• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.260-266
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• 2010

본 연구에서는 사질토 지반에서 펄스 방전(PDT)에 의한 확공 현상을 평가하기 위한 수치해석 연구를 수행하였다. 수중 폭발 모델을 기반으로 PDT적용을 통해 시추공 내부의 시멘트 페이스트에 발생하는 충격파를 모델링하였고, 이를 바탕으로 사질토 지반에 유발되는 변형을 유체-구조물 연동해석을 통해 예측하였다. 해석 결과, 수치해석을 통한 예측이 문헌에 언급된 지반 확공 정도에 대한 실험 결과와 부합하는 것으로 나타났다. 또한 펄스 방전에 의해 지반의 응력 증가 및 체적 압축 등의 지반 다짐효과를 파악할 수 있었다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.1
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• pp.25-36
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• 2021

Hydrogen in hydrogen-electric vehicles has a wide range of combustion and explosion ranges, and is a combustible gas with a very fast flame propagation speed, so it has the risk of leakage, diffusion, ignition, and explosion. The fuel tank has a Thermally active Pressure Relief Device (TPRD) to reduce the risk of explosion and other explosions, and in the event of an accident, hydrogen inside the tank is released outside before an explosion or fire occurs. However, if an accident occurs in a semi-closed space such as an underground parking lot, the flow of air flow is smaller than the open space, which can cause the concentration of hydrogen gas emitted from the TPRD to accumulate above the explosion limit. Therefore, in this study, the leakage rate and concentration of hydrogen over time were analyzed according to the diameter of the nozzle of the TPRD. The diameter of the nozzle was considered to be 1 mm, 2.5 mm and 5 mm, and ccording to the diameter of the nozzle, the concentration of hydrogen in the underground parking lot increases in a faster time with the diameter of the nozzle, and the maximum value is also analyzed to be larger with the diameter of the nozzle. In underground parking lots where air currents are stagnant, hydrogen concentrations above LFL (Lowe Flammability Limit) were analyzed to be distributed around the nozzle, and it was analyzed that they did not exceed UFL (Upper Flammability Limit).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.511-517
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• 2016

Current oil-type potential transformers for trains are filled with insulating oil, which could have problems like explosions due to rising inner pressure during train operation. Therefore, mold and dry-type potential transformers are being developed to prevent explosions. One problem in manufacturing mold-type transformers is preventing void formation around the coiled core inside the mold during epoxy filling, which could cause an electrical spark. Micro voids can remain in the resin after filling, and macro voids can occur due to the structure shape. A transformer that is being developed has a cavity at the junction of the core and the coil for better performance, and when highly viscous epoxy flows inside the cavity channel, macro voids can form inside it. Therefore, in this study, the free-surface flow of the mold filling procedure was analyzed numerically by applying the VOF method. The results were used to understand the phenomena of void formation inside the cavity and to modify the process conditions to reduce voids.

• Journal of the Korea Institute of Military Science and Technology
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• v.19 no.4
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• pp.462-468
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• 2016

In this paper, we present the results of the numerical analysis employing CONWEP, LS-DYNA FSI(Fluid Structure Interaction), AUTODYN FSI, LS-DYNA ALE(Arbitrary Lagrange Eulerian) and combination of CONWEP and LS-DYNA ALE for blast door fracture and wave propagation through the tunnel by the external explosion. We compared the numerical analysis results with the subscale test data and selected combination of CONWEP and LS-DYNA ALE method as adequate data generation method for the FRM(Fast Running Model) software development. It is expected to save much time and costs by using the numerical simulation data for the various test conditions.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1171-1176
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• 2004

To develop and improve a switchgear, the prediction of the pressure rising within the switchgear is very important. This study investigates the pressure rising characteristics of switchgear in order to evaluate the result of arc fault test. The pressure rising time at the four points of measurement calculated by CFD is well accord with the experimental results. The maximum pressure within the switchgear estimated by CFD is about 1.0bar, the pressure from experiment is 0.7 bar. The results of this study are able to be used to improve the performance of existing switchgear and to develop a new type switchgear.

• Journal of the Korean Institute of Gas
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• v.26 no.1
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• pp.34-40
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• 2022

Gas cylinder cabinets have risks such as cylinder explosion and scattering of debris when a fire occurs. These risks are likely to cause gas spills and cause secondary damage. In order to reduce damage, it is very important to secure the fire resistance performance of the gas cylinder cabinet. In foreign countries, NFPA codes in the United States and EN-14470-2 in Europe stipulate fire resistance test standards for gas cylinder cabinets to protect internal cylinders for a certain period of time in a situation where gas cylinder cabinets are exposed to flames. However, in Korea, only internal pressure performance and airtight performance standards are specified, and the target is limited to piping, and research and regulations for the fire resistance performance of gas cylinder cabinets are insufficient compared to overseas. Therefore, in this study, finite element analysis was used to establish fire resistance standards for domestic gas cylinder cabinets. In the event of a fire, optimal conditions are derived in terms of structure and material.

• Journal of the Korea Society for Simulation
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• v.26 no.3
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• pp.1-11
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• 2017

Blast injuries in a compartment are investigated, and the effects of obstacles on blast injury are particularly analyzed by comparing injuries in the compartments with or without protruding obstacles inside. Even if blast pressure profile tends to be complicated in a confined space unlike in open field, it can be obtained in a relatively short time by using some empirical fast running models for simple confined spaces. However, a finite element method should be employed to obtain blast pressure profiles in a case with obstacles in confined spaces, because the obstacles heavily disturb blast waves. On the other hand, Axelsson SDOF(Single degree of freedom) model and ASII(Adjusted severity of injury index) injury level are employed to estimate blast injury in compartments, because the usual pressure-impulse injury criterion based on the ideal Friedlander waves in open the field cannot be applied to personnel in a confined space due to complexity of blast waves inside. In cases with obstacles, chest wall velocity was reduced by 26 to 76 percent(%) and the personnel injury in the compartment caused by blast was also reduced.

• Tunnel and Underground Space
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• v.32 no.2
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• pp.160-172
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• 2022

The design regulations for simple explosive storage in Korea only stipulate standards for the materials and thickness of the wall of the structure because the amount of explosives that can be stored is small. There is concern about secondary damage during an internal explosion in a simple storage facility, and it is necessary to reexamine the current standards. The numerical analysis for the TNT 15 kg explosion inside the simple storage was carried out by setting the factors using the robust experimental design method. The displacement of the structure generated under the same time condition was analyzed, and the contribution was evaluated. The contribution of concrete thickness was the highest, and the contribution of concrete strength and rebar arrangement was lower than that of concrete thickness. The reinforcement diameter contributed extremely little to the displacement. The structural standards of the simple storage that are currently applied are insufficient on blast resistance, and it is necessary to present new design standards. Therefore, the design factor to be applied later analysis and actual experiments were taken into consideration. For the design variables, the thickness of the concrete was 15 cm considering the displacement, the concrete strength was selected as general concrete considering the inlet discharge pressure, the factor with the lowest average displacement was selected for the reinforcement arrangement and the diameter of the reinforcement, the factor with the smallest level was selected in consideration of economic feasibility because the difference in displacement was low.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.651-657
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• 2010

A composite piston with a crown made of steel and a skirt made of NCI is used in a marine diesel engine, which has a maximum firing pressure of over 180 bar and a high thermal load. In the fatigue design of the composite piston, the fatigue is influenced by factors such as the load type, surface roughness, and temperature; further, the distribution ratio of the firing force from the crown to the skirt is important for optimizing the design of the crown and skirt. In this study, the stress gradient method was used to consider the effect of the load type. The temperature field on the piston was predicted by cocktail-shaking cooling analysis, and influence of high temperature on fatigue strength was investigated. The load transfer ratio and contact pressure were optimized by design of the surface shape and accurate tolerance analysis. Finally, the cooling performance and durability design of the composite piston were verified by performing a long-term prototype test.

• Explosives and Blasting
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• v.40 no.2
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• pp.1-14
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• 2022

Numerical simulation is the most widely used methods for evaluating blasting performance. This study, conducted the numerical analysis of shock chamber model to evaluate the pressure confine effect of the stemming material and plug device. The stemming effect was compared and evaluated with that of the STF-based stemming material currently under development and sand, which is a commonly used blast stemming material. Furthermore, to verify of enhancement the confine effect inside blast hole pressure, three types of stemming plugs were adopted for the numerical analysis. The numerical simulation results revealed that the STF-based stemming materials were superior to the general stemming material. Also, It is evaluated that the STF-based stemming and Plug system can not only prevent detonation gas from overflowing the borehole prematurely, but also prolong the action time and scope of detonation gas in the borehole effective.