| With the rapid development of technology and economy,the “post high speed rail era” is about to emerge.Facing higher speed requirements in the next high speed rail era,high temperature superconducting(HTS)maglev has received a wide attention on its principle merits,such as levitation-guidance integration,passive self-stability,potential faster running speed,low energy consumption,friendly to environment and so on,comparing with many other rail traffic technologies.And the optimization of its levitation and guidance performances has been carried out in full swing.Among all of the optimization schemes,combining with the evacuated tube technology(ETT)is doubtlessly one of the most innovative and promising schemes.The HTS maglev-evacuated tube transport(HTS maglev-ETT)technology,which is born in the combination of the HTS maglev and the ETT,provides a new selection of solution for realizing the proposition of higher ground speed.Therefore,based on the engineering application of the HTS maglev-EET system,this thesis researched and clarified the influence of environment air pressure on the levitation and guidance performances in every step of the application.Initially,this thesis built a low pressure HTS magnetic levitation performance test platform,and studied the influence of the timing when the evacuated tube is pumped on the levitation and guidance performances of the HTS maglev system.The working condition of pumping during the field cooling stage was defined as “first evacuating and then levitating”(FETL).And the working condition of pumping after the stage of vehicle levitation was defined as “first levitating and then evacuating”(FLTE).Then,the research showed that the levitation force under the condition of FETL is better than that under the condition of FLTE while the guidance force under the condition of FLTE is better than that under the condition of FETL.Hence,during the practical engineering applications,an appropriate “levitating-pumping sequence”can be chosen between those conditions mentioned above according to the actual requirement.Simultaneously,the influence of environment pressure on the levitation and guidance performances was also discussed specifically under the two working conditions above,which can provide a reference for the engineering application and future design.Next,combined with the temperature measurement platform,this thesis studied three unconventional working conditions with high probability in the HTS maglev-ETT technology,which are preload,evacuated tube air leakage and liquid nitrogen solidification caused by too low pressure in the tube.And the experiment results showed that the low-pressure environment in evacuated tube is beneficial for preloading to suppress the levitation force decay caused by the lateral movement of vehicle.And environment pressure rising due to the air leakage will have a negative effect on the levitation force and guidance stability.However,this effect of environment pressure rising on guidance force depends on the field cooling height.Meanwhile,the liquid nitrogen solidification caused by too low pressure have a negative influence on the levitation and guidance performances,too.Eventually,based on the COMSOL Multiphysics simulation platform,a two-dimension electromagnetic simulation model was established to study the dynamic levitation performance under different environment pressures.And the influence of field cooling height,working height and the magnitude of magnetic field irregularity on the dynamic levitation force decay under different pressure conditions was analyzed.The study showed that,under every pressure condition,a lower field cooling height,a higher working height,and a smaller magnetic field irregularity amplitude can all lead to a smaller dynamic levitation force decay.And a lower environment pressure can not only cause a smaller dynamic levitation force decay,but also reduce the effect of these three factors mentioned above on the dynamic levitation force decay. |
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