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This study tries to observe the aerodynamics of a moving coil linear motor (MCLM) under the conditions of high frequency and high speed, a three-dimension aerodynamics analysis and experimental investigation of the designed MCLM provided with different thrust coil bobbins (TCBs) based on dynamic meshes technique using computational fluid dynamics (CFD) are proposed. Results show that with the increase of moving frequency and speed, the air damping of TCB subassembly is nearly proportional to the square of the speed. Punching a number of holes on the end face of the TCB could greatly improve the air flow capacity and enhance the distribution of pressure and velocity of the flow field around. Compared with proposal 1, the air damping of proposal 2 and proposal 3 is decreased by 64.3% and 97.1%, respectively. Simulation results show that the response time and frequency of the designed MCLM with proposal 3 is better than those with proposal 1 and proposal 2. In addition, the experimental frequency and response time of the designed MCLM with proposal 3 are 300Hz at 3dB and 4ms, respectively. As evident in this study, analysis and experimental results show that the air damping can be decreased by the structural optimization of the MCLM, and the designed MCLM with proposal 3 can realize good performance of high frequency and rapid response. DOI: http://dx.doi.org/10.5755/j01.mech.24.6.22463

The magnetic bearing is considered as one of the most prospective applications of high temperature superconductors (HTSs) which can realize stable levitation in a magnetic field generated by permanent magnet devices or coils. The exploration of this kind of HTS bearing through numerical investigation is usually made by assuming the induced current circulates only within the ab-plane and thus simplifying the actual three-dimensional problem to a two-dimensional one. In this paper, on the basis of the three-dimensional model of the HTS bulk established before, we further introduce the developed finite-element software to calculate the magnetic field generated by a magnetic rotor which is composed of permanent magnet (PM) rings and ferromagnet (FM) shims, and in this way, we can investigate the magnetic forces (radial force and axial force) of a simplified HTS bearing model, i.e., two symmetric HTS bulks and a magnetic rotor, at a three-dimensional level. The investigations performed in this paper lead to the observations: the favorable configuration to construct the HTS bearing is that the axial height of each HTS element should be equivalent to the axial heights of PM ring plus FM shim; the increase of the radial thickness of PM ring will improve both the radial force and the axial force considerably, but its margin decreases; the enhancement of critical current density of HTSs due to the decrease of operating temperature can result in a higher increase of both the radial and axial force with a lower nominal gap between the HTSs and the magnetic rotor.

High temperature superconducting (HTS) magnetic levitation (maglev) vehicle is a fascinating transportation tool due to its unique inherent stability. In order to improve performance of present HTS maglev vehicle system, a novel HTS maglev vehicle (aero-vehicle) utilizing aerodynamic designs from modern aircraft is proposed, which is driven by an engine positioned on the top of the car body. The aerodynamic designs of the aero-vehicle include the wings and the empennage, and these new designs are used to adjust and control the pitch, roll, and yaw of the car body. To analyze the feasibility of the aero-vehicle, its characteristics are investigated in the paper. Depending on ailerons of wings, elevator and rudder of the empennage, the aero-vehicle is capable to advance safety and ride comfort of present HTS maglev vehicle.

In the practical application of high-temperature superconducting (HTS) maglev vehicle, the vehicle body ascends and descends in the vertical direction frequently with the passengers on and off boarding, such vertical movement may change the levitation performance but this influence have not been researched. In this article, the influence of the vertical movement on the levitation force in two different types of permanent magnet guideway (PMG) and different movement displacements was experimentally analyzed. We found that the levitation force drastically decays first, and then decays slightly, which is similar to the relaxation phenomena. Meanwhile, the experimental results indicate that the levitation force decay trends to enlargement with the decrease of the working height (WH) and with the increase of the vertical displacements. These phenomena can be ascribed to the magnetic hysteresis loss in the bulk high-temperature superconductor (HTSC).

This paper focuses on the magnetic field inhomogeneity at the rail gap due to five kinds of position deviations between two segments of permanent magnet guideway (PMG). PMG model is built by the finite element analysis software, and effectiveness of the model is proven by comparing the actual magnetic field with the calculated value. The influence of the magnetic field by the gap, horizontal displacement and vertical displacement was investigated. Kinetic characteristics of HTS maglev when it passes the rail gap are studied. The change of magnetic field at the rail gap is also studied in these cases: one PMG rotates relative to another PMG and the gap is not perpendicular to the direction of PMG. It is found that magnetic force between two PMGs will enlarge the position deviations. Finally, the methods are introduced for improving the homogeneity of magnetic field of PMG and then reducing the magnetic loss due to magnetic field inhomogeneity.

Zero-field cooling (ZFC) and field cooling (FC) are the two most popular activation ways of the bulk high-temperature superconductors (HTSCs). The former can bring a big levitation force but a poor stability, while the latter can bring a good stability but a reduced levitation force due to the trapped flux. Under this rule, it is very difficult to improve the levitation force (load capability) and guidance force (stability) at the same time with the given bulk HTSCs and applied field in practice. In the paper, based on the re-magnetization ability of bulk HTSCs, the maglev performance of bulk HTSCs with a re-magnetization process after ZFC was experimentally investigated above a permanent magnetic guideway (PMG). The bulk HTSCs were firstly cooled down at a far distance above the PMG, but before moving to the working height, an additional process was introduced to descend the bulks to a lower height to magnetize again by the PMG field. Experimental results show that, at certain re-magnetization height above PMG, the levitation force and guidance force could be improved simultaneously compared with the results of normal FC cases, which is different from the present performance improvement with the sacrifice of one important force. This result presents a possible working way for the levitation applications of bulk HTSCs by employing a re-magnetization process after ZFC, and is also useful to optimize the performance of high-temperature superconducting Maglev vehicle systems.

The force-speed relationship of a bulk YBCO moving above a permanent magnetic guideway was studied. The experiments show that the levitation forces at the lowest position Fmax increase with the increment of descending speed and tend to approach a certain levitation force FS.max. Calculations based on a simplified superconducting ring and flux flow model show that the force variations can be ascribed to the resistive electric field produced by flux motion. Further calculation reveals that, by increasing the descending speed, the thermo-dissipation inside the superconducting ring immediately after the descending process exponentially declines, approaching zero while the speed approaches infinity, and Fmax reaches FS.max. Therefore, the thermo-dissipation inside the bulk YBCO can be defined as a parameter for evaluating levitation force losses. Those results might be useful in pragmatic design of high-Tc superconducting levitation devices and magnetization of type-II superconductors.

High temperature superconducting (HTS) bulk sample acts as quasi-permanent magnet when it traps magnetic field, and the superconducting bulk magnet can substitute the traditional permanent magnet in the engineering of the linear motor for the purpose of achieving higher efficiency. The electromagnetic forces between the HTS bulk magnets and the ac magnetic field are the most important parameters to consider for the engineering of a motor. We measured the static vertical and thrust forces of an HTS magnet subject to a sinusoidal traveling magnetic field at different trapped fields and at different current amplitude and frequencies. The force relaxation of the HTS bulk magnet was also compared with that of a traditional permanent magnet. The feasibility of replacing the conventional magnet in the ac application machines by HTS bulk ones was preliminary validated experimentally.

The high-Tc superconductive (HTS) hybrid Maglev with the auxiliary permanent magnet (PM) is a useful method to improve the system load density and stiffness. The auxiliary PM changes the magnetic circuits and increases the instability of the Maglev system. To investigate the levitation performance, different HTS hybrid Maglev arrangements involving PM and bulk HTS were tested above the permanent magnet guideway. Some useful conclusions and reference for relative design can be found from the experimental results and analyses.

Lateral reversible region of the bulk high-Tc superconductor (HTSC) above the permanent magnet guideway (PMG) is a key parameter for the high-Tc superconducting (HTS) maglev system. The lateral stability and guidance force are proportional to the width of the lateral reversible region. When the lateral displacement of the bulk HTSC exceeds the reversible region, the maglev system will return to a new lateral equilibrium position. The method with the use of pre-displacement can successfully increases the lateral reversible region of the bulk HTSC. By the correct choice of the maximum lateral offset and a new starting point, the instability of flux motion can be suppressed. Unsuitable usage of this method will cause the intersection of guidance force and reduce the reversible region. Analyses based on the magnetizing history and pinning metamorphoses well explain the experimental results. Difference between this method and the pre-load method is also discussed in this article.

The lateral restorable characteristics of a translational symmetry high- T c superconducting maglev system are investigated by measuring its resonant frequency ( f RF ) after a lateral displacement. The difference between whether this lateral displacement is restorable, meaning elastic or inelastic, is determined by whether or not the maglev body returns to its original position after a lateral displacement. The maximum restorable lateral displacement ( δ MRLD ) is determined by the sudden change of the f RF vs. the maximum lateral displacement ( δ MLD ) curve. The f RF of the high- T c superconducting maglev system with different field-cooling height (FCH) and working height (WH) was obtained from the frequency domain vibration curve which was measured by a vibration measurement system. The results showed that, the δ MRLD was reduced when the WH was decreased. The maximum restorable guidance force ( F MRGF ) was found to not always increase with the lowering of the WH for the same FCH. The lateral restorable stiffness ( k LRS ) was always enhanced with the decrease of the WH. The decrease of the δ MRLD with the WH is interpreted by the fact that, the tangential field component (Δ H ) across the surface of the high- T c superconductor (HTSC) is easier to exceed the J c λ value ( J c is the critical current density and λ is the London penetration depth) when the WH is lowered, and this makes the trapped flux lines become more susceptible in escaping its pinning sites.

A high-temperature superconducting (HTS) magnetic transmission device is introduced. The key part of the transmission device is an HTS magnetic helix transmission mechanism, which consists of a magnetic bolt and an HTS nut, and its strong points are being frictionless and having high efficiency. The transport platform is driven along the direction of the magnetic bolt. All moving parts of the device do not come into contact with the load that is transported by the transport platform. The basic mechanical properties of this device are studied. The position precision and angle precision of the transport platform are discussed.

Under the background of upgrading energy crisis, a double-axial superconducting magnetic bearing (SMB) system was designed and fabricated for a flywheel energy storage system (FESS) model to demonstrate high temperature superconducting (HTS) energy-saving technologies. In order to levitate and stabilize the shaft sufficiently, the static levitation force and lateral force between high temperature superconductor (HTSC) stator and permanent magnet (PM) rotors in two different sizes were checked. Based on the stable levitation, the dynamic characteristics of the SMB system were also investigated by the excitation experiments. The running experiments show that in the case of a driving motor the shaft can stably rotate along the central axis without any contact, while intensified vibration is also observed near two resonance rotational speeds. These results have been applied to construct and operate the FESS model using the SMB system.

In practical application of High- T c Superconducting (HTS) maglev, slant is an observable defect. It was caused by constantly one side on and off the vehicle by passengers. So far, this phenomenon has not been reported yet. In order to understand its influence on the stability of the HTS maglev, we experimentally studied the dynamic characteristic and slant effect of HTS maglev under center-load and side-load. It was found that load destabilizes the vehicle, and the side-load can obviously slant the vehicle body. In the end, the pre-load method was proposed to enhance the dynamic stability and suppress the slant, which proved to be considerably effective. These results are critical in practical running of HTS maglev.

High-Tc superconducting (HTS) maglev is considered as a perfect transportation type because of its unique inherent stability. A direct current (DC) linear motor using the permanent magnet guideway (PMG) as the stator and the on-board coil as the rotor instead of the present inductive or synchronous alternate current (AC) linear motor which has an economic disadvantage due to the necessity to lay primary coil along the guideway is proposed in this paper. In order to modulate the magnetic field under the PMG, an inverse E shape ferromagnetic device (IESFD) core is designed. The possible winding method for the on-board coil is listed, and the analytical result shows that a considerable net ampere force and thus the propulsion force can be generated by this special structure. The influence of the concentrated effect of the IESFD on the maglev performance of HTS bulk is studied by a numerical program, and the results show that the levitation force with the IESFD is 90% of that without. It is also indicated that the load capability and lateral performance of the maglev vehicle combined this propulsion method can be improved thanks to the attractive effect between the IESFD and PMG. The cost of the HTS maglev vehicle will be remarkably reduced and then shorten the distance to practical application with this propulsion method.

A method to transport up to 180 A of current into the sample space of a pressure cell without causing thermal instabilities at 77 K was developed in order to study the critical current Ic of samples of first-generation Bi-2223 superconducting wire at different hydrostatic pressures. Ic was found to linearly decrease with increasing application of external pressure and was found to be irreversible upon release of pressure. The n-value of the voltage-current curves at different pressure was also found to systematically decrease. The decrease in Ic and the irreversibility effect is attributed to the deformation of the filamentary walls of the wire.

National audience; Dans cet article, on étudie la forme de l'inducteur pour aimanter une pastille supraconductrice par la méthode PFM (Pulsed Field Magnetization). Nous avons testé deux inducteurs: une bobine vortex et un système de 3 bobines, et nous avons trouvé le meilleur résultat aves le système de 3 bobines. Puis, on présente deux procédés pour aimanter la pastille : aimantation directe et aimantation successive, et nous avons trouvé des résultats proches pour les deux procédés. En fin, on montre l'évolution temporelle du champ piégé dans la pastille. Nous avons trouvé qu'il faut environ (5-10) minutes, après l'aimantation avec une impulsion optimale, pour que le champ piégé se stabilise.

High temperature superconductor (HTS) Maglev is considered to be a potential transportation type to reach the speed of 600 km/h and is widely studied. Permanent magnet guideway (PMG) involved in HTS Maglev system is straight or circle. The turnout in the HTS Maglev system is indispensable but few works have done about it. This paper introduces three mechanical permanent magnet turnouts: lateral move turnout, lateral move and elevation type turnout, elevation type and rotary turnout. The applications and characteristic of each turnout are described. Magnetic forces between the mobile and fixed PMG in the process of switch are calculated by the finite element analysis software.

An improved high-temperature superconducting maglev measurement system (SCML-01) was designed and successfully developed to further study the maglev properties of YBaCuO bulks above permanent magnets (PM) or a PM guideway. The system includes a liquid nitrogen vessel, a cylinder PM or PM guideway, a set of two-dimensional motion mechanisms, a set of three-dimensional motion mechanisms, control hardware, and control processing software. In addition to keeping the previous capabilities, the most recent improvements include an integrated measurement of displacement, temperature, force, torque, and magnetic field signals all with higher precision. In particular, the three-dimensional motion mechanism can combine any two-dimensional direction to realize some complicated curve movements, such as z-type, slant-type, and circle-type back and forth many times. These new functions have an important meaning for practical application.

The critical current density of optimally doped bulk YBCO superconductor has been found to increase with the application of external hydrostatic pressure. This paper reports the transport measurements of the critical current (Ic) of YBCO in the form of a coated conductor (CC) wire under hydrostatic pressure up to 0.24 GPa at 77 K. No noticeable change was observed in both the Ic and n-value of the CC sample in the studied pressure range. Two possible scenarios are discussed to explain the observed effect.

The main characteristic of high temperature superconducting (HTS) maglev vehicle is the self-stable levitation. However, it will suffer from all kinds of lateral forces from the surrounding circumstance, i.e., crosswind and centrifugal force. An important issue is that the vehicle must remain in stable equilibrium when subjected to various external disturbances, so study regarding operation safety for HTS maglev vehicle is much necessary and very important under derailment. We researched levitation forces of the HTS maglev vehicle under these conditions, and investigated suitable parameters for the evaluation via experiments' method. The two different PMGs and three different bulk high temperature superconductors (HTSC) arrays are considered in these experiments. The analysis indicates that the HTS maglev vehicle has the ability to dampen the vehicle against external disturbances under the derailment.

A four pole superconducting excitation system that was part of a linear synchronous motor (LSM) system, was fabricated and its thrust and normal forces studied experimentally. Four cases were investigated, air-cored, with a ferromagnetic (FM) back plate, an FM core, and with both an FM back plate and core. With a total of only 15 m of YBCO coated conductor in the form of four coils as the excitation system, thrust output of up to 95 N while operating at 77 K with a magnetic gap of 10 mm was obtained in one particular case. The results of the studied superconducting LSM system help better understand the feasibility of their applications to drive systems for Maglev trains.

The mechanical bearing in the cryogenic liquid pump has short working life due to the low temperature environment. For conquering the disadvantage, the radial high temperature superconducting magnetic bearing (HTSB) is designed to be used in the cryogenic pump. The high temperature superconductors (HTSs) in the HTSB are cooled by the cryogenic liquid directly. The introduced cryogenic liquid pump can constrain the heat leakage. The equipment for the kinetic characteristics of the HTSB is introduced, and it can measure the axial forces of the HTS at different rotation speeds. Basic mechanical principle of the rotor of the pump is analyzed.

Four coils made of YBCO-coated conductor wire were fabricated and connected in series to make up the excitation system of a linear synchronous motor system with a stator made of ordinary copper wire. The electromagnetic forces experienced by the superconducting coils with respect to the stator were studied in the static case. We began with the study of one single coil, followed by two coils connected in series, and finally, four coils in series from which the largest force obtained was of 53.9 N at a gap of 10 mm at 77 K. The critical current, n-value, and inductance were also measured for the coils so that the power dissipation of the field windings can be calculated. This paper also helps us understand whether linear motors with superconducting components are currently economically feasible with present commercially available superconducting wire.

The bulk high temperature superconductors (HTSCs) with unique flux-pinning property have been applied to fabricate two superconducting axial bearings for an energy storage flywheel model. The two superconducting axial bearings are respectively fixed at two ends of the vertical rotational shaft, whose stator is composed of seven melt-textured YBa2Cu3O7-x (YBCO) bulks with diameter of 30 mm, height of 18 mm and rotor is made of three cylindrical axial-magnetized NdFeB permanent magnets (PM) by superposition with diameter of 63 mm, height of 27 mm. The experimental results show the total levitation and lateral force produced by the two superconducting bearings are enough to levitate and stabilize the 2.4 kg rotational shaft. When the two YBCO stators were both field cooled to the liquid nitrogen temperature at respective axial distances above or below the PM rotor, the shaft could be automatically levitated between the two stators without any contact. In the case of a driving motor, it can be stably rotated along the central axis besides the resonance frequency. This double-superconducting axial bearing system can be used to demonstrate the flux-pinning property of bulk HTSC for stable levitation and suspension and the principle of superconducting flywheel energy storage system to visitors.

A measurement testing setup of the characteristic properties for high temperature superconducting bearing (HTSB) systems is introduced in this paper. The equipment setup can measure the radial and axial forces, temperature, oscillation and rotary speed of the HTSB simultaneously, so the relation between these properties can be investigated. For example, the decrease of the radial and axial forces, and the increase of the temperature can be measured and analyzed during different rotary speeds of the permanent magnetic rotor. The measurement ranges for the radial and axial force will reach 5 kN and 10 kN. The temperature of the superconductors in HTSB can then be controlled by adjusting the air press inside the dewar which is an easier method compared with a cryocooler.

The stable levitation above permanent magnet is an important characteristic of the bulk high-Tc superconductor (HTS). When an external force pushes the bulk HTS up, down or sideways, or tries to tilt it, a restoring force can return it to its initial position. The HTS Maglev relied on this characteristic can overcome the external force from wind or pass the curve lines successfully. The change of guidance force (GF) during many times lateral movement is studied. Experiments show that GF increases during the lateral movement, no matter what kind of PMG or HTS is used, and the change of the GF slows down after 5 times lateral movement. The pre-load method can reduce the levitation force decay during lateral movement. So the influence of GF by the pre-load method is needed to be studied. It is found that the pre-load method can increase GF and reduce the change of the GF during lateral movement. The Halbach permanent magnetic guideway (PMG) can offer much more GF but the change is larger just as the levitation force decays. The GF of cylindrical bulk HTS increases more than of the rectangular bulk HTS in the pre-load case. The characteristics of the GF during the lateral movement are explained. These results are important for further HTS Maglev vehicle system designs.

The anisotropy properties of bulk high-temperature superconductors (HTSCs) are taken into consideration for the application of high-temperature superconducting (HTS) Maglev systems, which are especially based on the different flux-trapping capabilities as well as critical current density, J c, values between the growth section boundary (GSB) and the growth sections (GS) in bulk superconductors. By adjusting the angle between the GSB of bulk HTSCs and the strongest magnetic field position of a permanent magnet guideway (PMG), the levitation force and its relaxation processes are compared at different field-cooling conditions. Experimental results show that the levitation capability and the suppression of levitation force decay can be enhanced by optimizing the GS/GSB alignment of every bulk HTSC above the PMG. Meanwhile, our conclusions may provide references to other HTS maglev systems with small levitation gaps, i.e., superconducting magnetic bearings.