• Title/Summary/Keyword: 사고사례분석

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A Study on Characteristics and Modeling of CMV by Grounding Methods of Transformer for ESS (ESS용 변압기의 접지방식에 의한 CMV 모델링 및 특성에 관한 연구)

  • Choi, Sung-Moon;Kim, Seung-Ho;Kim, Mi-Young;Rho, Dae-Seok
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.22 no.4
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    • pp.587-593
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    • 2021
  • Since 2017, a total of 29 fire accidents have occurred in energy storage systems (ESSs) as of June 2020. The common mode voltage (CMV) is one of the electrical hazards that is assumed to be a cause of those fire accidents. Several cases of CMV that violate the allowable insulation level of a battery section are being reported in actual ESS operation sites with △-Y winding connections. Thus, this paper evaluates the characteristics of CMV. An ESS site was modeled with an AC grid, PCS, and battery sections using PSCAD/EMTDC software. As a result of a simulation based on the proposed model, it was confirmed that characteristics of CMV vary significantly and are similar to actual measurements, depending on the grounding method of the internal transformer for PCS. The insulation level of the battery section may be severely degraded as the value of CMV exceeds the rated voltage in case of a grounding connection. It was found that the value of CMV dramatically declines when the internal transformer for PCS is operated as non-grounding connection, so it meets the standard insulation level.

Evaluation and Determination of System Design Alternatives Utilizing a SysML-Based M&S Method for Achieving Functional Safety (SysML 기반 모델링 및 시뮬레이션 기법을 통한 기능안전 설계 대안들의 평가 및 결정 방법)

  • Jung, Ho-Jeon;Lee, Jae-Chon
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.19 no.11
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    • pp.574-582
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    • 2018
  • In systems such as railways, automobiles, and airplanes, system malfunctions may lead to accidents, which often cause serious personal injury and economic loss. In previous studies, failure analysis has been performed, and safety measures derived using the component level information to reduce damage when a failure occurs. However, in functional safety concept, a focus is placed on lowering the frequency of occurrence of failures by performing risks analysis, setting up safety goals, and designing safety functions. Therefore, it is necessary to study how to determine the required safety function that can reduce the failure frequency to the acceptable level. To achieve this, we first studied a failure modeling method using SysML. It was then presented how several alternatives can be assessed to determine the desired safety function by simulating the generated SysML failure models and calculating the ability to reduce the failure frequency. A case study of a railway signaling system was done, demonstrating the effectiveness of the approach. We assessed whether the safety objectives were met for the alternative design of the railway signaling system through M & S. The results can be useful in that it can be applied from the early design phase and allow to choose the appropriate safety function that satisfies safety objectives among various design alternatives.

Low-Voltage EM(Elasto-Magnetic) Sensing Technique for Tensile Force Management of PSC(Prestressed Concrete) Internal Tendon (PSC 내부 텐던의 긴장력 관리를 위한 저전압 EM 센싱 기법)

  • Park, Jihwan;Kim, Junkyeong;Eum, Ki-Young;Park, Seunghee
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.32 no.2
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    • pp.87-92
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    • 2019
  • In this paper, we have verified a low-voltage EM(elasto-magnetic) sensing technique for tensile force management of PSC(prestressed concrete) internal tendon in order to apply the technique to actual construction sites where stable power supply is difficult. From observation of past domestic and overseas PSC structural accident cases, it was found that PS tension is very important to maintain structural stability. In this paper, we have tried to measure the tensile force from a magnetic hysteresis curve through EM sensors according to voltage value by using relation between magnetostriction and stress of ferromagnetic material based on elastic-magnetic theory. For this purpose, EM sensor of double cylindrical coil type was fabricated and tensile force test equipment for PS tendon using hydraulic tensioning device was constructed. The experiment was conducted to confirm relationship between changes of permeability and tensile force from the measurement results of the maximum / minimum voltage amount. The change of magnetic hysteresis curve with magnitude of tensile force was also measured by reducing amount of voltage step by step. As a result, the slope of estimation equation in accordance with magnitude of magnetic field decreases with the voltage reduction. But it was confirmed a similar pattern of change of magnetic permeability for the magnetic hysteresis loop. So, in this study, it is considered that it is possible to manage the tensions of PSC internal tendon using EM sensing technique in low-voltage state.

Reserch On The Fundamental Technology To Utilization Of Platform To Providing Mobile Underground Geospatial Infomation Map (모바일용 지하공간통합지도 제공 플랫폼 활용을 위한 기반 기술 연구)

  • LEE, Tae-Hyung;KIM, Hyun-Woo
    • Journal of the Korean Association of Geographic Information Studies
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    • v.23 no.4
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    • pp.173-183
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    • 2020
  • In the midst of the aging of underground facilities in urban areas and anxiety about road excavation safety accidents, the Ministry of Land, Infrastructure and Transport began to build Underground Geospatial Infomation Map from 2015 as part of the 「ground subsidence prevention measures」 and efficient use of underground spaces. So, the scope is spreading every year. The current Underground Geospatial Infomation Map information is web-based and is operated in a desktop environment, so it is true that there are some limitations in its use in a field environment such as an excavation construction site. The Underground Geospatial Infomation Map, built and operated in a web-based environment, is a large-scale 3D data. Therefore, in order to service by transmitting data to the field without delay, it is necessary to lighten the Underground Geospatial Infomation Map data. In addition, the current Underground Geospatial Infomation Map is not unified in data formats such as 3DS and COLLADA, and the coordinate system method is also different in relative coordinates and absolute coordinates. In this study, by analyzing domestic and overseas prior research and technical use cases, a mobile Underground Geospatial Infomation Map data format and a lightweight method were presented, and a technology development was conducted to create a mobile underground space integration map in the presented format. In addition, the weight reduction rate was tested by applying 3D data compression technology so that data can be transmitted quickly in the field, and technology was developed that can be used by decompressing 3D data compressed in the field. finally, it aims to supplement the technology experimentally developed in this study and conduct additional research to produce it as software that can be used in the excavation site and use it.

Effectiveness of Dispersants for Very-Low-Sulfur Fuel Oil (저유황유(VLSFO)의 유처리제 효용성 연구)

  • Kim, Deuksan;Seo, Jeong Mog;Ahn, Suhyun;Lee, Heejin
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.27 no.1
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    • pp.113-118
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    • 2021
  • The International Maritime Organization (IMO) has confirmed a global limit of 0.5 % for sulfur in fuel oil used on board ships with effect from January 1, 2020. Among various alternatives to respond to these regulations on sulfur content in fuel oil, such as LNG ships, SOx scrubbers, and very-low-sulfur fuel oil (VLSFO). VLSFO is preferred owing to its low investment costs. As more ships are expected to use VLSFO, VLSFO spills are expected to increase. In particular, when the seawater temperature is below the pour point of VLSFO, VLSFO solidifies when it is spilled, which makes controlling spills difficult. In this study, six types of VLSFO produced in Korea and one type of high-sulfur fuel oil (MF380) were compared in terms of the dispersibility of dispersants according to the seawater temperature conditions. The results confirmed that the six type of VLSFO did not satisfy the domestic standards for dispersant rate (60 % or more for 0.5 min, 20 % or more for 10 min). Morever, the dispersant rate of the six types of VLSFO was low compared with that of the high-sulfur fuel oil. The results of this study are expected to be used to set the direction of dispersant control in the case of VLSFO spills.

The Transformation of Norms and Social Problems: Focusing on the COVID-19 Pandemic (규범의 전환과 사회문제: 코로나를 중심으로)

  • Lee, Jangju
    • Korean Journal of Culture and Social Issue
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    • v.28 no.3
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    • pp.513-527
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    • 2022
  • This study was conducted to examining the socio-cultural impact of the COVID-19 pandemic that swept the world around 2020, and the transformation of norms and social problems due to COVID-19. For this, the characteristics of changes in the socio-cultural norms of the 14th century European Black Death, a representative example of the pandemic, were derived, and based on this, the COVID-19 pandemic was analyzed. The Black Death served as an opportunity to change social norms based on the existing religious authority and the power of the feudal system to the Enlightenment. The population declination and labor shortage also promoted commercialization and mechanization. Printing, which spread during this period, led to the popularization of knowledge, which raised the level of thinking and led to epochal scientific development. This became the foundation of the Industrial Revolution. Like the recent Black Death, COVID-19 has triggered changes in social norms. The technological environment of metaverse, a mixture of virtual and reality, has changed the norm of a consistent identity into free and open identities exerting various potentials through alternate characters. In addition, meme, which are about people being friendly to those with the same worldview as him on the metaverse, weakened the sense of isolation in non-face-to-face situations. Artificial intelligence (AI), which developed during the COVID-19 pandemic, has entered the stage of being used for creative activities beyond the function of assisting humans. Discussions were held on what new social problems would be created by the social norms changed due to the COVID-19 pandemic.

An Interactive Method between HSE System and Wearable Components through Analysis on Risk Scenarios (위험 시나리오 분석을 통한 스마트 HSE 시스템 및 웨어러블 컴포넌트 연동방안)

  • Shon, DongKoo;Lim, Dong-Sun;Im, Kichang;Park, Jeong-Ho;Kim, Jong-Myon
    • Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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    • v.8 no.5
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    • pp.407-416
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    • 2018
  • The development of modern technology has rapidly grown the field of wearable devices. Wearable equipments should satisfy low power consumption and small/lightweight because of characteristics of body wearing. In this paper, an overview of wearable equipments is explained, and wearable device market is investigated. In addition, we investigate developed technology of wearable components, which is divided into component and communication technology. Meanwhile, a smart HSE system is required to meet the demand of the society for the serious industrial accident. To address this issue, we propose an interactive method between the wearable component and the HSE system, which are expected to be effective in safety management. As a detailed case study, a risk scenario is made with risk factors in welding workshop, and then we propose an interactive method between a wearable component and an HSE system that can reduce the risk. This proposed method is useful to achieve high level of worker's safety.

Student difficulties in constructed-response mathematics assessments: A case study of writing activities for low-performing first-year high school students (수학 서술형 평가의 어려움과 지도 방안: 고교 1학년 노력형 학생의 쓰기 활동 사례 연구)

  • Mihui Bae;Woong Lim
    • The Mathematical Education
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    • v.63 no.1
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    • pp.1-18
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    • 2024
  • This study aims to analyze low-performing high school students' difficulties in constructed response (CR) mathematics assessments and explore ways to use writing activities to support student learning. The participants took CR assessments, engaged in guided writing activities across 15 lessons, and provided responses to our interviews. The study identified 20 types of student difficulties, which were sorted into two main categories: "mathematical difficulties" and "CR difficulties." The difficult nature of mathematics as a school subject included a lack of understanding of mathematical concepts, students' difficulty with mathematical symbols and notations, and struggles with word problems. Challenges specific to CR assessments included students' difficulties arising from the testing conditions unlike those of multiple-choice items, and included issues related to constructing appropriate responses and psychological barriers. To address these challenges in CR assessments, the study conducted guided writing activities as an intervention, through which six themes were identified: (1) internalization of mathematical concepts, (2) mathematical thinking through relational understanding, (3) diverse problem-solving methods, (4) use of mathematical symbols, (5) reflective thinking, and (6) strategies to overcome psychological barriers.

The theory of lesson plannig and the instructional structuration : A case study for urban units in Japanese high school (수업설계론과 수업구조화 - 일본 고등학교 도시단원을 사례로 -)

  • ;Sim, Kwang Taek
    • Journal of the Korean Geographical Society
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    • v.29 no.2
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    • pp.166-182
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    • 1994
  • Kyonggi Province in the late Chosun dynasty was a center of superior government offices including 'Han' River water-road transportation and was located in the middle of an 'X'-shaped arterial road network. Because of these reasons, Kyonggi Province had a faster inflow of commodities, informations and technics compared with the other province. At this period of time, every local 'Eup' (name of administrative district) had not been affected by their above administrative districts and had their own autonomy. For this reason, every 'Eup' could be developed as a town, even if its size was small when it had sufficient internal growing conditions. Moreover, the markets ('Si-Jon') in big towns and periodical markets which were spread over the Kyonggi Province played role of commercial functions of town. And because military bases for the defence of the royal capital in Kyonggi Province also took parts of a non-agricultural city role, Xyonggi Provinc had much more possibilities of growing as a town rather than the other provinces. The towns of the late Chosun Dynasty were, except the capital and superior administrative districts which were governed by the 'You-Su', small towns which had only about 3, 000-5, 000 people. Most of the town dewellers were local officials, nobles, merchants, craftmen and slaves. And the farmers who lived near town became a pseudo-towner through suburb agriculture. Among these people, the merchants were leaders of townization. The downtowns were affected by the landform and traffic roads. The most fundamental function of towns were administrative. The opcial's grade, which was dispatched to the local administrative district ('Kun' or 'Hyun'), was decided by the size of population and agricultural land of each county. Large county which was governed by a high ranking opcial had more possibilities to develop as a large town. Because they supervised other opcials of lower rank and obtained more land and population for the town. The phonomena of farm abandonment after the Japanese Invasion of Korea in 1592-1598 stimulated the development of towns for commercial function. The commercial functions of towns were evident in the Si-Jon or Nan-Jon (names of markets) in the big cities such as Hansung and Kaesung, meanffwhile in the local areas it was emerged in the shape of periodical market networks as allied with near markets (which were called as Jang-Si) or permanent markets which were grown up from periodical markets. These facts of commercial development induced the birth of commercial town. Kyonggi Province showed the weak points of its defense system during both wars (Japanese Invasion in 1592 and Manchu's Invasion in 1636). The government reinforced its defense system by adding 4 'You-Su-Bus' and several military bases. Each local districts ('Eup'), where Geo-Jins were established, were stimulated to be a town while Jin-Kwan system were, adjusted and enforced. Among Dok-Jins(name of solitary military bases), Youngjongjin was grown up as a large garrison town which only played a role of defense. The number of towns that took roles of non-agricultural functions in Kyonggi Province was 52. Among these towns, 29 were developed as big towns which had above 3, 000 people and most of these towns were located on the northwest-southeast axes of 'X'-shaped arterial trafic network in the Chosn Dynasty, This fact points out that the traffic road is one of the important causes of the development of towns. When we make hierarchy of the towns of Kyonggi Province according to its population and how many functions it had, we can make it as 6 grades. The virst grade town 'Hansung' was the biggest central town of administration, commerce and defdnse. The 2nd grade town includes 'Kaesung' which had historical inertia that it had been the capital of the Koryo Dynesty. The 3rd grade towns include some 'You- Su-Bus' such as Soowon, Kanghwa, Kwangju and also include Mapo, Yongsan and from this we can imagine that the commercial development in the late Chosun Dynasty extremely affected the townization. The 4th-6th grade towns had smiliar population but it can be discriminated by how many town functions it had. So the 4th grade towns were the core of administration, commerce and defense function. 5th grade towns had administrative functions and one of commercial and defense functions. 6th grade towns had only one of these functions. When we research and town conditions of each grades as the ratio of non-agricultural population, we can find out that the towns from the 1st grade to 4th grade show difference by degree of townization but from the 4th grade to 6th grade towns do not show big difference in general.

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Development and Application of Theme-based Integrated Teaching/Learning Plan focused on Green Life of Clothing, Food, and Housing in Home Economics (가정교과내 의.식.주생활 영역의 주제중심 통합 교수.학습 과정안 개발 및 적용 - '가족의 생활'과 '가정생활의 실제' 단원의 녹색생활요소를 중심으로 -)

  • Kim, SunSoon;Cho, Jeasoon
    • Journal of Korean Home Economics Education Association
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    • v.26 no.1
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    • pp.1-16
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    • 2014
  • The purpose of this research is to develop a theme-based integrated teaching/learning plan in clothing, food, and housing in home economics and to apply the developed process in classes for evaluation in order to identify the suitability in schools. The theme-based integrated teaching/learning plan developed on the basis of textbooks consist four sub-themes; choosing($1^{st}$ and $2^{nd)$ lessons), using($3^{rd}$ lesson), processing ($4^{th}$ lesson), and alternatives($5^{th}$ and $6^{th}$ lessons) under the main theme of 'green family life'. The results from 20 individual and group activities showed that the students actively solved the problems when the presented cases were related to their own lives or experiences. The opportunity to implement green life through activities motivated students' willingness to proceed in real life. However, it is vital to assist integrated thinking through various examples before beginning due to students with difficulties connecting the issue from one area to the other during the problem-focused activity. The students' ability to solve the activity workbook had been improved as the lessons continued. From the survey questions on the theme-based integrated lessons, all items associated with integration of clothing, foods, and housing were positively responded. Also, questions regarding general understanding, suitability and satisfaction on the teaching/learning process were marked positive. The conclusion could be that the integrated theme related to clothing, food, and housing in our life would be appropriate for green family life. The theme-based integrated teaching/learning plan is effective in understanding the occurrence of green family life in relation with clothing, food, and housing, identifying the practical ideas implementing green life in those areas, and improving the integrated ability to solve the green life related problems. However, this research has its weakness in generalizing the results due to its limited survey respondents and post-evaluation being the only assessment conducted.

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