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RISS 인기검색어
- 검색키워드
- 저자 : Dongfang Ma (검색결과 3 건)
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Recognition of Critical Links for Gating Using Queue Detector Data
Dongfang Ma,Fengjie Fu,Sheng Jin,Fujian Wang,Hong Liu 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.7
This paper introduces the concept of rolling time occupancy, and presents a method for recognizing critical links for gating, where spillovers will occur or have done already. The key idea of this new method is that, when the queue length becomes sufficient for the end of the queue to approach the queue detector, the speed of vehicles arriving from upstream will be slower than the free flow speed, which implies that a series of rolling time occupancies will all be greater than a particular threshold. Given that the value of a single rolling time occupancy is strongly influenced by buses and other confounders during a minor time interval, the new criteria for critical link identification are divided into two parts: the occupancy threshold for possible congestion, and the number of rolling time occupancies for inevitable congestion. Next, this paper presents the relationship between queue length and rolling time occupancy, using traffic data procured using VISSIM simulations. On this basis, the queue length threshold at which a spillover can be judged to be going to occur or to have already occurred is determined. Finally, using the misjudgment ratio and the trigger postponement amount as evaluation indices, the method proposed in this paper is evaluated under ten different simulation conditions. The results show that the maximum and average misjudgment ratios are 32.32% and 10.11%, respectively; meanwhile, the average postponement amount is less than 50 seconds for all ten simulation conditions.
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Identification of Spillovers in Urban Street Networks Based on Upstream Fixed Traffic Data
Dongfang Ma,DianHai Wang,YiMing Bie,Sheng Jin,Zhenyu Mei 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.5
This paper presents a method to identify spillovers based on upstream fixed detector data, using occupancy per cycle as thedetermination index. The key idea of this new method is that when the queues extend to the detector position, there will be unusablegreen time to a certain degree, and the occupancy will be greater than a particular threshold. Firstly, this paper introduces traffic wavemodels modified by a kinematic equation, and provides a calculation method for the occupancy per cycle under different trafficconditions, based on the relationship between the three basic traffic flow parameters, speed, traffic flow, and density. Secondly, thethreshold of occupancy, which characterizes the appearance of spillovers, is determined by the premise that the stopping and startingwaves have the same speed, and then the accuracy of the new method are verified by VISSIM simulation, using the ratio ofmisjudgment as the evaluation index. Finally, the precision stability of the method is analyzed, and the results show that the precisionof this method is affected by the the detector location and bus ratio insignificantly.
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Influence of compressor’s tilt angle on the performance of miniature refrigeration system
Xia Chen,Yuting Wu,Chongfang Ma,Chunxu Du,Rui Ma,Dongfang Wang 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.1
Vapor compression refrigeration is considered as ideal miniature cooling system for miniature electronic systems and portable cooling systems. Many applications of the miniature refrigeration system are working under the situations (such as aviation field, individual combat system and automobile air conditioning, etc.) that exist bump, tilt, and even flip, which will severely degrade the performance of the miniature refrigeration system. In order to study the influence of compressor’s tilt angle on refrigeration system, a test bench was built and the performance experiments were made. The results show that the compressor’s tilt angle has a great impact on the refrigeration system performance. When the compressor worked at the maximum tilt angle of 60°, COP-c and COP-h of the system change periodically. When the compressor works in full load, the maximum tilt angle for compressor is 20°. When the compressor tilt angle is 15°, there is an optimal amount of refrigerant charge, and corresponding COP-c and COP-h reach the maximum of 2.9 and 3.9, respectively.
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