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Jia Long,Zixu Miao,Huihuang Chen,Rongdong Deng,Weiran Zuo,Bao Guo,Jiangang Ku 한국자기학회 2020 Journal of Magnetics Vol.25 No.1
Chain-like and diamond-shaped magnetic particle agglomeration (MPA) commonly forming in a weak magnetic field are simulated based on the finite element method (FEM), and the effects of particle diameter, magnetic field strength, particle relative magnetic permeability, and particle number in magnetic particle chains (MPCs) and diamond-shaped MPA on the strength of MPA are analysed in detail. The results show that magnetic forces on the centre contact points (CCPs) of MPA are positively correlated with the particle diameter, magnetic field strength, particle relative magnetic permeability, and particle number. In addition, the forces on the CCPs of the MPCs (N=2) have a square relationship with the particle diameter and magnetic field strength and have a power relationship of 1.25 with the particle relative magnetic permeability. The forces on each contact point decrease slowly from the centre to both ends in the MPCs and then rapidly decrease to one value (approximately 0.779 times the forces on the CCPs). As for the diamond-shaped MPA, with the increase in the angle α between the magnetic field and axis of diamond-shaped MPA, the force magnitude of the particle entrained parallelly in the diamond-shaped MPA shows a trend of a “cosine curve” shape and the minimum value is 2109 times that of the entrained particle’s gravity. The angle θ between the direction of the force and the negative X-axis shows a trend of a “sine curve” shape. When α = 25° and 155°, the angle θ of the force on the entrained particle reaches an extreme value, that is, θ = 21.87°. Only if the angle θ reaches 30º can the particle entrained parallelly escape from the diamond-shaped MPA. Thus, the diamond-shaped MPA remains in a stable state and it is difficult to disperse MPA by changing the direction of the magnetic field.
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A Generalized Markov Chain Model for IEEE 802.11 Distributed Coordination Function
( Ping Zhong ),( Jianghong Shi ),( Yuxiang Zhuang ),( Huihuang Chen ),( Xuemin Hong ) 한국인터넷정보학회 2012 KSII Transactions on Internet and Information Syst Vol.6 No.2
To improve the accuracy and enhance the applicability of existing models, this paper proposes a generalized Markov chain model for IEEE 802.11 Distributed Coordination Function (DCF) under the widely adopted assumption of ideal transmission channel. The IEEE 802.11 DCF is modeled by a two dimensional Markov chain, which takes into account unsaturated traffic, backoff freezing, retry limits, the difference between maximum retransmission count and maximum backoff exponent, and limited buffer size based on the M/G/1/K queuing model. We show that existing models can be treated as special cases of the proposed generalized model. Furthermore, simulation results validate the accuracy of the proposed model.
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Novel magnetorheological brake with self-protection and water cooling for elevators
Hui Huang,Shumei Chen,Kaifeng Chen 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.5
This study aims to design a magnetorheological (MR) brake with self-protection and heat dissipation functions for elevators. Using permanent magnet system technology, the MR brake can not only form a double magnetic field with excitation coils to improve braking torque under normal operation but also provide braking torque for protection in case of power failure. In addition, a cooling channel is designed in the braking shaft of the MR brake to ensure effective heat dissipation of the MR fluid. In this work, the structure, material, and magnetic circuit of the MR brake is first developed. Then, finite element, magnetic field, and thermal field analyses are conducted on the brake. Finally, a prototype of the brake is produced, and its performance is tested. Results show that the braking torque, especially the self-protection function, meets the demands of the elevator; the increase in temperature during braking is minor; and the noise level is low .
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