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이종 고분자간 상호작용 기반 계층적 나노섬유 집합체 형성 및 여과 특성 고찰
구은모,오현주,최영옥,이병선 한국섬유공학회 2024 한국섬유공학회지 Vol.61 No.1
Nanofibers with ultrafine diameters (< 50 nm) have been reported to exhibit a significant surface area and a high filtration efficiency. Recently, the ionic surfactants have been used for fabricating nanofibers with ultrafine diameters. However, the use of ionic surfactants is not desirable because of the electrophoretic behavior and following instability of the ions with the high electric potential during the electrospinning process. In this study, hierarchical nanofiber assemblies including ultrafine nanofibers with diameters < 50 nm were designed by utilizing heterogenous molecular interactions of different types of polymers with high dipole moments (polyacrylonitrile (PAN), poly(vinylidene fluoride-cohexafluoropropylene) (PVdF-HFP)), and their filtration performances were evaluated based on EN 143 standard. The fraction of nanofibers with ultrafine diameters was adjusted from 4% to 46%, and the b-phase fraction of PVdF increased from the initial 71.6% to a maximum of 85.37%. Among various PAN/PVdF samples, the PAN/PVdF 3:7 represented the highest efficiency of 87.6% even at low basis weight due to its ultrafine diameter, and all samples demonstrated efficiency exceeding 99.3% as basis weight increased. In conclusion, this study successfully achieved process stability and excellent filtration performance by establishing a method to manufacture hierarchical nanofiber assemblies without the use of ionic surfactants, relying solely on the interaction of heterogeneous polymers.
이주영,구은모,김형주,장기태,LEE, Jooyoung,Gu, Eunmo,KIM, Hyungjoo,JANG, Kitae 대한교통학회 2017 대한교통학회지 Vol.35 No.4
최근 국내에서는 대도시권의 교통혼잡 완화를 위하여 다양한 대중교통 활성화 정책을 시행중에 있다. 특히 대도시권역에서는 버스정보시스템이 도입되어 버스의 현재위치, 도착예정시간 등에 대한 정보를 제공하고 있다. 하지만 복잡한 도시부를 지나는 버스들의 경우 반복적인 교통혼잡과 버스몰림으로 인하여 정확한 통행시간 정보제공 시 정확도를 확보하는데 어려움이 있다. 기존 버스 통행시간 연구는 링크별 소통정보 제공방식으로 인하여 버스 이용자의 경로 통행시간 정보 제공 시 어려움이 있고, 데이터 기반의 단기 통행방식으로 중장기 정보 제공이 어렵다는 한계가 있다. 이에 본 연구에서는 경로기반의 중장기 버스통행시간 예측 방법론에 대한 연구를 실시한다. 이를 위하여 2015년 버스통행정보로 학습데이터, 2016년 자료로 검증데이터를 구성하였다. 학습데이터를 이용하여 버스통행정보를 분석하여 버스통행시간에 영향을 미치는 요인들을 출발시각, 요일, 그리고 기상요인 등으로 분류하고, 이들의 특성 값을 자기조직화지도를 활용하여 비슷한 통행 패턴을 가지는 군집으로 분류하였다. 도출된 군집들을 바탕으로 맑음과 우천시에 대한 요일/출발시각 별 버스통행시간 참조 테이블을 구성하였다. 검증데이터를 이용하여 본 연구에서 도출한 버스통행시간의 정확도를 검증하였다. 본 연구의 중장기 예측 알고리즘을 활용하여 기존의 직관적이고 경험적인 접근법의 한계를 극복할 수 있으며, 예측의 정확도 개선을 통한 버스이용자 만족도 향상 및 탄력적인 대중교통 정책 수립이 가능할 것으로 판단된다. Recently, various public transportation activation policies are being implemented in order to mitigate traffic congestion in metropolitan areas. Especially in the metropolitan area, the bus information system has been introduced to provide information on the current location of the bus and the estimated arrival time. However, it is difficult to predict the travel time due to repetitive traffic congestion in buses passing through complex urban areas due to repetitive traffic congestion and bus bunching. The previous bus travel time study has difficulties in providing information on route travel time of bus users and information on long-term travel time due to short-term travel time prediction based on the data-driven method. In this study, the path based long-term bus travel time prediction methodology is studied. For this purpose, the training data is composed of 2015 bus travel information and the 2016 data are composed of verification data. We analyze bus travel information and factors affecting bus travel time were classified into departure time, day of week, and weather factors. These factors were used into clusters with similar patterns using self organizing map. Based on the derived clusters, the reference table for bus travel time by day and departure time for sunny and rainy days were constructed. The accuracy of bus travel time derived from this study was verified using the verification data. It is expected that the prediction algorithm of this paper could overcome the limitation of the existing intuitive and empirical approach, and it is possible to improve bus user satisfaction and to establish flexible public transportation policy by improving prediction accuracy.
원심력 하에서의 용융금속의 유동 및 응고 특성에 대한 수치적 연구
이진호,목진호,구은모,홍준표,윤웅섭 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.3
A numerical analysis was carried out to predict the defects caused by fluid flow and heat transfer in the casting process under centrifugal force. The VOF method was adopted to deal with the behavior of free surface during filling and the Temperature Recovery method was used to treat the release of the latent heat during solidification. Thermal stresses were calculated by the Finite Element method. For a cylindrical model, two different angular velocities were applied (900 rpm and 1,500 rpm), and the result showed that the intensity of circulating flow was weaker in the case of 1,500 rpm than that of 900 rpm. Solidification proceeded faster in the upper part of the casts due to the thinner thickness caused by the gravitational force. Tensile stresses were distributed along the outer surface of the casts, while compressive stresses were distributed in the inner part.