Modeling And Analysis Of The Maglev System Of Superconducting Gravimeter

High precision gravimetry is the basis of many natural science research and development,which requires the combination of absolute gravimeter and relative gravimeter to complete the gravimetry and monitoring.As a kind of relative gravimeter,superconducting gravimeter can overcome the shortcomings of traditional mechanical spring gravimeter,such as creep,hysteresis and nonlinearity.The long-term stable and high precision measurement of gravity is realized.There is a wide market demand for superconducting gravimeters,but the commercialization of superconducting gravimeters has not been realized in China.This paper will complete the modeling of superconducting gravimeter magnetic levitation system and use more simple theoretical algorithm to analyze its levitation characteristics,in order to make up for the shortage of domestic research on superconducting gravimeter magnetic levitation system,and provide certain theoretical guidance for the development of superconducting gravimeter.The basic characteristics of superconductors and related theories of electromagnetics are studied,and the structure and working principle of the magnetic levitation system of superconducting gravimeter based on the zero-resistance characteristics of superconductors and Meissner effect are emphatically analyzed.Based on the GWR superconducting gravimeter,the physical model of magnetic levitation system of superconducting gravimeter is established,and the model parameters are given.According to the physical model of magnetic levitation system of superconducting gravimeter,the equivalent current loop method and the superconductor local model theory are respectively used to solve the magnetic levitation force.First of all,the magnetic levitation force is calculated by using the method of equivalent current loop to divide superconducting spheres and combining the superconductor's magnetic flux conservation,"virtual work"principle and linear summation.Then the local model theory of superconductor and the distribution of magnetic field in space of current-carrying coil are introduced.The superconducting sphere is divided into several microelements to establish a mathematical model and to solve the maglev force.Finally,combined with the actual demand in MATLAB to achieve the relevant calculation procedures.Two different methods are used to analyze the stress condition and the correlation error of the single-coil superconducting sphere system,and the difference between the two is compared.Compared with the method based on the local model theory,the equivalent current loop can analyze the suspension characteristics of superconducting spheres more comprehensively.By selecting the equivalent current loop method and the appropriate model parameters,the relationship between the maglev force and the system's geometry and coil current is analyzed in detail,and the important role of the double-coil system in adjusting the maglev force gradient is further explained.The concept of current ratio of upper and lower coils is introduced,and the variation of maglev force and its gradient with current ratio is analyzed.The appropriate model parameters were selected to calculate the maglev force of the coil pair superconducting ball with a mass of m=4.069g:F_total=3.988×10^-2 N,and the maglev force gradient was-9.699×10^-3 N/m.At this time,the maglev force and its gradient required for the measurement accuracy of the superconducting gravimeter were satisfied.