Experimental And Theoretic Investigations On The Nonlinear Dynamic Properties In High-Temperature Superconductors Levitation System

Levitation system is composed of high-temperature superconductors(HTSs)and permanent magnets with large levitation force,strong stability and no external energy input,has wide application prospect in energy,transportation,and materials science and other fields.The investigations of the interaction force between superconductor and permanent magnet and levitation system dynamic response characteristics is the cornerstone of security design.Now many studies on the quasi static levitation force system,part of the theoretical studies on dynamic characteristics under periodic excitation response,but the nonlinear motions caused by strong excitation such as chaos,bifurcation and so on are not involved,in particular the studies on the superconductor temperature change in the process of movement caused by energy loss has not been involved.From the point of view experimental investigation,the main difficulty is that when the levitation system show the bifurcation,chaos and nonlinear characteristics the superconductor surface temperature of multi-point real-time measurement limited by space in the low temperature,electromagnetic interference and other factors.From numerical simulation,high-temperature superconductors and permanent magnets relation strong nonlinear,superconducting materials and electromagnetic constitutive relation also strong nonlinear,superconducting material surface thermal diffusion process is strong nonlinear characteristics and coupling with the levitation dynamic equations of motion,which brought greater difficulty to solve the problem.In this doctoral dissertation,experimental and theoretical study the levitation system nonlinear motion in the external excitation,developed a real-time measurement system test superconducting material surface temperature and magnetic field.Experimental measurements levitation force characteristics and surface magnetic field and temperature characteristics in dynamic movement process.On the basis of the research work of the group completion the numerical solution procedure by add the temperature diffusion equation and to verify.Finally,experimental analysis of the crack tip current intensity factor ?-1? power in the superconductor,provides a basis for the study of the electromagnetic force and deformation characteristics of superconducting materials with cracks.Designed a HTSs levitation dynamic testing system with cantilevers.Main functions include: real-time measurement magnetic levitation force,levitation time response measurement,real-time measurement external excitation amplitude and multipoint real-time measurement the superconductor surface temperature.The system force resolution is mN order of magnitude,the temperature and displacement measurement accuracy is ±0.1K and ±5?m.According to different initial field cooling height and the vibration frequency or amplitude,obtain four types of nonlinear movement: period-doubling bifurcation motion,chaos movement,4th period-doubling and beat phenomenon.The permanent magnets diameter changes effect on surface temperature of superconductors in the process of the levitation dynamic movement.The temperature of superconductor jump in the bifurcation movement and the temperature jump amplitude is much greater than the critical temperature.Secondly,numerical simulate HTSs maglev system nonlinear motion.Calculate the HTSs electromagnetic field and temperature by the finite element method,solve the system nonlinear movement,then verify the accuracy of the program.Consider with and without temperature influence in period-doubling bifurcation motion,analysis of the bifurcation motion with magnetic instability phenomenon.Analysis the relationship between macro bifurcation in system and micro flux motion in superconductor.Finally,analysis of crack in superconductor effect on magnetic field and current distribution.The group has been focused on the theoretical analysis of the critical current distribution characteristics of the crack tip in the superconductor,considered the crack is in the center of the superconductor,which was difficulty to the experimental study.Therefore,this paper considers that the crack is at the edge of the superconductor,the critical current distribution of the crack tip is singular and the order of singularity is still ?-1?.In the superconductor surface,arranged 16 probes real-time measurement of the magnetic field around the crack in the field cooled magnetization process,calculated the current distribution around the crack with superconductor multi-point thermal magnetic testing system,the experimental results show that the critical current distribution of the crack tip is singular,and the order of singularity is ?-1.37?,analysis the difference between the theory and the experiments.