Motoo Tanaka

Three-dimensional eddy current analysis by the boundary element method using vector potential

A boundary-element method using a magnetic vector potential for eddy-current analysis is described. For three-dimensional (3-D) problems, the tangential and normal components of the vector potential, tangential components of the magnetic flux density, and an electric scalar potential on conductor surfaces are chosen as unknown variables. When the approximation is introduced so that the conductivity of the conductor is very large in comparison with the conductivity of air, the number of unknowns can be reduced; also, for axisymmetric models the scalar potential can be eliminated from the unknown variables. The formulation of the boundary-element method using the vector potential, and computation results by the proposed method, are presented. >

Computation accuracies of boundary element method and finite element method in transient eddy current analysis

The computation accuracies of the boundary-element method (BEM) and finite-element method (FEM) in transient eddy-current problems are compared by using a slot-embedded conductor model and a diffusion model that can be solved theoretically. For computing the vector potential or magnetic flux density it is shown that larger time-step width can be chosen in the BEM than in the FEM method for the same accuracy. >

External conditions for the vector potential in the boundary element method

The boundary element method using electric field and magnetic flux density has been applied to three-dimensional electromagnetic field problems. It is also possible to use the magnetic vector potential as an unknown vector variable. Formulas for the boundary element method using the vector potential are derived. Furthermore, the external conditions for the vector potential in the boundary element method are discussed in connection with a three-dimensional magnetostatic problem. The convergence characteristics of the proposed boundary element method are verified. >

A new approach to the transient analysis of magnetic field with variable transformation based on eigenvalues

A novel approach to the transient analysis of a magnetic field is presented that uses the formulation of a boundary-element model in two-dimensional problems. In order to solve the transient problems, state equations are formed using the boundary element model, and are solved using the variable transformation based on eigenvalues. The computational accuracy of the proposed method is evaluated by an infinite plate model and an infinite cylinder model in which the impressed magnetic flux densities are given by a unit step function and a sinusoidal function respectively. >

Extraction of stomach contour from X-ray image

The stomach contour can be automatically and accurately extracted from the characteristics of X-ray images. The approximate stomach is obtained from the combination image which is constructed from a binary version of the original image and its differential image. The stomach contour is extracted using the brightness of the differential image and the shape of stomach approximation.