Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The purpose of this project is to investigate the method and accuracy of simulating axial ow fans with three-dimensional axisymmetric CFD models. Two models are evaluated and compared with experimental fan data. Veri cation data is obtained from a prototype fan tested in a facility conforming to the BS 848 standards. The ow eld over the blade surfaces is investigated further with a visualization experiment comprising of a stroboscope and wool tufts. Good correlation is found at medium to high ow rates and recommendations are made for simulation at lower ow rates as well as test guidelines at the fan test facility. The results and knowledge gained will be used to amend currently used actuator disc theory for axial ow fan simulation. / AFRIKAANSE OPSOMMING: Die doel van hierdie projek is om die metode en akkuraatheid om aksiaalvloeiwaaiers met drie-dimensionele BVM modelle te simuleer, te ondersoek. Twee modelle word geëvalueer en met eksperimentele waaiertoetse vergelyk. Veri- kasie data is verkry vanaf 'n prototipe waaier wat in 'n fasiliteit getoets is en wat aan die BS 848 standaarde voldoen. Die vloeiveld oor die lemoppervlaktes word ondersoek met 'n visualisering eksperiment wat uit 'n stroboskoop en wolletjies bestaan. Goeie korrelasie word gevind vir medium tot hoë massavloeie en aanbevelings word gemaak vir die simulasie by laer massavloeie met riglyne vir toetswerk in die toets-fasiliteit. Die resultate en kennis opgedoen sal gebruik word in die verbetering van huidige aksieskyfteorie vir numeriese aksiaalvloeiwaaier simulasies.

Thesis (MScEng)--Stellenbosch University, 2010. / ENGLISH ABSTRACT: This project originated when a team of scientists at the Gobabeb training and research and centre observed seed accumulation sites on the slope of sand dunes in the Namib Desert. Seeds that accumulate on the slip face of a sand dune provide food for small desert creatures that in turn attract larger animals, resulting in a small ecosystem on the side of the dune. Since wind is the primary transport of seeds throughout the Namib Desert it is of interest to investigate wind patterns over the dune. In this project it is therefore desired to look at seed dynamics and deposition as a result of near surface wind patterns around a three-dimensional dune geometry using computational fluid dynamics. The project is a joint venture between the University of Stellenbosch and the University of Namibia. This document presents the South African MScEng thesis part. The literature review shows the dominant winds in the Namib Desert to be from the south to westerly direction. Previous studies on air flow over dunes focussed on sand movement and were often limited to simplified two-dimensional geometries and steady state simulations. From these studies the basic flow features associated with dunes can be identified. Lastly, factors that influence particle dynamics around dune geometries are looked at. These particle studies mostly involve the movement of sand rather than seeds but still provide valuable insight. The project methodology is explained and includes the equipment used, the considerations taken into account, the simplifications made as well as the procedure followed when conducting field work and simulations. A section of an actual Namibian linear dune is mapped in order to obtain a geometry for the simulations. Flow measurements are carried out with a wind mast to obtain velocity profile inlet conditions for the simulations. Furthermore, seed sampling is done by the collaborating Namibian team of which the data is used to obtain an effective seed particle model. Lastly, simulations are carried out using primarily OpenFOAM-1.5. The simulations look at general near surface wind patterns, time dependant flow features and particle movement and seed deposition around and on the linear dune. The results show different wind profiles for different wind direction. It is also possible to see how the profile changes as the flow accelerates up the dune slope. Two-dimensional results provide the opportunity to compare results with previous studies as well as to provide the basis for looking at aspects such as differencing schemes, turbulence models and parallel computing before three-dimensional simulations are carried out. The importance of higher order differencing schemes are confirmed in the two-dimensional results. The turbulence models, however, produce very similar results. The results from the two- and three-dimensional results show typical flow features associated with dunes. Transient flow features and separation vortex structures can be identified from time dependant simulations. Furthermore, particle simulations reveal how particles tend to be trapped in the recirculation regions. The conclusions explain how the project objectives were achieved and provide recommendations for future studies related to this project. / AFRIKAANSE OPSOMMING: Die projek het ontstaan toe naforsers areas van saad akumulasie op die hellings van duine in Namibë opgelet het. Hierdie akumulasie van plant materiaal verskaf die voedsel vir klein diere op die duin wat ‘n klein ekosisteem tot gevolg het. Aaangesien die primêre vervoermiddel vir sade in die woestyn wind is beoog die projek om deur die wind patrone oor die duin beter te verstaan die saad verspreiding te beskryf. Die doel is dus om saad verspreiding en akumulasie te beskryf deur die wind patrone te bekyk wat die verspreiding tot gevolg het deur gebruik te maak van numeriese vloei dinamika. Die projek is ‘n saamgestelde projek tussen die Universiteit van Stellenbosch en die Universiteit van Namibië. Hierdie dokument behels die Suid Afrikaanse MScIng gedeelte van die projek. Deur die hersiening van literatuur word daar gesien dat die domineerende wind rigtings as suid tot wes beskryf kan word. Vorige studies wat verband hou met wind vloei oor duine wys dat die meeste op twee-dimensionele eenvoudige geometrië gefokus het met tyd onafhankike simulasies. Dit is egter moontlik om die resultate te gebruik om karakteristieke vloei patrone te identifiseer wat met duin wind patrone geassosieer kan word. Laastens word daar gekyk na die faktore wat partikel beweeging beïnvloed, maar hierdie studies sluit hoofsaaklik sand partikels in eerder as sade. Die motodologie beskryf die toerusting, oorwegings en prosedures wat gevolg is tydens veld werk asook simulasies. Tydens die veld werk is ‘n gedeelte van ‘n Namib lineêre duin gemeet en so gebruik om ‘n geometrie te maak wat vir simulasie doeleindes gebruik kan word. Daar is ook wind meetings gedoen met ‘n wind mas om wind profiele vir inlaat kondisies vir die simulasies te kry. Verder het saad bestudeering die nodige data verskaf om ‘n voledige saad partikel model op te stel wat in die simulasies gebruik kan word. Laastens kyk die simulasies veral na algemene vloei patrone, tyd afhanklike vloei effekte en ook partikel beweging in die vloei veld. Die resultate wys hoe wind profiele verskil wat van verskillende rigtings af waai. Dit is ook moontlik on te wys hoe die wind profiele verander soos die wind versnel teen die duin op. Tweedimensionele simulasies verskaf die geleentheid om te kyk na die effek van verkillende numeriese modelle, turbulensie modelle en ook multi-prosesseerder verwerking. Tydens die twee-dimensionele simulasies is die belangrikheid van hoër orde numeriese metodes besef. Die verkillende turbulensie modelle het egter klein verkille gewys. Alby die twee- en driedimensionele resultate wys karakteristieke vloei patrone wat met duine geasosieer kan word. Verder het tyd afhanklike simulasies gewys hoe wind patrone verander met tyd. Die partikel simulasies wys ook die beweging van partikels deur die wind en hoe dit neig om te akumuleer in die hersirkulasie gebied agter die duin. Die gevolgtrekkings wys dat al die doelstellings bereik is en maak voorstelle vir toekomstige studies wat met hierdie studie verband hou.

Thesis (MScEng)--Stellenbosch University, 2005. / ENGLISH ABSTRACT: The convection heat transfer coefficient between an infinite, horizontal surface and the natural environment is determined experimentally. It is shown that, during daytime, heat is transferred due to natural and forced convection, while during nighttime heat is transferred due to conduction and forced convection. Equations that correlate the daytime and nighttime convective heat transfer coefficients respectively, are presented. The results are compared with values obtained by other investigators. The equations for the convection heat transfer coefficient are then used to predict the surface temperature and the temperature at depth of asphalt pavement samples using a simulation model. It is found that there is good agreement between the measured and the predicted asphalt pavement sample temperatures. / AFRIKAANSE OPSOMMING: Die konveksie warmteoordrags-koëffisiënt tuseen 'n oneindige, horisontale oppervlak en die natuurlike omgewing is eksperimenteel bepaal. Daar word getoon dat warmte, tydens die dag, oorgedra word deur natuurlike en geforseerde konveksie, terwyl warmte tydens die nag oorgedra word deur geleiding en geforseerde konveksie. Die resultate word vergelyk met die resultate van ander navorsers. Vergelykings wat die konveksie warmteoordrags-koëffisiënt gedurende die dag en nag onderskeidelik korreleer word voorgestel. Die vergelykings vir die konveksie warmteoordrags-koëffisiënt word dan gebruik in 'n simulasiemodel om die oppervlaktemperatuur en die temperatuur onder die oppervlakte van asfalt-padoppervlakmonsters te voorspel.

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: The main goal of the thesis is to validate the ability of discrete element methods (DEM) to predict forced granular flow. Granular flow occurs in a broad spectrum of industrial applications. The thesis focuses on earthmoving processes typical of the mining and agricultural industries. Existing soil mechanics soil-tool models are also investigated and general flow behaviour in and around blades and buckets are established. Soil mechanics theories are used to predict the draft forces on a flat blade moving through granular material. Com and wheat grains are used as material. The rupture (slip) lines in front of the blade are predicted by soil mechanics and compared to experimental results. A two-dimensional test bench is used to visualise the flow of the granular material. Forces and moments that act on the tools are measured. DEM can be used to model industrial granular flow with large displacements. Two types of earthmoving equipment are simulated. The first is a flat blade and the second is a bucket. The forces on these tools are determined using DEM and compared to experimental results. The ability of DEM to predict material compressibility, the flow of material in and around the tools, the rupture lines and the bucket fill rate are investigated. A particle relative displacement method is used to determine the rupture lines. / AFRIKAANSE OPSOMMING: Die hoofdoel van die tesis is om die vermoë van diskrete-element-metodes (DEM) om geforseerde partikelvloei te voorspel, te ondersoek. Partikelvloei word aangetref in 'n breë spektrum van industriële toepassings. Die tesis fokus op grondverskuiwing soos aangetref in myn- en landbouprosesse. Bestaande grondmeganika-modelle word ook ondersoek, asook die algemene gedrag van partikelvloei in en rondom lemme en bakke. Die grondmeganika-modelle word hoofsaaklik gebruik om die kragte op lemme te voorspel. Glip (skuif)-vlakke word ondersoek en vergelyk met eksperimentele resultate. 'n Twee-dimensionele toetsbank word gebruik om die vloei waar te neem. Die kragte en momente op die toerusting word ook gemeet. Mielie- en koringpitte word as materiaal gebruik. DEM kan gebruik word om industriële partikelvloei met groot verplasings te modelleer. Twee tipes toerusting word gesimuleer. Die eerste is 'n plat lem en die tweede 'n bak. Die kragte en momente op dié toerusting word bepaal m.b.V. DEM en dan vergelyk met die eksperimentele resultate. Die vermoë van DEM om materiaalsamedrukking, vloeipatrone, glipvlakke en bakvul-tempo's te voorspel word ondersoek. 'n Partikelrelatiewe- verplasings-metode word gebruik om die glipvlakke te voorspel.

Thesis (MScEng)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: This thesis describes a module that links AutoCAD and CeDeas (cost estimation software which was developed by Department of Mechanical Engineering, University of Stellenbosch). CeDeas is intended for estimating the direct manufacturing cost of simple welded assemblies in a batch production environment. It is aimed at use during late concept design or early detail design. The link module was developed in Borland C++ Builder. By using COM (Component Object Model) technology, the link module employs the methods and the properties of the AutoCAD automation interface to extract manufacturing information that is required by CeDeas. The link module prompts the user to pick objects in an AutoCAD drawing and then determines the values required by CeDeas to estimate the manufacturing cost. The user can choose between a "direct select method" (which uses the properties of geometric entities already in the drawing) and a "user define method" (whereby the user defmes temporary entities or combines aspects of existing entities in the AutoCAD drawing). With these results and some non-geometric inputs, the user can get a cost estimate of components and assemblies. After design changes, the link module can provide CeDeas with updated values with minimal user interaction in situations where the "direct select method" was used. The designer can therefore easily use the cost estimates to compare design alternatives to optimise the design. Validation studies demonstrated the numerical accuracy of the use of the link module. The link module can be regarded as an extension of CeDeas. At present it only supports AutoCAD R14, but can be extended to support AutoCAD 2000 and Mechanical Desktop. / AFRIKAANSE OPSOMMING: 'n Module wat dien as skakel tussen AutoCAD and CeDeas (kosteberamingsagteware ontwikkel deur die Departement van Meganiese Ingenieurswese, Universiteit van Stellenbosch) word in hierdie tesis beskryf. Die doel van CeDeas is om die direkte vervaardiginskoste van eenvoudige, gesweisde samestellings, in 'n lot-produksie omgewing, te beraam. Dit is gemik op gebruik tydens laat konsepontwerp en vroeë detailontwerp. Die skakelmodule is ontwikkel in Borland C++ Builder. Deur van COM (Component Object Model) tegnologie gebruik te maak, kry die skakelmodule toegang tot die funksies en eienskappe van AutoCAD se outomatisasie koppelvlak en kan sodoende die vervaardigingsinligting onttrek wat deur CeDeas benodig word. Die skakelmodule vra die gebruiker om voorwerpe in 'n AutoCAD tekening te kies en bepaal dan die waardes wat deur CeDeas benodig word om die vervaardigingskoste te skat. Die gebruiker kan kies tussen 'n "direkte keuse metode" (wat die eienskappe van geometriese entiteite wat reeds in die tekening is, gebruik) en 'n "gebruiker definieer metode" (waarin die gebruiker tydelike entiteite defmieer of kombinasies van aspekte van bestaande entiteite in die AutoCAD tekening gebruik). 'n Koste beraming van komponente of samestellings kan verkry word met hierdie inligting tesame met ander nie-geometriese inligting. Na ontwerpsveranderings, kan die skakelmodule hersiene waardes vir CeDeas voorsien met minimale gebruikers-interaksie in gevalle waar die "direkte keuse metode" gebruik is. Die gebruiker kan daarom maklik die kosteskattings gebruik om ontwerpsaltematiewe te vergelyk om die ontwerp te optimeer. Evalueringstudies het die numeriese akkuraatheid van die skakelmodule bevesting. Hierdie module kan as 'n uitbreiding van CeDeas beskou word. Tans werk die module slegs met AutoCAD R14, maar dit kan uitgebrei word om met AutoCAD 2000 en Mechanical Desktop te werk.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / Please refer to full text to view abstract.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / Please refer to full text to view abstract.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / Please refer to full text to view abstract. / Imported from http://etd.sun.ac.za. / np2011

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: A 1.5 x 1.5 m2 counter-flow fill performance test facility is described in detail. Instrumentation was selected and installed in the cooling tower fill test facility and calibrated to ensure measurement accuracy. A facility control program was written to simplify the operation of the test facility via a user interface. The program calculates automatically the Merkel number and loss coefficients as measures of fill thermal and flow performance respectively. A spray frame was designed and manufactured to ensure uniform water distribution to the fill. The water distribution through different fills with varying fill heights and different water flow rates was measured. The water attached to the walls of the test facility was examined. Film, trickle and splash fills are tested in the upgraded test facility. The film and trickle fill performance determined during testing is deemed acceptable as these fills have minimal migration effects. Fills with poor distribution effects and large migration of water towards the walls of the test facility, like the splash fill tested, cannot to be tested accurately in a 1.5 x 1.5 m2 test section as the results do not represent the performance of the fill in a relatively large cooling tower. Other aspects examined were: • air flow uniformity • air fill bypass effects • location of water inlet and outlet temperature measurement points • location of pressure measurement probes. It was determined that, in the current test facility: • air uniformity is suitable for performance testing • air bypass effects can be ignored for open fills and can be minimised for dense fills by packing sponge between the fill and walls • water inlet and outlet temperatures should be measured in the pipe-work, resulting in a measurement method that is not influenced by the relative weightings of each thermocouple • pressure difference over the fill height measured by the pressure measurement tap is independent of its location on the fill outlet plane provided the pressure measurement points are perpendicular to the air stream and are not against the walls. / AFRIKAANSE OPSOMMING: 'n 1.5 x 1.5 m² Teenvloei pakking werkverrigting toetsfasiliteit word in detail beskryf. Instrumentasie is gekies en geïnstalleer in die koeltoring pakking toetsfasiliteit en gekalibreer om akkuraatheid te verseker. 'n Fasiliteit beheer program is geskryf om die gebruik van die toetsfasiliteit te vereenvoudig. Die program het ‘n vriendelike gebruikers intervalk. Die program bereken outomaties die Merkel-getal en verlies koëffisiënte as mate van pakking termiese- en vloeiwerksverrigting. 'n Sproeiraam is ontwerp en vervaardig om uniforme water verspreiding aan die pakking te verseker. Die water verspreiding deur verskillende pakkings met verskillende pakking hoogtes en water vloei snelhede is gemeet. Die water aangeheg aan die mure van die toetsfasiliteit is ook ondersoek. Film, druppel en spat pakkings word in die opgegradeerde toetsfasiliteit getoets. Die film- en druppelpakking werksverrigting bepaal tydens die toetse is aanvaarbaar, aangesien hierdie pakkings minimale migrasie effekte het. Pakking met swak verspreiding effekte en 'n groot migrasie van water na die wande van die toetsfasiliteit, soos gevind met die spatpakking toetse, kan nie met akkuraatheid in 'n 1.5 x 1.5 m² toets seksie getoets word nie omdat die resultate nie die werkverrigting van die pakking verteenwoordig in 'n relatief groot koeltoring. Ander aspekte wat ondersoek was: • lugvloei uniformiteit • lug omleiding effeckte • die posisie van water in- en uitlaat temperatuur meetpunte • posisie van die drukmeetapparaat. Dit is vasgestel dat, in die huidige toetsfasiliteit • lugvloei eenvormigheid geskik is vir prestasietoetsing • lug omleiding effekte kan geïgnoreer word vir oop pakkings en kan verklein word vir digte pakkings deur spons tussen die pakking en mure te pak • water inlaat- en uitlaattemperature behoort gemeet te word in die pypwerk en lei tot 'n metings metode wat nie beïnvloed word deur die relatiewe gewigte van elke thermokoppel nie • die druk verskil gemeet deur die drupmeetpunte oor die pakkinghoogte is onafhanklik van hul posisie op die pakkinguitlaatvlak op voorwaarde dat die drukmeetpunte loodreg is teen die lugstroom en nie teen die mure nie.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The purpose of this study is to investigate the machinability of commercially pure (CP) titanium, manufactured using the press-and-sinter PM process. To this end, CP titanium powder (-200 mesh) was compacted and sintered in vacuum (10-4 torr) for two hours at 1200°C. Small cylindrical samples were compacted at pressures varying from 350 to 600 MPa in order to determine the compressibility of the powder. Following these tests, four larger stepped-cylinder samples were compacted at pressures close to 400 MPa and sintered under similar conditions. These samples had sintered densities varying between 3.82 and 4.41 g/cm3. They were used to evaluate the machinability of the sintered titanium using face turning machining tests. The samples were machined dry, using uncoated carbide (WC-Co) cutting tool. Cutting speeds between 60-150 m/min were evaluated while keeping the feed rate and depth of cut constant at 0.15 mm/rev and 0.5 mm, respectively. The final machined surface finish and the tool wear experienced during the face turning machining tests were monitored in order to evaluate PM titanium’s machining performance. This study showed that it is possible to use the press-and-sinter PM process with CP titanium powder, with a particle size of less than 75 μm (-200 mesh), to manufacture sintered titanium. However, particle shape influences the compressibility of the powder and pressing parts of larger volume, such as the machining test sample shape, is challenging when using such small particle size powder. Processing conditions, such as compaction pressure, sintering temperature and sintering time, influence the sintered density. Results from the machinability tests show that tool wear increases with a decrease in the porosity of the sintered titanium. A more porous sintered material has both lower strength and thermal conductivity. As these factors have opposing effects on the machinability of materials, it is concluded that the strength of the sintered titanium has a stronger influence on its machinability than the thermal conductivity. The cutting tool wear was uniform but showed indications of crater wear. The machined surface of the denser parts had minimal defects compared to less dense parts. Chip shape is long for the dense parts, and spiral for the less dense parts. The chips formed were all segmented, which is typical for titanium. The machinability of the sintered CP titanium was compared to that of wrought titanium alloys. As expected, it was found that the machinability of the sintered titanium was poor in comparison. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie is om die masjineerbaarheid van kommersieel suiwer (KS) titaan, wat deur die pers-en-sinter poeiermetallurgie (PM) metode vervaardig word, te ondersoek. Om hierdie doel te bereik, is KS titaan poeier (-200 ogiesdraad) gekompakteer en gesinter in ‘n vakuum (10-4 torr) teen 1200°C vir 2 ure. Klein silindriese monsters is tussen drukke van 350en 600 MPa gekompakteer om die samedrukbaarheid van die poeier te bepaal. Na aanleiding van hierdie toetse, is vier groter trapvormige-silinder monsters by drukke naby aan 400MPa gekompakteer en onder soortgelyke omstandighede gesinter. Hierdie monsters het gesinterde digthede tussen 3.82 en 4.41 g/cm3 gehad. Hulle is gebruik om die masjineerbaarheid van die gesinterde titaan te ondersoek deur middel van vlak-draai masjineringstoetse. Die monsters is sonder smeermiddel gemasjineer met onbedekte karbied (WC-Co) snygereedskap. Snysnelhede tussen 60 – 150 m/min is geëvalueer terwyl die voertempo en diepte van die snit konstant by 0.15 mm/rev en 0.5 mm, onderskeidelik, gehou is. Die finale gemasjineerde oppervlak afwerking en gereedskapsslytasie tydens die vlak-draai masjinering toets is van die faktore wat gemonitor is sodat PM titaan se optrede tydens masjinering geëvalueer kan word. Hierdie studie wys dat diepers-en-sinter metode wel met KS titaan poeier, met ‘n partikel grootte van minder as 75 μm (-200 maas), gebruik kan word om gesinterde titaan te vervaardig. Die partikelgrootte beïnvloed wel die samedrukbaarheid van die poeier. Die samedrukking van parte met groter volume, soos bv die masjinerings toetsmonster, is uitdagend wanneer klein partikelgrootte poeier gebruik word. Proses omstandighede, soos kompaksie druk, sinteringstemperatuur en sinteringstyd, beïnvloed die gesinterde digtheid. Resultate van die masjineerbaarheidstoetse wys dat beitelslytasie toeneem met ‘n afname in porositeit van die gesinterede titaan. ‘n Meer poreus gesinterde materiaal het beide laer sterkte en termiese geleidingsvermoë. Aangesien hierdie faktore teenoorgestelde uitwerkings op masjineerbaarheid het, word dit dan afgelei dat die sterkte van gesinterde titaan ‘n groter invloed het op sy masjineerbaarheid as die termiese geleidingsvermoë. Die beitel se slytasie is hoofsaahlik, maar het tekens van kraterslytasie getoon. Die gemasjineerde oppervlak van die meer digte onderdele of toetsmonters het min gebreke gehad in vergelyking met die minder digte dele. Die vorm van die spaanders is lank vir digte parte, en spiraalvormig vir minder digte toetsmonsters. Die spaanders wat gevorm het, was almal gesegmenteerd, wat tipies is vir titaan. Die masjineerbaarheid van die gesinterde KS titaan is met dié van gesmede titaanallooie vergelyk. Soos verwag is, is gevind dat die masjineerbaarheid van die gesinterde titaan in vergelyking swak is.