Study Of Material Modeling Problems In The Numerical Computation Of Magnetic Fields

Material Modeling problem is regarded as one of the three currently mainstream problems (material modeling, coupling and optimization) in the field of computational electromagnetism. It includes two aspects. One is investigating the electromagnetic properties of the media and finding the appropriate mathematical model .The other is studying the analysis method of the field taking account of the given material properties. This paper is concerned with several material-modeling problems related * to ferromagnetic materials. When magnetized by AC supply with DC bias, the ferromagnetic nonlinear magnetization status are getting much more complicated, which makes the original analysis methods of magnetic field are not functional or effective any longer. This brings the problems of how to model such kind of electromagnetic systems. In this paper, the double Epstein method for measuring DC-biased magnetic characteristics is proposed and the measuring equipment is developed. With the help of this equipment, the DC-biased magnetization phenomena are revealed; the describing method of DC biased magnetization and loss properties of ferromagnetic material are given; the corresponding numerical computation method of magnetic field and ferromagnetic loss is proposed and verified. Compared with the transient and time-periodic analysis method, time harmonic method is considered to be an effective and practical method for eddy current analysis. This paper studies the condition for introducing time harmonic method into nonlinear eddy current analysis and the method of obtaining effective magnetization curves. In order to simulate the eddy current distribution of iron core laminated with different length of steel sheets, an anisotropy conductivity model is proposed. And the deduction shows that the symmetry of the finite element equation is maintained. The selection of magnetization curve for transient eddy current analysis is discussed. According to the physical meanings of BmHb and BmHm curve and eddy current equation described with magnetic vector potential A and electrical scalar II potential V, the reason is given, which explains why m~1~1b curve should be used for the transient eddy current analysis. The computation of magnetic field taking into account hysteresis is just under beginning. In this part, first, Jiles-Atherson hysteresis model is studied, then the M-B finite element method taking into account hysteresis. It is found that M-B method has limits in dealing with material properties. In order to solve the problem mentioned above, a so-called direct magnetic field analysis method is proposed. For establishing the normal magnetization model and hysteresis model, it is very important to study the measurement of magnetization properties of ferromagnetic materials. In this paper, methods of measurement of the magnetic properties of magnetic steel sheet by means of a single sheet tester are studied and a double-yoke single sheet tester is produced. In addition, the uniqueness of vector potential in eddy current analysis is studies in this paper. When Coulumb gauge is applied, how are the A family and T family eddy current formulation. The corresponding differential equations, interface condition, boundary conditions and Galerkin dispersion are deduced in details.