Studies On Temperature Rise And Levitation Behaviors Of Bulk High Temperature Superconductor Under The Magnetic Field Fluctuation Of Permanent Magnet Guideway

Due to the unique flux pinning characteristics of onboard high temperature superconductors,high temperature superconducting(HTS)flux-pinning magnetic levitation(maglev)has distinct advantages of integration of levitation and guidance,no active control,environmental protection and so on.It is widely considered as an important direction for highspeed maglev in the post high-speed rail transit era.Previous research mostly focused on the levitation forces,guiding forces and stiffnesses of maglev systems.The basic theories of the quasi-static magnetism-force interaction characteristics between the bulk superconductor and the permanent magnet guideway(PMG)have been formed.With the development of research and engineering applications,the internal AC loss and the levitation force fluctuation of the bulk superconductor under dynamic excitations of irregular PMG magnetic field are important phenomena which cannot be ignored in the applications.Based on the background of engineering application,this thesis aims to explore the dynamic internal temperature rise and levitation behaviors of bulk superconductor under the excitation of the PMG magnetic field fluctuation through experiments and simulations.In terms of experimental tests,based on the laboratory-developed HTS dynamic measurement system SCML-03,the amplitude of magnetic field irregularity is artificially changed by improving the PMG.Combined with the self-built temperature rise detection platform,the internal dynamic temperature rise behavior of the bulk superconductor under the PMG magnetic field was tested.And the influence mechanism of different operating conditions(operating speed,operating time,working height and field cooling height)on the internal temperature rise of the bulk superconductor were studied as well.It was found that under the magnetic field environment of PMG,the internal temperature of the bulk superconductor increases rapidly at first and then tends to be stable,and the effect of operating time on the temperature rise behavior is small.And properly increasing the working height and reducing the field cooling height can reduce the internal temperature rise of the bulk superconductor and improve the system operation stability.In the simulation works,a two-dimensional simulation model of electromagneticthermal-force multi-field coupling model of the HTS maglev system was established by coupling PDE module and heat transfer module in the finite element software COMSOL Multiphysics.By establishing the conversion relationship between the magnetic intensity of permanent magnet and its space magnetic field,the simulation of the real magnetic field fluctuation of the PMG was realized,and then the multi-physical coupling model suitable for dynamic operation was improved.Based on it,the influence of the varying magnetic field fluctuation on the dynamic temperature rise and levitation behaviors of the bulk superconductor was simulated and analyzed including different magnetic field fluctuation forms,frequencies and amplitudes.Furthermore,the effect of HTS material parameters such as thickness and critical current density on its dynamic performances under fluctuating external magnetic fields was discussed.The results show that the amplitude of magnetic field fluctuation is an important factor affecting the internal temperature rise and levitation behaviors of the bulk superconductor.Compared with the vertical magnetic field fluctuation,the transverse magnetic field fluctuation has a greater effect on the temperature rise behavior of bulk superconductor.The simulation work verified the relevant experimental results,and also showed that the high temperature superconducting maglev has the potential of high-speed operation.These experimental data and simulation model will provide theoretical references for the optimization design and engineering application of the HTS maglev system.