Ho-ching Chris Wong

Application of a meshless method in electromagnetics

An improved meshless method is presented, with an emphasis on the detailed description of this new computational technique and its numerical implementations, by investigating the usefulness of a commonly neglected parameter. Two approaches to enforce essential boundary conditions are also thoroughly investigated. Numerical tests on a mathematical function are carried out as a means of validating the proposed method. It is seen that the proposed method is more robust than the conventional ones. Applications in solving electromagnetic problems are also presented.

An improved ant colony optimization algorithm and its application to electromagnetic devices designs

Based on the success in the design of a new global search procedure on the development of a novel trail updating mechanism and the introduction of an elitist strategy to available ant colony optimization (ACO) methods, an improved ACO algorithm is proposed. In order to facilitate the implementation of the search procedure, the available local search phase is simplified also. The algorithm is tested on a mathematical function and an inverse problem, and its performances are compared with those of other well designed methods.

Wavelet-Galerkin method for computations of electromagnetic fields-computation of connection coefficients

One of the key issues which makes the wavelet-Galerkin method unsuitable for solving general electromagnetic problems is a lack of exact representations of the connection coefficients. This paper presents the mathematical formulae and computer procedures for computing some common connection coefficients. The characteristic of the present formulae and procedures is that the arbitrary point values of the connection coefficients, rather than the dyadic point values, can be determined. A numerical example is also given to demonstrate the feasibility of using the wavelet-Galerkin method to solve engineering field problems.

A novel approach to circuit-field-torque coupled time stepping finite element modeling of electric machines

This paper presents a sub-block algorithm for the time stepping finite element solution of problems in which sets of electromagnetic field equations, circuit equations and mechanical equation are coupled together. The proposed method ensures that identical solutions are obtained for the sub-blocks by controlling the step size of the time stepping process. This new method simplifies the process of dealing with coupled-system problems and it also greatly reduces the computation time. A time stepping finite element model of an induction motor is used to demonstrate the proposed method in details.

A tabu method to find the Pareto solutions of multiobjective optimal design problems in electromagnetics

A tabu search algorithm is proposed for finding the Pareto solutions of multiobjective optimal design problems. In this paper, the contact theorem is used to evaluate the Pareto solutions. The ranking selecting approach and the fitness sharing function are also introduced to identify new current points to begin every iteration cycle. Detailed numerical results are reported in this paper to demonstrate the power of the proposed algorithm in ensuring uniform sampling and obtaining the Pareto optimal front of the multiobjective design problems. The most efficient method of implementing the proposed algorithm is also discussed.

A meshless collocation method based on radial basis functions and wavelets

A meshless method based on collocation with radial basis functions (RBFs) and wavelets is proposed. It is shown that the proposed method takes full advantage of both RBFs and wavelets. The bridging scales are employed to preserve the mathematical properties of the entire bases in terms of consistency and linear independence. A numerical example that is used to validate the proposed method is reported.

An improved Tabu search for the global optimizations of electromagnetic devices

An extended Tabu algorithm with an aspiration factor is proposed. The algorithm is based on the success of techniques such as the memorization of the previously visited subspaces, the systematic diversification as well as the intensification process for neighborhood creations. The numerical results obtained by solving a mathematical test function and the benchmark problem 22 of the TEAM Workshop reported in this paper demonstrate the usefulness of the proposed method.

Application of automatic choice of step size for time stepping finite element method to induction motors

Although the time stepping finite element method (FEM) is a powerful tool to simulate the operation of electrical machines, it has not been applied to practical problems widely because it requires a large amount of CPU time. This paper proposes to control the time step size automatically within the program to save computing time substantially. It is shown that only simple formulae for estimating the local truncation errors at each timestep using backward Eulers method or Crank-Nicolsons method are all that are required to be derived. These formulae require no extra complicated computation. Hence the reported algorithm can be extended easily to many finite element investigations to more FEM a practical tool to industrial problems. The strategy in choosing the optimal step size is described. The proposed algorithm is then used to study the transient behaviour of an induction motor.

A 3-D study of eddy current field and temperature rises in a compact bus duct system

In this paper, a three-dimensional eddy-current field model for calculating the eddy-current losses in a compact bus duct system is proposed. The temperature rises in the compact bus duct system, including both the long linear section and connecting unit, are evaluated using finite-element method when solving the governing thermal equations. The contact resistance between copper conductors and the corresponding temperature rises are measured in the test also. The computations are validated by test results and the results confirm the proposed algorithm is accurate and practical

Generation and rotation of 3-D finite element mesh for skewed rotor induction motors using extrusion technique

A simple method to generate and rotate 3-D finite element meshes for skewed rotor induction motors using extrusion techniques is presented. Special techniques to consider the geometrical structure of skewed rotor bars are described. With the proposed method, a change in the topology of the meshes at different rotor positions needs minor modifications only. The 3-D mesh for the rotor can thus be rotated with minimal extra computing time. Here the 2-D multi-slice mesh is used as the base-planes for extruding the 3-D mesh and the results of the 2-D multi-slice model can thus be used in the 3-D model. The techniques reported in this paper greatly simplifies the 3-D mesh generation, resulting in a considerable reduction in the computing time of the associated 3-D time stepping model. The generated meshes have been used successfully in constructing the 3-D time stepping finite element model for studying the electromagnetic field of induction motors.