Three-Dimensional Model Of High Temperature Superconducting Magnetic Levitation And Associated Numerical Investigation

Theoretical studies on high temperature superconducting (HTS) magnetic levitation (MagLev) are no longer limited to two-dimensional, axisymmetic, or three-dimensional (3D) cases, for which the latter one yields results that, are closer towards practical applications. The present 3D model neglects the electromagnetic (EM) anisotropy phenomena found present in high temperature superconductors (HTSC) and involves too many simplifications when taking this phenomena into account thereby lacking in the total understanding of the EM properties in HTSCs. Therefore, more effort should be done to further improve the theoretical studies of HTS MagLev.In this thesis, a current vector potential was introduced to establish the 3D EM governing equations of the HTSC on the basis of Maxwell's equations and the anisotropy of the resistivity in the HTSC combined with the EM constitutive relations of the HTSC. In order to take the thermal-magnetic coupling problem into account, a thermal governing equation was also presented. To numerically solve the governing equations, finite element method via Galerkin's method and finite-difference method via Crank-Nicolson-θmethod were employed, respectively, to implement the study of space discretization and time discretization. Moreover, to simulate the aperture between adjacent permanent magnets composing the Permanent Magnet Guidway (PMG), a 3D analytical model of the PMG was also performed based on the surface current model.To confirm the validity of the above-mentioned theoretical model, the numerical and experimental results under different movement types were discussed and compared in detail such as:Zero Field-Cooling (ZFC), Field-Cooling (FC) with levitation and suspension in translational symmetry and ZFC in axisymmetric applied fields under vertical movement; ZFC, identical Field-Cooling Height (FCH) and Levitation Height (LH) and suspension under transverse movement; and the relationship between levitation force (LF) and running time under longtitudinal movement, and the results indicated that the proposed 3D theorectical model is valid to describe the EM interaction between HTSC and applied field. Based on the above-mentioned analysis, the levitation performance of the HTS MagLev under 3D movement was theoretically investigated.For movement along the vertical direction, the performance of LF under different operating conditions, applied field structures, material properties and geometries were firstly analyzed, and then the relaxation characterstic of LF and associated rules of the various influencing factors were discussed, and the conclusion that, LF can be improved and the force decay can be suppressed by enhancing the material property or lowering the operating temperature of the HTSC, were derived. In the end, it is theoretically proved that pre-loading is an effective approach to reduce the force decay during relaxation, and then the stability of the levitation system can be improved by this approach.For movement along the transverse direction, the performance of the magnetic force under differenet operating conditions, maximum lateral diaplacements, material properties and geometries were firstly analyzed, and then the critical FCH problem of the HTSC was discussed, and we found that the critical FCH decreases with the increase of the LH, improvement of the material property as well as decrement of the the operating temperature. Subsequently, a minimum energy method to evaluate the restorable characteristics of a levitated body during transverse movement was proposed. Lastly, the changing trendency of the LF and guidance force under different operating conditions during continuous transverse movement was thoroughly studied. Furthermore, theoretical verification of pre-loading which is considered to be effective to reduce LF decay due to transverse movement was achieved.For movement along the longitudinal direction, two different appliacable fields were considered, MagLev launch and MagLev rail transit. For the MagLev launch application, the main aspects studied included the influence of the aperture of the PMG, exit velocities and operating temperatures on the LF and the changing rule of Maximum Temperature Raise (MTR) under different exit velocities and operating temperatures. For the MagLev rail transit application, the changing tendency of the LF under different FCHs, LHs, velocities and operating temperatures was calculated, and the velocity and operating temperature dependence of the MTR in the HTSC were also monitored. The results showed that, for any application, lowering the operating temperature of the HTSC can suppress not only the LF decay but also the temperature raise during the longitudinal movement. In addition, we also found that, the drag-to-lift ratio of levitated body is small, and this is beneficial for the application the HTS MagLev in the high-speed field.