Thesis (PhD)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: The engineering of dependable real-time systems for mission critical applications is a resource intensive and error prone process. Achieving dependability requires a general consensus on the correctness of a system with regard to its intended function. For a consensus to be achieved, the properties of the system must be well understood which, in turn, requires consensus on a rigorously defined computational architecture. There is currently no single agreed upon computational architecture at the application level which can serve as a common denominator for the design and implementation of real-time systems. It is the thesis of this dissertation that a rigorous computational architecture, applicable from design to implementation, enables engineers to better understand software for real-time systems. To substantiate this claim, the real-time data flow architecture RDF with its notation allowing the description of complete systems from design to implementation will be explored. Four distinct research areas for improving the engineering process of real-time systems are dealt with in the dissertation: 1) the development of an architecture for real-time systems being suitable for design and implementation in software and hardware, 2) the consolidation of a number of graphical languages into a graphical notation for functional specification, design and construction of real-time systems, 3) the development of a simple processor architecture for the execution of real-time applications, and 4) and the evaluation of the architecture in the framework of a microsatellite case study. In particular, the following original contributions are made: 1) the firing semantics of data flow systems are expanded to include disjunctive firing semantics in a novel way in addition to the classical conjunctive firing semantics, 2) the inherent real-time data flow property, Le. that a receiving task must be ready to receive the next incoming message when it is sent, is extended to the synchronous data flow model, 3) a notation for describing all properties of real-time systems is defined 'with the real-time data flow language RDF as base language, 4) two hardware processor architectures are introduced that offer one-to-one correspondence between design and implementation and, thus, reduce the semantic gap between design language and program execution, and 5) the class of systems that can be modelled with data flow architectures is shown to include control systems and data flow systems. The language set and processor architecture were applied to certain aspects of the SUNSAT microsatellite project. / AFRIKAANSE OPSOMMING:Die skep van betroubare intydsestelsels vir missie kritiese toepassings is 'n proses wat baie hulpbronne verg en waarin maklik 'n fout gemaak kan word. Om 'n betroubare stelsel te skep vereis 'n konsensus oor die korrektheid van 'n stelsel, wat bereik word wanneer die eienskappe van die stelsel goed verstaan word. Dit vereis op sy beurt weer 'n konsensus oor 'n goed gedefinieerde berekenings argitektuur. Daar is tans geen enkel ooreengekome berekenings argitektuur op die toepassingsvlak wat kan dien as 'n gemeenskaplike voertuig vir die ontwerp en implementering van intydsestelsels nie. Dit is die hipotese van die proefskrif dat 'n berekenings argitektuur met 'n streng basis, wat toegepas kan word vanaf ontwerp tot implementering, ingenieurs in staat sal stel om intydsestelsels beter te kan verstaan. Die hipotese word ondersoek deur die intydse datavloei argitektuur, RDF, te gebruik om 'n stelsel vanaf ontwerp tot implementering te beskryf. Daar is vier spesifieke navorsings areas ter verbetering van die ingenieurswese proses vir intydsestelsels, wat in die proefskrif aangespreek word: 1) die ontwikkelling van 'n argitektuur vir intydsestelsels wat geskik is vir die ontwerp en implementering in programmatuur en apparatuur, 2) . die konsolidering van 'n aantal grafiese tale in 'n grafiese notasie vir die funksionele spesifikasie, ontwerp en implementering van intydsestelsels, 3) die ontwikkelling van 'n eenvoudige verwerker argitektuur vir die uitvoering van intydse toepassings en 4) die evaluering van die argitektuur in die konteks van 'n mikrosatelliet gevallestudie. Die volgende oorspronklike bydraes word gemaak: 1) die sneller voorwaardes vir datavloei stelsels word uitgebrei met 'n disjunktiewe patroon saam met die tradisionele konjunktiewe patroon, 2) die inherente intydse datavloei eienskap, n.l. dat'n taak wat boodskappe ontvang, alle verwerking wat met 'n vorige boodskap gepaard gegaan het moet afhandel, voordat 'n volgende boodskap ontvang word, word uitgebrei na die sinkrone datavloei model, 3) 'n notasie om al die eienskappe van 'n intydsestelsel te beskryf word gedefinieer met RDF as die basis taal, 4) twee apparatuur verwerker argitekture word beskryf wat 'n een-tot-een kartering aanbied tussen die ontwerp en die implementering, en wat gevolglik die semantiese gaping verklein tussen ontwerpstaal en die uitvoeringsargitektuur en 5) die klasse van stelsels wat gemodelleer kan word met RDF sluit beheerstelsels en datavloeistelsels in. Die grafiese notasie en verwerker argitektuur was toegepas op sekere aspekte van die SUNSAT mikrosatelliet projek.

Thesis (MScIng)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: This dissertation's research aims at studying the viability of using both low cost consumer Commodity Off The Self (COTS) PCs and libn~software in implementing a distributed real-time system modeled on a real-world engineering problem. Debugging and developing a modular satellite system is both time consuming and complex, to this end the SUNSATteam has envisioned the Interactive Test System that would be a dual mode simulator/monitoring system. It is this system that requires a real-time back-end and is used as a real world problem model to implement. The implementation was accomplished by researching the available parallel processing software and real-time extensions to GNU/Linux and choosing the appropriate solutions based on the needs of the model. A monitoring system was also implemented, for system verification, using freely available system monitoring utilities. The model was successfully implemented and verified with a global synchronization of < 10ms. It was shown that GNU/Linux and libn~ software is both mature enough and appropriate in solving a real world distributed real-time problem. / AFRIKAANSE OPSOMMING: Die tesis se navorsing is daarop gemik om die toepaslikheid van beide lae koste verbruikers Komoduteits Van Die Rak (KVDR)persoonlike rekenaars en vemiet sagteware in die implementasie van verspreide intydse stelsels te ondersoek aan die hand van die oplossing van 'n gemodelleerde ingenieurs probleem. Die ontfouting en ontwikkeling van 'n modulere satelliet is beide tyd rowend en kompleks, om hierdie te vergemaklik het die SUNSAT span die Interaktiewe Toets Stelsel gekonseptualiseer, wat in wese'n dubbel modus simulator/moniteerings stelsel sou wees. Dit is hierdie stelsel wat 'n verspreide intydse onderstel benodig en dien as die regte wereld probleem model om op te los. Die implementasie is bereik deur die beskikbare verspreide verwerkings sagteware en intydse uitbreidings vir GNU/Linux te ondersoek en die toepaslike opsies te kies gegrond op die behoeftes van die model. 'n Moniteerings stelsel is ook geimplimenteer, met behulp van libn~sagteware, vir stelsel verifikasie. Die model was suksesvol geimplimenteer en geverifieer met 'n globale sinkronisasie van < 10ms. Daar is getoon dat GNU/Linux en libn~sagteware beide volwaardig en geskik is vir die oplossing van regte wereld verspreide intydse probleme.

Thesis (PhD (Electrical and Electronic engineering))--University of Stellenbosch, 2005. / Individuals can be identified by their handwriting. Signatures are, for example, currently used as a biometric identifier on documents such as cheques. Handwriting recognition is also applied to the recognition of characters and words on documents—it is, for example, useful to read words on envelopes automatically, in order to improve the efficiency of postal services. Handwriting is a dynamic process: the pen position, pressure and velocity (amongst others) are functions of time. However, when handwritten documents are scanned, no dynamic information is retained. Thus, there is more information inherent in systems that are based on dynamic handwriting, making them, in general, more accurate than their static counterparts. Due to the shortcomings of static handwriting systems, static signature verification systems, for example, are not completely automated yet. During this research, a technique was developed to extract dynamic information from static images. Experimental results were specifically generated with signatures. A few dynamic representatives of each individual’s signature were recorded using a single digitising tablet at the time of registration. A document containing a different signature of the same individual was then scanned and unravelled by the developed system. Thus, in order to estimate the pen trajectory of a static signature, the static signature must be compared to pre-recorded dynamic signatures of the same individual. Hidden Markov models enable the comparison of static and dynamic signatures so that the underlying dynamic information hidden in the static signatures can be revealed. Since the hidden Markov models are able to model pen pressure, a wide scope of signatures can be handled. This research fully exploits the modelling capabilities of hidden Markovmodels. The result is a robustness to typical variations inherent in a specific individual’s handwriting. Hence, despite these variations, our system performs well. Various characteristics of our developed system were investigated during this research. An evaluation protocol was also developed to determine the efficacy of our system. Results are promising, especially if our system is considered for static signature verification.

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / Higher-order Markov models are more powerful than first-order models, but suffer from an exponential increase in model parameters with order, which leads to data scarcity problems during training. A more efficient approach is to use mixed-order Markov models, which model data sequences with contexts of different lengths. This study proposes two algorithms for inferring mixed-order Markov chains and hidden Markov models (HMMs), respectively. The basis of these algorithms is the prediction suffix tree (PST), an efficient representation of a mixed-order Markov chain. The smallest encoded context tree (SECT) algorithm constructs PSTs from data, based on the minimum description length principle. It has no user-specifiable parameters to tune, and will expand the depth of the resulting PST as far as the data set allows it, making it a self-bounded algorithm. It is also faster than the original PST inference algorithm. The hidden SECT algorithm replaces the underlying Markov chain of an HMM with a prediction suffix tree, which is inferred using SECT. The algorithm is efficient and integrates well with standard techniques. The properties of the SECT and hidden SECT algorithms are verified on synthetic data. The hidden SECT algorithm is also compared with a fixed-order HMM training algorithm on an automatic language recognition task, where the resulting mixed-order HMMs are shown to be smaller and train faster than the fixed-order models, for similar classification accuracies.

Thesis (PhD)--University of Stellenbosch, 2004. / 242 Leaves printed single pages, preliminary pages i-viii and numberd pages. Includes bibliography. Tables and figures. / ENGLISH ABSTRACT:The aim of the proposed study was to develop an electrical utility organisational performance measure indicator that measures electrical network utilisation (U) for the actual maximum demand and total energy transferred. The scope of the study extended itself to include reliability and exogenous considerations. The scope of the research study included three primary variables with secondary variables as the performance measures. The available data was screened and filtered from outliers, and thereafter, multivariate analysis was applied in deriving the overall linear equation for each of the above primary variables. The statistical process included the application of principal component analysis and factor analysis, a comparison between the two, and the derivation of linear equations. The study produced linear equations relating to the former. The primary variables were presented in the form of a 3-Dimensional scatter plot. Each variable was inspected for linearity and clustering to validate the results and include any previously excluded outliers that complied with linear functionality. A practical application of the research findings was included. This included the extremes of linearity and clustering. The research concludes with further research opportunities in this study direction. / AFRIKAANSE OPSOMMING:Die doel van hierdie ondersoek was om 'n maatstaf te ontwikkel wat elektrisiteitsverskaffers in staat stel om die effektiwiteit en benutting van die elektriese transmissienetwerk te meet. Dit sluit die maksimum aanvraag en totale hoeveelheid energie wat deur die transmissienetwerk oorgedra word in. Die omvang van die studie is uitgebrei om ook eksterne faktore en betroubaarheidsoorwegings in te sluit. Die beskikbare inligting is gekeur en gefilter om uitskieters uit te skakel en daarna is multivariate analise gebruik om 'n lineêre vergelyking vir elk van die primêre veranderlikes te ontwikkel. Die statistiese analise het onder andere van hoofkomponente analise en faktor analise gebruik gemaak. 'n Vergelyking tussen die twee metodes is gemaak en liniêre vergelykings is afgelei. Die primere veranderlikes was gesamelik getoon in n’ 3-dimensionele grafik. Die lineariteit en groepering van elke veranderlike is egter ondersoek om die resultate te staaf en enige uitskieters wat voorheen uitgesluit is maar wel aan die lineêre verband voldoen het in te sluit. 'n Praktiese toepassing van die bevindings was uitgevoer en het die uiterstes van lineariteit en groepering ingesluit. Die ondersoek word afgesluit met 'n bespreking van moontlike verdere navorsingsgeleenthede.

Thesis (PhD)--Stellenbosch University, 1993 / ENGLISH ABSTRACT: An extensive literature study revealed numerous Jauman absorber examples with reasonable absorption properties. Unfortunately, tractable and detailed design techniques were found to be scarce, and often only applicable to absorbers with two or three layers. The research described in this report was therefore aimed at, and culminated in, general design methods for multilayered electric screen J auman absorbers. As a starting point, the synthesis problem is formulated by idealizing the spacers (assumed lossless and commensurate) and resistive sheets (assumed to have zero thickness), and by considering the absorption of a normally incident plane wave. An equivalent circuit model is derived, using the analogy between plane waves in stratified media, and guided waves in TEM transmission lines. The network is analyzed using Richard's frequency surrogate, S = tanh(s = cr +jw), and concise equations and algorithms are presented for symbolic and numerical analysis. Maximum bandwidth synthesis of the classic one-layer absorber, or Salisbury screen, proved to be simple, clearly illustrates the analytic approach, and apparently has not been published before. The two-layer absorber was also found to be algebraically simple enough to be synthesized in closed form, is dealt with comprehensively, and the treatment consolidates and formalizes many of the design techniques available in the literature. Networks comprising commensurate transmission lines and conductances have been investigated by Richardsl , but unfortunately the topology-driven realizability constraints on the input impedance of the Jauman network is only dealt with briefly. Fruitless investigations by the author showed this to be a formidable problem, and as a result the research concentrated on tractable and iterative synthesis algorithms for multilayered absorbers, instead of formal filter synthesis techniques. These algorithms may be summarized as follows: • A key concept in the multilayer zero-placement synthesis methods that will be presented, is the ability to physically realize a given set of reflection coefficientzeros. This involves solving a set of highly non-linear equations, and a gradientmethod iterative algorithm has been developed to achieve this . • The first application of the aforementioned algorithm is to synthesize all reflection zeros at S →∞, thereby obtaining a maximally flat reflection coefficient magnitude response. Stable and rapid convergence was found for up to at least 20 layers, thereby extending the two- and three-layer algebraic solutions available in the literature. It was found that a stringent restriction exists on the maximum dielectric constant (Er) of the spacers, thereby limiting the practical implementation of these solutions . • Through judicious manipulation of reflection zeros at distinct physical frequencies, an equiripple absorption response may be obtained. An elegant algorithm is presented to facilitate this, and it was found that these solutions represent substantial improvements over examples available in the literature. Restrictions still apply to the spacer Er, but these are more relaxed and practical equiripple absorbers are possible. In addition, the spread in sheet resistivities is much smaller than in comparable maximally flat solutions. • Numerical searches indicated that the aforementioned equiripple responses are very close to, but not absolutely optimal, in the sense of maximum bandwidth. The small bandwidth and/or absorption improvements that were found were almost negligible from a practical viewpoint, but the optimal synthesis problem is academically very important. Through use of the general Chebyshev approximation method, an algorithm is developed which finds the local optimal response in the vicinity of such a parent equiripple solution. Although it might be tempting to classify the algorithm as a brute force method, it will be shown that this is not the case, and that its solutions provide the answer to the fundamental and unsolved optimal design problem. These algorithms have been implemented, and tables of resistive sheet values are presented for N up to 8, a range of Er values corresponding to low loss foams, and for various absorption levels. / AFRIKAANSE OPSOMMING: geen opsomming

Thesis (PhD)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Keywords: software-defined radio, SDR, quadrature mixing, quadrature modulation, quadrature demodulation, digital compensation, software radio, direct-digital synthesis, DDS. An often-stated goal of software-defined transceiver systems is to perform digital signal conversion as close to the antenna as possible by using high-rate converters. In this dissertation, alternative design principles are proposed, and it is shown that the signal processing techniques based on these principles improve on the prior system's accuracy, while maintaining system flexibility. Firstly, it is proposed that digital compensation can be used to reverse the effects of hardware inaccuracies in the RF front-end of a software-defined radio. Novel compensation techniques are introduced that suppress the signal artefacts introduced by typical frontend hardware. The extent to which such artefacts may be suppressed, is only limited by the accuracy by which they may be measured and digitally represented. A general compensation principle is laid down, which formalises the conditions under which optimal compensation may be achieved. Secondly, it is proposed that, in the design of such RF front-ends, a clear distinction should be drawn between signal processing complexity and frequency translation. It is demonstrated that conventional SDR systems often neglect this principle. As an alternative, quadrature mixing is shown to provide a clear separation between the frequency translation and signal processing problems. However, effective use of quadrature mixing as design approach necessitates the use of accurate compensation techniques to circumvent the hardware inaccuracies typically found in such mixers. Quadrature mixers are proposed as general-purpose front-ends for software-defined radios, and quadrature modulation and demodulation techniques are presented as alternatives to existing schemes. The inherent hardware inaccuracies are analysed and simulated, and appropriate compensation techniques are derived and tested. Finally, the theory is verified with a prototype system. / AFRIKAANSE OPSOMMING: Sleutelwoorde: sagteware-gedefinieerde radio, SDR, haaksfasige menging, haaksfasige modulasie, haaksfasige demodulasie, digitale kompensasie, sagteware-radio, direk-digitale sintese, DDS. 'n Gewilde stelling is dat digitale seinomsetting in sagteware-gedefinieerde kommunikasiestelsels so na as moontlik aan die antenna moet geskied deur gebruik te maak van hoëspoed omsetters. Hierdie verhandeling stel alternatiewe ontwerpsbeginsels voor, en toon aan dat hierdie beginsels die eersgenoemde stelsel se akkuraatheid verbeter, terwyl stelselbuigsaamheid gehandhaaf word. Dit word eerstens voorgestel dat digitale kompensasie gebruik word om die effekte van hardeware-onakkuraathede in die RF-koppelvlak van sagteware-gedefinieerde radio's om te keer. Nuwe kompensasietegnieke, wat seinartefakte weens koppelvlak-onakkuraathede kan onderdruk, word aangebied. Die mate waartoe hierdie artefakte onderdruk kan word, word slegs beperk deur die akkuraatheid waarmee dit gemeet en digitaal voorgestel kan word. 'n Algemene kompensasiebeginsel word neergelê waarin die voorwaardes vir optimale kompensasie vasgelê word. Tweedens word voorgestel dat 'n duidelike onderskeid getref word tussen seinverwerkingskompleksiteit en seinverskuiwing in RF-koppelvlakke. Daar word getoon dat konvensionele SDR-stelsels dikwels nie hierdie beginsel handhaaf nie. 'n Alternatief, naamlik haaksfasige menging, word voorgehou as 'n tegniek wat duidelik onderskei tussen seinverskuiwing en seinverwerking. Akkurate kompensasietegnieke is egter nodig om effektief van sulke mengers gebruik te maak. Haaksfasige mengers word voorgestel as veeldoelige koppelvlakke vir sagteware-gedefinieerde radio's, en haaksfasige modulasie- en demodulasietegnieke word voorgestel as plaasvervangers vir bestaande tegnieke. Die inherente hardeware-onakkuraathede word geanaliseer en gesimuleer, en geskikte kompensasietegnieke word afgelei en getoets. Laastens word die teoretiese resultate met 'n praktiese prototipe bevestig.

Thesis (PhD)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Microwave heating technology is extensively used in households, is well-established in certain industries and is being explored in others. lts attraction is that it is quick, energy efficient, clean and can be used to heat materials of both high and low thermal conductivities. Successful application of the technology requires knowledge of both material properties and microwave equipment. Commercial fixtures for measuring dielectric properties are not widely available and are usually created in-house. The domestic oven magnetron is easily available and can be used in prototype microwave systems but applicators for specific applications need development. This thesis covers three main areas, namely; dielectric measurement fixtures, microwave applicators and chokes, and drying of wood. The first part of the thesis presents four dielectric measurement fixtures, one commercial and the others in-house. The design and calibration of the in-house fixtures is presented. An intercomparison of the performance of the four fixtures is carried out by measuring the permittivities of well characterised dielectrics: teflon and perspex. The most convenient fixture is used to measure the dielectric properties of wood at different moisture contents. The second part covers the design of a slotted waveguide fed microwave applicator and a choke. The design of the slotted feed is carried out analytically with and without mutual coupling between the slots. A semi-empirical design using a finite element package is done independent of the analytical approach and the results are compared. The choke is rigorously characterised using a procedure which avoids de-embedding. The third and last section reports on the wood drying experiments carried out in the applicator, simulated and mapped heating patterns of drying wood, and a mock-up industrial wood drying facility. / AFRIKAANSE OPSOMMING: Mikrogolfverhittingstegnologie word wyd gebruik in huishoudings, is goed gevestig in sekere nywerhede en moontlike gebruike daarvan op ander gebiede word gedurig ondersoek. Die vernaamste voordele is dat dit vinnig, energiedoeltreffend en skoon is en dat dit gebruik kan word om materiale van beide hoë en lae termiese geleidingsvermoë te verhit. Suksesvolle toevoeging van die tegnologie vereis kennis van beide materiale-eienskappe en mikrogolftoerusting. Kommersiële apparaat vir die meet van diëlektriese eienskappe is nie wyd beskikbaar nie en word gewoonlik "binnenshuis" ontwikkel. Die huishoudelike mikrogolfoond magnetron is geredelik beskikbaar en kan in prototipe mikrogolfstelsels gebruik word, maar toevoegers geskik vir spesifieke gebruike moet ontwikkel word. Hierdie proefskrif dek drie hoofgebiede, naamlik: diëlektriese metingsapparaat, mikrogolftoevoegers en smoorders, en die droging van hout. Die eerste deel van die proefskrif handeloor vier diëlektriese metingsapparate, een kommersiëel en die ander "binnenshuis". Die ontwerp en kalibrasie van die "binnenshuis" apparate word aangebied. 'n Tussenvergelyking van die verrigtinge van die vier apparate word gedoen deur die meting van baie bekende diëlektrikums: teflon en perspex. Die mees gerieflike apparaat word gebruik vir die meet van die diëlektriese eienskappe van hout teen verskillend voginhoude. Die tweede deel dek die ontwerp van 'n smoorder en 'n mikrogolf toevoeger wat deur 'n gegleufde golfgeleier gevoer word. Die ontwerp van die gegleufde golfgeleier word beide met en sonder wedersydse koppeling tussen die gleuwe, analities gedoen. 'n Semi-empiriese ontwerp wat van 'n eindige-element pakket gebruik maak, is onafhanklik van die analitiese benadering gedoen. Die resultate word dan vergelyk. Die smoorder word deur 'n prosedure wat "de-embedding" vermy, streng gekarakteriseer. Die derde en laaste afdeling behandel die eksperimentele droging van hout binne die toevoeger. Simulasies en verhittingspatrone van die hout wat gedroog word, sowel as die "mock-up(model van die voorgestelde)" nywerheids houtdroogkamer, word gegee.

Dissertation (PhD)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: The purpose of this dissertation is to provide methods for designing and managing low voltage residential feeders. These methods can be applied to the problem of planning residential networks under uncertainty while ensuring least life-cycle costs. By analysing collected load data from various communities in South Africa, a new probabilistic model for representing the load uncertainty of residential consumers was derived. This model uses the beta probability distribution to describe individual consumer loads over a period of time. Methods for combining the loads in linear combinations were used to derive a new probabilistic voltage regulation calculation procedure. This new method is different from previously developed voltage calculation methods in that it can be used to estimate the probable voltage performance of a feeder over a period of time. A simplification of the method is proposed which allows it to be implemented in any commercial spreadsheet program. The new probabilistic load model was also applied to the problem of calculating resistive losses in residential low voltage feeders. A new probabilistic method was formulated and this method can be used to estimate the probable range of resistive loss in a feeder for a period of time. This method is simple enough to implement in a commercial spreadsheet program. Probabilistic information about network and load parameter uncertainty is seldom available and these uncertainties are best modelled using fuzzy numbers. The probabilistic calculation methods cannot represent these uncertainties and only after applying a fuzzy-probabilistic approach can both types of uncertainties be used. This is a significant enhancement to the current methods and ensures that the uncertainty about the calculated results is realistically represented. The specification of load parameters for the methods was significantly simplified following a regression analysis of collected load data from South African communities. By specifying the distribution of the consumption of individual consumers in a community, the other load parameters can be estimated using a set of fitted linear regression equations. This greatly reduces the burden of specifying the load parameters and makes it possible for the proposed calculation methods to be applied to the design of new feeders in practice. The distribution of the consumption of individual consumers can be specified using the average and the standard deviation of the consumptions of individual consumers. Accurate estimates of these parameters can be obtained from sales information and can be used to manage existing networks effectively. Using the sales information with the proposed methods enables more cost-effective upgrades of existing feeders low voltage feeders. The identification of potential problems in existing low voltage networks is also possible if the layout of the feeders in a community is known. The use of the proposed methods is illustrated in step-by-step fashion. Typical input parameters are used and all the required calculations with intermediate results are presented. / AFRIKAANSE OPSOMMING: Die doel van hierdie proefskrif is die daarstelling van residensiële laagspanningsnetwerk ontwerp- en bestuursmetodes. Hierdie metodes kan toegepas word vir die beplanning van residensiële laagspanningsnetwerke waar onsekerheid bestaan oor toekomstige kragverbruik en die spesifikasie van die netwerkparameters. Lasdata, wat versamel is in verskeie Suid Afrikaanse gemeenskappe, is geanaliseer en 'n nuwe probabilistiese modellering van die onsekerheid oor die kragverbruik van residensiële verbruikers is ontwikkel. Gebruik is gemaak van die beta waarskynlikheidsdightheidsfunksie om die tydsgebonde kragverbruik van die verbruikers voor te stel. 'n Nuwe probabilistiese spanningsvalberekeningsmetode is ontwikkel en die metode maak gebruik van liniêre kombinasies van die lasstrome van die verbruikers. Die verskil tussen hierdie metode en bestaande metodes is dat dit die tydsgebonde waarskynlikheid van die spanningsregulasie van 'n kabel kan bereken. 'n Vereenvoudiging van die metode is ook verkry en dit kan in enige kommersiële sigblad geïmplementeer word. Die probabilistiese lasstroommodel is ook gebruik om 'n nuwe probabilistiese energieverliesberekeningsmetode te ontwikkel. Hierdie metode kan gebruik word om die tydsgebonde waarskynlikhede van 'n reeks van moontlike energieverlieswaardes te bereken. Die metode is eenvoudig genoeg om in enige kommersiële sigblad te implementeer. Onsekerheid oor die spesifikasie van die parameters van die nuwe metodes asook die netwerkparameters kan nie met probabilistiese metodes voorgestel word nie, aangesien inligting oor die waarskynlikhede van parameters selde beskikbaar is. Hierdie onsekerhede kan beter voorgestel word deur die gebruik van sogenaamde "fuzzy"-metodes. Die voorgestelde probabilistiese metodes is aangepas om hierdie tipe onsekerhede ook in ag te neem. "Fuzzy-probabilistic" metodes is gebruik vir dié aanpassings en word beskou as 'n noemenswaardige verbetering van die metodes. Die verbeterde metodes verkaf meer realistiese voorstellings van die onsekerheid oor berekende resultate. 'n Statisitiese analise van Suid Afrikaanse lasdata het 'n vereenvoudiging van die spesifisering van die parameters van die nuwe metodes tot gevolg gehad. Die waarskynlikheidsverspreiding van die energieverbruik van huishoudelike verbruikers kan gebruik word om akkurate skattings van die ander parameters te verkry. Hierdie vereenvoudiging het tot gevolg dat die nuwe metodes vir praktiese netwerkontwerp gebruik kan word. Die waarskynlikheidsverpreiding van die energieverbruik van verbuikers is beskikbaar in die vorm van energieverkope en kan gebruik word vir die effektiewe bestuur en opgradering van bestaande netwerke. As die uitleg van die bestaande netwerke in 'n gemeenskap beskikbaar is, kan die inligting wat bevat is in die energieverkope gebruik word om probleme in bestaande netwerke te identifiseer. Al die voorgestelde metodes is stap vir stap uiteengesit met voorbeelde van al die berekeninge met tipiese waardes.

Thesis (PhD) -- Stellenbosch University, 2001. / Some digitised pages may appear illegible due to the condition of the original hard copy. / ENGLISH ABSTRACT: A new technique for the design of multimode devices in overmoded waveguide is presented. The technique applies the principle of growth-based design and uses a conceptual functional block representation of the design structure to provide necessary flexibility to the design algorithms. Two growth based design strategies are proposed and evaluated. The first uses a generalized synthesis-oriented scanning technique, and the second uses an evolutionary strategy. The techniques provide reliable solutions to a variety of multimode design problems. In order to facilitate sufficiently fast numerical analysis, novel enhancements of the mode matching technique are developed and the use of surrogate models is investigated. In addition, to allow physical evaluation of the finished devices, original techniques of measuring multimode devices are formulated and utilised. Two practical problems are used to evaluate the performance of the design procedures. The first is the design of overmoded waveguide chokes for microwave heating facilities, and the second is the design of multimode horns for antenna and spatial power combining applications. Various examples of each type of problem are presented with measurements of manufactured solutions. / AFRIKAANSE OPSOMMING: ’n Nuwe tegniek vir die ontwerp van multimodusstelsels binne multimodus golfleier word voorgestel. Die tegniek maak gebruik van die beginsel van groei-georienteerde ontwerp en ontgin ’n konsepsuele funksionele module-voorstelling van die ontwerpstruktuur om die nodige buigsaamheid aan die ontwerpsalgoritmes te verleen. Twee groei-georienteerde ontwerpstrategiee word aangebied en geevalueer. Die eerste is gebasseer op ’n veralgemeende sintese-georienteerde skandeertegniek, en die tweede maak gebruik van ’n evolusie-strategie. Die tegniek verskaf betroubare oplossings vir ’n verskeidenheid van multimodusontwerpsprobleme. Ten einde ’n numeriese analise-tegniek daar te stel wat vinnig genoeg is, word oorspronklike verbeterings van die modal-pas metode ontwikkel en surrogaatmodelle is ook ondersoek. Verder, vir fisiese evaluasie, word oorspronklike meettegnieke vir multimodusstelsels geformuleer en gebruik. Twee praktiese probleme word gebruik om die ontwerpprosedures te evalueer. Die eerste is die ontwerp van multimodus golfleierdrywingsdempers vir mikrogolfverhitting, en die tweede is die ontwerp van multimodus horings vir antenna- en ruimtelike drywingskombineerdertoepasings. Verskeie voorbeelde van elke tipe probleem word gegee met metings van gei'mplementeerde oplossings.