• Journal of the Korean Society of Safety
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• v.38 no.5
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• pp.1-7
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• 2023

This study analyzes the operational characteristics of 311 aged and non-aged residual current circuit breakers (RCCBs) in low-voltage consumer contexts. It investigates the influence of external temperature and harmonics based on the rated current multiples. To simulate temperature variations, a convectional oven was used around the circuit breakers. Additionally, the generation of harmonic reference signals and data measurement for overcurrent experiments were conducted using NI SCXI, myDAQ, and LabVIEW. An observation revealed that as the ambient temperature increased, the operating time of RCCBs decreased in the time delay region. This was attributed to the faster response or bending of the bimetal, which is the tripping element. However, aged RCCBs encountered challenges with tripping outside the protective curve. The operating time of the circuit breakers exhibited an acceleration influenced by the order and content of harmonic currents, potentially leading to malfunctions. Aged RCCBs demonstrated faster operating times than their non-aged counterparts. However, the difference in operating time varied based on the manufacturer's and operating environment of the RCCBs. Frequent malfunctions of RCCBs can result in power outages. In cases where these circuit breakers fail to operate, they can lead to secondary damages, including electrical fires and shocks. Consequently, it is imperative to consider the operating environment of RCCBs and provide appropriate replacement cycles to mitigate these risks.

• The Journal of Engineering Geology
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• v.34 no.1
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• pp.107-115
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• 2024

This study assesses forest fire susceptibility in Gangwon-do, South Korea, which hosts the largest forested area in the nation and constitutes ~21% of the country's forested land. With 81% of its terrain forested, Gangwon-do is particularly susceptible to wildfires, as evidenced by the fact that seven out of the ten most extensive wildfires in Korea have occurred in this region, with significant ecological and economic implications. Here, we analyze 480 historical wildfire occurrences in Gangwon-do between 2003 and 2019 using 17 predictor variables of wildfire occurrence. We utilized three machine learning algorithms—random forest, logistic regression, and support vector machine—to construct wildfire susceptibility prediction models and identify the best-performing model for Gangwon-do. Forest and soil map data were integrated as important indicators of wildfire susceptibility and enhanced the precision of the three models in identifying areas at high risk of wildfires. Of the three models examined, the random forest model showed the best predictive performance, with an area-under-the-curve value of 0.936. The findings of this study, especially the maps generated by the models, are expected to offer important guidance to local governments in formulating effective management and conservation strategies. These strategies aim to ensure the sustainable preservation of forest resources and to enhance the well-being of communities situated in areas adjacent to forests. Furthermore, the outcomes of this study are anticipated to contribute to the safeguarding of forest resources and biodiversity and to the development of comprehensive plans for forest resource protection, biodiversity conservation, and environmental management.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.1
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• pp.63-73
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• 2021

This paper presents a algorithm for automatic target recognition robust to the influence of the flame in order to track the target by EOTS(Electro-Optical Targeting System) equipped on UAV(Unmanned Aerial Vehicle) when there is aerial target or marine target with flame at the same time. The proposed method converts infrared images of targets and flames into a gradient vector field, and applies each gradient magnitude to a polynomial curve fitting technique to extract polynomial coefficients, and learns them in a shallow neural network model to automatically recognize targets and flames. The performance of the proposed technique was confirmed by utilizing the various infrared image database of the target and flame. Using this algorithm, it can be applied to areas where collision avoidance, forest fire detection, automatic detection and recognition of targets in the air and sea during automatic flight of unmanned aircraft.

• Journal of the Korea Concrete Institute
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• v.26 no.4
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• pp.429-440
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• 2014

Since the World Trade Center and Pentagon attacks in 2001, terror, military attack, or man-made disaster caused impact, explosion, and fire accident have frequently occured on civil infrastructures. However, structural behavior researches on major Prestressed Concrete (PSC) infrastructures such as bridges, tunnels, Prestressed Concrete Containment Vessel (PCCVs), and LNG tanks under extreme loading are significantly lacking. Especially, researches on possible secondary fire scenarios after terror, bombing, collision of vehicles and vessels on concrete structures have not been performed domestically where most of the past researches related to extreme loadings on structures focused on an independent isolated extreme loading scenario. Due to the outcry of public concerns and anxiety of potential terrorist attacks on major infrastructures and structures, a study is urgently needed at this time. Therefore, in this study, the bi-directional prestressed concrete $1400{\times}1000{\times}300mm$ panels applied with 430 kN prestressing force using unbonded prestressing thread bars were experimentally evaluated under impact, fire, and impact-fire combined loadings. Due to test site restrictions, impact tests were performed with 14 kN impactor with drop heights of 10m and 3.5 m to evaluate impact resistance capacity. Also, fire and impact-fire combined loading were tested using RABT fire loading curve. The measured residual strength capacities of PSC and RC specimens applied with impact, fire, impact-fire combined loadings were compared with the residual strength capacity of undamaged PSC and RC specimens for evaluation. The study results can be used as basic research data for related research areas such as protective design and numerical simulation under extreme loading scenarios.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.285-290
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• 1994

The influence of elevated temperatures on the mechanical properties of concrete is important for fire-resistance studies and also for understanding the behavior of containment vessel, such as nuclear reactor pressure vessels, during service and ultimate condition. The present study is to clarify the damage/deterioration of concrete structures that are subjected to high temperature exposure. To this end, comprehensive experiments are conducted. The major test variables are the peak temperatures, rate of temperature increase, and sustained duration at peak temperature. The results include weight loss residual compressive strength and stress-strain curve. From those results, residua compressive strength formula and stress-strain relationship are proposed.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.291-300
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• 1994

The influence of elevated temperatures on the mechanical properties of concrete is important for fire-resistance studies and also for understanding the behavior of containment vessel, such as nuclear reactor pressure vessels, during service and ultimate condition. The present study is to clarify the damage/deterioration of concrete structures that are subjected to high temperature exposure. To this end, comprehensive experiments are conducted. The major test variables are the peak temperatures, rate of temperature increase, and sustained duration at peak temperature. The results include weight loss residual compressive strength and stress-strain curve. From those results, residua compressive strength formula and stress-strain relationship are proposed.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.477-478
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• 2009

The objective of this study is to increase the insight of the mechanical behaviour of high-strength concrete prepared with fiber reinforcement after exposure to elevated temperatures. In particular, the result of the effects of contents of polypropylene fiber and level of preload on the residual compressive strength, load bearing and stress-strain curve of concrete are discussed

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.667-670
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• 2003

The purpose of this study is to present data for the reusing, reinforcement and estimation of safety of the RC structure damaged by fire, and for the prevention of explosive spalling by checking the character of explosive spalling according to kinds of fine aggregate, admixture and water-cement ratios. The materials used fine aggregates were sea sand, crushed sand and recycled sand, and the admixtures were fly ash and blast-furnace slag. Also the water-cement ratios was 55% and 30.5%. After those were heated respectively for 30 and 60 minutes in accordance with Standard Time-Temperature Curve. And then conditions of explosive spalling were divided into five grades, and characters of explosive spalling were investigated.

• Journal of the Korean Society of Safety
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• v.29 no.3
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• pp.8-13
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• 2014

Accidents involving portable ranges occurred total 133 cases for the last five years(2008~2012). It accounted for 18.0% of all gas accidents(739 cases). Major causes of accidents are using of excessive hot grill, leaving a butane can near fire and overheating of a butane can during cooking. In this study, it is a desire to investigate the relationship between thermal behavior mechanism depending on characteristics of cooking equipment materials of portable gas ranges. It shows that slope of temperature change curve correlates with difference of heat capacity on thermal behavior characteristics experiment depending on materials of cooking equipment. In conclusion, temperature characteristics appear differently depending on variables such as materials of cooking equipment. Especially, it is necessary to restrict using cooking equipment made of stones, because it is very dangerous that temperature of can is rapidly increasing caused by high heat capacity of stone.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1557-1559
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• 2000

In this paper, we intend to establish the judgement of electrical fire through analysis of PT(Potential Transformer) using the power installation. The columnar structure and the void generated by abrupt heat grew at the tenter of boundary-face on the metallurgical microscope analysis. The detection of OK lines was confirmed by EDX(Energy Dispersive X-ray spectroscopy) as melting and recombination due to the layer-short of the wiring. We found that the thermal-weight decrease occurred at 300$^{\circ}C$ in case of being the thermal-deterioration on the base of the result that analyzed the insulated-materials by using TGA, and the thermal reaction limited-value of PT insulator was about 300$^{\circ}C$ on the DSC curve. As this analysis, we confirmed what the layer-short appeared in the wiring of PT.