The McTronX Research Group at the North-West University is conducting research in the field of Active Magnetic Bearings (AMBs) with the aim of establishing a knowledge base for future industry consultation. AMBs are environmentally friendly and are a necessity in the pebble bed modular reactor (PBMR), a South-African initiated project, which is predicted to be the means of supplying Africa and many other countries with modular energy in the future. Aside from the PBMR, there are numerous other AMB industrial applications. The aim of this project is to develop a comprehensive AMB model that considers the effect that rotor dynamics has on an AMB system. This model is used to analyse a double radial AMB, capable of suspending a rigid- and flexible rotor, to explain previously noticed phenomena. Two modelling methods are focussed on namely the System Matrix Method and Transfer Matrix Method (TMM) both of which are implemented in MATLAB®. The rigid rotor model is firstly implemented as a point mass in state-space form followed by use of the TMM to analyse its bending modes. The stability and critical speeds of the system are analysed due to a change in the supports' properties along with rotor gyroscopy and its effect on the system. During analysis of the flexible rotor the TMM was used via a similar approach as was followed with the rigid rotor. The results indicate that the system is experiencing lower than expected damping due to the model that is used within the control loop. The previously assumed rotor model in the control loop is not sufficient to describe its complex behaviour. This causes the unexpected damping characteristics. This project suggests future work to be conducted in expanding the frequency domain model of the rotor within the control loop to account for its physical shape. / Thesis (M.Ing. (Computer and Electronical Engineering))--North-West University, Potchefstroom Campus, 2009.

No description available.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 154-156).

Thesis (M.S.)--Ohio University, June, 1999. / Title from PDF t.p.

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 140-144). Also available on the World Wide Web.

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Mechatronics is an exciting research area that stemmed from huge progress in computer technology from the 1970s onwards. In such systems, computer controlled electronic and mechanical devices interact so intimately that it is impossible to tell where the one ends and the other begins. A mechatronic project aimed at automated manufacturing was undertaken by the Department of Industrial Engineering at the University of Stellenbosch as part of their programme in mechatronics. ROYIC was the industrial partner in the joint venture. ROYIC manufactures a front loader that is used on tractors. The front loader fits on a tractor by means of a kit that has to be manufactured specially for each type of tractor. The design of the kit needed many welding joints, which lead to a difficult and expensive manufacturing process. A bending press that was capable of bending pre-cut steel into a predefined shape was identified as a viable solution. The mechanical design for the project was done by ROYIC, while the University was responsible for the electronic control. Bending is carried out by pushing a flat bar over a Y-block into the bending position which can be read from a position encoder. The bending blade then bends the metal until the appropriate angle is reached. It is impossible to predict the resulting angle by means of analytical techniques. This is due to non-linear behaviour caused by spring-back. The position of the bending blade is read with an incremental encoder. An empirical equation is used to convert the distance read by the sensor into the appropriate angle. The parameters are deduced by means of non-linear regression methods. A mean square error of 0.069 was obtained for the equation when operating in the linear area of the plastic region of bending. A software application was written to enable ROYIC to deduce the needed parameters of the equation for all types of steel. Pulse control was used to control the bending blade. The blade moves continuously until a pulse band is reached. The blade is pulsed from there into a dead band. Consequently the accuracy of the machine is determined by the width of the dead band. The control program is capable of executing bend sequence files to enable the operator to perform a sequence of bends on a metal bar. Safety was of great importance in the design. The control system was designed to give priority to safety signals over other control signals. Dangerous situations owing to computer failure are thus prevented. / AFRIKAANSE OPSOMMING: Megatronika is 'n opwindende navorsingsarea wat ontstaan het uit groot vooruitgang in rekenaartegnologie vanaf 1970. In megatroniese sisteme werk rekenaar beheerde elektroniese en meganiese toestelle so nou saam dat dit onmoontlik is om agter te kom waar die een begin en die ander eindig. 'n Megatronika projek gerig op vervaardigings outomatisasie is onlangs onderneem deur die Departement van Bedryfsingenieurswese van die Universiteit van Stellenbosch as deel van hul program in megatronika. ROVle was die industriële vennoot in die projek. ROVle vervaardig implemente vir gebruik op plase. Een van hul produkte is 'n laaigraaf wat met 'n hegstuk op 'n trekker pas. Die hegstuk moet spesifiek vir elke tipe trekker ontwerp word wat gelei het tot 'n ontwerp met baie sweislaste wat 'n tydrowende vervaardigingsproses vereis. 'n Staal buigmasjien wat vooraf gesnyde staal in 'n spesifieke vorm kan buig sou hierdie probleem kon oorbrug. Die meganiese ontwerp vir die masjien is gedoen deur ROVle terwyl die Universiteit verantwoordelik was vir die elektroniese beheer. Staal word gebruik deur 'n staalbalk te skuif oor die buigbed tot in die buigposisie wat afgelees word vanaf' n posisie enkodeerder. Die buiglem buig dan die staal in die benodigde hoek. Geen analitiese metodes bestaan om die buighoek te voorspel nie weens terugspringing. Die posisie van die buiglem word ingelees met behulp van 'n inkrementeie enkodeerder. 'n Empiriese vergelyking word gebruik om die afstand beweeg om te skakel in 'n buighoek. Die verskillende parameters word afgelei deur middel van regressie metodes. Die gemiddelde foute kwadraat was 0.069 wat getoets is vir slegs die lineêre area van die plastiese gebied. 'n Program is geskryf wat ROVle instaat stelom die benodigde parameters self af te lei. Puls beheer is gebruik op die beheer van die buiglem. Die lem beweeg kontinu tot binne die puls band en word daarvandaan gepuls tot by die stopband. Die grootte van die stopband bepaal dus die akkuraatheid van die masjien. Die beheerprogram kan ook buig sekwensie lêers uitvoer wat die operateur instaat stelom 'n reeks van buigings op 'n staal balk uit te voer. Veiligheid het deurgaans 'n belangrike rol gespeel in die ontwerp van die masjien. Die stelsel is ontwerp om prioriteit te gee aan veiligheidseine bo enige ander beheersein. Gevaarlike situasies wat mag ontstaan as die rekenaar sou faal, word dus voorkom.

Made available in DSpace on 2014-10-09T12:37:08Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:56:40Z (GMT). No. of bitstreams: 1 01908.pdf: 6409813 bytes, checksum: a4da653568b2a1fde0228c02cc3838b9 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

abstract: Silicon nanowires were grown epitaxially on Si (100) and (111) surfaces using the Vapor-Liquid-Solid (VLS) mechanism under both thermal and plasma enhanced growth conditions. Nanowire morphology was investigated as a function of temperature, time, disilane partial pressure and substrate preparation. Silicon nanowires synthesized in low temperature plasma typically curved compared to the linear nanowires grown under simple thermal conditions. The nanowires tended bend more with increasing disilane partial gas pressure up to 25 x10-3 mTorr. The nanowire curvature measured geometrically is correlated with the shift of the main silicon peak obtained in Raman spectroscopy. A mechanistic hypothesis was proposed to explain the bending during plasma activated growth. Additional driving forces related to electrostatic and Van der Waals forces were also discussed. Deduced from a systematic variation of a three-step experimental protocol, the mechanism for bending was associated with asymmetric deposition rate along the outer and inner wall of nanowire. The conditions leading to nanowire branching were also examined using a two-step growth process. Branching morphologies were examined as a function of plasma powers between 1.5 W and 3.5 W. Post-annealing thermal and plasma-assisted treatments in hydrogen were compared to understand the influences in the absence of an external silicon source (otherwise supplied by disilane). Longer and thicker nanowires were associated with longer annealing times due to an Ostwald-like ripening effect. The roles of surface diffusion, gas diffusion, etching and deposition rates were examined. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2011

In the present thesis, the sensitivity of flame propagation to the turbulent motion of burning gases is investigated. The long-standing issue of the 'bending effect' is focused upon, which refers to the experimentally-observed inhibition of flame propagation velocity at high intensities of turbulence. Plausible mechanisms for the bending effect are investigated by isolating systematically the effects of turbulence intensity. By providing a novel perspective on this topic, the thesis addresses the fundamental limits of turbulent burning. The investigation employs Direct Numerical Simulation (DNS), which enables the basic conditions of burning to be controlled directly. A parametric DNS dataset is designed and generated by increasing turbulence intensity over five separate simulations. Effects of turbulent motion are isolated in this manner, such that the bending effect is reproduced in the variation of flame propagation velocity recorded. Subsequently, the validity of Damköhler's hypotheses is investigated to ascertain the mechanism of bending. Analysis of the DNS dataset highlights the significance of kinematic flame response in determining turbulent flame propagation. Damköhler's first hypothesis is found to be valid throughout the dataset, suggesting that the bending effect may be a consequence of self-regulation of the flame surface. This contradicts the dominant belief that bending occurs as a result of flame surface disruption by the action of turbulence. Damköhler's second hypothesis is found to be valid in a relatively limited regime within the dataset, its validity governed by flame-induced effects on the prescribed turbulent flow field. Therefore, this thesis presents turbulent flame propagation and the bending effect as emergent from the dynamics of a flame surface that retains its internal thermo-chemical structure. Finally, experimental validation is sought for the proposed mechanisms of bending. Comparisons have been initiated with measurements in the Leeds explosion vessel, based on which the widely accepted mechanism of bending was hypothesized twenty-five years ago. Modifications to the DNS framework warranted by this comparison have aided the development of novel computationally-efficient algorithms. The ongoing work may yield insights into the key mechanism of the bending effect in turbulent flame propagation.

An investigation into the processes taking place at the surface interface of ferroelectric Pb(Zr1-x,Tix)O3 immersed in metal salt solution under ultraviolet illumination is presented. The semiconducting and switchable dipolar nature of this material allows the spatial separation and control of photo-induced reduction and oxidation across its surface interface. These properties can be of application in novel techniques such as the controlled growth of metallic nanoparticles across specific polar domains. 70nm thick Pb(Zr0.3,Ti0.7)O3 samples, PZT(30/70), are manufactured using the sol gel methodology, two crystallographic orientations being produced. The orientation being controlled by the substrate used; Si was used for [111] orientation and MgO for [100]. The initial work with wideband ultraviolet light shows that the reduction and growth of silver on the PZT surface is greatly influenced by the structure of the film. The crystallographic orientation of the film affects metal deposition such that on [111] films the metal deposits only on positive domains, where as the [100] films experience deposition on both positive and negative domains. This is shown to be due to the difference in width of the space charge region, Δw = 4.4nm, between the [111] and [100] samples so that the negative domain on [100] samples have 10 19 times higher chance of electron tunnelling compared to the [111]. It is also shown that grain boundaries have the greatest effect on the growth of metal, with a metal cluster growth rate 51 times faster than elsewhere on the surface. This increased rate of growth is due to the effect a grain boundary has on the surrounding area, the energy band bending at the boundary attracting charge carriers from the grains around it. The interface types ranked from greatest to lowest influence are grain boundaries, positive domains, domain boundaries and finally interphase boundaries.ii It is shown that the stern layer, strongly adsorbed charged ions of opposite sign to the surface charge, at the PZT/solution interface act as an insulating layer to metal reduction. The accumulation of photoexcited charge carriers at points along grain boundaries causes the surface potential gradient to alter and allows metal reduction and thus clusters to nucleate. The energy required to cause this variation is investigated by use of narrow band, 5nm bandwidth, ultraviolet. For energy from 4.4eV to 5 eV, it is found there is an increase in the average silver cluster cross sectional area by a ratio of ca 1.6 to 1 for both the [111] and [100] orientations of PZT. Finally it is shown that the type of metal salt used in the photochemical process affects the type of reaction that takes place at the sample surface. For a cation to reduce on positive domains its reduction potential needs to be below the bottom edge of the conduction band of PZT. Chloride salts, that sit above the conduction band, cause decomposition of the negative domains. Use is made of these effects to find the position of the bottom of the conduction band for PZT. It is found that across similar [111] PZT samples FeCl2 can both reduce on positive domains and decompose negative domains, this puts the bottom of the conduction band for PZT(30/70) between 4.06 and 4.36 eV from vacuum. It is also discovered that the type of anion affects the decomposition of the negative domains. Nitrate salts with cations above the conduction band cause no decomposition whereas chlorides do. The decomposition is shown to be the loss of Pb from the negative surface.