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A study on the optimum design of high-speed low-floor bogie with independently rotating wheels
정낙탁,최성욱,이호용,백건희,한석윤,김원경,서명원 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.5
The low-floor bogie is a prior technology in countries and companies that want to develop the tram. The Low-floor tram (LFT), which includes low-floor bogies, is easy to embark and disembark because of the low floor height. In addition, it can be driven on urban as well as rural tracks. Furthermore, emissions such as NOx and SOx can be reduced. Due to these advantages, this innovative technology is expected to change the public transport system. To improve utilization in a downtown area, the technology for the low-floor bogie should satisfy conditions of a high-speed of over 80 km/h and minimum radius within a 25 mR curve for smooth running on a track that has a severe turning radius. Moreover, the wheelset should not be located in the bogie, and the components inside the bogie need to be wellarranged to satisfy the full low-floor condition. In this study, to develop an over-80 km/h class high-speed low-floor bogie that can be driven safely on a 25 mR curved track, a conceptual design of the LFT multibody dynamics model was constructed and dynamic characteristics were assessed by dynamic analysis. The modeling modification with Independently rotating wheels (IRW) needed to steer actively through semi-active suspension and the optimization using Design of experiments (DOE) were then performed. Through DOE method, the optimum combination of design parameters could be obtained and, the driving performances such as ride stability, comfort and safety of the LFT could then be improved about 7 %. The results of this work are available to detail design and development of LFT.
A Study on the Numerical Methodology for a Structural-safety Evaluation of Cable Braided Layer
정낙탁,서명원,권지운 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.3
The mechanical behavior of industrial cable with braided layer was investigated by a coordinated modeling and experimental effort and both results are compared for validation of newly developed finite element (FE) modeling. The feasibility of this FE model was verified by comparison with actual mechanical tests. FE model was firstly established and the specific torsional loading was applied to test specimens by utilizing a special test apparatus. After the above processes, the experimental and numerical results were successfully correlated. Finally, the constitutive behavior of braided layer was understood under mechanical loading and as a result, this research can improve the reliability of braided layer which is one of the critical components of the industrial cable.
정낙탁(Nak-Tak Jeong),양성모(Seong-Mo Yang),김광섭(Kwang-Seup Kim),이슬기(Seulgi Lee),신희진(Heehin Shin),김현수(Hyunsoo Kim),서명원(Myung-Won Suh) 한국자동차공학회 2014 한국자동차공학회 부문종합 학술대회 Vol.2014 No.5
Recently, due to various environmental problems such as global warming, increases of international oil prices, exhaustion of resource and so on, a paradigm of world automobile market is rapidly changing from internal combustion engine to eco-friendly vehicles using electric power such as EV (Electric Vehicle), HEV (Hybrid Electric Vehicle), PHEV (Plug-in Hybrid electric Vehicle) and FCEV (Fuel Cell Electric Vehicle). However, there are many driving cycles for performance evaluation of conventional vehicles but, there is a lack of researches on driving cycle for EV. In this study, in order to develop urban driving cycle for performance evaluation of electric vehicles, Gwacheon-city patrol route of police patrol car was selected, actual driving test was performed using EV. The driving data such as velocity, time, GPS information etc. was recorded. Through the analysis results of recorded data, GUDC-EV (Gwacheon-city Urban Driving Cycle for Electric Vehicles) including road gradient was developed.
Loosening mechanism of threaded fastener for complex structures
백건희,정낙탁,홍희록,최수빈,이은성,김형민,권지운,송석용,장홍석,이호용,서명원 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.4
Threaded fasteners are widely used in mechanical structures primarily owing to their easy disassembly for maintenance and low cost. However, the loosening mechanism of threaded fasteners due to dynamic loading has remained unclear for the past six decades. Current researches on complex structures comprising three or more components are insufficient. The two most common failure modes of threaded fasteners subjected to dynamic loading are fatigue and vibration-induced loosening. This study focuses on the failure of threaded fasteners by vibration-induced loosening due to dynamic shear loads. This study comprises experimental analysis and numerical analysis. The loosening mechanism of threaded fasteners for complex structures is analytically and experimentally identified. This work provides the equations and assessment method for the loosening, and the criteria of primary and secondary loosening are established. To verify the proposed loosening mechanism, tightening and loosening experiments are conducted for three types of bolted joints. The primary and secondary loosening forces of each bolt are thus obtained, and the proposed loosening mechanism can be verified for complex structures. In numerical analysis, a three-dimensional finite element (FE) model for tightening and loosening analysis is proposed. A FE model is used to study the loosening process which is characterized by a decline of the preload and moving distance for predicting loosening states. The model seems to be well agreement in comparison with theoretical and experimental results. As a result, the assessment method shows good performance in predicting loosening state. It is expected to verify the safety of bolted structures at the design stage. The FE model is expected to be used for the effective and safe design for joint components in various industrial fields such as wheel assemblies and other mechanical components under dynamic vibration.