• Korean Chemical Engineering Research
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• v.56 no.6
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• pp.811-818
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• 2018

A fire and explosion accident caused by a liquefied petroleum gas (LPG) welding and cutting torch gas leak occurred 10 m underground at the site of reinforcement work for bridge columns, killing four people and seriously injuring ten. We conducted a comprehensive investigation into the accident to identify the fundamental causes of the explosion by analyzing the structure of the construction site and the properties of propane, which was the main component of LPG welding and cutting work used at the site. The range between the lower and upper explosion limits of leaking LPG for welding and cutting work was examined using Le Chatelier's formula; the behavior of LPG concentration change, which included dispersion and concentration change, was analyzed using the fire dynamic simulator (FDS). We concluded that the primary cause of the accident was combustible LPG that leaked from a welding and cutting torch and formed a explosion range between the lower and upper limits. When the LPG contacted the flame of the welding and cutting torch, LPG explosion occurred. The LPG explosion power calculation was verified by the blast effect computation program developed by the Department of Defense Explosive Safety Board (DDESB). According to the fire simulation results, we concluded that the welding and cutting torch LPG leak caused the gas explosion. This study is useful for safety management to prevent accidents caused by LPG welding and cutting work at construction sites.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.29-30
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• 2013

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.931-932
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• 2013

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.39-40
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• 2010

• Journal of Korean Society of Forest Science
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• v.99 no.1
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• pp.136-143
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• 2010

This study was conducted to provide basic information on the management of natural deciduous forests by presenting suitable stand density over time for natural deciduous forests in Pyungchang Area. The stand density index(SDI) for the sampling point was also computed. The cutting scenarios were adopted by considering the SDI estimated in the sampling point. And then, simulation cutting was enforced to the stand. Cutting scenarios consisted of three cutting levels, with the period of 5 years where each suitable cutting level of selection system will not have the SDI over the maximum SDI throughout 30 years and consider harvest after 30 years. As a result of the simulation cutting, it was found that removing 12% and 14% of basal area per each time kept proper stand density while removing 10% exceed to the adequate basis. From an economic point of view, it was concluded that removal 12% of basal area would be the most suit cutting level in selection system.

• Korean Journal of Computational Design and Engineering
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• v.18 no.2
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• pp.148-154
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• 2013

Han-ok (the Korean traditional house) is famous for its beauty and healthful aspects. However, its construction cost is too high because of the manual process of parts such as rafter, timber, etc. These days, many people want to build a modernized Korean traditional house at a low cost. In order to do so, the rafter machining process is required to be automatized using a CNC machine. It is also observed that, generally the timber does not have a uniform shape. Therefore, it is also needed to examine the timber shape before starting its processing. This paper presents the concept design of the rafter processing CNC machine, and a 3D laser scanning system. The laser scanner is developed to acquire 3D details of the timber shape. Furthermore, the results of simulated experiments are presented to investigate surface roughness during the machining process of the timber. Since cutting parameters largely influence on surface roughness and cusps formation, it is needed to achieve optimal machining parameters. Several experiments were carried out changing cutting parameters such as cutting tool diameter, feed-rate, and spindle speed.

• Geomechanics and Engineering
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• v.8 no.4
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• pp.495-510
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• 2015

The applications of water jet cutting (WJC) in coal mine have progressed slowly. In this paper, we analyzed the possibility and reasonableness of WJC application to pressure relief in hard coal seam, simulated the distributive characteristics of stress and energy fields suffered by hard coal roadway wallrock and the internal relationships of the fields to the instability due to WJC (including horizontal radial slot and vertical annular slot) on roadway wallrock. The results showed that: (1) WJC can unload hard coal seam effectively by inducing stress release and energy dissipation in coal mass near its slots; its annular slots also can block or weaken stress and energy transfer in coal mass; (2) the two slots may cause "the beam structure" and "the small pillar skeleton", and "the layered energy reservoir structure", respectively, which lead to the increase in stress concentration and energy accumulation in coal element mass near the slots; (3) the reasonable design and optimization of slots' positions and their combination not only can significantly reduce the scope of stress concentration and energy accumulation, but also destroy coal mass structure on a larger scale to force stress to transfer deeper coal mass.

• Journal of Korean Society of Water and Wastewater
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• v.26 no.3
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• pp.361-372
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• 2012

In order to establish the methodology for estimating an emergency drinking water supply in Korea, overseas cases and accidents history of cutting off water supply were investigated, and questionnaire was conducted. Investigating accidents history of cutting off water supply in Korea, actual cutting off times of most cases were less than 13hours. Also, cases related with water quality and facility failure have been not enough to derive useful information for estimating an emergency water. From the results of questionnaire and cross-tabulation analysis, about 1,066 lpcd(liter per capita${\cdot}$day) as an emergency water and 14 days as tolerable outages time could be estimated. The results of water quality simulation could tell us that it might take 5-16 days for pollutant matter to travel from 15 contamination points to source water intake point in the selected reservoir(D-dam). This travel time was in good accordance with the estimated tolerable outage time, 14days.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.97.1-97.1
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• 2014

We clarify the dynamics connecting a solar flare and a coronal mass ejection (CME) based on the results of a magnetohydrodynamic (MHD) simulation starting from a nonlinear force-free field (NLFFF) in Inoue et al. 2014. In previous studies, many authors proposed numerous candidates for triggering processes of a solar flare and the associated CME. Among them, the tether-cutting reconnection or the torus instability has been supported by recent simulations and observations. On the other hand, our MHD simulation in accordance with more realistic situations show that highly twisted field lines are first produced through a tether-cutting reconnection between the twisted field lines in the NLFFF, and then the newly formed, strongly twisted field erupts away from the solar surface because of a loss of equilibrium. This dynamics corresponds to the onset of a solar flare. Furthermore we have found that the strongly twisted erupting field reconnect with the weakly twisted ambient field during the eruption, creating a large flux tube, and then it rises over a critical height of the torus instability to trigger a CME. From these results, we conclude that the coupled process of tether-cutting reconnection and torus instability is important in the flare-CME relationship.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.684-687
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• 2002

The authors have developed two devices which cuts the spend fuel rod to an optimal size and extracts fuel pellet from the pieces of cut fuel rods. These devices are so important to reduce radioactive wastes that some advanced countries developed their own methods and devices. The authors have benchmarked from these methods and devices. For spent fuel rod cutting, the tube cutting method has been chosen. some mechanical properties of the fuel tube and pellet has been carefully considered for an optimal cutting size. For fuel pellet extraction, a mechanically extracting method has been adopted. The existing chemical method have turned out to be inappropriate because it produced large amount of radioactive wastes, in spite of its high fuel recovery characteristics. The developed method has an advantage that it can be applied to other fuel rods that have different shapes and sizes. The two devices are set up and operated in the hot cell where people can not go in, so that the devices have been designed to be controlled remotely and modulated for easy maintenance. And the performance of the devices has been tested by using simulated fuel rod. From the experimental results, the devices are supposed to be useful for reducing radioactive wastes.