PhD, EngD, MPhil and MSc by research theses (SAS)
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Browsing PhD, EngD, MPhil and MSc by research theses (SAS) by Course name "PhD"
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Item Open Access The application of electrolytic in-process dressing to precision grinding processes(2007-06) Zervos, Charilaos; Stephenson, David J.; Robinson, M. J.Electrolytic In-Process Dressing (ELID) has attracted a lot of attention in recent years as it is a promising method of grinding a wide range of materials, including ones that are difficult to machine, to high quality finishes. The EC funded project Nanogrind undertook the construction of a high precision grinding machine which will incorporate an ELID system, applying the technique on a spherical wheel for the production of components with intricate geometries (e.g. freeforms, aspherics). In this project, the main objective was to understand the basic features of ELID, such as the electrochemical properties of the oxide layer and its effect on the final finish of the produced components (glass, a hard and brittle material was the main focus). Acoustic emission studies, a promising in-process monitoring tool, verified the effectiveness of ELID grinding when the contact area between the wheel and workpiece is increased. Compared to conventional resin bond wheel grinding, ELID ground components were of higher quality with less damage introduced in them. ELID current monitoring also gave excellent results when it was correlated to surface finish achieved across the surface of the testpieces ground. Electrochemical Impedance Spectroscopy was an innovative technique that was applied in order to acquire basic information about the metal bond wheel, such as the charge transfer resistance. Its correlation to the oxide layer thickness gave an indication of the way corrosion rates change with the presence or not of an oxide film on the wheel surface. Finally, sub-surface damage introduced into glass components was evaluated and was compared to the depths of damage predicted by theoretical models, giving further insight into the way the overall processing time of a component should be optimised in order to acquire high quality, damage-free finished components in a time efficient, cost effective way.Item Open Access The damaging effect of surface-traffic-generated soil pressures on buried archaeological artefacts(2010-04-12) Dain-Owens, Anne Peregrine; Kibblewhite, Mark G.; Godwin, R. J.; Hann, Michael J.The aim of this work was to investigate the influence of surface loading from conventional field operations on the damage to buried artefacts, both pots and bones. The objectives of this research were a) to investigate the influence of surface loading and resulting breakage relating to the material strengths of buried objects - ceramic (unglazed), and aged bone; b) to assess the magnitudes of peak subsurface pressures transferred through soil under the dynamic surface loading from tyres and other field operations; c) to develop and test an empirical model for predicting the effects of subsurface pressure application on buried objects from surface loads; and d) to explore ways of identifying the potential for damage to buried artefacts under agricultural and other field operations. Experimental investigations were performed in both the laboratory and field. The laboratory work was undertaken to determine the magnitude of subsurface pressure at which buried objects were damaged. Conducted in a sandy-loam-filled soil bin, instrumented ceramic and bone artefacts were buried alongside pressure sensors and subjected to loading by a single smooth tyre appropriately loaded and inflated for subsurface pressure generation. The breakage of the buried objects and the pressures under the moving tyre were recorded in order to allow correlation of the subsurface pressures to buried artefact breakage. The fieldwork was done to determine the magnitudes of subsurface pressure generated by individual field operations whilst travelling in a similar sandy loam field soil. Four plots were established, with each assigned a particular cultivation regime. An accelerated timeframe was utilized so that a years’ series of field operations could be driven over pressure sensors buried in the soil. The peak pressures from each field operation within each plot were recorded and summarized, and the data was analysed relative to field operation type and cultivation regime type. Multiple statistical analyses were performed, as the laboratory data and field data were independently evaluated before being correlated together. An empirical relationship between buried object damage and subsurface pressure magnitude was developed. The different pot types and bone orientations broke at different subsurface pressures. The four pot types listed in ascending order of strength to resist damage (with breakage pressure threshold value) are: shell tempered (1.3 bar), grog tempered (1.6 bar), flint tempered (3.1 bar), and sand tempered (3.6 bar). Aged human radius bones were tested, and the parallel bone orientation proved stronger than the perpendicular orientation, where 2.8 bar was the lowest subsurface pressure found to cause damage. The primary field operations, presented in ascending order relative to peak magnitude of subsurface pressure per specific operation, are: roll (0.68 bar), drill (1.03 bar), heavy duty cultivator (1.21 bar), spray 1 (1.27 bar), harvester (1.30 bar), spray 2 (1.31 bar), tractor / trailer (1.46 bar), shallow mouldboard plough (1.61 bar), deep mouldboard plough (2.04 bar). The relationships between vehicle specification and subsurface pressure generation potential were described, relating to the vehicle mass, tyre/track physical properties, and tyre inflation pressure. The effect of cultivation method on overall magnitude of subsurface pressure was defined, with lowest pressure generation within a zero-till cultivation regime (1.08 bar), higher in a non-inversion cultivation regime (1.13 bar), followed by the shallow inversion regime (1.22 bar), and highest within a conventional inversion scheme (1.30 bar). The laboratory and field results were correlated by a statistical analysis comparing breakage point to peak subsurface pressure. The shell tempered pot was found to be most susceptible to damage. The grog tempered pot was less vulnerable to damage, followed by the flint tempered pot. The quartz tempered pot was predicted to survive intact under all field operations within this research. In conclusion, this research has developed a functional and predictive empirical relationship between damage to pot and aged bone artefacts from subsurface soil pressures generated by surface traffic. It has been found that different types of buried pot and bone artefacts break at different subsurface pressures. In addition, a complete dataset consisting of peak subsurface pressures recorded under a year’s range of field operations within a sandy loam soil at field-working moisture content has been compiled. The effect of different cultivation methods on the generation of subsurface pressures was also evaluated. The breakage thresholds specific to each artefact type have been related to the in-field subsurface soil pressures. A correlation of breakage to the subsurface pressures under each operation yields a prediction of percentage of artefact-type breakage. From this correlation, relationships are observed between vehicle specification, subsurface pressure generation, and consequential artefact breakage. The achievements provide knowledge about how field operations affect specific types of buried archaeology, providing a valuable asset to farmers, land managers, and regulatory bodies. It is evident that agricultural practices, choice of track or tyre type, and inflation pressures must be carefully managed if the intention is to protect or mitigate damage to buried archaeological artefacts. Thus, a contribution has been made to the development of ‘best management practices’ and to the specification and use of field operations relative to intended mitigation of buried artefact damage.Item Open Access The influences of post-preparative treatments on luminescence from CdTe nanoparticles(2008) Gardner, Hannah Catherine; Dunn, S. C.Nanotechnology has seen an explosion of research interest in recent years. Nanoparticles are finding applications in an ever growing list of applications. To further develop these applications an understanding of the properties of a nanoparticle is needed. This thesis prevents an investigation of the photoluminescent properties of CdTe nanoparticles as a function of various post-preparative treatments. Changing the inter-particle distance is found to cause photoluminescence wavelength shifts. These shifts are determined by the amount of energy transferred between nanoparticles. The effects of interparticle distance are seen when a suspension is diluted, re-concentrated or deposited as a thin film. In a thin film format similar effects are seen if the number of layers in a thin film is increased. Changing the temperature of either a thin film or suspension of nanoparticles produces both reversible and irreversible photoluminescence wavelength shifts. The reversible changes are mainly found to be due to the presence of thermally activated trap states within the nanoparticles. Finally, formation of a thin film via the layer-by-layer deposition method is studied. A real time in-situ analysis technique is used to monitor the whole deposition process. The deposition is found to take place in a series of stages with nanoparticles becoming either strongly or loosely bound to the surface. Optical waveguide lightmode spectroscopy is found to be an extremely useful technique for monitoring this thin film deposition as it allows researchers the opportunity to quickly and easily characterize individual experimental setups.Item Open Access Investigating the relationship between shear and floe fate using CFD(2006-11) Bridgeman, Jonathan Matthew; Parsons, Simon; Jefferson, BruceThe size, density and strength of floes play a major role in the removal of contaminants from water in physico-chemical treatment processes. The efficiency of the main removal processes is a function of floe size, strength and density. Changes in these parameters affect floe removal and hence the removal of adsorbed organic matter. Coagulation and flocculation efficiency and floe strength are often assessed using ajar tester. Here, computational fluid dynamics (CFD) was used to model the flow field within standard jar test apparatus and, using a Lagrangian particle trajectory model, to study the effects of turbulence on individual floes. The hydrodynamic environments were also investigated experimentally using laser Doppler anemometry (LDA) and particle image velocimetry (PIV) measurement techniques. Combining numerical and experimental data, velocity gradient values at which floe breakage occurs were postulated for three different floe suspensions. Although the threshold values are determined using jar test and CFD data in combination, they are based on the floes’ resistance to induced velocity gradients. This is a significant result, as previous breakage thresholds have been expressed only in terms of mixing speed and cannot be applied at full scale. With this in mind, work was subsequently undertaken to use CFD to model numerically the hydrodynamic conditions within two full scale flocculation vessels; one mechanically mixed, the other hydraulically mixed. This section of work had two principal aims; firstly, to investigate the perceived benefits of using CFD to model the hydraulic performance of the flocculation process at two large surface water treatment works, and secondly, to investigate the practicality and effectiveness of using CFD and jar test results in combination to consider floe fate in the flocculation vessels (in terms of growth, breakage and residence time). This work drew upon the results and conclusions of the previous laboratory scale work and facilitated a greater insight into flocculation processes. Improved understanding of flocculator hydrodynamics can only serve to improve design procedures and standards for future installations.Item Open Access A process-based approach to engineering design knowledge reuse(2007-06) Baxter, David; Gao, James X.Manufacturing enterprises are under increasing pressure to produce products of higher quality at lower cost in shorter time frames if they are to remain competitive. Engineering design support methods can help companies to achieve these goals. One such approach is ,,design knowledge reuse. Industrial requirements have been identified as (i) the ability to rapidly create product variants; (ii) the ability to capture and re-use design knowledge, and; (iii) the capability to support the design effort across a distributed enterprise. The research aim is developed to assist the manufacturing enterprise in meeting the industrial requirements in the following way: a design solution to a new product requirement can be supported using an application package that is developed for a specific product domain. The application package consists of knowledge about previous products and projects, and procedures for using the knowledge to achieve a new solution. An initial investigation showed that design reuse in practice is lacking in specific areas: access to relevant and contextualised captured design knowledge; the relationship between design reuse and the product development process; integrated engineering and business objectives. Literature gaps were also identified. They include: (i) knowledge reuse for the whole product life cycle (particularly early design); (ii) integrated product and design process models; (iii) a 'how-to' element of the product design process. The aim of this research is to provide a method for reusing engineering design knowledge. The research method is 'interview case study', which supports a flexible approach and enables the research to develop according to the findings. The research was carried out with four companies, one of which took part in a detailed case study, providing case data to develop, populate and validate the proposed system. The outcome of the research is a proposal for a process based engineering design reuse method. The method consists, of a combination of product, process and task knowledge to support the design process. Product knowledge is represented using a product ontology. Process knowledge is represented using the Design Roadmap method. Task knowledge is represented using a template developed to record the critical aspects of the task, including 'how-to' knowledge. Case studies are used to validate the proposed framework and the developed prototype system. The proposed design knowledge reuse framework is applicable to a range of industries in which mature, complex products are developed.Item Open Access Thermal and deformation analysis of joint interfaces in machine tools(2008-05) Gashi, Bekim; Shore, Paul; Stephenson, David J.Machine tools are made up of many different parts connected together. In order to understand and create more accurate thermal and deformation numerical models the heat transfer characteristics of machine tool interfaces need to be understood. Previously heat transfer across interfaces has not been incorporated in finite element models in thermal and deformation analysis of machine tools. To a varying degree the issue of interfaces will have an effect on the overall performance of machine tools, and clearly if not considered and resolved at the strategic design stage they may be difficult and expensive to correct, once machine tools are operational. An inability to adequately understand and model the interfaces in machine tools is therefore a major limitation to current knowledge. In this research programme heat transfer and corresponding thermal deformation of metal blocks in contact having pre-defined interface geometries, were experimentally and numerically investigated. Factors such as the contact pressure, the contact conformance, and the interface material were investigated. It was found that the most influential factors were contact pressure and contact conformance. Interface material was also found to have a bigger influence if the contact area was non-conforming. When interface material was thicker than the surface roughness, the heat flow across the interface was reduced as fewer contact asperities came into contact. In order to optimise modelling it was necessary to optimise the convection coefficient - this was found to have an effect on overall heat transfer across the interface. It was also found that the overall contact area is important and not the spread of contact regions for the same overall contact. This was investigated using two different contact geometry arrangements. The numerical prediction of heat transfer across an interface is accurate if the contact is conforming. However, if the contact is non-conforming an accurate prediction is not possible. This is due to the fact that direct modelling of non-conformance is not achievable. It was found that the most influential factor on thermal deformation is contact pressure, on the other hand factors such as interface material and interface geometry showed very little effect.Item Open Access Towards sustainable landfill management(2006-11) Smith, Richard; Pollard, SimonThe UK is reliant on landfill as a waste management option with some 72% w/w of municipal waste landfilled in 2003/04. This thesis advances an argument that landfill, as practised historically and currently, is unsustainable. This thesis demonstrates, specifically, that current legislative aftercare provisions of 30-60 years are inadequate with reference to modelled landfill completion times (the achievement of equilibrium status) of up to 2,000 years. Uniquely, the research quantifies the scale and significance of methane emissions during the early stages (up to 28 months waste age) of landfill operations at 21 UK landfills using a modified flux box. The onset of methanogenesis is quantified for the first time, using a series of in situ monitoring probes installed at one UK landfill site. A significant and novel finding is that the advective flow of landfill gas is preferentially dominated by lateral movement, evidenced here by examination of a predominantly municipal solid waste (MSW) landfill site in Southern England. The direct implications of this finding for the design of landfill gas management systems are discussed. For future landfills, this research has examined a number of UK scenarios in which the gas and leachate characteristics from waste residues going to landfill are modelled to the point of completion or achievement of equilibrium status. This analysis now allows for a comparative assessment of the future performance of landfills. Under these scenarios, completion times can be reduced in some instances {e.g. landfilling of compost and mechanical biological treatment residues) and extended in others (incinerator bottom ash). Problematic contaminants remain; notably arsenic, chromium and lead. Using the research herein, the work describes the application of a landfill gas management hierarchy. In part response to the requirements of the EU Landfill Directive, this provides a science-based framework for operators to maximise protection of the environment and human health from gaseous emissions. The research provides evidence that can be used by landfill managers seeking to maximise landfill collection efficiency. This contributes to regulators managing public and environmental health and is increasingly significant for climate change.