A lack of separation of scales is the major hurdle hampering predictive and computationally tractable simulations of fracture over multiple scales. In this thesis an adaptive multiscale method is presented in an attempt to address this challenge. This method is set in the context of FE2 Feyel and Chaboche [2000] for which computational homogenisation breaks down upon loss of material stability (softening). The lack of scale separation due to the coalescence of microscopic cracks in a certain zone is tackled by a full discretisation of the microstructure in this zone. Polycrystalline materials are considered with cohesive cracks along the grain boundaries as a model problem. Adaptive mesh refinement of the coarse region and adaptive initiation and growth of fully resolved regions are performed based on discretisation error and homogenisation error criteria, respectively. In order to follow sharp snap-backs in load-displacement paths, a local arc-length technique is developed for the adaptive multiscale method. The results are validated against direct numerical simulation.

Electrical power generation using hydrocarbons presents a huge potential owing to their higher power densities and environmental factors associated with lithium ion batteries. Small scale combustors have been widely developed and tested for power generation purpose employing Thermoelectrics and Thermophotovoltaic conversion of combustion heat into electricity. This thesis is concerned with development and investigation of a novel non-catalytic meso scale self-aspirating premixed burner integrated thermoelectric generator for a CO2 Generator device having its application in the insect control industry. Flame stabilisation has been one of the main issues in small scale combustion systems due to higher surface to volume ratio associated with small size of the combustor. Previous research has shown that catalytic combustion is one way of improving flame stabilisation, however employing a catalyst into the system increases the manufacturing cost which can be a significant downside. This research work studies flame stabilisation mechanisms in meso-scale burner which mainly focuses on Backward Facing Step or Sudden Expansion Step and secondary air addition into the combustion chamber. A 250 W premixed burner was developed which was classified as a meso scale burner whose operating parameters were in a range of micro-combustors whereas the size was comparatively bigger due to its integration with standard size thermoelectric modules. The first phase of the research was concerned with development of the burner which included optimisation of the design to achieve a stable enclosed premixed flame as per the design and operational requirements. It was found that flame blowoff can be prevented by addition of secondary air into the combustion chamber downstream of the step. The second phase of the research focused on the integration of the burner with thermoelectric power generators. This involved investigation of various configurations to optimise the electrical power output. The burner integrated thermoelectric unit was then tested in the actual field to validate the concept of integrating combustion and thermoelectrics for small scale power generation applications. The final phase of the research involved a study on the effect of secondary air addition on flame stabilisation in burners employing backward facing step. The minimum secondary air requirement for burner with different step heights was determined. The addition of secondary air cross-stream into the combustion chamber creates stable recirculation zone which reduces the local stream velocity and hence prevents flame blowoff.

Compacted bentonites and compacted sand-bentonite mixtures have been proposed as suitable barrier and backfill materials for the disposal of municipal solid waste and high level radioactive waste. Although unsaturated on placement, the barrier and backfill materials can become saturated subject to the availability of fluid. Detailed understanding of the saturated hydraulic conductivity of compacted bentonites and sand-bentonite mixtures is essential to ensuring the integrity of the waste disposal facility and the long-term protection of the geoenvironment. This thesis is concerned with the experimental determination of the hydraulic conductivity of compacted MX80 bentonite and sand-bentonite mixtures (30% MX80 bentonite to 70% sand). A high capacity fixed ring modified swelling pressure cell was used for carrying out the hydraulic conductivity tests. High precision pressure-volume controllers were used to apply a range of hydraulic gradients between about 1250 and 12500 under constant head conditions. The expansion of the measuring system was studied to account for differences between inflow and outflow water volumes during the hydraulic conductivity tests. The hydraulic gradient was increased and decreased during the hydraulic conductivity tests. Chemical analysis of fluid samples collected from the inflow and outflow reservoirs after each hydraulic conductivity tests provided information about the type and amount of exchangeable cations expelled from the specimens. The inflow volume was calculated based on the system expansions. The hydraulic conductivities were calculated from Darcy’s law. The saturated hydraulic conductivity of compacted bentonite and sand-bentonite specimens were also calculated based on the consolidation tests results. The gas permeability of compacted unsaturated bentonites was determined. The saturated hydraulic conductivity of compacted bentonites was assessed using various existing models. A model based on parallel plate flow was proposed in the current study. The proposed model considered the viscosity of water in the inter-platelet region and its influence on the hydraulic conductivity of compacted bentonites. The correction of the water inflow volume by accounting for the system expansion during the hydraulic conductivity tests provided good compatibility between the inflow and outflow water volumes. The equilibrated inflow and outflow rates were found to be similar during the hydraulic conductivity tests. A linear relationship was noted between hydraulic gradient and hydraulic flux indicating the validity of Darcy’s law for calculating the hydraulic conductivity of compacted bentonites. An expulsion of exchangeable cations from the compacted bentonite specimens occurred during the hydraulic conductivity tests. The amount of expelled cations was found to be less than about 6% of the total exchangeable cations present in the bentonite. The gas permeability of compacted unsaturated bentonite was found to decrease within an increase in compaction dry density. The calculated hydraulic conductivity of compacted unsaturated bentonite based on the measured gas permeability was found to be greater than the measured hydraulic conductivity of compacted saturated bentonite indicating that swelling reduces the hydraulic flow paths. The saturated hydraulic conductivities calculated from the Kozeny-Carman model were found to better describe the measured saturated hydraulic conductivities than the other available models. The model proposed in this study did not satisfactorily establish the hydraulic conductivity of compacted saturated bentonite due to uncertainties associated with the assumptions made regarding the viscosity of the bulk fluid.

The past decade has seen a significant rise in the interest of deploying Marine Renewable Energy technologies. Tidal stream technology is developing rapidly, and developers are favouring horizontal axis turbines (HAT’s). However, vertical axis turbines (VAT’s) are better suited for shallow waters, and higher efficiencies can potentially be gained by utilising shallow water blockage effects. The Severn Estuary is an ideal deployment area in this context. Additionally, due to a large tidal range the estuary has long been the subject of tidal barrage proposals. The original ebb-only STPG barrage has recently been superseded by a two-way generation scheme, therefore the need exists for renewed research into the hydrodynamic impacts of this proposal. Furthermore, little is known about the interaction between tidal range and tidal stream technologies, and if they could coexist in the Severn Estuary. This thesis uses physical and numerical modelling techniques to assess a range of MRE technologies, with particular focus on their deployment in the Severn Estuary. Physical model tests of a number of VAT’s were conducted in a recirculating flume. Device performance and the wake characteristics were assessed, and it was demonstrated that VATS’s could potentially provide competitive performance values if deployed in shallow waters. The CFD code ANSYS CFX was used to predict the unsteady turbine behaviour at the physical model scale; good agreement was achieved with the laboratory data, particularly in predicting the wake behaviour. The CFD model TRIVAST was then applied to the Severn Estuary. Comparisons were made of the Severn Barrage schemes, as well as two hypothetical HAT and VAT arrays. The model results confirmed that vertical axis turbines are better suited to the Severn Estuary, provided that the technology is feasible. Finally, whilst the Severn Barrage proposals would eradicate the HAT resource, a lesser impact on the VAT resource was observed.

A three-dimensional layer integrated morphodynamic model has been developed to predict the hydrodynamic, sediment transport and morphological processes in a regulated reservoir. The model was based on an existing sediment transport model, with improvements being made. A bed evolution module based on the mass balance equation has been developed to determine the bed level change due to sediment transport. The horizontal eddy viscosity coefficient was equated to the depth averaged eddy viscosity, based on the horizontal velocity distribution while the vertical eddy viscosity coefficient was evaluated using the layer integrated form of the - equations. This scheme enhances the accuracy of the computed velocity and suspended sediment concentration distributions. The highly accurate ULTIMATE QUICKEST scheme was used to represent the advective terms in solving the advective-diffusion equation for suspended sediment transport. An explicit finite difference scheme has been developed for the bed sediment mass balance equation to calculate bed level changes. The numerical model was verified against laboratory data obtained from experiments in a trench and a partially closed channel. A physical model was constructed to represent the flow, sediment transport and morphodynamic processes in Hamidieh regulated reservoir. The physical model was designed based on the Froude similarity law and was undistorted. The model sediment size was determined in such a manner that the same ratio of particle fall velocity to shear velocity is maintained for both the model and prototype reservoir. Stokes law was used in calculating the particle fall velocity. The physical model results confirmed that the normal water surface elevation in the reservoir should increase by up to 25 cm in order to reach the nominal flow discharge diverted to the intakes. The numerical model was then applied to the scaled physical model of the reservoir and the associated water intakes and sluice gates. Various scenarios were tested to investigate the effects of different situations of diverting flow and sediment transport regimes, as well as to establish how these operations affect the morphodynamic processes in the reservoir and the vicinity of hydraulic structures. The model predictions agreed with measured data generally well. The numerical model results revealed the possibility of forming sedimentary islands in the regulated reservoir and it is uneconomical to set up a dredging zone near the one of the intakes. In summary, the integrated numerical and physical modelling approach showed many benefits and could help to optimize time and budget for design hydraulic structures. Key words: morphodynamic numerical model, turbulent flow, regulated reservoir, three- dimensional flow, laboratory tests.

In this thesis, two practical models for predicting the drag force exerted on flexible riparian vegetation under hydrodynamic loading have been developed. The models were formulated based on the results of a unique experimental data set that consisted of high resolution force-velocity and physical property measurements for twenty-one full-scale riparian trees, in both foliated and defoliated conditions. One of the models has then been used to numerically simulate the impact of riparian woodland on the flooding characteristics of a mid-catchment river site. Analysis of photographs and video footage of the trees from the experimental study during drag force testing allowed the frontal projected area to be determined, both in still air and as a function of flow velocity. The observed reductions in projected area and drag coe�cient with velocity were normalized using the projected area in still air to provide an empirical relationship between the ‘rigid’ drag coe�cient and area Reynolds number. The resulting drag force predictions were found to be accurate when properly calibrated against the vegetation under consideration. A second, more physically based model to predict the reconfiguration of flexible vegetation has been developed based on dimensional analysis of the relevant parameters, including flexural rigidity. The model utilizes a novel vegetative Cauchy number to determine the extent of the reconfiguration and has been shown to be more accurate than two existing drag force models. The model has also been validated against independent drag force data, demonstrating that it is applicable to vegetation of di�ering scale, morphology and flexibility. Serial and parallel optimizations of an existing two-dimensional hydrodynamic modelling code have enabled detailed numerical simulations of extreme flood events to be undertaken for a mid-catchment river site in Somerset, UK. The results indicated that riparian vegetation has a minimal impact on the downstream flooding characteristics, at least for the small site investigated herein. Significant reductions in key flow properties, namely velocity and bed shear stress, were however observed within the vegetated areas.

Overhead lines are the backbone of electrical power transmission. In most cases, the overhead line provides the best economic and practical solution for energy transmission. Nevertheless, overhead lines suffer more faults due to the vulnerability of the overhead lines to adverse weather condition, transient overvoltage and falling trees. An extensive literature review of existing condition monitoring and impulse a voltage measurement technique of overhead lines are covered in this work, and ultimately leads to the development of the proposed voltage transducer. Although conventional transducers such as voltage transformers and voltage dividers are widely used for monitoring and voltage measurement, yet they have several drawbacks in terms of their size and cost. These are the key factors that limit their widespread deployment for monitoring and measuring voltage on overhead lines and, in particular, rural areas. The proposed transducer is based on a non-contact capacitive voltage probe developed at Cardiff University. However, the proposed transducer uses a high voltage conductor rather than the ground as a measurement reference. The proposed transducer is based on a cylindrical-shaped in order to avoid sharp edges, which can initiate a partial discharge effect. Commercial numerical field computation software packages are used to assist in the development of the proposed transducer for simulation of the electric field distributions around the HV conductor and the transducer. The computed electric field magnitudes obtained on the sensing probe surface are then used for calibration of the proposed transducer. The proposed transducer is developed using low cost materials and tested in a laboratory environment with a low amplitude impulse supply using a surge generator and the corresponding output voltage amplitude obtained from the transducer was validated against a low ac voltage supply using variable output voltage source. The effects of variation in the input voltage, the integrating capacitor inserted between the HV conductor and the sensing probe and height of the transducer above ground on the output voltage amplitude are also investigated. The developed transducer is subsequently tested in field experiments using test overhead lines with low and high voltage supplies. Only a single-phase measurement setup was used in this test as there is only one voltage transducer fabricated in this work. Therefore, each phase of the overhead line was tested individually. Results obtained from the laboratory and field experiments have demonstrated the suitability of the developed transducer for measuring both ac and impulse voltages, which would be useful for fault monitoring on the high voltage overhead lines. However, the computed results obtained from the simulation demonstrated the presence of end-effects at the transducer sensing probe edges. Therefore, an improved design was proposed in this work by introducing a floating electrode between the sensing probe and the guard electrode, with the aim to reduce the fringing effects by preventing the sensing probe from sensing unwanted electric field. The physical development of this improved transducer design is yet to be initiated, and is thus proposed for future work.

Landfill leachate is generated as a consequence of water percolation through the solid wastes, oxidation of the wastes, and corrosion of the wastes. Underdesigned landfill sites allow the leachate to easily pass through the soil strata. This may have an impact on the engineering properties of soils, such as the shear strength and the volume change (compressibility and swelling), and the chemical properties (adsorption and retention of heavy metals). In this thesis, a detailed experimental investigation was undertaken to investigate the effects of landfill leachate contamination on the geotechnical and geo-environmental properties of natural soils of Kuwait. Two soils (a silty sand and a clayey sand) were used in the study. The soils were obtained from the Al-Jahra landfill site based in Kuwait. The leachate was collected from the Al-Qurain landfill site in Kuwait. The results from the direct shear and consolidation tests on compacted soil specimens that interacted with leachate and water indicated that, the influence of contamination was severe on the engineering properties of the clayey sand than that of the silty sand. The geoenvironmental properties of the soils were studied to assess the transport and fate of heavy metals in the soils. Leaching column tests were carried out to establish the breakthrough curves which showed retention of heavy metals (As, Cr, Cu and Ni) by both soils. The results from batch isotherm adsorption tests were used to study the ability of the soils to adsorb heavy metals. The test results showed that, heavy metal adsorption was superior in the clayey sand than that occurred in the silty sand. The leaching column test results was used to validate the HYDRUS 1D software package. The results from the model and the laboratory tests results were found to be in good agreements. The bearing capacity and settlement behavior of the soils were modelled. The settlement behavior of the soils was found to be more pronounced due to the presence of landfill leachate. The conclusions drawn from the experimental and numerical investigations favour a further understanding of some of the key issues associated with the transport and fate of leachate in the surrounding environment of a landfill site.

This thesis presents a study of the bond strength between corroded and uncorroded steel reinforcement and the surrounding concrete within steel reinforced structures. The work is based on concretes manufactured with different types of cement replacement materials, and investigates the influence of the corrosion rate of steel as predicted by concrete permeability. The cement replacement binders included CEM II, blended cements of fly ash (PFA), ground granulated blast-furnace slag (GGBS), metakaolin (MK) and silica fume (SF). The experimental work was conducted by placing 200mm cube test specimens in a saline solution (3.5% NaCl) for different exposure times (3, 7, 10, 14 and 20 days) with an applied external current of 10 mA between the reinforcing steel and a stainless steel counter electrode. Pull-out tests were conducted to evaluate the bond strength between the concrete and the steel reinforcement. The permeability coefficients of concretes were investigated using a relative gas permeability test. The specimens used for determining permeability were cylindrical 100mm diameter and 100mm length, which were oven dried at 105 ºC. The experimental results indicated that the bond strength was governed by concrete properties. Furthermore, the bond strength of the corroded specimens was found to depend on the corrosion levels and varied across all concrete types, depending on the concrete microstructure. Moreover, when the corrosion level exceeded 1.74%, the bond strength began to decline. Thereafter, the bond strength continued to reduce as the corrosion time of the reinforced concrete increased. The relationship between the compressive strength and gas permeability of concretes was inconclusive but the latter does depends on the cement replacement levels. The PFA concretes had the lowest permeability compared to the other two types of concrete (CEM II and GGBS). The permeability of concretes and corrosion rates with different types and levels of cement replacement materials significantly decreased as the age of concretes increased. The improvements in gas permeability and corrosion rate were observed when 40% of cement weight was replaced with PFA. The ABAQUS program was used to model the bond-slip behaviour of different concrete mixes, in addition to a plastic damage model. A cohesive zone element was employed for the steel-concrete interface. During analysis, the numerical model was validated against the results obtained from the experimental tests. The numerical results showed good agreement with the experimental results for CEM II, GGBS and SF concrete specimens, but in the case of PFA concrete where the numerical result of bond strength was overestimated by to the experimental ones.

A direct method for controlling nodal displacements and/or internal bar forces has been developed for prestressable structural assemblies including complex elements (“macro-elements”, e.g. the pantographic element), involving Matrix Condensation. The method is aimed at static shape control of geometrically sensitive structures. The dissertation discusses identification of the most effective bars for actuation, without incurring violation in bar forces, and also with objective of minimal number of actuators or minimum actuation. The method can also be used for adjustment of bar forces to either reduce instances of high forces or increase low forces (e.g. in a cable nearing slack). The techniques of controlling nodal displacement, bar force and simultaneously nodal displacement and bar force for a structure made of non-complex elements have been verified by experiments on the physical model of a cable-stayed bridge. Likewise the technique of joint displacement controlling of structures constructed from complex structural elements, has been also been confirmed by experiments on the physical model of an aerofoil shaped morphing pantographic structure. Overall, experimental results agree well with theoretical prediction. This dissertation also concerns with morphing structures, e.g. as applied in the aerospace industry. A morphing aerofoil structure capable of variable geometry was developed, which was shown to be able to cater for the different aerodynamic requirements at different stages of flight. In this thesis, two suitable morphing aerofoil structures were made of curved pantographic units. Results show that the configuration with a large number of small pantograph elements exhibits a wider range of Lift Coefficient (CL) and Drag Coefficient (CD) than achievable by the first, and also by the standard NACA2415 aerofoil with flaps. In addition, it was found that the morphing aerofoil can decrease the drag by more than 18%, especially in the early stages of morphing. Finally, two useful and relatively simple methods have been presented in this dissertation which provide a direct method for calculating required morphing shape displacements and calculating set of length actuations for bar assembly to adjust shape imperfection. Keywords: Static shape control, Prestress control, Displacement control, Actuator placement, Force Method, Pantographic unit, Morphing structure, Morphing aerofoil, NACA aerofoil, Aerodynamic characteristics.