Myung Ki Baek

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.

Design sensitivity and LSM for topology and shape optimization in electromagnetic system

Purpose – The purpose of this paper is to propose a level set method (LSM) for topology optimization of an electromagnetic system.Design/methodology/approach – The classical shape optimization method has a meshing problem for shape changes and so the level set method is employed to overcome this difficulty, due to its efficient representation of evolving geometry. The velocity field is required to solve the level set equation of the Hamilton‐Jacobi equation. It is obtained using the continuum shape sensitivity in a closed form by the material derivative concept. The optimization problem is modeled as a coupled system of Poissons equation and the level set equation. They are solved using a standard FEM in the time domain.Findings – Numerical examples are shown to test an optimization problem in the electric and magnetic field system. The design goal is to obtain the maximum torque for an operating electrostatic actuator and synchronous reluctance motor (SynRM), respectively. The results of the optimal sha...

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.

Magnetic Separation for Contaminants in Wastewater Using Magnetic Micro Bead

In this paper, a new physical method for wastewater treatment that uses magnetic micro beads and a magnetic field is proposed. An experimental jar test for the separation of micro particle is carried out to show its feasibility. In the stirring process, contaminants of wastewater can adhere to magnetic beads, and then magnetic floc can be formed around the beads. This magnetic floc can be separated from the wastewater by an external magnetic field. A separation system is also designed, and its performance is numerically analyzed using the electromagnetic finite element method coupled with the fluid equation and the dynamic equation of particles wherein the driving force includes the magnetophoretic force, gravity, buoyancy, and drag force.

Experiment and Analysis for Effect of Floating Conductor on Electric Discharge Characteristic

In this paper, we present a numerical analysis method for analyzing the discharge characteristic with the presence of a floating conductor. Space charges generated during the discharge process can accumulate on the surface of the floating conductor, or be emitted from its surface. An intensification of the electric field around the floating conductor is affected by those space species. Therefore, it is important to calculate the space-charge distributions considering the surface charge on a floating conductor because the discharge occurs at the floating conductor, which is placed around the cathode. An axial symmetry finite-element model is used to analyze this floating conductor discharge system, and Poissons equation is coupled with the hydrodynamic drift-diffusion equation to calculate space charge distributions. Fowler–Nordheim electron emission is employed for the boundary condition at conductor surfaces. The analysis results show the variation of the electric field due to the space charges and the surface charge density on the floating conductor. Experiments using corona generators are carried out, and the current data obtained show the space charge generated by the presence of a floating conductor.

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.

Nonlinear magnetic method for estimation of wall thinning in carbon steel pipe

This paper proposes a nonlinear magnetic method to estimate the thickness of carbon steel pipe used in the secondary steam cycle of nuclear power plants. The principle of the proposed method is based on utilizing the nonlinear property of magnetic saturation in carbon steel. A magnetic sensor system for the nonlinear magnetic method is designed by the magnetic circuit concept, and is modeled and analyzed with the finite element method and an equivalent electric circuit. The sensor system is built to experimentally test its performance in the estimation of wall thinning. To demonstrate the feasibility and validity of the proposed nonlinear magnetic method, the measured data from the sensor system are used to estimate the wall thinning, and are compared with the analysis results.

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.