Magnetic Drag Research Articles

CFD study on the magnetic fluid delivering in the vessel in high-gradient magnetic field

This paper simulated the advection and diffusion behaviors of the moving magnetic fluid in the vessel in the high-gradient magnetic field using Navier–Stokes equations. The particles accumulation behavior and the streamlines and the contour of concentration are all affected by the susceptibility, intensity of magnetic field and its gradient, and the flow velocity and also by the difference in size of vessels. The typical accumulation behaves as a solid obstacle in the flow as result of the competing between magnetic and fluid drag forces, and gives rise to a rigidly bound core region followed by a wash away region near the vessel boundary under the condition of 10 mm vessel in width. While the vessel is near 1 mm in width, the magnetic force is exerted almost on the whole vessel area, the vortex is not seen, the wash away area disappears and the concentration changes in the whole vessel. The results of the analysis provide meaningful information on ferrofluid transport and stabilization for various magnetic drug targeting and the magnetic fluid sealing, and other use in industrial and medical fields.

Planetary magnetic signature of the storm wind disturbance dynamo currents: Ddyn

During magnetic storms, Joule heating and ion drag, in auroral zones, strongly influence the circulation of thermospheric neutral winds. Joule heating produces equatorward neutral winds at F‐region heights with return flow at E‐region altitudes around the equator, the so‐called Hadley cell. The modified thermospheric circulation produces upwelling of molecule‐enriched air at high latitudes and global changes in the atmospheric composition. The equatorward neutral winds extending from the auroral zone to mid and low latitudes through the Coriolis force create westward storm wind which drives an equatorward dynamo current. In this paper, we detect for the first time, in the three longitude sectors, the planetary magnetic signature (Ddyn) of ionospheric disturbance dynamo with its main features: (1) the decrease of the equatorial electrojet due to a westward electric current flow opposite to the regular eastward current flow and (2) the equatorward ionospheric disturbance dynamo currents at midlatitudes.

Modeling of Moving-Conductor Type Eddy Current Damper

When a conducting plate moves through a nonuniform magnetic field, electromotive forces are induced in the conducting plate. According to Fleming's right-hand rule and left-hand rule, the induced currents produce a magnetic drag force. In these rules, a magnetic field perpendicular to the direction of movement generates a magnetic damping force. In the present work, we provide a possible resolution to the modeling of moving-conductor type eddy current dampers, using infinitesimal loop coils. Our model has three advantages: the equation of the magnetic damping force is simple; we can use the static magnetic field obtained by using the finite element method (FEM), the Biot-Savart law or experiments; and the model automatically satisfies boundary conditions. Using infinitesimal loop coils, we have modeled the magnetic damping force produced by a moving-conductor type eddy current damper composed of electromagnets and a conducting disk. Furthermore, the experimental setup has been fabricated, and damping ratios from experiments are compared to the analytical results and are found to be in good agreement with them.

Single magnetic particle dynamics in a microchannel

Functionalized magnetic particles are used in micrototal analysis systems since they act as magnetically steered mobile substrates in microfluidic channels, and can be collected for bioanalytical processing. Here, we examine the motion of magnetic microbeads in a microfluidic flow under the influence of a nonuniform external magnetic field and characterize their collection in terms of the magnetic field strength, particle size, magnetic susceptibility, host fluid velocity and viscosity, and the characteristic length scale. We show that the collection efficiency of a magnetic collector depends upon two dimensionless numbers that compare the magnetic and particle drag forces.

A study on magnetically targeted drug delivery system using superconducting magnet

A number of targeted drug delivery methods currently have been developed. One of these, magnetically targeted-drug delivery system (MT-DDS) will be a promising way, which involves binding a drug to small biocompatible magnetic particles, injecting these into the blood stream and using a high gradient magnetic field to pull them out of suspension in the target region. It is one of the problems on MT-DDS that controlling magnet is difficult because diameter of treating magnetic particle is a few hundred millimeters. In this study, the trajectory of Fe3O4 nanoparticle in blood vessel by using magnetic force and drag force is calculated. Accumulation experiment of Fe3O4 nanoparticle in glass tube under blood flow using permanent magnet is performed. Results of experiment are corresponding with the results of calculation. In accordance with the result of the study, it has succeeded in accumulation of ferromagnetic nanoparticles under blood flow 20mm above Bulk superconducting magnet.

Investigation of Magnetic Drag Torque in Permanent Magnet Brushless Motors

In permanent magnet (PM) brushless motors, a magnetic drag torque, which results from the effect of magnetic hysteresis, exists at low speeds but is often neglected. However, in some applications it can have potentially serious consequences. In this paper, a practical method for predicting the magnetic drag torque in a PM brushless motor is presented. It is based on the fact that the average drag torque over one mechanical revolution can be determined from the energy associated with excursions around appropriate hysteresis loops of the steel. Finite element analysis is employed to calculate the variation of flux in each element throughout the stator core, as the rotor rotates, and, hence, the hysteresis loss. The method is applied to two PM brushless motors having 18-slots/12-poles, 12-slots/10-poles, respectively. The predicted magnetic drag torques are compared with the measurements

Multiscale Finite Element Modeling of Arc Dynamics in a DC Plasma Torch

The dynamics of the electric arc inside a direct current non-transferred arc plasma torch are simulated using a three-dimensional, transient, equilibrium model. The fluid and electromagnetic equations are solved numerically in a fully coupled approach by a multiscale finite element method. Simulations of a torch operating with argon and argon–hydrogen under different operating conditions are presented. The model is able to predict the operation of the torch in steady and takeover modes without any further assumption on the reattachment process except for the use of an artificially high electrical conductivity near the electrodes, needed because of the equilibrium assumption. The results obtained indicate that the reattachment process in these operating modes may be driven by the movement of the arc rather than by a breakdown-like process. It is also found that, for a torch operating in these modes and using straight gas injection, the arc will tend to re-attach to the opposite side of its original attachment. This phenomenon seems to be produced by a net angular momentum on the arc due to the imbalance between magnetic and fluid drag forces.

Design of a magnetic braking system

A non-contact method, using magnetic drag force principle, was proposed to design the braking systems to improve the shortcomings of the conventional braking systems. The extensive literature detailing all aspects of the magnetic braking is briefly reviewed, however little of this refers specifically to upright magnetic braking system, which is useful for industries. One of the major issues to design upright magnetic system is to find out the magnetic flux. The changing magnetic flux induces eddy currents in the conductor. These currents dissipate energy in the conductor and generate drag force to slow down the motion. Therefore, a finite element model is developed to analyze the phenomena of magnetic flux density when air gap and materials of track are varied. The verification shows the predicted magnetic flux is within acceptable range with the measured value. The results will facilitate the design of magnetic braking systems.

Recovering Solar Toroidal Field Dynamics from Sunspot Location Patterns

We analyze both Kitt Peak magnetogram data and MDI continuum intensity sunspot data to search for the following solar toroidal band properties: width in latitude and the existence of a tipping instability (longitudinal m =1 mode) for any time during the solar cycle. In order to determine the extent to which we can recover the toroidal field dynamics, we forward-model artificially generated sunspot distributions from subsurface toroidal fields that we have assigned certain properties. Sine-curve fitting of Kitt Peak magnetogram data provided an upper limit of 15 to the tipping amplitude but could not adequately separate the tip from the width of the toroidal band. We then analyzed two sunspot distribution parameters using MDI and model data: the average latitudinal separation of sunspot pairs as a function of longitudinal separation and the number of sunspot pairs creating a given angle with respect to the east-west direction. A toroidal band of 10 width with a constant tipping of 5 best fits MDI data early in the solar cycle, when the sunspot band is at high latitudes (>18.5). A toroidal band of 20 width with a tipping amplitude decreasing in time from 5 to 0 best fits MDI data late in the solar cycle when the sunspot band is at low latitudes (<18.5). Model data generated by untipped toroidal bands cannot fit MDI high-latitude data using 2 goodness-of-fit criteria and can fit only one sunspot distribution parameter at low latitudes. Tipped toroidal bands satisfy 2 criteria at both high and low latitudes for both sunspot distribution parameters. We conclude that this is evidence to reject the null hypothesis—that toroidal bands in the solar tachocline do not experience a tipping instability—in favor of the hypothesis that the toroidal band experiences an m=1 tipping instability for a significant portion of the solar cycle. Our finding that the band widens from10 early in the solar cycle to 20 late in the solar cycle may be explained in theory by magnetic drag spreading the toroidal band due to altered flow along the tipped field lines. Higher m modes, most notably m = 2 and 6, are apparent in MDI data, but further analysis is needed to determine this property in detail.

Linear Analysis and Nonlinear Evolution of Two‐Dimensional Global Magnetohydrodynamic Instabilities in a Diffusive Tachocline

We develop a more realistic two-dimensional model for global MHD instabilities in the solar tachocline, by including diffusion in the form of kinetic and magnetic drag (following Newton's cooling law formulation). This instability has previously been studied by us and others for an idealized tachocline with no kinematic viscosity and magnetic diffusivity. Since radial diffusion is more important than latitudinal diffusion in the thin solar tachocline, diffusive decay of flow and magnetic fields can be considered as proportional to those variables. We find that, for solar-like toroidal magnetic fields of ~100 kG, instability exists for a wide range of kinetic and magnetic drag parameters, providing a mechanism for enhanced angular momentum transport in latitudes, which could explain how thin the solar tachocline is. From a detailed parameter space survey, we set upper limits of 5 × 1011 and 3 × 1010 cm2 s-1 for kinematic viscosity and magnetic diffusivity, respectively, such that this instability occurs in the solar tachocline on a timescale shorter than a sunspot cycle. We find that magnetic drag has much more influence than kinetic drag in damping this instability. This happens because the sink due to magnetic drag dissipates perturbation magnetic energy faster than the vorticity sink from kinetic drag dissipates perturbation kinetic energy. Consequently, in the presence of a large enough magnetic drag, the nonsolar-like clamshell pattern, found by Cally to be an inevitable final state of a broad profile undergoing an ideal MHD tachocline instability, is suppressed, whereas a banded profile still tips with no reduction in tip angle. We discuss how tipping may affect various surface manifestations of magnetic features, such as the latitudes and orientations of bipolar active regions.

A Study on the Development of an Open-Gradient Magnetic Separator Under Dry Condition

This is an attempt to explore feasibility to develop an open gradient magnetic separator for mixed powder under dry condition. The magnetic separator proposed here is intended to separate the ferromagnetic particles from mixed powder, being based on the consideration that the separation efficiency depends upon changing systematically the particle sizes and its surface properties such as hydrophobicity and cohesive force. As a result, it is found that the separation efficiency became lower as the particle size of the mixed particles became smaller. This is supposed to be caused by the cohesive force between the particles of ferrite and alumina which are easily affected by the magnetic drag force and the gravity difference. But the result is encouraging because the separation efficiency will be enhanced if the magnetic gradient is increased and if air flow in the separator is optimized in the appropriate system of the open-gradient magnetic separator proposed in this paper.

The Solar Tachocline: Limiting Magneto-Tipping Instabilities

Two dimensional magneto-shear instabilities in the solar tachocline have been extensively explored in recent years. One of their most notable traits over a wide range of shear and magnetic profiles is a propensity for the magnetic field to tip substantially from its initial axisymmetric configuration, with possible implications for patterns of flux emergence. However, it is found that modifications of the standard models to include either kinetic and magnetic drag, or prograde toroidal velocity jets associated with magnetic bands, can suppress the instabilities, or considerably reduce their nonlinear development. In the case of tip reduction by jets, for a toroidal field of around 100kG in the tachocline (required for sunspots to emerge in sunspot latitudes), simulations indicate that jets capable of reducing tipping below the limits of detection from sunspot patterns at the surface are potentially detectable by helioseismic methods, and should be looked for. Establishing an upper limit to the jet may result in a lower limit for the amount of tipping to be expected.

Magnetic trapping and self-assembly of multicomponent nanowires

Magnetic nanowires suspended in fluid solutions can be assembled and ordered by taking advantage of their large shape anisotropy. Magnetic manipulation and assembly techniques are demonstrated, using electrodeposited Ni nanowires, with diameter 350 nm and length 12 μm. Orienting suspended nanowires in a small magnetic field H≈10 G promotes self-assembly of continuous chains that can extend over several hundred μm. The dynamics of this process can be described quantitatively in terms of the interplay of magnetic forces and fluid drag at low Reynolds number. In addition, a new technique of magnetic trapping is described, by which a single magnetic nanowire can be captured between lithographically patterned magnetic microelectrodes. The use of three-segment Pt–Ni–Pt nanowires yields low resistance, Ohmic electrical contacts between the nanowires and the electrodes. This technique has potential for use in the fabrication and measurement of nanoscale magnetic devices.

The mode of mechanical integrin stressing controls intracellular signaling in osteoblasts.

Following the idea that integrin receptors function as mechanotransducers, we applied defined physical forces to integrins in osteoblastic cells using a magnetic drag force device to show how cells sense different modes of physical forces. Application of mechanical stress to the beta1-integrin subunit revealed that cyclic forces of 1 Hz were more effective to stimulate the cellular calcium response than continuous load. Cyclic forces also induced an enhanced cytoskeletal anchorage of tyrosine-phosphorylated proteins and increased activation of the focal adhesion kinase (FAK) and mitogen activated protein (MAP) kinase. These events were dependent on an intact cytoskeleton and the presence of intracellular calcium. Analyses of the intracellular spatial organization of the calcium responses revealed that calcium signals originate in a restricted region in the vicinity of the stressed receptors, which indicates that cells are able to sense locally applied stress on the cell surface via integrins. The calcium signals can spread throughout the cell including the nucleus, which shows that calcium also is a candidate to transmit mechanically induced information into different cellular compartments.

Superconducting magnets for Maglifter launch assist sleds

The Maglifter is an electromagnetic catapult being considered by NASA to reduce the cost of lifting a payload into space. The system would accelerate a vehicle of up to 590 tonnes to a final velocity of 268 m/s at an acceleration of 2 g. Superconducting coils are considered for levitation because they permit track-to-vehicle clearances of more than 95 mm. The high clearances reduce tolerances and maintenance costs, and allow a system with permanently deployed wheels for take- off and emergency landing. Cable-in-conduit conductors (CICC) were selected because of their high electrical and mechanical strength, as well as high energy margin for stability. The selected coil shape is a pair of racetrack coils forming a module with four modules on a sled. The superconducting levitation modules weigh about 4% of the gross lift off weight and are capable of achieving lift off at about 20 m/s. The maximum magnetic drag power is negligible compared to the power required for acceleration.

Kinematics of the H2O Masers in W49N: Analysis of the Velocity Variance‐Covariance Matrix

The proper motions of the H2O masers in W49N have been measured with multiepoch very long baseline interferometry (VLBI) by Gwinn, Moran, & Reid. The number of motions derived is large (105), and the spatial coverage of the source by maser spots is excellent, making W49N a natural candidate for analytic tools based on diagonalization of the velocity variance-covariance matrix (VVCM). The velocity dispersions (or internal relative velocities) used in VVCM analysis are the quantities directly determined by VLBI proper motion experiments, which lack an absolute phase reference. I apply the VVCM diagonalization procedure to the H2O masers in W49N, deriving in an objective, model-independent way the kinematic axes of the outflow. I then compare these local axes with various geometrical axes suggested by the morphology of an apparent ring of H II regions that accompany the one containing H2O masers, and with the axis of the large-scale outflow seen in molecular emission. I also present kinematic evidence not revealed by previous modeling for pronounced asymmetry of the collimating mechanism that channels the maser outflow, and propose an explanation in terms of magnetic drag.

Figuring Flow

NASA and the US Navy are exploring magnetic fields in search of quicker, smoother, and cheaper launches. A Navy program based in Lakehurst, NJ, wants to learn if magnetic propulsion is the answer. It awarded two contracts in December for what it calls the electromagnetic aircraft launch system. One award went to Northrop Grumman of Sunnyvale, California, and the other to General Atomics in San Diego. NASA is in the second year of a three-year program to investigate magnetic launch technology. The systems under study by NASA combine linear induction, to accelerate the vehicle to launch speed, with magnetic levitation, using opposing magnetic fields to suspend the vehicle above its track. The Navy’s catapult program does not require magnetic levitation. The US Maglev Technology Assessment, written jointly by the Corps of Engineers and the Department of Transportation, points out that since ‘magnetic drag is small at high speeds, only aerodynamic drag consumes appreciable energy.

Induction for the Birds

NASA and the US Navy are exploring magnetic fields in search of quicker, smoother, and cheaper launches. A Navy program based in Lakehurst, NJ, wants to learn if magnetic propulsion is the answer. It awarded two contracts in December for what it calls the electromagnetic aircraft launch system. One award went to Northrop Grumman of Sunnyvale, California, and the other to General Atomics in San Diego. NASA is in the second year of a three-year program to investigate magnetic launch technology. The systems under study by NASA combine linear induction, to accelerate the vehicle to launch speed, with magnetic levitation, using opposing magnetic fields to suspend the vehicle above its track. The Navy’s catapult program does not require magnetic levitation. The US Maglev Technology Assessment, written jointly by the Corps of Engineers and the Department of Transportation, points out that since ‘magnetic drag is small at high speeds, only aerodynamic drag consumes appreciable energy.

Configuration of Superconducting Magnet for the reduction of leakage magnetic field and improvement of electromagnetic force characteristics

In this paper, we consider configurations of the superconducting magnet (so call SCM) for reduction of weight of magnetic shielding and improvement of electromagnetic force characteristics. We can reduce leakage flux by SCM configuration with small size superconducting coils (so call SC coils) on these ends and make use of it to reduce the weight of magnetic shielding. We vary SCM size (parameter), keeping constant length of bogie, to seek optimal configuration of SCM. Generally speaking, SCM configuration with smaller size SC coils on these ends of coil array (and long pitch SCM configuration) is more advantageous for magnetic shielding, magnetic drag force and levitation force. On the other hands, propulsion force decreases in this case. Therefore compromise must be taken between the former and latter. Optimal SCM configuration designed from the viewpoint of magnetic shielding is consistent with the one which is designed from the viewpoint of electromagnetic characteristics.

Multi-epoch Doppler tomography and polarimetry of QQ Vul

We present multi-epoch high-resolution spectroscopy and photoelectric polarimetry of the long-period polar (AM Herculis star) QQ Vul. The blue emission lines show several distinct components, the sharpest of which can unequivocally be assigned to the illuminated hemisphere of the secondary star and used to trace its orbital motion. This narrow emission line can be used in combination with Na i absorption lines from the photosphere of the companion to build a stable long-term ephemeris for the star: inferior conjunction of the companion occurs at HJD = 244 8446.4710(5)+E×0·d154 520 11(11). The polarization curves are dissimilar at different epochs, thus supporting the idea of fundamental changes of the accretion geometry, e.g., between one- and two-pole accretion modes. The linear polarization pulses display a random scatter by 0.2 phase units and are not suitable for the determination of the binary period. The polarization data suggest that the magnetic (dipolar) axis has a colatitude of 23°, an azimuth of −50°, and an orbital inclination between 50° and 70°. Doppler images of blue emission and red absorption lines show a clear separation between the illuminated and non-illuminated hemispheres of the secondary star. The absorption lines on their own can be used to determine the mass ratio of the binary by Doppler tomography with an accuracy of 15–20 per cent. The narrow emission lines of different atomic species show remarkably different radial velocity amplitudes: K = 85–130 km s−1. Emission lines from the most highly ionized species, He ii, originate closest to the inner Lagrangian point L1. We can discern two kinematic components within the accretion stream; one is associated with the ballistic part, and the other with the magnetically threaded part of the stream. The location of the emission component associated with the ballistic accretion stream appears displaced between different epochs. Whether this displacement indicates a dislocation of the ballistic stream, e.g. by a magnetic drag, or emission from the magnetically threaded part of the stream with near-ballistic velocities, remains unsolved.