Levitation Pressure Research Articles

S114063 ナノテクスチャリングによる動圧気体軸受の設計指針([S11406]機素潤滑設計部門 第17回卒業研究コンテスト(6))

Recently, the effect of textured surface facing narrow gap, where gases cannot be treated as continuum fluid even at atmospheric pressure, on the properties of air bearings is focused on. For example, Nakamori et al. reported that the friction between a dimpled surface, which is fabricated by partial polishing of diamond-coated surface, and a flat metal surface was drastically decreased to almost zero with increasing relative speed of sliding. In this work, we tried to generate such floating force between a flat surface and a textured surface fabricated by shot-peening of fine particles followed by buffing. In addition, MGL calculation was conducted to investigate the effect of textured surface shape on the floating force induced by rarefied gas flow in the narrow gap between the sliding surfaces. As a result, the ratio of metal contact and friction between the sliding surfaces was decreased to almost zero at relative sliding speeds u >2.0 m/s; MGL calculation showed that levitation pressure equal to that (1630 Pa) by the own weight of the specimen is induced by rarefied gas flow at u =2.0 m/s in the narrow gap of 0.009 pm. Furthermore, we found an optimized shape of textured surface; it was indicated by MGL calculation that the floating force induced at u=2.0 m/s and a gap height of 0.1 pm by the optimized shape is increased by 8 times from the conventional shape where a dimple fabricated by shot-peening is modeled by an isosceles triangle. Note that the air bearing (inside diameter 11 mm, length 9.6 mm) employing the optimized shape as a texturing on the sleeve was estimated to support an axle of 4 g without contact at u=2.0 m/s and floating height of 0.1 pm.

An ultrasonically levitated noncontact stage using traveling vibrations on precision ceramic guide rails

This paper presents a noncontact sliding table design and measurements of its performance via ultrasonic levitation. A slider placed atop two vibrating guide rails is levitated by an acoustic radiation force emitted from the rails. A flexural traveling wave propagating along the guide rails allows noncontact transportation of the slider. Permitting a transport mechanism that reduces abrasion and dust generation with an inexpensive and simple structure. The profile of the sliding table was designed using the finite-element analysis (FEA) for high levitation and transportation efficiency. The prototype sliding table was made of alumina ceramic (Al2O3) to increase machining accuracy and rigidity using a structure composed of a pair of guide rails with a triangular cross section and piezoelectric transducers. Two types of transducers were used: bolt-clamped Langevin transducers and bimorph transducers. A 40-mm long slider was designed to fit atop the two rail guides. Flexural standing waves and torsional standing waves were observed along the guide rails at resonance, and the levitation of the slider was obtained using the flexural mode even while the levitation distance was less than 10 microm. The levitation distance of the slider was measured while increasing the slider's weight. The levitation pressure, rigidity, and vertical displacement amplitude of the levitating slider thus were measured to be 6.7 kN/m2, 3.0 kN/microm/m2, and less than 1 microm, respectively. Noncontact transport of the slider was achieved using phased drive of the two transducers at either end of the vibrating guide rail. By controlling the phase difference, the slider transportation direction could be switched, and a maximum thrust of 13 mN was obtained.

Magnetic levitation by height temperature superconductor plates short secondary interacting with translating field: experiences, measurements and modelling

An experimental set-up has been designed and built in order to investigate and evaluate the forces of interaction between a circular primary fed by tree-phase voltage and a high temperature superconducting plate short secondary. This equipment simulates, by analogy, the electromagnetic behaviour of levitated vehicle, with passive superconducting sheets on board, that rides along an active way with translating field. Static and dynamic performances have been evaluated in terms of specific traction thrusts and levitation pressures. Moreover numerical analyses have been carried out by 3D finite element parametric model: the results are presented in terms of thrusts, eddy current and flux density distribution.

High levitation pressures with cage-cooled superconductors

We present an analysis of and experimental results from a levitational system comprising a stationary, bulk high-temperature superconductor (HTS) and a levitated component (rotor) that consists of a cylindrical permanent magnet surrounded by an annular HTS. The rotor is cooled below the critical temperature of the HTS while surrounded by a ferromagnetic cage. When the ferromagnetic cage is removed, the flux from the permanent magnet is essentially excluded from the interior of the HTS. When brought into proximity with the HTS stator, the cage-cooled rotor experiences a levitational force. The levitational force may be calculated by applying magnetic circuit theory. Such calculations indicate that for a sufficiently high critical current density, the levitational pressure may exceed that between the permanent magnet and its mirror image. We constructed a rotor from an NdFeB permanent magnet and YBCO bulk HTS with a critical current density of ≈5 kA cm−2. A soft ferromagnetic steel cage was constructed in segments. The critical current density of the stator HTS was also ≈5 kA cm−2. Experimental results obtained with the cage-cooled rotor and stationary HTS show a significant increase in force over that of an equivalent PM rotor and stationary HTS.

Stable magnetic levitation with adjustable ratio of levitation force torestoring force using rings of zero-field cooled YBa2Cu3Oysamples

Both high levitation pressures (up to 22 N cm-2) and highrestoring pressures (up to 11 N cm-2) are obtained for a superconductingtrapped field magnet of 1.5 T levitating above the centre of a ring ofzero-field cooled high-temperature superconductors. The ratio of levitationforce to restoring force can be varied between 2.9 and 0.3 by changing thequality of the superconductors. This significantly improves the stability oflevitation compared to commonly used single sample configurations.

Thermodynamically controlled melt processing to improve bulk materials

High quality melt textured YBCO samples have been prepared on a modified MTG route. A trapped magnetic field of 8.5 T at 51.5 K was measured in the gap of 1 mm in a mini-magnet from two YBCO cylinders (d=26 mm, h=12 mm). At 77 K, each single domain cylinder traps more than 600 mT and the levitation pressure of 15 N/cm/sup 2/ in a distance of 0.5 mm was achieved by a 0.4 T SmCo magnet. The thermodynamic background of the preparation method is outlined. A thermodynamic approach to control growth and stoichiometry y in the alternative material Nd/sub 1+y/Ba/sub 2-y/Cu/sub 3/O/sub x/ is discussed. Critical currents of 46 kA/cm/sup 2/ (77 K) have been achieved by a modified recipe.

Radiation-pressure-induced capillary waves

Capillary waves are often observed on the surface of acoustically levitated drops, bubbles, and shells. The onset and parameter dependences of such waves on bubbles and shells have been investigated. Via video and light scattering it has been established that the mechanism for converting the acoustic energy into wave motion is the Faraday instability. Measurements of pattern formation, fluctuation, and transition will be presented, as well as investigations of temporal dynamics. In particular, the transition to spatiotemporal chaos and/or turbulence is investigated. The shell is the primary ‘‘laboratory’’ for turbulence, since, for certain wall thicknesses and levitation pressures, the entire surface becomes covered with apparently turbulent capillary waves, accompanied by a reduction of the gravity-induced pooling. The potential uses of this knowledge to produce more uniform coatings in certain applications will be discussed. [Work supported by NASA.]

Magnetic bearings using high Tc superconductorsconfigurations and first results

The development achieved with superconducting oxides makes possible the design of magnetic bearings in association with permanent magnets. The inherent properties of these superconductors ensure passive stability in opposition to classical systems which need at least one actively controlled direction. This paper reports some results about levitation performances between permanent magnets and YBaCuO samples at 77 K. The force-displacement measurements are corroborated by magnetization curves. Several structures are proposed including different magnet configurations and hybrid system consisting in magnets providing high levitation pressure stabilized by superconductors. In order to investigate optimum configurations some first numerical modellings have been developed.

Estimation of hysteretic levitation pressure and stiffness in high Tc superconducting bearings

The properties of a high T c superconducting bearing consisting of a set of alternating-polarity magnets and a superconductor are investigated. Hysteretic pressure-displacement relations are observed in the bearings. To analyse the levitation pressure of the superconducting bearing, distribution models of the magnetic flux densities at the surface of the superconductor based on Bean's critical state model were constructed. The results of the analyses show that it is possible to estimate the hysteretic levitation pressure and the stiffness using Bean's critical state model.

Magnetic flux penetration in high Tc superconducting bearing in zero-field cooling process

The properties of high T c superconducting bearings, consisting of a set of alternating-polarity magnets and a superconductor, are studied in this paper. The superconducting bearing has a large surface area, contributing to levitation forces, and is zero-field cooled in liquid nitrogen. To investigate the mechanisms related to the levitation pressures of the superconducting bearing, the distribution of the magnetic flux density at the surface of the superconductor is studied. The results indicate that the magnetic flux density perpendicular to the superconductor plays an important role in flux penetration. The Maxwell stress tensor is applied to estimate the levitation pressure of a superconducting bearing with a large surface area and the results show that this method is applicable, to a certain extent, for such an estimation. This paper discusses the possibility of applying the Maxwell stress tensor to the estimation of the pressure.

Levitation pressure and stiffness of a high T c superconducting bearing in field-cooling process

Properties of a high Tc superconducting bearing consisting of a set of alternating-polarity magnets and a superconductor are investigated. The superconducting bearing is field-cooled in liquid nitrogen, because it is expected that field-cooling process will be used for superconducting bearings in the future. To analyze the levitation pressures of the superconducting bearing Bean’s critical state model was applied. The results of the analyses show that it is possible to estimate the levitation pressures to some extent by using the model.

Magnetic levitation and stiffness in melt-textured Y-Ba-Cu-O

Magnetic levitation and stiffness have been measured in several systems composed of a permanent magnet elastically suspended above a stationary melt-textured sample of Y-Ba-Cu-O. The levitation force and vertical stiffness have been calculated on the basis of magnetization measurements of the same system, and the calculated results showed excellent agreement with the experimental measurements. Based on the force and magnetization measurements, it is predicted that the same Y-Ba-Cu-O material configured in a geometry suitable for magnetic bearings could produce a levitation pressure of 100–400 kPa at 20 K.

Static levitation in a high-T c superconductor tile on magnet arrangements

Static characteristics of a levitational mechanism are studied. The levitational mechanism consists of a high-Tc superconductor tile (type-II superconductor) and a magnet arrangement of the same size bar magnets with alternating magnetic pole pattern. The levitation pressures have hysteresis loops because of the flux pinning effect. By using the alternating pole pattern of magnets larger static levitation pressure in proportion to the arrangement can be obtained over a wide area. Moreover the levitation pressure can be optimized with respect to the width of a bar magnet of the alternating pole pattern.