• 대기
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• 제29권2호
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• pp.197-211
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• 2019

The observational sensitivity of dual-polarization weather radar was quantitatively analyzed by using two different pulse widths. For this purpose, test radar scan strategy which consisted of consecutive radar scan using long (LP: $2{\mu}s$) and short (SP: $1{\mu}s$) pulses at the same elevation angle was employed. The test scan strategy was conducted at three operational S-band dual-polarization radars (KSN, JNI, and GSN) of Korea Meteorological Administration (KMA). First, the minimum detectable reflectivity (MDR) was analyzed as a function of range using large data set of reflectivity ($Z_H$) obtained from JNI and GSN radars. The MDR of LP was as much as 7~22 dB smaller than that of SP. The LP could measure $Z_H$ greater than 0 dBZ within the maximum observational range of 240 km. Secondly, polarimetric observations and the spatial extent of radar echo between two pulses were compared. The cross-polar correlation coefficient (${\rho}_{hv}$) from LP was greater than that from SP at weak reflectivity (0~20 dBZ). The ratio of $Z_H$ (> 0 dBZ) and ${\rho}_{hv}$(> 0.95) bin to total bin calculated from LP were greater than those from SP (maximum 7.1% and 13.2%). Thirdly, the frequency of $Z_H$ (FOR) during three precipitation events was analyzed. The FOR of LP was greater than that of SP, and the difference in FOR between them increased with increasing range. We conclude that the use of LP can enhance the sensitivity of polarimetric observations and is more suitable for detecting weak echoes.

• 한국안전학회지
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• 제33권6호
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• pp.102-114
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• 2018

The Railway Safety Management System is based on risk management and the basic purpose of risk management is safety management activities to prevent railway accidents and operational obstacles in advance. In order to manage risk, an acceptable risk standard must be established. This risk criterion is used to evaluate the railway risk with both frequency and severity. In the case of overseas railway or other industrial sectors, various factors are reflected in the main variables that constitute the occurrence frequency, but this is no the case in the domestic railway sector. In particular, the current risk assessment criteria in the railway sector remain at a level that exploits the incidents that have occurred in the past and the severity of the property damage and it dose not properly reflect complex and diverse environmental and situational changes in railway operations. Therefore, in this study, it is possible to calculate the potential occurrence of future events instead of occurrence frequency as a component of the risk assessment criteria, focusing on the High-Speed Railway. In addition to the property damage to the consequence, we suggest a rational methodology, development direction, and theoretical implications for constructing accurate and reasonable risk criteria including actual damage such as human injury and time loss.

• 대기
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• 제32권2호
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• pp.135-148
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• 2022

This study investigates the influence of atmospheric river (AR) on precipitation over South Korea with a focus on regional characteristics. The 42-year-long catalog of ARs, which is obtained by applying the automatic AR detection algorithm to ERA5 reanalysis data and the insitu precipitation data recorded at 56 weather stations across the country are used to quantify their relationship. Approximately 51% of the climatological annual precipitation is associated with AR. The AR-related precipitation is most pronounced in summer by approximately 58%, while only limited fraction of precipitation (26%) is AR-related in winter. The heavy precipitation (> 30 mm day^-1) is more prone to AR activity (59%) than weak precipitation (5~30 mm day^-1; 33%) in all seasons. By grouping weather stations into the four sub-regions based on orography, it is found that the contribution of AR precipitation to the total is largest in the southern coast (57%) and smallest in the eastern coast (36%). Similar regional variations in AR precipitation fractions also occur in weak precipitation events. The regional contrast between the northern and southern stations is related to the seasonal variation of AR-frequency. In addition, the regional contrast between the western and eastern stations is partly modulated by the orographic forcing. The fractional contribution of AR to heavy precipitation exceeds 50% in all seasons, but this is true only in summer along the eastern coast. This result indicates that ARs play a critical role in heavy precipitation in South Korea, thus routine monitoring of ARs is needed for improving operational hydrometeorological forecasting.

• 한국정보통신학회논문지
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• 제26권8호
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• pp.1205-1212
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• 2022

산업제어시스템 (ICS)을 공격 대상으로 하는 사이버 보안 위협들이 지속적으로 증가하는 추세이며 특히 발전, 가스, 정유 시설과 같은 국가 기반시설에서 발생할 수 있는 사이버 보안 사고는 인명 손실 및 대형 화재와 같이 재난 수준의 사고로 이어질 수 있다. 제어시스템을 목표로 하는 사이버 공격에 효과적으로 대응하기 위해서는 ICS 환경을 고려한 다 계층 방어 전략이 필요하며, 특히 제어 망과 IT 환경에서 발생하는 보안 로그들을 통합된 환경에서 운영하는 전략은 기반시설 침해사고 대응에 있어 효과적인 역할을 한다. 본 연구에서는 제어 망에서 발생하는 보안 로그들을 IT 환경에서 운영하는 SIEM (Security Information and Event Management)으로 전송 하는 방법으로 OPC 프로토콜을 활용하는 방안을 소개하고, 이를 통하여 IEC 62443에서 정의하는 제어시스템 전 계층 (Level 0 ~ Level 4)에서 발생하는 이벤트를 통합할 수 있는 보안 로그 서버 구축 방안을 제시한다.

• 한국안전학회지
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• 제37권6호
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• pp.136-147
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• 2022

The purpose of this study is to analyze four cases of firefighter burns in various fire scenes and to find prevention measures to decrease firefighter injuries. Among the analysis reports prepared by the National Fire Research Institute of Korea from 2016 to 2020, four burn-related accidents are summarized and the main causes are conveyed. The four accidents include second-degree burns from using extinguishers during containment of fires; nine firefighters burned due to re-ignition in the LPG car repair shop; two firefighters injured with third-degree burns from using fire extinguishers during life-saving events in residential housing; and injuries from the radiant heat of the tank BLEVE near the factory fire. These cases are comprehensively investigated in their respective scenes and analyzed based on the fire site investigation reports from the fire department and related theoretical explanations of risk for each accident scene. In the third case study, some experimental research is conducted to evaluate the risk involved with the use of safety gloves. This is evaluated by reviewing Fire Tactics and Standard Operational Procedures (SOP) to determine improvements and recommendations for an efficient firefighting response. Results show that the main causes of burn accidents are the insufficient use of personal protective equipment (PPE), such as safety gloves, and the failure to follow firefighting tactics or SOPs. Through the accident investigation and assessment, it is concluded that to reduce the frequency of burn accidents, the performance of firefighting equipment, SOPs, protection tactics, and safety policy systems require improvement.

• Steel and Composite Structures
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• 제44권2호
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• pp.199-210
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• 2022

This study build finite element analysis (FEA) models describing the bending events of coiled tubing (CT) at the wellhead and trips into the hole, accurately provide the state of stress and strain while the CT is in service. The bending moment and axial force history curves are used as loads and boundary conditions in the diametrical growth models to ensure consistency with the actual working conditions in field operations. The simulation diametrical growth results in this study are more accurate and reasonable. Analysis the factors influencing fatigue and diametrical growth shows that the internal pressure has a first-order influence on fatigue, followed by the radius of the guide arch, reel and the CT diameter. As the number of trip cycles increase, fatigue damage, residual stress and strain cumulatively increase, until CT failure occurs. Significant residual stresses remain in the CT cross-section, and the CT exhibits a residual curvature, the initial residual bending configuration of CT under wellbore constraints, after running into the hole, is sinusoidal. The residual stresses and residual bending configuration significantly decrease the buckling load, making the buckling and buckling release of CT in the downhole an elastic-plastic process, exacerbating the helical lockup. The conclusions drawn in this study will improve CT models and contribute to the operational and economic success of CT services.

• 한국지형학회지
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• 제28권1호
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• pp.83-99
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• 2021

Burn severity analysis using satellite imagery has high capabilities for research and management in inaccessible areas. We extracted the forest fire area of the DMZ (Demilitarized Zone) in the western Imjin Estuary which is restricted to access due to the confrontation between South and North Korea. Then we analyzed the forest fire severity and recoverability using atmospheric corrected Surface Reflectance Level-2 data collected from Landsat-8 OLI (Operational Land Imagery) / TIRS (Thermal Infrared Sensor). Normalized Burn Ratio (NBR), differenced NBR (dNBR), and Relative dNBR (RdNBR) were analyzed based on changes in the spectral pattern of satellite images to estimate burn severity area and intensity. Also, we evaluated the recoverability after a forest fire using a land cover map which is constructed from the NBR, dNBR, and RdNBR analyzed results. The results of dNBR and RdNBR analysis for the six years (during May 30, 2014 - May 30, 2020) showed that the intensity of monthly burn severity was affected by seasonal changes after the outbreak and the intensity of annual burn severity gradually decreased after the fire events. The regrowth of vegetation was detected in most of the affected areas for three years (until May 2020) after the forest fire reoccurred in May 2017. The monthly recoverability (from April 2014 to December 2015) of forests and grass fields was increased and decreased per month depending on the vegetation growth rate of each season. In the case of annual recoverability, the growth of forest and grass field was reset caused by the recurrence of a forest fire in 2017, then gradually recovered with grass fields from 2017 to 2020. We confirmed that remote sensing was effectively applied to research of the burn severity and recoverability in the DMZ. This study would also provide implications for the management and construction statistics database of the forest fire in the DMZ.

• 대기
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• 제33권5호
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• pp.531-548
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• 2023

We developed the Aviation Convective Index (ACI) for predicting deep convective area using the operational global Numerical Weather Prediction model of the Korea Meteorological Administration. Seasonally optimized ACI (ACI_SnOpt) was developed to consider seasonal variabilities on deep convections in Korea. Yearly optimized ACI (ACI_YrOpt) in Part 1 showed that seasonally averaged values of Area Under the ROC Curve (AUC) and True Skill Statistics (TSS) were decreased by 0.420% and 5.797%, respectively, due to the significant degradation in winter season. In Part 2, we developed new membership function (MF) and weight combination of input variables in the ACI algorithm, which were optimized in each season. Finally, the seasonally optimized ACI (ACI_SnOpt) showed better performance skills with the significant improvements in AUC and TSS by 0.983% and 25.641% respectively, compared with those from the ACI_YrOpt. To confirm the improvements in new algorithm, we also conducted two case studies in winter and spring with observed Convectively-Induced Turbulence (CIT) events from the aircraft data. In these cases, the ACI_SnOpt predicted a better spatial distribution and intensity of deep convection. Enhancements in the forecast fields from the ACI_YrOpt to ACI_SnOpt in the selected cases explained well the changes in overall performance skills of the probability of detection for both "yes" and "no" occurrences of deep convection during 1-yr period of the data. These results imply that the ACI forecast should be optimized seasonally to take into account the variabilities in the background conditions for deep convections in Korea.

• 한국항행학회논문지
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• 제28권2호
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• pp.185-192
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• 2024

항공산업은 기술적인 혁신을 통해 안전성을 향상했으며, 항공 당국의 안전 규제와 감독을 통해 비행안전을 강화해 왔다. 항공산업의 안전 접근 방식이 항공기 시스템 전체에 대한 체계적인 접근 방식으로 발전함으로써 항공사는 새로운 안전 관리시스템을 구축하게 되었다. 항공기의 기술적 결함이나 비정상적인 데이터는 사고로 이어질 수 있는 전조 징후가 될 수 있으며, 이러한 징후를 조기에 식별하고 대처함으로써 사고 발생의 위험을 감소시킬 수 있다. 따라서 비정상적인 전조 징후의 관리는 데이터 기반 의사결정을 촉진하고, 항공사의 운영 효율성 및 안전수준을 강화하는 데 있어 필수적인 요소이다. 본 연구에서는 항공기 착륙 시에 활주로 이탈로 이어질 수 있는 크랩랜딩 이벤트의 패턴과 원인 분석을 위한 사전적 분석 단계에서 QAR (quick access recorder) 비행 데이터 통계 분석 모델을 제시하여 착륙 이벤트의 전조 징후와 원인을 식별 및 제거하는 안전관리의 효율성을 제고하고자 한다.

• 한국습지학회지
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• 제16권3호
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• pp.431-440
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• 2014

국내 10개 댐저수지 인공습지를 대상으로 수심분포, 유입량 및 유출량, 물흐름분포, 체류시간, 수처리효율, 종횡비, 개방수역/폐쇄수역 구성비 등 습지의 운영현황 및 구조적 형상에 대한 분석을 통해 인공습지의 수질정화기능을 회복시킬 수 있는 개선대책 및 운영방안을 제시하였다. 조사대상 인공습지의 처리수는 하수처리장 방류수 또는 하천수였으며, 처리수의 수질은 외국의 인공습지에 비해 전반적으로 낮은 것으로 나타났다. 특히 처리수의 BOD는 모든 습지에서 3 mg/L 이하로 매우 낮았는데, 이는 하수처리장의 고도처리 및 평수기 저농도 하천수 취입에 기인된 것으로 판단된다. 수처리효율은 TN이 7.6~67.6%(평균 24.9%), TP가 -4.9~74.5%(평균 23.7%)의 범위로 하수처리장 방류수를 처리수로 하는 인공습지에서 높은 값을 보였다. BOD는 -133.3~41.7% 범위로 습지에 따라 큰 차이를 보였으며, 대부분 습지에서 처리효율이 없거나 낮은 것으로 나타났다. 인공습지의 낮은 처리효율은 습지의 부적합한 종행비, 과도한 개방수역 면적 등의 구조적인 문제와 수위관리 미흡, 초기우수 취입시스템 및 운영관리 미흡, 강우시 모니터링 부재 등의 운영적인 문제에 의한 것으로 나타났다. 그러므로 댐저수지 인공습지가 비점오염 저감시설로서의 역할을 할 수 있기 위해서는 댐저수지 인공습지에 적합한 습지설계 및 운영방안이 필요하다. 또한 습지 운영매뉴얼에 비점오염물질이 유출되는 강우시 모니터링이 반드시 포함되어야 하며, 댐저수지 인공습지의 수처리효율도 강우시 모니터링 자료를 토대로 평가되어야 할 것이다.