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Title: Electromagnetic transient analysis using the frequency domain method of moments
Author: Tham, C. Y.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2000
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The relative merits of frequency domain (FD) electromagnetic transient analysis against the time domain approach are discussed. When used on highly resonant systems, conventional FD methods which rely on the FFT, can yield erroneous results. This is shown to be due to inadequate sampling resolution, which is determined empirically. The collection of analytical tools for FD analysis is reviewed with emphasis on the control of errors. From these principles a systematic and objective methodology to extract a system's transient response from FD data is proposed. The methodology is extended with a further proposal using dynamic adaptive sampling to obtain an accurate frequency response spectrum efficiently. The proposal is based on the adaptive integration principle but uses a relative convergence limit based on the most recently computed value of integral. The frequency samples obtained are non-uniformly spaced and a modified inverse DFT formula is developed. The sampling strategy results in a very substantial reduction in computational demand over the conventional FFT technique. Accurate transient results can be obtained with typically less than 10% of the samples of the conventional approach. The sampling strategy also enables highly resonant structures to be analysed in the frequency domain. To sample an extremely resonant spectrum accurately, resolution in the order of 1 in 106 is required. This level of computational demand is beyond the practical limit of the conventional FFT methods. The methodology has been used to model transients on resonant wires and transmission lines of various configurations in both antenna and scattering modes. A particular case studied uses an equivalent antenna model of a human body which is standing on a perfect ground and exposed to low frequency radiations. The resulting currents flowing at the feet into the ground, which is adopted as a measure for exposure level, are predicted accurately. The methodology's relative performance in terms of efficiency, accuracy, utility and ease of use against a thin wire time domain integral equation formulation is discussed in some detail.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available