There is an ongoing trend towards advanced fixturing systems that can be automatically reconfigured for different workpieces and dynamically adapt the clamping forces during the manufacturing process. However, the increased utilisation of computer technology and sensor feedback currently requires a significant amount of programming effort during the development phase and deployment of such fixtures which impairs their successful industrial realisation. This research addresses the issue by developing the core concepts of a novel software framework that facilitates the deployment and operation of reconfigurable and adaptive fixturing systems. This includes a new data model for the representation of the fixturing system, using object-oriented modelling techniques. Secondly, a generic methodology for the automatic reconfiguration of fixturing systems has been developed that can be applied to a plethora of different fixture layouts. Thirdly, a flexible communication infrastructure is proposed which supports the platform-independent communication between the various parts of the fixturing system through the adoption of a publish/subscribe approach. The integration of these core knowledge contributions into a software framework significantly reduces the programming effort by providing a ready-to-use infrastructure that can be configured according a given fixture layout. In order to manage the complexity of the research, a structured research methodology has been followed. Based on an extensive literature review, a number of knowledge gaps have been identified which were the basis for the definition of clear research objectives. A use case analysis has been conducted to identify the requirements of the software framework and several potential middleware technologies have been assessed for the communication infrastructure. This was followed by the development of the three core knowledge contributions. Finally, the research results have been demonstrated and initially verified with a prototype of a reconfigurable fixturing system, indicating that the utilisation of the software framework can eliminate the need for programming, thereby drastically reducing deployment effort and lead time.

Fixtures are devices designed to repeatedly and accurately locate the processed workpiece in a desired position and orientation, and securely hold it in the location throughout the manufacturing process. Fixtures are also charged with the task of supporting the workpiece to minimise deflection under the loads arising from the manufacturing process. As a result, fixtures have a large impact on the outcome of a manufacturing process, especially when the workpiece presents low rigidity. Traditionally, in manufacturing environments, where thin-walled components are produced, the utilised fixtures are dedicated solutions, designed for a specific workpiece geometry. However, in the recent decades, when the manufacturing philosophy has shifted towards mass customisation, there is a constant technological pull towards manufacturing equipment that exhibits high production rates and increased flexibility/reconfigurability, without any compromise in the quality of the end result. Therefore, fixtures have been the focal point of a plethora of research work, targeting mainly towards either more reconfigurable, or more intelligent/adaptive solutions. However, there have been no attempts so far to merge these two concepts to generate a new fixturing approach. Such an approach, referred to in this work as fully-active fixrturing, would have the added ability to reposition its elements and adapt the forces it exerts on-line, maximising the local support to the workpiece, and thus reducing vibration amplitude and elastic deformation. This results in a tighter adherence to the nominal dimensions of the machined profile and an improved surface-finish quality. This research work sets out to study the impact of such fixturing solutions, through developing suitable models which reflect the fixture-workpiece system behaviour, and a design methodology that can support and plan the operation of fully-active fixtures. The developed model is based on a finite elements representation of the workpiece, capturing the dynamic response of a thin-walled workpiece that is being subjected to distributed moving harmonic loads. At the same time, the workpiece is in contact with an active element that operates in closed-loop control. An electromechanical actuator is charged with the role of the active elements, and it is modelled via first-principle based equations. Two control strategies are examined experimentally to identify the best performing approach. The direct force/torque control strategy with a Proportional-Integral action compensator is found to lead to a system that responds faster. This control architecture is included in the model of the active elements of the fixture. The behaviour of the contact between the fixture and the workpiece is approximated via a combination of a spring and a damper. The overall model is assembled using the impedance coupling technique and has been verified by comparing its response with the time-domain response of an experimental set-up. The developed model serves as the backbone of the fully-active fixture design methodology. The latter is capable of establishing important fixturing parameters, such as the pattern of motion of the movable fixture element, the points on the surface of the workpiece that formulate the motion path of the fixture element, the time instant at which the element needs to change position, and the clamping forces the fixture needs to apply and maintain. The methodology is applied on a thin plate test case. Such a plate has been also used in a series of machining experiments, for which the fixturing parameters used are those that resulted from the test case. A very good quantitative agreement between both experiments and theory was observed, revealing the capabilities of the methodology itself and of the fully-active fixturing approach in general.

This thesis presents an investigation on the churn to annular flow pattern boundary in an 11 m tall, 127 mm id vertical riser. Experimental data on film thickness, pressure drop and drop size and velocity was analysed and interpreted. Entrained fraction, interfacial and wall shear stresses and the interfacial friction were calculated from the experimental data. A new churn-annular flow transition boundary was derived based on trends, and in particular changes of slopes, observed in film thickness, pressure drop and structure velocity data. This is supported by observations made using high speed photography. Minima in slopes are found in plots of film thickness and pressure gradient with gas superficial velocity at low liquid flow rates. These minima are however not clearly visible at higher liquid flow rates in the data obtained. Dimensional analysis of this transition boundary and those proposed by other workers, using Froude and Weber numbers, resulted in a closer agreement between transition boundaries then was achieved till present. The correlation found, which describes the boundary, performs well for different pipe diameters, fluid properties and experimental flow conditions. It was observed that existing models for the calculation of interfacial and wall shear stresses, including the interfacial friction factor, do not perform well in churn type flows. Their performance and agreement with the present data at high gas flow rates, thus annular flow, was however better. This indicated that these models do not take some of the characteristics of the flow into account, e.g., gas core density. It was found that the latter parameter plays an important role in churn flow since the gas core density increases steeply with decreasing gas flow rate. New relationships for these parameters are suggested for a more accurate prediction in large diameter pipes. The diameter, velocity, and entrained fraction of drops show similar trends to that of the liquid film thickness and pressure drop. The velocity and the entrained fractions show most profound information. The entrained fraction increases in churn flow with gas flow rate. It then shows a steep decrease in a transitional area. In this area it may be that the entrained fraction is more contained in large waves and wisps than in drops. At higher gas flow rates, the entrained fraction increases again, as is well reported by other researchers. Here the breakup and atomisation of large waves and wisps play an important role. From comparison between drop fractions deposited by diffusion and direct impaction in the CFD and experimental results, there is evidence that in large diameter pipes a third deposition mechanism applies: Transitional deposition. Analysis shows that transitional impaction occurs at medium sized drops at medium gas flow rates. Around these conditions, large waves are present in the flow as described above. The third deposition mechanism probably occurs when the majority of entrained liquid is carried in large waves and wisps as reported above. Therefore, at the transition from churn to annular flow in large diameter vertical pipes, the behaviour of the flow is not typical to that observed in smaller diameter pipes.

The behaviour of gas-liquid two-phase flow has been studied extensively in the past at near atmospheric pressure in small diameter pipes. However, the industrial reality is the utilisation of large diameter pipes at elevated pressures and there is significantly less information available in this area due principally to the cost of investigating large diameter pipes. This research relied on using large-scale laboratory facilities at the University of Nottingham, and on using newly developed state of the art multiphase instrumentation. This study tested and applied the wire mesh sensor (WMS). The work included in this thesis utilised the two variants of the WMS; the already established Conductivity WMS and the recently developed Capacitance WMS and the two sensors were compared against each other. The Capacitance WMS was recently supplied by HZDR (Research Institution, Germany) to the University of Nottingham. Extensive experimental campaigns were carried out with this novel sensor. The WMS was initially tested and validated against several other instruments such as high speed camera and gamma densitometry. It was subsequently applied to a large diameter bubble column and large diameter pipe with two phase flow. The aims of this project was to gain a better understanding of the flow patterns and their transitions in large diameter pipes and to provide real experimental data to assist researchers and engineers in producing relevant and physically sound models for use in larger diameter pipes. As a result of this study, novel and interesting structures which have been labelled as wisps were discovered in large diameter pipes. In addition the WMS was used extensively for the first time on bubble columns in order to assess its suitability for such an application.

Automated Tape Laying (ATL) trials using low cost wind energy suitable material and mould tools have been conducted. New materials proved problematic during ATL lay-up and observations of the ATL process show that the prepreg tack and stiffness properties significantly affect lay-up performance. Prepreg tack has not been widely researched within the composites industry due to the absence of a standardised method for characterisation. A new tack and stiffness test has therefore been developed which is representative of the ATL process. The new test was used to investigate the response to process and material variables. Two failure modes were observed and compared to those found in Pressure Sensitive Adhesives (PSA). Failure modes are associated with the viscoelastic stiffness of the resin. High stiffness appears to result in interfacial failure turning to cohesive failure when stiffness is reduced. A peak in tack is observed to correspond with the transition in failure mode leading to the conclusion that prepreg tack is the result of a chain system rather than a single property. The chain system consists of an interface and bulk components each having individual time and physical variable dependant properties. Tack and stiffness is shown to conform to the Williams-Landel-Ferry (WLF) time-temperature superposition principle for both cohesive and interfacial failure modes. Cohesive viscoelastic and surface energy interface failure mechanisms may be theoretically linked via the Lennard-Jones energy well with molecular jumps triggered by thermal vibrations. This analogy allows both failure phenomenon to simultaneously follow the time temperature superposition principle and is typically demonstrated in LJ dynamic mechanical modelling. The theoretical analogy is used in the explanation of experimental results where tack is essentially thought of as a low energy non-covalent molecular bond or reaction. The experimental technique developed here could allow for the standardisation of tack and stiffness specification for manufacturers. The application of results to ATL production is explored and demonstrated using ATL equipment. The results show that optimum lay-up conditions may be explored offline using the new tack and stiffness test. Results also show promising signs that the WLF relationship could be exploited to greatly Increase lay-up speed and consistency, increasing the attractiveness of the process to wind turbine blade manufacturers. A theoretical results curve is also presented which may allow manufacturers to determine the effect of changes in surface conditions and resin properties on tack.

This thesis is concerned with the dominant leakage characteristics of an axial piston pump. Results have been obtained from a combination of analysis, Computational Fluid Dynamics (CFD) and experimental work, and have added to existing knowledge in this field. The measurement of slipper leakage within an axial piston pump is impossible due to additional leakage from the pistons and between the cylinder barrel and port plate. It may only be determined by analysis and this aspect has been studied via a new CFD simulation. Further progress has been made experimentally on slipper leakage. A new test apparatus was designed and developed by the author and comparisons have been made with parallel analytical work. Previous research in this area has concentrated on single-landed slippers and leakage rates from such slippers have been examined, however only under static conditions. The work in this thesis is the first to consolidate experimental studies on multiple-land slippers, and the first to measure slipper leakage under dynamic conditions. These results have been compared with both CFD simulations and a new theoretical study undertaken in parallel with this work. The new test apparatus allowed measurement of both leakage and groove pressure under a range of operating conditions. It was established that the presence of a groove reduces the restoring moment produced, and hence enables the slipper to operate with an appropriate angle of tilt, thus permitting hydrodynamic lift to more readily exist. However, this occurs at a cost of increased leakage. In addition to the experimental work on slippers, the time-varying pressures within selected cylinders of an axial piston pump were measured. In parallel, a fully dynamic CFD model of a pump was produced. This model included all leakage paths from the pump. It was discovered that the port plate leakage dominated the overall leakage, with slipper leakage still being significant, but with piston leakage insignificant. This model was also used to predict the flow and pressure ripple from the pump and the predictions were compared with experimental measurements.

A cone crusher is a crushing machine which is widely used in the mining, construction and recycling industries. Previous research studies have proposed empirical mathematical models to simulate the operational performance of a cone crusher. These models attempt to match the size distributions of the feed and product streams. The flow of the rock and its breakage within the cone crusher chamber are not explicitly modelled by these methods. Moreover, the ability to investigate the changes in crusher performance affected by changes to the crusher design geometry and/or operating variables (including cavity profile, closed size setting and eccentric speed) are not easily achieved. Improvements to system design and performance are normally achieved by the combination of iterative modifications made to the design and manufacture of a series of prototype machines, and from a subsequent analysis of the results obtained from expensive and time consuming rock testing programs. The discrete element method (DEM) has in recent years proved to be a powerful tool in the execution of fundamental research to investigate the behaviour of granular material flow and rock breakage. Consequently, DEM models may provide the computational means to simulate the flow and breakage of rock as it passes through a cone crusher chamber. Thus, the development of field validated models may provide a cost effective tool to predict the changes in crusher performance that may be produced by incremental changes made to the dimensions or power delivered to the crusher chamber. To obtain an improved understanding of the fundamental mechanisms that take place within a cone crusher chamber, the two processes of rock flow and rock breakage may be decoupled. Consequently, this study firstly characterised the flow behaviour of broken rock through a static crusher chamber by conducting a series of experiments to investigate the flow of regular river pebbles down an inclined chute. A parallel computational study constructed and solved a series of DEM models to replicate the results of these experimental studies. An analysis of the results of these studies concluded that an accurate model replication of the shape of the pebbles and the method used to load the pebbles into the inclined chute were important to ensure that the DEM models successfully reproduced the observed particle flow behaviour. These studies also established relationships between the chute geometry and the time taken for the loaded pebble streams to clear the chute. To investigate the rock breakage behaviour observed within a cone crusher chamber, thirty quasi-spherical particles of Glensanda ballast aggregate were diametrically crushed in the laboratory using a Zwick crushing machine. The crushed rock particles used were of three sieve size fractions: 14-28mm, 30-37.5mm and 40-60mm. The effects that either a variation in the particle size or strength has on and the number and size distribution of the progeny rock fragments produced on breakage were studied. Subsequently, a series of DEM simulation models were constructed and solved to replicate the experimental results obtained from these crushing tests. The aggregate particles were represented by agglomerates consisting of a number of smaller diameter bonded micro-spheres. A new method was proposed to generate a dense, isotropic agglomerate with negligible initial overlap between the micro-spheres by inserting particles to fill the voids in the agglomerate. In addition, the effects that a variation in the particle packing configurations had on the simulated strength and breakage patterns experienced by the model agglomerate rock particles were investigated. The results from these DEM model studies were validated against the experimental data obtained from the ballast rock breakage tests. A comparative analysis of the experimental and modelling studies concluded that once the bond strengths between the constituent micro-spheres matched the values determined from the rock breakage tests, then the numerical models were able to replicate the measured variations in the aggregate particle strengths. Finally, the individual validated DEM aggregate particle flow and breakage modes were combined to construct a preliminary coupled prototype DErvl model to simulate the flow and breakage of an aggregate feed through a cone crusher chamber. The author employed two modelling approaches: the population balance model (PBM) and bonded particle model (BPM) to simulate the observed particle breakage characteristics. The application of the PBM model was successfully validated against historical experimental data available in the literature. However, the potential wider use of the BPM model was deemed impractical due to the high computation time. From a comparative analysis of the particle size distributions of the feed and computed product streams by the two modelling approaches, it is concluded that the simpler PBM produces more practical computationally efficient numerical solutions.

Gas turbines are extensively used in combined cycle power systems. These form about 20% of global power generating capacity, normally being fired on natural gas, but this is expected in the future to move towards hydrogen enriched gaseous fuels to reduce CO2 emissions. Gas turbine combined cycles can give electrical power generation efficiencies of up to 60%, with the aim of increasing this to 70% in the next 10 to 15 years, whilst at the same time substantially reducing emissions of contaminants such as NOx. The gas turbine combustor is an essential and critical component here. These are universally stabilized with swirl flows, which give very wide blowoff limits, and with appropriate modification can be adjusted to give very low NOx and other emission. Lean premixed combustion is commonly used at pressures between 15 to 30 bar, these even out hot spots and minimise formation of thermal NOx. Problems arise because improving materials technology/improved cooling techniques allow higher turbine inlet temperatures, hence higher efficiencies, but with the drawback of potentially higher emissions and stability problems. This PhD study has widely investigated and analysed two different kinds of gas turbine swirl burners. The research has included experimental investigation and computational simulation. Mainly, the flashback and blowoff limits have been comprehensively analysed to investigate their effect upon swirl burner operation. The study was extended by using different gas mixtures, including either pure gas or a combination of more than one gas like natural gas, methane, hydrogen and carbon dioxide. The first combustor is a 100 kW tangential swirl combustor made of stainless steel that has been experimentally and theoretically analysed to study and mitigate the effect of flashback phenomena. The use of a central fuel injector, cylindrical confinement and exhaust sleeve are shown to give large benefits in terms of flashback resistance and acts to reduce and sometimes eliminate any coherent structures which may be located along the axis of symmetry. The Critical Boundary Velocity Gradient is used for characterisation of flashback, both via the original Lewis and von Elbe formula and via new analysis using CFD and investigation of boundary layer conditions just in front of the flame front. Conclusions are drawn as to mitigation technologies. It is recognized how isothermal conditions produce strong Precessing Vortex Cores that are fundamental in producing the ii final flow field, whilst the Central Recirculation Zones are dependent on pressure decay ratio inside the combustion chamber. Combustion conditions showed the high similarity between experiments and simulation. Flashback was demonstrated to be a factor highly related to the strength of the Central Recirculation Zone for those cases where a Combustion Induced Vortex Breakdown was allowed to enter the swirl chamber, whilst cases where a bluff body impeded its passage showed a considerable improvement to the resistance of the phenomenon. The use of nozzle constrictions also reduced flashback at high Reynolds number (Re). All these results were intended to contribute to better designs of future combustors. The second piece of work of this PhD research included comprehensive experimental work using a generic swirl burner (with three different blade inserts to give different swirl numbers) and has been used to examine the phenomena of flashback and blowoff in the swirl burner in the context of lean premixed combustion. Cylindrical and conical confinements have been set up and assembled with the original design of the generic swirl combustor. In addition to that, multi-fuel blends used during the experimental work include pure methane, pure hydrogen, hydrogen / methane mixture, carbon dioxide/ methane mixture and coke oven gas. The above investigational analysis has proved the flashback limits decrease when swirl numbers decrease for the fuel blends that contain 30% or less hydrogen. Confinements would improve the flashback limit as well. Blowoff limits improve with a lower swirl number and it is easier to recognise the gradual extinction of the flame under blowoff conditions. The use of exhaust confinement has created a considerable improvement in blowoff. Hydrogen enriched fuels can improve the blowoff limit in terms of increasing heat release, which is higher than heat release with natural gas. However, the confinements complicate the flashback, especially when the fuel contains a high percentage of hydrogen. The flashback propensity of the hydrogen/methane blends becomes quite strong. The most important features in gas turbines is the possibility of using different kinds of fuel. This matter has been discussed extensively in this project. By matching flashback/blowoff limits, it has been found that for fuels containing up to 30% of hydrogen, the designer would be able to switch the same gas turbine combustor to multifuels whilst producing the same power output.

A novel study on biomass-air gasification using a horizontal entrained-flow gasifier and catalytic processing of the product gas has been conducted. The study was designed to investigate the effect of catalyst loading on the product gas. The use of a horizontal entrained-flow gasifier reactor was used to assess the effect of the gasifier reactor orientation on the gasification process. Both experimental and computational fluid dynamics (CFD) approaches were employed. The gasification tests were conducted at 800 oC and equivalence ratio of 0.23 while the product gas was catalysed at 350-400 oC and a gas hourly space velocity (GHSV) of 8000 h-1. Preparation and characterisation of wood powder and catalysts were performed using classical methods. Moreover, the syngas and tar composition were analysed using a gas chromatograph (GC) and GC-mass spectrometer (GC-MS) respectively. The research findings showed that maximum fuel conversion and cold gas efficiency using a horizontal entrained-flow gasifier were 99 % and 70 % respectively. The gasifier length can also be reduced from the common 1000-2000 mm to 500 mm. The catalysis study showed that pumice and kaolin have limited catalytic effect on the product gas. However, doping with CeO2, ZrO2, CuO and NiO improved the syngas heating value, coking resistance and tar conversion. A notable increase in syngas LHV was achieved using ceria doped pumice (8.97 MJ/Nm3) and copper doped pumice (8.66 MJ/Nm3) compared to 6.67 MJ/Nm3 of non-catalytic test. For the tested catalysts, CeO2 doped pumice exhibited highest coking resistance. Furthermore, catalytic tar conversion was mainly through cracking and partial oxidation reactions. The lowest tar yield was found to be 3.55 g/Nm3 using kaolin-ceria-zirconia catalyst compared to 14.92 g/Nm3 of non-catalytic gasification. Tar reduction using untreated pumice was through adsorption and ranged 4-6 g/Nm3. In general, the results of this study suggest that there exist a sensitivity to the gasifier orientation on the overall gasification process. It has also shown that metal oxides have both beneficial and detrimental effects of syngas composition. Although syngas heating value increased with increasing catalyst loading, H2 showed a decreasing trend highlighting that further catalyst modification is required. Furthermore, pumice and kaolin can be utilised as catalyst support in the gasification technology. However, further experimental investigation on doping various catalytic metals and testing at different operating conditions are hereby proposed.

This thesis presents advances and applications of the eXtended Finite Element Method (XFEM). The novelty of the XFEM is the enrichment of the primary variables in the elements intersected by the discontinuity surface by appropriate functions. The enrichment scheme carries the local behaviour of the problem and the main advantage is that the method does not require themesh to conform to the internal boundaries. But this flexibility comes with associated difficulties: (1) Blending problem; (2) Numerical integration of enrichment functions and (3) sub-optimal rate of convergence. This thesis addresses the difficulty in the numerical integration of the enrichment functions in the XFEM by proposing two new numerical integration schemes. The first method relies on conformal mapping, where the regions intersected by the discontinuity surface are mapped onto a unit disk. The second method relies on strain smoothing applied to discontinuous finite element approximations. By writing the strain field as a non-local weighted average of the compatible strain field, integration on the interior of the finite elements is transformed into boundary integration, so that no sub-division into integration cells is required. The accuracy and the efficiency of both the methods are studied numerically with problems involving strong and weak discontinuities. The XFEM is applied to study the crack inclusion interaction in a particle reinforced composite material. The influence of the crack length, the number of inclusions and the geometry of the inclusions on the crack tip stress field is numerically studied. Linear natural frequencies of cracked functionally graded material plates are studied within the framework of the XFEM. The effect of the plate aspect ratio, the crack length, the crack orientation, the gradient index and the influence of cracks is numerically studied. LATEX-ed Friday, October 14, 2011; 10:55am © Sundararajan Natarajan