Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Carbon dioxide is a natural gas that has been used as a refrigerant as far back as the 1850s. It was then primarily used because it was easily obtainable and non-toxic. Due to the high operating pressure and relatively low critical temperature (and high critical pressure) of CO2, it was gradually phased out and replaced with hydrochlorofluorocarbons and chlorofluorocarbons. With the discovery of the greenhouse effect, greenhouse gasses and ozone depleting gasses, the Montreal Protocol and the Kyoto Protocol were placed into effect. These two protocols call for the reduction in use of certain greenhouse gasses and the complete exclusion of others. The focus turned to natural gasses that are more environmentally friendly and easier to come by. Carbon dioxide is one such gas. However, CO2 has a low critical temperature and high pressure, 33.98 °C and 73.77 bar respectively. CO2 refrigeration systems are more effective, have a greater coefficient of performance and have a greater operating temperature difference (over the gas-cooler) when used under transcritical conditions. It is preferred to have transcritical CO2 refriger-ation systems. The drawback of such a system is the extreme operating conditions. A special system must be designed, built and commissioned at the University of Stellenbosch. The system will demand the use or manufacture of unique, special-ised components. Most of the components utilised are extremely expensive and/or difficult to come by, or designed and manufactured specifically for this system. The CO2 system at the University of Stellenbosch is exceptional and stands out from conventional systems in that: - it can operate under both the subcritical and transcritical conditions; - it has multiple expansion units, which can be alternated, giving a total of four different operating configurations; - the system can run with fully automated controllers or as a static system; - the internal heat exchanger can be included or excluded from the system; - all the heat exchangers can run in counter flow or parallel flow; and - The system has multiple testing points, for both temperature and pressure, to give the operator accurate measurements to be used in comparison with design software, etc. Three simulation programs are given that describe the physical system. The first simulation program is a steady-state simulator used to aid in the design of the heat exchangers and the capillary tube. The second simulator is a steady-state program that determines the mass flow rate in the capillary tube. The third simulation is a transient program, programmed to determine the steady-state conditions of a sys-tem, given set initial conditions and a transient start-up. / AFRIKAANSE OPSOMMING: Koolstofdioksied is 'n natuurlike gas wat gebruik word as 'n verkoelingsmiddel so ver terug as die 1850's. Dit is toe hoofsaaklik gebruik omdat dit maklik verkrygbaar en nie giftig is nie. As gevolg van die hoë werksdruk en relatief lae kritiese temperatuur (en hoë kritiese druk) van CO2, is dit geleidelik uitgefaseer en vervang met hidrochloorfluoorkoolstof en chloorfluoorkoolstowwe. Met die ontdekking van die kweekhuiseffek, kweekhuisgasse en osoon-afbrekende gasse, is die Montreal-protokol en die Kyoto-protokol in werking gestel. Hierdie twee protokolle vereis die afname in die gebruik van sekere kweekhuisgasse en die algehele uitsluiting van ander. Die fokus het verskuif na natuurlike gasse wat omgewingsvriendeliker en makliker is om te bekom. Koolstofdioksied is so 'n gas. Maar CO2 het 'n lae kritiese temperatuur en hoë kritiese druk, 33.98 °C en 73.77 bar onderskeidelik. CO2 verkoelingstelsels is meer effektief, het 'n groter koëffisiënt van werksverrigting en het 'n groter bedryfstemperatuur-verskil (oor die gas-verkoeler) wanneer dit gebruik word onder transkritiese toestande. Dit is dus verkieslik om transkritiese CO2 verkoelingstelsels te hê. Die nadeel van so 'n stelsel is die relatief uiterste bedryfstoestande. 'n Spesiale stelsel moet ontwerp word, dikwels met die gebruik of vervaardiging van unieke, hoogs gespesialiseerde komponente. So 'n stelsel is ontwerp vir die Universiteit van Stellenbosch. Die meeste van die komponente wat gebruik is, is baie duur en/of moeilik om te bekom, of is spesifiek ontwerp en vervaardig vir hierdie stelsel. Die CO2-stelsel by die Universiteit van Stellenbosch is uitsonderlik en staan uit bo konvensionele stelsels deurdat: - dit kan funksioneer onder beide subkritiese en transkritiese toestande; - dit verskeie gasuitsettings-eenhede het, wat afgewissel kan word, wat 'n totaal van vier verskillende bedryfskonfigurasies gee; - die stelsel bedryf kan word met volle outomatiese beheerders of as 'n statiese stelsel; - die interne hitte-uitruiler óf in-, óf uitgesluit kan word van die stelsel; - al die hitte-uitruilers bedryf kan word in kontra-vloei of parallelle vloei; en - die stelsel verskeie toetspunte het, vir beide temperatuur en druk, wat die operateur akkurate metings gee om te vergelyk met die ontwerp sagteware, ens., wat gebruik word. Drie gegewe simulasieprogramme beskryf die fisiese stelsel. In een simulasie word 'n bestendige toestand-simulator gebruik om te help met die ontwerp van die hitteruilers en die kapillêre buis. Die tweede simulasie program is 'n bestendige toestands-program wat die algehele vloeitempo in die kapillêre buis bepaal. Die laaste simulasie is 'n vlugtige program, geprogrammeer om die tydelike toestande van 'n stelsel te bepaal, gegewe vasgestelde aanvanklike toestande en 'n kortstondige aanskakeling.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Patients in critical care with lung injuries need to be assisted with regards to breathing function, but current methods are not applicable for all situations. The most common method, Extracorporeal Membrane Oxygenation (ECMO) is an expensive procedure and requires trained staff to operate the equipment at all times. Lung injury may lead to the inability of the lungs to be perfused and the blood oxygenated by tracheal intubation, whereas mechanical ventilators can injure the lungs further. Especially at risk are preterm neonates, where congenital disorders or complications during birth render ECMO the only viable option. Respiratory Assist Catheters (RACs) could be used as an alternative because they do not place extra stress on the lungs, are easy to implement, cost-effective and are available for immediate use in clinical settings or in first aid situations. The development of such a device requires knowledge of possible oxygenation methods as well as the risks involved in implementing such a device. The possibility of oxygenating the blood via microbubbles by means of a RAC is promising due to the high gas transfer rates common in bubble oxygenators. It is the aim of this study to develop a prototype that could function as a RAC and to evaluate the feasibility of oxygenation by using microbubbles. The method used to design a prototype included selection of various materials and finalization of a design to be tested. The tests selected were in vivo tests and ex vivo tests using animal models to investigate the dissolution times of the microbubbles, as well as the physiological effects of an intravenously placed device. Measurements of oxygen saturation of the blood in arterial blood (SaO2), venous blood (SvO2) and pulmonary pressure allowed the oxygen transfer rates and risks involved to be evaluated, and also gave an indication regarding the formation dynamics of microbubbles in the blood. An in vitro test was also performed with the aim of determining the rate of dissolving of oxygen, and hence to give an indication regarding microbubble dissolution times. Mathematical simulations based on the dissolution rate of oxygen in venous blood confirmed the abovementioned results. The tests and simulations were analysed in order to evaluate the feasibility of intravenously oxygenating the blood using microbubbles. Approximate bubble dissolution times were an indicator of the feasibility of the concept and showed that very large bubble dissolution times renders intravenous bubble oxygenation unfeasible. These large dissolution times also lessen the possibility of implementing bubble oxygenation in an intravenous device. / AFRIKAANSE OPSOMMING: Pasiënte wat a.g.v. longbeserings in hoë-sorg behandel word het hulp nodig om asem te haal, maar bestaande metodes werk nie in alle omstandighede nie. Die mees algemene metode is ekstrakorporeale membraan suurstofverbinding (Extracorporeal Membrane Oxygenation (ECMO)), maar hierdie metode is duur en het voltyds opgeleide personeel nodig om dit te beheer. Longbeserings kan lei tot die onvermoë van die longe om bloed te ontvang en ook dat die bloed suurstof kry d.m.v. trageale intubasie. Meganiese ventilators kan die longe verder beskadig. Vroeggebore babas word blootgestel aan risiko’s veral waar oorerflike afwykings/steurnisse aanwesig is of komplikasies tydens geboorte en dus die EMCO die enigste lewensvatbare opsie maak. Kateters wat asemhaling aanhelp (Respiratory Assist Catheters (RACs)) kan as alternatief gebruik word aangesien dit nie ekstra spanning op die longe plaas nie, maklik is om te implementeer, koste-effektief is en beskikbaar is vir onmiddellike gebruik in kliniese omstandighede of in noodhulpsituasies. Die ontwikkeling van hierdie tipe toestel vereis kennis van moontlike suurstofverbindingsmetodes en ook die risiko’s verbonde aan die implementering van die toestel. Die moontlikheid om die bloed van suurstof te voorsien d.m.v. mikroborrels deur die RAC lyk belowend a.g.v. die hoë gasoordrag-koers wat algemeen is by borrel suurstofverbinders. Hierdie studie het ten doel om ʼn prototipe te ontwikkel wat kan dien as ʼn RAC en ook om die lewensvatbaarheid van suurstofverbinding met mikroborrels te bepaal. Die metode wat gebruik is om die prototipe te ontwerp sluit in die kies van verskeie materiale en die finalisering van die ontwerp wat getoets moet word. Die geselekteerde in vivo en ex vivo toetse is afgeneem deur gebruik te maak van dier-modelle om sodoende ondersoek in te stel na die oplossing van die mikroborrels en ook die fisiologiese gevolge van die toestel wat binne die aar geplaas is. Metings van die suurstofversadiging van bloed in slagaarbloed (SaO2), aarbloed (SvO2) en pulmonêre druk het toegelaat dat die koers en risiko’s verbonde aan suurstofoordrag geëvalueer word. Hierdie metings gee ook ’n aanduiding van die vormingsdinamika van die mikroborrels in die bloed. ’n In vitro toets is gedoen met die doel om die koers te bepaal van die oplossing van suurstof, en dus ’n aanduiding te gee van die tyd verbonde aan die oplossing van die mikroborrels. Wiskundige simulasies gebaseer op die oplossingskoers van suurstof in are het die bogenoemde toetse bevestig. Die toetse en simulasies is geanaliseer om die lewensvatbaarheid te bepaal om suurstof binne-aars te verskaf deur mikroborrels. Geskatte tye waarteen die borrels oplos is as aanduiding gebruik vir die lewensvatbaarheid van die konsep en ook die moontlike inwerkingstelling van die binne-aarse toestel.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The complexity of adopting a new crop-based biodiesel feedstock into South Africa given the prevailing environmental, economic and social concerns facing the country are addressed in this study by utilising a Systems Thinking approach. Solaris is a new variety of Tobacco developed specifically as an energy crop over the last twelve years by Italian companies Plantechno and Sunchem. Small-scale trials have been underway over the last year in the Loskop Valley farming community in the Limpopo Province of South Africa. These trials have been managed by the newly-formed local entity, Toboil (Pty) Ltd. In order to assess the viability of introducing Solaris into Loskop in terms of addressing the current diesel and electricity needs of the community and larger over-arching biofuel goals of South Africa, the full System Dynamic Modelling process was employed. This included significant research, stakeholder engagement, a Systems Thinking workshop as well as model development and simulation using the System Dynamics programming tool, Vensim. Following the simulation of various scenarios, it was determined that in order for Solaris implementation to have the greatest impact on the diesel and electricity independence desires of the community, as well as maximising job creation and avoided greenhouse gas emissions, the first five to ten years of implementation may only achieve low to moderate profitability. It was further concluded that if crop-based biofuels are to help meet the rural development goals of South Africa then significant investment and skills transfer is required. In order to address both of these, a modular development process is advocated and should be aided and mentored by members of the commercial farming industry. / AFRIKAANSE OPSOMMING: Die kompleksiteit van die aanvaarding van ‘n nuwe oes-gebaseerde bio diesel roumateriaal in Suid-Afrika in die heersende omgewings-, ekonomiese- en sosiale kommer wat die land ervaar, word in hierdie studie aangespreek deur gebruik te maak van ‘n Sistemiese Denke Benadering (Systems Thinking approach) Solaris is ‘n nuwe variasie Tabak wat deur twee Italiaanse maatskappye Plantechno en Sunchem oor die afgelope twaalf jaar spesifiek as ‘n bron van energie ontwikkel is. Kleinskaalse proewe is gedurende die afgelope jaar in die Loskop Vallei Landbougemeenskap in die Limpopo-provinsie van Suid-Afrika gedoen. Hierdie proewe word onder die toesig van die nuut gevormde plaaslike entiteit, Toboil (Pty) Ltd uitgevoer. Aansienlike navorsing, die aktiewe deelname van die onderskeie belanghebbende partye, ‘n Sistemiese Denke werkswinkel sowel as die ontwerp van ‘n simulasie model deur die gebruik van Sisteem Dinamieke Programerings program, naamlik Vensim, is ingespan om die lewensvatbaarheid van die moontlike aanplanting van Solaris te beoordeel. Die spesifieke gemeenskap se huidige behoeftes aan diesel en elektrisiteit sowel as Suid-Afrika se breër doelwitte aangaande bio-brandstowwe was as die grondslag gebruik waarop die volle Sistemiese Denke Benadering toegepas is. In Loskop omgewing was verskeie moontlike scenarios beproef en daar is op grond daarvan vasgestel dat ten einde die grootste moontlike inpak te maak op die afhanlikheid van diesel en elektrisiteit behoeftes van die gemeenskap, sowel as om die grootste moontlik werkskepping potensiaal te verwesenlik – terwyl die afskeiding van kweekhuis gasse verhoed word - die eerste vyf tot tien jaar van implementering baie lae winsgrens tot gevolg sal hê. Daar is ook verder afgelei dat afsienbare beleggings en opleiding benodig gaan word indien aangeplante bio-brandstowwe aangewend sou word om die landelike ontwikkelingsdoelwitte in Suid-Afrika te verwesenlik. Ten einde beide hierdie doelwitte aan te spreek, word ‘n modulêre ontwikkelings proses aanbeveel waar gevestigde lede van die kommersiële lanbou industrie, bystand en leierskap voorsien.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The potential benefits from saving energy have driven most industrial processing facilities to pay more attention to reducing energy wastage. Because the industrial sector is the largest user of electricity in South Africa (37.7% of the generated electricity capacity), the application of waste heat recovery and utilisation (WHR&U) systems in this sector could lead to significant energy savings, a reduction in production costs and an increase in the efficiency of industrial processes. Turbines are critical components of WHR&U systems, and the choice of an efficient and low cost turbine is crucial for their successful implementation. The aim of this thesis project is therefore to validate the use of a turbine for application in a low grade energy WHR&U system. An experimental turbine kit (Infinity Turbine ITmini) was acquired, assembled and tested in a specially designed and built air test bench. The test data was used to characterise the turbine for low temperature (less than 120 Celsius) and pressure (less than 10 bar) conditions. A radial inflow turbine rotor was designed, manufactured and then tested with the same test bench, and its performance characteristics determined. In comparison with the ITmini rotor, the as-designed and manufactured rotor achieved a marginally better performance for the same test pressure ratio range. The as-designed turbine rotor performance characteristics for air were then used to scale the turbine for a refrigerant-123 application. Future work should entail integrating the turbine with a WHR&U system, and experimentally determining the system’s performance characteristics. / AFRIKAANSE OPSOMMING: Die potensiële voordele wat gepaard gaan met energiebesparing het die fokus van industrie laat val op die bekamping van energievermorsing. Die industriële sektor is die grootse verbruiker van elektrisiteit in Suid-Afrika (37.7% van die totale gegenereerde kapasiteit). Energiebesparing in die sektor deur die toepassing van afval-energie-herwinning en benutting (AEH&B) sisteme kan lei tot drastiese vermindering van energievermorsing, ‘n afname in produksie koste en ‘n toename in die doeltreffendheid van industriële prosesse. Turbines is kritiese komponente in AEH&B sisteme en die keuse van ‘n doeltreffende lae koste turbine is noodsaaklik in die suksesvolle implementering van dié sisteme. Die doelwit van hierdie tesisprojek is dus om die toepassing van ‘n turbine in ‘n lae graad energie AEH&B sisteem op die proef te stel. ‘n Eksperimentele turbine stel (“Infinity Turbine ITmini”) is aangeskaf, aanmekaargesit en getoets op ‘n pasgemaakte lugtoetsbank. Die toetsdata is gebruik om die turbine te karakteriseer by lae temperatuur (minder as 120 Celsius) en druk (minder as 10 bar) kondisies. ‘n Radiaalinvloeiturbinerotor is ook ontwerp, vervaardig en getoets op die lugtoetsbank om die rotor se karakteristieke te bepaal. In vergelyking met die ITmini-rotor het die radiaalinvloeiturbinerotor effens beter werkverrigting gelewer by diselfde toetsdruk verhoudings. Die werksverrigtingkarakteristieke met lug as vloeimedium van die radiaalinvloeiturbinerotor is gebruik om die rotor te skaleer vir ‘n R123 verkoelmiddel toepassing. Toekomstige werk sluit in om die turbine met ‘n AEH&B sisteem te integreer en die sisteem se werksverrigtingkarakteristieke te bepaal.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The ability of concentrating solar power (CSP) to efficiently store large amounts of energy sets it apart from other renewable energy technologies. However, cost reduction and improved efficiency is required for it to become more economically viable. Significant cost reduction opportunities exist, especially for central receiver system (CRS) technology where the heliostat field makes up 40 to 50 per cent of the total capital expenditure. CRS plants use heliostats to reflect sunlight onto a central receiver. Heliostats with high tracking accuracy are required to realize high solar concentration ratios. This enables high working temperatures for efficient energy conversion. Tracking errors occur mainly due to heliostat manufacturing-, installation- and alignment tolerances, but high tolerance requirements generally increase cost. A way is therefore needed to improve tracking accuracy without increasing tolerance requirements. The primary objective of this project is to develop a heliostat field control system within the context of a 5MWe CRS pilot plant. The control system has to govern the tracking movement of all heliostats in the field and minimize errors over time. A geometric model was developed to characterize four deterministic sources of heliostat tracking errors. A prototype system comprising 18 heliostats was constructed to function as a scaled down subsection of the pilot plant heliostat field and to validate the chosen control method and system architecture. Periodic measurements of individual heliostats’ tracking offsets were obtained using a camera and optical calibration target combined with image processing techniques. Mathematical optimization was used to estimate model coefficients to best fit the measured error offsets. Real-time tracking error corrections were performed by each heliostat’s local controller unit to compensate for a combination of error sources. Experimental tracking measurements were performed using the prototype system. Daily open-loop RMS tracking errors below one milliradian were obtained, thereby satisfying the project’s primary objective. The thesis concludes that high tracking accuracy can be achieved using the control method proposed here. This could potentially lead to a reduction in heliostat cost, thereby lowering the levelised cost of electricity for CRS plants. / AFRIKAANSE OPSOMMING: Gekonsentreerde sonkrag se vermoë om groot hoeveelhede energie effektief te stoor onderskei dit van ander hernubare energie tegnologieë. Kostebesparing en hoër effektiwiteit word egter vereis om dit ekonomies meer lewensvatbaar te maak. Beduidende kostebesparingsgeleenthede bestaan wel, spesifiek vir tegnologieë vir sentraal-ontvangerstelsels (central receiver system (CRS)) waar die heliostaatveld 40 tot 50 persent van die totale kapitaalbestedings uitmaak. CRS aanlegte gebruik heliostate om sonlig op ’n sentrale ontvanger te reflekteer. Heliostate met ’n hoë volgingsakkuraatheid word vereis om hoë sonkragkonsentrasieverhoudings te laat realiseer. Dit maak hoë werkstemperature moontlik vir effektiewe energie-omsetting. Volgingsfoute kom hoofsaaklik voor a.g.v. die heliostaat se vervaardigings-, installasie- en instellingstoleransies, maar hoë toleransie-vereistes verhoog gewoonlik die koste. Daar is dus ’n manier nodig om volgingsakkuraatheid te verbeter sonder om die toleransie-vereistes te verhoog. Die primêre doel van hierdie projek is om ’n heliostaat aanleg kontrole-stelsel te ontwikkel binne die konteks van ’n 5 MWe CRS toetsaanleg. Die kontrole-stelsel moet die volgingsbeweging van al die heliostate in die aanleg bestuur en ook met verloop van tyd volgingsfoute verminder. ’n Geometriese model is ontwikkel om die vier bepalende bronne van heliostaat volgingsfoute te karakteriseer. ’n Prototipe stelsel met 18 heliostate is gebou om as ’n funksionele skaalmodel van die toetsaanleg heliostaatveld te dien en om die gekose kontrole-metode en stelselargitektuur geldig te verklaar. Periodieke metings van die individuele heliostate se volgingsafwykings is verkry deur ’n kamera en optiese kalibrasie teiken te kombineer met beeldprosesseringstegnieke. Wiskundige optimering is gebruik om die model se koëffisiënte te skat om die beste passing te bepaal vir die gemete foutafwykings. Intydse volgingsfoutregstellings is deur elke heliostaat se plaaslike beheereenheid gedoen om te vergoed vir ’n kombinasie van foutbronne. Eksperimentele volgingsmetings is uitgevoer met die prototipestelsel. Daaglikse ooplus RMS volgingsfoute onder een milliradiaan is verkry, en sodoende is die projek se primêre doel behaal. Die tesis maak die gevolgtrekking dat hoë volgingsakkuraatheid behaal kan word deur die gebruik van die beheer-metode soos hier voorgestel. Dit kan potensieel bydra tot kostebesparing in die heliostaatveld van CRS aanlegte om sodoende die geykte koste van elektrisiteit te verminder.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: We investigate the simultaneous analysis and design (SAND) formulation of the topology optimisation problem. The characteristics of the formulation are presented considering the simple compliance/weight constrained problem and the more complex local stress constrained case. The problems are solved in an efficient sparse sequential approximate optimisation (SAO) framework with the SAND formulation showing an significant reduction in computational requirements compared to the traditional and inherently expensive nested analysis and design (NAND) approach. In SAND the state equations are included in the optimisation problem as a set of equality constraints and not solved exactly in each iteration, as would be the case in NAND. Decision and state variables are thus independent, resulting in an immensely sparse optimisation problem. The availability of simple exact analytic expressions for all the constraint functions (via the finite element method) allows for the construction of accurate approximate subproblems with little computational effort. Furthermore, material can be removed completely from the design domain with few complications, resulting in a decrease in subproblem size as the algorithm progresses, further reducing computation time. The inclusion of void material in the design domain leads to the formulation of stress constraints as so-called ‘vanishing’ constraints. Furthermore, the SAND formulation provides a new perspective on the infamous singularity problem. Amongst other results, we present some test cases that seem to scale linearly in computational requirements for a specific range of problem sizes. / AFRIKAANSE OPSOMMING: Die formulering van die topologie optimerings probleem as ’n gelyktydige analise en ontwerp (simultaneous analysis and design (SAND)) formulering word ondersoek. Die eienskappe van die formulering word bespreek in die konteks van die eenvoudig begrensde styfheid/gewig geval en die meer komplekse plaaslike spanning begrensde geval. Die probleme word opgelos in ’n sekwenti¨ele benaderde optimering (SBO; sequential approximate optimisation (SAO)) raamwerk met die SAND formulering, wat lei tot ’n wesenlike vermindering in berekenings vereistes benodig in vergelyking met die tradisionele en inherente duur geneste analise en ontwerp (nested analysis and design (NAND)) geval. In SAND word die vergelykings wat die respons van die struktuur beskryf met gelykheidsbegrensings in die optimerings probleem verteenwoordig. Die respons van die struktuur word dus nie presies opgelos in elke iterasie nie, soos in die geval van NAND wel gebeur. Alle optimerings veranderlikes is dus onafhanklik en lei tot ’n baie yl optimerings probleem. Deur middel van die eindige element metode is die analitiese vorm van alle begrensings beskikbaar en kan dit gebruik word om akkurate benaderde subprobleme op te stel sonder ekstra berekenings koste. Verder kan materiaal heeltemal verwyder uit van die ontwerpsgebied met weinig komplikasies. Dit lei tot ’n verkleining van subprobleme soos die algoritme vordering maak wat berekenings tyd nog meer verminder. Die feit dat materiaal heeltemal verwyder kan word van die ontwerp gebied lei tot die formulering van spannings begrensings as sogenaamde ‘verdwynende’ begrensings. Verder gee die SAND formulering ’n nuwe uitsig op die bekende singulariteitsprobleem. Met verskeie ander resultate word daar ook gewys dat dit voorkom of ’n spesifieke stel toetsprobleme lineˆer skaal in berekenings tyd.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Muscular dystrophy, spinal cord injury, or amyotrophic lateral sclerosis (ALS) are injuries and disorders that disrupts the neuromuscular channels of the human body thus prohibiting the brain from controlling the body. Brain computer interface (BCI) allows individuals to bypass the neuromuscular channels and interact with the environment using the brain. The system relies on the user manipulating his neural activity in order to control an external device. Electroencephalography (EEG) is a cheap, non-invasive, real time acquisition device used in BCI applications to record neural activity. However, noise, known as artifacts, can contaminate the recording, thus distorting the true neural activity. Eye blinks are a common source of artifacts present in EEG recordings. Due to its large amplitude it greatly distorts the EEG data making it difficult to interpret data for BCI applications. This study proposes a new combination of techniques to detect and correct eye blink artifacts to improve the quality of EEG for BCI applications. Independent component analysis (ICA) is used to separate the EEG signals into independent source components. The source component containing eye blink artifacts are corrected by detecting each eye blink within the source component and using a trained wavelet neural network (WNN) to correct only a segment of the source component containing the eye blink artifact. Afterwards, the EEG is reconstructed without distorting or removing the source component. The results show a 91.1% detection rate and a 97.9% correction rate for all detected eye blinks. Furthermore for channels located over the frontal lobe, eye blink artifacts are corrected preserving the neural activity. The novel combination overall reduces EEG information lost, when compared to existing literature, and is a step towards improving EEG pre-processing in order to provide cleaner EEG data for BCI applications. / AFRIKAANSE OPSOMMING: Spierdistrofie, ’n rugmurgbesering, of amiotrofiese laterale sklerose (ALS) is beserings en steurnisse wat die neuromuskulêre kanale van die menslike liggaam ontwrig en dus verhoed dat die brein die liggaam beheer. ’n Breinrekenaarkoppelvlak laat toe dat die neuromuskulêre kanale omlei word en op die omgewing reageer deur die brein. Die BCI-stelsel vertrou op die gebruiker wat sy eie senuwee-aktiwiteit manipuleer om sodoende ’n eksterne toestel te beheer. Elektro-enkefalografie (EEG) is ’n goedkoop, nie-indringende, intydse dataverkrygingstoestel wat gebruik word in BCI toepassings. Nie net senuwee aktiwiteit nie, maar ook geraas , bekend as artefakte word opgeneem, wat dus die ware senuwee aktiwiteit versteur. Oogknip artefakte is een van die algemene artefakte wat teenwoordig is in EEG opnames. Die groot omvang van hierdie artefakte verwring die EEG data wat dit moeilik maak om die data te ontleed vir BCI toepassings. Die studie stel ’n nuwe kombinasie tegnieke voor wat oogknip artefakte waarneem en regstel om sodoende die kwaliteit van ’n EEG vir BCI toepassings te verbeter. Onafhanklike onderdeel analise (Independent component analysis (ICA)) word gebruik om die EEG seine te skei na onafhanklike bron-komponente. Die bronkomponent wat oogknip artefakte bevat word reggestel binne die komponent en gebruik ’n ervare/geoefende golfsenuwee-netwerk om slegs ’n deel van die komponent wat die oogknip artefak bevat reg te stel. Daarna word die EEG hervorm sonder verwringing of om die bron-komponent te verwyder. Die resultate toon ’n 91.1% opsporingskoers en ’n 97.9% regstellingskoers vir alle waarneembare oogknippe. Oogknip artefakte in kanale op die voorste lob word reggestel en behou die senuwee aktiwiteit wat die oorhoofse EEG kwaliteit vir BCI toepassings verhoog.

Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: This work is concerned with the hydrodynamic design of hydrofoil-assisted catamarans. Focus is placed on the development of new and suitable design methods and application of these to identify the most important geometric parameters of catamaran hulls and hydrofoil configurations that influence efficiency and performance. These goals are pursued by firstly gaining a thorough understanding of the governing hydrodynamic principles involved in the design process. This knowledge is then applied to develop new and improved experimental techniques and theoretical methods needed for design. Both are improved to the extent where they can be applied as design tools covering the important semi-displacement and semi-planing speeds, which are the focus of this study. The operational speed range of hydrofoil-assisted catamarans is shown to consist of three distinct hydrodynamic phases (displacement, transition and planing) and that different hydrodynamic principles govern vessel performance in each phase. The hydrodynamics are found to differ substantially from that of conventional high-speed craft, primarily due to the interaction between the hull and the hydrofoils, which is found to vary with speed and results in the need for more complex experimental procedures to be followed if accurate predictions of resistance are to be made. Experimental predictions based on scaled model tests of relatively small hydrofoilassisted catamaran models are found to be less accurate than that achievable for conventional ships because of the inability to correct for all scaling errors encountered during model testing. With larger models scaling errors are encountered to a lesser degree. The most important scale effect is found to be due to the lower Reynolds number of the flow over the scaled foils. The lower Reynolds number results in higher drag and lower lift coefficients for hydrofoils compared with those achieved at full scale. This effect can only be partially corrected for in the scaling procedure using the available theoretical scaling methods. Presently available theoretical methods commonly used for the design of conventional ships were found to be ill adapted for modeling the complex hydrodynamics of hydrofoil-assisted catamarans and required further development. Vortex lattice theory was chosen to model the flow around hydrofoil-assisted catamarans as vortex theory models the flow around lifting surfaces in the most natural way. The commercial code AUTOWING is further developed and generalized to be able to model the complex hull-hydrofoil interactions that change with speed. The method is shown to make good predictions of all hydrodynamic quantities with accuracies at least as good as that achievable through model testing and therefore fulfills the requirements for a suitable theoretical design tool. The developed theoretical and experimental design tools are used to investigate the design of hydrofoils for hydrofoil-assisted catamarans. It is found that the main parameter needing consideration in the hydrofoil design is selection of a suitable hydrofoil lift fraction. A foil lift fraction in the order of 20-30% of the displacement weight is needed if resistance improvements using hydrofoil assistance are to be obtained over the hull without foils. It is often more favorable to use higher foil lift fractions (50%+) as the resistance improvements are better, although careful attention should then be given to directional and pitch-heave instabilities. The Hysuwac hydrofoil system patented by the University of Stellenbosch is found to be hydrodynamically optimal for most hullforms. The hullform and in particular the curvature of the aft buttock lines of the hull are found to have an important influence on the achievable resistance improvements and behaviour of the hydrofoil-assisted hull at speed. Hull curvature is detrimental to hydrodynamic performance as the suction pressures resulting from the flow over the curved hull counter the hydrofoil lift. The hullform best suited to hydrofoil assistance is found to be one with relatively straight lines and hard chine deep- V sections. The main conclusion drawn from this study is that hydrofoil-assistance is indeed suitable for improving the performance and efficiency of catamarans. The design and optimization of such vessels nevertheless requires careful consideration of the various resistance components and hull-foil interactions and in particular, how these change with speed. The evaluation of resistance for design purposes requires some discipline between theoretical analysis and experimental measurements as the complexity of the hydrodynamics reduce the accuracies of both. Consideration of these factors allows hulls and hydrofoils to be designed that are efficient and also free of dynamic instabilities. / AFRIKAANSE OPSOMMING: Hierdie studie is gerig op die hidrodinamiese ontwerp van hidrovleuel-gesteunde katamarans. Daar word gefokus op die ontwikkeling van nuwe en geskikte ontwerpmetodes, asook die toepassing van hierdie metodes om die belangrikste geometriese parameters van katamaranrompe en hidrovleuel-konfigurasies wat 'n invloed op doeltreffendheid en werkverrigting het, te identifiseer. As aanloop tot die studie is 'n deeglike begrip van die onderliggende hidrodinamiese beginsels bekom. Hierdie kennis is toegepas om nuwe en verbeterde eksperimentele en teoretiese tegnieke te ontwikkel wat nodig is vir die ontwerp van hidrovleuel-gesteunde katamarans in die belangrike deels-verplasing en deels-planering spoedbereike. Daar word getoon dat die bedryfspoedbereik van 'n hidrovleuel-gesteunde katamaran uit drie onderskeibare hidrodinamiese fases bestaan, naamlik verplasing, oorgang en planering, en dat verskillende hidrodinamiese beginsels die vaartuig se werkverrigting in elke fase bepaal. Daar is ook gevind dat die hidrodinamika wesentlik verskil van dié van konvensionele hoëspoed-vaartuie, hoofsaaklik as gevolg van die interaksie tussen die romp en die hidrovleuels wat wissel na gelang van die spoed. Hierdie interaksies moet in ag geneem word gedurende die ontwerpproses en beide eksperimentele en teoretiese metodes is nuttig om die omvang daarvan te bepaal. Daar is gevind dat die eksperimentele voorspellings gebaseer op toetse met relatief klein skaalmodelle van hidrovleuelgesteunde katamarans minder akkuraat is as dié wat bereik kan word met konvensionele skepe. Dit is omdat al die skaalfoute wat tydens die toetsing met die model ontstaan, nie gekorrigeer kan word nie. Die belangrikste skaaleffek is as gevolg van die laer Reynoldsgetal van die vloei oor die afgeskaalde vleuels. Groter modele Die laer Reynoldsgetal lei tot hoër sleur- en hefkoëffisiënte in vergelyking met dié vir die volskaal-hidrovleuels. Wanneer die beskikbare teoretiese metodes gebruik word, kan daar slegs gedeeltelik vir hierdie effek in die skaalprosedure gekorrigeer word. Daar is ook vasgestel dat die skaaleffekte op die Reynoldsgetal verminder word wanneer die hidrovleuels baie nabyaan die vrye oppervlakte is. Dit lei daartoe dat eksperimentele voorspellings van werkverrigting meer akkuraat is vir die ontwerpe waar die hidrovleuels nie so diep onder die water is nie. Daar is gevind dat die teoretiese metodes wat tans beskikbaar is en algemeen vir die ontwerp van konvensionele skepe gebruik word nie die komplekse hidrodinamika van hidrovleuel-gesteunde katamarans kan modelleer nie. Die werwelroosterteorie is gekies om die vloei om hidrovleuel-gesteunde katamarans te modelleer aangesien dié teorie die vloei om hefvlakke op die natuurlikste manier weergee. Die kommersiële kode AUTOWING is verder ontwikkel en veralgemeen om ook die komplekse spoed-afhanklike interaksies van die romp en hidrovleuel te kan modelleer. Hierdie metode lewer goeie voorspellings van al die hidrodinamiese maatstawwe met akkuraathede wat ten minste so goed is soos di wat met modeltoetsing bereik word en voldoen daarom aan die vereistes vir 'n geskikte teoretiese ontwerpmetode. Die teoretiese en eksperimentele ontwerpmetode wat ontwikkel is, word gebruik om die ontwerp van hidrovleuels vir hidrovleuel-gesteunde katamarans te ondersoek. Daar is gevind dat die belangrikste parameter wat in die hidrovleuel-ontwerp in ag geneem moet word, die keuse van 'n geskikte hidrovleuelhefverhouding is. Om in rompe met hidrovleuelsteun verbeterings in die weerstand te kry in vergelyking met rompe sonder vleuels, is 'n vleuel-hef-verhouding van 20-30 persent van die verplasingsgewig nodig. Dit is dikwels beter om hoër vleuel-hef-verhoudings (van 50 persent of meer) te gebruik omdat die verbetering in weerstand dan groter is. Daar moet dan egter gewaak word teen rigtings- en hei-hef-onstabiliteite. Daar is gevind dat die Hysuwachidrovleuel- stelsel wat deur die Universiteit van Stellenbosch gepatenteer is, hidrodinamies optimaal is vir die meeste rompvorms. Daar is gevind dat die vorm van die romp en veral die kromming van die lyne gevorm deur vertikale snitte deur die romp (Engels: "aft buttock lines") van die romp 'n belangrike invloed het op die bereikbare weerstandsverbeterings en die gedrag van die hidrovleuel-gesteunde romp wat op spoed is. Die kromming van die romp is nadelig vir die hidrodinamiese werksverrigting aangesien die suigdruk as gevolg van die vloei oor die gekromde romp die hefkrag van die hidrovleuels teenwerk. Die rompvorm wat die geskikste is vir hidrovleuel-ondersteuning is 'n romp met relatiewe reguit lyne en skerp hoekige diep- V seksies. Die belangrikste gevolgtrekking waartoe tydens die studie gekom is, is dat hidrovleuelondersteuning wel geskik is vir die verbetering van die werkverrigting en die doeltreffendheid van katamarans. Die ontwerp en optimering van sodanige vaartuie verg nogtans die noukeurige oorweging van die verskeie weerstandskomponente en rompvleuel- interaksies en veral hoe hierdie interaksies verander met spoed. Die evaluering van die weerstand vir die doeleindes van ontwerp verg dissipline tussen die teoretiese analise en die eksperimentele metings aangesien die kompleksiteit van die hidrodinamika die akkuraatheid van die algemeen-gebruikte teoretiese en eksperimentele metodes vir die hidrodinamiese ontwerp verminder. As hierdie faktore in ag geneem word, kan rompe en hidrovleuels ontwerp word wat doeltreffend is en ook vry is van dinamiese onstabiliteite.

Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This research focuses on the development of new efficient algorithms for multi-path planning and multi-rigid body constrained attitude control. The work is motivated by current and future applications of these algorithms in: intelligent control of multiple autonomous aircraft and spacecraft systems; control of multiple mobile and industrial robot systems; control of intelligent highway vehicles and traffic; and air and sea traffic control. We shall collectively refer to the class of mobile autonomous systems as “agents”. One of the challenges in developing and applying such algorithms is that of complexity resulting from the nontrivial agent dynamics as agents interact with other agents, and their environment. In this work, some of the current approaches are studied with the intent of exposing the complexity issues associated them, and new algorithms with reduced computational complexity are developed, which can cope with interaction constraints and yet maintain stability and efficiency. To this end, this thesis contributes the following new developments to the field of multipath planning and multi-body constrained attitude control: • The introduction of a new LMI-based approach to collision avoidance in 2D and 3D spaces. • The introduction of a consensus theory of quaternions by applying quaternions directly with the consensus protocol for the first time. • A consensus and optimization based path planning algorithm for multiple autonomous vehicle systems navigating in 2D and 3D spaces. • A proof of the consensus protocol as a dynamic system with a stochastic plant matrix. • A consensus and optimization based algorithm for constrained attitude synchronization of multiple rigid bodies. • A consensus and optimization based algorithm for collective motion on a sphere. / AFRIKAANSE OPSOMMING: Hierdie navorsing fokus op die ontwikkeling van nuwe koste-effektiewe algoritmes, vir multipad-beplanning en veelvuldige starre-liggaam beperkte standbeheer. Die werk is gemotiveer deur huidige en toekomstige toepassing van hierdie algoritmes in: intelligente beheer van veelvuldige outonome vliegtuig- en ruimtevaartuigstelsels; beheer van veelvuldige mobiele en industrile robotstelsels; beheer van intelligente hoofwegvoertuie en verkeer; en in lug- en see-verkeersbeheer. Ons sal hier “agente” gebruik om gesamentlik te verwys na die klas van mobiele outonome stelsels. Een van die uitdagings in die ontwikkeling en toepassing van sulke algoritmes is die kompleksiteit wat spruit uit die nie-triviale agentdinamika as gevolg van die interaksie tussen agente onderling, en tussen agente en hul omgewing. In hierdie werk word sommige huidige benaderings bestudeer met die doel om die kompleksiteitskwessies wat met hulle geassosieer word, bloot te l^e. Verder word nuwe algoritmes met verminderde berekeningskompleksiteit ontwikkel. Hierdie algoritmes kan interaksie-beperkings hanteer, en tog stabiliteit en doeltreffendheid behou. Vir hierdie doel dra die proefskrif die volgende nuwe ontwikkelings by tot die gebied van multipad-beplanning van multi-liggaam beperkte standbeheer: • Die voorstel van ’n nuwe LMI-gebasseerde benadering tot botsingsvermyding in 2D en 3D ruimtes. • Die voorstel van ’n konsensus-teorie van “quaternions” deur “quaternions” vir die eerste keer met die konsensusprotokol toe te pas. • ’n Konsensus- en optimeringsgebaseerde padbeplanningsalgoritme vir veelvoudige outonome voertuigstelsels wat in 2D en 3D ruimtes navigeer. • Die bewys van ’n konsensusprotokol as ’n dinamiese stelsel met ’n stochastiese aanlegmatriks. • ’n Konsensus- en optimeringsgebaseerde algoritme vir beperkte stand sinchronisasie van veelvoudige starre liggame. • ’n Konsensus- en optimeringsgebaseerde algoritme vir kollektiewe beweging op ’n sfeer.

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The research presented in this dissertation establishes a micro-CMM parallel manipulator as a viable positioning device for three degree of freedom micro measurement applications. The machine offers the advantages associated with parallel kinematic manipulators, such as light carrying weight, high stiffness and no accumulation of errors, while avoiding some of the traditional disadvantages of parallel manipulators such as the associated effects of angular errors (Abbé error), singularity problems, work space limitation and the extensive use of spherical joints. In this dissertation, the direct position kinematic solution is developed analytically and the solution of the inverse position kinematic is solved numerically. A workspace analysis has been performed. A fully functional prototype demonstrator is fabricated to demonstrate this machine. While the demonstrator was not intended to achieve submicron accuracy, it was intended to validate the error models. Computer controlled measurement is developed and used to position the probe and to record measurements. A reliable kinematic error model based on the theory of error propagation is derived analytically. A numerical method is used to verify the analytical results. Comparison shows that the results of the error model, both analytical and numerical, represent a very good match and follow the same trend. The kinematic position model is validated using a conventional CMM. Results show that an average difference of less than 0.5 mm over a set of 30 points is achieved. This result of the micro-CMM demonstrator measurements falls within the error budget of approximately 0.75 mm estimated by the proposed analytical error model. / AFRIKAANSE OPSOMMING: Die navorsing in hierdie tesis vestig ‘n mikro-CMM parallelle manipuleerder as ‘n lewensvatbare posisioneringstoestel vir drie vryheidsgraad-mikrometing toepassings. Die masjien bied voordele geassosieer met parallelle kinematiese manipuleerders, bv. ligte dra-gewig, hoë styfheid en geen ophoping van foute nie. Die tradisionele nadele van parallelle manipuleerders soos die geassosieerde gevolge van hoekfoute (Abbé fout), enkelvoudigheidsprobleme, werkspasiebeperking en die uitgebreide gebruik van sferiese koppelings word vermy. In hierdie tesis word die direkte posisie kinematiese oplossing analities ontwikkel en die oplossing van die omgekeerde posisie kinematies word numeries opgelos. ‘n Werkspasie analise is uitgevoer. ‘n Ten volle funksionele prototipe demonstrasie-model is vervaardig om hierdie masjien te demonstreer. Die model is nie vervaardig om submikron akkuraatheid te bereik nie, maar eerder om foutmodelle geldig te verklaar. Rekenaar-beheerde metings is ontwerp en gebruik om die toetspen te posisioneer en om metings te neem. ‘n Betroubare kinematiese foutmodel gebaseer op die teorie van foutvoortplanting is analities afgelei. ‘n Numeriese metode word gebruik om die analitiese resultate te bevestig. Vergelyking toon aan dat die resultate van die foutmodel, beide analities en numeries, goeie pasmaats is en dieselfde tendens volg. Die kinematiese posisie model word geldig verklaar deur gebruik te maak van ‘n konvensionele CMM. Resultate wys dat daar ‘n gemiddelde verskil van minder as 0.5 mm oor ‘n stel van 30 punte behaal word. Die resultate van die mikro-CMM model se metings val binne die foutbegroting van ongeveer 0.75 mm geskat by die voorgestelde analitiese foutmodel.