This thesis presents the computational evaluation of the system configuration and optimisation of a recuperated SOFC-GT system with combined heating cooling and power (CCHP) or trigeneration for marine applications. A comprehensive configuration analysis of a SOFC-GT system is needed to characterise the performance of different system configuration across a range of operating conditions, in order to choose a design point with optimum performance, and carry out off-design analysis. Then, a sensitivity analysis of the effects of changing the components, ambient temperature and air utilisation and fuel utilisation within a safe operating range is carried out. The fuel cell module within the Matlab model simulates methane reforming reactions; and fuel cell electrochemical reaction with the use of Voltage-current (V-i) curve from Siemens Westinghouse experimental SOFC data. The trigeneration model was calculated based on the outlet temperature of the SOFC-GT system as well as the inlet flow rates into the system. A number of system configurations of air conditioning system with conventional Heating Ventilation and Air Conditioning (HVAC) coils, absorption chiller and desiccant wheel are integrated with the existing SOFC-GT system, in order to extract waste heat from the SOFC-GT system exhaust for heating and cooling purposes for the ship. It is found that the recuperated SOFC-GT system is the optimum system configuration. The system efficiency and specific power are both high, when the compressor is operating at 4 bar pressure, with 1250K of turbine entry temperature, fuel cell operating at 1273K, current density at 300mA/cm2, corresponding to 0.704V of fuel cell voltage. When the compressor and turbine designed by the National Technical University of Athens are used in the system with power turbine, the overall thermal efficiency at design point is 59.7%. The hybrid system can operate from 31% to 100% of design point power, when running the system in off-design with air utilisation between 0.1 and 0.25. The choice of compressor and turbine will lead to variations in operating range for off-design. The operating range of the system is bounded by a safety range of air utilisation, which has major effect on the efficiency, total specific power, and gas turbine power split; and fuel utilisation, which is negligible effect on system performance criteria. The ambient condition changes have little effects on the total specific power. However, at higher temperature, the operating line moves closer but not near to the surge line. By using variable geometry compressor and turbine, the operating line can be moved even further away from surge, and this is useful in maintaining system stability when operating in tropical areas. There are also additional benefits of extending the operating range and increasing overall system efficiency, by a maximum of 3% and 1.5% respectively. The Trigeneration model results show that the double effect absorption cooler is the most energy efficient heat recovery unit to be integrated with the SOFC-GT system. When there are fewer occupants in the ship, running fewer HVAC units than designed can reduce the volume of hot air from outdoor, hence requiring less electrical energy for cooling and dehumidification, increasing overall system efficiency. When the number of HVAC units in operation is reduced from 7 to 3 in Ship 1, the maximum number of people allowed indoors (with 18 litres/s per person of air flow rate to ensure freshness of air) is reduced from 138 to 59 persons, but the indoor heat needed to be removed is reduced from 321kW to 242kW. The absorption chiller removes nearly 50% of the heat from the indoor environment when 3 HVAC units are in operations. Hence, the net overall efficiency of the 250kWe Combined Heating, Cooling and Power system is increased from 43.2% for 7 units to 64% for 3 units. Moreover, the net electric power (after air conditioning) available for base load is increased from 74kW to 116kW.

The automotive rear axle is a part of the final drive for front engine, rear wheel drive, road vehicles. The axle is an important component in vehicle dynamics. The task of the axle is to transfer drive to the road surface as efficiently and with as low a mechanical loss as possible. Usually, the rear axle consists of a hypoid bevel geared transmission and a differential. A thermally coupled mathematical model of a hypoid axle is developed to calculate the total power loss in the rear axle. The drive cycle and gear and bearing details along with operating conditions are used as input data. The model also considers gradient, tyre pressure, aerodynamics and external temperature for a given drive cycle. The heat liberated due to mechanical losses at each time step and removed by convection is found, leading to the temperature of the bulk oil and components. Buckingham’s approximate analysis is used to define contact conditions for the hypoid gear pair. Elastohydrodynamic theory is applied to calculate film thickness and traction at the gear and bearing contacts. A tribometer (MTM) is used to obtain lubricant rheological parameters. Empirical formulae are used to find churning, seal and bearing losses. The efficiency of the axle is derived for different lubricants for the specified drive cycle. The prediction of the axle power loss is validated through comparisons with extensive experiments performed on the Ford F150 2010 model and a separate axle test rig, over a wide range of operating conditions. The comparisons between modelling results and test measurements demonstrate that the thermally coupled model is indeed capable of predicting the axle efficiency or temperatures reasonably well. The findings showed that the intended use of the vehicle greatly affected the temperature in the axle and hence determines the ranking order of lubricants. Lubricant rheology strongly influenced the overall efficiency of the axle. A lubricant boundary friction additive was only effective for the most severe drive cycle giving a significant reduction in the axle temperature. A simple test rig was built up to study churning losses of a partly immersed spur gear. This is similar to dip lubrication used in the axle. The influence of variation in air pressure within a cylindrical enclosure was investigated. This test was used to investigate the effect of the gear speed, air density and fluid properties, and used as a lubricant ranking method for churning losses. Lubricant base oils, water and aqueous glycerol solutions were tested using the inertia rundown method. The findings showed that the principal effects are those due to inertia and weight of the oil on the churning power loss. High viscosity lubricants impede gravitational reflow reducing overall losses. When air pressure varied, vacuum (0 bar) in the enclosure increased the power loss by up to 4.5 times, while Compressed air (2 bar) reduced the power loss by up to 2.2 times, compared to atmospheric pressure, for the more viscous oils. Glycerol aqueous solutions give similar trend curve for the losses comparable to oils but an effect of surface tension is predominant. Adding a surfactant to water led to a reduction in the power loss possibly resulting from the effect of the surface tension of the fluid.

Electric vehicles (EVs) are seen as a key future trend in the automotive industry. These vehicles rely on rechargeable batteries to store energy on board. The optimum size of this energy store, often referred to as the battery capacity measured in ampere-hours (Ah) or kilowatt-hours (kWh), depends on the specific application, design limitations, costs and the degradation of the particular battery pack. Validated by 'real-world' driving data from the Imperial College Racing Green Endurance (RGE) flagship electric supercar, the SRZero, a software model following a quasi-steady, backward-forward facing and equivalent circuit approach is introduced. This model is also supported by the results of the 2010, 2011 and 2012 RAC Future Car Challenges as well as by battery life testing from a lab environment. Furthermore, travel surveys from the United Kingdom (UK), Germany and the United States (US) have been analysed and then converted into input parameters for this algorithm. The work considers five different electric vehicle classes ranging from mini cars to sport utility vehicles (SUVs). Results show that varying kerb weights combined with differing levels of driving resistances (aerodynamic drag, rolling resistance, climbing resistance, etc.) lead to reference 'driving forces' of 70-290 Wh/km for the five reference vehicle classes. On average, SUVs consume more than four times as much energy per unit distance as mini cars. Also, driving behaviour has a significant impact on energy consumption and thus on the optimum nominal battery capacity. Empirical data has shown that the mean driving force can vary up to 23% between drivers who follow exactly the same route at comparable traffic conditions and driving another vehicle of exactly the same make and model. Daily range requirements of EVs vary between 150-700 km based on the 95th percentile of the number of all daily trips or the cumulative distance of all trips combined for the UK, Germany and the US. Thus, optimum nominal battery capacities range between 11-203 kWh. In addition, it is shown that the optimum actual size of a battery pack for an electric vehicle depends on the battery's degradation as well. Over time and number of cycles the available capacity as well as the available power fades. This is mainly due to the effects of increased internal resistance, polarisation, corrosion and passivation. Therefore, first it is recommended to reduce the depth of discharge (DOD) to 80% when the battery is in use. Second, a spare capacity at the beginning of life of around 20-40% is recommended in order to satisfy range and power requirements also towards the end of the EV’s lifetime. It follows that the optimum actual battery capacity is around 1.25-1.75 times the optimum nominal battery capacity for an EV.

Environmental, financial and legal reasons demand the development of cleaner diesel engines. Atomization, evaporation and mixing phenomena observed during injection of Diesel fuel affect the produced emissions. To study these phenomena, under engine-like conditions (50bar, 1000K), a chemically preheated constant volume chamber was built. A system of sensors, driven in real-time by a FPGA (Field Programmable Gate Array) and controlled by a Real Time Controller, was built to monitor and control the operations. A modern common rail fuel injection system (Bosch CP3) was driven by a purpose-modified Hartridge 1100 test stand and controlled by the FPGA (Field Programmable Gate Array). Chemical heating is a technique used widely to simulate the ambient conditions of an industrial combustor in a constant volume vessel. A flammable mixture is ignited in an optically accessible vessel, attempting to produce a post-combustion high pressure and high temperature environment. The flammable mixture usually consists of Hydrogen and a Hydrocarbon. Hydrogen is added, to assist with the ignitability of the pre-ignition mixture and to simulate the water present in industrial combustors as a result of exhaust gas recirculation. To this direction, the mole ratio of Hydrogen to Hydrocarbon and the mixture molecular weight were introduced as independent variables for the first time in the literature of constant volume combustion. An initial computer model, assuming perfect combustion, was used for calculation of adiabatic temperature and pressure. A second computer model investigated the effect of chemical dissociation by solving for the minimization of Gibbs energy and was compared to the former one. To verify the calculations, a dual pressure transducer technique and a High-Speed Schlieren technique were used to validate the combustion conditions inside the vessel To further understand the atomization, evaporation and mixing phenomena in sprays, a Diesel spray was visualized using back-illumination and Schlieren High-Speed cinematography at high pressure and room temperature. To understand the evaporation behaviour of a spray and map the vapour fuel distribution, a tracer Laser Induced Fluorescence was applied on a Dodecane/Methyl-naphthalene spray under evaporating and non-evaporating conditions. To compare the experimental findings to the theoretical models in literature, the evaporation of a single droplet in post-combustion vessel gases was simulated using a purpose-programmed FORTRAN code. A supercritical phase change was suggested to explain the sudden phase change and large differences between the theoretical model and the experimental results.

The overarching aim of this work was to concentrate on the mechanical modelling and experimental characterisation of novel open-cell aluminium foam core sandwich panels for prospective use as an airplane wing skin material. A repeating unit cell 2D FE model was created to assess the mechanical behaviour of infinitely long, regularly tessellated honeycomb core sandwich panels. An analytical model using Timoshenko beam theory was developed to predict the Young’s modulus of a hexagonal honeycomb core; there is good agreement between the two models. A microtensile test procedure was developed to determine the mechanical properties of individual foam struts. A FE model of the as-tested struts was created, using XMT scans of the undeformed struts to define the geometry, to establish a method that compensates for grip slippage inherent in the testing of the struts. Strut deformation was described by a calibrated continuum viscoplastic damage model. The damage model was implemented into 3D FE models of an open-cell aluminium alloy foam core sandwich panel subjected to uniform compression to study the effect of varying the strut aspect ratio on the mechanical properties of the core. FE models of the panel subjected to three and four point bending were created to provide a virtual standardised test to assess the core elastic properties. The extent of structural damage in the panels was simulated for indentation loading indicative of a tool strike; an optimal strut aspect ratio was identified providing the best energy absorption per unit mass whilst ensuring core damage is detectable. The effect of morphological imperfections on the mechanical properties and extent of detectable damage of the core was studied. The shear modulus of the core was greatly reduced under the presence of both fractured cell walls and missing cells. The extent of visible damage was largely unaffected by either type of defect.

This thesis presents a detailed study of the performance of a nozzled, double entry turbine. This configuration is primarily found in the turbocharger application and encompasses two different entries, each feeding 180° of a single turbine wheel. The primary motives for this research are to enhance the knowledge and understanding of the behaviour of such a device under steady and pulsating flows including the effect of three different nozzle vane geometries. The work incorporates both experimental and computational analyses. Experimental results show that with unequal admission between the two volute entries the performance of the turbine is greatly affected compared to when both entries are flowing equally. A methodology was developed which successfully linked the unequal admission performance of the turbine to the full admission maps which are more readily available. Pulsating flow was found to affect the average performance of the turbine compared to the steady state characteristics. Examination of the instantaneous mass flow showed a large degree of mass storage in the turbine domain for all conditions of pulsating flow. A new parameter was developed based upon the conservation of mass in order to quantify unsteadiness taking into account both pulse amplitude and frequency. Steady and unsteady computational simulations were undertaken for one of the different nozzle configurations. Entropy generation rate was used to establish the distribution of loss within the turbine. In partial admission the loss distribution within the rotor wheel was found to be different to any case during full admission operation. Under pulsed flow conditions the computational analysis showed that the loss distribution changes throughout a pulse cycle showing that the flow regime will also undergo a large change. The loss distribution within the rotor wheel at one point within the pulse cycle was found to be very similar the equivalent steady state condition.

Interventional Magnetic Resonance Imaging (MRI) is a developing field that aims to provide intra-operative MRI to a clinician to guide diagnostic or therapeutic medical procedures. MRI provides excellent soft tissue contrast at sub-millimetre resolution in both 2D and 3D without the need for ionizing radiation. Images can be acquired in near real-time for guidance purposes. Operating in the MR environment brings challenges due to the high static magnetic field, switching magnetic field gradients and RF excitation pulses. In addition high field closed bore scanners have spatial constraints that severely limit access to the patient. This thesis presents a system for MRI-guided Endoscopic Retrograde Cholangio-pancreatography (ERCP). This includes a remote actuation system that enables an MRI-compatible endoscope to be controlled whilst the patient is inside the MRI scanner, overcoming the spatial and procedural constraints imposed by the closed scanner bore. The modular system utilises non-magnetic ultrasonic motors and is designed for image-guided user-in-the-loop control. A novel miniature MRI compatible clutch has been incorporated into the design to reduce the need for multiple parallel motors. The actuation system is MRI compatible does not degrade the MR images below acceptable levels. User testing showed that the actuation system requires some degree of training but enables completion of a simulated ERCP procedure with no loss of performance. This was demonstrated using a tailored ERCP simulator and kinematic assessment tool, which was validated with users from a range of skill levels to ensure that it provides an objective measurement of endoscopic skill. Methods of tracking the endoscope in real-time using the MRI scanner are explored and presented here. Use of the MRI-guided ERCP system was shown to improve the operator's ability to position the endoscope in an experimental environment compared with a standard fluoroscopic-guided system.

This dissertation addresses two central aspects of bypass transition to turbulence. In the first part, streak instabilities, often referred to as harbingers of breakdown to turbulence, are investigated by means of direct stability analysis. The base flow is computed in direct simulations of bypass transition. The random nature of the free-stream perturbations causes the formation of a spectrum of streaks inside the boundary layer, with breakdown to turbulence preceded by the amplification of localized instabilities of individual streaks. Detailed analyses of two common types of instabilities are performed. The capability of the instability analysis to quantitatively capture the properties of the instabilities observed in the DNS and to identify the particular streaks that break down to turbulence farther downstream is established. Finally, the influence of pressure gradients on the growth of the instabilities is investigated. The second part of the work establishes a novel mechanism for the suppression of bypass breakdown by means of time-harmonic wall forcing. DNS studies show that at the optimal forcing parameters, a substantial stabilization of the laminar flow regime is achieved. The Reynolds number at the onset of fully-turbulent flow increases by a factor of more than three compared to an unforced reference case. Transition delay is attributed to a material weakening of boundary layer streaks. The underlying flow physics are explained through linear analyses. Studies of free-stream disturbances show that the shielding of the boundary layer from external vortical perturbations is significantly increased in presence of the forcing. Furthermore, optimal growth computations demonstrate a substantial reduction of the achievable energy gain through the nonmodal growth mechanism associated with the formation of boundary layer streaks. Stability analyses nonetheless show that forcing with high amplitudes gives rise to an inviscid instability that swiftly undermines the stabilizing effect on the transition process.

The prospects of utilising the laser induced phosphorescence emission of common ketone tracers in the study of multi-phase (gas-liquid) flows are investigated within the context of this thesis. The quantification of evaporated fuel concentrations in the vicinity of liquid droplets by means of the laser induced fluorescence imaging technique, and the measurement of fuel concentrations in sprays containing sub-pixel sized droplets by means of the laser induced exciplex imaging technique suffer from well-known limitations; the former is plagued by low vapour phase signal intensities and halation, and the latter by liquid-vapour crosstalk and quenching. Therefore, a literature research was initially carried out, focusing on two main topics: the underlying photophysics of the processes involved in the excitation and deexcitation mechanism of the tracers under investigation, and the relevant optical techniques available for carrying out vaporized fuel concentration measurements in two-phase flow environments. Following a description of the experimental apparatus, a series of calibration experiments is presented. The liquid phase phosphorescence properties of acetone and 3-pentanone were investigated in the bulk and in liquid streams, and the phosphorescence emission characteristics of both tracers were quantified for different bath gas compositions. The phosphorescence signal of gaseous acetone was calibrated for the excitation energy and concentration dependencies. Based on the calibration data, a new technique was developed for the purpose of investigating the vapour phase concentration in the vicinity of liquid droplets. The proposed technique utilizes the phosphorescence rather than the fluorescence emission of vapour and liquid acetone, and is compared with the well-established laser induced fluorescence technique (LIF), in both evaporative and non-evaporative monodisperse droplet streams. The obtained results suggest that laser induced phosphorescence (LIP) imaging clearly improves upon laser induced fluorescence imaging, by successfully addressing both the high signal intensity disparity between the two phases and the ensuing halation that plague measurements carried out by deployment of LIF. The fluorescence and phosphorescence emission of acetone and 3-pentanone, the latter considered in order to demonstrate the feasibility of LIP imaging by deployment of other common ketone tracers apart from acetone, were also examined in sprays by means of a high-pressure gasoline direct injection system. Experiments examining the emission from both electronic states and their potential correlation are presented for non-evaporative sprays.; in particular, liquid phase corrections are carried out in LIF images by deployment of their corresponding LIP images and the obtained correlation functions, and the ensuing errors are quantified. Finally, mean and median filters are employed in limiting these errors and assessing the feasibility of the proposed technique. The obtained results are rendered encouraging, with suggestions for improvement focusing on reducing the noise observed in the LIP images by both signal augmentation and enhancement in the efficiency of the collection optics.

Aircraft, containers, and storage tanks contain plate-like structures that are safety critical. The structures often undergo non-destructive inspections. The inspection frequency tends to be over-conservatively high, and it may be possible to reduce the intervals between inspections to realize cost savings. This goal can possibly be realized by automated structural health monitoring (SHM) of structures using sparse active guided wave sensor arrays. Guided waves are sensitive to small defects and can propagate long distances across feature dense plates. Thus, a guided wave SHM system that enables reliable detection of critical defects or monitoring of their growth can potentially be used to reduce the frequency of inspections for real structures. Industrial guided wave SHM systems must be reliable throughout prolonged exposure to temperature, humidity, and loading changes encountered in operation. Research at Imperial College shows that temperature compensation and subtraction between monitored guided wave signals and baselines acquired from healthy plates enables detection of 1.5% reflection change over areas ~1 m^2 in the presence of thermal swings and uniform liquid layers. These results and findings from scattering studies indicate it may be possible to detect reflections from hole type defects and notches affecting structures during their operation. An issue is that demonstrations of SHM system capabilities have only been shown in controlled laboratory tests within short periods following baseline acquisition. There is concern whether sustained exposure to service conditions will subject transducer elements to irreversible changes and introduce variability in baseline subtraction results that would mask signals due to slowly growing damage. This thesis studies the reliability of guided wave SHM for monitoring plate-like structures over longer time periods. The theoretical characteristics of the fundamental Lamb waves and their use to monitor and detect damage are reviewed. Strategies for sensing and signal processing are described alongside experimental validation of their performance. The effectiveness of the SHM system is tested in experiments where damage-free plates are exposed to British weather as well as thermal variations in an environmental chamber. The monitoring capabilities of bonded piezoelectric sensors are quantified and compared to the performance achieved using electromagnetic acoustic transducers. Experimental results and findings from simulations of bonded piezoelectric transduction establish that performances achieved with bonded sensors degrade due to variations in the properties of adhesives used to attach sensors to plates. EMATs are relatively stable and capable of enabling detection of 1.5% reflection change at points away from the edges of plates after sustained exposure to thermal cycling loads.