Study Of Levitation Force Charactericstics Of High-T_c Superconductor Bulk Over Permanent Magnetic Guideways By Experiment And Simulation

The discovery of high-temperature superconductors (HTS) in 1986 and YBCO in 1987 made HTS operable at temperatures within the cooling capabilities of liquid nitrogen. Ever since, many scientists have expressed great interest in HTS phenomena and its potential applications and have done a lot of research, for example, YBCO can be argued to be the most studied material in the world. Hence, performance in HTS is constantly improved, making its applications in engineering easier and more realistic. Given the fact that HTS, more specifically YBCO bulks, have a strong flux pinning effect, the stability of the its levitation above a permanent magnet (PMG) can be achieved without any complex control systems making bulk superconductors have great potential. Our research group has performed a lot of research on HTS maglev vehicle systems and was successful in developing the first man-loading HTS maglev test vehicle in Dec 31, 2000.In order to promote the application of the HTS maglev vehicle system in engineering applications, a 3D-modeling numerical solutions of electromagnetic behavior of HTS bulk is given in this thesis. In this 3D-modeling, the virtual conductivity method is used; two virtual superconductors were taken in nestification to simulate the anisotropic property of the current density in the interior of the HTS bulk. The magnetic flux density on two different types of PMG were calculated and analyzed with this method. Iteration methods were used to resolve the nonlinear coupling problem. The resolved code of the 3D-modeling of the HTS Maglev was developed using the FORTRAN language. The results of the work presented provide important scientific theories for the optimum design and numerical simulation of HTS Maglev vehicle systems.The magnetic behavior of an HTS bulk over a symmetric PMG was computationally simulated with the mentioned 3D-modeling. The results show that the component of the magnetic field, H_z, is not equal to zero because of the terminal-face affection of the limited size of the HTS bulk even though the component of H_z of the external magnetic field generated by the PMG does not exist. This simulation result is different than most HTS maglev magnetic behavior over a PMG in 2D-modeling from other reports.The magnetic levitation behavior of the HTS bulk over the symmetrical PMG and a PMG with a Halbach array was studied by numerical simulation and experimental methods. The relationship of the magnetic levitation curve of the HTS bulk with the lateral displacement over the symmetrical PMG and the Halbach PMG was investigated. The relationship of the maximum value of the magnetic levitation of the HTS bulk over the two types PMG with the lateral displacement is also was studied. The experimental and computational results are in good agreement with each other.Furthermore, influences of the symmetry geometry and physical parameters of the HTS maglev system to the magnetic levitation behavior was studied by 3D-modeling numerical simulation. For a symmetrical PMG, the behavior of the magnetic levitation is enhanced with the increase of the height and width of the PMG For the Halbach PMG, the behavior of the magnetic levitation of HTS bulk is complicated. The enhancement of the magnetic levitation of the HTS bulk not only depends on the proportionality of the main permanent magnet's (PM) width with the PM assembly but also depends on the proportionality of the main PM width with the height of the PMG There is strong correlation between the magnetic levitation behavior of the proportionality of the main PM with the width assembly and the proportionality of the main PM width with the height of the PMG When the above mentioned proportionalities are kept constant, an increase of the cross-sectional area can enhance the magnetic levitation behavior to within a certain range.The magnetic levitation curves of the HTS bulk over the symmetrical PMG and the Halbach array PMG are calculated with 3D-modeling at different critical current densities. The simulation results show that the critical current density can improve the magnetic levitation force, but it is also tightly related to the external magnetic field. Simply improving the critical current density of the HTS samples may not always optimize the magnetic levitation behavior of the HTS maglev system.