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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

Life-time monitoring of in service switches and crossings through field experimentation

Cornish, Andrew January 2014 (has links)
In financial year 2011/2012, Switches and crossings (S&C) cost the UK rail infrastructure owner, operator and maintainer, Network Rail, over £220m in maintenance and £189m in renewals. This represented 24% of the total track maintenance budget, whilst accounting for only 5% of the network mileage. The large costs are due to the complex S&C design that allows network flexibility whilst supporting a vehicle traversing from the switch rail to the stock rail and through the crossing. The motivation for undertaking this research was to understand how S&C reacts to dynamic loading imposed by the vehicles, and to gain a better knowledge of the deterioration of the asset. The understanding and measurement of S&C degradation has never been scientifically measured in real time before, which means that currently the maintenance schedules are cyclic or reactive. The outcome from this investigation could be used to provide a finely calibrated pre-emptive schedule for more effective S&C maintenance and investment. Eight sites were outlined in the design of experiments, of which four were instrumented as part of the first phase of the research in this thesis. High wear and fatigue rates from prior failure statistical analysis showed the need to understand the loading and degradation of S&C. Strain gauges, geophones and accelerometers were used to understand the system reaction to loading, through strain and the sleeper deflection within S&C. The results show that the largest increase in strain over time was at the stock rail with the closed switch rail. The degradation is due to the increased dynamic forces of the vehicle transferring from one line to another. The change in strain indicates that the additional vibrations/frequencies will occur over time, increasing the rate of material change. As speed increases through switches and crossings, a reduction in the strain generated is seen at the gauge locations. This indicates that switches demonstrate lower levels of wear with a higher speed at the locations of the gauges. Degradation of vertical motion of sleepers at the crossing is shown, with no change in the bending strain generated due to the whole asset deforming at a similar rate.
32

The computational enhancement of automated non-destructive inspection

Brierley, Nicholas January 2014 (has links)
In industrial NDE it is increasingly common for data acquisition to be automated, driving a recent substantial increase in the availability of data. The collected data need to be analysed and currently this is largely done manually by a skilled operator - a rather painstaking task given how rarely defects occur. Moreover, in automated NDE a region of an inspected component is typically interrogated several times, be it within a single data channel due to multiple probe passes, across several channels acquired simultaneously or over the course of repeated inspections. The systematic combination of these diverse readings is recognised to offer an opportunity to improve the reliability of the inspection, for example by enabling noise suppression, but is not achievable in a manual analysis. Hence there is scope for the inspection reliability to be improved whilst reducing the time taken for the data analysis by computational means. This thesis describes the development of a software framework providing a partial automation capability, aligning then fusing the available experimental data to declare regions of the component defect-free to a very high probability whilst readily identifying indications, thereby optimising the use of the operator's time. The framework is designed to be applicable to a wide range of automated NDE scenarios, but the focus in development has been on two distinct, industrial inspections: the ultrasonic inspection of power station turbine rotor bores and the ultrasonic immersion inspection of aerospace turbine disks. Results obtained for industrial datasets from these two applications convincingly demonstrate the benefits of using the developed software system.
33

Effect of grain boundary chemistry and grain morphology on the mechanical behaviour of silicon carbide

Al Nasiri, Nasrin January 2014 (has links)
Silicon carbide based materials are being increasingly used as a room temperature structural material. Unfortunately, there have been very few studies of the mechanical behaviour of SiC at room temperature especially studies incorporating slow crack growth. In order to address this gap, this thesis will focus on room temperatures only. SiC materials are produced with a wide range of grain boundary chemistries and grain morphologies with the aid of sintering additives. Therefore, in this thesis two different chemistries were produced using solid state (SS-SiC) sintering with carbon and boron or liquid phase sintering (LP-SiC) using alumina and yttria, materials with fine and coarse grains were produced for each chemistry. The fracture toughness at room temperature is improved by a factor of two using LP- sintering and by introducing elongated grains. The toughening mechanisms responsible for this improvement are discussed. The magnitude of the short range closing forces becomes larger as grain size increases irrespective of chemistry. This was expected for materials with intergranular failure, but not for materials that exhibit transgranular failure. FIB technique was used to investigate the toughening mechanisms of short range cracks and new findings are proposed. Slow crack growth (SCG) investigations in air and in water at room temperature show that the presence of glass pockets and oxide complexions makes LP-SiC materials prone to stress corrosion, while materials such as SS-SiC with no glass or oxides in their microstructure are immune to SCG. Possible suggestions are discussed to quantify the effect of grain size on SCG. For all the studied materials no apparent cyclic fatigue in air was observed. This was expected for brittle materials such as SS-SiC, but not for LP-SiC. In order to clarify the significance of the measured mechanical properties, a lifetime analysis in the presence of artificial and natural defects is presented.
34

Improving the energy efficiency of high speed rail and life cycle comparison with other modes of transport

Zhou, Jing January 2014 (has links)
The world energy crisis and global warming call for a reduction of energy consumption. High speed rail, increasingly viewed as an effective solution to inter-city passenger transportation challenge of the 21st century, has the significant ability of increasing passenger capacity and reducing journey time. The advent of high speed rail provided many research opportunities. So far studies have been contributed from different perspectives: economical, environmental, and technical. The main research gaps are: addressing the problem of the effects of route geometry on train energy consumption and quantifying the contributing factors towards differences in energy consumption between different types of high speed trains. In addition, this energy assessment cannot be based solely on the energy consumption in the operation phase. In the life cycle assessment of the whole railway system, the vehicle evaluation is relatively straightforward, but the infrastructure raises many difficult issues. In this thesis, an existing approach for modelling the traction energy of electric trains is developed and extended to simulate the train operation under different driving strategies. Baseline simulation is carried out to estimate the journey time and energy consumption of a High Speed 2(HS2) reference train running on the London-Birmingham proposed high speed route. The influence of route geometry and train configuration on energy consumption is investigated, based on the metric of energy consumption per passenger kilometre. Simulations are also carried out of different types of high speed rolling stock running on the proposed HS2 route, to identify the key areas of vehicle design which help to minimise the energy consumption of high speed rail travel. The life cycle assessment of railway infrastructure is carried out in four stages of a whole life cycle: production, operation, maintenance and disposal, the influence of route parameters on life cycle cost is also investigated. Finally, high speed rail is compared with competing modes of transport, i.e. the aircraft, the automobile and the conventional train, in both operational energy efficiency and whole life cycle analysis. The high speed rail transportation has great advantage over the road and air transport, giving a reduction of carbon emission by roughly 95%, among which the operation stage contributes the largest reduction.
35

Droplet preferential concentration in homogeneous and isotropic turbulence

Lian, Huan January 2014 (has links)
In particle-laden turbulent flow, it has been found both experimentally and numerically that when the particle response time is similar to a turbulent characteristic timescale, particles tend to preferentially concentrate and form clusters. This phenomenon of non-uniform particle dispersion has been referred as preferential concentration. The thesis studies experimentally the preferential concentration of poly-dispersed droplets in homogeneous and isotropic turbulence generated in the facility referred to as the 'box of turbulence' and includes comparisons with Direct Numerical Simulations (DNS). It discusses the effect of poly-dispersion on droplet preferential concentration, temporal evolution of droplet clustering and the turbulent mechanisms (i.e. topological turbulent flow patterns) that may be responsible for the droplet clustering dynamics. The thesis is structured into six chapters. Motivations, theoretical background and related literature of this work are discussed in Chapter 1. Chapter 2 describes the experimental setup and the applied laser diagnostic techniques. Chapter 3 focuses on the effect of poly-dispersion on droplet preferential concentration. The techniques used in quantifying the preferential concentration are the Radial Distribution Function (RDF) and Voronoï analysis. An image processing method for locating droplets from droplet Mie-scattering images has been proposed and evaluated. Chapter 4 reports the time-resolved dispersion measurements of poly-dispersed droplets. The fine scale topological turbulent patterns (i.e. zero velocity/acceleration) are extracted from the fluid flow velocity measurements, considering the effect of experimental noise, and are observed to follow a non-uniform spatial distribution and form clusters. The clustering of zero velocity/acceleration points are quantified by RDF and Voronoï analysis and compared with the dispersed droplet clusters. A cluster identification method based on the mean shift pattern space analysis and the Voronoï tessellation has been proposed and applied to all the temporally resolved images to obtain cluster time scale and length scale statistics. Chapter 5 compares the results from experiments and corresponding DNS calculations using the same data processing methods. The clustering of experimentally and numerically acquired zero velocity/acceleration points and dispersed droplets are quantified and compared. Chapter 6 is the conclusion of the thesis and possible directions of future work.
36

Linear and non-linear ultrasonic NDE of titanium diffusion bonds

Escobar-Ruiz, Edwill Alejandro January 2014 (has links)
Diffusion bonding is an attractive solid-state welding technique that promises weight reduction and improved performance in the aerospace industry. However, its adoption in fracture critical titanium components has been limited by the complications that macroscopic anisotropy introduces to typical ultrasonic NDE. Two strands of ultrasonic NDE, linear and non-linear acoustics, have been studied with the aim of overcoming these complications. A promising linear technique that uses the phase of reflected diffusion-bond signals to extract otherwise hidden interface information was selected for further development. The principal parameters that affect the phase analysis of ultrasonic signals were investigated and their optimisation resulted in up to an order of magnitude improvement in phase measurement reliability, even at low signal-to-noise ratios. The application of these optimised parameters without a priori knowledge of the signal arrival time was illustrated, and the sensitivity of the approach to ambient temperature and annealing effects was also explored. The original technique was susceptible to measurement error and proved impractical for typical aerospace component geometries, but these shortcomings have been overcome by the improvements and adaptations proposed here. However, it was shown that the efficacy of the technique depends on the relative acoustic impedances of the bonded media and, coupled with the sensitivity limit intrinsic to linear acoustic methods, this dependence acted to curtail the benefits of the approach and prompted the exploration of alternative techniques. Non-linear ultrasonic methods are significantly more sensitive than their linear counterparts to the imperfections likely to be present at diffusion-bonded interfaces, but suppressing extraneous contributions to the non-linear response of the interface is not trivial. An approach that succeeds in suppressing such contributions was studied and developed here. The technique, which is based on the non-collinear mixing of ultrasonic waves to generate a spectrally, modally and spatially dissociable third wave, was used to reliably characterise a set of samples whose bond quality was indeterminable using linear ultrasonic methods. Application of the technique to diffusion-bonded titanium aerospace components has been demonstrated and a significant improvement in ultrasonic NDE capability was achieved.
37

The effect of implant misalignment on shoulder replacement outcomes

Sukjamsri, Chamaiporn January 2015 (has links)
Total shoulder arthroplasty is a well-established treatment to relieve pain and restore joint function particularly in arthritis patients. The damaged shoulder joint is replaced with humeral and glenoid components. For success, all replacement components must be aligned properly. However, errors in glenoid component alignment particularly in version is not infrequent due to the complexities such as limited monitoring available during the surgical procedure and glenoid posterior wear, commonly observed in glenohumeral osteoarthritis. Glenoid component version has been found to induce eccentric load and may result in component loosening which is the main indicator for revision surgery. The overall aim of this thesis is to gain the in-depth understanding of how the component version affects the fixation loosening in both cementless and cemented shoulder arthroplasty. Early loosening in cementless arthroplasty is associated with failed biological fixation due to excessive micromotion at the implant-bone interface. To measure interface micromotion, this thesis developed an in-vitro technique based on the application of digital volume correlation (DVC) and micro-computed tomography (μCT). This technique was validated and verified the use of the finite element (FE) method as a tool for investigating the effect of glenoid component version on micromotion. The FE predicted micromotion during a full range of shoulder abduction confirmed that 60° of abduction was the critical position inducting the largest micromotion and large micromotions were shown to be related to increased component retroversion. The condition of the bone was also found to be an important parameter as less stiff bone caused large micromotions.
38

High repetition rate temperature and velocity imaging in turbulent flows using thermographic phosphors

Abram, Christopher January 2014 (has links)
Turbulent flows involving heat transfer and chemical reactions are prevalent in a huge range of applications such as combustors and engines, boilers, and heating and cooling devices. Directly measuring important variables using laser-based techniques has significantly contributed to our understanding of the underlying flow physics. However, many flows of interest exhibit infrequent or oscillatory behaviour, such as flame extinction or instabilities in thermal boundary layers. Capturing the flow dynamics requires simultaneous, two-dimensional temperature and velocity measurements at sampling rates commensurate with turbulent timescales. Typically this means measuring many thousands of temperature and velocity fields per second, yet there are no high repetition rate diagnostics for temperature imaging in practical, oxygen-containing systems, with the essential capability of simultaneous velocity measurements. This thesis presents a novel laser-based imaging technique based on thermographic phosphor particles. There are a huge variety of thermographic phosphors, which are solid materials with luminescence properties that can be exploited for remote thermometry. Here, phosphor particles are seeded into the flow as a tracer. An appropriate phosphor must be selected, and the particle size chosen so that the particle temperature and velocity rapidly assume that of the surrounding fluid. The particles are probed using high-speed lasers and their luminescence and scattering signals are detected using high-speed cameras to measure the flow temperature and velocity at kHz repetition rates. The development of this method is described in detail. Using the thermographic phosphor BAM:Eu, examples of simultaneous time-resolved measurements are presented in turbulent air flows between 300 and 500 K, consisting of a heated jet (Re = 10,000) and also a flow behind a heated cylinder (Re = 700). The technique permits kHz-rate temperature imaging in oxygen-containing environments. These combined diagnostics currently provide a unique capability for the investigation of transient, coupled heat and mass transfer phenomena in turbulent flows of practical engineering importance. A second objective of this work is to improve the precision of the temperature measurement. The characterisation of a different thermographic phosphor with a high temperature sensitivity, zinc oxide (ZnO), is also reported. Temperature imaging using these tracer particles is demonstrated in a jet (Re = 2,000) heated to 363 K, with a temperature precision of 1%. This extends the capabilities of this versatile technique toward the study of flows with small temperature variations. Also, unlike the majority of phosphors previously investigated for thermometry, this phosphor is a semiconductor. Exploiting the temperature-dependent luminescence of this class of materials presents interesting new opportunities for remote temperature sensing.
39

Ship design decision support for a carbon dioxide constrained future

Calleya, J. N. January 2014 (has links)
The future may herald higher energy prices and greater regulation of shipping's greenhouse gas emissions. Especially with the introduction of the Energy Efficiency Design Index (EEDI), tools are needed to assist engineers in selecting the best solutions to meet evolving requirements for reducing fuel consumption and associated carbon dioxide (CO₂) emissions. To that end, a concept design tool, the Ship Impact Model (SIM), for quickly calculating the technical performance of a ship with different CO₂ reducing technologies at an early design stage has been developed. The basis for this model is the calculation of changes from a known baseline ship and the consideration of profitability as the main incentive for ship owners or operators to invest in technologies that reduce CO₂ emissions. The model and its interface with different technologies (including different energy sources) is flexible to different technology options; having been developed alongside technology reviews and design studies carried out by the partners in two different projects, ``Low Carbon Shipping - A Systems Approach'' majority funded by the RCUK energy programme and ``Energy Technology Institute Heavy Duty Vehicle Efficiency - Marine'' led by Rolls-Royce. The model has been used alongside a wider economic and logistic model of the international shipping system, the focus of which is on large cargo ships engaged in ocean-crossing trade, to potentially advise on regulation and what CO₂ emission reductions are possible from shipping. The Ship Impact Model (SIM) allows a large design space to be explored quickly, incorporating economic considerations at a single ship level and supporting combinations of technologies and design and operational parameters. Whilst considering that comparisons against actual ship data have been limited, the model has a high enough fidelity and accuracy to be used as a decision tool in the selection between different technologies (providing the technologies are adequately described).
40

Fabrication of porous particulate scaffolds using electrohydrodynamics and thermally induced phase separation for biomedical engineering applications

Ghanbar, H. January 2015 (has links)
The availability of forming technologies able to mass produce porous polymeric microspheres with diameters ranging from 150 to 300 µm is significant for some biomedical applications where tissue augmentation is required. Moreover, appropriate assembly of microspheres into scaffold is an important challenge to enable direct usage of the scaffolds in chronic wound treatments. In this thesis, the feasibility of the electrohydrodynamic (EHD) atomization forming combined with thermally induced phase separation (TIPS) for production of such drug delivery carriers, using biodegradable polymers (poly (lactic-co-glycolic acid) and poly (ε-caprolactone)) was explored. To achieve this goal, the first part of the thesis describes comprehensive parametric mode mappings of the diameter distribution profiles of the microspheres obtained over a broad range of key processing parameters and correlating this with the material parameters of five different polymer solutions of various concentrations. Based on the mode mapping studies, combination of poly (lactic-co-glycolic acid) (PLGA) and dimethyl carbonate (DMC) was found to be ideal for generating the microspheres within the targeted diameter range (150-300 µm). Surface porosity was achieved by electrospraying the PLGA/DMC solution and collecting the required size of the polymer particles in liquid nitrogen followed by lyophilisation. The second aim of this thesis was the in vitro release studies. In order to conduct this part of the study, the single needle and co-axial needle EHD/TIPS methods were used to generate the dye loaded microspheres of the required size. Three different dyes (Erythrosin B, Pyronin B and Reichardt’s) were selected as model drugs to be encapsulated separately in the produced microspheres. The purpose of selecting three different dyes was to have a prediction on the release profile of immunosuppressants with high toxicity used for treatment of chronic wounds such as perianal fistulae. The in vitro release studies showed that the dyes were released with the high initial burst release phase in 3.5-5.5 hours followed by a long and sustained release phase (in 30-360 hours). Systematic investigations using different external stimuli such as temperature, fresh media and sonication exposure was also carried out to observe their effects on the release rate of the encapsulated materials from the produced microspheres. The results acquired from the in vitro release studies showed that the temperature variations and the sonication with different frequencies have significant effects on the release rates of the incorporated materials from the polymeric microspheres. Moreover, the results demonstrated that the products collected by the single needle EHD/TIPS method is more capable of releasing the payload in a longer period of time with more sustained manner compared to their counterparts obtained from the co-axial needle method.

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