Dynamic Characteristics Of Triaxial Force Of High Temperature Superconducting Maglev System Under Fluctuating Magnetic Field

With the development of human civilization,in order to achieve a more convenient and efficient way to travel,people study various dynamic technologies,among which the high temperature superconducting maglev train is one of the new technologies that people pay close attention to.In the study of the dynamic characteristics of HTS-Maglev system,the dynamic stability problem caused by the magnetic track inhomogeneity has been paid more and more attention.In the existing HTS-Maglev system,the permanent magnet guideway is composed of neodymium magnet(Nd Fe B)and iron.The isolation layer between the adjacent permanent magnets makes the magnetic field distribution along the magnetic track present nonuniformity.For the HTS-Maglev train running on this kind of track,the non-uniform mag-netic field distribution in the direction of the magnetic track is similar to an alternating external magnetic field applied to the train.When the HTS-Maglev train moves on the permanent magnet track,the onboard HTS bulk will be exposed to the external magnetic field changing with time.Different from the operation in uniform magnetic field,high temperature super-conductor bulks will produce AC loss in alternating magnetic field.This will lead to the increase of temperature,the decrease of critical current density(J_c),the decrease of capture magnetic field and so on.In addition,as a nonlinear dynamic system,the periodic external force exerted by alternating magnetic field will cause a series of complex changes in the dynamic characteristics of HTS-Maglev.In this paper,the three-dimensional dynamic characteristics of YBCO superconducting bulk moving over a permanent magnet track with nonuniform surface magnetic field are studied by establishing a high-precision HTS-Maglev system experimental simulation platform and combining with numerical simulation.By observing and analyzing the dynamic response of HTS-Maglev system under different operating speed,field cooling height and field change amplitude,the dynamic stability of HTS-Maglev system is studied,some non-linear vibration phenomena and their characteristics are observed,as well as the evolution law of the system from periodic vibration to chaotic motion.In the structure of this paper,firstly,the basic theory of superconductivity,the characteristics of materials,and the general situation of the development of HTS-Maglev train are briefly introduced and summarized,and the existing problems are briefly analyzed.On this basis,the research ideas of this paper are put forward.In the second chapter,the research platform,measurement methods and research scheme are introduced.Compared with the previous related research,the research platform of this paper has higher measurement accuracy,and extends from the single measurement of levitation force in the past to the three-dimensional dynamic research at the same time,significantly expanding the scope of research,which provides favorable conditions for deepening the dynamic research of HTS-Maglev and further clarifying its regularity.This paper introduces the dynamic analysis of the system in small wave field.Under the condition of not covering the iron sheet,using the tiny magnetic field fluctuation of the permanent magnet track itself to set different field cooling height,external magnetic field changing frequency and unified working height,using the timedomain method,frequencydomain method and chaos kinematics to analyze the dynamic characteristics of the levitation force on the YBCO bulk,and get the best operating conditions and optimal operation Programme.Combined with the dynamic analysis of small wave field,a huge magnetic field wave is produced by superposing iron sheets.Under the large wave changing magnetic field,different field cooling height,changing frequency of external magnetic field,different iron sheet thickness and unified working height are set.The dynamic characteristics of threeaxis force on YBCO bulk are analyzed by time-domain method,frequency domain method and chaos kinematics Its motion law under the change of huge magnetic field gradient,the difference between its dynamic characteristics and that under the small wave magnetic field are analyzed,and the optimal operation conditions and motion scheme are summarized.Finally,by combining the experimental research results of the third and fourth chapter,the relevant mathematical model and the motion simulation equation of YBCO superconductor bulk are established.Different external magnetic field change amplitude,external magnetic field change waveform and different system operation speed are set up to simulate the motion law of HTS-Maglev system,and compared with the results of the first two parts,the operation rules of the system are summarized law.