Applicability Research On Different Constitutive Laws Of High Temperature Superconductor In High Speed Maglev System

The high temperature superconducting（HTS）maglev has received wide attention since its birth due to its advantage as self-stabilization and free of active control,etc.However,for the limitation of experimental conditions and methods,it is difficult to analyze the correlation among complex physical phenomena and parameters,which makes numerical calculation and finite element simulation an important means to study the electromagnetic properties of HTS bulks.And the most important issue in the calculation of the HTS maglev system is to select an appropriate E-J electromagnetic constitutive law of the superconductor.Therefore,in an attempt to reveal the impact of the constitutive law selection on the numerical modeling and analysis of the electromagnetic properties of HTS maglev system,this thesis studied the accuracy and rationality of different E-J material laws with an eye on the application of high-speed HTS maglev.Based on the finite element software,COMSOL Multiphysics,considering the heat exchange between the liquid nitrogen environment and the HTS bulks,a two-dimensional model of electromagnetic-thermal-force multi-field coupling model of HTS maglev system was constructed.And high-speed dynamic operating conditions can also be realized.On the basis of this simulation model,combining with related experimental data,the impact of the relationships between temperature or magnetic field and the critical current density was discussed.And results showed that,from a qualitative point of view,although all different relations can reflect the electromagnetic characteristics of superconductors to some extent.However,from the point of view of accuracy,it is suggested to consider the effect of temperature and magnetic field on the critical current density simultaneously.Or the effect of temperature can be ignored when the temperature change of the bulks is negligible.Furthermore,for the PMG-YBa Cu O HTS maglev system,the appropriate range of values of the material parameter B₀ in different J_c（B,T）relationships was suggested.On the basis of the reasonable selection of J_c（B,T）relationships,three different E-J electromagnetic constitutive laws are further discussed in this thesis,including the power law model（PLM）,the flux flow model（FFM）and the flux flow and creep model（FFCM）.Also,the related parameters of these constitutive laws are discussed.The results show that the PLM and the FFCM are consistent and the performance of PLM is better in terms of computational efficiency.While the FFM are not able to accurately reflect the dynamic characteristics of the HTS bulks.And the computation time of the FFM is always the longest.This thesis further studies the dynamic properties of HTS bulks above the Halbach array permanent magnet guideway under ultra-high-speed dynamic operating conditions,which verifies the high-speed and ultra-high-speed operation potential of the HTS maglev.