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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Analytical and a numerical ground resonance analysis of a conventionally articulated main rotor helicopter

Eckert, Bernd 03 1900 (has links)
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / The helicopter is a prime example of a nonlinear multi-body dynamic system that is subjected to numerous forces and motions to which the system must react. When a helicopter, with a conventionally articulated rotor head, is resting on the ground with its rotor spinning, a condition called ground resonance can develop. Ground resonance is a specific self-excited oscillation of the helicopter and is caused by the interaction between the main rotor blades and the fuselage structure. Inertia forces of the blades perform an out-of-phase lagging motion, which reacts with the elastic landing gear of the helicopter. For certain values of the main rotor angular velocity, the frequency of these inertia forces coincides with a natural vibration frequency of the fuselage structure. If this occurs, the inertia forces of the lagging blades produce oscillations of the fuselage, which then further excite the lagging motion of the blades. This interaction is responsible for an instability of conventionally articulated main rotor helicopters, which is called ground resonance. The ground resonance phenomenon is investigated by means of a classical analytical approach in which the ground resonance equations are derived from Euler-Bernoulli beam theory and verified with results in literature. These equations are required to discuss ground resonance stability in further detail and determine the specific regions in which the phenomenon occurs. These results are incorporated in a simplified numerical model using an elastic multiple-body dynamics analysis program called DYMORE to simulate the South African Rooivalk Combat Support Helicopter. DYMORE is a program that offers nonlinear multi-body dynamic analysis code, using the finite element method, which was specifically developed for helicopter modelling. The complexity of helicopter modelling generally requires large amounts of computing power to ensure reasonable processing time. In order to prevent excessive computational time, the numerical model will be simplified in terms of aerodynamic and structural aspects. The scope of the numerical investigation is, therefore, limited to the ground resonance phenomenon without the effect of aerodynamic forces and representing the fuselage as multi-body beam structures of specified stiffness.
12

Analytical modelling and optimization of a thermal convective microfluidic gyroscope

Vosloo, Surika 03 1900 (has links)
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: This thesis deals with the mathematical optimization of the detecting chamber of a thermal convective microfluidic gyroscope and the comparison of several different optimization strategies. An analytical model is developed for the gyroscope and some design considerations are discussed. Sequential approximate optimization strategies are explained and compared to each other by implementing test problems fromthe literature. The optimization problem is formulated from the analytical model and implemented using the different optimization strategies. Results are presented and compared to find the most effective optimization strategy. A sequential approximate optimization algorithm is implemented in MATLAB and tested using the gyroscope design problem and common test problems from the literature. Results and iteration history are compared with an existing FORTRAN implementation. / AFRIKAANSE OPSOMMING: Hierdie tesis handel oor die wiskundige optimering van die deteksiekamer van n termies-konvektiewe mikrovloeier giroskoop en die vergelyking van verskeie optimeringsstrategieë. ’n Analitiese model is opgestel vir die giroskoop en verskeie ontwerpsoorwegings word bespreek. Sekwensiëel benaderde optimeringsstrategieë word bespreek en met mekaar vergelyk, deur dit op toetsprobleme uit die literatuur toe te pas. Die optimeringsprobleem is geformuleer uit die analitiese model en geimplementeer deur gebruik te maak van verskeie optimeringsstrategieë. Resultate word getoon en vergelyk, omdie mees effektiewe optimeringsstrategie te vind. ’n Algoritme vir sekwensiëel benaderde optimeringsprobleme is inMATLAB geimplementeer. Die giroskoop probleem, asook probleme uit die literatuur, is gebruik om resultate en iterasie geskiedenis te vergelyk met ’n bestaande FORTRAN implementasie.
13

Evaluation of natural draught wet-cooling tower performance uncertainties

Van Der Merwe, Daniel 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2007. / ENGLISH ABSTRACT: A natural draught wet-cooling tower (NDWCT) was modelled using the Merkel method with an improved energy equation as recommended by Kloppers and Kroger (2005a) - referred to as the Improved Merkel method. The improved energy equation is used for calculating the heat rejection rate of the tower and includes the energy associated with water evaporation. The sensitivity indexes of a NDWCT were calculated numerically with the Improved Merkel method model. It was found that the perfonnance of a NDWCT is most sensitive to the fill Merkel number. The "Natklos" fill test facility at Stellenbosch University was used to estimate typical uncertainties found in fill performance characteristics. The zeroth order uncertainty for the Merkel number and loss coefficient was calculated to be 0.2100 m-1 and 0.4248 m- 1 , respectively, while the first order uncertainty for the Merkel number and loss coefficient was calculated to be 0.1933 m- 1 and 0.2008 m-1 , respectively. ASME requires that the uncertainty in tower capability has to be less than 6 % for a NDWCT perfonnance test to be deemed ASME approved. Propagating typical measurement uncertainties found in NDWCT test standards and experimental data into the tower capability showed that the 6 % uncertainty limit imposed by ASME is unrealistic and too stringent. Performance curve generator (PCG) is a software package developed that generates NDWCT perfonnance curves. With these performance curves it is possible to easily and effectively adjust the off-design test results in order to detennine whether the NDWCT has met its guarantee or not. / AFRIKAANSE OPSOMMING: Die werksverrigting van 'n natuurlike trek nat koeltoring (NTNT) is gemodelleer deur gebruik te maak van die Merkel metode met 'n verbeterde energie vergelyking, soos aanbeveel deur Kloppers en Kroger (2005a) - Verbeterde Merkel metode. Die energie vergelyking word gebruik om die toring se tempo van warmteoordrag te bereken en sluit die energieverlies as gevolg van verdamping in. Die Verbeterde Merkel metode model was gebruik om die sensitiwiteits-indekse van 'n NTNT te bepaal. Die analise toon dat die toring se werksverrigting die sensitiefste is vir die pakking se Merkel getal. Die Natklos pakkingstoetsfasiliteit aan die Universiteit van Stellenbosch was gebruik om tipiese onsekerheid in die pakkingsprestasiekarakteristieke te bepaal. Die zero-orde onsekerheid in die Merkel getal en verlieskoeffisient was bereken as 0.2100 m· 1 en 0.4248 m· 1 , onderskeidelik, terwyl die eerste-orde onsekerhede bereken was as 0.1933 m·1 en 0.2008 m· 1 , onderskeidelik. Die toelaatbare onsekerheid in toringvennoe vir 'n NTNT aanvaardingstoes volgens ASME is 6 %. Deur tipes meetonsekerhede, soos gegee deur NTNT aanvaardings-toesstandaarde sowel as eksperimentele data, deur te propageer, word 'n onsekerheid veel groter as die toelaatbare 6 % gegenereer. 'n Renekaarpakket, genaamd Performance Curve Generator (PCG), is ontwikkel om werksverrigtinskurwes vir 'n NTNT te genereer. PCG se werksverrigtinskurwes maak dit moonltik om maklik te bepaal of a NTNT sy ontwerpskriterea bereik het of nie.
14

Losses in the inlet section of counterflow wet-cooling towers

De Villiers, Eugene 12 1900 (has links)
One copy microfiche. / Thesis (MEng)--Stellenbosch University, 1998. / ENGLISH ABSTRACT: The flow resistances in the inlet sections of counterflow wet-cooling towers are investigated and correlations are derived for inclusion in a one-dimensional tower performance model. The rain zone loss is modelled using analytical-numerical methods. Experimental verification of the model produces satisfactory confirmation of the method's general validity. Semi-empirical correlations are produced to predict the loss coefficient as a function of six dimensionless variables for both rectangular and circular cooling towers. In addition, a study is made of the heat and mass transfer in the rain zone and its influence on tower performance. The inlet loss coefficients for dry, isotropically packed, circular and rectangular counterflow cooling towers are determined experimentally and empirical correlations are formulated to fit this data. The inlet losses for isotropic-resistance-fill towers are found to be higher than those for orthotropic-resistance-fill towers. Computational fluid dynamics is used to investigate the dependence of the inlet loss coefficient on the rain zone characteristics. The rain zone loss generally dampens the inlet loss, but this coupling is indirect and necessitates a large amount of dependent variables. The numerical model is validated by means of experimental data for dry towers and it is found that the degree of accuracy achieved for circular towers exceeds that for rectangular towers. Consequently, the correlation derived to predict this occurrence for circular towers, can be applied more confidently than its rectangular counterpart. An example is presented wherein the improved accuracy iQ tower performance prediction, when applying this correlation, is shown. Additional measures for tower performance enhancement are also explored. / AFRIKAANSE OPSOMMING: 'n Studie is gemaak van vloeiweerstande in die inlaat seksie van nat teenvloei koeltorings met die oog op die afleiding van korrelasies om die verskynsels, vir gebruik in puntmodel koeltoring simulasies, te voorspel. Die reensone verlies is gemodelleer met behulp van 'n analities-numeriese metode. Die model is geverifieer met behulp van eksperimentele toetse. Semi-empiriese korrelasies word afgelei wat die verlies, as 'n funksie van ses dimensielose veranderlikes, vir beide ronde en reghoekige koeltorings, voorspel. Daar word ook 'n studie gemaak van die hitte en massa oordrag in die reensone en hoe dit koeltorings se termiese oordrags vermoe be'invloed. Die inlaat verlies vir droe, isotropies gepakte, ronde en reghoekige koeltorings is eksperimenteel bepaal en empiriese korrelasies is geformuleer om die data te pas. Daar is gevind dat die inlaat verlies vir isotropies gepakte torings hoer is as die vir ortotropies gepakte torings. Numeriese vloei dinamika is gebruik om die afuanklikheid van die inlaat verlies se grootte op die reensone se eienskappe te ondersoek. Die algemene tendens is vir die reensone om die inlaat verlies te demp, maar die afuanklikheid is indirek sodat 'n groot aantal veranderlikes benodig word om die demping te karakteriseer. Die numeriese model word geverifieer deur middel van eksperimentele data vir droe koeltorings en daar word tot die gevolgtrekking gekom dat ronde torings heelwat meer akuraat gemodelleer word as reghoekige torings. Dit veroorsaak dat die korrelasie wat afgelei is om die demping te voorspel vir ronde torings, met baie meer vertroue toegepas kan word as sy reghoekige eweknie. 'n Voorbeeld word gedoen om die verbeterde akuraatheid in koeltoring modellering, wat verkry kan word met behulp van die vergelyking, te wys. Bykomende matrieels, om torings se verkoelings vermoe te verbeter, word ook ondersoek.
15

Design, manufacture and test of a bearingless rotor hub for the 24% scale model of the Rooivalk attack helicopter

Steyn, J. (Johannes) 12 1900 (has links)
Thesis (MEng) -- Stellenbosch University, 2000. / Some digitised pages may appear illegible due to the condition of the original hard copy. / ENGLISH ABSTRACT: This document contains the work done on the bearingless rotor hub for the 24% scale model of the Rooivalk Attack Helicopter situated at the CSIR in Pretoria. This work forms part of the MSc Ing degree of Johannes Steyn. This work was deemed necessary because of a movement away from the fully articulated rotor to one of hingeless and more recently bearingless rotors. The main emphasis of this thesis is to be a technology demonstrator more than the design of a fully working bearingless rotor hub. With this in mind the final design in this report is not an optimal one, but the procedures and methodology in getting to a design are laid out in this document. To verify the design, tests were identified and created. The procedures for these tests are also included in this document. For the fatigue test a test bench had to be designed and built. This document also includes the design of this test bench / AFRIKAANSE OPSOMMING: Die dokument lewer verslag van die aktiwiteite vir die ontwerp van ‘n laerlose rotor van die 24% skaal model van die Rooivalk Helikopter, gelee by die WNNR in Pretoria. Die werk gedoen vorm deel van die MSc Ing graad van Johannes Steyn. Die werk is nodig geag omdat daar ‘n tendens is om weg te beweeg van die volledig geartikuleerde rotor na die van ‘n skanierlose en meer huidig ‘n laerlose rotor. Die hoof klem van die tesis is om as tegnologie demonstrator op te tree, eerder as die daarstel van ‘n werkende laerlose rotor. Na aanleiding van bogenoemde stelling kan die finale ontwerp nie as optimaal beskou word nie. Die prosedures en metodiek wat gevolg is om die ontwerp te kry word uitgele in die dokument. Om die ontwerp te verifieer is toetse gei'dentifiseer. Die prosedures vir elk van die toetse word ook in die dokument ingesluit. Vir die uitputtingstoetse moes ‘n spesiale toetsbank ontwerp en gebou word. Die ontwerp van hierdie toetsbank is ook in die dokument.
16

Evaluate the use of elliptical finned tubes in heat exchanger design and performance : 'the structural characteristics of finned tubes'

Sizani, Xolile L. 04 1900 (has links)
Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: This report describes the Experimental and Numerical Investigations conducted, during the determination of the structural mechanics of elliptical tubes, viz. the F- and the Atubes. This report is requested in an endeavour to assist Sasol, who is currently busy developing and updating specifications on Air Cooled Heat Exchangers. The objectives of this report therefore are to : (1) determine the strength and the effectiveness of the tube-to-tube-sheet joints. (2) determine the allowable pressure limits on the tubes and (3) investigate the effects of thermal load and vibration on the tube bundle. A series of experiments were conducted to meet these objectives. From a Shear Load experiment it was found that the maximum allowable axial load on the Fand the A-tube is 14.55 kN and 20. 86 kN respectively. Fin Plates were found to have little effect on the bending strength of the tube, w~ilst they have significant effect on the resistance to volumetric expansion of the tube. In fact the more fins per unit length the greater the resistance to volumetric expansion of the tube. These conclusions were drawn from Bending and Pressure Load experiments respectively and supported by FEM analysis of the tube using NASTRAN. When the design pressure limit given by the manufacturer (GEA Air Cooled Systems), were tested using FEM analysis, it was found that they cause no significant deformation and failure of the tubes. Thermal stresses on the tube bundle greatly affect the first tube in the first row (row closest to the flanges) of the tube bundle and it is recommended that provision for thermal expansion be made to reduce these stresses. To reduce vibrations induced by the fan, it is recommended that the natural frequency of the tube bundle must not equal the number of blades (N) times the angular frequency (co) of the fan, or multiples thereof, of each mode of vibration. / AFRIKAANSE OPSOMMING: Hierdie tesis beskrywe die Numeriese en Eksperimentele ondersoeke na die sterkte van elliptiese verkoelingsbuise, naamlik die F- en A- tipes. Hierdie werk sal Sasol, wat huidiglik besig is met die opgradering, van spesifikasies vir lugverkoelde hitteuitruilers van nut wees. Die doelwitte van hierdie tesis is om: (1) die sterkte en effektiwiteit van die buis laste was die buis and die buisplaat verdind, te ondersoek, (2) die toelaatbare druklimiete, sowel as (3) die effek wat hitte en vibrasie op 'n buisbundel het, te ondersoek. 'n Reeks eksperimente is uitgevoer om hierdie doelwitte te bevredig. 'n Skuifbelastingseksperiment het aangedui dat die toelaatbare krag wat op 'n F- en A-buis respektiewelik aangewend kan word 14.55 kN en 20.86 kN is. Die ondersoek het aangetoon dat vinne geen noemenswaardige effek op die buigsterkte van die buise gehad het nie, maar dat dit 'n aansienlike verstywingseffek teen volumetriese verandering as gevolg van interne druk, gehad het. Hierdie gevolgtrekkings is bereik deur die Druk- en Buigtoetse wat numeries bevestig is met die NASTRAN eindige element analise (EEA) pakket. EEA het aangetoon dat die druklimiete voorgeskryf deur die buisvervaardiger (GEA Air Cooled Systems) nie noemenswaardige vervorming van die buise tot gevolg gehad het nie. Termiese belastings het 'n groot invloed op die eerste buise (die rye naaste aan die flense) van 'n buisbundel. Die invoeging van uitsettingslaste word aanbeveel om die spannings hier te verminder. Om vibrasie van die buisbundel te verhoed word aanbeveel dat die resonansfrekwensie van die buisbundel nie gelyk is aan die aantal lemme (N) vermenigvuldig met die rotasie frekwensie (co)van die waaier vir elke vibrasiemode.
17

Design and evaluation through simulation and experimental apparatus of a small scale waste heat recovery system

Lotun, Devprakash 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Realisation of the depletable nature of fossil fuel has increased the need for its optimal use. Increasing global pressure to reduce the emission of greenhouse gases and other harmful gases that affect the chemical cycles or destroy the greenhouse gases in the tropospheric ozone, has attracted a increased worldwide concern. Waste heat recovery devices have been around for more than 50 years and researches and scientists have been very much involved in identifying the correct type of systems to meet the requireme?ts of industries and mankind more efficiently. Waste heat can be identified in the form of unburned but combustible fuel, sensible heat discharges in drain water, and latent and sensible heat discharge in exhaust gases. In this project the feasibility of a small scale waste heat recovery system has been investigated. Sets of preliminary investigations were performed to evaluate the amount of waste heat that can be extracted from the exhaust gases of typical diesel powered truck engines. A waste heat recovery unit was designed, implemented and evaluated through simulation and experimental investigations. Preliminary calculations were performed usmg the readings presented by Koorts (1998) for a typical 6-litre diesel engine. The calculations showed that it is possible to extract about 77kW of waste heat from the exhaust gases from such an engine. A simple Rankine cycle was then investigated to be operated on the waste heat recovered. The optimal parameters for such a Rankine cycle was determined using a spreadsheet program and was found to be an optimal pressure of 800kPa with a temperature of 227.2°C and a water mass flow rate of 0.0015kgls as the working fluid. For such a Rankine cycle, based on the efficiencies of commercially available pumps, turbines and heat exchangers it was found that it is possible to extract 2782kW of power per unit mass flow rate of water. The next stage of the project was designing and implementing an exhaust gas pipe network from the engine test cells at the Centre for Automotive Engineering (CAE) located on the ground floor to the Energy Systems Laboratory (ESL) at the first floor. This pipe network was equipped with a valve system that can be operated from the ESL and allows the selection of the route of the exhaust gases and two bellows to compensate for thermal expansion. A continuous combustion unit was also linked to the exhaust gas supply pipes as an alternative source of exhaust gases. The waste heat exchanger designed and selected was purchased and linked into the exhaust gas stream after calibration tests were carried out on the same in the wind tunnel. The water supply and a steam separator were then connected to the waste heat exchanger. In the final experimental stage of the project, two sets of tests were carried out. The first set of tests was performed using exhaust gases from the continuous combustion unit and the second using exhaust gases from the internal combustion engines in CAE. Superheated steam was obtained in both cases indicating the possibility of operating a turbine with the dry steam generated. With exhaust gases originating from the continuous combustion unit, an air fuel ratio of9.14:1 was used and exhaust gases at a temperature of 540°C were obtained with an air inflow of 1400kglh and a fuel consumption rate of7.11 kg/h. The exhaust gases degraded to 360°C at the waste heat recovery inlet due to losses through the bare pipes. 11.12kW of energy was extracted from the exhaust gases to the water stream with an efficiency of 98%. With the exhaust gases from the 10-litre diesel internal combustion engine, an exhaust gas flow rate of O.22kgls was used and with a heat transfer efficiency of 89%, 18.5kW of power was extracted at the waste heat recovery unit. This represents a 4.9% of the thermal content of the fuel used. A rate of energy production balance on the internal combustion engine showed that 34% is lost in exhaust gases and 29% in coolant and other losses while only 37% is used produced as shaft power. The results obtained therefore show that there is ample room for further investigation for the use afwaste heat in exhaust gases of typical diesel engines. It can therefore be concluded that the aims of the project that were to set up a testing facility and an exhaust gas pipe network and evaluation of a small scale waste heat recovery apparatus were achieved. The tests performed can still be optimised with more waste heat removal from the exhaust gases of typical diesel truck engines and hence better recovery of waste heat and a reduction of fuel consumption. / AFRIKAANSE OPSOMMING: Met die besef van die kwynende beskikbaarheid van fosielbrandstof het die behoefte vir die optimale benutting van die brandstof toegeneem. Toenemende globale druk om die emissies van groenhuis gasse en ander gevaarlike gasse wat chemiese siklusse beïnvloed in die troposfeer te verrniner, geniet wêreldwye aandag. Oorskotenergie-toestelle is alreeds beskikbaar die afgelope 50 jaar en navorsers en wetenskaplikes was tot op hede betrokke met die identifisering van die korrekte tipe sisteme om meer effektief aan die industrie en samelewing se behoeftes te voldoen. Oorskotenergie bestaan uit onder andere onverbrande maar brandbare brandstof, voelbare warmte in dreinwater, en latente en voelbare warmte in uitlaatgasse. In hierdie projek word die lewensvatbaarheid van 'n kleinskaal oorskotenergie herwinningsisteem ondersoek. Voorlopige ondersoeke was gedoen om die hoeveelheid oorskotenergie te bepaal wat herwin kan word uit die uitlaatgasse van 'n tipiese 6 liter vragmotor dieselenjin. 'n oorskotenergie herwinningseenheid was ontwerp, geïmplimenteer en ge-evalueer deur similasies en eksperimentele ondersoeke. Voorlopige berekeninge was uitgevoer op data wat deur Koorts (1998) saamgestel is vir 'n tipiese vragmotor dieselenjin. Die berekeninge toon dat dit moontlik is om ongeveer 77kW oorskotenergie van die uitlaatgasse van so enjin te onttrek. Die moontlikheid was toe ondersoek om die herwinne energie te gebruik om 'n eenvoudige Rankine siklus aan te dryf. Die optimale parameters vir die Rankine siklus was bereken deur van 'n sigblad program gebruik te maak en dit was gevind dat die optimale druk is 800kPa, die optimale temperatuur is 227.2°C teen 'n water massa vloeitempo van 0.0015kg/s. Vir so 'n Rankine siklus, gebaseer op die effektiwiteit van kommersiële beskikbare pompe, turbines en warmteruilers, was dit gevind dat dit moontlik is om 2782kW drywing per eenheidsmassa vloeitempo van water, te onttrek. Die volgende stadium van die projek was die ontwerp en implimentering van 'n uitlaatgas pypnetwerk vanaf die toetsselle van die Centre for Automotive Engineering (CAE) op die grondvloer na die Energy Systems Laboratory (ESL) op die eerste vloer. Die pypnetwerk was toegerus gewees met 'n kleptstelsel wat vanaf ESL bedryf kan word en wat dit moontlik maak om die roete van die uitlaatgasse te beheer. Twee samedrukbare koppelstukke was ook ingesluit in die lang reguit pypseksie om vir termiese uitsetting te kompenseer. 'n Aaneenlopende verbrandingseenheid was ook gekoppel met die uitlaatgasse toevoerpype as 'n alternatiewe bron van uitlaatgasse. Die oorskotenergie warmteruiier wat ontwerp en geselekteer was, was aangekoop en opgekoppel met die uitlaatgas-stroom nadat kalibrasie toetse op die warmteruiier gedoen was in 'n windtonnel. Die watertoevoer en 'n stoomskeier was gekoppel aan die oorskotenergie warmteruiler. Twee toetse was uitgevoer in die finale eksperimentele stadium van die projek. Die eerste stel toetse was uitgevoer deur gebruik te maak van die uitlaatgasse van die aaneenlopende verbrandingseenheid en met die tweede toets is van die uitlaatgasse van die interne verbrandingsenjins van CAE gebruik gemaak. Oorverhitte stoom was verkry in beide gevalle en wys dus dat daar 'n moontlikheid is om 'n turbine met droë stoom aan te dryf. 'n Lug tot brandstof verhouding van 9.14 : 1 was gebruik gewees in die aaneenlopende verbrandingseenheid om uitlaatgasse te verskaf teen 540°C. Die massavloeitempo van die lug was 1400kg/h en die brandstof 7.11kg/h. Die uitlaatgasse se temperatuur het afgeneem tot 360°C tot voor die oorskotenergie herwinningseenheid as gevolg van hitteverliese vanaf die ongeïsoleerde pypnetwerk. 11.12kW energy was onttrek vanaf die uitlaatgasse en oorgedra aan die waterstroom met 'n effektiwiteit van 98%. Die 10 liter diesel interne verbrandingsenjin het uitlaatgas gelewer met 'n massa vloeitempo van O.22kg/s. 18.5kW energie was herwin gewees met 'n effektiwiteit van 89%. Dit verteenwoording 4.9% van die termiese inhoud van die brandstof gebruik. 'n Energie balans op die interne verbrandingsenjin het getoon dat 34% energie gaan verlore in die uitlaatgasse, 29% word aan die verkoelingsmiddeloorgedra en 37% is bruikbare meganiese drywing. Die resultate wat verkry is, wys daarop dat daar nog groot ruimte is vir verdere ondersoeke in die gebruik van oorskotenergie in uitlaatgasse van tipiese vragmotor dieselenjins. Die gevolgtrekking kan dus gemaak word dat die doelwitte van die projek naamlik die opstel van 'n toetsfasiliteit, installering van 'n uitlaatgasse pypnetwerk en die toets van a kleinskaalse oorskotenergie herwinningseenheid, bereik was. Die toetse wat uitgevoer was kan nog ge-optimeer word om meer energie te herwin vanaf die uitlaatgasse van 'n tipiese vragmotor dieselenjin om sodoende beter brandstofverbruik te bewerkstellig.
18

Thermal management of casting moulds using heat pipes

Groenewald, Abraham 04 1900 (has links)
Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The use of cylindrical heat pipes for the thermal control and management of casting moulds have been investigated. Heat pipes are tubes that possess a high capability to transfer heat, up to a thousand times or more than an equivalent solid copper rod. The heat pipes used in this thesis are copper tubed, use water as working fluid and have (phosphor-bronze) screen mesh wicks. Experiments relating to practical casting situations in industry were designed and performed, using pure tin as the casting metal. Three cases pertaining to the requirements of an industrial casting mould were considered. The first case considered heating of a mould through heat pipes, in order to keep it at a specific temperature. The second case relates to the situation where metal is cast around a core, and the core is cooled by a heat pipe connected to a heat sink. The heat sink in this case was an air cooled fin. The third case is representative of the situation where molten metal is cast into an external mould and the mould heats up due to the energy flowing in from the casting. In order to cool the mould, heat pipes are used to transport the heat to a water cooled heat sink. These three cases were modeled theoretically, which included using a standard finite element method (FEM) computer package, NASTRAN 2.0 for Windows. For the FEM simulations, the heat pipes are modeled using an equivalent conductivity approach. Theoretical and experimental results are to within ± 30% of each other, but better results could possibly be achieved using a better finite element model for the heat pipes. A simulation case was performed to compare the use of an uncooled mould with a heat pipe cooled mould, and a two and a half time improvement of production rate was achieved. In support of the above mentioned casting related experiments, experiments have also been performed on a specially designed cylindrical heat pipe to determine the evaporator and condenser heat transfer coefficients. It was found that the heat pipe can transfer more than 500 W for vertical operation and around 160 W for horizontal operation. The heat transfer coefficients of the condenser and evaporator ends are in the order of 1800 to 2000 W/mK. Experiments were also performed on the fins used as the heat sink in the experiment where core cooling is investigated, to compare the experimentally determined fin heat transfer coefficient with the theoretically predicted coefficient. A theoretical study was also performed for an inclined ammonia thermosyphon in order to compare the theory to a set of previously determined experimental results. The theory produced accurate results for vertical operation, but it is clearly limited for inclined operation, and can lead to inaccurate results. A special correlation factor, the splashing factor, was defined to analyse the deviation between the theoretical and experimental results. The splashing factor can be used in two ways. Firstly, it can be used as a design correction factor and secondly, it can be processed to indicate which operational variables have the highest impact on the discrepancy between the theory and the experimental data. It is recommended that further research into the use of heat pipes for the thermal control of moulds be considered, based on the results achieved in this thesis. Furthermore, a finite element model for a heat pipe can also be considered. It is also recommended that the use of the splashing factor be considered for the analysis of thermosyphons. / AFRIKAANSE OPSOMMING: Die moontlikheid om hittepype te gebruik in die termiese beheer van gietvorms is ondersoek. Hittepype is buise wat oor 'n baie goeie warmte-oordragsvermoë beskik, 'n duisend maal of beter as 'n ekwivalente soliede koper staaf. Die hittepype wat gebruik is in die tesis is gesëelde koperbuise, wat water gebruik as werksvloeier en ook 'n (fosfor-brons) sifdraad pitmateriaal bevat. Eksperimente wat verband hou met industriële gietprosesse is ontwerp en uitgevoer. Suiwer tin is gebruik as die gietmateriaal. Drie giet gevalle is ondersoek. Die eerste geval het die verhitting van 'n gietvorm met hittepype behels. Die tweede geval hou verband met die situasie waar metaalom 'n kern gegiet word en die kern word afgekoel deur middle van 'n hittepyp wat gekoppel is aan 'n hitteput, wat in die geval 'n lugverkoelde fin is. Die derde geval hou verband met die situasie waar gesmelte metal gegiet word in 'n eksterne gietvorm en die gietvorm verhit as gevolg van die energie wat vanaf die gietstuk invloei. Hierdie drie gevalle is teoreties gemodelleer, wat die gebruik van 'n eindige element analise (EEA) rekenaarpakket insluit (NASTRAN 2.0 for Windows). Tydens die EEA simulasies is die hittepype gemodelleer met behulp van die ekwivalente geleidingskoëffisiënt metode. Teoretiese en eksperimentele resultate is binne .± 30% van mekaar. Beter resultate kan moontlik verkry word as 'n verbeterde eindige element model vir die hittepype ontwikkel kan word. 'n Simulasie geval is uitgevoer om die produksietempo van 'n onverkoelde gietvorm te vergelyk met 'n hittepyp-verkoelde gietvorm, en 'n verbetering van twee en 'n half maal is gevind vir die verkoelde gietvorm. Ter ondersteuning van die bogenoemde gietverwante eksperimente en teoretiese modelle, is eksperimente ook op 'n spesiaalontwerpte silindriese hittepyp uitgevoer om die kondeser en verdamper hitte-oordragskoëffisiënte te bepaal. Daar is bevind dat die hittepyp meer as 500 W kan oordra tydens vertikale gebruik en ongeveer 160W tydens horisontale gebruik. Die hitte-oordragskoëffisiënte vir die kondenser en verdamper is in die orde van 1800 tot 2000 W/m2K. Eksperimente is ook uitgevoer op die finne wat gebruik is as die hitteput in die geval waar die kern verkoeling ondersoek is, om die eksperimenteel bepaalde fin hitteoordragskoëffisiënte te vergelyk met die teoretiese koëffisiënt. 'n Teoretiese studie is ook uitgevoer vir 'n skuins termoheuwel sodat die teorie vergelyk kan word met In stel bestaande resultate. Die teorie gee akkurate voorspellings vir vertikale gebruik, maar is duidelik beperk en kan lei tot onakkurate resultate vir skuins gebruik. 'n Spesiale faktor (splashing factor) is gedefiniëer om die verskil tussen die teoretiese en eksperimentele resultate mee te analiseer. Hierdie factor kan op twee maniere gebruik word. Eerstens kan dit gebruik word as 'n korreksiefaktor en tweedens kan dit geprosesseer word om aan te dui watter veranderlikes die hoogste impak het op die verskil in eksperimentele en teoretiese resultate. Dit word aanbeveel dat verdere navorsing gedoen word op die gebruik van hittepype vir die termiese beheer van gietvorms, gebasseer op die resultate wat verkry is uit die tesis. Verder kan 'n eindige element model vir 'n hittepyp ontwikkel word. Dit word ook aanbeveel dat die "splashing factor" oorweeg word in die analise van termohewels.
19

Helicopter tail boom vibration analysis and suppression

Funnell, M. E. (Marc Edwin) 04 1900 (has links)
Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: An experimental investigation was conducted usmg a cantilever beam to illustrate an understanding of vibration techniques and phenomena. The [Tee and forced vibration of the cantilever beam was investigated using various modelling strategies. Theoretical models such as the Lumped parameter, Myklestad, Distributed Parameter and Finite Element Methods were analysed and compared with experimental measurements. Excellent agreement of the natural frequencies, mode shapes and the harmonic transfer functions were found. To investigate tail boom vibration, a Finite Element Model of a simplified helicopter tail boom design was tested against experimentally measured data. The results correlated accurately and the model was used to evaluate the effectiveness of a vibration suppression system designed for the tail boom. The vibration suppression system was designed using two, parallel dynamic absorbers to reduce tail boom vibrations at its two dominant frequencies. For the purposes of this thesis, the dynamic absorbers were tuned to reduce the resonant peaks at the dominant excitation frequencies of the excitation force in-line with the thrust of the tail rotor only. This excitation force was estimated using a simplified tail rotor dynamic model, which when compared with actual vibration data was assumed to predict the basic frequency trends of the force, reliably. Incorporating the designed components into an accurate Lumped Parameter model of a cantilever beam structure and simulating the response of the structure at the dominant excitation frequencies of the calculated excitation force, tested the vibration suppression system. The results of this investigation proved the effectiveness of the design procedure and optimisation process of the design parameters. A similarly designed suppression system was incorporated into the Finite Element tail boom model and from the analytical results obtained it was shown to cause a fair reduction in the vibration response at the two dominant frequencies of the excitation force. Finally, two possible applications were suggested from the research presented in this thesis. The first application was the simplified configuration of a vibration monitoring system for the tail boom. The second application was the possible development of a system using the response of vibration suppression absorbers to predict the magnitudes of the excitation forces on the tail boom. / AFRIKAANSE OPSOMMING: 'n Experimentele ondersoek is ondemeem deur gebruik te maak van 'n ingeklemde balk om vibrasie tegnieke te illustreer. Die vrye en geforseerde vibrasie van die ingeklemde balk is ondersoek deur verskillende model tegnieke te gebruik. Teoretiese modelle soos die Lumped parameter, Myklestad, Distributed Parameter en Eindige Element Metodes was geanaliseer en vergelyk met die eksperimentele waardes. Uitstekende ooreenstemmings was gevind tussen die natuurlike frekwensies, die eievektore en die harmoniese oordragsfunk:sie. Om stert vibrasie te ondersoek, was'n eindige element model van 'n helikopter stert getoets teenoor die eksperimentele data. Die resultate het akuraat gekorreleer en dus was die model gebruik om die effektiwiteit van 'n vibrasie supressie sisteem te evalueer. Die vibrasie supressie sisteem was ontwerp deur gebruik te maak van twee parallele dinamiese absorbeerders om die helikopter stert se eerste twee dominante vibrasie frekwensies te minimeer. Vir die doel van hierdie tesis was die dinamiese absorbeerders ingestel om net die resonante pieke van die opgewende krag wat in lyn is met die drykrag van die stert rotor te minimeer Hierdie opgewende krag was, deur gebruik te maak van 'n basiese stert rotor dinamiese model, aanvaar om die basiese frekwensie tendense van die krag te voorspel. Die supressie sisteem wat ontwerp was, was getoets op die lumped parameter balk en het veroorsaak dat die voorspelde opgewende krag by al twee van sy dominante . frekwensies baie geminirneer was. Die effektiwiteit van die sisteem was dus bewys en die sisteem was gebruik om die respons van die eindige element model van die stert te verbeter. Die resultate het 'n aanvaarbare reduksie in die respons by die twee dominante frekwensies van die opgewende krag, gewys. Laastens, deur gebruik te maak van die resultate in hierdie tesis. was twee moontlikhede voorgestel. Die eerste een was die konfigurasie van 'n vibrasie moniterings sisteem vir die helikopter stert. Die tweede mmontlikheid was die moontlike ontwikkeling van 'n sisteem wat die grootte van die opgewende krag by die stert rotor kon voorspel, deur gebruik te maak van die vibrasie suppressie absorbeerders.
20

Aerodynamic characteristics of a mission-adaptive stealthy air inlet

Marais, Louwrens 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The aerodynamic performance of a mission-adaptive air inlet for a stealthy unmanned aircraft was examined using CFX 5.5, a commercial Computational Fluid Dynamics package. In order to ensure that the numerical results were reliable, the package was validated against a number of flow situations for which previously-known results exist. This was done for both external and internal flow, and in all cases the conclusion could be made that the code produces realistic results. The simulation of the inlet was done in two steps. A first-order design was simulated using robust simulation parameters: the focus was on obtaining a "picture" of the flow into the inlet, not on the quantitative values of flow variables. On account of the results of these simulations, the design was suitably modified. This second-order design was then simulated using more accurate simulation parameters, and the results analysed in detail. Comparative simulations between the two design iterations showed that their pressure recoveries are similar, but that the distortion of the velocity profile at the engine compressor face is lower for the second-order design than for the first-order design over a significant portion of the operational range. When compared with an idealized theoretical analysis, the numerical results showed that the performance of the inlet was severely degraded at most operating conditions. This is mainly due to the effects of flow separation ahead of the inlet capture plane. To alleviate this problem, recommendations for the modification of the design are proposed. This thesis demonstrates that CFD is a valuable tool for both qualitative and quantitative evaluation of performance during the design process of an air inlet. / AFRIKAANSE OPSOMMING: Die lugdinamiese werkverrigting van 'n missie-aanpasbare luginlaat vir 'n radarontduikende onbemande vliegtuig is ondersoek, deur gebruik te maak van CFX 5.5, 'n kommersiële numeriese vloeidinamika-sagteware pakket. Om te verseker dat die numeriese resultate betroubaar was, is die pakket gevalideer teen 'n aantal gevalle waarvoor vooraf-bekende resultate bestaan. Dit is gedoen vir beide interne en eksterne vloei, en die gevolgtrekking kon gemaak word dat die kode wel realistiese resultate lewer. Die simulasie van die inlaat is in twee stappe gedoen. 'n Eerste-orde ontwerp is gesimuleer deur gebruik te maak van robuuste simulasieparameters: die fokus hiervan was om 'n visuele indruk van die vloeipatrone in die inlaat te kry, nie op kwantitatiewe waardes van die vloeiveranderlikes nie. Na aanleiding van hierdie resultate van hierdie simulasies is die ontwerp dienooreenkomstig aangepas. Hierdie tweede orde ontwerp is dan gesimuleer deur gebruik te maak van meer akkurate simulasieparameters, en die resultate is in detail geanaliseer. Vergelykende simulasies tussen die twee ontwerps-iterasies het gewys dat hulle drukherwinnings soortgelyk is, maar dat die distorsie in die snelheidsprofiel by die enjin kompressor-vlak laer is vir die tweede-orde ontwerp as vir die eerste-orde ontwerp, oor 'n beduidende gedeelte van die operasionele bestek. Wanneer dit met 'n ideale teoretiese analise vergelyk word, het die numeriese resultate getoon dat die werkverrigting van die inlaat ernstig gedegradeer is by meeste operasionele toestande. Dit kan meestal toegeskryf word aan die effekte van vloei-wegbreking voor die intreevlak van die inlaat. Om hierdie probleem te verlig, word aanbevelings vir die aanpassing van die ontwerp voorgestel. Hierdie tesis demonstreer dat numeriese vloeidinamika waardevolle gereedskap is vir beide kwalitatiewe en kwantitatiewe evaluering van werkverrigting tydens die ontwerpsproses van 'n luginlaat.

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