Electromagnetic Brake Research Articles

Electromagnetic braking of the flow of a liquid metal with a free surface

The electromagnetic braking of liquid metal flowing over a moving boundary is considered. The flow is two dimensional and the upper boundary is a free surface. The main interest of this flow originates from the application of horizontal belt strip casting. In this process, the liquid metal is fed onto a single endless horizontal belt that runs between two rollers. The bottom of the belt is cooled by water and the liquid is fed onto the belt through a slit. This results in a flow that can be modelled as a flat free jet impinging onto a horizontally moving boundary. The flow after the impingement region is analysed using the boundary layer equations. Here, the flow depends on the Reynolds number R, the Froude number F, the Hartman number M, and the ratio of the belt velocity to jet velocity, β. For β< F −2/3, we have a supercritical flow which terminates in a hydraulic jump. For β> F −2/3, there is no hydraulic jump and the film thickness grows smoothly into the final state with constant thickness and uniform velocity. The braking length for the case without hydraulic jump is shown to be of order O( F 2/3 Ra/2) without magnetic field and of order O( M −2 Ra/2) with magnetic field, where a is the jet width. Thus, the magnetic field decreases the braking distance considerably. This result is favourable for both the stability of the flow and for the solidification process in the horizontal belt strip casting process.

Spin-down of an oblique rotator with a current-starved outer magnetosphere

A variant of the vacuum-dipole model of rotation-powered pulsars is presented that accounts for the observed spin-down properties of all three pulsars with braking indices measured from absolute pulse numbering (the Crab, PSR B0540 — 69 and PSR B1509 — 58). In the model, the neutron star and inner magnetosphere are treated phenomenologically as a single unit, a magnetized, perfectly conducting sphere of radius rv rotating rigidly in vacuo. The ‘vacuum radius’ rv corresponds to the innermost point in the magnetosphere where field-aligned flow breaks down and the plasma becomes three-dimensional, that is, the point where cyclotron losses occur slowly enough to allow electrons (or positrons) to move an appreciable distance before decaying to the l = 0 Landau state. For young, Crab-like pulsars, one typically finds r* ≪rv <rL, where r* is the stellar radius, and rL is the light-cylinder distance. The model therefore differs from standard vacuum-dipole theories, in which the dipole has radius r* and is treated as point-like. Three observable pulsar parameters — the rotation frequency ω, its time derivative ώ), and the angle α between the rotation and magnetic axes — uniquely determine rv and hence the electromagnetic braking torque exerted on the star, calculated from the Deutsch radiation fields of the rotating dipole. With no free parameters, the theory yields braking index values for the Crab, PSR B0540 — 69 and PSR B1509 — 58 that agree with timing data to 4 per cent. The second deceleration parameter is also predicted for each object, but cannot be verified to useful precision using data available at present. The relationship between our idealized yet successful spin-down model and a genuine pulsar magnetosphere is discussed, and further observational tests of the theory are proposed.

Dynamics of respiratory response to sinusoidal work load in humans.

The present study was undertaken to investigate possible distortion in responses of respiratory variables including O2 uptake (VO2), CO2 output (VCO2), and ventilation (VE) to sinusoidal work load, and to find out whether the conventional transfer models were applicable to analyze the dynamics of these variables. Six healthy subjects performed exercise for 32 min on a bicycle ergometer with electro-magnetic braking. The work load was varied sinusoidally between 30 W and 60% of maximum O2 uptake (VO2max) during periods from 1 to 16 min. The respiratory variables were measured on a breath-by-breath basis with a mass spectrometer and a computer system. The responses of VO2, VCO2, and VE to sinusoidal work load were not completely sinusoidal in form but were somewhat distorted, forming saw-tooth waves with steeper down-slopes during periods of 4-16 min, but this distortion was not observed at 1 min or 2 min periods. However, the results could be approximately described by a first-order model without or with time delay. Time constants of the first-order model without time delay were 46 sec for VO2, 62 sec for VCO2, and 73 sec for VE, respectively. We also found a close relationship between the time constants of VO2 and VCO2 and VO2max. These results suggested that exponential functions may be applied and are expected to yield valid results in assessing physical fitness, although the control of ventilatory and gas exchange in exercise does show non-linear characteristics.

Electromagnetic processing of liquid steel

The use of electromagnetic processing of liquid steel at Inland Steel Company is in various stages, ranging from commercial usage, with suggestions to vendors for improvements, to new application research. The status of commercially available electromagnetic stirring and electromagnetic braking are discussed. Application research of electromagnetic containment and electromagnetic throttling are also discussed. The basic theory for electromagnetic processing of liquid steel is presented.

96/04219 Electromagnetic braking improves steel quality in continuous casting

96/04219 Electromagnetic braking improves steel quality in continuous casting

The numerical modelling of DC electromagnetic pump and brake flow

The interaction of an externally imposed magnetic and electric field on the laminar flow of a conducting fluid in a channel is studied using computational techniques. The Navier-Stokes equations and the equations describing the electromagnetic field are solved simultaneously in a single control volume-type computational fluid dynamic code, in a moderate Hartmann number and interaction parameter regime. The flow considered is two-dimensional, with an imposed magnetic field acting in the third dimension over the central region of the channel and decaying exponentially in the remainder. A pair of electrodes placed at right angles to the magnetic field exercises control over the resultant Lorentz force and hence the velocity profile shape. This configuration has application in direct-current electromagnetic pumps or, conversely, electromagnetic brakes. The initial parabolic flow profile acquires an M-shape / W-shape mode in the magnetic field fringe regions, corresponding to a pump / brake. A novel coupled procedure is described to model magnetohydrodynamic phenomena and is used to explore the effects of the Reynolds number, interaction parameter, and applied voltage on the pump / brake configuration.

Design of an electromagnetic accelerator for turbulent hydrodynamic mix studies

An electromagnetic accelerator in the form of a linear electric motor (LEM) has been designed to achieve controlled acceleration profiles of a carriage containing hydrodynamically unstable fluids for the investigation of the development of turbulent mix. Key features of the design include: (1) independent control of acceleration, deceleration and augmentation currents to provide a variety of acceleration-time profiles, (2) a robust support structure to minimize deflection and dampen vibration which could create artifacts in the data interfering with the intended study, and (3) a compliant, nonarcing solid armature allowing optimum electrical contact. Electromagnetic modeling codes were used to optimize the rail and augmentation coil positions within the support structure framework. Design of the driving armature and the dynamic electromagnetic braking system is based on results of contemporary studies for nonarcing sliding contact of solid armatures. A 0.6 MJ electrolytic capacitor bank is used for energy storage to drive the LEM. This report will discuss a LEM and armature design which will accelerate masses of up to 3 kg to a maximum of about 3000g/sub 0/, where g/sub 0/ is acceleration due to gravity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Intraoperative fusion of field images with CT/MRI data by means of a stereotactic mechanical arm.

In this paper we describe a neurosurgical articulated arm used as a pointer and as a support for intraoperative image acquisition, integrated with a graphic 3-D rendering system. The patient's anatomy is volumetrically displayed, from stereotactically acquired CT, MRI, and DSA images; the head holder is the common reference system for image reconstruction and for the calibration of the surgical arm. Arm orientation in stereotatic space is displayed, together with the surgical arm. Arm orientation in stereotatic space is displayed, together with the volumetric reconstruction of cerebral lesions and surrounding healthy tissue. The arm, equipped with fail-safe electromagnetic brakes, can be employed to support imaging sources such as an endoscope, an echographic probe, or a CCD camera, whose images can be stereotactically integrated with preoperative data in performing minimally invasive neurosurgical procedures.

The New Ceiling Mount with “Space Pointer/Cygnus” System for the Leica Wild M690 Operating Microscope

The new ceiling mount with the "Space Pointer/Cygnus" system for the Leica Wild M690 operating microscope (Leica AG, Heerbrugg, Switzerland) is reported. Two modes of action, "focus lock" and "point lock", are used with this system, in addition to counterbalanced free motion and electromagnetic brakes. The system also considerably improves space factors around the microscope.

The EMBr : a new metallurgical instrument for clean steel ? First results at Hoogovens IJmuiden

An ElectroMagnetic Brake (EMBr) has been installed on one mould of CC 22 in Hoogovens BOS No.2. The aim is a 50 % decrease of the number of inclusions through reduction of the velocities of the steel in the mould. Trials indicate an improved stability of the meniscus and an increase in temperature at the meniscus. Some results from intermediate and final products are presented.

The Braking Law of Solar Type Stars as Derived from Close Binary Dynamical Evolution

The orbital period of a close binary system (P ~ a few days), formed by two solar type components, evolves under the influence of angular momentum loss (AML) by electromagnetic braking and of spin↔orbit angular momentum transfer (AMT) by tidal coupling. Because of AMT, which tends to reestablish the spin-orbit synchronization destroyed by AML, the loss of AM takes finally place at the expenses of the orbital reservoir and produces shrinking of the orbit and spinning-up of the components. The variation with time of wK and w, respectively the orbital and the rotational angular velocity, is expressed by a system of (stiff) ordinary differential equations and the results of the (numerical) integration strongly depend on the AML and AMT laws. A series of recent papers (Maceroni and Van ’t Veer 1991, 1992, Van’t Veer and Macerord 1992, hereafter MVI, MV2 and VM) presents the resulting orbital period evolution function (PEF) with a variety of choices. A typical result, in terms of orbital period, and for a binary formed by two identical G5 V components, is shown in fig. IA. The solution shown here corresponds to the braking law a) of fig. IB, to the AMT according to Zahn (1977) and to stars rotating as rigid bodies; different assumptions have been tried in MVland VM.

Pulsar glitches as probes of neutron star interiors

PULSAR rotation rates generally decrease steadily owing to external electromagnetic braking torques, but occasionally show sudden increases ('glitches') followed by gradual recoveries that may last days or years. These events are thought to be consequences of angular momentum transfer between a solid crust, which rotates at the measured pulsar periodicity, and a more rapidly rotating "loose' component of the neutron star interior. Sudden braking of the differential rotation between the two components will cause a glitch1, and the subsequent re-establishment of rotational equilibrium between the two components represents the recovery2. Earlier studies, using particular models for the coupling between crust and interior, showed that the loose component carries ∼2.8% and ≳1% of the total moment of inertia of the Vela pulsar3 and PSR 1737 – 30 (ref. 4) respectively. Here, we analyse post-glitch recovery in four pulsars, and deduce that the loose component carries at least 0.8% of the total moment of inertia, independent of the form of the coupling. In the context of the 'vortex creep' model of recovery, in which the loose component is the inner-crust neutron superfluid2'5–7, the constraint on the moment of inertia rules out equations of state that are soft at high densities.

Physiological responses to maximal exercise on arm cranking and wheelchair ergometer with paraplegics

This study describes the responses of 20 paraplegic athletes (mean age: 26.8 +/- 1.6 years) to a continuous incremental workload test until exhaustion on an arm cranking ergometer (ACE) and on a wheelchair ergometer (WCE). Both ergometers used the same electromagnetic braking device allowing a fair comparison between results. Tests were conducted at a 24 hour interval at the same time of the day. Oxygen uptake (VO2), heart rate (HR), workload (W), blood pressure (BP), Borg index, and mechanical efficiency (ME) were measured at every minute during the effort and the cool down periods of both tests. The purpose of this study was to analyse the different responses obtained on ACE and on WCE during maximal effort by paraplegics, and also to determine which ergometer permits the higher ME. Results indicate that paraplegics reached the same max HR on ACE and on WCE (97% of the predicted max HR). The lack of significant difference (p less than 0.05) between ACE and WCE in terms of maximal values of VO2, VE and HR suggests that the subjects reached their maximal capacity on each test regardless of the type of ergometer. Nevertheless, W max (in Watts) was 26% higher on ACE than on WCE. Maximal ME values were respectively 16% and 11.6% on ACE and WCE. Results suggest that ergometers and protocol used in this study are appropriate to measure physiological responses of paraplegic athletes during arm cranking and wheelchair exercise without excessive or early arm fatigue.

A mechanism of squeal in electromagnetic friction clutches and brakes.

In this paper, the generation of squeal noise in electromagnetic friction clutches or brakes is explained by the energy which flows from a frictional surface into a disk. If an infinitesimal change of the bending moment caused by a frictional force effects positive work on the disk during a cycle, the energy flows into a disk and squeal is generated. When the thickness of the stationary disk is greater than that of the stationary disk, the waves of the self-excitation. The linear component of the spring characteristic on a contact surface is related to self-excitation. The positive work performed by the linear component is converted into the additional kinetic energy of the increased vibration. The work performed by the nonlinear component is always negative, and it dissipates the kinetic energy of the disk.

Changing patterns of eye-head coordination during 6 h of optically reversed vision.

1) This study investigates the early development of adaptive changes in oculomotor function associated with coordinated eye-head tracking of the optically reversed image of an earth-fixed target seen through horizontally reversing dove prism goggles attached to the skull. 2) Two tasks comprised a) fixation of a single target during head rotation which causes the seen target's image to move in the direction of head motion by an amount exactly equal to the head movement itself (the 1-Target task), and b) change of gaze onto a displaced target with head free to move (2-Target task). 3) The 1-Target task requires the eyes to move in a direction opposite to that of the normal vestibulo-ocular reflex (VOR). The 2-Target task is identical, except that reorientation onto the new target calls for an initial saccadic eye movement in a direction opposite to that of the ensuing head movement, which is contrary to the normal pattern of eye-head coordination during gaze shifts. 4) Eye (EOG) and head (potentiometer) movements were continuously recorded (0-250 Hz) in an apparatus which permitted sudden, unexpected, electromagnetic braking of the head movement, either just before or during the intended manoeuvre. 5) Early adaptive strategies employed reduction of VOR gain, rearrangement of timing, amplitude and shape of "catch-up" saccades and the introduction of centrally programmed eye movements uncovered by the braking manoeuvres. 6) All of these phenomena were detectable in an initial series of 60 trials, in which the total exposure to visual-vestibular conflict was less than 30 s. They became more systematized and more marked after 6 h of active reversed vision experience. 7) Specifically, mean VOR gain, measured within the first 80 ms of head movement (deemed free of visuomotor influence), became markedly attenuated (25% in the first test series; 66% after 6 h of active vision-reversed exercise). In addition (not included in the above percentages) there were numerous occasions of complete absence of measurable VOR during head rotation, in both the first and final test series. 8) In the 1-Target task, the latency of the first "catch-up" saccade (re onset of head movement) tended to offset residual VOR by becoming shortened to the point of synchrony with head movement onset. This saccade (not present in control tests) continued to occur on those occasions when the head was unpredictably prevented from moving, and when head movements were made in the dark.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of a contact region in a frictional surface on squeal in electromagnetic friction clutches and brakes.

A squeal phenomenon in an electromagnetic clutch depends not only on time-independent factors (shape and size, natural frequencies and damping ratios of a rotor and an armature) but also on variable factors (a contact region and a contact position). In this paper, the stability of a two-disk system modeled after a practical clutch is discussed theoretically. Numerical calculations based on this squeal theory show the influence of a contact region and a contact position on the squeal : (1) the fourth mode squeal is generated when an armature is in contact with the outer pole of a rotor ; (2) the lower mode squeal is generated when the armature is in contact with the outer part of the facing surface of the rotor ; (3) no squeal is generated when the armature is in contact with the entire facing surface or with the inner pole of the rotor.

Influence of slits on squeal in electromagnetic friction clutches and brakes.

This paper describes an investigation into influence of the lengths of the slits and the number of those on squeal. In a disk with four slits at regular intervals there are two 2-0 modes which have two nodal diameters. One has a node in the center of a slit (sine mode), and the other has a node between two adjacent slits (cosine mode). The difference Δf1 between the natural frequency of the sine mode and that of the cosine mode becomes greater as the slits grow longer. On the other hand, there is only one natural frequency of the 3-0 mode in the disk. Our squeal theory predicts that the second mode squal is reduced as theΔf1 of 2-0 modes grows greater. Experimental results show that the second mode squeal disappears and the third one is generated when the slits are long. In conclusion, four slits are effective on the second mode squeal, but not on the third one. And also the n-th mode squeal is not generated when theΔf1 of n-0 modes is large.

Influence of damping on squeal in electromagnetic friction clutches and brakes.

Influence of damping on squeal in electromagnetic friction clutches and brakes.

The finite element solution of transient axisymmetrical nonlinear Eddy-current field problems

In this paper, the procedure that is available for computing transient nonlinear axisymmetrical eddy-current field problems with the finite element method under the condition of the source voltage, not the exciting current, to be given is described. The transient diffusion equation is discretized by Galorkin projective technique in space, and implicit forward differential scheme in time. The quasilinearization of the nonlinear equation is handled by the Newton-Raphson scheme. The transient values of exciting current are determined by the combination of computations of field and circuit at each discrete time step, and an iterative procedure is needed. In order to reduce the computing time, the accelerating convergence factor α is indroduced. The method is applied to the disc electromagnetic brakes. The combination of the finite element method with the Maxwell's stress view is accepted for calculating the electromagnetic force. The computing values all coincide with the experimental results.

Electromagnetic braking of a metallic projectile in flight

A simple model for the electromagnetic deceleration of a moving metallic projectile is described. It incorporates the influence of magnetic field parameters, time-dependent field diffusion, and device geometry on braking action, albeit in an approximate fashion. The model predicts that a viable experimental braking device can be designed.