This thesis investigates the combustion of fuel compositions representative of those produced by the integrated steelmaking process. As organisations strive for improvements in utilisation efficiency with increasingly complex technologies, more detailed understanding is required to accurately simulate combustion of the potentially weak and dilute fuels, and thereby aid design processes. Dynamic fuel properties have been characterised through experimentation, in addition to a comparison of numerically simulated results obtained from chemical kinetics. The parameters identified to investigate fuel behaviour were laminar burning velocity and Markstein Length, and characterised with regard to operational instability in practical combustion systems. The design and construction of a suitable experimental rig is detailed, as required to facilitate the accurate determination of burning velocities by quantifying the outward propagation of spherical flames. A regressive analytical technique was developed based on previous studies, nonlinearly relating propagation to change in stretch rate. The developed solution was benchmarked against analogous studies in literature, and ensured experimental performance was accurate and repeatable for the well documented combustion of methane. Steelworks gases were tested to attain representative burning velocities, with significant attention paid to the change resulting from fluctuation in blast furnace gas H2 fraction. The study characterised the observed sensitivity to change in flame speed and discussed the implications with regard to practical combustion systems. Several methods of reducing the measured fluctuation are subsequently quantified, including change in ambient condition, and relative humidity. Non-monotonic behaviour was observed for the latter effect, with a suggested trade-off between a chemically catalytic influence on intermediate species, and lowering of flame temperature. Consequently this suggested water addition could be an effective mechanism for the reduction of H2 induced flame speed variation for blast furnace gas, and influence other synthesised fuels comprising large quantities of CO, including BOS gas. Additional steelworks gases were blended in different ratios to assess dynamic combustive properties relating to fuel flexibility, and the effectiveness of minimising fluctuation in combustion behaviour.

Due to the fast growth of digital technology, daily activities can be easily captured and saved in digital images, and then transmitted via the Internet. Therefore, the huge amount of digital images need to be protected through authentication techniques. This thesis is concerned with digital image authentication (DIA) techniques used for anti-falsification, copyright protection and access control. DIA techniques can be generally categorised into data-hiding-based digital image authentication (DHBDIA) techniques and non-data-hiding-based digital image authentication (NDHBDIA) techniques, which are both studied in this thesis. DHBDIA techniques, which are also called watermarking schemes, realise image authentication by imperceptibly embedding a piece of authentication information into images. In this thesis, three watermarking schemes are proposed to serve different purposes. To improve the performance of current clustering-based watermarking schemes, an expandable progressive exponential clustering (EPEC)-based watermarking scheme is proposed, which embeds secret data in the host image by progressively and exponentially clustering the colour intensities in the spatial domain, expanding the cluster table under predetermined constraints and substituting the intensities in the same clusters. This scheme strikes a better balance between embedding capacity and embedding distortion than traditional clustering-based watermarking schemes. To enhance the security of current quantisation-based watermarking schemes, an adaptive quantisation index modulation (AQIM)-based watermarking scheme is proposed, which adaptively modifies the quantised values in the embedding phase, consequently preserving the histogram of the image and closes the security gap. For the image authentication, a repetitive index modulation (RIM)-based watermarking scheme is proposed to set up a non-deterministic dependence among pixels. This scheme achieves higher security and lower distortion than traditional LSB-based watermarking schemes. Meanwhile, to study the applicability of DHBDIA techniques, a multifunction digital image authentication system for medical image management on PACSs is proposed to perform three different security assurance functions, namely role-based access control, patient’s medical information integration with mammograms and forgery detection. In the study of the NDHBDIA techniques, a colour-decoupled photo response non-uniformity (CD-PRNU) is devised to serve as a camera fingerprint for both source camera identification and content integrity verification. In the image acquisition process, colour filtering and interpolation are two important operations that introduce large amounts of noise, which are not included in the traditional PRNU definition. The proposed CD-PRNU extends the traditional photo response non-uniformity (PRNU) extraction model by including such types of noise. As a result, the CD-PRNU is more accurate and effective in camera identification and content integrity verification. The main feature of the proposed CD-PRNU extraction algorithm is that it can separate physical colour components and artificial colour components without the prior knowledge about the Colour Filter Array (CFA) and then extract the PRNU from each individual colour channel, thus preventing interpolation noise of artificial components from diffusing into the sensor pattern noise of the physical colour components.

Autonomous navigation, e.g., for mobile robots and vehicle driver assistance, rely on intelligent processing of data acquired from different resources such as sensor networks, laser scanners, and video cameras. Due to its low cost and easy installation, video cameras are the most feasible. Thus, there is a need for robust computer vision algorithms for autonomous navigation. This dissertation investigates the use of multiresolution image analysis and proposes a framework for autonomous navigation. Multiresolution image representation is achieved via complex wavelet transform to benefit from its limited data redundancy, approximately shift invariance and improved directionality. Image enhancement is developed to enhance image features for navigation and other applications. The colour constancy is developed to correct colour aberrations to utilize colour information as a robust feature to identify drivable regions. A novel algorithm which combines multiscale edge information with contextual information through colour similarity is developed for unsupervised image segmentation. The texture analysis is accomplished through a novel multiresolution texture classifier. Each component of the framework is initially evaluated independent of the other components and on various and more general applications. The framework as a whole is applied for drivable region identification and obstacle detection. The drivable regions are identified using the colour information. The obstacle is defined as vehicles on a road and other objects which cannot be part of a road. Multiresolution texture classifier and machine learning algorithms are applied to learn the appearance of vehicles for the purpose of vehicle detection.

This thesis is concerned with an investigation into some aspects of the permeability measurement and permeability characteristics of reconstituted saturated supreme kaolin clay. Development of permeability anisotropy is investigated when the sample has experienced: (1) anisotropic consolidation, and (2) undrained shear. Conventional step-loaded consolidation tests, constant flow rate and some constant head permeability tests were conducted on the kaolin slurry and block samples. For every conduct of testing, a pair of identical samples were tested: one underwent vertical drainage and the other radial drainage conditions. Both, however, were subjected to one dimensional deformation in the vertical direction. Permeability of the clay was evaluated both directly and indirectly, from results of the permeability tests and consolidation tests, respectively. Data from the constant flow rate and constant head permeability tests yield the same values of permeability for both cases of vertical or radial flow (kv not necessarily equal to Kh). Theoretical considerations of the transient phase of the experimental record of the constant flow rate permeability test are found to be applicable to form the basis of evaluation of permeability, coefficient of consolidation, and coefficient of volume compressibility of the clay sample. Experimental results showed that during the progress of anisotropic consolidation of the kaolin slurry, the clay's vertical and horizontal permeability exhibited unique relationships with the void ratio which are linear on the logarithmic-linear scale [linear (lg k vs e) plot ]. These relationships were found to be independent of the overconsolidation ratio. A lack of permeability anisotropy was observed in the early part of compression or at the initial void ratio, e = 3.1, but as the compression proceeds, development of permeability anisotropy was observed to reach a value of up to 2.1 which correspond to a void ratio of 1.30, where the corresponding vertical effective stress was 530kPa. Experimental results for the block samples that had experienced undrained shear also showed the unique relationships of the clay's vertical and horizontal permeability with void ratio. Development of permeability anisotropy, however, was somewhat in opposition with that of the slurry sample observed during anisotropic consolidation. For samples sheared to vertical strains of 7.9 to 11.5%, an initial permeability anisotropy of 1.3 at a void ratio of 1.66 was observed to decrease with compression and developed into isotropic condition at a void ratio of 1.50, where the corresponding vertical effective stress was 120kPa. For samples sheared to vertical strains of 2.0 to 5.0%, an initial permeability anisotropy of 2.5 at a void ratio of 1.30 was observed to decrease very little with compression and the degree of anisotropy remained to a value xiv of 2.3 at a void ratio 1.05, where the corresponding vertical effective stress was 480kPa. Solutions from both the Terzaghi's and Biot's consolidation theories were used to evaluate the experimental data of the axisymmetric problem of consolidation with radial drainage to inner and outer fixed boundaries. Compared with measured values, permeabilities of the samples calculated from both the Terzaghi's and the Biot's solutions and using the Taylor'S square root of time method, are underestimated by a factor of 10 to 100 (ie. kcal/km = 1110 to 11100). Furthermore, the calculated permeabilities are less orderly in the l9.k vs e plot while the variation is more ordered and linear for the measured values.

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This thesis has presented experimental and finite element (FE) analyses of the static and ultrasonic forming of two metals; aluminium 1050 and magnesium AM50. Aluminium and magnesium are considered to be soft metals and can be easily shaped by any of the main industrial metalworking processes. Frequently aluminium and magnesium have been the subject of research studies. These two metals most commonly chosen in manufacturing industry because of their cost, mechanical properties and flexibility in processing. In this research, simple compression and forming tests were designed and the effects of superimposed ultrasonic excitation on workpiece and die, which is tuned to a longitudinal mode at 20.8 kHz, were studied via stress-strain measurements. Research through experiments and finite element simulations studies in the application of ultrasonic excitation has been carried out to gain quantitative understanding of the mechanisms of improvement in ultrasonic forming characteristics, such as a reduction in material flow stress and oscillatory stress. This research study has shown these mechanisms by applying ultrasonic vibration to the tool and die in the forming test and, similarly, effects were measured and predicted in the experimental and numerical analysis. The development and application of high power ultrasonic techniques in forming processes required the use of specifically designed ultrasonic components to correctly transmit the energy from the transducer to the workpiece and die interface. The application along with the ultrasonic vibration amplitude required for the process, were considered in order to design the most suitable horn profile. In this study, a 20 kHz transducer was used to provide up to 10 µm of peak-to-peak vibration amplitude, depending on the generator setting. Therefore, the booster and horn were designed to provide a range of ultrasonic vibration amplitudes between 5 to 20 µm and also used as a tool and die in the study of ultrasonic metal forming. The horn was designed using finite element modelling (FEM), and modal frequencies and associated mode shapes were subsequently confirmed using experimental modal analysis (EMA). The ultrasonic system has been measured and calculated as having a longitudinal mode of vibration at 20.8 kHz and to provide an amplitude gain of four. In this study, a generator uses mains electricity to generate a high frequency ultrasonic signal to drive the transducer, which is tuned to a specific frequency of 20 kHz. The booster and horn were designed to meet the criteria of transducer, which is to provide a longitudinal vibration at tuned frequency of 20 kHz. However, the profile of booster and horn have been measured and calculated as having a longitudinal mode of vibration at 20.8 kHz, which is considered close to the transducer tuned frequency. The review of previous studies of superimposed ultrasonic excitation on upsetting showed that the most experimental characterisations of the volume effects mainly depended on an interpretation of measurements of the mean flow stress, and have neglected the oscillatory stress. In this study, the characteristics of oscillatory stress and the material behaviour in plastic deformation when superimposed ultrasonic excitation is applied on a static compression test under dry friction were considered. The effects were explained in terms of flow stress reduction, oscillatory stress, mean flow stress, maximum and minimum path of oscillatory stress in the stress-strain diagram. The results showed that the static flow stress of compressive deformation was lowered by the ultrasonic vibration superimposed on the static load and this phenomenon has been referred to as the material softening mechanism which is influenced by volume and surface effects. The volume effect is defined as a reduction in flow stress of the material being formed and the surface effect is defined as a reduction in frictional conditions at the interface between the vibrating device and the workpiece. Finite element models were used to investigate numerically the volume and surface effects during ultrasonically assisted compression. The finite element models were developed using material model parameters which were identified from the experimental analysis. The influence of volume and surface effects were investigated separately in the FE model and it was shown that the volume effect dominated the effective material softening results during ultrasonic excitation. The application of ultrasonic excitation on metals under plastic deformation conditions has been investigated previously. Most researchers have reported that superimposing ultrasonic excitation on metal working processes reduced the material flow stress. A further study of superimposed ultrasonic excitation on a static load during elastic deformation in metal working was not investigated, so it is not possible to determine the effect of ultrasonic excitation on the material. In this study, the investigation of oscillatory stress behaviour in the ultrasonic compression test of cylinder metal specimens during elastic deformation was carried out. In the stress-strain diagram, the ultrasonic vibration was shown to have lowered the static flow stress during elastic deformation under dry contact conditions and it was found that the reduction in static flow stress linearly increased with ultrasonic vibration amplitude. The stress reduction was influenced by volume and surface effects which occurred during the superimposed ultrasonic excitation. The results also showed that the maximum path of oscillatory stress exceeded the static flow stress, however, the mean flow stress is lower than the static flow stress at the onset of ultrasonic excitation. To investigate the influence that volume and surface effects have on material softening during experimental compression tests, a series of FE models were developed. As mentioned previously, the FE models were developed using material model parameters which were identified from the experimental analysis in Figure A1, however, the mechanism of flow stress reduction which is related to acoustic softening and friction reduction which is labelled as (i) cannot be predicted in FE models. The FE models adopted the material softening effects in order to simulate realistic stress reduction compared with experimental results. The significant stress reduction in the FE analysis was obtained by adjusting the yield stress and contact conditions parameter. It was concluded that the surface effect dominated the stress reduction during metal upsetting test in elastic deformation. The study continued to a simple forming test where samples of flat sheet metal were forced into a shaped die by a shaped plunger on a test machine. The results of this study illustrated how ultrasonically assisted metal forming resulted in a lowering of the static forming force during ultrasonic excitation of the die. As a result, the static forming force was seen to be reduced by ultrasonic excitation of the die and the path of the maximum oscillatory force was observed to be parallel to or below the path of the static forming force. Force reduction was measured in these experiments using a high power ultrasonic transducer and also by tuning the die and then the punch during the metal forming test. It was found that a good coupling between punch, specimen and die allowed ultrasonic energy to be effectively transferred into the materials during superimposed ultrasonic excitation in the static forming test. This thesis has concluded that evaluation of the benefits of ultrasonic excitation not only relied on measurements of the mean flow stress alone but also on measurement of the oscillatory stress during superimposed ultrasonic excitation on forming tests.

Gallium nitride based transistors will make up a large portion of the power electronics and the microwave electronics sectors in the very near future, replacing traditional materials such as silicon (Si) and gallium arsenide (GaAs). The work in this thesis focuses on AlGaN/GaN high electron mobility transistors (HEMTs) in particular, with the aim of gaining the maximum potential out of them with regards to breakdown voltage. GaN based devices are able to breakdown at higher voltages compared to Si or GaAs due to its wider band gap (3.4 eV compared to 1.1 eV and 1.4 eV respectively) and although a lot of work has been invested into these devices over the last two decades or so, their full potential has yet to be realised and new solutions are still sought to provide a complete engineering solution which will make them competitive and commercially viable. One of the main obstacles is the high electric fields generated at the drain side of the gate which have prevented these devices from reaching their theoretical breakdown fileld of around 300 V/um. In an attempt to overcome this, several approaches have been investigated in this thesis including metal insulator semiconductor HEMTs (MIS-HEMTs), `gate overlapping' HEMTs, where the gate partially overlaps the source and drain contacts and finally a device employing a Schottky source and a Schottky drain contact. The results given show that a MIS-HEMT can have a substantially larger breakdown voltage compared to a Schottky gate HEMT which is clarified through qualitative simulated electric field work and experimental work. Further, the MIS-HEMT shows a high breakdown field of about 87 V/um when a Schottky drain contact is incorporated. The gate overlapping HEMTs attempts to mitigate completely the large electric field found at the drain edge of the gate. Simulated and experimental results are given for this device concept and reveal that the large electric field peak is indeed removed, however, low breakdown voltages are still incurred due to the closeness of the gate edge to the drain contact. Finally, results are given for a device employing Schottky source and Schottky drain contacts and reveals that present theory may not completely describe the operation of this device.

This work is primarily concerned with the structural response of steel I-section beams and columns heated along one flange to the elevated temperatures likely to be reached in real fires in buildings or ISO 834 fire resistance tests. Experiments have employed nominally full size models, heated using high powered, ceramic insulated, electrical heating elements at temperatures up to 1000°C. The experiments have been conducted on: a non-loaded, simply supported beam; a design-loaded, simply supported beam; a non-loaded 2-span beam on simple supports; and design-loaded, pin-ended columns free to bow about both axes. Load, displacement and temperature data have been recorded and analysed for a number of heating, imposed loading and restraint conditions likely to be met in practice. One of the experiments simulates the loading and restraint conditions used in the BS 1476 : Part 8 : 1972 standard fire resistance test on beams. The data may be used as benchmarks for the validation of analytical studies. Simple theories f or the bowing displacements of non-loaded members having temperature gradients across the section have been derived and validated not only with the model experiments but also with data from full scale compartment fires in a collaborative programme of research undertaken by the British Steel Corporation Swinden Laboratories and Fire Research Station. The practical application of the theory has been demonstrated in other ways. A finite element method, using the PP.FEC program, has also been used which takes account of phase transformation - the sudden temporary shrinkage in steel as it is raised above a temperature of 720°C - but it has not proved possible to use PAFEC for plasticity analyses of beams or columns at elevated temperatures. The phenomenon of' reverse direction bowing has been observed In the model column tests and this confirms observations made by other workers.

The main objective of this work is to study the applications of critical state soil mechanics to simple shear testing. The problems with the simple shear apparatus and the approach for interpreting simple shear test results are described. Laboratory tests were conducted using the NGI simple shear apparatus, standard shear box arid computer controlled stress path testing equipment for samples with 38 mm and 100 mm diameter. The test programme comprised simple shear and shear box tests on remouled, reconstituted and undisturbed samples of Cowden till and London clay, undrained triaxial tests on reconstituted arid undisturbed London clay and stress probing tests on undisturbed London clay. Simple shear samples were tested under either constant effective vertical stress or constant volume condition. Basic results for one-dimensional compression arid for shearing obtained from 72 simple shear tests, 27 shear box tests and 16 stress path tests are presented. Analyses of the simple shear test results indicate that the critical state friction angle for horizontal planes is dependent on whether the sample was sheared under constant or constant volume condition and on the pre-shearing value of K0 which is a function of overconsolidation ratio. A theory for the critical states of simple shear tests which takes into account the influence of K0 is proposed. The normalised test data show that the overall patterns of the simple shear and triaxial tests are as predicted by the critical state model. Tangent stiffnesses instead of secant stiffnesses were calculated. For simple shear tests, the shear stiffnesses obtained from constant shearing are the same as those obtained from constant volume shearing. For London clay, the normalised shear moduli for undrained triaxial tests have the same order of magnitude as those for constant volume simple shear tests. Results of probing tests show that undisturbed London clay is linear anisotropic elastic. The elastic parameters for the constitutive equations can be measured from special stress paths.