Ki-Sik Lee

Implementation of hysteresis characteristics using the Preisach model with M-B variables

A method that uses the magnetization M and the magnetic flux density B instead of using M and the magnetic field intensity H in the Preisach model is proposed. The Preisach distribution function and the Everett function obtained from M-B curves are compared with those of the conventional method. The former functions are much smoother than the latter, and this improves convergence and efficiency in computations because the slope of the M-B curves is lower than that of the M-H curves. A two-permanent-magnet system is analyzed as an example. The results are in good agreement with experiment. It is concluded that M-B variables are better than the M-H variables in the Preisach model for numerical analysis. >

Coupling finite elements and analytical solution in the airgap of electric machines

A method for coupling an analytical magnetic field solution in the airgap of an electric machine with standard finite element equations used to model the rest of the machine is presented. The proposed method eliminates the need for finite elements in the airgap, thereby facilitating the modeling of rotor motion and allowing for higher accuracy in the airgap field solution. An example compares the accuracy of a standard finite element solution with one obtained from the proposed method, using a purely analytical solution as a reference. >

Comparison of mechanical deformations due to different force distributions of two equivalent magnetization models

In magnetic systems, electromagnetic force density distribution may cause mechanical deformation, which results in the mechanical noise and vibration. The electromagnetic force density can be analyzed with several techniques such as stress tensors, equivalent magnetization models and energy approaches and etc. that may produce different force densities. From the view-point of mechanical deformation, they are theoretically analyzed and compared to explain the differences between the force fields using the property of scalar pressure. In uncompressible media the gradient of scalar pressure, which is a term of Korteweg-Helmholtz force density, does not cause any mechanical deformation. In this paper, two magnetization source models of magnetic charge and magnetization current, which produce quite different distributions of force density, are employed to see their mechanical deformations. Three numerical examples are tested to examine their validity and usefulness.

Design sensitivity analysis for transient eddy current problems using finite element discretization and adjoint variable method

For shape design problems subjected to the transient eddy current equation, a shape design sensitivity expressed explicitly in terms of design variables is derived using a discrete system equation of finite elements and an adjoint equation method. The original state equation is an initial-value problem which is to be solved by time-stepping finite element method. On the other hand, the adjoint equation is obtained as a terminal-value problem which is also to be solved by time-stepping finite element method. With the state and adjoint variables solved, the sensitivity is evaluated, which is employed in a gradient-based optimization algorithm. As a numerical example, an eddy current distribution control on a metal surface is treated using the proposed method in an induction heating system.

Temperature analysis of induction motor with distributed heat sources by finite element method

This paper presents a more accurate method to estimate the temperature distribution of the induction motor. Distributed heat sources are calculated by solving the voltage source eddy current problem. The analyzed model has several equivalent layers replacing the very narrow region such as the contact of frame and stator core. The numerical results shows the heat sources and temperature distribution well in a full FE analysis model.

Shape optimization of H-plane waveguide tee junction using edge finite element method

The shape of conducting post in H-plane waveguide tee-junction is optimized to maximize the transmitting power. The method employs an edge finite element technique with magnetic fields as state variables. Sensitivity analysis and steepest descent algorithm are used for the optimization. >

Dynamic vibration analysis of switched reluctance motor using magnetic charge force density and mechanical analysis

This paper presents a dynamic vibration analysis of switched reluctance motor. The main exciting force of the vibration is electromagnetic force in the stator that is calculated using the magnetic charge method. The force densities obtained by the FE magnetic field analysis are applied to the FE mechanical modal analysis. A numerical model of 3-phase 6/4 SRM is tested to obtain the natural frequencies and deformation of the stator. The radial and transverse vibration amplitudes are obtained in time domain. Transient dynamic analysis is also accomplished to compare its results with the ones obtained using the modal method.

Torque computation of hysteresis motor using finite element analysis with asymmetric two dimensional magnetic permeability tensor

This paper deals with the analysis of the generated torque of the hysteresis motor using finite element method, The material property of the hysteresis ring in the hysteresis motor is characterized by the asymmetric two dimensional magnetic permeability tensor. The torque has been computed effectively by using permeability tensor instead of full hysteresis modeling or Maxwell stress tensor. The proposed method has been applied to the sample hysteresis motor to compute the torque and the results are in good agreement with the experimental results.

Numerical algorithm for analyzing the magnetic fluid seals

This paper presents the numerical algorithm to obtain the boundary surface configurations of magnetic fluid seals. The surface boundary is obtained without several assumptions. In the analysis of the fluid system, surface configuration of fluid and magnetic field pattern affect each other. To solve this problem iterative computation is adopted in this algorithm. The magnetic field is computed by nonlinear finite element method considering the saturation of magnetic fluid and pole piece. The surface equilibrium condition in ferrohydrodynamics are used in the algorithm. The movement of boundary surface configuration is simulated and compared with experimental results, and the influences of fluid volume, shape of pole piece, and forces due to magnetization, rotation of the shaft and gravitation on the seal capacities are analyzed. >

Design sensitivity analysis for shape optimization of 3-D electromagnetic devices

A three-dimensional shape optimization algorithm is developed by combining design sensitivity analysis and the boundary element method (BEM). The design sensitivity is derived by implicitly differentiating the boundary integral equation with respect to the design variables. The proposed algorithm is validated by applying it to the pole shape optimization of three-dimensional electromagnets. The objective function has been observed to monotonically converge, and the final optimized shape is obtained within a reasonable number of iterations. >