Levitation Stiffness Research Articles

Design of a Noncontact Bending Testing Device Using Magnetic Levitation Mechanism

This article proposes a non-contact bending testing device using magnetic levitation mechanism, which is expected to facilitate material testing in special environments. To stabilize global levitation degrees of freedom (DOFs) while saving hardware, a structure allowing four levitation DOFs to be passively stabilized was designed, in particular, the principle by which a special configuration passively stabilize one of the levitation DOFs was explained using FEM analysis. In addition, since the levitated object will bear a wide range of bending force, which will pose a disturbance on the levitation, a fixed stiffness-damping controller was designed based on PD-controller to deal with the disturbance. Control simulation results demonstrated that the adopted control method can effectively keep levitation stiffness and levitation damping constant even under the bending force. Moreover, a force control system with a PI-controller was designed to control the loading of the bending force. Finally, two groups of experiments were performed with a high-stiffness material and a low-stiffness material respectively. Experiment results demonstrated that the special configuration can passively stabilized the levitation DOF, and the fixed stiffness-damping control method allow the device to withstand a bending force up to 50N while keeping levitation stable. Also, the force control system was proved to be feasible even when specimen deflection was large.

Influence of cooling temperature on load-carrying performance of a radial HTS magnetic bearing

High temperature superconducting (HTS) magnetic bearing can operate in the harsh environment of low temperature and negative pressure with low loss and self-stability. Therefore, it has been gradually applied in flywheel energy storage, cryogenic liquid pump, cold compressor and some other cryogenic rotating machinery. The load-carrying performance of HTS magnetic bearing is affected by the cooling temperature of HTS directly. In this paper, the linear model is used to modify the temperature dependence to evaluate the influence of cooling temperature on load-carrying performance quantitatively, and the results are analyzed and displayed from the aspects of maximum levitation force, levitation stiffness and hysteresis effect. The research results of this paper have practical significance for the design and safe operation of HTS levitation system.

Design and Construction of a Superconducting Gravimeter Prototype

To promote China’s research on fields related to high-accuracy gravity measurement, the Institute of Electrical Engineering, Chinese Academy of Sciences (IEECAS), is committed to developing superconducting gravimeters. A superconducting gravimeter prototype has been successfully designed, fabricated, and tested through continuous improvement and optimization design. This article describes the main components of the prototype: superconducting gravity sensor, magnetic shield, cryogenic system, and displacement detection and feedback system. The novel work improves the superconducting gravity sensor on the persistent current switch and superconducting joint. Furthermore, the method for testing the levitation stiffness is also introduced, and the result demonstrates that an electromagnetic force method is a feasible approach with fast and good linearity. Finally, experimental test results on the prototype are shown, where solid Earth tide, temperature effect, and parasitic mode are obtained in the prototype signal. Moreover, it is shown that the levitation stiffness obtained by the electromagnetic force method and the tidal observation method are close to each other.

Stiffness characteristic of high temperature superconducting upper maglev system

High temperature superconducting (HTS) magnetic levitation (maglev) train, by virtue of its passive stabilization, has the potential to become the next generation high-speed rail transit mode. For the further practical HTS maglev dynamic study and design, the levitation stiffness between the superconductors and the permanent magnet plays a significant role. Due to the nonlinear characteristics and the hysteresis phenomenon of the levitation force, the levitation stiffness is a variadic value. This varying stiffness complicates the vibration reduction design. And the violent vibrations caused by the lack of reasonable design can endanger the safety and comfort of the vehicle. In this paper, the levitation stiffness of a YBaCuO superconductor vessel levitating above a permanent magnetic guideway (PMG) in Halbach-array was measured and analyzed. First, a quasi-static experiment was designed to measure the levitation stiffness, which will be assessed during different vessel movement, separately. Subsequently, the natural frequencies of the levitation system under different working loads were measured by a series of dynamic experiments, and the levitation stiffness calculated by vibration was compared with the test result of the quasi-static experiment. Finally, a systematic differential equation was proposed to describe the levitation stiffness varying phenomena, and its dynamic characteristics were analyzed and verified by simulations as well. The result of this paper shows that the levitation stiffness does not have a strong regular relation with the levitation height as prediction but has a linear relation with the levitation force in the limit space above the PMG. And the studies about the stiffness characteristics with the proposed stiffness model in this paper can provide reference for engineering application and relative dynamic calculations.

Design and research of magnetically levitated testbed with composite superconductor bearing for micro thrust measurement

A high temperature superconducting (HTS) magnetically levitated testbed has been developed for the steady thrust measurement of miniature ion electrospray thruster. The structure of the testbed mainly consists of an HTS composite bearing, a magnetic shielding plate, an active electromagnetic brake and a laser displacement sensor. The steady thrust is described as a function of the equilibrium angle displacement of the floating frame. Furthermore, the mechanical behaviors of HTS composite bearing were studied via finite element simulation and experiments, which include the load capacity, levitation stiffness and background noise. The results show that the thrust testbed can keep in low noise and have a load capacity up to 4 kg. According to the ignition testing of the electrospray thruster, the thrust force of 25.2 was measured by the testbed, which is close to the design value of miniature ion electrospray thruster.

Capsule Vehicle Dynamics Based on Levitation Coil Design Using Equivalent Model of a Sidewall Electrodynamic Suspension System

A levitation system based on sidewall electrodynamic suspension (EDS) is considered for a capsule vehicle, which is a next-generation high-speed transportation system currently being studied. This levitation system does not require controlling of the gap between the guideway and the vehicle on which the superconducting electromagnet is mounted. However, when the vehicle is operated in a levitated state, the ride comfort is worse than that of the levitation system based on electromagnetic suspension (EMS), making it necessary to develop methods that can ensure good riding comfort. In addition, because the EDS system is complex and nonlinear with a combination of electromagnetics and mechanical dynamics, it is complicated to analyze the dynamic characteristics of the capsule vehicle, and the corresponding numerical analysis is time-consuming. Therefore, to easily understand the running dynamics of a capsule vehicle in the sidewall EMS system, the magnetic suspension characteristics corresponding to the primary suspension are simply modeled by considering the levitation stiffness in the vertical direction and the guidance stiffness in the lateral direction, similar to that in the case of the mechanical suspension. In this study, mathematical models of the levitation and guidance stiffnesses with respect to the speed and position of a vehicle body running at high speeds in a levitated state in the sidewall EDS system were derived for three design proposals of the levitation coil. The dynamic behavior of the vehicle based on the three design proposals was investigated by simulating a capsule vehicle model with 15 degrees of freedom.

Characteristics of cross stiffness with different physical and geometrical parameters in a high-temperature superconductor levitation system

Cross stiffness is usually defined as a change in the vertical force when the levitating body moves a small lateral displacement in a high-temperature superconductor (HTS) magnetic levitation system. In most of the existing research reports, the improvement of the levitation stiffness is usually focused on the radial (lateral) and axial (vertical) stiffnesses. The cross stiffness should be studied carefully because it can be used to analyze the stability and dynamical properties of the HTS levitations. In this paper, the quantitative properties of the cross stiffness have been investigated by a numerical method. The variations of the cross stiffness at different lateral positions are analyzed for some physical and geometrical parameters, cooling conditions and movement history of a levitated permanent magnet. The reasons for the characteristics of the cross stiffness can be obtained by the vertical force–lateral displacement curves with some minor loops under different parameters and cooling conditions.

Retracted: Analysis of Suspension and Guidance System of EDS Maglev Based on a Novel Magnetomotive Force Model

Due to the existence of the end effect of vehicle coils in the electrodynamic suspension (EDS) maglev, the fluctuation of the output parameters of the suspension and guidance system is common, which has an impact on the stability of the motor driving system. In this article, considering the end effect of vehicle coils, a new magnetomotive force (M.M.F) distribution model suitable for the suspension and guidance system of EDS maglev is proposed. First, considering the end effect of vehicle coils, an M.M.F model of array of vehicle coils is established. Then, based on the space harmonic method and the equivalent circuit of suspension and guidance loop, the expressions of levitation current, guidance current, drag force, levitation force, levitation stiffness, guidance force, and guidance stiffness are presented. Finally, the characteristics of the suspension and guidance system are analyzed under different running conditions. The numerical results are compared with the 3-D finite-element method simulation results and the experimental results of the Yamanashi test line. The relative error is almost within 10%, which verified the feasibility and accuracy of the M.M.F model and analytical method.

Vibrational Properties of High- $$T_{c}$$ T c Superconductors Levitated Above a Bipolar Permanent Magnetic Guideway

A bipolar permanent magnetic guideway (PMG) has a unique magnetic field distribution profile which may introduce a better levitation performance and stability to the high-\(T_{c}\) superconducting (HTS) maglev system. The dynamic vibration properties of multiple YBCO bulks arranged into different arrays positioned above a bipolar PMG and free to levitate were investigated. The acceleration and resonance frequencies were experimentally measured, and the stiffness and damping coefficients were evaluated for dynamic stability. Results indicate that the levitation stiffness is closely related to the field-cooling-height and sample positioning. The damping ratio was found to be low and nonlinear for the Halbach bipolar HTS-PMG system.

The Relationship between Temperature and Levitation Stiffness of YBCO Bulk for Maglev Vehicle

In order to make the levitation performance of the high temperature superconducting (HTS) magnetic levitation (Maglev) vehicle more stable and safer, in this paper, using a cryogenic measurement system, we measured the levitation forces of YBCO bulk above halbach-type permanent magnet guideway (Halbach PMG) in the temperature range from 77 K to 60 K, then in the condition of deep cryogenic, the levitation forces of YBCO bulk at different field cooling heights (FCHs) were also measured, according to which the levitation stiffness were calculated. The results show that the levitation stiffness of HTS/PMG Maglev system is better at lower temperature. Moreover, when the temperature of YBCO bulk decreases from 77 K to 73 K, the levitation stiffness largely increases in any FCHs. However, after the temperature of the bulk decreases to 73 K, the rate of the levitation stiffness increased gradually reduces. The results are helpful to HTS Maglev vehicle application.

Flux Concentrator Optimization of PMG for High-Temperature Superconducting Maglev Vehicle System

The permanent magnetic guideway (PMG) composed of permanent magnet (PM) and steel is developed under flux concentration principle, which is the crucial component of high-temperature superconducting (HTS) maglev vehicle system. Optimum PMG design is an effective way to increase levitation force and associated stiffness for improving the load capability of HTS maglev vehicle. In order to realize higher vertical field component B z in upper surface, three PMG demonstrators with three different forms of flux concentrator are fabricated with same volume of magnet. The levitation performances of onboard HTS bulks array over them are studied. The experimental results indicate that the PMG with a permanent magnet as the flux concentrator would produce biggest levitation force, levitation stiffness and trapped flux when interacting with HTS superconductor.

Influence of the ramp angle on levitation characteristics of HTS maglev

The gradeability is one of the advantages of the high-temperature superconducting (HTS) maglev vehicle, and it is relative to the levitation characteristic of the maglev system on the ramp. The influence of the ramp angle on the levitation characteristics of the HTS maglev model was investigated. Some levitation characteristic parameters on the uphill guideway with different ramp angles were studied by the equivalent experiment, such as the levitation force, the levitation gap, the levitation stiffness and the guidance force. Compared with the experimental results on the horizontal guideway, it was found that the levitation gap increased, but the levitation force and the levitation stiffness decreased. The levitation gap and the levitation stiffness are considered as the main maglev characteristic parameters needed to be taken into account.

The relationship between levitation force and stiffness in symmetrical and unsymmetricalapplied fields

The two key parameters for levitation performance over a permanent magnet (PM)guideway are the levitation force and the stiffness of the high temperature superconductor(HTS) YBaCuO bulk. Their distributions along a lateral displacement (LD) were measuredin zero-field-cooling (ZFC) and in field-cooling (FC) conditions. There are two cases ofapplied magnetic field for a single HTS bulk: symmetrical or unsymmetrical about the bulkaxis. Although the levitation force has a linear relationship with the applied field in thesymmetrical case, such a linear relationship disappears once the applied field becomesunsymmetrical. Furthermore, the levitation stiffness is measured in FC, and they stillchange more drastically than the levitation force in ZFC. In particular, the levitationstiffness has a linear relationship with the associated levitation force, whether the appliedfield is symmetrical or unsymmetrical. Its lateral distribution at a gap of 20 mmin FC agrees with the levitation force distribution at a gap of 10 mm in ZFC.