Takayoshi Nakata

Improvements of the T- Omega method for 3-D eddy current analysis

An improved T- Omega method that can analyze magnetic fields produced not only by eddy currents but also by magnetizing currents is proposed. The method is applied to the analysis of 3-D eddy-current models with holes. The usefulness of the method is investigated by comparing calculated results with measured results and with results obtained by the A- Phi method. The T- Omega method has the advantage that the CPU time can be considerably reduced when most of the analyzed region is current-free and the eddy current flows two-dimensionally. The method is especially effective when the shape of the winding is simple and the distribution of magnetizing current is known beforehand. It is not effective when most of the analyzed region is current-carrying. >

3-D finite element method for analyzing magnetic fields in electrical machines excited from voltage sources

A method for analyzing 3-D magnetic fields and currents in electrical machines excited from voltage sources has been developed. It was obtained by expanding the 2-D finite-element method into three dimensions, using the A phi method. The basic idea and the finite-element formulation are described. The effectiveness of the method is shown by some application examples. >

Method for determining relaxation factor for modified Newton-Raphson method

In order to reduce the CPU time for the modified Newton-Raphson method which introduces a relaxation factor, the effect of the relaxation factor on the residual of the Galerkin method is examined in detail. It is shown that a relaxation factor which always provides convergent solutions can be easily searched. Various methods of searching for the relaxation factor to be used are compared. >

Numerical analysis of transient magnetic field in a capacitor-discharge impulse magnetizer

A method for analyzing the magnetic field in a capacitor-discharge impulse magnetizer is established by modifying the finite element method. The effects of charging voltage, capacitance and resistance on the behaviour of the localized fluxes in the Impulse magnetizer are analyzed quantitatively. As the detailed distribution of the flux density can be obtained, the optimum design of the magnetizer which produce desired magnet will be possible using our new method.

Improvement of convergence characteristic of ICCG method for the A-/spl phi/ method using edge elements

The effect of the scalar potential /spl phi/ in the A-/spl phi/ method on the convergence characteristic of the incomplete Cholesky conjugate gradient (ICCG) method using the edge element is investigated. Several 3-D eddy current models are analyzed both by taking into account /spl phi/ and neglecting /spl phi/ to compare the convergence characteristics. It is illustrated that the CPU time using /spl phi/ is less than 1/2 of that neglecting /spl phi/, and there are some models in which the use of /spl phi/ enables us to obtain convergent solutions.

Effects of Stress Due to Cutting on Magnetic Characteristics of Silicon Steel

Although deterioration of the magnetic characteristics of silicon steel due to shearing stress has been observed, the degree of deterioration has not previously been assessed quantitatively. With the recent development of a technique for measuring the microscopic distribution of flux density, the effects of stress on flux distribution can now be investigated quantitatively. In this paper the deterioration of the magnetization curve of nonoriented silicon steel due to shearing stress is examined.

Acceleration of convergence characteristic of the ICCG method

The effectiveness of renumbering for the incomplete Cholesky conjugate gradient (ICCG) solver, which is usually applied to direct solvers, is examined quantitatively by analyzing 3D standard benchmark models. On an acceleration factor which is introduced to obtain convergence quickly, indices for determining the optimum value of the acceleration factor, which minimizes the number of iterations, are discussed. It is found that the renumbering is effective to use with the ICCG solver, and the solver using the acceleration factor gives a good convergence characteristic even in the case when the conventional solver fails to provide convergent solutions. >

Improvements of convergence characteristics of Newton-Raphson method for nonlinear magnetic field analysis

In order to overcome the divergence of the Newton-Raphson iteration in the nonlinear magnetic field analysis, a relaxation factor is introduced and its optimum value is examined. It is shown that the modified Newton-Raphson method proposed exhibits quick and successful convergence even in the case when the conventional Newton-Raphson method fails in convergence. >

Comparison of coordinate systems for eddy current analysis in moving conductors

The moving and fixed coordinate systems for eddy current analysis with moving conductors are examined and compared. It is shown that the moving coordinate system is superior for transient analysis from the standpoints of accuracy, computer storage, and CPU time. In DC steady state analysis of large Peclet number, spurious oscillations occur when using the fixed coordinate system with the ordinary Galerkin finite element method. The solution using the moving coordinate system, however, can be obtained stably. >

3D magnetic field analysis using special elements

Three-dimensional special elements, called the gap element, the expanding element, and the shielding element, have been conceived for discretizing narrow gaps in an iron core, the long legs of a transformer core, and thin shielding plates. The concept of the 3D special element and its finite-element formulation are described. The special elements are applied to several models, and the effects of the elements on accuracy and CPU time are discussed. It is shown that CPU time can be reduced by using the special elements. >