Toshihisa Honma

Estimation of effective permeability of magnetic composite materials

This paper describes a method to estimate effective permeability of magnetic composite materials for static field. In the present method, the structures of the composite materials are assumed to be periodic, and the unit cell is defined. The effective permeability is determined on the basis of magnetic energy balance in the unit cell. The present method considers magnetic interaction between inclusions of the composite materials, and is more accurate and useful. Therefore, the present method can be more widely applied than conventional models, for example, the Maxwell-Garnett formula and the Bruggeman formula. Validity of the present method is confirmed by numerical analyses. This approach can be applied also to nonlinear magnetic composite materials.

Analysis of magnetic shielding effect of layered shields based on homogenization

This paper describes a nonlinear analysis of magnetic field based on homogenization. The analysis of a magnetic field is time-consuming when the problem includes magnetic substance with fine structure. Simplification of the fine structure by homogenization makes it possible to analyze them efficiently. The authors have introduced a homogenization method to estimate effective permeability of magnetic composite structure for a static field. This method can be applied not only for linear problems but also nonlinear ones. In this paper, the magnetic shielding effect of layered nonlinear material is analyzed by using the homogenization method, and the applicability of this method is discussed

On mixed boundary element solutions of convection-diffusion problems in three dimensions

Abstract Three-dimensional boundary element solutions of steady convection-diffusion problems are presented. Numerical properties such as stability and accuracy on boundary element solutions based on a discretization using mixed boundary elements are compared with those of constant elements. It is found that boundary element solutions are unconditionally stable in space, nd that their relative errors to exact solutions hardly depend on the Pecler number. These results prove that the boundary element method is superior to domain-type numerical techniques which have a criterion of numerical stability and whose approximate solutions depend to some extent on the Pecelet number. The advantage of BEM using mixed elements, as compared with constant element solutions is also shown.

Numerical analysis of frozen field model for levitation force of HTSC

Abstract The levitation force and the stable equilibrium between a permanent magnet and a high T c superconductor are analysed numerically under the assumption of a frozen field. The constitutive relation of a frozen field model is discussed to clarify the differences between it and the critical state model. The vertical levitation force and the horizontal restoring force are evaluated using the frozen field model, and the numerical solutions agrees well with experimental results.

A three dimensional analysis of magnetic fields around a thin magnetic conductive layer using vector potential

This paper describes a method for the three dimensional analysis of quasi-static magnetic fields around a thin magnetic conductive layer. The impedance boundary conditions (IBCs) for the vector potential are introduced on both sides of the layer surface. The magnetic field around the layer is numerically determined under the IBCs. The present method does not require numerical analysis of the electromagnetic field inside the layer which is formidable due to its extreme spatial structure. The present method gives reasonable solutions to numerical examples.

Numerical analysis of magnetization of a bulk high T/sub c/ superconductor

Magnetization of a bulk high T/sub c/ superconductor (HTSC) is evaluated with the numerical simulation codes. The field-cooled magnetization of the HTSC is analyzed by using the critical state model. The pulse magnetization process is also analyzed by using the flux creep-flow model. The numerical solutions are discussed to clarify the time dependent effects in the reported experimental results on the pulse magnetization.

A boundary element method for potential fields with corner singularities

Abstract It is known that the spatial derivatives of a potential function become infinite at corner points on a boundary under certain conditions. Numerical methods such as finite and boundary element methods cannot adequately analyse the potential fields with those field singularities since they conventionally employ piecewise polynomials. This paper presents a boundary element formulation for the accurate analysis of two-dimensional potential fields with the field singularities. In this method boundary integral equations are formulated for unknown regularised functions, which are introduced by subtracting off the field singularities from the original potential function. Moreover, at the singular corner points boundary integral equations are formulated to determine the unknown expansion coefficients that characterize the behavior of the potential function around the singular corner points. By simultaneously solving the boundary integral equations for the regularized function and the expansion coefficients the original potential function is accurately determined.

An axisymmetric boundary element analysis of levitation force on high-Tc superconductor

Abstract The electromagnetic force acting on a high- T c superconductor (HTSC) is evaluated in an axisymmetric problem by using the boundary element method (BEM). Application of the BEM is useful since the open boundary is treated in the problem. Nonlinear constitutive relations between screening current and electric field are important in the numerical analysis. When a permanent magnet is moved towards and away from the HTSC, the levitation force between the magnet and the HTSC shows hysteresis properties, and repulsive force often changes to attractive force. The BE solutions are in good agreement with experimental results. Gradients of major and minor loops of the force are also evaluated with respect to spring constants.

Numerical evaluation of levitation force of HTSC flywheel

Levitation force between permanent magnets and high-T/sub c/ superconductors (HTSCs) is evaluated numerically based on the critical state model. The bulk HTSC is approximated to a thin plate multilayer model from its anisotropic structure. The thin plate eddy current code with the finite element method is applied to the analysis of the HTSC flywheel, where ring magnets and the HTSC are arranged in triple concentric circles. The size and the combination of the magnets are examined to obtain the large levitation force. It is shown that the levitation force of the HTSC flywheel depends strongly on the magnetic field configuration.<<ETX>>

A Boundary-Element Analysis of TEM Cells in Three Dimensions

Transverse electromagnetic (TEM) transmission-line cells are modeled and analyzed in three dimensions based on a mixed discretization using both constant and linear boundary elements. In particular, the distributed characteristic impedance along the line is evaluated for symmetrical square TEM cells of the type built at the National Bureau of Standards (NBS) in order to confirm the validity of the present numerical technique. Comparison with experimental results is shown. This paper shows that our numerical approach should contribute to TEM cell design.