Jae Seok Choi

Optimization of Magnetization Directions in a 3-D Magnetic Structure

This study introduces a design method for determining the optimized magnetization directions in 3-D magnetic systems. Based on a modified topology optimization method, discrete magnetizations are investigated in six directions . The finite-element method is used for the 3-D magnetostatic field analysis. The proposed method is applied to the design of a magnet pattern having ¿one-sided flux¿ and the design results show that the optimized magnet pattern appears as one or two Halbach arrays according to the shape of the design domain. The optimization process is accomplished by using sequential linear programming and the adjoint variable method.

Topology Optimization of the Stator for Minimizing Cogging Torque of IPM Motors

This study presents a topology optimization method to reduce cogging torque, applied to the design of the stator core of an interior permanent magnet motor. The proposed method uses a reaction-diffusion equation and optimization is separately performed based on two objective functions: 1) minimization of the cogging torque itself, for a number of rotor positions; and 2) minimization of the magnetic energy variation. The optimization results show that configurations having dummy slots are desirable, but the number of dummy slots differs according to the objective function used.

Structural Topology Optimization of Magnetic Actuators Using Genetic Algorithms and ON/OFF Sensitivity

In genetic algorithm (GA) based topology optimization problems, characteristics of an initial population are important for the rapid and stable convergence. This paper introduces an algorithm generating randomly an initial population with superior hereditary characteristics. To avoid the generation of small structural spots, the blurring technique is proposed. The connectivity of seed elements considerging the magnetic flux flow in the design domain is focused. Differently from the classical GA by linear strings, this study deals with two-dimensonal chromosomes and the geographic crossover method to increase the diversity of offspring. The proposed design algorithm is applied to the yoke optimization of magnetic actuators.

Optimal Design of an Electromagnetic Coupler to Maximize Force to a Specific Direction

This study suggests a concept design for an electromagnetic (EM) coupler, using the topology optimization method. To maximize the force generated by magnetic flux, the magnetic energy generated must be differentiable, at the location where the force is acting, in a prescribed force direction. This study proposes a topology optimization scheme for maximizing the force in a specific direction, using a commercial analysis program, ANSYS, to provide the force value. We use ANSYS for obtaining the resultant force as well as analyzing the magnetic field. We adopt a density calculation method called SIMP (solid isotropic material with penalization), and compute the sensitivity of the objective function according to the density change of each finite element in the design domain. As a result, optimal shapes of the core and the armature of the coupler are obtained and the performance is verified.

Multi-Material Optimization of Magnetic Devices Using an Allen-Cahn Equation

Magnetic devices such as actuators and sensors are composed of ferromagnetic materials, permanent magnets, and coils. Thus, in optimizations of magnetic problems, consideration of multi-materials is very important. This work presents a phase field-based design method that simultaneously considers iron cores and permanent magnets, where the time evolution of the phase fields is based on an Allen-Cahn equation. The proposed method is numerically implemented to design a C-core actuator, a Halbach magnet, and a magnetostrictive sensor. The design sensitivities are derived using the adjoint variable method, and the augmented Lagrangian is employed to deal with the volume constraints.

Design of an Eddy Current Brake System Using Microstructures

For the design of the eddy current brake system, this study presents the optimization method using a microstructure concept. The proposed microstructure is a sort of a stacked composite composed of a very thin ferromagnetic membrane and paramagnetic materials and its exact geometry is calculated based on the homogenization theory. The layered structures of the composites are attached to the left and the right sides of the yoke of a brake system and are expected to play a role as a guide to control the magnetic field. The appropriate change of the arranged direction of each composite in the design domain helps the increase of the braking force by modulating the magnetic flux flow. To determine the optimal arrangement directions of the composites, we use the numerical optimization techniques such as the sequential linear programming and the adjoint variable method. The analysis of the magnetic system is based on the two-dimensional finite element analysis.

Optimal shape design of flux barriers in IPM synchronous motors using the phase field method

Purpose – The purpose of this paper is to present an optimization method for flux barrier designs in interior permanent magnet (IPM) synchronous motors that aims to produce an advantageous sinusoidal flux density distribution in the air-gap. Design/methodology/approach – The optimization is based on the phase field method using an Allen-Cahn equation. This approach is a numerical technique for tracking diffuse interfaces like the level set method based on the Hamilton-Jacobi equation. Findings – The optimization results of IPM motor designs are highly dependent on the initial flux barrier shapes. The authors solve the optimization problem using two different initial shapes, and the optimized models show considerable reductions in torque pulsation and the higher harmonics of back-electromotive force. Originality/value – This paper presents the optimization method based on the phase field for the design of rotor flux barriers, and proposes a novel interpolation scheme of the magnetic reluctivity.

Design guide of bolt locations for bolted-joint plates considering dynamic characteristics

Abstract In this study, a simplified finite-element (FE) modelling method is proposed, which simulates the dynamic characteristics of a bolted-joint structure having a large interface area, by utilizing the concept of the cone-frusta method for the jointed parts and spring elements to represent the contact effects occurring in the interfaced area. A method for providing design guidelines for the selection of additional bolt locations is also proposed based on the natural frequencies and mode shapes of the bolted-joint plates. The natural frequency of a specific mode and its mode shape can be controlled by adjusting bolt locations and the number of bolts, considering the effects of the relative deformations in mode shapes, at the plate interfaces. The proposed modelling method and design guidelines are verified based on the experimental results and the FE analysis.

Simultaneous Optimal Design of the Yoke and the Coil in the Perpendicular Magnetic Recording Head

The optimal design of magnetic recording head with the coil is an important issue for the high magnetic recording density with small magnetic field leakage. This work proposes a topology design of the yoke and the coil in the perpendicular magnetic recording (PMR) head based on the density method. In order to determine the shape of the coil as well as the yoke in the head, the topology optimization method combined with the finite-element method (FEM) is used. The numerical result shows significant improvement, that is, the recording flux increasing in the magnetic recording region with the leakage reduction in the adjacent area. Results are verified through the commercial package simulation using Maxwell.

Optimal Shape Design of the Perpendicular Magnetic Recording Head

It is necessary to develop a perpendicular magnetic recording head for the high magnetic field density of the recording region with small magnetic field leakage. This work suggests a topology design of the perpendicular magnetic recording head based on the density method. In order to determine the shape of a magnetic head with the return yoke, the topology optimization method is combined with the finite element method. Obtained results are also compared with results of the previous studies.