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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.
31

An emotional journey : from sensory attributes to packaging and back again!

Ng, May Ling January 2013 (has links)
With the rapid proliferation of new products into the marketplace, understanding emotional responses may offer a differential advantage beyond traditional hedonic measures. Thomson et al. (2010) argued that consumers also associate other functional connotations (e.g. refreshing) and abstract feelings (e.g. sophisticated) to a product, referring to these associations (emotional, abstract and functional) as 'conceptualisations'. The aim of this project was to investigate the effect of the sensory attributes and packaging cues of commercial blackcurrant squashes on consumers' liking and conceptualisations. Initially, the sensory attributes of the squashes were characterised using a sequential approach of quantitative descriptive analysis (QDA) and temporal dominance of sensations (TDS). Using QDA and TDS in tandem was revealed to be more beneficial than each on its own, providing a fuller sensory profile. Next, emotional response and liking within the squash category was measured using the EsSense Profile TM, in which consumers rated a predefined emotion lexicon (n=100) under three conditions: (1) blind, (2) pack and (3) informed (product and packaging). The project also measured how emotional, abstract and functional responses changed across blind, pack and informed conditions. A conceptual lexicon was defined by consumers (n=29), after which a different group of subjects (n=100) rated the squashes using the lexicon and a check-all-that-apply (CATA) approach (CD-CATA). The findings of both EsSense Profile and CD-CATA experiments revealed that intrinsic sensory attributes had more association with emotions and liking, than the packaging. Interestingly, the CD-CATA experiment suggested that extrinsic packaging cues had more association with abstract/functional conceptual responses. The relationship between liking and emotional responses to debranded squash (sensory attributes) was investigated comparing EsSense Profile and CD-CATA approaches. Both approaches yielded emotional data that clearly discriminated across the products more effectively than the hedonic scores. In addition, both approaches produced similar emotional spaces and product configurations. A two dimensional structure (pleasantness vs. engagement/activation) corresponding to published circumplex emotion models was observed in each method. The final phase of the PhD was to determine the relationship between sensory attributes of the squashes (as measured by QDA and TDS) and consumer responses (EsSense Profile and CD-CATA approaches). Sensory attributes in squashes that were found to drive liking and positive conceptual responses in consumers were 'natural processed blackcurrant' and 'natural sweetness'. The study also shows how some temporally dominant sensory attributes (e.g. 'minty') evoked positive conceptual responses in consumers. Throughout the thesis, recommendations regarding practical implications for emotion measurement and general ideas for future research are discussed.
32

Mechanical properties of laser beam welded Ti6Al4V

Fan, Yu January 2010 (has links)
Many items of medical, aeronautical, electronic and military equipment exposed to corrosive conditions, or required to have extreme performance characteristics, are sealed hermetically into micro packages. Laser beam welded (LBW) Ti6AI4V alloy has been adopted in anti-corrosion micro packages for the impeller of a left ventricular assistance device (LVAD). Thin and narrow welds were required for such medical equipment. A wide variety of laser types can be applied in sealing micro packages, which include traditional lasers (CO2, Diode and Nd: YAG) to the newest laser types (fibre). Compared with other LBW types, continuous wave fibre laser welds are well known for exhibiting narrow weld zones, low distortion, lower heat input and high efficiency. However, in this work significant porosity was found in the continuous wave fibre laser welds due to the high traverse speeds and high associated solidification rates. The largest distortion and melting area was found in the continuous wave diode laser welds due to the high heat generation. A pulsed Nd: YAG welding was suggested as the hermetic laser welding technique for sealing the micro packages, since it is a good-balance between low porosity, less distortion and a narrow weld zone. The microstructures of Ti6AI4V were complex and strongly affected the mechanical properties. These structures include: a' martensite, metastable ß, Widmanstätten, bimodal, lamellar and equiaxed microstructure. Bimodal and Widmanstätten structures exhibit a good-balance between strength and ductility. The microstructure of laser beam welded Ti6AI4V was primarily a' martensite, which showed the lowest ductility but not significantly high strength. A heat treatment at 950°C followed by furnace cooling can transform the microstructure in the weld from a' martensite structure into Widmanstätten structure. The fatigue fracture behaviour of laser beam welded thin sheet Ti6AI4V was examined in this project as the lifetime of the LVAD impeller has been seen to be limited by fatigue cracking. Grain size, phase content, stress ratio and frequency are all affected fatigue fracture behaviour. A transformed Widmanstätten structure in the weld gave the highest fatigue fracture life. A time of 8 hours heat treatment gave the highest fatigue fracture life due to a good-balance between the grain size and phase content; the existence of metastable (3 limits the crack propagation as well. The geometries, distortion and porosity of the welds were variable and depended on the types of the laser used for the welding process. These factors significantly affected the local stress levels during the tensile testing and fatigue testing. FEA was used to understand and evaluate these influences. By simulation in FEA, the maximum stress locations were observed to be strongly dependent on the specifics of the crosssectional geometries of the welds. For the pulsed Nd: YAG weld in the fatigue testing, the FEA-derived modified local stress amplitudes exhibited a increase of about 40% compared to the nominal applied stress.
33

A study of bonding mechanisms and corrosion behaviour of cold sprayed coatings

Hussain, Tanvir January 2011 (has links)
Cold gas dynamic spraying (CDGS) is a material deposition technique, in which powder particles are accelerated to speeds of between 300-1200 m/s and upon impact deform plastically and adhere. The overall aims of this research project were to understand the bonding behaviour in cold spraying of copper, aluminium and titanium, and to produce corrosion resistance barrier layer of titanium coatings using cold spraying. The mechanism of bonding in cold spraying is still a matter of some debate. In this thesis, copper has been cold sprayed onto aluminium alloy substrates, the surfaces of which had been prepared in a variety of ways. The coating - substrate bonding was assessed via a novel intermetallic growth method along with adhesive pull-off testing. The bond strength has been rationalised in terms of a modified composite strength model, with two operative bonding mechanisms, namely (i) metallurgical bonding and (ii) mechanical interlocking of substrate material into the coating. In most cases, mechanical interlocking is able to account for a large proportion of the total bond strength, with metallurgical bonding only contributing significantly when the substrate had been polished and annealed prior to spraying. In addition, grit-blasting has been shown to significantly reduce the bond strength compared to other substrate preparation methods. Aluminium has also been cold sprayed onto copper substrates, the mechanical interlocking of substrate material was not observed and the bond strength was relatively low. Titanium particles have been deposited onto three different steel substrates, namely low carbon steel, an Armco iron, and an austenitic stainless steel. Using the novel intermetallic growth method it was found that a barrier does exist at the interface of the titanium deposited onto the low carbon steel and Armco iron substrates which is not removed in either of the stages of impact or during the heat treatment process. On the other hand, in the case of titanium deposited onto the austenitic stainless steel, the barrier is removed. Cold spraying is believed to have the potential for the deposition of corrosion resistant barrier coatings. However, to be effective, a barrier coating must not have interconnected porosity. Titanium coatings were sprayed using nitrogen as an accelerant gas at two process gas temperatures of 600 and 800˚C to reduce porosity. A modified in-situ grit blasting was used to improve the coating-substrate adhesion. The mean bond strength of the titanium deposits was ~70 MPa and tensile strength was 250 MPa. Mercury intrusion porosimetry (MIP) was used to characterize the interconnected porosity over a size range of micrometers to nanometers. The MIP results showed that in cold sprayed deposits a significant proportion of the porosity was sub-micron and so could not be reliably measured by optical microscope based image analysis. A set of free standing deposits was also vacuum heat treated to further decrease porosity levels. The effect of porosity on the corrosion behaviour of titanium coatings onto carbon steels was investigated in 3.5 wt.% NaCl. The electrochemical measurements of the coatings showed significant substrate influence when the interconnected porosity of the coating was 11.3 vol.% but a decreased substrate influence with a porosity level of 5.9 vol.%. Salt spray (fog) tests confirmed these electrochemical findings and showed the formation of corrosion products following 24-h exposure. Laser surface melting (LSM) was used to seal the top ~140 μm of the coating to eliminate any interconnected porosity. The LSM titanium coatings showed no sign of corrosion after 100-h of salt spray tests, and the open circuit potential and passive current density values were similar to those of the bulk titanium.
34

Congruence and its role in manufacturing strategy : an audit of goals and systems

Neely, Andy January 1993 (has links)
This thesis is concerned with the realisation of manufacturing strategies. It describes the development and testing of a structured methodology which can be used to determine some of the reasons why a firm may be unable to implement its manufacturing strategy. The methodology is known as a "congruence audit". It is widely accepted that manufacturing strategies are important, but little has been written about how they should be developed and implemented. In the literature which does exist, however, a key theme is consistency, with many authors arguing that strategies can only be realised through consistency of decision making and action. Given that people are ultimately accountable for most of the decisions and actions taken in an organisation, it can be argued that consistency of decision making and action might best be achieved if; (a) there is widespread empathy with the organisation's strategic goals (goal congruence), and (b) the organisation's signalling systems - especially those concerned with goal setting, performance measurement, feedback and reward - induce decision making and action which is consistent with these goals (system congruence). This research set out to test two propositions: (a) That a process which can be used to identify areas of either goal or system incongruence (a congruence audit) can be developed. (b) That such a process can be used to identify some of the reasons why a firm may be unable to realise its manufacturing strategy. There were three main phases to the research. Phases one and two involved the development and testing of processes for identifying areas of either goal or system incongruence. Phase three involved the integration of these processes and the application of the resultant congruence audit. In total four companies participated directly in the study. Managers from a further fourteen were consulted. The key findings can be summarised under the categories of content and process. In terms of content, the data gathered during the congruence audits indicate that the level of goal congruence is highest between a firm's senior managers and those employees who work on the shop floor. Furthermore they suggest that the way in which the goal setting, performance measurement, feedback and reward systems influence employees, varies both from firm to firm and across the organisation's hierarchy. Most importantly, they imply that one of the main reasons firms are unable to realise their manufacturing strategies is that senior managers often inadvertently encourage their subordinates to pursue courses of action which are inappropriate. In terms of process, the congruence audit serves as a structured means of: - Defining what a management group believes manufacturing should be doing. Identifying what other employees think manufacturing actually is doing. Establishing whether any mismatches in perception occur. Determining whether such mismatches in perception are a function of the organisation's goal setting, performance measurement, feedback or reward systems. Provoking debate so that the issues raised can be resolved. It should be noted that as this thesis focuses on the development and testing of a process within a limited set of firms, further research is required to confirm the findings and to explore whether the congruence audit can be used more widely.
35

Novel approaches to cyclic job-shop problems with transportation

Groenemeyer, Sven January 2012 (has links)
Scheduling problems can be found in almost any field of application in the real world. These problems may not only have different characteristics but they also imply more or less complex requirements. One specific class within this domain is the cyclic job-shop problem. It occurs in various areas reaching from industrial production planning down to the systems architecture of computers. With manufacturers in particular, one can find increasing demand for effective solution methods in order to tackle these scheduling problems efficiently. This thesis will deal with the Cyclic Job-Shop Problem with Blocking and Transportation. It arises in modern manufacturing companies, where the products move automatically between the different workstations, for instance. The problem itself is not new to the research community, but hardly any work has been done in solving it. Within this thesis we will try to close this gap and present some first approaches, discussing the structure of the problem and how it can be solved. As a result, we will provide three different solution methods, including an integer programming formulation, which is solved with a commercial solver, a branch and bound algorithm and a tabu search heuristic. All algorithms are tested on a range of data sets and compared with each other. Additionally, we have worked on a polynomial solvable subproblem, which has gained more interest in the literature. As a result, a new polynomial algorithm, that outperforms the existing ones in theory as well as in empirical tests (except for some special cases) is presented. This thesis concludes with a discussion about ideas of how to improve the presented methods and some other extensions to the investigated problem.
36

Cold gas spraying of copper and tin onto metallic and non metallic substrates

Calla, Eklavya January 2005 (has links)
Cold gas dynamic spraying (CGDS) is a recent development in the field of thermal spraying in which a powder feedstock can be deposited onto a substrate to form a coating without it being heated significantly. The aim of the present study was to investigate the potential for manufacturing electrical circuits for automobile applications by depositing copper tracks on non-metallic substrates. Powders were sprayed using He gas at room temperature and elevated temperatures onto a number of different polymers, ceramic and metal substrates to understand the factors controlling deposit formation and the development of adequate adhesion between track and substrate. The use of tin as an interlayer to improve adhesion was a novel development in this study. The deposits were characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), profilometry, microhardness, tensile testing, adhesion testing and resistivity measurements. Investigations were also performed to study thermal stability since as sprayed deposits are in non-equilibrium state. Copper could be deposited on aluminium for a wide range of deposition parameters. Sprayed copper had nanometre size grains and demonstrated high hardness and tensile strength. Annealing resulted in recrystallization and grain growth and decrease in hardness and tensile strength. Copper could be deposited on polymers like nylon (PA66), glass reinforced nylon (PA6T) and poly (butylene terepthalate) (PBT). Copper could be deposited on a wide range of polymers when a layer of tin was deposited as a bond coat. The use of tin bond coat improved the overall adhesion of tin + copper tracks. Intermetallic compound formation was observed in tin - copper tracks after annealing at 343 K and 443 K. The formation of the intermetallic compound did not increase the resistance of tin - copper couples as the resistance of the couples after annealing were found to be below that of the as - sprayed couples where the intermetallic compound formation had not taken place. This effect is a result of the recovery/recrystallization taking place in copper which reduces the resistance.
37

Through thickness air permeability and thermal conductivity analysis for textile materials

Saldaeva, Elena January 2010 (has links)
Woven fabrics have found enormous application in our daily life and in industry because of their flexibility, strength and permeability. The aim of this work was to create a general model for through thickness air permeability and thermal conductivity for different types of textile fabrics because of their applications in industries and everyday life. An analytical model to predict through thickness air permeability was developed. The objective was to create a model which will take into consideration the two primary mechanisms of air flow in fabrics: through the gaps between yarns and through the yarns. Through thickness air permeability was measured according to British Standard BS EN ISO 9237: 1995. Several fabrics were tested including plain weave, twill weave and satin weave fabrics. The analytical model is a combination Kulichenko and Van Langenhove's analytical model which predicts the permeability through gaps between yams with Gebart's model to predict permeability within yams. Analytical predictions were compared to the experimental data. Computational modelling of through thickness air permeability using Computational Fluid Dynamics CFD software is presented in this thesis. The Polymer Composites Research Group in the University of Nottingham has created a textile schema, named TexGen. The prerequisites of this software were to be able to model various types of textile structures. A CFD model using CFX 11.0 was developed to be able to predict fabric permeability. In addition, an analytical model was developed for fabrics deformed by shear, compaction and tension. Experimental work for through thickness air permeability of sheared fabric was used to verify predicted results. An analytical model for thermal conductivity of fabrics was developed including the influence of moisture content on thermal conductivity. Two existing approaches for single-layer fabrics are described and compared: rule of mixtures and thermal resistance approach. A me6iod for thermal conductivity prediction for multiple layer fabrics is presented. The results are compared to the experimental data and analysed. Some predicted results were in excellent and good agreement with experimental data whereas other predicted results were in poor agreement with experimental data as they were dramatically affected by the assumptions made in the analytical model.
38

An agent-based self-configuration methodology for modular assembly systems

Ferreira, Pedro January 2011 (has links)
Assembly systems today are exposed to market trends that have become increasingly more dynamic and unpredictable, requiring product changes and adjustments which emphasise de need for more flexible systems. The requirement for increased responsiveness has led to the development of new modular concepts which provide the bases for achieving higher system adaptability through increased component/module interchangeability and reusability. The modularization of physical and control infrastructure does, however, only address one aspect of the issue and there is still a lack of appropriate tools and methods to support the rapid configuration and reconfiguration of such systems for changing sets of requirements. This work proposes a new distributed methodology for the configuration and reconfiguration of Modular Assembly Systems (MAS) through the use of agent technology. The new methodology defines a comprehensive model for the structured description of the MAS requirements, equipment modules and the configuration results. This thesis proposes a new agent architecture for the self-configuration of equipment modules into systems based on a given set of requirements, as the core of the self-configuration methodology. This architecture introduces the overall behaviour of the methodology through the definition of agent types, roles and overall interactions. Furthermore this work describes the development of the specific models and methods for the local behaviour of each agent. These enable the actual decision making method for the agents to achieve configuration solutions. This work also reports on a new methodology for the early performance simulation of MAS characteristics that can be used in conjunction with the configuration methodology.
39

The impact of manufacturing flexibility on system performance : a simulation based approach

Gomez Valdez, Carlos Rafael January 2010 (has links)
Manufacturing systems face now more than ever the effects of an uncertain environment, which is triggered by constantly changing customer needs. Numerous approaches have been proposed to provide manufacturing systems with the capability to satisfactorily perform under situations of uncertainty, particularly by improving their level of responsiveness. Manufacturing flexibility is a dimension of responsiveness which aims at reacting to unpredictable events with little penalty on performance. Nonetheless, there is a strong perception that the achievement of manufacturing flexibility exclusively depends on the availability of highly automated equipment. This is a misleading belief considering that manufacturing systems are a collection of interacting components sharing a common objective and therefore there must be alternative system’s aspects, other than automation, contributing to the achievement of manufacturing flexibility. This study expands on existing knowledge by exploring the concept of manufacturing flexibility through the investigation of the dimension of uniformity. The analysis of this dimension has provided a valuable perspective from which to improve understanding of flexibility in manufacturing and identify alternative ways to achieve it. By combining the analytical capabilities of discrete event simulation, statistical design of experiments and optimisation, it has been possible to identify specific factors, optimal system configurations and response trade-offs that, within the context of semi-automated cellular manufacturing systems, constitute a significant contribution in the attainment of manufacturing flexibility.
40

Algorithms and data structures for three-dimensional packing

Allen, Sam D. January 2011 (has links)
Cutting and packing problems are increasingly prevalent in industry. A well utilised freight vehicle will save a business money when delivering goods, as well as reducing the environmental impact, when compared to sending out two lesser-utilised freight vehicles. A cutting machine that generates less wasted material will have a similar effect. Industry reliance on automating these processes and improving productivity is increasing year-on-year. This thesis presents a number of methods for generating high quality solutions for these cutting and packing challenges. It does so in a number of ways. A fast, efficient framework for heuristically generating solutions to large problems is presented, and a method of incrementally improving these solutions over time is implemented and shown to produce even higher packing utilisations. The results from these findings provide the best known results for 28 out of 35 problems from the literature. This framework is analysed and its effectiveness shown over a number of datasets, along with a discussion of its theoretical suitability for higher-dimensional packing problems. A way of automatically generating new heuristics for this framework that can be problem specific, and therefore highly tuned to a given dataset, is then demonstrated and shown to perform well when compared to the expert-designed packing heuristics. Finally some mathematical models which can guarantee the optimality of packings for small datasets are given, and the (in)effectiveness of these techniques discussed. The models are then strengthened and a novel model presented which can handle much larger problems under certain conditions. The thesis finishes with a discussion about the applicability of the different approaches taken to the real-world problems that motivate them.

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