One-sided Flux Research Articles

The VEM-based positivity-preserving conservative scheme for radiation diffusion problems on generalized polyhedral meshes

In this paper, for the 3D radiation diffusion equation on generalized polyhedral meshes, we construct a positivity-preserving conservative scheme based on the virtual element method (VEM). Firstly, the equation is discretized by finite volume, and the one-sided flux on the cell-face is discretized by using the fixed stencil of all vertices. Then, the nonlinear two-point flux approximation is used to obtain the equations about cell-centered unknowns and vertex unknowns; the lowest order VEM solves the vertex values of the mesh. Finally, the conservative equations containing only cell-centered unknowns are solved. This scheme ensures the high accuracy of VEM and embodies the local conservation and positivity-preserving. Compared with the existing nonlinear positivity-preserving finite volume schemes, the new scheme does not need nonlinear iteration for linear problems. For nonlinear problems, it only needs to use the VEM to solve the nonlinear system. Numerical results show that the new scheme can achieve the optimal convergence order and maintain the nonnegativity of the solution for generalized polyhedral meshes and arbitrary diffusion tensors.

The cell-centered positivity-preserving finite volume scheme for 3D anisotropic diffusion problems on distorted meshes

In this paper, a new cell-centered positivity-preserving finite volume scheme is proposed for the 3D anisotropic diffusion problems on distorted meshes. The primary unknowns and auxiliary unknowns are used in this scheme. First, the one-sided flux on each cell facet is discretized by a fixed stencil. Then, the nonlinear two-point flux approximation is applied to get the cell-centered discrete scheme. Besides, a second-order interpolation algorithm is constructed to eliminate the auxiliary unknowns in flux expressions. Furthermore, an improved Anderson acceleration method is given to accelerate the convergence of Picard iterations. Finally, several numerical examples are presented to show the accuracy and efficiency of the proposed scheme.

Design of coaxial magnetic gear utilising a novel permanent magnet Halbach array structure

Mechanical gears are constrained due to wear and tear and call for lubrication. A magnetic gear, utilising permanent magnet (PM) arrays, facilitates the mechanical gear roles. It can withstand high-speeds and large loads with zero friction. The magnetic gear is more efficacious on account of the least noise, performance, overload protection, and physical isolation between parts than conventional mechanical gears. The quantity of PMs in magnetic structures plays a principal role in its total price, which necessitates optimal arrangements for PMs. Halbach array provides a bigger torque density according to its one-sided flux. In this research, proposing a novel Halbach array structure, leads to intensification in the one-sided flux in a much sinusoidally waveform that consequently increases the magnetic torque. These all lead to gain higher torques in constant volumes of magnets. Besides, the magnetic torque ripple and the modulators’ losses are decremented. The new model is based on the variation of the magnetisation angles of the adjacent permanent magnet blocks, in the array. Various states of the magnetisation angles in the array are optimised based on a heuristic method. This is studied in the whole trigonometric range for magnetisation angles characteristics. The prototype is fabricated based on the optimised magnetic gear design and complies with the results.

A Novel Coaxial Magnetic Gear With Unequal Halbach Arrays and Non-Uniform Air Gap

In order to improve the output torque and transmission stability of coaxial magnetic gear (CMG), a novel CMG with unequal Halbach arrays of the inner rotor and non-uniform air gap is proposed in this paper. According to the principle of magnetic field modulation and “one-sided flux” structures, the unequal Halbach arrays could augment the magnetic field in the inner air gap. Moreover, the permanent magnets (PMs) of the eccentric structure could obtain non-uniform air gap, which is helpful to enhance the flux-modulation effect. The proposed CMG topology with 4 inner and 17 outer pole pairs is established. The topology performance is assessed and calculated by finite element analysis (FEA).

Hierarchical shape optimization of one-sided transverse flux heating induction coil

Purpose The transverse flux heating (TFH) concept offers very high electrical efficiency in combination with unique technological flexibility. Numerous advantages make this method beyond competition to be applied in e.g. processing lines. However, all potential advantages of TFH can be realized in practice only by optimal design of the inductor shape using numerical modelling and optimization techniques. This paper aims to describe a hierarchical approach to the optimal design of a one-sided induction coil, which will be used for one-sided TFH of continuous moving thin metal strip to achieve a homogeneous temperature distribution along the strip width. Design/methodology/approach Depending on the design step, 2D or 3D FEM simulations using ANSYS® Mechanical including the electromagnetics package are used. The harmonic electromagnetic solution is coupled to a transient thermal model which takes the strip movement into account. All models use the symmetries of the inductor workpiece arrangement to keep the calculation times as low as possible. Findings Due to the geometry of a TFH coil, the models can image a quarter or half of the arrangement. Preliminary investigations of different inductor head shapes can be carried out quickly and then further improved on more complex models in combination with the use of optimization algorithms. Practical implications Using hierarchical structure for designing a one-sided TFH coil, offers an efficient and quick way to create a coil which is adapted to the application. Originality/value The one-sided inductor design is considered, and the results are generally valid.

The coupled method for singularly perturbed Volterra integro-differential equations

In this work a coupled (LDG-CFEM) method for singularly perturbed Volterra integro-differential equations with a smooth kernel is implemented. The existence and uniqueness of the coupled solution is given, provided that the source function and the kernel function are sufficiently smooth. Furthermore, the coupled solution achieves the optimal convergence rate p+1 in the L^{2} norm and a superconvergence rate 2p at nodes for the numerical solution hat{U}_{N} with the one-sided flux inside the boundary layer region under layer-adapted meshes uniformly with respect to the singular perturbation parameter ϵ.

Hypervapotron Mockup Experiment and Analysis for Application into the Plasma Facing Components

A hypervapotron mockup was fabricated and used in the Neutral Beam Injection (NBI) heating system at KAERI. During the test, especially with the JAEA ion source, which has a focused beam and a long pulse, some failures in the mockup were experienced. Using the existing correlation for a critical heat flux (CHF), the incident CHF was assessed, in which the modified Tong-75 CHF correlation for the one-sided heat flux was used. In addition, using the conventional CFD and FEM codes such as ANASYS-CFX and ANYS-mechanical, the thermal lifetimes were evaluated according to the beam operation and water cooling conditions. The evaluated ICHF is 28.6 MW/m2 and is much higher than the loaded peak heat of about 8.7 MW/m2 at a 2.3 MW heat load. The cause of failure seems not to be the CHF considering the existing correlations. The thermal lifetimes were evaluated to be about 100 cycles and 11 cycles for 1.56 MW and 2.3 MW heat load conditions, respectively. When the dump heat is reached in the mockup frequently, it can fail in the corner of the inlet region below 11 cycles when a 2.3 MW heat is loaded.

Optimization of Magnetization Directions in a 3-D Magnetic Structure

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This study introduces a design method for determining the optimized magnetization directions in 3-D magnetic systems. Based on a modified topology optimization method, discrete magnetizations are investigated in six directions <formula formulatype="inline"><tex Notation="TeX">$(\pm{x},\pm{y},\pm{z})$</tex></formula>. The finite-element method is used for the 3-D magnetostatic field analysis. The proposed method is applied to the design of a magnet pattern having “one-sided flux” and the design results show that the optimized magnet pattern appears as one or two Halbach arrays according to the shape of the design domain. The optimization process is accomplished by using sequential linear programming and the adjoint variable method. </para>

Characterization of Skip or Far Track Erasure in a Side Shield Design

Side track erasure (STE), either skip or far track, has been studied for a PMR writer with side shielded (SS) design. Both bit error rate (BER) and noise amplitude based STE measurements indicate the side writing fields are strong at SS bottom corners and/or inner edges. With DC background low-frequency noise amplitude measurement, the root cause of the STE is characterized as flux from main pole tip going into media soft under-layer (SUL) and returning to SS bottom corners and/or inner edges. Moreover, the return flux path is identified with a unique one-sided signature depending on the pole polarity and shield initialization direction and can switch side when pole polarity or shield initialization direction is changed. By employing magnetic force microscope (MFM) analysis of a SS head under two shield initialization directions, we can explain this unique one-sided flux path by the observed SS domain structure. Furthermore, a micro-magnetic modeling of the SS design is constructed to understand the observation qualitatively.

Uniform superconvergence analysis of the discontinuous Galerkin method for a singularly perturbed problem in 1-D

It has been observed from the authors' numerical experiments (2007) that the Local Discontinuous Galerkin (LDG) method converges uniformly under the Shishkin mesh for singularly perturbed two-point boundary problems of the convection-diffusion type. Especially when using a piecewise polynomial space of degree k, the LDG solution achieves the optimal convergence rate k+1 1 under the L 2 -norm, and a superconvergence rate 2k+1 1 for the one-sided flux uniformly with respect to the singular perturbation parameter ∈. In this paper, we investigate the theoretical aspect of this phenomenon under a simplified ODE model. In particular, we establish uniform convergence rates √∈ (1nN/N) k+1 for the L 2 -norm and ( ln N / N ) 2k+1 for the one-sided flux inside the boundary layer region. Here N (even) is the number of elements.

Magnetostatic energy of structures with rotating vector magnetizations

We show that, no matter which of two methods of calculating the change in magnetostatic energy is used, there is no change in energy when a hollow cylinder with a one-sided flux, rotating vector magnetization is placed in a uniform magnetic field. Similarly, there is no energy change when a planar one-sided flux structure is exposed to a uniform field. Only one case has been found where a one-sided flux, spherical structure shows no such energy change. We show this phenomenon to be a result of the rotating magnetization and not a property of one-sided flux structures.

One-sided fluxes in planar, cylindrical, and spherical magnetized structures

In planar structures, magnetization patterns exist that have the surprising property that all the external fringing field of flux emerges from one side of the structure, with precisely none appearing on the other side. In the last 25 years, this fact has led to a number of useful applications. More recently, the same concept has been found to hold for both cylindrical and spherical hollow structures, where all the fringing flux emerges either inside or outside the structure, with precisely none appearing on the other side. Again, this has led to a number of important practical applications. While many of the concepts have been published previously, this paper contains, for the first time, a uniform mathematical analysis of these one-sided flux configurations. Additionally, the paper reviews the principal applications of one-sided flux structures.

One-body nuclear friction

We have calculated the velocity dependent forces acting between two nuclei that arise due to one-body mechanism of nuclear excitation when they are dragged against one another with constant velocity. The nuclear friction coefficients are then extracted from the velocity dependence of these forces which is found to be strongly linear. The one-body force is calculated by solving the time-dependent Schrödinger equation for all the occupied single-particle states of a nuclear system in a central collision. Each nucleus in this model is assumed to be described by a single-particle Woods-Saxon potential filled with 40 nucleons each. The magnitude of the resulting one-body friction is found to be in between the proximity and surface frictions. The proximity-friction is too small by about an order of magnitude. To check this result, we calculated the one-sided flux from one nucleus to the other. The friction force connected to this flux (i.e. the one-body exchange friction) turns out to be about half or less than the one body friction. We conclude that theproximity-friction grossly underestimates the one-body exchange friction. Furthermore,inelastic excitations are at least as important for one-body dissipation at distances beyond the touching point as is particle exchange.

Experimental demonstration of one-sided flux in magnetic recording tape

It is shown that a magnetic tape can be magnetized so that the fringing field exists on only one side of the tape, a behavior predicted several years ago but never previously confirmed by direct experiment. This one-sided flux requires a tape specially produced to have equal remanence in any direction normal to the transverse axis.

Independent particle model for nucleon transfer in heavy ion collisions

We formulate a three-dimensional quantum-mechanical model for the study of nucleon transfer in heavy ion collisions. This model describes the independent particle motion of nucleons initially separated in two adjacent cubic boxes and brought into contact through a window created in the separating wall. We calculate the one-sided flux and the spread of the mass distribution and compare them with results derived from other models.

Wigner function and the one-sided flux

We calculate the Wigner function of the one-body density of a system of 32 independent particles moving in two adjacent cubic boxes communicating through a window. We discuss the applicability of the currently used definition of the classical analog of the one-sided flux obtained from the Wigner function.[NUCLEAR REACTIONS Wigner function for a simple quantum mechanical model, nucleon exchange, static one-sided flux.]

Quantum mechanical model for the one-sided flux in heavy ion collisions

We construct a three-dimensional quantum mechanical model relevant for nucleon transfer in heavy ion collisions. It consists of two adjacent cubic boxes with a rectangular window in the wall which separates them. We calculate the one-sided flux as a function of the window size and compare it with previous results.

A numerical method of solving the radiation transfer equation in one-dimensional problems of radiation gas dynamics

Integration over the angles and quanta energies, of the exact solution of the spectral radiation transfer equation is used to approximate the profiles of the gas dynamic parameters in a spherical geometry. The averaging coefficients, describing the absorption and emission of radiation of a difference-mesh cell are found. A difference scheme for the averaged transfer equations with respect to one-sided radiant flux through a sperical surface is constructed. The scheme enables calculations of media of any optical thickness to be carried out. By passing to the limit a scheme for a plane layer is obtained. The results of numerical calculations, found by the method described, are given for the plane problem of the effect of laser radiation on an obstacle in a vacuum. The results obtained take into account in detail the angular and spectral composition of the thermal radiation of a plasma.

On the properties of two-dimensional dipoles and magnetized bodies

Several little-known relationships between the two-dimensional magnetic dipole and its external field are discussed in both the spatial and spatial frequency domains. Extensions of the theory to arbitrary magnetization patterns are made, which lead to the familiar Wallace results as a special case. The magnetization conditions yielding one-sided flux patterns are analyzed. Several of the results are expressed in matrix notation, facilitating brevity. Finally some limitations on determining internal magnetization patterns from measurements of the external field alone are discussed.

One-sided fluxes -- A magnetic curiosity?

It is shown that a previously unknown class of magnetization patterns exists in planar structures which have the unique property that all the flux escapes from one surface with none leaving the other side. A simple case is a constant amplitude rotating vector magnetization where the sense of rotation dictates which surface has no flux. More complicated magnetization patterns are elucidated. The likelihood that the one-sided flux phenomenon occurs partially in the normal write, the contact-printing and the print-through processes of tape recording is discussed. It is concluded that significant improvements in tape recording performance would ensue if means could be found to enhance the effect.