Objective of this research was to develop models that capture the entrainment, breakup and transport of gas bubbles in solidifying TiAl castings. The candidate has reviewed the literature, programmed in FORTRAN code, and validated a number of competing techniques for two phase flow relevant to the filling of moulds. He has developed a hybrid (Donor-acceptor/ Level Set) method, which captures the characteristics of gas bubbles based on the surface tension —fluid inertia balance on the free surface. He has demonstrated the ability of this method to reproduce observed phenomena. The candidate also conducted an experimental campaign in Birmingham University under the supervision of Dr R.A. Harding to provide real casting data for his simulations. KAP Edited extract from RD3 MPhil/PhD form: "This research was carried out at the University of Greenwich in conjunction with the University of Birmingham as part of a larger EPSRC- funded project concerned with the development of a casting process route for the production of gamma-TiAl components. Focus of the research was the development of a model of entrained bubbles in the metal casting process. This model comprises the combination of several physical phenomena coupled within the PHYSICA multi-physics framework. The key areas the research has touched on are, surface tension modelling and free-surface modelling using the finite volume technique. A model has been developed that simulates bubble formation during the filling of castings due to surface entrainment and subsequent motion. Once entrained these bubbles tend to solidify in the casting where the rate of solidification is too fast for escape by buoyancy. This problem is particularly acute in thin blade sections of TiAl, where sufficient superheat cannot be maintained during the casting process. Mould filling techniques have to be modified accordingly to improve the mechanical integrity of components. Two phase systems with a sharp, well-defined interface governed by surface tension are required to be modelled. The Level Set Method (LSM) is such a method, used to maintain the position of the interface as it moves through a fixed computational grid. The interface is moved or distorted by the advection equation. In this case two numerical methods are used in differencing: Van-Leer and Donor Acceptor. The Donor Acceptor method is of use when modelling highly dynamic surfaces, such as those encountered during the metal pouring phase in castings, or when fuel sloshes in a fuel tank. This method is best for capturing the entrapment of large bubbles of gas by surface folding. A process directly related to the moving surface. However, the LSM, which allows many surface properties to be calculated, cannot be used in conjunction with the Donor Acceptor method which uses heuristics to sharpen the interface in each compu6tational cell. Once bubbles are formed, their existence and motion are governed by the action of surface tension, therefore the mathematically more rigorous Van-Leer differencing scheme is used in conjunction with the LSM. Bubbles are then tracked using the freesurface method. The tracking limit is determined by the fineness of the mesh used. Sub grid bubbles or bubbles that only occupy a small number of cells can no longer be tracked in a continuum Eulerian simulation. Lagrangian particle tracking is then necessary. The original work in this research can be described as the coupling of the formation of bubbles using the Donor Acceptor method, with the LSM / Van-Leer technique for their subsequent motion and behaviour. This involves: • Modelling the initial free-surface dynamics with the Donor Acceptor technique. • Modelling bubble formation using the Donor Acceptor technique. • Using Results from bubble formation database to "re-start" the simulation with the inclusion of surface tension. • Tracking bubbles as a free-surface, computing their subsequent break up or coalescence • Once the bubbles reach a minimum size for a given mesh, continue tracking using the Lagrangian particle tracking technique. The model was applied to: • Simple validation experiments to test the correctness of the coding • Sloshing/collapsing column experiments to evaluate bubble formation • Simple geometry situations where the combined model is used with Bubble Formation/Tracking Surface Tension • Model the filling of the flat plate experimental setup Future work (not completed ...) • Develop criteria for switching between the Eulerian (free surface) and Lagrangian (particle tracking) scheme • Compare with Experimental Data obtained at the University of Birmingham • Run 3D Cases representing real geometries with HT and solidification • Model the counter-gravity filling process"

This research was initiated by carrying out an extensive literature survey on the current inter-relationships between Manufacturing Business Improvement Methods (MBIMs). The review highlighted that one particular improvement concept is lean manufacture. This review carried out an investigation into the lean environment and assessed many applications of the concept. The literature survey also highlighted restrictions to lean thinking. It is been proposed how some of these limitations can be alleviated by introducing other MBIMs into an integrated methodology. The research assesses currently practised MBIMs and reveals that these methodologies have differentiating relationships, thus producing many types of implementation strategies. The research resulted in studying the inter-relationships between these MBIMs including cultural issues surrounding process improvement initiatives, so they can be unified into an integrated methodology creating a unique strategy that can be correctly tailored to a chosen environment. This research outlines a proposed design methodology that involves ten stages of change including the planning, creating, data collection, analysis and strategic implementation to apply. The approach flows through the change process systematically highlighting how to achieve the best outcome. Feedback into the system is also visible. The proposed design methodology incorporates significant findings from the research, as it highlights the originality of the amalgamation of both the technical and cultural transformations, which are two very different aspects, but highly important factors of change. By considering the two factors, a more harmonious approach in implementing the MBIMs within a company is achieved, therefore resulting in a higher success rate of change. A number of case studies illustrating the implementation of the proposed design methodology is also presented.

In the current, environmentally-aware, climate aircraft designers are under increasing pressure to produce fuel efficient vehicles. Weight reduction is an important method for increasing fuel efficiency. Fibre reinforced polymer (FRP) composites are known to offer weight savings over traditional metallic components, due to their excellent stiffness and strength to weight ratios. However, the major limiting factor for the use of aerospace quality composites is the manufacturing cost. The costs incurred in the conventional process of prepreg cured in an autoclave are well documented. The research in this thesis is concerned with reducing the cost of manufacturing aircraft standard carbon fibre composite sandwich panels, whilst maintaining mechanical performance. The overall aim of the EngD is to provide a unified approach for assessing the performance of carbon fibre sandwich secondary structure that are manufactured using several different techniques. Cost and performance criteria are defined so that an optimal panel can be produced. The work has been motivated by the industrial sponsor, GE Aviation Systems. Five combinations of raw material and processing techniques, manufacturing options (MOs) were considered in incremental steps from the baseline of unidirectional prepreg cured in an autoclave to the noncrimp fabric (NCF) infiltrated using resin film infusion (RFI) and cured in a conventional oven. For cost and performance analysis a generic panel has been designed that is representative of secondary wing structure on commercial passenger aircraft. The cost was estimated by monitoring the manufacture of generic panels using each MO, whilst the performance was measured by both mechanical characterisation tests and by full scale tests on a custom designed rig. The rig applies a pressure load using a water cushion and allows optical access to the surface of the panel enabling the use of optical techniques, i.e. thermoelastic stress analysis (TSA) and digital image correlation (DIC). Feasibility tests on TSA and DIC demonstrated their use on the materials considered in this thesis, and were used to validate finite element (FE) models. The RFI out-of-autoclave process was found to reduce generic panel manufacture time by almost 30%, and the material cost was reduced by almost 40%. The mechanical characterisation tests suggested the ‘new’ process could produce laminates with a similar fibre volume fraction to that of the original process and similar in and out-of-plane mechanical properties. The in-plane stiffness was slightly reduced by 7 %, but the strength showed an increase of 12%. Full scale tests on the generic panels using point out-of-plane deflection measurements and full field TSA demonstrated the panel produced using the ‘new’ process has adequate performance. Moreover the full-field tests indicated an improvement in performance. Further work is required to optimise the design of the panel for weight, in particular the weight of the raw material, and investigating methods for modelling the NCF for certification.

The role of voids in composite failures has not been well understood or been characterized. This study presents the result of an investigation aimed at examining the mechanical behaviour of unidirectional carbon fibre-reinforced polymer matrix materials as used by the wind turbine industry. The experimental program investigates the effect of the void content, different manufacturing methods, type of loading (the three-point bending vs. the four-point bending) on the static strength and fatigue life under a flexural load. The four ply unidirectional carbon/epoxy composites were manufactured using the SPRINT and prepreg manufacturing methods. Manufacturing by these methods has successfully produced the composite materials with varied void contents and the voids are found to concentrate primarily in the area where the adjacent plies meet. The SPRINT materials contain voids in the range of 1.63- 2.89% while the prepreg laminates have an average void content of 3.6% for the debaulked laminates and 6.8% for the non-debaulked laminates. The voids in the SPRINT laminate are small and they are distributed inhomogeneously. The majority of the voids are less than 0.04 mm2 in size with a shape between a circle and an ellipse. The three point bending tests show that the flexural strength exponentially decrease as much as 6.4% for the SPRINT and 6% for the prepreg for every 1% increase of the void content. The similar void effect for both materials may be due to their similar microstructures. There is a similar effect on the increase in the void content for the flexural strength and the flexural fatigue sensitivity for both the three and four point bending tests. This means that the voids do not play any large role in the three-point bending as compared to the four point bending. The mechanism of failure is observed using the optical microscopy and the X-ray tomography of the polished edge and cross section of the area near the failure. The voids are found to interact with the cracks in both the static and fatigue failures. The image of the cross section near the failure area of the static test samples seem to suggest that the voids coalesce to each other under loading. By using the acoustic emission, it can be confirmed that a major failure occurs due to the fibre breakage. In addition, the acoustic emission results also show that the failure behaviour of the low and high void content specimens is significantly different.

Laminated fibre reinforced polymer matrix composites have been used in design and manufacture for more than 50 years, exploiting desirable material properties such as high specific strength and stiffness, enabling large weight savings to be made on structural components. To take full advantage of this class of materials a comprehensive knowledge of behaviour under different service conditions is required. This thesis illustrates the degree to which this is currently achieved, and describes the motivation and progression of an experimental and theoretical analysis of the static damage growth in carbon fibre reinforced polymers. Notched carbon fibre-epoxy cross-ply composite samples have been manufactured and loaded in uni-axial tension. Synchrotron radiation computed tomography (SRCT) has been used to characterise in 3-D the initiation and evolution of damage during in situ loading. Characteristic splitting, off-axis matrix cracking, interlaminar cracking and fibre failure within the samples were identified and the interaction of the damage mechanisms during crack growth has been evaluated. Splitting in the plies aligned with the loading direction was studied in greater detail, including measurements of crack opening displacement and shear deformation at crack flanks. 3-D finite element models of splitting have been developed based on the observed damage and specimen microstructure from the SRCT results. Thermal residual stress and mechanical loading conditions were simulated for comparison with the experimental findings. Effects of local microstructural inhomogeneities were also embedded in models of varying complexity to assess the degradation of the results or model predictions due to simplifications or homogenisation. Significant discrepancy was found between the measured experimental data and finite element predictions due to simplifications in the model. Likely candidates for the over-prediction of crack growth include the effects of transverse ply cracks, delaminations and the lack of symmetrical damage formulation. Of particular significance is the confirmation that, via qualitative observations and quantitative data extraction, SRCT has facilitated the first known instance of direct full field comparison of model predictions for composite damage for a practical engineering layup.

Leisure boatbuilding is an industry that has tight profit margins and growing competition due to the global nature of the industry. It is a growth market with the number of high-earning potential customers increasing worldwide. For British boatbuilding to retain and increase its high standing within these global markets investment is required to develop larger profits and market share. Concurrent engineering is a method of design that has given large benefits to a multitude of industries but is ill-defined within leisure boatbuilding. This thesis investigates the nature of British boatbuilding and develops concurrent engineering within this context. To develop faster design while increasing quality this thesis concentrates on automated communication. A number of tools are developed focusing on structures and production. These include a mass and cost multi-objective optimisation tool further developing first principles rules using a Genetic Algorithm, a reliability tool to increase the speed of iterative design and a design history tool focusing on data mining using neural networks within a grid computing structure. Furthermore, a concurrent engineering methodology specific to leisure boatbuilding has been developed leading to a design environment for use within this sector. The resulting work develops techniques that increase the knowledge available to engineers in an intuitive, quantitative, manner.

Compressor blades are subtle aerodynamic shapes designed after years of research and insight. They inevitably show deviations from their desired shapes due to manufacturing errors, erosion or foreign object damage. In the present study we focus on seeking compressor blade geometries, that are robust in performance in the presence of geometric uncertainty. Sophisticated tools for representing and propagating uncertainty are employed. Novel method for modeling eroded blade geometry and simulating manufacturing variations with process capability data are presented. These are combined with an automatic meshing routine and a high fidelity viscous flow solver for performance analysis. A combination of Design of Experiment techniques and Gaussian Process emulators are employed to develop efficient surrogate models for uncertainty analysis and exploring the design space. Efficient multiobjective optimization based robust design methodologies are presented. The robust design methods in conjunction with the surrogate model are used to seek blades that have less variation in performance in the presence of erosion and manufacturing variations. Main effects and sensitivity analysis are also performed to understand the effect of each noise variable on the performance. The performance of the robust blades obtained are compared to that of deterministic optimal blades in the presence of the uncertainties. The robust optimal blades exhibit considerably less variability and mean shift in performance as compared to the optimal blades. Finally, a probabilistic framework is developed to deal with randomness in objectives during multiobjective optimization and is applied in conjunction with Gaussian Process emulators for robust design.

This report presents the design, simulation and fabrication of a spin qubit platform on ultrathin SOI (Silicon-on-Insulator) using A1 FinSET (Single electron transistor) gates and Si side gates. A new design layout is proposed for the double spin qubits co-integrated with a single electron electrometer, a waveguide and a nanomagnet. This platform aims to demonstrate the full operation of double spin qubits by integrating the following three key techniques in one compact footprint: a precisely controlled single electron transfer technology, a high speed charge detection technique and a single spin detection technology based on spin to charge conversion. A single electron transfer device (SETD) integrated with an electrometer is introduced here as the main building block of the spin qubit platform. The single electron transfer device consists of three nanowire (MOSETs) connected in series, and is capacitively coupled to an SET electrometer. A unique layout design for the SETD and a novel single electron transfer voltage pulse sequence are introduced. Simulation and dynamic analysis of this device operation are preformed using a finite element capacitance based simulation method and a Monte Carlo based single electron circuit simulation. The simulations demonstrated the ability of this platform to transfer single electrons and these characteristics are analyzed to optimize the layout. A novel fabrication process to realize high density silicon quantum dots (QDs) with A1 FinSET gates and close proximity Si gates on ultrathin SOI, for single electron transfer and detection, is successfully established with a number of different device layouts realized. In these devices, A1 FinSET gates surround an SOI nanowire channel forming electrically tunable potential barriers and defining QDs among them; Si plunger side gates are included to enable precise control of the QDs potential. Five SETD and electrometer device generations have been realized, tested and analyzed to improve the device yield; this extensive process development work is concluded with a novel fabrication approach to demonstrate successful FinSET A1 gae technology for SOI nanowires. This QDs platform is fabricated using a multi-layer electron beam lithography process that is fully compatible with metal oxide semiconductor technology. The fabrication process is fully developed with a yield of 92% and a great flexibility to enable the realization of more complex structures and even for devices beyond the scope of this project as shown in the appendices of this report.

This thesis deals with issues arising in manufacturing, in particular related to production efficiency. Lot streaming refers to the process of splitting jobs to move production through several stages as quickly as possible, whereas batch scheduling refers to the process of grouping jobs to improve the use of resources and customer satisfaction. We use a network representation and critical path approach to analyse the lot streaming problem of finding optimal sublot sizes and a job sequence in a two-machine flow shop with transportation and setup times. We introduce a model where the number of sublots for each job is not predetermined, presenting an algorithm to assign a new sublot efficiently, and discuss a heuristic to assign a fixed number of sublots between jobs. A model with several identical jobs in an multiple machine flow shop is analysed through a dominant machine approach to find optimal sublot sizes for jobs. For batch scheduling, we tackle the NP-hard problem of scheduling jobs on a batching machine with restricted batch size to minimise the maximum lateness. We design a branch and bound algorithm, and develop local search heuristics for the problem. Different neighbourhoods are compared, one of which is an exponential sized neighbourhood that can be searched in polynomial time. We develop dynamic programming algorithms to obtain lower bounds and explore neighbourhoods efficiently. The performance of the branch and bound algorithm and the local search heuristics is assessed and supported by extensive computational tests.

The objective of this research is to develop a methodology for incorporating cost models based on manufacturing process information within multidisciplinary design optimisation problems. Although cost considerations are critical in product design and development, cost models are rarely used in opti¬mising designs mainly due to the inability in acquiring accurate manufacturing cost estimates in early design. In this thesis, we present a new technique for embedding manufacturing process knowledge within a modelling tool which can be utilised to provide accurate cost estimates in design optimisation applications. We use the proposed cost estimating technique for optimising the geometry of two components from a Rolls-Royce civil aircraft engine by designing a sequential workflow consisting of CAD, analysis and cost models along with optimisation algorithms within an integrated system. Initial results from the first component (which is treated as a model problem) show that significant cost savings as well as shape changes can be achieved by using an accurate cost model in the objective function. The second case study dealt with is the shape optimisation of the initial 2D profile of a high pressure turbine disc. We develop highly flexible geometry parameterisation schemes to accurately represent manufacturing, supplier and inspection constraints inherent in the cost model for the disc. Significant differences in the geometry are achieved when the design is optimised for low manufacturing cost as compared to traditional weight minimisation leading to the second part of this thesis that deals with the hypothesis that low volume and low cost are conflicting attributes. Multiobjective optimisation approaches are then utilised to generate a Pareto front of designs with optimum combinations of both objectives. We then proceed to list the obstacles which prevent a straightforward application of multiobjective techniques to sophisticated design problems and propose modifications which enhance the quality of results achieved. Finally, a flowchart detailing the design optimisation framework used in this thesis is described for the benefit of future applications. We then conclude by stating the salient contributions of this work and interesting avenues of future research that can be pursued.