Ni Guangzheng

An improved genetic algorithm for global optimization of electromagnetic problems

An improved genetic algorithm (GA) for design optimization of electromagnetic devices is developed in this paper. Numerical test is done on a classical mathematical problem, and it shows that the proposed method has noticeable advantages over standard GAs. To demonstrate its applicability in engineering optimal design problems, the proposed algorithm, together with the charge simulation method, is used to solve the optimization of a bar-plane electrode model.

A universal tabu search algorithm for global optimization of multimodal functions with continuous variables in electromagnetics

A universal tabu search algorithm for the optimization of functions with continuous variables is presented based on the tabu method so far used, Essentially, the improvements include the transition criterion for different states, the determination of the step vector, the cancellation of tabu list, the stop criteria, and the restart from the optimum, etc. The numerical performances of the present algorithm are investigated using a benchmark problem and the geometry optimization of the multisection arc pole shoe in large salient pole synchronous generators.

Wavelet-Galerkin method for computations of electromagnetic fields

A general wavelet-Galerkin method for the numerical computation of electromagnetic fields of bounded regions involving multimedia and an efficient approach to handle arbitrary boundary conditions are presented in this paper. The numerical results indicate that the present method is a strong contender to the well established finite element method.

An improved tabu algorithm applied to global optimizations of inverse problems in electromagnetics

This paper proposes an improved tabu search algorithm for global optimizations of multimodal functions with continuous variables of inverse problems in electromagnetics. The improvements include the introduction of a multistart process, the new neighborhood generating mechanism, and the memorization of the previously searched subspaces as well as the stop criteria for different termination purposes. The numerical results on solving a mathematical test function reveal that the proposed method is more robust in finding the global optimum compared with other kinds of tabu search algorithms. The shape optimization of an electrode demonstrates its value in practical engineering.

A new generalized perfectly matched layer for terminating 3D lossy media

A new perfectly matched layer (PML) formulation is presented for the truncation of finite-difference time-domain lattices with general lossy and dispersive media. It is shown that the PML-type absorbing boundary condition can be constructed in a unified manner. The numerical implementation of the new generalized PML (N-GPML) is straightforward without any splitting of the fields, lowering computational costs. A fully three-dimensional example with a z-directed pulse point source is illustrated to demonstrate the effectiveness of the algorithm.

A new numerical technique for calculating current distributions on curved wire antennas - parametric B-spline finite element method

A new numerical technique is presented for calculating the current distributions on wire antennas with a high degree of curvature. The geometry of the wire antenna is expressed by a parametric equation and the current is directly expanded into a series of quadratic B-spline basis functions of the parameter, so that the truncation error in modeling the curved wire structure is avoided. This algorithm is used to analyze a circular loop antenna, a conical equiangular-spiral antenna, and a four-arm Archimedian spiral antenna to demonstrate its validity and practical value.

FEM analysis of 3-D transformer leakage field and eddy current loss in the windings

The authors present a method which resolves the three-dimensional eddy current field into a 3-D time harmonic field external to the windings and n axisymmetric eddy current fields near the coils as an approximation for engineering applications. Because the isoparametric FEM (finite element method) with 3-D vector potential, is used in the time harmonic field analysis whereas, in the n axisymmetric eddy current field analysis, B-spline FEM is used, the method presented can give a solution with an accuracy quite acceptable for engineering purposes. The distributions of leakage fields, eddy current losses, and heat source in the windings obtained are compared with the test results. >

B-spline finite-element method in polar coordinates

A numerical solution method for two-dimensional electromagnetic field problems is presented using the B-spline finite-element expression based on polar coordinates. The technique has two main advantages: (1) to avoid the truncation errors at some curved boundaries and (2) to improve the accuracy of singular boundary-value problems with a sharp corner. The B-spline finite-element formulation in polar coordinates is derived and its numerical applications are illustrated by an eddy current problem and several waveguide eigenvalue problems.

Shape optimization of pole shoes in harmonic exciting synchronous generators using a stochastic algorithm

The optimization of pole shoes in harmonic exciting synchronous generators is effectively performed using the combined strategy of improved simulated annealing and genetic algorithms with some new improvements made in this paper. The improvements include a rule for the generation of new states, an adaptive regulation schedule for the length of the interval of the pseudo-random parameter and the addition of geometrical constraints. Numerical results on different machines reveal that the iterative number used by executing the combined strategy with improvements is only about 50% of that used by executing the original method, whilst that the optimization results obtained using different algorithms are nearly the same.

Negative sequence eddy current field analysis of a 1055 MVA turbogenerator by using 3D finite element methods

The 3D negative sequence currents arising from unbalance system operations in large turbogenerators are studied by using the finite element method. The mathematical models of the three dimensional negative sequence eddy current fields of large turbogenerators considering the flexible slots are firstly proposed. To emulate the distributed exciting sources of the negative sequence current fields with enough precisions, the geometrical complication of the stator are accurately modeled in the proposed solid models, making it be readily to take into account of practical distributions of the negative sequence exciting currents. And finally, the negative sequence eddy current fields of a 1055 MVA turbogenerator are studied extensively by using numerical simulation results