Nan Qian

Levitation Performance of YBCO Bulks in Supercooling Condition Under a Low-Pressure Environment

Taking the influence of low pressure on levitation performance of high temperature superconducting (HTS) maglev into account, we established a simple super-cooling platform based on pumping method to study the levitation performance of YBCO bulks above the Halbach permanent magnet guideway (PMG) under different pressure conditions. Through measuring the temperature of liquid nitrogen (LN2) during the decreasing process of pressure, it is known that the LN 2 would turn into a super-cooling state as the pressure reduction. Measurements of the levitation force versus vertical motion and the force relaxation were performed both in case of zero-field-cooling (ZFC) and field-cooling (FC). The experimental result showing that the decreasing pressure is beneficial to improve the levitation performance of HTS bulks, and the maximum force increase up to 23.5% and 22.1% were realized in ZFC and FC compared with the atmospheric pressure, respectively. Moreover, the low pressure could also reduce the hysteresis loop area and restrain the relaxation decay of levitation force. These results imply that, the low pressure environment in evacuated tube will be beneficial to the levitation performance of HTS maglev system

Vibration Characteristics of the HTS Maglev Vehicle Running on a 45-m-Long Ring Test Line

With further studies of high-temperature superconducting (HTS) maglev in recent years, several countries have built short-distance test lines for proving the feasibility of HTS maglev in the long-term running status, and the scientific exploration gradually develops from stable levitation experiments to dynamic performance tests. In previous studies, the sufficient levitation and guidance forces have been verified, but they ignore the influence of external disturbances in practical operations such as inhomogeneous magnetic fields along the permanent-magnet guideway, which limits the operation speed and causes potential vibrations. Meanwhile, the overlarge vibration might reduce the comfort of passengers and bring bad stability of the vehicle. Hence, the research of the dynamic characteristics in the actual operation process is an important process of the HTS maglev system. This paper makes use of the latest research result of a 45-m-long HTS maglev ring test line to study the dynamic vibration characteristics of the maglev vehicle under different running conditions, including different velocities, loads, and sections of the ring test line. Experimental results show that the amplitude of vibration acceleration increases with the velocity of the vehicle. In the vertical direction, the vibration acceleration curves reflect favorable axis symmetry, which confirms an excellent self-stable characteristic of the HTS maglev system, whereas in the lateral direction, the vibration acceleration has different trends on straight and curve lines. The lateral vibration acceleration on the straight lines is always fluctuating around the equilibrium position, and it has a rising trend on curve sections caused by stronger centrifugal phenomenon. Moreover, a proper increase in the levitation load can weaken the vibration, particularly with an enhancing velocity. These results help us to have a deep insight into the potential of HTS maglev and make preparations for the following long-distance dynamic tests.

Dynamic Vibration Characteristics of HTS Levitation Systems Operating on a Permanent Magnet Guideway Test Line

With the development of high temperature superconducting (HTS) maglev stepping in a key period of test line applications, the test and analysis of the dynamic operation parameters become more and more crucial. In this paper, the dynamic operating characteristics of single-cryostat and multicryostat levitation systems were comparatively studied on a 45-m-long permanent magnet guideway test line with different working conditions. Vibration acceleration signals of three levitation systems (a single cryostat, a bogie with two cryostats, and a car with four cryostats) were measured in the running experiments. The vibration characteristics were analyzed in both time domain and frequency domain. Results show that the multicryostat levitation system has better dynamic performance of stiffness than those of the single-cryostat system. The experimental data also indicates a positive correlation between the stability of the HTS maglev vehicle and the number of the cryostat. This work is helpful to understand the essential characteristics of HTS maglev vehicle system, and will be beneficial to the future design.