Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: This thesis comprises of the development of a facility were spark ignition engine fuels can be tested. Development of the facility included the installation of a standard spark ignition engine, an engine dynamometer, control and monitoring equipment, control and monitoring software, and an in-cylinder pressure measurement setup. The system was tested using petrol as well as a petrol-ethanol blend. The results indicated good accuracy and repeatability of the system. Analysis of the performance and combustion of the petrol-ethanol blend showed no significant difference in comparison to the petrol fuel. The petrol-ethanol blend showed a slight increase in oxygen content and fuel consumption as well as an increase in CO2 emissions and a decrease in CO emissions. During the project, a comparison was also made between the performance of fibre optic transducers and a piezoelectric transducer. It was found that the fibre optic transducers performed similarly to the piezoelectric transducer during low engine load conditions. At high load conditions however, the fibre optic transducers were not able to produce the same accuracy as the piezoelectric transducer. / AFRIKAANSE OPSOMMING: Hierdie tesis bestaan uit die ontwikkeling van 'n fasiliteit waar brandstowwe vir 'n vonkontsteking binnebrandenjin getoets kan word. Ontwikkeling van die fasiliteit sluit in die installering van 'n standaard vonkontsteking binnebrandenjin, 'n enjin rem, beheer en monitering toerusting, beheer en monitering sagteware, en 'n insilinder drukmeting opstelling. Die fasiliteit is getoets met suiwer petrol sowel as 'n petrol-etanol mengsel. Die resultate het hoë vlakke van akkuraatheid en herhaalbaarheid getoon. Ontleding van die werksverrigting en verbranding van die petrol-etanol mengsel het geen beduidende verskil getoon in vergelyking met die suiwer petrol brandstof nie. Die petrol-etanol mengsel het 'n effense toename in suurstofinhoud, brandstofverbruik, sowel as CO2 vrylating en 'n afname in CO vrylating getoon. Tydens die projek is 'n vergelyking getref tussen die akkuraatheid van optiese vesel drukmeters en 'n piësoëlektriese drukmeter. Daar is bevind dat die akkuraatheid van die optiese vesel drukmeters soortgelyk is aan die piësoëlektriese drukmeter gedurende lae enjin lastoestande. By hoë las omstandighede was die optiese vesel drukmeters egter nie in staat om dieselfde akkuraatheid as die piësoëlektriese drukmeter te handhaaf nie.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Micro gas turbines used in the aerospace industry require high performance with a compact frontal area. These micro gas turbines are often considered unattractive and at times impractical due to their poor fuel consumption and low cycle efficiency. This led to a joint effort to investigate and analyze the components of a particular micro gas turbine to determine potential geometry and performance improvements. The focus of this investigation is the radial vaned diffuser which forms part of a centrifugal compressor. The size of the diffuser is highly constrained by the compact gas turbine diameter. The micro gas turbine under consideration is the BMT 120 KS. The radial vaned diffuser is analyzed by means of 1-D and 3-D (CFD) analyses using CompAero and FINETM/Turbo respectively. The aim is to design a diffuser that maximizes the total-to-static pressure recovery and mass flow rate through the compressor with minimal flow losses. An experimental test facility was constructed and the numerical computations were validated against the experimental data. Three new diffusers were designed, each with a different vane geometry. The static-to-static pressure ratio over the radial diffuser was improved from 1.39 to 1.44 at a rotational speed of 120 krpm. The static pressure recovery coefficient was improved from 0.48 to 0.73 with a reduction in absolute Mach number from 0.47 to 0.22 at the radial diffuser discharge. / AFRIKAANSE OPSOMMING: Mikro-gasturbines wat in die lugvaart industrie gebruik word, vereis ‘n hoë werkverrigting met ‘n kompakte frontale area. Hierdie gasturbines word menigmaal onaantreklik geag weens swak brandstofverbruik en n lae siklus effektiewiteit. Dit het gelei tot ‘n gesamentlike projek om elke komponent van ‘n spesifieke mikro-gasturbine te analiseer en te verbeter. Die fokus van dié ondersoek is die radiale lem diffusor wat deel vorm van ‘n sentrifugaalkompressor. Die deursnee van die diffusor word deur die kompakte gasturbine diameter beperk. Die mikro gasturbine wat ondersoek word is die BMT 120 KS. Die radiale lem diffusor word geanaliseer deur middel van 1-D en 3-D (BVD) berekeninge met behulp van CompAero en FINETM/Turbo onderskeidelik. Die doelwit is om ‘n diffusor te ontwerp met ‘n verhoogde massavloei en drukverhouding oor die kompressor. ‘n Eksperimentele toetsfasiliteit is ingerig om toetse uit te voer en word gebruik om numeriese berekeninge te bevestig. Die staties-tot-stasiese drukstyging oor die radiale diffusor is verbeter van 1.39 tot 1.44 by ‘n omwentelingspoed van 120 kopm. Die statiese drukherwinningskoeffisiënt is verbeter van 0.48 tot 0.73 met ‘n vermindering in die absolute Machgetal vanaf 0.47 tot 0.22 by die radiale diffusor uitlaat.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Production of graphite dust inside the Pebble Bed Modular Reactor (PBMR) influences the reactor operation negatively. Graphite is used as a moderator in the reactor core and the formation and transportation of graphite dust away from the reactor core decreases the amount of moderator which in turn has a negative impact on the reactor operation. High levels of radioactive dust may also contaminate reactor components which may pose a health risk to maintenance personnel. In this study a pressure vessel was designed and used to measure the wear of a graphite pebble in helium at elevated temperatures. By means of a multi-linear regression analysis a proper mathematical function was established in order to relate graphite wear to certain tribological parameters. These parameters were identified through a literature study. Discrete Element Modelling (DEM) was used to simulate the gravitational flow of graphite pebbles through the reactor core. The experimentally determined mathematical function was incorporated into the DEM simulation to estimate the annual mass of graphite dust to be produced by the PBMR pebble bed as a result of pebble-pebble interaction and pebble-wall interaction during refuelling. / AFRIKAANSE OPSOMMING: Die vorming van grafiet stof binne die korrelbed-modulêre reaktor (PBMR) beïnvloed die werking daarvan negatief. Grafiet word gebruik as 'n moderator in die reaktor kern en die vorming en vervoer van grafietstof weg van die reaktor kern lei tot 'n afname in die hoeveelheid moderator en dit het 'n negatiewe impak op die werking van die reaktor. Hoë vlakke van radioaktiewe grafietstof kontamineer ook reaktorkomponente wat 'n gesondheidsrisiko vir onderhoudspersoneel inhou. In hierdie studie was 'n drukvat ontwerp en gebruik om die slytasie van 'n grafietkorrel in helium by verhoogde temperature te meet. 'n Multi-lineêre regressie analise is dan gebruik om 'n wiskundige funksie daar te stel wat die verband tussen grafietslytasie en die eksperimentele parameters vas stel. Hierdie parameters was met behulp van 'n literatuurstudie geïdentifiseer. Diskrete Element Modellering (DEM) was gebruik om die gravitasionele vloei van grafietkorrels in die reaktor te modelleer. Die eksperimenteel bepaalde wiskundige funksie word in die DEM simulasie ge-inkorporeer om 'n skatting te maak van die jaarlikse massa grafietstof wat gevorm sal word in die PBMR korrelbed as 'n gevolg van korrel-korrel interaksie en korrel-wand interaksie gedurende hersirkulasie.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In this study, Ti6Al4V machining is modelled using finite element analysis of orthogonal machining. Orthogonal turning tests are conducted for the verification of FE models in terms of machining forces, temperatures, and chip geometry. Milling force predictions are made using the "unified" mechanics of cutting model which is applied to ball nose milling for this study. The model makes use of orthogonal cutting data, collected from the turning tests, to model milling forces. Model predictions are compared with test data from slot milling tests for verification. Finally a hybrid form of the "‘unified"’ model is presented in which orthogonal data, obtained from the FE simulations, is used to model ball nose milling operations. / AFRIKAANSE OPSOMMING: In hierdie studie word titaanmasjinering (Ti6Al4V) gemodelleer deur gebruik te maak van eindige element analise van ortogonale masjinering. Ortogonale draai toetse word uitgevoer om eindige element (FE) modelle te verifieer in terme van masjineringskragte, temperatuur en spaandergeometrie. Freeskragte word voorspel deur gebruik te maak van die "Unified Mechanics of Cutting" model wat toegepas word op ’n balneusfrees operasie in hierdie studie. Die model maak gebruik van ortogonale snydata, versamel gedurende snytoetse, om die freeskragte te modelleer. Die model word vervolgens vergelyk met die toetsdata afkomstig van die freestoetse vir verifikasie. Ten slotte word ’n hibriede weergawe van die model aangebied waarin ortogonale data verkry word van die FE simulasie om balneus freesoperasies te simuleer.

Thesis (MEng)-- Stellenbosch University, 2014. / ENGLISH ABSTRACT: The South African industry has an increasing need for manufacturing automation. However, the classical form of automation is not cost effective for the low volumes and high variance of products that are produced there. The industry may use the reconfigurable manufacturing system (RMS) concept to improve production of its products. However, industry has been unwilling to adopt the reconfigurable manufacturing systems developed in recent research projects. Due to industry’s hesitance to adopt the control platforms on which reconfigurable manufacturing systems are currently based, the focus of the thesis is on creating a reconfigurable control system using industry accepted technologies. This research focused on evaluating a Beckhoff embedded PC’s suitability as a station controller that controls a reconfigurable subsystem in an RMS. The control system for the station controller was developed using only the IEC 61131-3 programming languages and the Beckhoff programming software. This control system was evaluated by using it to control a station that is responsible for testing a circuit breaker’s tripping current and time. The developed control system was based on the ADACOR architecture because of its optimisation capabilities that were necessary to keep the cycle time of the station as low as possible. The design and implementation of the physical configuration and control system of the station is described in this thesis. The station was designed to meet the requirements of both an RMS and the case study. Because of the limitations of the IEC 61131-3 programming languages, dynamic instantiation of holons is not possible and a method was developed to simulate dynamic task holons. By making use of the embedded PC’s ability to run multiple PLCs at the same time, each type of holon was run in its own PLC thread. The developed control system and station was evaluated by conducting experiments using a laboratory test setup. The evaluation of the developed control system in this thesis proved that an RMS can be created, in the context of station control, using IEC 61131-3 and industry accepted technologies, if a hardware platform is used that allows multiple PLCs to be run in individual threads. The control approach that was created in this thesis can be used to create station control systems that offers optimised cycle times, the benefits of an RMS and the benefits of industry accepted technology. / AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse bedryf het 'n toenemende behoefte aan geoutomatiseerde vervaardiging. Die klassieke vorm van outomatisasie is egter nie koste effektief vir die lae volumes en hoë variansie van produkte wat in Suid Afrika geproduseer word nie. Die bedryf kan moontlik die konsep van 'n herkonfigureerbare vervaardigingstelsel (HVS) gebruik om vervaardiging te outomatiseer. Die bedryf is egter nie bereid om die herkonfigureerbare vervaardigingstelsels wat in onlangse navorsingsprojekte ontwikkel is, te aanvaar nie. As gevolg van die bedryf se huiwering om die beheerplatforms waarop herkonfigureerbare vervaardigingstelsels tans gebaseer word, te aanvaar, is die fokus van die tesis om industrie-aanvaarde tegnologie te gebruik om ‘n herkonfigureerbare beheerstelsel te skep. Hierdie navorsing fokus op die evaluering van 'n “Beckhoff embedded PC” se geskiktheid as 'n stasiebeheerder van 'n herkonfigureerbare substelsel in 'n HVS. Die beheerstelsel vir die stasie beheerder is ontwikkel deur slegs van die IEC 61131-3 programmeringstale en die Beckhoff programmering-sagteware gebruik te maak. Hierdie beheerstelsel is geëvalueer deur dit op die beheer van 'n stasie wat verantwoordelik is vir die toets stroombrekers, toe te pas. Die beheerstelsel was gebaseer op die ADACOR argitektuur as gevolg van die optimeringsvermoëns wat noodsaaklik was om die siklustyd van die stasie so laag as moontlik te hou. Die ontwerp en implementering van die fisiese konfigurasie en beheerstelsel van die stasie word in hierdie tesis beskryf. Die stasie was ontwerp om aan die vereistes van beide 'n HVS en die gevallestudie te voldoen. As gevolg van die beperkings van die IEC 61131-3 programmeringstale, is dinamiese instansiëring van holons nie moontlik nie, en 'n metode is ontwikkelom dinamiese taakholons na te boots. Deur gebruik te maak van die "embedded PC" se vermoë om meervoudige PLCs terselfdetyd te hanteer, kan elke holon tipe in sy eie "thread" loop. Die ontwikkelde stelsel en die stasie is geëvalueer in 'n laboratorium deur middel van eksperimente. Die evaluering van die beheerstelsel in hierdie tesis bewys dat 'n HVS geskep kan word, in die konteks van ‘n stasiebeheerder, deur IEC 61131-3 en tegnologie wat wyd in die industrie aanvaar word, te gebruik mits die hardeware-platform wat gebruik word toelaat dat verskeie PLCs terselfde tyd op een beheerder kan loop. Die beheerbenadering wat geskep is in hierdie tesis kan gebruik word om stasie- beheerstelsels te skep wat optimale siklus tye, die voordele van 'n HVS en die voordele van industrie-aanvaarde tegnologie bied.

Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006. / This thesis describes the design and incorporation of a twin-stream fan into the CIRSTEL tail boom. The Combined Infra-Red Suppression and Tail rotor Elimination (CIRSTEL) tail boom is a system designed to replace the tail rotor on a conventional helicopter. It relies on the Coanda effect to create circulation around the helicopter tail boom when exposed to the rotor downwash. This generates sideways-directed lift to counter the main rotor torque, and a tail thruster adds extra torque and directional control. A twin-stream fan supplies separate air streams to each of the Coanda and tail thruster sections. The first section of the study describes the experimental tests done on an 83% scale demonstrator of the twin-stream fan with the objective to verify the concept and determine the fan section efficiencies. Subsequent modifications done to the fan stator blades are also evaluated. The efficiencies of the design were shown to exceed the targets in both sections. The section concludes with design recommendations for a future fan, based on the findings of the experiments. A brief analysis of the CIRSTEL system is presented and by using optimisation techniques the predicted power demand of the system could be significantly reduced from a conventional tail rotor. The second section of the study details the conceptual design and CFD evaluation of air intakes for the fan that can be fitted to the helicopter. The objective here was to study the flow affecting helicopter intakes as well as to establish design considerations for a fan intake. A basic intake concept was developed for the Alouette III/CIRSTEL combination and modified according to results based on the CFD simulations. The intake design was evolved to the point were it was shown that the concept is feasible. These CFD simulations were an initial effort to design the fan intakes with the help of a simplified rotor flow field. The investigation was subsequently extended to investigate helicopter intake design considerations in the presence of a representative rotor, which was modelled as an actuator disk in the CFD simulations. In this investigation top and side mounted intake concepts were compared and analysed for suitability as a fan intake. Each intake concept showed its own advantages. Due to the proximity of the rotor hub to the intake, distortion and total pressure levels at the fan face are influenced negatively. The report is concluded with design recommendations for the intake as applied to the current Alouette III configuration, as well as for implementation on helicopters in general.

Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / This dissertation describes the design analysis of a lomolder (a machine similar to an injection moulding machine). It focuses on key design aspects that will drive the purchase cost of the machine and that will also influence the maintenance and operating cost. The main objective of the study is to provide an understanding of the key factors that influence the cost of a lomolder as well as the factors that contributes to a quality manufactured part. A semi-analytical flow model was developed to predict cavity pressure drops for a range of part sizes. This model was necessary to eliminate time consuming numeric simulations required for machine optimisation. Numerous machine concept designs were developed and a final layout design chosen. A parametric CAD model was built for the lomolder. Layout designs for different sized lomolders can be generated with this model. The dissertation concludes with a cost study that focuses on the purchase cost of a lomolder unit. Key elements such as choice of actuator and piston to part area ratio are described.

Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2004. / Granular flow occurs in a broad spectrum of industrial applications that range from separation and mixing in the pharmaceutical industry, to grinding and crushing, blasting, stockpile construction, flow in and from hoppers, silos, bins, and conveyer belts, agriculture, mining and earthmoving. Two totally different approaches of modelling granular flow are the Discrete Element Method (DEM) and continuum methods such as Finite Element Methods (FEM). Continuum methods can be divided into nonpolar or classic continuum methods and polar continuum methods. Large displacements are usually present during granular flow which, without remeshing, cannot be solved with standard finite element methods due to severe mesh distortion. The Particle-in-Cell (PIC) method, which is a so-called meshless method, eliminates this problem since all the state variables are traced by material points moving through a fixed mesh. The main goal of this research was to model the flow of noncohesive granular material in front of flat bulldozer blades and into excavator buckets using a continuum method. A PIC code was developed to model these processes under plane strain conditions. A contact model was used to model Coulomb friction between the material and the bucket/blade. Analytical solutions, published numerical and experimental results were used to validate the contact model and to demonstrate the code’s ability to model large displacements and deformations. The ability of both DEM and PIC to predict the forces acting on the blade and bucket and the material flow patterns were demonstrated. Shear bands that develop during the flow of material were investigated. As part of the PIC analyses, a comparison between classic continuum and polar continuum (Cosserat) results were made. This includes mesh size and orientation dependency, flow patterns and the forces acting on the blade and the bucket. It is concluded that the interaction of buckets and blades with granular materials can successfully be modelled with PIC. In the cases conducted here, the nonpolar continuum was more accurate than the polar continuum, but the polar continuum results were less dependent on the mesh size. The next step would be to apply this technology to solve industrial problems.

Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006. / The research described in this dissertation examined the effects that fuel formulation can have on the regulated exhaust emissions produced by spark ignition engines in a South African context. Typical South African engine technology, and fuels representative of available fuels were investigated. To broaden the scope and provide information on as many fuel parameters as possible, fuel formulations other than typical retail fuels were also investigated. In order to gain insight into the mechanisms taking place, combustion analysis was performed on measured cylinder pressure traces

Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2002. / This project investigates the performance of solar chimney power plant turbines. A solar chimney power plant consists of a tall chimney surrounded by a transparent deck or solar collector. The sun heats the air in the collector through the greenhouse effect. A turbine extracts energy from the hot air rising up the chimney. An investigation of the requirements and operation of such turbines is needed. Correct matching of the turbine to the plant requires the determination of the turbine operational range and other requirements. An air-standard cycle analysis is extended to include component and system losses. Simple steady-state and transient collector models are added to take into account the coupling effect of the collector air temperature rise and mass flow rate on the turbine operation. The predicted turbine operational range for a representative day shows that the expected pressure drop in a full-scale solar chimney turbine is significantly higher than has previously been predicted. A turbine design method is developed and used to design a turbine for the representative day. The methods can easily be extended to include more operating points for a full year of operation. A turbine layout is suggested that uses the chimney support pillars as inlet guide vanes (IGVs). These introduce pre-whirl to the turbine and reduce the amount of exit whirl thus decreasing the kinetic energy at the turbine exit. Non-radial inlet guide vanes add to the torsional stiffness of the chimney base. A matrix throughflow method is used to design the radial to axial duct between the IGVs and rotor. The turbine blade profiles are simulated using a surface-vortex method. This is coupled to an optimisation scheme that minimises both the chord length and maximum flow velocity of the profile to reduce blade drag. An experimental program investigates the performance of the turbine. Volume flow, pressure drop, torque and speed are measured on a scale model turbine to map the turbine performance over a wide range. The velocity and pressure profiles are measured at two design points to investigate the flow through the turbine in more detail. These are compared to the design predictions and used to improve the design method. The experiments show that the design of a solar chimney turbine with a total-to-total efficiency of 85 % - 90 % and total-to-static efficiency of 75 % - 80 % is possible. Analysis of the experimental results shows that the turbine efficiency can be improved.