Various problems, which examine the propagation of gas dynamic disturbances, through an explosive atmosphere, are considered. The first set studies a model relaxing gas, and asymptotic methods are employed. A high frequency expansion is used to investigate piston oscillations in an infinite half space. The first two terms in the velocity perturbation are found in the acoustic case. The amplitude and frequency change on a wavelet are given; the wave number alters from wavelet to wavelet. For an enclosed volume the multi-time method is employed. When a standing wave exists in the vessel the frequency changes: when the vessel oscillates the wave number changes. The situation when forced oscillations at a natural frequency of the container is discussed. Also finite amplitude oscillations in a vessel are considered by using the multi-time method. An integral equation for the amplitude growth is found. A numerical solution of outward wave propagation, in spherical and cylindrical coordinates until shock formation, is given. The second group of problems considers a multi-component gas which can be analysed numerically. The effect of the homogeneous explosion in amplifying or damping a weak ii discontinuity is simulated. Thus proposals for reaction schemes can be analysed. It is found there is a relation- ship between amplification/damping and strong/weak ignition, in a mixture of hydrogen and oxygen in a shock tube. The reactions liberating a significant amount of energy in the chemical reaction, are the reactions causing greatest amplification.

Differential surface tension is a common phenomenon in many chemical and biomedical processes. Localised surface tension gradients due to differential surface loading in thin films give rise to a moving shock front in the direction of higher surface tension. Existence of a background flow enhances the shock wave giving rise to wave breaking and wave separation mechanisms. The effect of a background flow field on Marangoni stress induced shock fronts were investigated in this thesis. Furthermore, a numerical procedure to find approximate solutions to the fully nonlinear flow problem that arises due to Marangoni spreading is proposed. A set of surface evolution equations that incorporates the effects of the background flow field is studied in two major respects: (i) breaking the horizontal symmetry and (ii) nonlinear accretion leading to shock front breaking or separation. The evolution of the surface is evaluated by numerical simulations for a wide range of parameter values. The investigation showed that there are two breaking mechanisms switched by the value of Peclet number. Furthermore it showed that the life time of the shock front is determined by the volumetric flow rate of the film. It is shown here that a weak Marangoni force generates a pure capillary gravity wave that propagates faster than the surfactant front. It is customary to use the lubrication approximations to simplify thin film problems. As a result, the inertial terms in flow equations and nonlinear terms in surface stress balances become excluded. To analyse the fully nonlinear flow, a finite element (FEM) analysis is proposed. The simulations shows that the lubrication theory holds globally in predicting the spreading rates but fails to do so locally until a quasi-steady state is reached. The FEM model shows the formation of two counter-rotating vortices at the beginning which diminish as time evolves. The FEM results are compared with the lubrication theory simulations. FEM model shows rapid film thinning forming extremely thin films within a short period of time. Though detailed transport mechanisms differ, both methods are in close agreement in predicting the spreading rates.

The phase behaviour and thermodynamic properties of simple model mixtures are examined using the statistical associating fluid theory as extended to chain molecules interacting with potentials of variable range (SAFT-VR), and by computer simulation. The SAFT-VR approach is based on an accurate and compact representation of the free energy of chain molecules. We present the SA FT -VR methodology as applied to mixtures of non-conformal molecules. A series of mixing rules are presented, beginning with the van der Waals one-fluid prescription and including more complex treatments. The vapour-liquid equilibria of a mixture consisting of hard spheres and square-well monomers is examined with the SAFT-VR equation of state, together with the liquid-liquid equilibria of a symmetrical square-well mixture with no unlike interactions. Additionally, we examine the vapour-liquid equilibria of a square-well monomer-dimer mixture, composed of equal-sized segments, both with the SAFT-VR approach and by Gibbs ensemble Monte Carlo simulation. The simulation data are used to determine the vapourliquid critical line of the mixture. An extension of the SAFT-VR approach to describe the phase behaviour of chain molecules interacting with a soft repulsive potential and an attractive well of variable range is presented. We focus on the vapour-liquid properties of Lennard-Jones chains using a simple recipe for the evaluation of the chain free energy. We also perform a case study for a specific class of phase equilibria exhibited by binary mixtures, where systems are seen to posses a region of closed-loop immiscibility in their phase diagrams. We examine the nature of this type of pl1ase behaviour using the SA FT· VR equation of state and Gibbs ensemble simulation for a simple model system with an anisotropic bonding site, which is seen to be the governing factor in the appearance of the region of low-temperature miscibility for this system. The model is chosen in order to mimic the physical features of real systems which exhibit this type of re-entrant phase behaviour. The critical regions of this model are examined using a finite-size scaling analysis performed in the semigrand canonical ensemble.

LKAB’s underground mine in Kiirunavaara has experienced an increasing seismic activity the last ten years. This seismic activity is caused by the stress redistribution resulting from the mining method of large-scale sublevel caving. The energy from the seismic events propagate in the rock mass as seismic waves. If one of these waves interacts with an excavation, it will be subjected to dynamic loads, and damage can potentially occur. Damage can be caused by different mechanisms depending on many factors such as pre-existing structures in the rock mass and the state of stress. To prevent these damages, LKAB has installed a rock support system for handling dynamic loads. This thesis has analysed available damage mapping reports, investigations, pictures, seismic data and history, in order to evaluate the function of the support system when subjected to dynamic loads. The conclusion of the analysis is that the support system is well designed, but there are areas of improvement. The main damage mechanisms are bulking without ejection and rockfall due to seismic shaking. Bulking with ejection and ejection due to seismic energy transfer were concluded to not yet be a problem in the Kiirunavaara mine. This result implies that an improved stiffness, static strength and yieldability are to be considered in order to decrease the amount of bulking. For rockfall due to seismic shaking, there are two main areas of improvement. The structural mapping has to be given higher priority, and it should provide direct support recommendations if needed. The second part is to increase the static strength of the system in order to survive rockfall due to seismic shaking. Since bulking with ejection and ejection due to seismic energy transfer are not yet considered significant problems, there is no need to improve the support system with respect to absorption of kinetic energy. The location of the damages in the drift profiles were also analysed, and it was concluded that a majority of the damages that occurred in the footwall drifts were located in the corner of the abutment facing the orebody. In the crosscuts, a majority of the damages occurred in the abutment and roof. Based on this, it is suggested that the support should be improved in the abutment and roof of the crosscuts, and in the abutment facing the ore of the footwall drifts.

This document describes the development of a computational model to study the movement and breakup _of droplets in turbulent two-component flows. The aim is to produce a suitable model which will be economical of computing resources and practical for engineering applications. The application of particular interest here is that of water droplets in fully developed turbulent pipe flows of oil. The computational method uses Vortex filaments to produce, in a novel way, instantaneous fluctuating velocities within the flow domain. The trajectory of a particle within this field is predicted by integrating the theoretical law of motion for the particle. In addition, the breakup of a fluid particle in the turbulent field may be predicted using an empirical criterion formulated using data obtained from a series of experiments. The tests were designed to study the deformation and breakup of a single water droplet in oil subjected to shear. Wherever possible the results of each development stage of the model were compared with work published in the literature.

<p> Interest in thermoelectric devices (TEDs) for waste-heat recovery applications has recently increased due to a growing global environmental consciousness and the potential economic benefits of increasing cycle efficiency. Unlike conventional waste-heat recovery systems like the organic Rankine cycle, TEDs are steady-state, scalable apparatus that directly convert a temperature difference into electricity using the Seebeck effect. The benefits of TEDS, namely steady-state operation and scalability, are often outweighed by their low performance in terms of thermal conversion efficiency and power output. To address the issue of poor device performance, this dissertation takes a multi-faceted approach focusing on device modeling, analysis and design and material processing.</p><p> First, a complete one-dimensional thermal resistance network is developed to analytically model a TED, including heat exchangers, support structures and thermal and electrical contact resistances. The purpose of analytical modeling is twofold: to introduce an optimization algorithm of the thermoelectric material geometry based upon the realized temperature difference to maximize thermal conversion efficiency and power output; and to identify areas within the conventional TED that can be restructured to allow for a greater temperature difference across the junction and hence increased performance. Additionally, this model incorporates a component on the numerical resolution of radiation view factors within a TED cavity to properly model radiation heat transfer. Results indicate that geometric optimization increases performance upwards of 30% and the hot-side ceramic diminishes realized temperature difference. The resulting analytical model is validated with published numerical and comparable analytical models, and serves as a basis for experimental studies.</p><p> Second, an integrated thermoelectric device is presented. The integrated TED is a restructured TED that eliminates the hot-side ceramic and directly incorporates the hot-side heat exchanger into the hot-side interconnector, reducing the thermal resistance between source and hot-side junction. A single-state and multi-stage pin-fin integrated TED are developed and tested experimentally, and the performance characteristics are shown for a wide range of operating fluid temperatures and flow rates. Due to the eliminated to thermal restriction, the integrated TED shows unique performance characteristics in comparison to conventional TED, indicating increased performance.</p><p> Finally, a grain-boundary engineering approach to material processing of bulk bismuth telluride (Bi₂Te₃) is presented. Using uniaxial compaction and sintering techniques, the preferred crystallographic orientation (PCO) and coherency of grains, respectively, are controlled. The effect of sintering temperature on thermoelectric properties, specifically Seebeck coefficient, thermal conductivity and electrical resistivity, are determined for samples which exhibited the highest PCO. It is shown the performance of bulk Bi₂Te₃ produced by the presented method is comparable to that of nano-structured materials, with a maximum figure of merit of 0.40 attained at 383 K.</p>

No description available.

A numerical approach for modelling variable stator stagger in multistage stage axial flow compressors is presented. The development of such an approach has been motivated by the requirements of an optimisation methodology for stator vane setting and active control of instability using controlled stator vane setting. The optimisation methodology has been further developed but active control approaches are discussed as future considerations. Varying upstream stator vane stagger . changes the incident flow angle on . the downstream rotor thus affecting the entire flow distribution within the compression systems. The approach therefore begins by investigating the effect of a change in stator stagger setting on stage performance. A meanline method was used for nu- merical prediction of stage characteristics as it can simulate the effect of a change in stagger settings and ( or) in rotational speeds. Overall compressor performance was obtained by stacking the (experimental or predicted) stage characteristics and the surge conditions predicted using a stage-by-stage dynamic compression model where the compressibility was considered explicitly. This approach for variable stagger set- ting was incorporated into a FORTRAN code and validated using the data from the 12-stage HP SPEY jTAY variable geometry compressor. To optimise the setting, a direct search method incorporating a Sequential Weight Increasing Factor Technique (SWIFT) algorithm was incorporated into the variable stagger model. The objective function in this optimisation is penalised externally 11 with an updated factor which helped to accelerate convergence. The methodology has been incorporated into a FORTRAN program and its validations were conducted using the data from the 7-stage LP OLYMPUS and the 12-stage HP SPEY /TAY compressors. Results have demonstrated that variable stagger setting is a powerful method to rematch stages and which can be used to improve the desired overall performance, and that the potential benefits of introducing additional rows of variable setting vanes can be achieved. Future work arising from the present study has been discussed and highlighted, which involves the enhancement of the model capacity and development of active control approaches. In addition the thesis involves several reviews focusing on different topics. Most reviews contain considerable information and it is expected that the information can be of help for the interested readers to trace more relevant references. These reviews consist of a general review in chapter 1; a brief review on stage characteristics modelling in chapter 2; a comparative review on incompressible and compressible surge models in chapter 3; a review of various optimisation methods for practical problems, especially for constrained non-smooth problems, in chapter 4; and a review of the state-of-the-art active approaches in chapter 7. The suitability of various approaches has been highlighted. Steinke's meanline method is suitable for investigating the in- influence of stagger resetting on stage performance. To predict the surge conditions for a (high-speed) multistage environment, the stage-by-stage compressible models are III more promising. For constrained non-smoothed optimisation, the SWIFT algorithm can be an alternative. The controlled stator vane regulated through nonlinear control law will permit the robust control of compressor instabilities.

For the efficient design of transonic turbomachinery systems, understanding of the complex flow phenomena inherent in the flow passages is essential. In the present study, a computational technique is adopted to meet this formidable goal. A code using a time-marching technique has been developed first for quasi three-dimensional cascades (that is two-dimensional computation with the varying streamtube height in the third dimension taken into consideration) and then extended to fully three-dimensional flows within the rotating flow passages. Each code has a built-in switch for in viscid and viscous flows. The basis of the codes is the conservative form of the Reynolds- averaged Navier-Stokes equations in a rotating framework. This is supplemented by either the Baldwin-Lomax (algebraic) or the k-e (two-equation) turbulence model. For solving the hyperbolic type governing equations, spatial derivatives are first discretized on the easily-constructed H-type grid system using a central-difference finite-volume approximation with the flow variables stored at the cell centre. An explicit multistage Runge-Kutta scheme is then employed for the time integration o f the resulting ordinary differential equations. The accuracy of the quasi three-dimensional code is initially evaluated by predicting the flows through cascades with simple geometry. Its robustness is then confirmed by two realistic configurations with a wide range o f operating conditions. Finally the fully three-dimensional code is applied to two highly loaded transonic rotors with complicated geometry at peak efficiency and near stall operating conditions. An extensive comparison in terms of detailed flowfield and overall performance between the predictions and experiments with laser anemometry and conventional probes shows the accuracy o f the codes and also indicates that the present study has great potential to be a viable aerodynamic design and analysis tool in the development of transonic turbomachinery systems.

Every time we breathe in we inhale thousands of particles, some of which may become trapped in the liquid lining of the airway wall. In this thesis we use theoretical fluid dynamics to model various aspects of the dynamics of these particles after their initial deposition on the airway wall. In Chapter 2 we consider the behaviour of an inhaled particle trapped in an alveolar corner, modelled as a two-dimensional cylinder partially immersed in a liquid pool in the corner of a rigid-walled wedge. We balance quasistatic capillary forces acting on the particle with viscous forces, modelled using lubrication theory, acting in a small gap between the particle and the wall. The direction of particle motion is non-intuitive and we obtain predictions for the fate of a particle dependent on the wedge angle, liquid volume and the size and deposition site of the particle. In practice, surface forces have been shown to pull particles into the airway liquid lining with sufficient force to depress underlying epithelial cells. In Chapters 3 and 4, using elastohydrodynamics, we consider the unsteady motion of a particle close to a deformable surface and the effect of wall deformation on the particle's behaviour. We model this initially as a two-dimensional cylinder moving in fluid perpendicularly and transversely close to a spring-backed plate, using simulations and asymptotic analysis based on lubrication theory. Viscous forces cause a transient overshoot of the force acting on the particle following a prescribed perpendicular displacement. Transverse motion of the particle causes the formation of a `corner' in the wall, which is particularly sharp immediately following the particle's initial displacement. In addition we consider the extension of the model into three dimensions and examine a sphere moving close to a deformable plane in a fluid environment. In Chapter 5 we consider the motion of a particle trapped in a mucus layer which is propelled by cilia acting within an underlying serous layer. We model this as a cylindrical disk moving within a viscous sheet, with a uniformly distributed body force in the lower layer representing the cilia. We predict the speed of the particle as a function of disk shape, ciliary activity and other material parameters.