Dynamic performance of the SRI Maglev vehicle

The stability and ride quality of a small scale MAGLEV test vehicle were determined by measuring its motions in five degrees of freedom during levitated flight. Various offsets were introduced into the guideway to stimulate strongly different modes of oscillation and to search for instabilities. These offsets, that were up to 25% of the equilibrium suspension height, induced motions that were analyzed to evaluate both passive and active damping systems used on the vehicle. In more than thirty tests of the vehicle, including stimulations of the heave, roll, pitch, yaw, and slip modes of oscillation, no instabilities were observed in any degree of freedom whether using passive or active damping. The active damping system, used in conjunction with the passive system, provided greater stability and ride quality than the passive system alone. The passive system, however, provided enough damping to achieve stability and is therefore a desirable back-up in the event of a failure in the active control system. The tests were simulated on a computer using a completely nonlinear dynamics model and provided good approximations to the data. Extrapolations to full-size vehicles have not been made.     

Magnetic levitation technology and its applications in exploration projects

An energy efficient cryogenic transfer line with magnetic suspension has been prototyped and cryogenically tested. The prototype transfer line exhibits cryogen saving potential of 30–35% in its suspension state as compared to its solid support state. Key technologies developed include novel magnetic levitation using multiple-pole high temperature superconductor (HTS) and rare earth permanent-magnet (PM) elements and a smart cryogenic actuator as the warm support structure. These technologies have vast applications in extremely low thermal leak cryogenic storage/delivery containers, superconducting magnetic bearings, smart thermal switches, etc. This paper reviews the development work and discusses future applications of established technologies.     

The Stable Magnetic Levitation of a Cylindrical Ferromagnetic Object

This paper introduces a control method using a ring magnet for the stable levitation of a cylindrical ferromagnetic object. The levitation has a strong stability with anti-disturbance abilities, and weight can be placed on the floating magnet. The magnetic field created by the ring magnet provides stabilities in 3 degrees of freedom of the floating magnet, and a feedback control in the horizontal plane is introduced to the control system. Analytical calculation and experiments have been done to prove the feasibility of this control method.     

Application of the preview compensation control method to large gap control in hybrid magnetic suspension

ABSTRACT

Large-gap magnetic suspension is a conceptual design for experiments which can be used to investigate technical issues associated with magnetic suspension and accurate suspended-load control for large gaps. The traditional linear control strategy has significant limits to its control area, usually around the chosen operating points. With increase in the suspension gap, the nonlinearity and time delay of a system will become more serious. Additionally, the interaction of an estimation scheme and corresponding controller has not been fully examined in the literature. This paper examines a developed compound control method, Smith forecast compensation control with proportional-integral-derivative control (PID control) , as a means of advancing the achievable performance of magnetic suspension. We designed and built a laboratory testbed to determine the feasibility of utilizing proposed methods in these types of applications. The analytical results are supported by the simulations and experiments, showing our research approach to be fairly successful at providing satisfactory performance for motion control under conditions involving a large air gap.     

Design and failure modes of automotive suspension springs

This paper is a discussion about automotive suspension coil springs, their fundamental stress distribution, materials characteristic, manufacturing and common failures. An in depth discussion on the parameters influencing the quality of coil springs is also presented.

Following the trend of the auto industry to continuously achieve weight reduction, coil springs are not exempt. A consequence of the weight reduction effort is the need to employ spring materials with significantly larger stresses compared to similar designs decades ago. Utilizing a higher strength of steel possesses both advantages and disadvantages. The advantages include the freedom to design coil springs at higher levels of stress and more complex stresses. Disadvantages of employing materials with higher levels of stress come from the stresses themselves. A coil’s failure to perform its function properly can be more catastrophic than if the coil springs are used in lower stress. As the stress level is increased, material and manufacturing quality becomes more critical. Material cleanliness that was not a major issue decades ago now becomes significant. Decarburization that was not a major issue in the past now becomes essential.

To assure that a coil spring serves its design, failure analysis of broken coil springs is valuable both for the short and long term agenda of car manufacturer and parts suppliers. This paper discusses several case studies of suspension spring failures. The failures presented range from the very basic including insufficient load carrying capacity, raw material defects such as excessive inclusion levels, and manufacturing defects such as delayed quench cracking, to failures due to complex stress usage and chemically induced failure. FEA of stress distributions around typical failure initiation sites are also presented.     

Cross-tie—Néel domain wall transition in thin magnetic films

A theoretical consideration of the hysteresis change of the domain wall structure in flat uniaxial thin magnetic films under the influence of a magnetic field parallel to the hard axis has been carried out. The theory is based on a cross-tie wall model defined in a more precise manner than that of Middelhoek. The circular Bloch line shift as a function of a magnetic field and estimates for the critical fields of both the direct “cross-tie Néel” wall transition and the inverse transition have been obtained.     

Linear synchronous motor development for urban and rapid transit systems

The following paper presents and discusses technical variants in magnetic suspension-repelling permanent magnets, electrodynamic and electromagnetic suspension methods, controlled lift magnets. In addition, propulsion methods for magnetically suspended vehicles are also shown. The synchronous long stator linear motor has achieved particular importance since it makes possible an efficient energy conversion. The load-carrying capacity is not reduced by the weight of the drive and the layout enables a very good integration of the lift and thrust functions. A further reduction of the on-board power requirements can be achieved by using permanent magnets to generate the rated induction in the air gap. Several magnetic suspension systems constructed or under construction with the long stator method are also mentioned.     

Optical Reflectance Sensor Measures Displacement in Magnetic Suspension

In active magnetic suspension systems, electromagnetic forces are used to keep a body in stable equilibrium without mechanical contact. Basically, an active magnetic suspension is a position servomechanism. Thus, accurate measurement of the position of the levitated part is important. A variety of displacement transducers has been in use, the eddycurrent sensor being the most favored one at present. This paper describes an optical reflectance sensor used in a novel configuration to measure the position in a levitation setup. A sensitivity of 10.5 V/mm, and a linearity range of about 0.5 mm, were obtained by this method. The sensor and the measurement technique are described in detail here.     

Film depth and concentration banding in free-surface Couette flow of a suspension

The film depth of a free-surface suspension flowing in a partially filled horizontal concentric-cylinder, or Couette, device has been studied in order to assess its role in the axial concentration banding observed in this flow. The flow is driven by rotation of the inner cylinder. The banding phenomenon is characterized by particle-rich bands which under flow appear as elevated regions at the free surface separated axially by regions dilute relative to the mean concentration. The concentric cylinders studied had outer radius R(o) = 2.22 cm and inner radii R(i) = 0.64, 0.95 and 1.27 cm; the suspension, of bulk particle volume fraction phi = 0.2 in all experiments described, was composed of particles of either 250-300 microm diameter or less than 106 microm diameter, with the suspending fluid an equal density liquid of viscosity 160 P. The ratio of the maximum to the minimum particle volume fraction along the axis in the segregated condition varies from O(1) to infinite. The latter case implies complete segregation, with bands of clear fluid separating the concentrated bands. The film depth has been varied through variation of the filled fraction, f, of the annular gap between the cylinders and through the rotation rate. Film depth was analysed by edge detection of video images of the free surface under flow, and the time required for band formation was determined for all conditions at which film depth was studied. The film depth increases roughly as the square root of rotation speed for f = 0.5. Band formation is more rapid for thicker films associated with more rapid rotation rates at f = 0.5, whereas slower formation rates are observed with thicker films caused by large f, f > 0.65. It is observed that the film depth over the inner cylinder grows prior to onset of banding, for as yet unknown reasons. A mechanism for segregation of particles and liquid in film flows based upon 'differential drainage' of the particle and liquid phase in the gravity-driven flow within the film over the inner cylinder is formulated to describe the onset of concentration fluctuations. This model predicts that suspension drainage flows lead to growth of fluctuations in phi under regions of negative surface curvature.     

A new iterative order reduction (IOR) method for eigensolutions of large structures

Order reduction is a computationally efficient method to estimate some lowest eigenvalues and the corresponding eigenvectors of large structural systems by reducing the order of the original model to a smaller one. But its accuracy is limited to a small range of frequencies that depends on the selection of the retained degrees of freedom. This paper proposes a new iterative order reduction (IOR) technique to obtain accurately the eigensolutions of large structural systems. The technique retains all the inertia terms associated with the removed degrees of freedom. This hence leads to the reduced mass matrix being in an iterated form and the reduced stiffness matrix constant. From these mass and stiffness matrices, the eigensolutions of the reduced system can be obtained iteratively. On convergence the reduced system reproduces the eigensolutions of the original structure. A proof of the convergence property is also presented. Applications of the method to a practical GARTEUR structure as well as a plate have demonstrated that the proposed method is comparable to the commonly used Subspace Iteration method in terms of numerical accuracy. Moreover, it has been found that the proposed method is computationally more efficient than the Subspace Iteration method. Copyright © 2003 John Wiley & Sons, Ltd.     

Collapse of magnetic moment drives the Mott transition in MnO

The metal-insulator transition in correlated electron systems, where electron states transform from itinerant to localized, has been one of the central themes of condensed-matter physics for more than half a century. The persistence of this question has been a consequence both of the intricacy of the fundamental issues and the growing recognition of the complexities that arise in real materials, when strong repulsive interactions play the primary role. The initial concept of Mott was based on the relative importance of kinetic hopping (measured by the bandwidth) and onsite repulsion of electrons. Real materials, however, have many further degrees of freedom that, as is recently attracting note, give rise to a rich variety of scenarios for a 'Mott transition'. Here, we report results for the classic correlated insulator MnO that reproduce a simultaneous moment collapse, volume collapse and metallization transition near the observed pressure, and identify the mechanism as collapse of the magnetic moment due to an increase of crystal-field splitting, rather than to variation in the bandwidth.     

Fuzzy logic control of vehicle suspensions with dry friction nonlinearity

We design and investigate the performance of fuzzy logic-controlled (FLC) active suspensions on a nonlinear vehicle model with four degrees of freedom, without causing any degeneration in suspension working limits. Force actuators were mounted parallel to the suspensions. In this new approach, linear combinations of the vertical velocities of the suspension ends and accelerations of the points of connection of the suspension to the body have been used as input variables. The study clearly demonstrates the effectiveness of the fuzzy logic controller for active suspension systems. Suspension working space degeneration is the most important problem in various applications. Decreasing the amplitudes of vehicle body vibrations improves ride comfort. Body bounce and pitch motion of the vehicle are presented both in time domain when travelling over a ramp-step road profile and in frequency domain. The results are compared with those of uncontrolled systems. At the end of this study, the performance and the advantage of the suggested approach and the improvement in ride comfort are discussed.     

Performance of different vector potential formulations in solvingmultiply connected 3-D eddy current problems

The authors describe their numerical experiences in applying FEM (finite-element method) solution techniques to a 3-D (three-dimensional) eddy-current problem with a coil-driven multiply connected conductor, the benchmark problem No.7 of the International TEAM Workshops. Several formulations have been tried using a magnetic vector and electric scalar potential or an electric vector and a magnetic scalar in the conductor and a magnetic vector or scalar potential outside. The problem has been solved at two frequencies. The authors briefly describe the formulations used and compare the performance. Magnetic field and current density plots are also compared. The advantages and disadvantages of the various versions are pointed out. The use of a magnetic scalar potential H rather than a magnetic vector potential A outside the conductor and the hole substantially reduces the number of degrees of freedom and thus the computational effort. The versions using it in the conductor yield relatively ill-conditioned systems. Also, at the higher frequency, the conditioning deteriorates considerably     

Superconducting Vortex Pinning with Magnetic Dots: Does Size and Magnetic Configuration Matter?

The pinning of superconducting vortices in type-II superconductors has been studied for a long time due to the wide variety of unusual flux flow phenomena and more importantly, for its relevance in applications, since vortex pinning is one of the essential parameters controlling the enhancement of critical currents. A case of particular interest is the use of artificial magnetic pinning centers, since they can be fabricated to match well the characteristic length scales relevant for superconductivity and their magnetization offers another degree of freedom to influence the pinning properties. This article reviews our work on the role of the size and separation of the magnetic dots. Furthermore, we also show that the magnetic configuration can influence significantly the pinning strength, through the magnetic stray fields penetrating the superconductor, which can be drastically different.     

An investigation of two HSGT magnetic suspension systems (attraction)

Two alternate attraction magnetic suspension systems are discussed on a magnetic performance basis, as well as on their lift-to-weight (L/W) capabilities. On an equal current basis, the lower reluctance, flat track configuration has higher lift force and betterL/Wthan the U-shaped track configuration with its larger leakage flux. With equal magnetization (unequal currents) and low guidance forces (F_{G}/F_{L} leq 0.3), the U-shaped track has a higherL/Wratio, but both attraction systems suffer from lowL/Wwhen all elements of the suspension system are considered.     

Effect of Nuclear Quadrupole Interaction on the Relaxation in Amorphous Solids

Recently it has been experimentally demonstrated that certain glasses display an unexpected magnetic field dependence of the dielectric constant. In particular, the echo technique experiments have shown that the echo amplitude depends on the magnetic field. The analysis of these experiments results in the conclusion that the effect seems to be related to the nuclear degrees of freedom of tunneling systems. The interactions of a nuclear quadrupole electrical moment with the crystal field and of a nuclear magnetic moment with magnetic field transform the two-level tunneling systems inherent in amorphous dielectrics into many-level tunneling systems. The fact that these features show up at temperatures T<100 mK, where the properties of amorphous materials are governed by the long-range R⁻³ interaction between tunneling systems, suggests that this interaction is responsible for the magnetic field dependent relaxation. We have developed a theory of many-body relaxation in an ensemble of interacting many-level tunneling systems and show that the relaxation rate is controlled by the magnetic field. The results obtained correlate with the available experimental data. Our approach strongly supports the idea that the nuclear quadrupole interaction is just the key for understanding the unusual behavior of glasses in a magnetic field.     

微传感器最新发展

近年来，微传感器受到国际传感技术界的广泛关注，本文介绍十多个微传感器，包括三轴加速度计，单，双轴加速度计片，表面微机械陀螺（角速度传感器），微惯性导航系统，微磁通门传感器，磁阻传感器，纳米皮拉尼压力传感器，微科氏质量流量计，毫米波图像传感器，GPS手表（1cm^3)，二氧化碳传感器和微/超微角位移传感器，文事简要介绍它们的基本结构。敏感机理，特点等，从中可以看出微传感器已成为传感技术中有重要应用前景的组成部分。     

Novel Magnetorheological Suspensions Based on Co-Phthalocyanine/Fe Nanocomposite Particles

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Analysis of the collapse mechanisms in uncracked arches: The role of friction forces and stereotomy in masonry

This paper examines the stability of uncracked masonry arches for the purpose of exploring their collapse mechanism. Two situations that warrant analysis may occur during the lifetime of a voussoir arch that forms part of a structural system in a heritage construction. The first situation is related to the stability of the arch before the appearance of hinges or relative displacements (sliding) of a group of voussoirs with respect to an adjacent uncracked arch. The second situation is related to the stability of the cracked arch when some damage has already occurred.The first of these situations is analyzed in this paper, with the goal of detecting where damage will initiate. The classical stability conditions of a group of voussoirs G_ij considered as a whole within the arch are considered to apply. The movement of a solid in a plane has three degrees of freedom: two translations (one in each coordinate axis) and one rotation with respect to the normal axis to the plane where the 2D solid is contained. All possibilities of movement of any G_ij group have been analyzed. An arch with a radius of 100 cm at the intrados was constructed of wood in a laboratory to observe its collapse mechanism. The collapse of the arch can be predicted analytically.     

Force model identification for magnetic suspension systems viamagnetic field measurement

In magnetic suspension analysis, a simplified model of the current-to-distance relationship is not sufficient to design an optimal control. Due to the nonlinearity of the magnetic field, an accurate model, which is a function of the suspended object, suspension distance, core material, and operation conditions, is difficult to obtain. An improved force-model-identification method for magnetic suspension systems establishes reliable parameters for describing the magnetic field characteristics. The parameter for each test sample can be calculated under the specified operating conditions after some magnetic field measurements. The results lead to effective controller design for magnetic suspension systems