Kang Hyouk Lee

Adaptive level set method for accurate boundary shape in optimization of electromagnetic systems

Purpose – The purpose of this paper is to present a new numerical technique, called adaptive level set method, for use with the finite element method. Design/methodology/approach – A conventional level set method using the smeared Heaviside function has been employed for shape and topology optimizations. The smeared Heaviside function yields an indistinct interface boundary, and so can increase computational time and cause numerical errors. The adaptive level set method does not use the smeared Heaviside function. To coincide with the material interface, it processes the zero level as the boundary data of element meshing. Findings – Usefulness and accuracy of shape optimization using the adaptive level set method are shown by comparison to the conventional level set method. A shape optimization procedure using the adaptive level set method is introduced. Numerical examples are employed to explain how the adaptive level set method is applied. Originality/value – The adaptive level set method is proposed to...

Alleviation of Electric Field Intensity in High-Voltage System by Topology and Shape Optimization of Dielectric Material Using Continuum Design Sensitivity and Level Set Method

A new design method for topology and shape optimization to preserve high-voltage systems is proposed. The level set technique for the topology optimization is employed with the finite-element method. For the velocity field in the level set equation, the continuum sensitivity formula is used for accurate information of the electric field effect on the topology and shape variation. This technique is applied to three practical examples and the optimum designs of insulating dielectric for the systems are obtained. The optimum designs could suppress troubles, such as thermal deterioration or electrical breakdown, in the systems.

Estimation of Deep Defect in Ferromagnetic Material by Low Frequency Eddy Current Method

This paper presents a low frequency eddy current method to estimate internal deep defects in ferromagnetic material. A magnetic system for an exciting field is designed to generate sufficient coil flux to enhance sensitivity and to make certain of signal linearity. The existence and shape of a defect can be recognized by observing the difference in variation of the equivalent impedance. Magnetic systems with various interior deep defects are numerically analyzed by finite element method and their data is compared with those of experimental systems. The measured data of the impedance variation are distinguishable enough to be used to estimate the existence and shape of defects in the steel structure.

Hole Sensitivity Analysis for Topology Optimization in Electrostatic System Using Virtual Hole Concept and Shape Sensitivity

In this paper, the hole sensitivity analysis is proposed for topology optimization in the electrostatic system. The hole sensitivity formula is derived using the virtual hole concept and the continuum shape sensitivity. Since the derived formula is expressed as a closed form, it is simple and easy to implement and apply to real problems. The hole sensitivity analysis provides information for topology variation. The geometrical expression of the topology variation is obtained using the level set method. Two numerical examples are tested to show the usefulness of the hole sensitivity analysis.

Derivation of Hole Sensitivity Formula for Topology Optimization in Magnetostatic System Using Virtual Hole Concept and Shape Sensitivity

In this paper, hole sensitivity formula is analytically derived for topology optimization in magnetostatic system. With the concept of virtual hole, the hole sensitivity is obtained using continuum shape sensitivity. To demonstrate the validity of the hole sensitivity, topology optimization of synchronous reluctance motor is tested. Since the hole sensitivity formula is represented only with electromagnetic field, it is easily implemented for topology optimization.

Shape and topology optimization of rotor in synchronous reluctance motor using continuum sensitivity and adaptive level set method

In this paper, the rotor shape of synchronous reluctance motor (SynRM) is designed using the sensitivity analysis along with the level set method. To reduce numerical errors of sensitivity value on the interface, the adaptive level set method is adopted. The rotor shape of the SynRM is designed to maximize average torque or to minimize cogging torque by distributing the ferromagnetic material over the design domain of the rotor.

Numerical Analysis and Experiment of Floating Conductive Particle Motion Due to Contact Charging in High-Voltage System

In this paper, the motion of conductive particles is modeled and analyzed using a coupled equation. A neutral conductive particle obtains charge when it comes into contact with an electrode. The forces acting on a particle consist of electric, drag, and gravitational forces. When the electric force is dominant over the other forces, a particle lifts up toward the upper electrode. The electric force on a particle is calculated using surface charge distribution, which is analyzed using the finite-element method. The dominant forces on the particles are used as a driving force in Newtons motional equation to analyze a particle motion. The analysis results show that the total charge, which enables the particle to lift off, is calculated using the coupled equation with respect to the applied voltage. The experiment using a spherical conductive particle is conducted, and the experiment result is compared with the numerical one to validate the numerical method.

Magnetic separation and transfer of wastewater contaminants using magnetic travelling wave and micro magnetic bead

Water treatment technologies have been developed to purify wastewater containing contaminants much and efficiently. In a typical chemical method, reagent and polymer material are added to the wastewater in a stirring process and then the contaminants in the wastewater form flocculation by the chemical additive. The formed flocculation sinks to the bottom of precipitation tank by gravity. In this process, a huge precipitation tank and a long process time are needed. Furthermore, the addition of the chemicals requires much cost, and can be also another source of environmental problems.

Numerical Analysis Method for Multi-Scale Coupled Problem of Dielectric Barrier Discharge With Moving Electrode

A multi-scale problem with respect to time scale occurs in dielectric barrier discharge with moving electrode. The discharge system is modeled with the coupled equation, which consists of a discharge equation for space charge density variation and Poissons equation for electric field distribution. The analysis model consists of two parallel cylinder electrodes covered with dielectric material. Space charges generated during discharge are accumulated on dielectric barrier, and it affects electric field distribution and the following discharges. In the proposed method, the multi-scale analysis is divided into several steps considering the movement of the surface charge accumulated on the dielectric barrier. The surface potential of electrode is measured and compared with the calculated one. The analysis results show good agreement with the measured surface potential.

Characteristics of Electric and Magnetic Circuit Parameters in Thread-Type Magnetic Core System

This paper presents the characteristics of a thread-type magnetic core system in terms of the electric and magnetic circuit parameters. The thread-type core, a magnetic core with a new structure, is composed of iron threads surrounded by an insulator. In the previous study, it was shown that the thread-type core can reduce an amount of iron loss [1]. In this study, the characteristics of the thread-type core are quantified in terms of the electric and magnetic circuit parameters such as iron loss resistance, magnetizing inductance, and reluctance. These parameters are compared with those of bulk- and lamination-type core systems. The circuit parameters are calculated using a numerical analysis of the finite-element method, and the calculated parameters are also compared with experimental data. The comparison shows that the thread-type core exhibits improved system parameters for magnetic systems, particularly in the high-frequency range. This means that the thread-type core has advantages in efficiency, core size, and power capacity. An additional numerical analysis shows that the more segmented thread-type core results in further improved performance.