based on the density-weighted averaged Navier-Stokes equations together with a k-epsilon. turbulence model and a modified eddy-breakup combustion model. The PISO algorithm is employed for solution of thel Navier-Stokes system. Comparison between measurements and predictions are made for a centerline axial velocities, location of stagnation points, strength of recirculation zone, and temperature profile. Even though the numerical simulation gives acceptable agreement with experimental data in many respects, the present model is defictient in predicting the recoveryt rate of a central near-wake region, the non-isotropic turbulence effects, and variation of turbulent Schmidt number. Several possible explanations for these discrepancies have been discussed.