Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This project comprises the design, analysis, and construction of a Rotman lens with reduced conjugate-port coupling. The Rotman lens is a beam-forming network, used in wide-angle scanners to feed an antenna array. The scanning operation is based on optics and is therefore frequency invariant, a desirable feature of the Rotman lens compared to other beam-forming networks which employ phase shifters. The antenna array is connected to the lens's array ports via transmission lines. These array ports lie on the array contour which is designed so that a signal incident onto the antenna array will propagate into the lens and focus at a particular point. The position of this focal point depends on the signals direction of arrival at the array. Ports are placed on these focal points to feed and receive signals. Bootlace lenses allow up to four focal points for linear arrays whereas the Rotman lens is designed for three foci. Scanners usually require to scan many beam-widths, thus ports are employed along a focal arc which intersect these foci. Inter-focal ports do not focus perfectly and result in phase errors distributed across the array aperture. The derivation of three and four foci lenses is provided. There are several degrees of freedom at the designer's disposal, the e ect which these available parameters have on the lens geometry and phase errors is investigated. The waveguide implementa- tion of these lenses is examined, in which we use vertically polarised horns as feed ports and coaxial probes as array ports. Some designs of Rotman lenses published in literature show excess mutual cou- pling between symmetrically opposed feed ports. Using a model which approximates the array contour as a re ecting wall, we show that this is due to the re ected energy focusing on conjugate ports. It is identi ed that Rotman lenses designed for mini- mum phase errors will have near maximum conjugate-port coupling. Two Rotman lenses have been designed at 3; 5GHz for ve feed ports, eleven elements, and up to 30 scan angles. The rst is designed for minimum phase errors, and the second for the defocusing of the re ected energy from the focal arc. Simulations show up to a 10dB reduction in conjugate-port coupling for the second lens with a negligible degradation in performance from the phase errors. Measurements show that the re ected energy is spread between the feed ports as expected, compared to the focusing at a single port of the traditional Rotman lens. / AFRIKAANSE OPSOMMING: Hierdie projek behels die ontwerp, analise en konstruksie van 'n Rotmanlens met verminderde simmetries oorstaande poort koppeling. Die Rotmanlens is 'n patroon- vormingsnetwerk wat gebruik word as samestellingvoer in wye hoek skandeerders. 'n Gewensde eienskap van die Rotmanlens bo faseskuif voernetwerke is dat die skan- deerwerking gebasseer is op optika en dus frekwensie onafhanklik is. Die antennasamestelling word deur transmissielyne verbind aan die antennapoorte van die lens. Hierdie poorte l^e op die samestellingkontoer wat ontwerp is om te verseker dat seine wat inval op die antennasamestelling sal voortplant in die lens en fokus op 'n spesi eke punt. Die posisie van die fokuspunt hang af van die invalshoek van die sein op die samestelling. Poorte word op hierdie fokuspunte geplaas om te seine te ontvang en te lanseer. Hierdie tipe lense kan tot vier fokuspunte h^e , waar die Rotman lens spesi ek vir drie fokuspunte ontwerp word. Skandeerders moet normaalweg etlike bundelwydtes wyd kan skandeer, en daarom word poorte geplaas op 'n straal wat die fokuspunte onderskep. Poorte wat weg van die fokus geplaas word toon 'n e ens uit fokus gedrag, wat vertaal na fasefoute in die samestelling stralingsvlak. Die a eiding van drie en vier fokus lense word verskaf. Daar is verskeie grade van vryheid tot die beskikking van die ontwerper, en die e ek wat die beskikbare parameters op die geometrie van die lens en die fase foute het word ondersoek. Die gol eier implimetering van hierdie lense word beskryf, waar vertikaal gepolariseerde horings as voerpoorte, en ko-aksiale lyne as antennapoorte gebruik word. Sommige Rotman lens ontwerpe in die literatuur toon beduidende koppeling tussen die simmetries oorstaande voerpoorte. Deur van 'n model gebruik te maak wat die samestellingkontoer as 'n weerkaatsende muur benader toon ons aan dat die koppeling geskied as gevolg van die weerkaatsde energie wat fokus in die simme- tries oorstaande poorte. Dit word identi seer dat Rotman lense wat vir minimum fasefoute ontwerp word bykans maksimum koppeling tussen simmetries oorstaande poorte tot gevolg het. Twee Rotman lense is ontwerp by 3; 5GHz vir vyf voerpoorte, elf antenna ele- mente en skandeer hoeke van 30. Die eerste is ontwerp vir minimum fasefoute en die tweede vir uit fokus weerkaatsde energie vanuit die fokus straal. Simulasies toon tot 10 dB vermindering in koppeling tussen simmetries oorstaande poorte vir die tweede lens met weglaatbare werkverrigting verswakking as gevolg van fasefoute. Metings toon dat die weerkaatsde energie, soos verwag, versprei word tussen die voerpoorte vergeleke met energie gefokus in 'n enkele poort soos by die tradisionele Rotman lens.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Power utilities are expected to keep the cost of electricity as low as possible. They are also expected to be environmentally friendly and, amongst other things, not to produce unacceptable audible noise. When the electric field on a conductor is high enough corona is produced and this is accompanied by audible noise. Air pressure, which is directly related to altitude, has an effect on the voltage at which corona will start. It is more difficult to ionise the air at sea level (high air pressure) than at high altitude (low air pressure). Altitude does not only affect the corona inception voltage, but also the intensity of the audible noise. A thorough scan of literature revealed that there is very little evidence of prior research work on the effect of air density on corona under fair weather (dry) conditions. In South Africa, transmission lines are built at altitudes higher than 1800 m above sea level. The cost of a 400 kV line is in the region of R2M per km. It is important to predict the noise levels under a proposed line accurately, before it is energised. This research indicated that the altitude correction for conductor corona audible noise, under dry conditions, might be steeper than the general accepted correction of 1 dB/300m. This correction, however, appears to be valid for heavy rain conditions. Under heavy rain conditions the corona is mainly determined by the water droplets, whereas under dry conditions the condition of the conductor plays the biggest role. The air density therefore has a bigger effect on the corona performance under dry conditions. The implication of a steeper altitude correction for dry conditions is that too low noise levels will be predicted for a higher altitude, which could lead to complaints. On the other hand, predictions for lower altitudes will be too conservative. / AFRIKAANSE OPSOMMING: Daar word van kragvoorsieners verwag om die koste van elektrisiteit so laag as moontlik te hou. Hulle is verder onder druk om omgewingsvriendelik te wees en om onder andere nie onaanvaarbare hoorbare geraas te veroorsaak nie. Wanneer die elektriese veld op ‘n geleier hoog genoeg is, kan korona ontstaan wat dan hoorbare geraas veroorsaak. Die lugdruk, en daarom die hoogte bo seevlak, beïnvloed die spanning waarby ‘n geleier in korona sal gaan. Dit is moeiliker om die lug te ioniseer by seevlak (hoë lugdruk) as hoog bo seevlak (lae lugdruk). Die hoogte bo seevlak beïnvloed daarom nie net die spanning waarby korona sal begin nie maar ook die intensiteit van die hoorbare geraas. Dit wil voorkom of die effek van hoogte bo seevlak, op hoorbare geraas, a.g.v. geleier korona tot op datum baie skraps nagevors is. Baie min kon in die literatuur gevind word op die effek onder droë toestande. In Suid-Afrika is dit nodig om transmissielyne op hoogtes van 1800 m en hoër te bou. So ‘n lyn (400 kV) kos in die omgewing van R2M per km. Dit is daarom van uiterste belang om die geraasvlakke wat ‘n beplande lyn sal veroorsaak, akkuraat te bepaal, voordat so ‘n lyn aangeskakel word. Hierdie navorsing het gewys dat die effek van hoogte bo seespieël op hoorbare korona geraas onder droë toestande groter kan wees as wat algemene aanvaar word. Die helling van die korreksiefaktor vir hoogte bo seevlak blyk steiler as 1 dB/300 m te wees vir droë toestande. Die implikasie hiervan is dat geraas voorspellings vir hoër hoogtes bo seespieël te laag sal wees en die vir lae hoogtes te konserwatief kan wees. Die navorsing stem egter saam met die korreksiefaktor van 1 dB/300 m onder swaar reën toestande. Dit wil voorkom of die invloed van die waterdruppels op geleier korona groter is as lugdruk. Onder droë toestande speel die toestand van die geleier 'n groter rol en is die effek van lugdruk groter.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Airborne seeker antennas are usually enclosed within a dielectric radome for protection against their harsh operational environment. However the presence of a radome can introduce serious degrading effects on the radiation and electrical performance of the enclosed antenna. The degradation effect studied in this report is that of Bore Sight Error (BSE). BSE is a squint in the pointing accuracy of the antenna due to the enclosing radome. A ray-tracing approach is presented that is able to analyse the BSE of seeker radomes in general and is especially suited to electrically large radomes where other computational electromagnetic techniques become overly computationally intensive. The ray-tracing algorithm is wrapped in a GUI which, given the radome, antenna, polarisation and incidence plane parameters will compute the BSE for any set of requested scan angles. Close agreement was obtained with measured BSE performance available in literature. Due to easy setup and fast computation time it is demonstrated that the GUI can be efficiently used for iterative radome design and optimisation. / AFRIKAANSE OPSOMMING: Luggedrae soekantennes is normaalweg omhul binne ‘n dielektriese antennekoepel vir beskerming teen ‘n strawwe omgewing. Die teenwoordigheid van ‘n antennakoepel kan egter ernstige nadelige effekte op die straling en elektriese werkverrigting van die omhulde antenne hê. Die nadelige effek wat in hierdie verslag ondersoek word, is dié van die “Bore Sight Error (BSE).” BSE is ‘n afwyking in die akkuraatheid van die antenna se rigtingwysing as gevolg van die antennakoepel. Straal-natrekking wat die BSE van soek-antennekoepels in die algemeen kan analiseer word beskryf. Hierdie tegniek is veral gepas vir elektries groot antennekoepels waar die berekenige vir EM tegnieke te intensief raak. Die straalnatrekkingsalgoritme word omvat in ‘n grafiese gebruikerskoppelvlak. Gegee die parameters van die antennekoepel, antenne, polarisasie en invallende vlak, sal die BSE vir enige stel skandeerhoeke bereken word. Goeie ooreenstemming was verkry, vergeleke met gemete BSE vanuit die literatuur. Die eenvoudige opstel van die koppelvlak en vinnige berekeningstyd wys daarop dat die koppelvlak doeltreffend gebruik kan word vir iteratiewe antennekoepel ontwerp en optimering.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The successful operation of a man-pack VHF jamming system requires a compact and efficient antenna operating over a wide bandwidth. The design of such an antenna is the focus of this thesis. The antenna should be of a practical size for a portable system and it must radiate energy efficiently across a frequency bandwidth in excess of a decade. A practical „target‟ specification of such an antenna has been drawn up based on the performance of a commercially available system. Several possible antenna topologies, each with a variety of loading section options, are tested using “Full wave” electromagnetic modelling (FEKO). Each topology/loading-section is numerically optimised for load element values by considering both its gain and reflection coefficient. Results of the „optimally loaded‟ solution for each topology are then compared to each other to arrive at the best overall design. The best result is found to be the traditional monopole whip-type antenna, with four R-L loading sections spread along its length. The simulated results show that the proposed antenna can be expected to meet the target standing wave ratio (SWR) specifications while offering a gain advantage of between 5 and 10 dBi higher than is available commercially. The selected design is constructed and its performance measured. / AFRIKAANSE OPSOMMING: Die suksesvolle werking van ʼn mobiele VHF "jammer‟ benodig ʼn kompakte antenna met ʼn bruikbare benuttingsgraad wat oor ʼn wyeband funksioneer. Die ontwerp van so ʼn antenna is die fokus van hierdie tesis. Die antenna moet kompak genoeg wees om draagbaar te wees en moet ʼn bruikbare benuttingsgraad hê oor ʼn frekwensie-bandwydte van meer as 10:1. ʼn Praktiese spesifikasie is opgestel vir die antenna deur te kyk na die sigblaaie van beskikbare stelsels. “Volgolf” elektromagnetiese modelleringsagteware is daarna gebruik om ʼn parametriese ondersoek te loods van verskillende antennas. Verskillende topologieë is getoets met ʼn verskeidenheid van belaaide seksies waar die topologieë ge-optimaliseer was vir wins en weerkaatskoëffisiënt. Die resultate vir elke optimale oplossing is vergelyk.Opgrond van hierdie resultate is bevind dat die beste topologie die tradisionele monopoolmas "whip-type‟ antenna is met vier RL lading afdelings langs die lengte versprei. Analise word gebruik om te wys dat verwag kan word dat dit aan die aanwins en staande golf verhouding (SGV) spesifikasies sal voldoen met n 10 dB verhoging in aanwins vir n laer SGV. Die geselekteerde ontwerp is gebou en gemeet om te verifieer dat dit aan die spesifikasies voldoen.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The objective of this thesis is to develop a 9.2 GHz low phase noise oscillator with a cylindrical cavity resonator. A cylindrical metal cavity with air as dielectric was used as a resonator. To minimise the phase noise of the oscillator, the resonator must be designed to have a high Q-factor. A high Q-factor was obtained by designing the resonator to operate in the TE011 mode. A tuning screw was used to tune the resonant frequency without significantly affecting the Q-factor. The tuning screw also separates the resonant frequencies of the degenerate TE011 and TM111 modes. The signal is coupled to the resonator by means of rectangular apertures. The coupling was designed to minimise the phase noise of the oscillator. A dual mode waveguide filter was developed and inserted into the oscillator loop in order to prevent oscillation at unwanted frequencies. Due to the excellent phase noise performance of the oscillator, it was not possible to measure the phase noise directly with the available phase noise meter. A measurement setup using two similar oscillators tuned to oscillate at frequencies differing by about 60 MHz was implemented. The output signals were down-converted to the difference frequency where the phase noise could be measured accurately. The output signal of the oscillator was measured at different locations in the loop and clearly showed that the resonator can be used as a filter to minimise the phase noise. The performance of the oscillators met all expectations. Phase noise levels of -115 dBc/Hz and -146 dBc/Hz were obtained at offset frequencies of 10 and 100 kHz. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis is om ‘n 9.2 GHz lae faseruis ossillator met 'n silindriese holte resoneerder te ontwikkel. 'n Silindriese metaal golfleier holte met 'n lug diëlektrikum was gebruik as die resoneerder. Om die faseruis van die ossillator te minimeer moet die resoneerder ontwerp word om 'n hoë Q-faktor te hê. Om 'n hoë Q-faktor te behaal was die resoneerder ontwerp om in die TE011 orde te werk. Die resoneerder is toegerus met 'n verstelskroef wat die bedryfsfrekwensie verstel sonder om die belaste Q-faktor aansienlik te beïnvloed. Die verstelskroef skei ook die frekwensie van die degeneratiewe TE011 en TM111 ordes. Drywing word na die resoneerder gekoppel deur middel van reghoekige openinge. Die koppeling is ontwerp om die faseruis van die ossillator te minimeer. 'n Tweede orde dubbelmodes golfleier filter is ontwerp en in die ossillatorlus ingevoeg om ossillasie by ongewenste frekwensies te voorkom. Vanweë die baie lae faseruis van die ossillator was dit nie moontlik om die faseruis direk met die beskikbare faseruismeter te meet nie. 'n Meetopstelling met twee soorgelyke ossillators waarvan die frekwensies met ongeveer 60 MHz verskil is geïmplementeer. Die uittreeseine van die ossillators is afgemeng na die verskilfrekwensie waar die meetinstrument meer sensitief is en die faseruis akkuraat gemeet kan word. Die uittreesein van die ossillator is by verskillende punte gemeet en het duidelik getoon dat die resoneerder as filter gebruik kan word om die faseruis te minimeer. Die ossillators se werkverrigting het aan die verwagtinge voldoen. Faseruis vlakke van -115 dBc/Hz en -146 dBc/Hz by afsetfrekwensies van onderskeidelik 10 en 100 kHz is verkry.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: This dissertation presents the design and practical demonstration of a flight control system (FCS) that is capable of autonomously landing a fixed-wing, unmanned aerial vehicle (UAV) on a stationary platform aided by a high-precision differential global positioning system. This project forms part of on-going research with the end goal of landing a fixed-wing UAV on a moving platform (for example a ship’s deck) in windy conditions. The main aim of this project is to be able to land the UAV autonomously, safely and accurately on the runway. To this end, an airframe was selected and equipped with an avionics payload. The equipped airframe’s stability derivatives were analysed via AVL and the moment of inertia was determined by the double pendulum method. The aircraft model was developed in such a way that the specific force and moment model (high bandwidth) is split from the point-mass dynamics of the aircraft (low bandwidth) [1]. The advantage of modelling the aircraft according to this unique method, results in a design that has simple decoupled linear controllers. The inner-loop controllers control the high-bandwidth specific accelerations and roll-rate, while the outer-loop controllers control the low-bandwidth point-mass dynamics. The performance of the developed auto-landing flight control system was tested in software-in-the-loop (SIL) and hardware-in-the-loop (HIL) simulations. A Monte Carlo non-linear landing simulation analysis showed that the FCS is expected to land the aircraft 95% of the time within a circle with a diameter of 1.5m. Practical flight tests verified the theoretical results of the developed controllers and the project was concluded with five autonomous landings. The aircraft landed within a circle with a 7.5m radius with the aiming point at the centre of the circle. In the practical landings the longitudinal landing error dominated the landing performance of the autonomous landing system. The large longitudinal error resulted from a climb rate bias on the estimated climb rate and a shallow landing glide slope. / AFRIKAANSE OPSOMMING: Hierdie skripsie stel die ontwikkeling en praktiese demonstrasie van ʼn self-landdende onbemande vastevlerkvliegtuigstelsel voor, wat op ʼn stilstaande platform te lande kan kom met behulp van ʼn uiters akkurate globale posisionering stelsel. Die projek maak deel uit van ʼn groter projek, waarvan die doel is om ʼn onbemande vastevlerkvliegtuig op ʼn bewegende platform te laat land (bv. op ʼn boot se dek) in onstuimige windtoestande. Die hoofdoel van die projek was om die vliegtuig so akkuraat as moontlik op die aanloopbaan te laat land. ʼn Vliegtuigraamwerk is vir dié doel gekies wat met gepaste avionica uitgerus is. Die uitgeruste vliegtuig se aerodinamsie eienskappe was geanaliseer met AVL en die traagheidsmoment is deur die dubbelependulum metode bepaal. Die vliegtuigmodel is op so ‘n manier onwikkel om [1] die spesifieke krag en momentmodel (vinnige reaksie) te skei van die puntmassadinamiek (stadige reaksie). Die voordeel van hierdie wyse van modulering is dat eenvoudige ontkoppelde beheerders ontwerp kon word. Die binnelusbeheerders beheer die vinnige reaksie-spesifieke versnellings en die rol tempo van die vliegtuig. Die buitelusbeheerders beheer die stadige reaksie puntmassa dinamiek. Die vliegbeheerstelsel is in sagteware-in-die-lus en hardeware-in-die-lus simulasies getoets. Die vliegtuig se landingseienskappe is ondersoek deur die uitvoer van Monte Carlo simulasies, die simulasie resultate wys dat die vliegtuig 95% van die tyd binne in ʼn sirkel met ʼn diameter van 1.5m geland het. Praktiese vlugtoetse het bevestig dat die teoretiese uitslae en die prakties uitslae ooreenstem. Die vliegtuig het twee suksesvolle outomatiese landings uitgevoer, waar dit binne ʼn 7.5m-radius sirkel geland het, waarvan die gewenste landingspunt die middelpunt was. In die outomatiese landings is die longitudinale landingsfout die grootse. Die groot longitudinale landingsfout is as gevolg van ʼn afset op die afgeskatte afwaartse spoed en ʼn lae landings gradiënt.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: As control problems become more and more complex, techniques are required that surpass the capabilities of simple controllers that are linearized about certain parametric set points. Controllers that can operate over a large range of model parameter variations and even controllers that are largely model-independent are becoming more valuable and necessary. In this control application, voltage regulation is done on a direct AC-AC medium voltage regulator, making use of a type of regulated autotransformer configuration. The fifth order system is shown to be prone to oscillations on the input bus. This, together with the control requirement of robustness to load variations, provides a challenging control problem that is rarely addressed in literature. This thesis solves the control problem by means of applying sliding mode control on voltage regulator module level, and supervisory control on system level. / AFRIKAANSE OPSOMMING: Soos die soeke na oplossings vir hedendaagse beheer probleme al hoe meer uitdagend raak, word die behoefte vir model onafhanklike en robuuste beheerders dienooreenkomstig groter. Eenvoudige beheerders wat gelineariseer is om ’n parametriese werkpunt raak ondoeltreffend vir vandag se vereistes vir doeltreffende beheer ongeag van parametriese veranderinge. In hierdie tesis word spanning regulasie toegepas deur ’n direkte WS-na-WS medium spanning reguleerder in te span. Hierdie toestel maak gebruik van ’n tipe van outotransformator opstelling waar die sekondêre wikkelings gereguleer word deur die skakelaksie van die drywingselektroniese regulasie modules. Die vyfde-orde stelsel se intree bus is geneigd om onstabiel te raak, en moet dus aktief gedemp word terwyl die uitreespanning reguleer word. Die vereiste dat die beheer boonop robuus ten opsigte van las veranderings moet wees maak hierdie probleem ’n monster van ’n uitdaging wat skaars in die literatuur aangeraak is. Hierdie tesis los die probleem van robuuste beheer op deur glymodus beheer toe te pas op reguleerder module vlak, en ook deur toesighoudende beheer op stelsel vlak toe te pas.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: This work focussed on a local multiple chamber falling film evaporator (FFE). The FFE is currently under operator control and experiencing large amounts of lost production time due to excessive fouling. Furthermore, the product milk dry mass fraction (WP) is constantly off specification, negatively influencing product quality, while the first effect temperature (TE1) runs higher than the recommended 70°C (this is a main cause of fouling). A two month period of historical data were received with the aim to develop a controller that could outperform the operators by keeping both control variables, WP and TE1, at desired set points while also increasing throughput and maintaining product quality. Access to the local plant was not possible and as such available process data were cleaned and used to identify two data based models, transfer function and autoregressive with exogenous inputs (ARX) models, as well as a semi-empirical-model. The ARX model proved inadequate to predict TE1 trends, with an average TE1 correlation to historical data of 0.36, compared to 0.59 and 0.74 for the transfer function and semi-empirical-models respectively. Product dry mass correlations were similar between the models with the average correlations of 0.47, 0.53 and 0.51 for the semi-empirical, transfer function and ARX models respectively. Although the semi-empirical showed the lowest WP correlation, it was offset by the TE1 prediction advantage. Therefore, the semi-empirical model was selected for controller development and comparisons. The success of the semi-empirical model was in accordance with previous research [1] [2] [3], yet other studies have concluded that ARX modelling was more suited to FFE modelling [4]. Three controllers were developed, namely: a proportional and integral (PI) controller as base case, a linear quadratic regulator (LQR) as an optimal state space alternative and finally, to make full use of process knowledge, a predictive fuzzy logic controller (PFC). The PI controller was able to offer zero offset set point tracking, but could not adequately reject a feed dry mass (WF) disturbance (as proposed and reported by Winchester [5]). The LQR was combined with a Kalman estimator and used pre-delay states. In order to offer increased disturbance rejection, the feedback gains of the disturbance states were tuned individually. The altered LQR and PFC solutions proved to adequately reject all modelled disturbances and outperform a cascade controller designed by Bakker [6]. The maximum deviation in WP was a fractional increase of 0.007 for LQR and 0.005 for FPC, compared to 0.012 for PI and 0.0075 for the cascade controller [6] (WF disturbance fractional increase of 0.01). All the designed controllers managed to reduce the standard deviation of operator controlled WP and TE1 by at least 700% and 450%, respectively. The same level of reduction was seen for maximum control variable deviations (370%), the integral of the absolute error (300%) and the mean squared error (900%). All these performance metrics point to the controllers performing better than the operator based control. In order to prevent manipulated variable saturation and optimise the feed flow rate (F1), a fuzzy feed optimiser (FFO) was developed. The FFO focussed on maximising the available evaporative capacity of the FFE by optimising the motive steam pressure (PS), which supplied heat to the effects. By using the FFO for each controller the average feed flow rate was increased by 4.8% (±500kg/h) compared to the operator control. In addition to flow rate gain, the controllers kept TE1 below 70°C and WP on specification. As such, the overall product quality also increased as well as decreasing the down time due to less fouling. / AFRIKAANSE OPSOMMING: Hierdie projek het op ‘n vallende film verdamper (VFV) gefokus. Die VFV word tans beheer deur operateurs en ondervind groot hoeveelhede verlore produksie tyd a.g.v oormatige aangroeisels. Die vorming van aangroeisels is grootliks te danke aan die eerste effek temperatuur (TE1) wat gereeld 70°C oorskrei. Die produk droë massa fraksie (WP) is ook telkens nie op die gewenste vlak nie, wat produk kwaliteit negatief beinvloed. Data, wat oor ‘n twee maand periode strek, was verkry met die doelstelling om ‘n beheerder te ontwerp wat beter sou vaar as die operateurs, deur beide WP en TE2 om ‘n nou stelpunt te beheer. Ter selfde tyd moet die ontwerpte beheerder die produksie tempo en produk kwaliteit verhoog. Geen toegang tot die plaaslikke VFV was moontlik nie, dus was die data skoongemaak en gebruik om twee data gebasseerde modelle te identifiseer, nl. oordragsfunksie en outoregressiwe met eksogene insette (ORX) modelle, asook ‘n semi-empiriese model. Die ORX model kon nie TE1 goed voorspel nie, met ‘n korrelasie faktor (tot die historiese data) van 0.36, vergeleke met die 0.59 en 0.74 van die oordragsfunksie en semi-empiriese modelle onderskeidelik. WP korrelasie faktore was meer konstant tussen die modelle, met waardes van 0.47, 0.53 en 0.51 vir die semi-empiriese, oordragsfunskie en ORX modelle onderskeidelik. Alhoewel die semi-empiriese model die laagste WP korrelasie vertoon het, was die tekortkoming vergoed deur die beter TE1 voorspelling. Gevolglik was die semi-empiriese model gebruik vir beheerder ontwerp en vergelyking. Die sukses van die semiempiriese model stem ooreen met vorige studies [1] [2] [3], tog het ander studies al bevind dat die ORX model beter gepas is vir die VFV proses [4]. Drie beheerders was ontwikkel, nl. ‘n proporsionele en integreerder (PI) beheerder as basis geval, ‘n liniêre kwadratiese reguleerder (LKR) as optimale toestands beheer alternatief en laastens ‘n voorspellende wasige logika beheerder (VWB) om volle gebruik van proseskennis te maak. Die PI beheerder kon foutlose volging van die stelpunte lewer, maar kon nie ‘n inset voer droë massa fraksie (WF) versteuring (soos voorgestel en weergegee deur Winchester [5]) na wense verwerp nie. Die LKR was saamgevoeg met ‘n Kalman afskatter en het gebruik gemaak van onvertraagde toestande. Die versteuringstoestande was individueel verstel om beter versteurings verweping te weeg te bring. Die aangepaste LKR en VWB kon beide die WF versteuring verwerp en het beter gevaar as ‘n kaskade beheer oplossing wat deur Bakker [6] ontwerp was. Die WP afwyking is beperk tot ‘n fraksie droë masse verandering van 0.007 vir LKR en 0.005 vir VWB, vergeleke met die afwykings van 0.012 vir die PI beheerder asook die 0.0075 van die kaskade beheerder [6]. Die ontwerpte beheerder kon ook die standaard afwyking van beide WP en TE1 met ten minste 700% en 450% onderskeidelik verminder. Soortgelyke verbeterings was gesien vir die maksimum beheer veranderlikke afwyking (370%), die integraal van die absolute fout (300%) en die gemiddelde fout (900%). Dus het die ontwerpte beheerders wesenlik verbeter op die operateur beheer. Ten einde om gemanipuleerde veranderlikke versadiging te voorkom, asook die voer vloei (V1) te optimiseer, was ‘n wasige logika optimiseerder (WVO) ontwerp. Die WVO het die beskikbare verdampingskapasiteit ten volle benut deur te sorg dat die stoom druk (PS), wat energie verskaf vir verdamping, ge-optimiseerd bly. ‘n Gemiddelde V1 stygging van 4.8% (±500kg/uur), vergeleke met operateur beheer, is waargeneem. Al die beheerders kon steeds die WP en TE1 stelpunte volg en dus TE1 onder 70°C hou (wat verminderde vormasie van aangroeisels tot gevolg gehad het). Daarom het die produk kwailiteit verhoog en die verlore produksie tyd verminder.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: A secure product entitlement system allows one party, such as a pay-TV operator, to broadcast the same collection of information to several receiving parties while only allowing a certain subset of the receiving parties to access the information. This system must still be secure in the scenario where all receiving parties who are not allowed access to the information, pool their resources in an attempt to gain access to the information. Such a product entitlement system must also be bandwidth e cient since it can be deployed in networks where bandwidth is at a premium. The foundations of modern encryption techniques is reviewed and a survey of existing techniques, used to secure content in broadcast environments, is studied. From this collection of techniques two were identi ed as bandwidth e cient and are discussed in more detail before being implemented. An attempt is then made to design a new secure bandwidth e cient encryption scheme for protecting content in a broadcast environment. Several iterations of the design is detailed, including the security aw which makes each design insecure. The nal design was implemented and compared in several metrics to the two previously selected bandwidth e cient schemes. A framework to test the correctness of the schemes over a network is also designed and implemented. Possible future avenues of research are identi ed with regards to creating a secure broadcast encryption scheme and improving the software solution in which to use such a scheme. / AFRIKAANSE OPSOMMING: 'n Veilige produk-aanspraak-stelsel stel een party, soos byvoorbeeld 'n betaal-TV-operateur, in staat om dieselfde versameling inligting na verskeie partye uit te saai, terwyl slegs 'n bepaalde deelversameling van die ontvangende partye toegelaat sal word om toegang tot die inligting te bekom. Hierdie stelsel moet steeds die inligting beskerm in die geval waar al die ontvangende partye wat toegang geweier word, hul hulpbronne saamsmee in 'n poging om toegang te verkry. So 'n produk-aanspraak-stelsel moet ook bandwydte doeltre end benut, aangesien dit gebruik kan word in netwerke waar bandwydte baie duur is. Die fondamente van die moderne enkripsietegnieke word hersien. 'n Opname van bestaande tegnieke wat gebruik word om inligting te beskerm in 'n uitsaai omgewing word bestudeer. Uit hierdie versameling tegnieke word twee geïdenti seer as tegnieke wat bandwydte doeltre end benut en word meer volledig bespreek voordat dit geïmplementeer word. 'n Poging word dan aangewend om 'n nuwe veilige bandwydte doeltre ende enkripsietegniek te ontwerp vir die beskerming van inligting wat uitgesaai word. Verskeie iterasies van die ontwerp word uiteengesit, met 'n bespreking van die sekuriteitsfout wat elke ontwerp onveilig maak. Die nale ontwerp is geïmplementeer en aan die hand van verskeie maatstawwe vergelyk met die twee bandwydte doeltre ende tegnieke, wat voorheen gekies is. 'n Raamwerk om die korrektheid van die tegnieke oor 'n netwerk te toets, is ook ontwerp en geïmplementeer. Moontlike toekomstige rigtings van navorsing word geïdenti seer met betrekking tot die skep van 'n veilige uitsaai enkripsietegniek en die verbetering van die sagtewareoplossing wat so 'n tegniek gebruik.

Thesis (PhD (Electric and Electronic Engineering))--University of Stellenbosch, 2007. / There is increasing use of commercial components in space technology and it is important to recognize that the space radiation environment poses the risk of permanent malfunction due to radiation. Therefore, the integrated circuits used for spacecraft electronics must be resistant to radiation. The effect of using the MOSFET device in a radiation environment is that the gate oxide becomes ionized by the dose it absorbs due to the radiation induced trapped charges in the gate-oxide. The trapped charges in the gate-oxide generate additional space charge fields at the oxide-substrate interface. After a sufficient dose, a large positive charge builds up, having the same effect as if a positive voltage was applied to the gate terminal. Therefore, the transistor source to drain current can no longer be controlled by the gate terminal and the device remains on permanently resulting in device failure. There are four processes involved in the radiation response of MOS devices. First, the ionizing radiation acts with the gate oxide layer to produce electron-hole pairs. Some fraction of the electron-hole pairs recombine depending on the type of incident particle and the applied gate to substrate voltage, i.e. the electric field. The mobility of the electron is orders of magnitude larger than that of the holes in the gate oxide, and is swept away very quickly in the direction of the gate terminal. The time for the electrons to be swept away is on the order of 1ps. The holes that escape recombination remain near their point of origin. The number of these surviving holes determines the initial response of the device after a short pulse of radiation. The cause of the first process, i.e. the presence of the electric field, is the main motivation for design method described in this dissertation. The second process is the slow transport of holes toward the oxide-silicon interface due to the presence of the electric field. When the holes reach the interface, process 3, they become captured in long term trapping sites and this is the main cause of the permanent threshold voltage shift in MOS devices. The fourth process is the buildup of interface states in the substrate near the interface The main contribution of this dissertation is the development of the novel Switched Modular Redundancy (SMR) method for mitigating the effects of space radiation on satellite electronics. The overall idea of the SMR method is as follows: A charged particle is accelerated in the presence of an electric field. However, in a solid, electrons will move around randomly in the absence of an applied electric field. Therefore if one averages the movement over time there will be no overall motion of charge carriers in any particular direction. On applying an electric field charge carriers will on average move in a direction aligned with the electric field, with positive charge carriers such as holes moving in the direction of field, and negative charge carriers moving in the opposite direction. As is the case with process one and two above. It is proposed in this dissertation that if we apply the flatband voltage (normaly a zero bias for the ideal NMOS transistor) to the gate terminal of a MOS transistor in the presence of ionizing radiation, i.e. no electric field across the gate oxide, both the free electrons and holes will on average remain near their point of origin, and therefore have a greater probability of recombination. Thus, the threshold voltage shift in MOS devices will be less severe for the gate terminal in an unbiased condition. The flatband conditions for the real MOS transistor is discussed in appendix E. It was further proposed that by adding redundancy and applying a resting policy, one can significantly prolong the useful life of MOS components in space. The fact that the rate of the threshold voltage shift in MOS devices is dependant on the bias voltage applied to the gate terminal is a very important phenomenon that can be exploited, since we have direct control and access to the voltage applied to the gate terminal. If for example, two identical gates were under the influence of radiation and the gate voltage is alternated between the two, then the two gates should be able to withstand more total dose radiation than using only one gate. This redundancy could be used in a circuit to mitigate for total ionizing dose. The SMR methodology would be to duplicate each gate in a circuit, then selectively only activating one gate at a time allowing the other to anneal during its off cycle. The SMR algorithm was code in the “C” language. In the proposed design methodology, the design engineer need not be concerned about radiation effects when describing the hardware implementation in a hardware description language. Instead, the design engineer makes use of conventional design techniques. When the design is complete, it is synthesized to obtain the gate level netlist in edif format. The edif netlist is converted to structural VHDL code during synthesis. The structural VHDL netlist is fed into the SMR “C” algorithm to obtain the identical redundant circuit components. The resultant file is also a structural VHDL netlist. The generated VHDL netlist or SMR circuit can then be mapped to a Field Programmable Gate Array (FPGA). Spacecraft electronic designers increasingly demand high performance microprocessors and FPGAs, because of their high performance and flexibility. Because FPGAs are reprogrammable, they offer the additional benefits of allowing on-orbit design changes. Data can be sent after launch to correct errors or to improve system performance. System including FPGAs covers a wide range of space applications, and consequently, they are the object of this study in order to implement and test the SMR algorithm. We apply the principles of reconfigurable computing to implement the Switched Modular Redundancy Algorithm in order to mitigate for Total Ionizing Dose (TID) effects in FPGA’s. It is shown by means of experimentation that this new design technique provides greatly improved TID tolerance for FPGAs. This study was necessary in order to make the cost of satellite manufacturing as low as possible by making use of Commercial off-the-shelf (COTS) components. However, these COTS components are very susceptible to the hazards of the space environment. One could also make use of Radiation Hard components for the purpose of satellite manufacturing, however, this will defeat the purpose of making the satellite manufacturing cost as low as possible as the cost of the radiation hard electronic components are significantly higher than their commercial counterparts. Added to this is the undesirable fact that the radiation hard components are a few generations behind as far as speed and performance is concerned, thus providing even greater motivation for making use of Commercial components. Radiation hardened components are obtained by making use of special processing methods in order to improve the components radiation tolerance. Modifying the process steps is one of the three ways to improve the radiation tolerance of an integrated circuit. The two other possibilities are to use special layout techniques or special circuit and system architectures. Another method, in which to make Complementary Metal Oxide Silicon (CMOS) circuits tolerant to ionizing radiation is to distribute the workload among redundant modules (called Switched Modular Redundancy above) in the circuit. This new method will be described in detail in this thesis.