Vibration Characteristics Analysis of Rotor System with Permanent Magnet Drive Considering Misalignment and Unbalance

Abstract

Misalignment and unbalance are two major mechanical faults in rotating machinery. In recent years, with the increasing application of permanent magnet coupling in rotating machinery, it is necessary to study the misalignment and unbalance of rotor system with permanent magnet drive. In this paper, the vibration characteristics of centrifugal pump rotor system driven by asynchronous disc permanent magnet coupling（ADPMC）considering misalignment and unbalance faults will be discussed. First, the three-dimensional models of ADPMC with axial and radial misalignments are established respectively, and the axial and radial unbalanced magnetic pull of ADPMC are solved. Second, the axial force of angular contact ball bearing and radial force of cylindrical roller bearing are calculated under different operating conditions. Further, the radial support stiffness of each bearing is obtained. Third, the modal analysis of rotor system driven by ADPMC is carried out to obtain the natural frequencies and modal shapes. Finally, the radial unbalanced magnetic pull of ADPMC and unbalanced force caused by mass eccentricity of impeller are taken as the excitation sources, and the harmonic response of rotor system are calculated. The results show that the axial misalignment of ADPMC will cause a larger unbalanced magnetic pull, and the radial misalignment of ADPMC will lead to a smaller unbalanced magnetic pull. When ADPMC has different misalignment faults, the natural frequencies of same modal order of rotor system are basically the same. In the vicinity of the operating frequency, the vibration displacement at two journal of the rotor system excited by dual excitation sources are both small. Therefore, large radial misalignment of ADPMC can be allowed in rotor system, and ADPMC has good vibration isolation characteristics between the driver shaft and the driven shaft. The results provide important engineering references for the application of ADPMC in rotating machinery.