Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: As the demand for less expensive energy is increasing world-wide, energy conservation is becoming a more-and-more important economic consideration. In light of this, means to recover energy from waste fluid streams is also becoming more-and-more important. An efficient and cost effective means of conserving energy is to recover heat from a low temperature waste fluid stream and use this heat to preheat another process stream. Heat pipe heat exchangers (HPHEs) are devices capable of cost effectively salvaging wasted energy in this way. HPHEs are liquid-coupled indirect transfer type heat exchangers except that the HPHE employs heat pipes or thermosyphons as the major heat transfer mechanism from the high temperature to the low-temperature fluid. The primary advantage of using a HPHE is that it does not require an external pump to circulate the coupling fluid. The hot and cold streams can also be completely isolated preventing cross-contamination of the fluids. In addition, the HPHE has no moving parts. In this thesis, the development of a range of air-to-air HPHEs is investigated. Such an investigation involved the theoretical modelling of HPHEs such that a demonstration unit could be designed, installed in a practical industrial application and then evaluated by considering various financial aspects such as initial costs, running costs and energy savings. To develop the HPHE theoretical model, inside heat transfer coefficients for the evaporator and condenser sections of thermosyphons were investigated with R134a and Butane as two separate working fluids. The experiments on the thermosyphons were undertaken at vertical and at an inclination angle of 45° to the horizontal. Different diameters were considered and evaporator to condenser length ratios kept constant. The results showed that R134a provided for larger heat transfer rates than the Butane operated thermosyphons for similar temperature differences despite the fact that the latent heat of vaporization for Butane is higher than that of R134a. As an example, a R134a charged thermosyphon yielded heat transfer rates in the region of 1160 W whilst the same thermosyphon charged with Butane yielded heat transfer rates in the region of 730 W at 23 °C . Results also showed that higher heat transfer rates were possible when the thermosyphons operated at 45°. Typically, for a thermosyphon with a diameter of 31.9 mm and an evaporator to condenser length ratio of 0.24, an increase in the heat transfer rate of 24 % could be achieved. Theoretical inside heat transfer coefficients were also formulated which were found to correlate reasonably well with most proposed correlations. However, an understanding of the detailed two-phase flow and heat transfer behaviour of the working fluid inside thermosyphons is difficult to model. Correlations proposing this behaviour were formulated and include the use of R134a and Butane as the working fluids. The correlations were formulated from thermosyphons of diameters of 14.99 mm, 17.272 mm, 22.225 mm and 31.9 mm. The evaporator to condenser length ratio for the 31.9 mm diameter thermosyphon was 0.24 whilst the other thermosyphons had ratios of 1. The heat fluxes ranged from 1800-43500 W/m2. The following theoretical inside heat transfer coefficients were proposed for vertical and inclined operations (READ CORRECT FORMULA IN FULL TEXT ABSTRACT) φ = 90° ei h = 3.4516x105Ja−0.855Ku1.344 φ = 45° ei h = 1.4796x105Ja−0.993Ku1.3 φ = 90° l l l ci l l v h x k g 1/ 3 2.05 2 4.61561 109Re 0.364 ν ρ ρ ρ − ⎡ ⎡ ⎛ ⎞⎤ ⎤ = ⎢ ⎢ ⎜ ⎟⎥ ⎥ ⎢ ⎢ ⎜ − ⎟⎥ ⎥ ⎣ ⎣ ⎝ ⎠⎦ ⎦ φ = 45° l l l ci l l v h x k g 1/ 3 1.916 2 3.7233 10 5Re 0.136 ν ρ ρ ρ − ⎡ ⎡ ⎛ ⎞⎤ ⎤ = ⎢ ⎢ ⎜ ⎟⎥ ⎥ ⎢ ⎢ ⎜ − ⎟⎥ ⎥ ⎣ ⎣ ⎝ ⎠⎦ ⎦ The theoretically modelled demonstration HPHE was installed into an existing air drier system. Heat recoveries of approximately 8.8 kW could be recovered for the hot waste stream with a hot air mass flow rate of 0.55 kg/s at an inlet temperature of 51.64 °C and outlet temperature of 35.9 °C in an environment of 20 °C. Based on this recovery, energy savings of 32.18 % could be achieved and a payback period for the HPHE was calculated in the region of 3.3 years. It is recommended that not withstanding the accuracies of roughly 25 % achieved by the theoretically predicted correlations to that of the experimental work, performance parameters such as the liquid fill charge ratios, the evaporator to condenser length ratios and the orientation angles should be further investigated. / AFRIKAANSE OPSOMMING: As gevolg van die groeiende aanvraag na goedkoper energie, word die behoud van energie ‘n al hoe belangriker ekonomiese oorweging. Dus word die maniere om energie te herwin van afval-vloeierstrome al hoe meer intensief ondersoek. Een effektiewe manier om energie te herwin, is om die lae-temperatuur-afval-vloeierstroom (wat sou verlore gaan) se hitte te gebruik om ‘n ander vloeierstroom mee te verhit. Hier dien dit dan as voorverhitting van die ander, kouer, vloeierstroom. Hittepyp hitteruilers (HPHR’s) is laekoste toestelle wat gebruik kan word vir hierdie doel. ‘n HPHR is ‘n vloeistof-gekoppelde indirekte-oordrag hitteruiler, behalwe vir die feit dat dié hitteruiler gebruik maak van hittepype (of hittebuise) wat die grootste deel van sy hitteoordragsmeganisme uitmaak. Die primêre voordele van ‘n HPHR is dat dit geen bewegende dele het nie, die koue- en warmstrome totaal geïsoleer bly van mekaar en geen eksterne pomp benodig word om die werkvloeier mee te sirkuleer nie. In hierdie tesis word ‘n ondersoek gedoen oor die ontwikkeling van ‘n bestek van lug-totlug HPHR’s. Hierdie ondersoek het die teoretiese modellering van so ‘n HPHR geverg, sodat ‘n demonstrasie eenheid ontwerp kon word. Hierdie demonstrasie eenheid is geïnstalleer in ‘n praktiese industriële toepassing waar dit geïvalueer is deur na aspekte soos finansiële voordele en energie-besparings te kyk. Om die teoretiese HPHR model te kon ontwikkel, moes daar gekyk word na die binnehitteoordragskoëffisiënte van die verdamper- en kondensordeursneë, asook R134a en Butaan as onderskeie werksvloeiers. Die eksperimente met die hittebuise is gedoen in die vertikale en 45° (gemeet vanaf die horisontaal) posisies. Verskillende diameters is ook ondersoek, maar met die verdamper- en kondensor-lengteverhouding wat konstant gehou is. Die resultate wys dat R134a as werksvloeier in die hittebuise voorsiening maak vir groter hitteoordragstempo’s in vergelyking met Butaan as werksvloeier by min of meer dieselfde temperatuur verskil – dít ten spyte van die feit dat Butaan ‘n hoër latente-hittetydens- verdampings eienskap het. As voorbeeld gee ‘n R134a-gelaaide hittebuis ‘n hitteoordragstempo van omtrent 1160 W terwyl dieselfde hittebuis wat met Butaan gelaai is, slegs ongeveer 730 W lewer by 23 °C. Die resultate wys ook duidelik dat hoër hitteoordragstempo’s verkry word indien die hittebuis bedryf word teen ‘n hoek van 45°. ‘n Tipiese toename in hitteoordragstempo is ongeveer 24 % vir ‘n hittebuis met ‘n diameter van 31.9 mm en ‘n verdamper- tot kondensor-lengteverhouding van 0.24. Teoretiese binne-hitteoordragskoëffisiënte is ook geformuleer. Dié waardes stem redelik goed ooreen met die meeste voorgestelde korrelasies. Nieteenstaande die feit dat gedetailleerde twee-fase-vloei en die hitteoordragsgedrag van die werksvloeier binne hittebuise nog nie goed deur die wetenskaplike wêreld verstaan word nie. Korrelasies wat hierdie gedrag voorstel is geformuleer en sluit weereens die gebruik van R134a en Butaan as werksvloeiers in. Die korrelasies is geformuleer vanaf hittebuise met diameters van onderskeidelik 14.99 mm, 17.272 mm, 22.225 mm en 31.9 mm. Die verdamper- tot kondensor-lengteverhoudings vir die 31.9 mm deursnit hittebuis was 0.24 terwyl die ander hittebuise ‘n verhouding van 1 gehad het. Die hitte-vloede het gewissel van 1800-45300 W/m2. Die volgende teoretiese geformuleerde binne-hitteoordragskoëffisiënte word voorgestel vir beide vertikale sowel as nie-vertikale toepassing (LEES KORREKTE FORMULE IN VOLTEKS OPSOMMING) φ = 90° ei h = 3.4516x105Ja−0.855Ku1.344 φ = 45° ei h = 1.4796x105Ja−0.993Ku1.3 φ = 90° l l l ci l l v h x k g 1/ 3 2.05 2 4.61561 109Re 0.364 ν ρ ρ ρ − ⎡ ⎡ ⎛ ⎞⎤ ⎤ = ⎢ ⎢ ⎜ ⎟⎥ ⎥ ⎢ ⎢ ⎜ − ⎟⎥ ⎥ ⎣ ⎣ ⎝ ⎠⎦ ⎦ φ = 45° l l l ci l l v h x k g 1/ 3 1.916 2 3.7233 10 5Re 0.136 ν ρ ρ ρ − ⎡ ⎡ ⎛ ⎞⎤ ⎤ = ⎢ ⎢ ⎜ ⎟⎥ ⎥ ⎢ ⎢ ⎜ − ⎟⎥ ⎥ ⎣ ⎣ ⎝ ⎠⎦ ⎦ Die wiskundig-gemodelleerde demostrasie HPHR is geïnstalleer binne ‘n bestaande lugdroër-sisteem. Drywing van om en by 8.8 kW kon herwin word vanaf die warm-afvalvloeierstroom met ‘n massa vloei van 0.55 kg/s teen ‘n inlaattemperatuur van 51.64 °C en ‘n uitlaattemperatuur van 35.9 °C binne ‘n omgewing van 20 °C. Na aanleiding van hierdie herwinning, kan energiebesparings van tot 32.18 % verkry word. Die HPHR se installasiekoste kan binne ‘n berekende tydperk van ongeveer 3.3 jaar gedelg word deur hierdie besparing. Verdamper- tot kondensator-lengteverhouding, vloeistofvulverhouding en die oriëntasiehoek vereis verdere ondersoek, aangesien daar slegs ‘n akkuraatheid van 25 % verkry is tussen teoretiese voorspellings en praktiese metings.

Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This study investigates energy generation by large-scale solar tower power plants. The performance characteristics of a so-called reference plant with a 4000 m diameter glass collector roof and a 1500 m high, 160 m diameter tower are determined for a site located in South Africa. The relevant draught and conservation equations are derived, discretized and implemented in a numerical model which solves the equations using speci ed meteorological input data and determines the power delivered by the plant. The power output of a solar tower power plant over a twenty-four hour period is presented. Corresponding temperature distributions in the ground under the collector are shown. Variations in seasonal generation are evaluated and the total annual electrical output is determined. The dependency of the power output on collector diameter and tower height is illustrated, while showing that greater power production can be facilitated by optimizing the roof shape and height. The minor in uence of the tower shadow falling across the collector is evaluated, while the e ect of prevailing winds on the power generated is found to be signi cant. / AFRIKAANSE OPSOMMING: Hierdie studie ondersoek elektrisiteitsopwekking deur grootskaalse sontoringkragstasies. Die uitsetkarakteristieke van 'n sogenaamde verwysings-kragstasie met 'n 4000 m deursnee glas kollektor en 'n 1500 m hoë, 160 m deursnee toring word ondersoek vir 'n spesi eke ligging in Suid-Afrika. Die toepaslike trek- en behoudsvergelykings word afgelei, gediskretiseer en geimplementeer in 'n numeriese rekenaarmodel. Die rekenaarmodel los die betrokke vergelykings op deur gebruik te maak van gespesi seerde meteorologiese invoerdata en bepaal dan die uitset gelewer deur die kragstasie. Die uitset van 'n sontoring-kragstasie oor 'n periode van vier-en-twintig uur word getoon. Ooreenstemmende temperatuurverdelings in die grond onder die kollektor word geïllustreer. Die variasie in seisoenale elektrisiteitsopwekking word ondersoek en die totale jaarlikse elektriese uitset bepaal. Die invloed wat die kragstasie dimensies (kollektor deursnee en toring hoogte) op die uitset het, word bestudeer en resultate getoon. Daar is ook bevind dat verhoogde uitset meegebring kan word deur die vorm en hoogte van die kollektordak te optimeer. Die geringe e ek van die toringskadu op die kollektor word bespreek, terwyl bevind is dat heersende winde 'n beduidende e ek op die kragstasie uitset het.

Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: A rough road vibration stimulus was reconstructed on a shaker platform to assess the dynamic comfort of seven seats by six human subjects. The virtual seat method was combined with a paired comparison procedure to assess subjective dynamic seat comfort. The psychometric method of constants, 1-up-1-down Levitt procedure and a 2-up-1-down Levitt procedure were compared experimentally to find the most accurate and efficient paired comparison scheme. A two-track interleaved, 2-up-1-down Levitt procedure was used for the subjective dynamic seat comfort assessment. SEAT value is an objective metric and has been widely used to determine seat vibration isolation efficiency. There was an excellent correlation (R2 = 0.97) between the subjective ratings and estimated SEAT values on the seat top when the values are averaged over the six subjects. This study suggests that the SEAT values, estimated from averaged seat top transmissibility of six carefully selected subjects, could be used to select the best seat for a specific road vibration input. / AFRIKAANSE OPSOMMING: Ses persone het deelgeneem aan ‘n eksperiment, om die dinamiese ritgemak van sewe stoele te karakteriseer. ‘n Rowwe padvibrasie is vir die doel op ‘n skudplatform geherkonstrueer. Subjektiewe ritgemak is bepaal deur die virtuelestoel metode met ‘n gepaarde, vergelykingstoets te kombineer. Die psigometriese metode van konstantes, die 1-op-1-af Levitt procedure en die 2-op- 1-af Levitt procedure is vergelyk om die mees effektiewe en akkurate vergelykingstoets te vind. ‘n Tweebaan, vervlegde , 2-op-1-af Levitt prosedure het die beste resultate gelewer en is gekies vir die subjektiewe evaluasie van dinamiese ritgemak. SEAT-waarde is ‘n objektiewe maatstaf, wat gebruik word om te bepaal hoe effektief ‘n stoel die insittende van voertuigvibrasie isoleer. Daar was ‘n uitstekende korrelasie (R2 = 0.97) tussen subjektiewe dinamiese ritgemakevaluesies en SEAT-waardes in die vertikale rigting op die stoelkussing as die gemiddelde oor die ses persone bereken word. Uit die resultate van hierdie studie blyk dit dat SEAT-waardes, wat bereken is vanaf die gemiddelde sitplektransmissie van die ses persone, wat verteenwoordigend van die teikenbevolking is, gebruik kan word om die beste stoel vir ‘n spesifieke vibrasieinset te kies.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Stellenbosch University participated in a project to re-design the compressor section of a diesel locomotive turbocharger. Tests conducted on the prototype compressor showed possible rotating stall in the diffuser section before the designed higher pressure ratio could be achieved. When approaching the higher pressure ratio, the compressor inlet trunk started to rhythmically collapse (due to suction), the engine shook and bellows of black smoke were exhausted by the engine. It was decided to simulate the prototype compressor's operation by using the 1-D theory of Aungier (2000) and to perform a 3-D CFD analysis of the compressor using FINE/Turbo of NUMECA International. A veri cation process was followed to show the accuracy of the 1-D and 3-D modelling methods using two well-known centrifugal compressor test cases found in the literature, namely the O-Rotor by Eckardt (1975, 1976, 1980) and the "Radiver" open CFD test case by Ziegler et al. (2003c). Results from the models were compared to available experimental results and the accuracy was found to be su cient to investigate the prototype compressor's impeller and diffuser. Both prediction methods con rmed separation in the vaned di user across the entire operating ow range of the prototype compressor at the design impeller speed. The 3-D method identi ed supersonic ow at the vaned diffuser inlet at the operating point and also predicted a smaller operating range than originally anticipated. Both the 1-D and 3-D methods also predicted impeller blade stall over the entire operating ow range at the design impeller speed. A recommendation was made to redesign the impeller and diffuser of the prototype compressor. / AFRIKAANSE OPSOMMING: Die Universiteit van Stellenbosch het deel geneem aan 'n projek om die kompressor gedeelte van 'n diesel lokomotief se turbo-aanjaer te herontwerp. Toetse uitgevoer op die prototipe kompressor het moontlike roterende wegbreking in die diffuser seksie uitgewys voordat die ontwerpte hoër drukverhouding bereik kon word. Toe die hoër drukverhouding genader is, het die kompressor inlaatpyp begin ritmies inmekaar vou (as gevolg van die suig aksie), die enjin het geskud en wolke swart rook is deur die enjin uitgeblaas. Die besluit is geneem om die prototipe kompressor se werking te simuleer met behulp van die 1-D teorie van Aungier (2000) en om ook 'n 3-D berekenings vloeimeganika (BVM) analise op die kompressor uit te voer met behulp van FINE/Turbo van NUMECA Internasionaal. 'n Veri kasieproses is gevolg om die akkuraatheid van die 1-D en 3-D modelle te illustreer met behulp van twee welbekende sentrifugaal kompressor toetsgevalle beskikbaar in die literatuur, naamlik die O-Rotor deur Eckardt (1975, 1976, 1980) en die "Radiver" oop BVM toetsgeval deur Ziegler et al. (2003c). Resultate van die modelle is vergelyk met beskikbare eksperimentele resultate en die bevinding is gemaak dat die akkuraatheid genoegsaam is om die prototipe kompressor se rotor en diffuser te ondersoek. Beide voorspellingsmetodes het wegbreking bevestig in die gelemde diffuser oor die hele werksbestek van die prototipe kompressor teen die ontwerp rotorspoed. Die 3-D metode het supersoniese vloei by die gelemde diffuser se inlaat by die bedryfspunt geïdenti seer en het ook 'n kleiner werksbestek voorspel as wat vroeër verwag is. Beide die 1-D en 3-D metodes het ook wegbreking in die rotor oor die hele werksbestek teen die ontwerp rotorspoed voorspel. 'n Voorstel is gemaak om die rotor en diffuser van die prototipe kompressor te herontwerp.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: As the push continues for increased use of renewables on the electricity grid, the problem of energy storage is becoming more urgent than ever. Flywheels with wound, composite rotors represent an efficient and environmentally friendly option for energy storage. They have already been applied successfully for voltage control on electrical rail networks and for bridging power in backup UPS systems, but lately they have also proven useful for grid-scale frequency regulation. For flywheels to be deployed on a wider scale, the high cost associated with the technology will have to be addressed. An important driver of cost is the density at which energy can be stored. Currently, flywheel designs do not consistently achieve high energy density, and this study investigates the reasons for this. A critical analysis is made of the design methodologies that have been proposed in the available literature, and some improvements are suggested. Most notably it is shown that significant improvements in energy density may be possible if the design optimization problem is formulated carefully. In addition, the problem of material selection is discussed, because material properties have a significant influence on energy density. Some guidance is given for flywheel designers on how to choose an optimal set of materials without invoking undue computational effort. It is hoped that these suggestions may be carried forward as a topic of further research. / AFRIKAANSE OPSOMMING: Namate die aanvraag vir hernubare energie op die elektrisiteit netwerk vergroot, word die probleem van energie berging van kardinale belang. Vliegwiele met silindriese rotors van samegestelde materiale bied ’n effektiewe en omgewingsvriendelike opsie vir energieberging. Hierdie tipe vliegwiele is reeds suksesvol aangewend vir spanningsbeheer op elektriese spoornetwerke en om oorbruggingskrag te voorsien aan rugsteun sisteme. Meer onlangs is hulle ook nuttig bewys vir die regulasie van frekwensie op die elektrisiteit netwerk. Grootskaalse aanwending van vliegwiele kan egter slegs oorweeg word indien die hoë koste van die tegnologie aangespreek word. Een van die onderliggende redes vir die hoë koste van vliegwiele is die relatiewe lae digtheid waarby energie geberg kan word, en hierdie studie ondersoek die redes hiervoor. Die ontwerpmetodiek wat in die beskikbare literatuur voorgestel is, word krities geanaliseer en ’n paar verbeteringe word aanbeveel. Mees noemenswaardig is die opmerklike verbeteringe in energie-digtheid wat soms moontlik is indien die optimerings-probleem deurdag geformuleer word. Omdat materiaaleienskappe ’n bepalende invloed op energie digtheid uitoefen word die probleem van materiaalseleksie ook verder bespreek. ’n Paar riglyne vir die seleksie van ’n optimale stel materiale sonder om oordrewe berekenings-inspanning te veroorsaak, word aan vliegwielontwerpers gegee. Hierdie voorstelle kan hopelik in die toekoms verder deurgetrap word as onderwerp vir verdere studies.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006. / Successful housing and breeding of exotic animals or plants often requires an environment that is quite different to the ambient conditions present. The current study approached the problem of sub-optimal water temperatures experienced by Central African Bream (Tilapia) housed within a South African greenhouse during winter months. A theoretical and experimental study of fundamental heat and mass transfer processes relevant to an aquacultural greenhouse was conducted. Experimental results were generally in agreement with those of previous researchers; while evaporation tests were found to concur particularly well with an analytical equation developed. The experimental results were used to develop a simple glass greenhouse model to evaluate the expected thermal behaviour during the coldest time of the year. Manipulation of the model revealed that water has the ability to absorb large quantities of solar radiation and regulate temperature fluctuations within such a system, and that the appropriate use of thermal insulation during both the night and day can maintain acceptable water temperatures for extended periods of time. With the conclusions drawn from the experimentation and modelling done, an optimised conceptual greenhouse design was presented, along with associated guidelines and principles for attaining the required water temperatures, and consequently providing the exotic fish specie with a healthy environment.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Turbomachines are exposed to several environmental factors which may cause failure of components. One of these factors, high cycle fatigue, is often caused by blade utter. This thesis forms part of a project of the European Seventh Framework Programme (FP7), called project Future. Project Future is doing theoretical and experimental investigation into the occurrence of utter in turbomachinery. The objective of this thesis was to evaluate the effectiveness of a gas injection system as a means of exciting vibrations on the rst stage rotor blades of a compressor. Unsteady simulations of the excitation velocity perturbations were performed in the Computational Fluid Dynamics (CFD) software, Numeca FINE/Turbo. Experimental testing on the in-house Rofanco compressor test bench, using one prototype of the 15 injector system, provided data that was used to implement boundary conditions and to verify certain aspects of the unsteady simulation results. The simulation results revealed the following: the injector bypass frequency was so dominant that the excitation frequency was hardly detectable in the majority of cases. Furthermore, several secondary frequencies were consistently present. The injector bypass frequency, as well as the secondary frequencies, occurred as a result of the convolution of Fast Fourier Transforms. While the injector bypass frequencies can theoretically be eliminated, it will not be possible to eliminate the secondary frequencies from the blade response. In conclusion, according to the CFD results, it will not be possible to excite a single excitation frequency by making use of a nite number of gas injector vibration exciters. / AFRIKAANSE OPSOMMING: Turbomasjiene word onderwerp aan verskeie omgewingsfaktore wat falings van komponente kan veroorsaak. Een van hierdie faktore, naamlik hoëfrekwensie vermoeidheid, word onder andere veroorsaak deur lem adder. Hierdie tesis is deel van 'n projek in die Sewende Europese Raamwerk Program (European Seventh Framework Programme - FP7), projek Future. Projek Future doen teoretiese en eksperimentele ondersoek na die voorkoms van lemfl adder in turbomasjienerie. Die doelwit van hierdie tesis was om die effektiwiteit van 'n gasinspuiter vibrasie-opwekkingstelsel te evalueer, deur gebruik te maak van onbestendige simulasie in die berekenings vloei-meganika sagtewarepakket, Numeca FINE/Turbo. Eksperimentele toetswerk op die plaaslike Rofanco kompressortoetsbank, met 'n prototipe van die 15 inspuiter stelsel, het inligting verskaf wat gebruik is om die inlaattoestande te spesi seer en simulasieresultate te korreleer. Die simulasieresultate het getoon dat die frekwensie waarteen 'n lem by die inspuiters verbybeweeg, so prominent is, dat dit in die meerderheid van gevalle baie meer prominent is as die opwekkingsfrekwensie. Verder was daar ook deurgaans 'n aantal sekondêre frekwensies teenwoordig. Die teenwoordigheid van die inspuiter verbybeweeg frekwensie en die sekondêre frekwensies is die resultaat van die konvolusie van Vinnige Fourier Transforme. Alhoewel dit in teorie moontlik sal wees om die inspuiter verbybeweeg frekwensie te elimineer, is dit onmoontlik om die sekondêre frekwensies uit die lem vibrasie te elimineer. Ter opsomming, volgens die berekenings vloei-meganika resultate, is dit nie moontlik om met 'n stelsel van 'n eindige aantal inspuiters, 'n enkele vibrasie frekwensie op te wek nie.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Although a numerical model of the mirror support truss of the Southern African Large Telescope (SALT) has already been developed during the design thereof, this thesis focuses on the development of the methods and techniques that would result in a more accurate numerical model of the actual structure that could be used as a basis for a numerical control system. This control system will compensate for de ections in the structure by adjusting the positioning of the individual mirror segments of the primary mirror. The two main components from which the support truss is constructed are the steel nodes, and the struts that connect to them. For this project a smaller, simpler laboratory model was designed and built to have geometrical properties similar to that of the support truss. The methods and techniques that were investigated were carried out on this model. By using numerical design optimisation techniques, improved numerical models of the different strut types were obtained. This was done by performing tests on the struts so that the actual responses of the struts could be obtained. Numerical models of the struts were then created and set up so that they could be optimised using structural optimisation software. Once accurate strut models had been obtained, these strut models were used to construct a numerical model of the assembled structure. No additional optimisation was performed on the assembled structure and tests were done on the physical structure to obtain its responses. These served as validation criteria for the numerical models of the struts. Because of unforeseen deformations of the structure, not all of the measured structural responses could be used. The remaining results showed, however, that the predictive accuracy of the top node displacement of the assembled structure improved to below 1.5%, from over 60%. From these results it was concluded that the accuracy of the entire structure's numerical model could be signi ficantly improved by optimising the individual strut types. / AFRIKAANSE OPSOMMING: Alhoewel daar reeds 'n numeriese model van die spieëlondersteuningsraamwerk van SALT ontwikkel is gedurende die ontwerp daarvan, fokus hierdie tesis op die ontwikkeling van metodes en tegnieke om 'n numeriese model van steeds hoër gehalte van hierdie spesi eke struktuur te verkry wat kan gebruik word as 'n basis vir 'n numeriese beheerstelsel. Hierdie beheerstelsel sal kan kompenseer vir die ondersteuningsraamwerk se vervormings deur om die individuele spieëlsegmente van die primêre spieël se posisionering te verstel. Hierdie stuktuur bestaan uit hoofsaaklik twee komponente, naamlik staalnodusse en die stutte wat aan hulle koppel. Vir hierdie projek is 'n kleiner, eenvoudiger laboratorium-model ontwerp en gebou om geometriese eienskappe soortgelyk aan die van die ondersteuningstruktuur te hê. Die metodes en tegnieke wat ondersoek is, is op hierdie model uitgevoer. Verbeterde numeriese modelle van die verskillende stut-tipes is ontwikkel deur middel van numerieseoptimeringstegnieke. Dit is gedoen deur toetse op die stutte uit te voer sodat hul werklike gedrag bepaal kon word. Numeriese modelle van die stutte is toe geskep en opgestel sodat hulle geoptimeer kon word om dieselfde gedrag as wat gemeet is, te toon. Hierdie geoptimeerde modelle is toe gebruik om numeriese modelle van die toets-struktuur te skep. Geen verdere optimering is op die numeriese model uitgevoer nie en toetse is op die struktuur gedoen om sy werklike gedrag te meet. Data wat deur die toetse verkry is het as validasie kriteria gedien om die akkuraatheid van die numeriese modelle van die stut-tipes te bepaal. Weens die struktuur se onvoorsiene vervorming kon alle gemete struktuurdata nie gebruik word nie. Die oorblywende data het egter getoon dat die akkuraatheid van die finale numeriese modelle van die struktuur verbeter het en dat dit die translasie van die top-node met 'n speling van 1.5% akkuraatheid kon voorspel, teenoor die oorsponlike speling van meer as 60%. Daar is bevind dat die akkuraatheid van die numeriese model van die hele struktuur noemenswaardig verbeter kan word deur die numeriese modelle van die stut-tipes te optimeer.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2005. / Parabolic trough solar collectors (PTSCs) constitute a proven source of thermal energy for industrial process heat and power generation, although their implementation has been strongly influenced by economics. In recent years, environmental concerns and other geopolitical factors have focused attention on renewable energy resources, improving the prospects for PTSC deployment. Further work is needed to improve system efficiencies and active areas of research include development of advanced heat collecting elements and working fluids, optimisation of collector structures, thermal storage and direct steam generation (DSG). A parabolic trough collector, similar in size to smaller-scale commercial modules, has been developed locally for use in an ongoing PTSC research programme. The aim of this study was to test and fully characterise the performance of the collector. Specialised logging software was developed to record test data and monitor PTSC performance in real-time. Two heat collecting elements were tested with the collector, one unshielded and the other with an evacuated glass cover. Testing was carried out according to the ASHRAE 93-1986 (RA 91) standard, yielding results for the thermal efficiency, collector acceptance angle, incidence angle modifier and collector time constant. Peak thermal efficiency was 55.2 % with the unshielded receiver and 53.8 % with the glass-shielded unit. The evacuated glass shield offered superior performance overall, reducing the receiver heat loss coefficient by 50.2 % at maximum test temperature. The collector time constant was less than 30 s for both receivers, indicating low thermal inertia. Thermal loss tests were conducted and performance of the trough’s tracking system was evaluated. The measured acceptance angles of 0.43° (unshielded) and 0.52° (shielded) both exceeded the tracking accuracy of the PTSC, ensuring that the collector operated within 2 % of its optimal efficiency at all times. Additionally, experimental results were compared with a finite-volume thermal model, which showed potential for predicting trough performance under forced convection conditions.

MScEng / This project entails the design and development of a new 2-DOF articulated dump truck (ADT) suspension seat. A study of the ADT vibration environment was conducted using data measured with accelerometers inside the cabin. With the system’s required operational capabilities determined, the concept design phase resulted in a feasible concept. The first prototype was manufactured based on the initial set of specifications. A variety of numerical modelling techniques were used to analyse and evaluate the seat’s dynamic response. Vertical and lateral laboratory tests of the suspension seat with human occupants were completed. The vertical lumped parameter model of the suspension seat with a human occupant gave good correlation with the laboratory measured frequency response. A broad band input signal, and not the ISO 7096 (2000) EM1 signal, was used to obtain the frequency response used to verify the lumped parameter model. The SEAT values for the ISO 7096 (2000) EM1 signal and various ADT road conditions were calculated using the lumped parameter models for a small, medium and large subject, the same three subjects used in the laboratory tests. SEAT values using the ISO 7096 (2000) EM1 signal of 0.94, 0.93 and 0.88 were obtained for the small, medium and large subjects. The lowest SEAT values obtained using the road data were 0.63, 0.56 and 0.48 for the small, medium and large subjects. The transmissibility curves determined from the lateral laboratory tests were used to calculate the SEAT values for the lateral ADT cabin vibrations. The lowest SEAT values obtained were 0.83, 0.83 and 0.82 obtained for the small, medium and large subjects. After all the results from the testing and modelling were evaluated the design was assessed. All the data and information collected was used as input for the design of a second prototype, which was not manufactured. Not all the set specifications were achieved for the first prototype, but the new suspension seat gave comparable vertical vibration isolation performance to that of expensive commercially available ADT suspension seats. The lateral suspension demonstrated good lateral vibration isolation and is a feature not currently available in current ADT suspension seats.