The modelling, design, construction and experimental testing of a carbon-ammonia adsorption heat pump is presented. The main objective of the research was to design, manufacture and test an adsorption generator with low thermal mass and high power density. The adsorption generator developed was a stainless steel, nickel brazed plate heat exchanger. Computational modelling of the generator with thermal wave and multiplebed cycles revealed that multiple-bed cycles give a superior trade-off between efficiency and power density. Further modelling was carried out to evaluate the performance of the adsorption generator in a four-bed gas-fired domestic heat pump system. The proposed system is air-source and could deliver a nominal heating power of 7 kW and a seasonal heating COP of 1.35, equivalent to a one third reduction in gas consumption in comparison to a condensing boiler. The systems performance was compared to a vapour compression heat pump on running costs and CO2 emissions and was found to be similar or better in all cases. The adsorption generator was tested in a two-bed air-source heat pump system and achieved heating powers from 7 to 11 kW and a heating COP of between 1.4 and 1.6. Specific heating power ranged from 3.9 kW kg-1 to 6.1 kW kg-1, equivalent to specific cooling powers of between 1.1 kW kg-1 and 2 kW kg-1, which is a significant increase in power density compared to the state of the art.

Combining modes of vibration, such as longitudinal and torsional vibration, is advantageous in many ultrasonic applications such as ultrasonic drilling, welding, and motors. In this work we present a novel approach to the design a longitudinal-torsional (LT) ultrasonic horn which adapts the front mass in a traditional Langevin transducer. Different approaches, such as degeneration of longitudinal vibration and coupling between longitudinal (L) and torsional (T) modes, have been used to generate the LT mode of vibration. The degeneration approach creates a non-uniform section, by cutting and twisting a number of slots along the path of the L wave such that part of the wave converts into T wave whilst the remaining part propagates unchanged through the section; these two parts are recombined near the output surface to form LT vibration. The mode coupling approach uses two set of vibration generators, usually piezoelectric elements, where one set generates L vibration whilst the second set generates T vibration. An exponential cross-sectional horn uses to combine the two modes where the area reduction factor is selected such that these modes resonate at the same frequency. However, many limitations prevent the wide usage of these methods in ultrasonic applications. These limitations are the complex design and excitation, possible coupling with surrounding modes, instability in operating at different boundaries, difficulty in securing the structure without influencing the vibrational response and the low produced torsionality, which is the ratio of torsional to longitudinal response at the output face. The new approach is based on combining the principles of these methods to overcome the previously stated limitations, the slotting technique is incorporated into the exponential cross-sectional path and the horn produced is utilised as the front mass of a Langevin transducer. A set of design and performance criteria are used to optimise the transducer and includes applicable design; methods of securing the transducer; and the excitation features of LT transducer such that it can operate without the effects of surrounding modes of vibration and can produce high response and torsionality at the output surface. A methodology which combines mathematical and experimental modelling is used to optimise LT transducer design. The mathematical modelling, which includes finite element (FE) and analytical methods, is performed to optimise the geometry and to predict electromechanical parameters, modal parameters and the dynamic behaviour of LT transducer. The experimental modelling is used to validate the mathematical results and to characterise the fabricated prototypes under different operating conditions. The dimensions of the initial design of the L mode Langevin transducer are derived from the principles of the wave equation. This transducer has a set of piezoceramic components sandwich between a cylindrical back mass and an exponential front mass connected by a pre-stressed bolt. The dimensions are used to create the FE model, using the FE software package ABAQUS, where different shapes of cut at different dimensions and at various angle of twist along the front mass are introduced and examined by a modal analysis procedure to the front mass. An optimised model is then utilised in a size scaling study to confirm the suitability of using this approach for different ultrasonic applications. The dimensions of the optimised design are also used in the analytical study, based on Mason’s electric equivalent circuit approach, to predict the electromechanical parameters where a one-dimensional equivalent circuit approach is created separately for each part whilst the combination vibrational motion in the front mass is represented by two, longitudinal and torsional, equivalent circuits. The complete equivalent network of the LT transducer is then solved using the mathematical software package MATHEMATICA. The analytical model is also extended to validate some of particular FE findings such as the distribution of the response amplitude and the location of the longitudinal nodal plane along the transducer’s structure. Two optimised models of different sizes are fabricated and characterised through different testing techniques including electrical impedance analysis, experimental modal analysis (EMA) and experimental harmonic analysis. Optimisation of the pre-stressing of the transducer is performed by applying different torques to the pre-stressed bolt and measuring the electrical impedance spectra where the results are compared to analytical findings. EMA is then used to describe the natural characteristics of the structures where the results are used to accurately extract the modal parameters and to validate the predictions of the FE and analytical model. Different levels of harmonic excitation are used to characterise the fabricated prototypes where the results are compared to the findings of the mathematical modelling. A case study of the design of the LT drill is presented to validate the design approach for real ultrasonic applications. A similar methodology is applied and the resulting LT drill is tested for both unloaded and loaded operating conditions. The results obtained show that this new approach can be easily and successfully applied to ultrasonic applications to produce a torsional to longitudinal amplitude response of 0.8 which is measured on a fabricated prototype.

The majority of failures of mechanical components are caused by fatigue. Unlike many conventional engineering components, implants in the body are subjected to complex multidirectional loading patterns, thus fatigue not only occurs under axial, fully or partly reversed loading, but also under torsional loading. The fatigue behaviours of self-reinforced poly lactide composite (PLA) of unidirectional PLA fibres in PLA matrix containing tricalcium phosphates (TCP), (PLA-PLA-TCP) produced via pre-pregging technique has been investigated. Quasi-static test results indicated that PLA-PLA-TCP is stronger in tension than in compression and torsion and is significantly influence by moulding temperature. Uniaxial fatigue testing at 37° C in saline solution established S-N (Wöhler) curves for both axial and torsional loading for two moulding temperatures (140°C and 150°C). Compression loading showed significant effect on the axial fatigue behaviour. Biaxial fatigue results showed that the addition of torsion to axial loading significantly reduced the fatigue life. Out-of-phase loading was less detrimental to the fatigue life than in-phase. Fatigue development was evaluated by reduction in secant modulus and increase in energy absorbed. The threshold number of cycles at which damage starts to accumulate in the composite was found to be load ratio and direction dependent. The effects of the degradation process in saline solution on the fatigue behaviour of the composite were also studied at 25% of the ultimate tensile and shear stresses. The specimens were immersed for 8, 12, 16 and 20 weeks periods before testing. The results indicated that even though immersion in saline solution reduced the static and cyclic properties of the composite, it still had good strength retention and comparable to the cortical bone at the end of 20 weeks of degradation period. Microscopy examination on the fracture surface indicated that in uniaxial tension-compression fatigue, the failure was dominated by compression and failed via microbuckling mechanism. Biaxial fatigue failure was dominated by shear mechanisms with evidence of interfacial failure and fatigue striations.

Porous materials possessing random microstructures exist in both organic (e.g. polymer foam, bone) and in-organic (e.g. silica aerogels) forms. Foams and aerogels are two such materials with numerous engineering and scientific applications such as light-weight cores in sandwich structures, packaging, impact and crash structures, filters, catalysts and thermal and electrical insulators. As such, design and manufacture using these materials is an important task that can benefit significantly from the use of computer aided engineering tools. With the increase in computational power, multi-scale modelling is fast becoming a powerful and increasingly relevant computational technique. Ultimately, the aim is to employ this technique to decrease the time and cost of experimental mechanical characterisation and also to optimise material microstructures. Both these goals can be achieved through the use of multi-scale modelling to predict the macro-mechanical behaviour of porous materials from their microstructural morphologies, and the constituent materials from which they are made. The aim of this work is to create novel software capable of generating realistic randomly micro-structured material models, for convenient import into commercial finite element software. An important aspect is computational efficiency and all techniques are developed paying close attention to the computation time required by the final finite element simulations. Existing methods are reviewed and where required, new techniques are devised. The research extensively employs the concept of the Representative Volume Element (RVE), and a Periodic Boundary Condition (PBC) is used in conjunction with the RVEs to obtain a volume-averaged mechanical response of the bulk material from the micro-scale. Numerical methods such as Voronoi, Voronoi-Laguerre and Diffusion Limited Cluster-Cluster Aggregation are all employed in generating the microstructures, and where necessary, enhanced in order to create a wide variety of realistic microstructural morphologies, including mono-disperse, polydisperse and isotropic microstructures (relevant to gas-expanded foam materials) as well as diffusion-based microstructures (relevant for aerogels). Methods of performing large strain simulations of foams microstructures, up to and beyond the onset strain of densification are developed and the dependence of mechanical response on the size of an RVE is considered. Both mechanical and morphological analysis of the RVEs is performed in order to investigate the relationship between mechanical response and internal microstructural morphology of the RVE. The majority of the investigation is limited to 2-d models though the work culminates in extending the methods to consider 3-d microstructures.

An experimental apparatus was designed and built to study the film cooling effectiveness from a single row of holes at various angles and hole spacings, using a foreign gas technique. Mixtures of Freon 12 and air were injected into an air mainstream to give a range of density ratios encompassing the values found in a gas turbine. The density ratio was found to be of importance and none of the commonly used parameters - e.g. blowing parameters - can be used to scale results, unless the density ratio is correctly modelled. The boundary layer thickness was varied independently of other parameters, and an increase in thickness was found to decrease the effectiveness, for normal and angled injection geometries for 20 hole diameters downstream. Favourable and adverse pressure gradients over the injection holes were tested and found to have little effect on the film cooling effectiveness. Changing the hole spacing produced considerable variations, with the smallest hole spacing giving the best performance in all respects. A hole spacing of greater than 3.75 diameters was found to be the maximum to give overall coverage above 0.10 effectiveness. The injection angle was also investigated and for low blowing rates the shallow angles gave the best results; but at high blowing rates, i.e. greater than 1.4, normal injection gave the best performance as the shallow angles rapidly became detached from the surface with increasing velocity ratio. The normal injection was also superior in terms of lateral distribution of coolant at all values of blowing rate. A correlation was proposed that included the density and velocity ratios and hole spacing for normal injection and, in a modified form, for angled injection at 3 diameter spacings. This was found to work well for the experimental results obtained here and by other researchers.

This thesis describes the use of swirl-inducing pipes in water and water/mixture flows, with a particular emphasis on production of swirl before a bend. The author takes ideas for imparting swirling action to particle laden liquids which have occurred in one form or another throughout the 20th Century. The aim of the project was to reduce wear and produce better particle distribution throughout a bend. In the present investigation two methods were used in the examination of swirl-inducing pipes, namely experimental and numerical. The experimental method made use of a Swirly-flo pipe, which is normally found in marine boilers and is used to improve heat exchanger efficiency. The Swirly-flo was then placed onto an experimental test rig, which was specifically designed to provide insight into the use of swirl-inducing pipes. The numerical method came from a commercial Computational Fluid Dynamics (C.F.D.) package which allowed the author to examine various shapes for pipes and provided information on the flow fields in a swirl-inducing pipe. From the experimental results it was shown that swirling the flow before a bend produced less pressure drop across the bend than non-swirling flow. However, the Swirly-flo pipe produced a greater pressure loss across its length than the standard pipe. By swirling the particles before the bend the particles were more evenly distributed throughout the bend, which has the potential to remove the characteristic wear zones. Computational Fluid Dynamics was used to investigate various Swirly-flo designs. These studies indicated that the optimum pitch to diameter ratio was shown to be 8 for a constant pitch Swirly-flo pipe, which was consistent with previous work.

Abrasive waterjet (AWJ) technology is used in a routine manner in manufacturing industry to cut materials that are difficult to cut by other methods. Whilst the technology for through cutting of materials is mature, the process is also being developed for controlled depth milling (CDM) of materials. The aerospace industry have a requirement to remove redundant material from components manufactured from difficult to machine Ti6Al4V and titanium aluminide alloys and thus reduce component weight. The two main processes available to facilitate this are chemical milling and AWJ-CDM. The two processes have the advantage that they impose negligible forces, thus allowing flexible structures to be processed. However, the process of chemical milling is under threat due to the high costs associated with the disposal of the spent acids. Thus, this research seeks to evaluate the A WJ-CDM process as a replacement for chemical milling for Ti6A14V and titanium aluminide alloys. The magnitude and effect of the process characteristics of chemical milling on fatigue life are well established; however, this is not the case for AJW-CDM. The aerospace industry considers the characteristics of surface roughness, grit embedment and surface morphology to be significant parameters in determining the fatigue life of components manufactured using AJW-CDM. Therefore, before AJW-CDM can be considered a viable alternative, the effect of the process variables on the workpiece characteristics have first to be established. The current research has determined the role of a number of process parameters on the material removal rate, roughness and waviness, grit embedment and surface morphology in the AJW-CDM of Ti6AI4V and titanium aluminide. Nozzle traverse speed and jet impingement angle are shown to govern the operative mechanism of material removal and thus the material removal rate. It is also shown that the surface waviness can be reduced as the traverse speed is increased and as the jet impingement angle is decreased, but it should be noted that waviness increases with number of passes of the jet over the workpiece. The surface roughness is not strongly dependent on traverse speed. Surface waviness and roughness are strongly dependent on jet impingement angle; significant reductions are possible by employing low angle milling techniques. Smaller sized grit leads to a reduction in material removal rate but also to a decrease in both waviness and roughness. It has been demonstrated that grit embedment can be minimised either by milling with a high jet traverse speed at low impingement angles or by low speed milling at jet impingement angles up to 45°in the backward direction only. However, even in the best cases, 5% of the area of a milled surface comprised of embedded grit. Surface morphology can either exhibit directional grooving or cratering, depending upon complex interactions of the various processing parameters. The understanding of the role of various process parameters on the workpiece characteristics will allow the process parameters to be optimised for given requirements. Future work needs to examine the fatigue performance of the AJW-CDM structures, and again optimisation of the processing parameters to maximise fatigue life can be performed. Masking has been employed to provide an economic manufacturing solution for the AJW-CDM process for a specific component. Thus, AJW-CDM has been established as a potential replacement process for chemical milling.

Diamond reinforced metal-matrix composites (MMCs) are utilised for cutting, drilling, grinding and polishing a variety of materials, in many cases being the most efficient and economic choice. The increased cost of synthetic diamond abrasives has led to constant search for ways to extent diamond tool life. This has been realised by introducing chemical reactions at the interfaces in order to develop chemical bridges between diamonds and metals that prolong the retention of crystals at the operating surfaces of the tools. Alloying the matrix with carbide forming metals is a way to introduce interfacial reactivity, but involves problems with concentrating the alloying element at the interfacial region and may cause alteration of the wear resistance characteristics of the binder, which may be an undesirable effect. A recent development and alternative method to alloying is the coating of the diamonds with carbide forming metals, offering unique advantages. Although metal-coated diamonds are commercially available, the effectiveness of their usage and the understanding of interfacial phenomena occurring in composites reinforced with such abrasives still remain unexplored. The work carried out in this research has examined the interfacial bonding in diamond MMCs reinforced with metal-coated crystals. The work described in this thesis included a preliminary study on diamond/metal reactivity serving the need to identify the mode and intensity at which synthetic diamonds and elemental metals interact at various conditions. This was achieved by examining the changes occurring to diamond surfaces when crystals were heated in the presence of various elemental metals. The latter were brought in contact with the diamonds either in the form of loose or hot-pressed metallic powders or in the form of thin metal coatings deposited onto the crystals by vapour deposition methods. Results showed that metals, depending on their electronic configuration, either catalyse the graphitisation of diamond surfaces and dissolve carbon or react at the diamond surfaces to form carbide crystallites. Dissolution of the diamond occurred by formation of oriented hexagonal/triangular and rectangular pits on octahedral {111} and cubic {100} surfaces respectively. Intensity of interactions strongly depended on heating temperature and time. Metal coatings were found to efficiently react with the diamonds only after annealing at temperatures of the order of 1000°C subsequent to the deposition. The diamond impregnated MMCs investigated in this research were reinforced with various types of metal-coated and metal-powder encapsulated diamonds of the carbide forming metals of Ti, Cr and W. The tested composites included two types of metal-matrices that of standard plain cobalt as well as some selected alloyed matrices typically employed in practice. Interfacial bonding characterisation and assessment of the potential capability of the metal-coatings to offer enhanced diamond retention has been made by determining the mechanical properties of the composites and by conducting extensive microscopic analysis of the developed fracture surfaces. The results suggested that incorporating metal-coated crystals could be beneficial in improving the diamond retention, provided that consolidation temperature is sufficiently high to favour diamond/metal reactions. Results showed improvements in mechanical properties to be achieved when reinforcing with the coated diamonds compared to non-coated grit. The characteristics of the interactions at the diamond surfaces in the composites conformed to the findings of the preliminary study on the fundamentals of diamond/metals interactions. Reactions on crystal surfaces took place at the locations where prior dissolution of the diamond had occurred. Metal coatings were found to provide excellent protection to the diamonds against catalysed dissolution by aggressive binders. Thin coatings suffered from loss of continuity in systems were the coating metal atoms were readily soluble in the metal-matrix. This was avoided with thicker coatings that also appeared to provide a supplementary mechanical effect in addition to the chemical bonding in improving the retention of the diamond crystals. Encapsulation of diamond with carbide forming metals was a hybrid method between alloying the metal-matrix and coating the crystals. Although encapsulation provided sufficient levels of chemical interactions, it was shown that diamonds could not be efficiently protected from aggressive binders. In addition, composites impregnated with powder-encapsulated diamonds suffered from inadequate sintering of the carbide forming metal zones surrounding the crystals when consolidation was performed at relatively low temperatures which was reflected in inferior mechanical properties.

Second order matrix equations arise in the description of real dynamical systems. Traditional modal control approaches utilise the eigenvectors of the undamped system to diagonalise the system matrices. Any remaining off-diagonal terms in the modal damping matrix are discarded. A regrettable automatic consequence of this action is the destruction of any notion of the skew-symmetry in the damping. The methods presented in this thesis use the `Lancaster Augmented Matrices' (LAMs) allowing state space representations of the second order systems. `Structure preserving transformations' (SPTs) are used to manipulate the system matrices whilst preserving the structure within the LAMs. Utilisation of the SPTs permits the diagonalisation of the system mass, damping and stiffness matrices for non-classically damped systems. Thus a modal control method is presented in this thesis which exploits this diagonalisation. The method introduces independent modal control in which a separate modal controller is designed in modal space for each individual mode or pair of modes. The modal displacements and velocities for the diagonalised systems are extracted from the physical quantities using first order SPT-based filters. Similarly the first order filters are used to translate the modal force into the physical domain. Derivation of the SPT-filters is presented together with a method by which one exploits the non-uniqueness of the diagonalising filters such that initially unstable filters are stabilised. In the context of active control of rotating machines, standard optimal controller methods enable a trade-off to be made between (weighted) mean-square vibrations and (weighted) mean-square control forces, or in the case of a machines controlled using magnetic bearings the currents injected into the magnetic bearings. One shortcoming of such controllers for magnetic bearings is that no concern is devoted to the voltages required. In practice, the voltage available imposes a strict limitation on the maximum possible rate of change of control force (force slew rate). This thesis presents a method which removes the aforementioned existing shortcomings of traditional optimal control. Case studies of realistic rotor systems are presented to illustrate the modal control and control force rate penalisation methods. The system damping matrices of the case studies contain skew-symmetric components due to gyroscopic forces typical of rotating machines. The SPT-based modal control method is used to decouple the non-classically damped equations of motion into n single degree of freedom systems. Optimal modal controllers are designed independently in the modal space such that the modal state, modal forces and modal force rates are weighted as required. The SPT-based modal control method is shown to yield superior results to the conventional notion of independent modal space control according to reasonable assessment.

The finite element method has been used to predict the effect of rotation on the vibrational characteristics of structures. Kinematics of rotary motion were studied and numerical adaptation for the calculation of the acceleration matrices has been accomplished. Successful computation of the eigenvalue equation was achieved and a solution algorithm based on a modified QL method was then used. Existing three dimensional isoparametric finite elements were modified to add the extra acceleration matrices. Comparison with existing methods shows a very good agreement, typical discrepancies being 1-2%. It was shown that the centrifugal loading creates an initial stress field the effect of which can incorporated by the introduction of a geometric stiffness matrix. While the initial stresses are the largest contributors to the changes in the natural frequencies, they had only a very small effect on the mode shapes of any of the structures that were examined. The centripetal accelerations were found to have a smaller influence on the natural frequencies. It was found that the natural frequences changed with the angular speed according to the Southwell equation. The effect of the Coriolis acceleration on the natural frequencies is negligibly small. The mode shapes of rotating structures are affected by the Coriolis acceleration component and for some structures this effect is significant.