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우회전 상황 하에서 보행자 횡단 정보제공으로 인한 안전성 효과
류민환,김병철,김홍균,김도경 한국도로학회 2023 한국도로학회논문집 Vol.25 No.3
PURPOSES : This study aims to evaluate the traffic safety by collecting and analyzing vehicle speed and conflict frequency data based on the provision of information to vehicle drivers and crosswalk pedestrians under right-turn conditions. METHODS : Two evaluation scales, namely speed of access and number of conflicts, were used to quantitatively evaluate the effects of the new information provision method. Data on access speed and the number of conflicts according to information provision were collected and compared before and after information provision. RESULTS : Analysis of the pre- and post-spot speed reduction rates revealed an overall reduction rate of 32.6%. The conflict ratio was 81.0% before information provision but increased to 83.3% after information provision. CONCLUSIONS : When LED display information was provided, the effect of decelerating the approaching speed of vehicles in the rightturn torpedo section was statistically significant, but the reduction in the conflict ratio was not. Factors such as intersection status, traffic volume and vehicle speed, affect the approach speed and increase or decrease the number of conflicts. Regardless of whether information is provided, the average compliance rate of the Road Traffic Act when turning right in the channelization area is 16.7%, which is significantly different from the average compliance rate of 48.4% immediately after the Road Traffic Act was revised in July 2022.
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중도절단 자료를 포함한 서울시 장애인콜택시 대기시간의 시공간적 영향요인 분석
손종훈,류민환,김도경 한국도로학회 2022 한국도로학회논문집 Vol.24 No.3
PURPOSES : The objective of this study is to investigate the spatiotemporal factors influencing the waiting time of special transportation systems for disabled people in Seoul, Korea. METHODS : A parametric survival analysis was employed to identify the primary factors influencing longer waiting times, primarily because censoring data were included in the analysis. For the analysis, one-year historical data collected from the Seoul Call-taxi for the disabled in 2019 were used. Using normal probability plots and Anderson-Darling statistics, a log-normal model was estimated to fit the data. RESULTS : In terms of time, there was a time zone in which the service level in terms of waiting time, such as late-night and dawn, decreased depending on the time of day called by call taxi users with disabilities in Seoul. Moreover, the waiting time on weekends was shorter than on weekdays. Spatially, when a user requests a service, there are many nearby vehicles when the traffic conditions nearby are good, and the waiting time tends to decrease near the depot. CONCLUSIONS : The existing system needs to reflect the increase in vulnerable times and the improvement of the dispatch method, considering the difference in the primary purpose of travel on weekdays and weekends. Additionally, to resolve the phenomenon in which vehicles are concentrated in a specific area, waiting time can be improved using operational strategies that can uniformly distribute vehicles in space, such as spatial subdivision of depots, real-time monitoring, and relocation.
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김성진,최정후,김민희,류민환,박재현,신재혁,신우철,김민욱,정재길,이석재 한국열처리공학회 2024 熱處理工學會誌 Vol.37 No.4
SCr420H steel which is commonly utilized for automotive components requires the carburizing heat treatment process. Abnormal grain growth during this treatment significantly affects the mechanical properties of the steel parts. Consequently, a process designed to prevent abnormal grain growth at certain elevated temperatures is essential. For enhanced grain refinement, we considered the addition of Nb in SCr420H steel. The experimental condition of the carburizing heat treatment involved reheating the steel sample to temperatures between 940oC and 1080oC. Using scanning electron microscopy, we examined the microstructure of specimens treated with the secondary solution, revealing an organization of bainite and ferrite. Transmission electron microscopy was utilized to determine the type, shape, and size of the carbonitrides, showing a high fraction of AlN at the secondary solution treatment temperature of approximately 1050oC and of (Nb,Ti)(C,N) around 1200oC. AlN particles measured about 100 nm and (Nb,Ti)(C,N) about 50 nm. Optical microscopy was utilized to assess grain size variations at different secondary solution treatment temperatures. It is noted that the temperature at which abnormal grain coarsening occurred rose with increasing secondary solution treatment temperatures, indicating a greater influence of (Nb,Ti)(C,N) with higher heat treatment temperatures. This research provides reference data for preventing abnormal grain growth in Nb-added low alloy steels undergoing carburizing heat treatment.
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SCR420H강의 미세조직과 결정립 조대화에 미치는 Ti 첨가 영향
최정후,김성진,김민희,박재현,신재혁,류민환,신우철,김민욱,이석재,정재길 한국열처리공학회 2024 熱處理工學會誌 Vol.37 No.4
SCR420H steel is a low-carbon chromium alloy steel designed for carburizing heat treatment. Recently, research is being conducted on high-temperature carburization heat treatment to reduce costs and CO2 emissions by shortening the carburization time to meet the international carbon neutral policy. However, this high-temperature carburization heat treatment coarsens the steel grains and causes a decrease in mechanical properties. In this study, a large amount of Ti was added to increase the grain refinement effect in the high-temperature carburizing process. We investigated the microstructure and precipitates of SCR420H steel without Ti (Al steel) and with Ti (AlTi steel). Thermodynamic calculations showed that the AlN and (Ti,Nb)(C,N) precipitated in Al steel, while (Ti,Nb)(C,N) and Ti4C2S2 precipitated in AlTi steel. Addition of Ti increases the fraction of bainite after reheating process. Transmission electron microscopy analysis shows that small amounts of AlN and (Ti,Nb)(C,N) precipitates are formed in the Al steel. The addition of Ti increases the density of (Ti,Nb)(C,N) precipitates and induces the formation of Ti4C2S2 precipitates, increasing the grain coarsening temperature (GCT) under all heat treatment conditions. Higher reheating temperatures also resulted in higher GCT values due to increased precipitation.
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