Hong Soon Choi

General formulation of equivalent magnetic charge method for force density distribution on interface of different materials

The conventional force calculation methods can be applied only for the total force of the objects surrounded by air or vacuum. In this paper, a new general form of equivalent magnetic charge method is proposed for calculating force density and total forces of materials in contact including ferromagnetic and permanent magnet. It provides surface force density on the interface of different materials. The validity of this method is shown by direct observation of the formulas and numerical tests.

Simulation of Hydrostatical Equilibrium of Ferrofluid Subject to Magneto-static Field

In this paper, a numerical scheme for obtaining ferrofluid shape formation is presented using the revisited Kelvins force formula. The formula adopts the newly appreciated field intensity from the original Kelvins concept and the virtual air gap scheme. For the hydrostatic equilibrium subject to magneto-static field, both electromagnetic and gravitational body forces should be considered. The free surface profile of ferrofluid can be obtained through numerical iterations based on the fact that the pressures on the free surface should be the same. Test models are presented as validations of the proposed scheme.

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...

Shape formation of ferrofluid under external magnetic fields using level set method

The shape formation of ferrofluid under magnetic field has been considered to be one of most difficult problems to analyze. In this paper we present a numerical implementation of the level set method for the equilibrium shape calculation of ferrofluid under magnetic field. The magnetic-fluid coupled system has an extremum value of electromagnetic system energy. When the system is composed of magnetic permeable material and current sources, the system energy is a maximum at the equilibrium state. The level set method is adopted for shape capturing since it can easily handle shape variations of fluid including topological changes such as merging, splitting, and even disappearing of connected material regions. The velocity field for the level set method is calculated using a shape derivative of continuum sensitivity analysis that is derived by employing the material derivative concept. The numerical results for a model problem of some ferrofluid on a glass plate show that the level set method works well for ...

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.

A back EMF optimization of double layered large scale BLDC MOTOR by using hybrid optimization method

This paper presents an optimization method of the back EMF for the double layered (double air gap) large-scale BLDC motor by using a Latin-hypercube sampling strategy. In order to drive the large-scale BLDC motors in parallel and multiphases, the back EMF of inner stator is equal to the back EMF of the outer. A new configuration of the double layered BLDC motor is also proposed for the compactness and high efficiency of the system. By the optimization, it is concluded that the skew angle and the thickness difference between the outer and inner magnets have important roles in synchronization and same magnitude of the back EMF, respectively.

Cogging Torque Calculation for IPM Having Single Layer Based on Magnetic Circuit Model

This research shows that it is possible and effective to predict the cogging torque waveform of the interior permanent magnet (IPM) machine using only an analytical model. Based on the proposed virtual permanent magnet (PM) concept, IPM can be considered as surface PM having zero height and unit relative permeability, and then it is used for calculating the cogging torque with conventional technique. Among the evaluation methods for cogging torque, lateral force method, which is based on lateral force acting on stator teeth, is selected. For the validation of proposed concept, finite element analysis is used. From the analysis results, it is shown that our new proposed concept presents good performance in terms of optimal position of peak cogging torque, cogging torque waveform, and the peak value. Therefore, the proposed concept can be useful in design of IPM requiring several computation processes.

Analytical Modeling for Calculating Cogging Torque in Interior Permanent Magnet Machine With Multi Flux-Barriers

This paper presents a new analytical model for estimating the cogging torque in a multi flux-barrier interior permanent magnet machine (IPM). The model is based on a lumped circuit that considers the saturated bridge in the rotors iron core. Finally, the cogging torque waveform of a multi flux-barriers IPM can be effectively predicted with the assistance of both the proposed virtual permanent magnet concept and the superposition principle. Utilizing the proposed concept, an IPM containing multi flux-barriers may be recognized as a multiple surface permanent magnet machine (SPM) having zero height and unit relative permeability. After decomposing the flux density of air-gap (Bg) in the IPM into multiple air-gap flux densities for a virtual SPM, the model is used for estimating the individual cogging torques which will be added or subtracted to the total cogging torque. For validation of our proposed concept, finite element analysis (FEA) was used. From the analysis results, it is shown that the proposed concept is practically effective in terms of finding optimal position, peak cogging torque, and waveform.

Implementation of Virtual Work Principle in Virtual Air Gap

In this paper, an implementation of virtual work principle in virtual air gap is proposed for the calculation of contact and body forces. To calculate the proper values of the magnetic field at virtual air-gap, we exploit the generalized magnetic source methods. It is shown that appropriately sized virtual elements can be allocated in the virtual air-gap by one-dimensionally extending the virtual gap while keeping the previously calculated field intensity. Both an elements and total forces can be obtained by virtual distortion of the concerned virtual elements. The proposed method provides a good accuracy even when the two contacting objects have the different permeability. As a validation, numerical examples are presented for the force distribution and total force.

Application of the Level Set Method to Finite Element Modeling of Moving Objects in Electromagnetic Field

In this paper, we present an efficient modeling scheme based on a level set approach for electromagnetic systems including moving parts. The combination of finite elements and the level-set technique allows us to trace the interface variation on a fixed mesh of finite element. It does not require remeshing for the evolving geometry. The material data of moving objects is easily set using the Heaviside function obtained from the level set equation. For the driving force of dynamics equation, the total force on dielectric object is obtained by integrating the body force density of electric charge method. The numerical results of the test model show usefulness of the proposed scheme.