Magnetic Flux Intensity Research Articles

Multiple parallel symmetric permeable model-III cracks in a piezoelectric/piezomagnetic composite material plane

In this paper, the interactions of multiple parallel symmetric and permeable finite length cracks in a piezoelectric/piezomagnetic material plane subjected to anti-plane shear stress loading are studied by the Schmidt method. The problem is formulated through Fourier transform into dual integral equations, in which the unknown variables are the displacement jumps across the crack surfaces. To solve the dual integral equations, the displacement jumps across the crack surfaces are directly expanded as a series of Jacobi polynomials. Finally, the relation between the electric field, the magnetic flux field and the stress field near the crack tips is obtained. The results show that the stress, the electric displacement and the magnetic flux intensity factors at the crack tips depend on the length and spacing of the cracks. It is also revealed that the crack shielding effect presents in piezoelectric/piezomagnetic materials.

Performance analysis of magnetic flux compression by plasma liner

The paper presents the results of the theoretical and numerical performance analysis of the experimental scheme for amplification of magnetic flux intensity via its compression by plasma liner. 0D estimations and 2D computations results are compared. The simulations were carried out with the use of RMHD code MARPLE (IMM RAS). The scheme performance affected by the Rayleigh-Taylor instability, developed in the case of initially disturbed plasma shell density, is studied. The possible penetration of the compressor shell plasma from the discharge chamber into the load area results in the nonuniformity of magnetic pressure in it. The simulation proves the possibility of elimination of this unwanted effect by proper selection of the experiment’s parameters. The correlation of the numerical results for this kind of problems using a simplified 0D model and 2D RMHD simulation with the MARPLE code are demonstrated. The prospects of the plasma magnetic flux compression scheme are discussed.

Magnetohydrodynamic analysis of the interaction of magnetized plasma flow with a perfect-conducting object

In this study, a supersonic and super-Alfvénic magnetized plasma flow past a perfect-conducting cylinder was simulated based on single-fluid ideal magnetohydrodynamics to clarify the piling-up process of the magnetic field frozen in the plasma flow. Therefore, the magnetic field is assumed to be perpendicular to both the cylinder axis and the flow direction. Simulation results indicated that the cylinder continuously traps the magnetic field and an unsteady flow field is generated. Even though the drag force exerting on the cylinder is expected to continuously increase with the continuous increase in the trapped magnetic field and the shock layer, the intensity of magnetic flux density at the cylinder surface is saturated at a certain value and the drag force is also saturated. The saturated values are characterized by the Alfvén Mach number of the mainstream. Furthermore, on this flow structure the wake flow in which magnetic reconnection plays an important role was found to have a strong influence by using the pseudomagnetic reconnection in the ideal magnetohydrodynamic flow.

Structural Invariance of Sunspot Umbrae over the Solar Cycle: 1993 – 2004

Measurements of maximum magnetic flux, minimum intensity, and size are presented for 12 967 sunspot umbrae detected on the National Aeronautics and Space Administration/National Solar Observatory (NASA/NSO) spectromagnetograms between 1993 and 2004 to study umbral structure and strength during the solar cycle. The umbrae are selected using an automated thresholding technique. Measured umbral intensities are first corrected for center-to-limb intensity dependence. Log-normal fits to the observed size distribution confirm that the size-spectrum shape does not vary with time. The intensity – magnetic-flux relationship is found to be steady over the solar cycle. The dependence of umbral size on the magnetic flux and minimum intensity are also independent of the cycle phase and give linear and quadratic relations, respectively. While the large sample size does show a low-amplitude oscillation in the mean minimum intensity and maximum magnetic flux correlated with the solar cycle, this can be explained in terms of variations in the mean umbral size. These size variations, however, are small and do not substantiate a meaningful change in the size spectrum of the umbrae generated by the Sun. Thus, in contrast to previous reports, the observations suggest the equilibrium structure, as manifested by the invariant size-magnetic field relationship, as well as the mean size (i.e., strength) of sunspot umbrae do not significantly depend on the solar-cycle phase.

Effects of magnetic field and electric current on the solidification of AZ91D magnesium alloys using an electromagnetic vibration technique

Using an electromagnetic vibration (EMV) technique, we solidified the AZ91D magnesium alloys at different magnetic flux densities and electric current levels when the vibration frequency was kept at 900 Hz so as to find the optimum processing parameters. The microstructure and microtexture of the alloy were examined under various magnetic fields, revealing that with the increase of the magnetic flux density, B 0, the microstructure becomes finer and finer and eventually consists of equiaxed grains with the average diameter approximately 57 μm at the magnetic flux intensity of B 0 = 10 tesla (T). In terms of the effect of the electric current on microstructure formation, the average grain size first decreases when the effective electric current, J e, increases from 10 to 60 ampere (A) and then increases when the electric current is further increased from 80 to 120 A. The grain refinement mechanism is clarified when considering the overall EMV process during solidification. The competition between the Lorentz force due to the imposition of the alternating current and the static magnetic force is also incorporated, which is of great importance in elucidating the microstructure and the microtexture formation.

Connectionist approach for modeling the dry roll magnetic separator

Magnetic separation is an age-old technique for mineral beneficiation operations. The existing mathematical models for magnetic separators are quite complicated, and it is very difficult to measure the theoretical separation efficiency. The connectionist approach of modeling, to establish the relationships of the inputs and outputs, is preferred for this kind of problem. Experiments were carried out on a high-intensity roll magnetic separator to develop a database using four input variables (magnetic flux intensity, particle size, splitter position and roll speed) and two output variables (weight recovery and Fe recovery). The artificial neural network (ANN) and statistical methods (MLRG) were used to model the magnetic separation process. For the ANN, the regression coefficient (R2) values between the predicted and measured results were 0.89 and 0.94 for Fe recovery and weight recovery, respectively. Compared to ANN, the multivariable linear regression analysis showed inferior performance in predicting the weight recovery and the Fe recovery. The ANN models for the roll magnetic separator can predict the separation efficiency up to an acceptable limit. These models can be used to modify the operational parameters at mineral beneficiation plants to minimize the effects of variations in the raw material characteristics.

Separation behaviour of zinc dross from hot dip galvanising melts of different aluminium concentrations by alternating magnetic field

Dross in zinc pots is the most important factor that impairs the surface quality of hot dip galvanising automobile steel sheet. Separation behaviour of zinc dross from galvanising melts of different Al concentrations (0·12, 4·5 and 55·0 wt-% by an alternating magnetic field has been investigated in order to reduce the dross defects on steel sheets. The properties of different zinc drosses were investigated by means of EDAX and the quantitative metallographic method and the conductivities were measured by physics property measurements system. The experimental results show that the zinc dross in different hot dip galvanising melts has different morphologies, compositions and structures, and the average particle size of the dross increases with the Al concentration. In the case of extra iron (above the solubility limit) in the zinc melt, zinc dross quantity also increases with the Al concentration. All of the three types of zinc dross particles >5 μm can be successfully separated when the magnetic frequency is 17·5 kHz, effective magnetic flux intensity is 0·05 T, imposed time is 15 s and the cross-section of the ceramic square pipe is 5 × 5 mm.

Dynamic response of magneto-rheological fluid channel flow with fluid-wall interactions

The objective of this study is to provide the fundamental data for the novel application of MR fluid plugging(MRF plugging) to a medical or safety devices for flow control. Experimental evaluation on dynamic response of MRF plugging in pressure mode was conducted to clarify the effect of piston velocity, magnetic flux intensity and wall surface roughness to its plugging performance. MRF plugging performance has been discussed through the evaluation of the endurance pressure of MRF plugging and flow rate. It is shown that the endurance pressure of MRF plugging is increased by the piston velocity, the magnetic flux intensity, and the adoption of wall surface structure. Furthermore, the endurance pressure is decreased for the circular and elastic tube, assuming a biological tube.

Coupled field state around three parallel non-symmetric cracks in a piezoelectric/piezomagnetic material plane

In this paper, the behavior of three parallel non-symmetric permeable cracks in a piezoelectric/piezomagnetic material plane subjected to anti-plane shear stress loading was studied by the Schmidt method. The problem was formulated through Fourier transform into three pairs of dual integral equations, in which unknown variables are jumps of displacements across the crack surfaces. To solve the dual integral equations, the jumps of displacements across the crack surfaces were directly expanded as a series of Jacobi polynomials. Finally, the relations among the electric displacement, the magnetic flux and the stress fields near the crack tips can be obtained. The results show that the stress, the electric displacement and the magnetic flux intensity factors at the crack tips depend on the lengths and spacing of cracks. It was also revealed that the crack shielding effect is present in piezoelectric/piezomagnetic materials.

Two collinear Mode-I cracks in piezoelectric/piezomagnetic materials

In this paper, the behavior of two collinear Mode-I cracks in piezoelectric/piezomagnetic materials subjected to a uniform tension loading was investigated by the generalized Almansi's theorem. Through the Fourier transform, the problem can be solved with the help of two pairs of triple integral equations, in which the unknown variables were the jumps of displacements across the crack surfaces. To solve the triple integral equations, the jumps of displacements across the crack surfaces were directly expanded as a series of Jacobi polynomials to obtain the relations among the electric displacement intensity factors, the magnetic flux intensity factors and the stress intensity factors at the crack tips. The interaction of two collinear cracks was also discussed in the present paper.

Optimal design and experimental verification of a magnetically actuated optical image stabilization system for cameras in mobile phones

A novel miniaturized optical image stabilizer (OIS) is proposed, which is installed inside the limited inner space of a mobile phone. The relation between the VCM electromagnetic force inside the OIS and the applied voltage is first established via an equivalent circuit and further validated by a finite element model. Various dimensions of the VCMs are optimized by a genetic algorithm (GA) to maximize sensitivities and also achieving high uniformity of the magnetic flux intensity.

Design of a direct sliding gearless electrical motor for an ergonomic electrical wheelchair

The use of the electrical wheelchairs designed for the disabled people should be easy and flexible. A brushless DC motor with a permanent magnet that can operate without gears was designed to be used in an ergonomic electrical power supported wheelchair. This motor will be placed within the hub of rear wheel with standard diameter of the wheelchair and it will have the capacity of producing high torque at low speed. The stator structure of the designed motor, its physical measurements and features, appearance of its iron sheet package, its mesh production, magnetic flux intensity, and flux lines and performance characteristic values were obtained. The results obtained showed that this new design with low speed and high torque can be an alternative in electrically driven devices and systems. Ill.18, bibl. 8 (in English; summaries in English, Russian and Lithuanian).

Radiative and magnetic properties of solar active regions

Context. The relationships between the photospheric magnetic flux and either the X-ray or extreme ultraviolet emission from the solar atmosphere have been studied by several authors. Power-law relations have been found between the total magnetic flux and X-ray flux or intensities of the chromospheric, transition region, and coronal emission lines in solar active regions. These relations were then used to infer the mechanism of the coronal heating. Aims. We derive accurate power laws between EUV line intensities and the total magnetic flux in solar active regions and discuss their applications. We examine whether these global power laws are capable of providing the diagnostics of the coronal heating mechanism. Methods. This analysis is based on EUV lines recorded by the Coronal Diagnostic Spectrometer (CDS) on SOHO for 48 solar active regions, as they crossed the central meridian in years 1996–1998. Four spectral lines are used: He I 584.3 A (3 × 10 4 K), O V 629.7 A (2.2 × 10 5 K), Mg IX 368.06 A (9.5 × 10 5 K), and Fe XVI 360.76 A (2.0 × 10 6 K). In particular, the Fe XVI 360.76 A line, seen only in areas of enhanced heating in active regions or bright points, has not been used before for this analysis. Results. Empirical power laws are established between the total active region intensity in the lines listed above and the total magnetic flux. We demonstrate the usefulness of some spatially integrated EUV line intensities, IT, as a proxy for the total magnetic flux, Φ, in active regions. We point out the approximate, empirical nature of the IT − Φ relationships and discuss the interpretation of the global power index. Different power index values for transition region and coronal lines are explained by their different dependence on pressure under the assumption of hydrostatic loop models. However, the global power laws are dominated by the size of the active regions, and we demonstrate for the first time the difficulties in uniquely relating the power index in the global IT − Φ relationship to the power index for individual loops and comment on results obtained by other authors. We caution against using global power laws to infer the coronal heating mechanism without a detailed knowledge of the distributions of the magnetic flux densities and instrumental response as a function of temperature. Despite these uncertainties, we show that the intensities of the transition region lines in individual loops depend on the photospheric magnetic flux density, φ, through Itr ∝ φ δt , δt 1, and under the assumption of hydrostatic loops we can place a constraint on the coronal heating models, obtaining the volumetric heating rate, EH (erg cm −3 s −1 ), EH ∝ φ γ ,w here 0.6 <γ <1.1.

Basic solution of four parallel non-symmetric permeable Mode-III cracks in a piezoelectric/piezomagnetic composite plane

The interaction of four parallel non-symmetric permeable cracks in a piezoelectric/piezomagnetic composite plane subjected to anti-plane shear stress loading was studied by the Schmidt method. The problem was formulated through a Fourier transform into four pairs of dual integral equations, in which unknown variables are jumps of displacements across the crack surfaces. To solve the dual integral equations, the jumps of displacements across the crack surfaces were directly expanded as a series of Jacobi polynomials. Finally, the relationships among the electric displacement, magnetic flux and stress fields near the crack tips were obtained. The results show that the stress, the electric displacement and the magnetic flux intensity factors at the crack tips depend on the lengths and spacing of cracks. It was also revealed that the crack shielding effect is present in piezoelectric/piezomagnetic composites.

An interface crack between two dissimilar functionally graded piezoelectric/piezomagnetic material half infinite planes subjected to the harmonic anti-plane shear stress waves

In this paper, the dynamic behavior of an interface crack between two dissimilar functionally graded piezoelec- tric/piezomagnetic material half infinite planes subjected to the harmonic anti-plane shear stress waves is investigated. To make the analysis tractable, it is assumed that the material properties vary exponentially with coordinate vertical to the crack. By using the Fourier transform technique, the problem can be solved with the help of a pair of dual integral equations in which the unknown variable is the jump of displacements across the crack surfaces. These equations are solved by using the Schmidt method. The relations among the electric filed, the magnetic flux field and the dynamic stress field near the crack tips can be obtained. Numerical examples are provided to show the effect of the functionally graded parameter and the circular frequency of the incident waves upon the stress, the electric displacement and the magnetic flux intensity factors of the crack.

Continuous separation of Fe–Al–Zn dross phase from hot dip galvanised melt using alternating magnetic field

Experiments to continuously separate Fe–Al–Zn dross phase from hot dip galvanising zinc melt were conducted on a laboratory scale apparatus by using high frequency alternating magnetic field. Effects of processing time (t) on separation efficiency were investigated. The experimental results show that using the electromagnetic repulsive force resulting from the electrical conductivity difference between zinc melt and Fe–Al–Zn dross phase, the deleterious zinc dross particles causing surface defects of galvanising steel sheets can be continuously separated from the zinc bath under alternating magnetic field, and the separation efficiency increases with the increase in processing time. When the magnetic frequency is 17·5 kHz, the effective magnetic flux intensity is 0·1 T, the cross-section of the ceramic square pipe is 10 × 10 mm, and the processing time is 0·6–2·5 s, the separation efficiency of zinc dross varies from 43·76 to 85·71%, and the experimental results are in reasonable agreement with the theoretical results.

The dynamic behavior of two parallel symmetric cracks in functionally graded piezoelectric/piezomagnetic materials

The dynamic behavior of two parallel symmetric cracks in functionally graded piezoelectric/piezomagnetic materials subjected to harmonic antiplane shear waves is investigated using the Schmidt method. The present problem can be solved using the Fourier transform and the technique of dual integral equations, in which the unknown variables are jumps of displacements across the crack surfaces, not dislocation density functions. To solve the dual integral equations, the jumps of displacements across the crack surfaces are directly expanded as a series of Jacobi polynomials. Finally, the relations among the electric, magnetic flux, and dynamic stress fields near crack tips can be obtained. Numerical examples are provided to show the effect of the functionally graded parameter, the distance between the two parallel cracks, and the circular frequency of the incident waves upon the stress, electric displacement, and magnetic flux intensity factors at crack tips.

Solutions to two or four parallel Mode-I permeable cracks in magnetoelectroelastic composite materials

The solutions to two or four parallel Mode-I permeable cracks in magnetoelectroelastic composite materials are derived using the generalized Almansi's theorem under permeable electric and magnetic boundary conditions. The problem can be solved through the Fourier transform with the help of two pairs of dual integral equations, in which unknown variables were jumps of displacements across crack surfaces, not dislocation density functions. To solve the dual integral equations, the jumps of displacements across crack surfaces were directly expanded in a series of Jacobi polynomials to obtain the relations among the electric displacement intensity factors, the magnetic flux intensity factors and the stress intensity factors at the crack tips. The paper presents the interactions of two or four parallel Mode-I cracks in magnetoelectroelastic composite materials and the crack-shielding effect in magnetoelectroelastic composite materials.

A Catastrophic Flux Rope in a Quadrupole Magnetic Field for Coronal Mass Ejections

We propose a flux-rope model for the initiation of flare-associated CMEs. The model triggers the eruption with a catastrophic loss of MHD equilibrium and then requires magnetic reconnection to sustain the eruption's acceleration. We carry out 2.5-dimensional time-dependent resistive MHD simulations, choosing the initial state such that a flux rope embedded in a quadrupole field is attached to the solar surface; we then increase the magnetic flux of the rope by two different amounts, thus obtaining two cases. One exhibits a gradual acceleration of the flux rope, whereas the other produces an immediate acceleration. In both cases, the maximum speed of the flux rope is representative of a fast CME. Thus, we conclude that the flux-rope dynamics depends on the intensity of the emergent magnetic flux. Our model does reproduce the three-component structure of CMEs.

Optimal Design of Magnetic Zooming Mechanism Used in Cameras of Mobile Phones via Genetic Algorithm

One of the important features for the cameras in cell phones today is the optical zooming. This paper presents design and optimization of a zooming mechanism via genetic algorithm (GA). The goal is to maximize voice coil motor (VCM) sensitivity in the zooming mechanism and, simultaneously, to keep various dimensions under physical limitation. The optimization first chooses key independent dimensions as design variables, and then establishes the computation procedure for the VCM sensitivity via equivalent circuitry. The correctness of the expression is validated by finite element analysis (FEA). Optimization results lead to that dimensions of the yokes and magnets reach optima at their extremes in preset constraints, and in result, high uniformity of the magnetic flux intensity along guide ways of the VCM is achieved