Browsing by Author "Davidson, David Bruce"
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- ItemContributions to engineering electromagnetics(Stellenbosch : Stellenbosch University, 2017-12) Davidson, David Bruce; Meyer, Petrie; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: The dissertation presents an overview of the publications of the candidate, and his research group, on engineering electromagnetics — in particular computational electromagnetics (CEM) — which have advanced the field in a number of aspects. They have also impacted materially on local and now international industry. Applications discussed focus initially on primarily defence work, moving through a period of development of advanced CEM methods (many subsequently incorporated in commercial software) to his appointment to the Square Kilometre Array (SKA) South African Research Chair in Engineering Electromagnetics in 2011, in support of South Africa’s MeerKAT radio telescope and SKA program. The golden thread of his work has been modelling full-wave electromagnetic fields in increasingly complex environments. This has now expanded to include work on applying these methods to antenna design in the context of radio astronomy. His recent work also addresses other topics in applied engineering electromagnetics, including calibration and imaging for radio astronomy (some of which leverages CEM simulations) as well as antenna metrology and electromagnetic wave propagation modelling.
- ItemParallel algorithms for electromagnetic moment method formulations(Stellenbosch : Stellenbosch University, 1991-12) Davidson, David Bruce; Cloete, J. H.; McNamara, D. A.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: This dissertation investigates the moment method solution of electromagnetic radiation and scattering problems using parallel computers. In particular, electromagnetically large problems with arbitrary geometries are considered. Such problems require a large number of unknowns to obtain adequate approximate solutions, and make great computational demands. This dissertation considers in detail the efficient exploitation of the potential offered by parallel computers for solving such problems, and in particular the class of local memory Multiple Instruction, Multiple Data systems. A brief history of parallel computing is presented. Methods for quantifying the efficiency of parallel algorithms are reviewed. The use of pseudo-code for documenting algorithms is discussed and a pseudo-code notation is defined that is used in later chapters. A new parallel conjugate gradient algorithm, suitable for the solution of general systems of linear equations with complex values, is presented. A method is described to handle efficiently the Hermitian transpose of the matrix required by the algorithm. Careful attention is paid to the theoretical analysis of the algorithm's parallel properties (in particular, speed-up and efficiency). Pseudo-code is presented for the algorithms. Timing results for a moment method code, running on a transputer array and using this conjugate gradient solver, are presented and compared to the theoretical predictions. A parallel LU algorithm is described and documented in pseudo-code. A new graphical description of the algorithm is presented that simplifies the identification of the parallelism and the analysis of the algorithm. The use of formal methods for extracting parallelism via the use of invariants is presented and new examples given. The speed-up and efficiency of the algorithm are analyzed theoretically, using new methods that are simpler than those described in the literature. Techniques for optimizing the efficiency of parallel algorithms are introduced, and illustrated with pseudo-code. New parallel forward and backward substitution algorithms using the data distribution required for the parallel LV algorithm are described, and documented with pseudo-code. Results obtained with a Occam 2 moment method code running on a transputer array using these parallel LU solver and substitution algorithms are presented and compared with the theoretical predictions. PARNEC, a new Occam 2 implementation of the thin-wire core of NEC2, is discussed. The basic 'theory of NEC2 is reviewed. Problems with early attempts at combining Occam and FORTRAN are reported. Methodologies for re-coding an old code written in an unstructured language in a. modern structured language are discussed. Methods of parallelizing the matrix generation are discussed. The accuracy of large moment method formulations is investigated, as is the effect of machine precision on the solutions. The use of the biconjugate gradient method to accelerate convergence is briefly considered and rejected. The increased size of problem that can be handled by PARNEC, running on a transputer array, is demonstrated. Conclusions are dra.wn regarding the contributions of this dissertation to the development of efficient parallel electromagnetic moment method algorithms.