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        Discrete theory of rolling elements for a cageless ball bearing

        Yanling Zhao,Qiyu Wang,Mingzhu Wang,Chengyi Pan,Yudong Bao 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.4

        For the case of magnetic levitation loss, the rotor of an active magnetic bearing is forced by gravity to drop onto stator laminations, and cageless touchdown bearings with high rigidity and load-bearing capacity ensure back-up support. However, the contact collision of rolling elements in a cageless bearing will lead to deterioration of bearing performance and instability of the rotor system. For this purpose, a method based on noncontact between adjacent rolling elements in cageless bearings is proposed in this paper. First, combined with space geometry, the contact process and the change in radius of rotation when a rolling element passes through a discrete groove are analysed, and a clearance between the adjacent rolling elements is generated by changing the rotation speed. Based on this, a design principle for setting a discrete groove on an outer ring raceway is proposed, and the equation for the circumferential discrete clearance for the rolling element based on bearing kinematics is given. Combined with the characteristics of discrete groove structures, a differential equation for the discrete dynamics of rolling elements with variable stiffness coefficients is proposed. We then determine the influence of the discrete groove structure on the discrete motion of the rolling element and bearing dynamic characteristics. Third, the dynamics simulation is combined with a vibration characteristics experiment and discrete motion experiment for a rolling element in a cageless bearing. Our research results show that a discrete groove design for the raceway can be used to realize stable discrete motion of the rolling element, and that such a discrete groove structure will not adversely affect the vibration characteristics of the bearing. The feasibility of the discrete design of cageless bearings with rolling element is verified, and theoretical guidance for the development and application of cageless bearings is provided.

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        Impurity Behaviors under Wall Conditioning in HL-2A

        Zhengying Cui,Chenghe Cui,Mingxu Wang,Ping Sun,Quanming Wang,Wei Li,Yudong Pan,Zeng Cao 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III

        Impurities are one of the key issues of tokamak plasma research, as they are directly related to plasma quality and steady-state operation. The HL-2A device with two close divertor is the first divertor tokamak in China. It was successfully constructed in 2002 and has been operated for three 3 years up to now. In the 2004 campaign, siliconization as a wall conditioning was first done on the HL-2A tokamak by using glow discharge cleaning (GDC) with a gas mixture of SiH4 + He. The effects of siliconization on impurities and recycling are investigated, as well as the lifetime of siliconization, in this paper. The intensity of oxygen line is remarkably decreased after siliconization. Radiation of silicon line rapidly decreases shot by shot just after siliconization, but the effect of siliconization on the plasma properties is present all along and decreases gradually for a large amount of discharges. The effect of the siliconization can be maintained to about 180 discharges with similar discharge parameters.

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