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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Gas-Liquid Dispersion and Mixing in Mechanically Agitated Vessels with a Range of Fluids

Allsford, K. V. January 1985 (has links)
This study aims at understanding the effect of fluid rheology on gas dispersion and mixing in mechanically agitated vessels. Bulk flow is linked with the two-phase flow in the impeller region and the power drawn by the rotating agitator(s). A base case study using a Rushton Disc Turbine in water is initially reported. Model Newtonian, viscoelastic and shear-thinning fluids (corn syrup, Boger fluids and Carbopol solutions respectively) and a typical fluid (CMC solution) were then used to determine the effects of fluid rheology on flow phenomena and power consumption for single agitators (Disc Turbines and Angle-Bladed Impellersl dual combinations thereof, and InterMIGs under gassed and ungassed conditions in a 0.61 m diameter vessel. Similar experiments were performed in smaller vessels. The relative effectiveness of all the agitator configurations studied at achieving bulk liquid mixing was also determined using a redox reaction technique. The most energy efficient configuration proved to be a large Disc Turbine combined with an equisized Angle-Bladed Impeller (pumping upwards) in both the gassed and ungassed cases. The results presented in this thesis are also related to process design considerations and a technique which predicts the agitator rotational speed and diameter required for achieving optimal mass transfer is developed.
2

Low energy quantum gravity

Mackay, Paul January 2012 (has links)
This thesis investigates two very different aspects of quantum gravity. In the first - and main - section, we examine the question of quantum gravitational contributions to the running of a coupling parameter alongside the various problems and issues that this raises. We treat quantum gravity as an e ective eld theory and use perturbative methods to address issues. Speci cally, we look at a '4-type scalar coupling. In a gauge-invariant way, we consider a non-minimally coupled, massive scalar eld, with non-constant background, in the presence of a cosmological constant and contrary to most of the literature, we also calculate all derivative terms. An e ective action is constructed, renormalization counterterms calculated, and we nd that, within certain bounds, gravity leads to asymptotic freedom of scalar eld theory. Furthermore, we investigate whether considering quadratic divergences in gravitational calculations can tell us anything useful. In this case we nd non-vanishing quadratic divergences. However, we also recognise the possibility that quadratic divergences are somewhat of a red herring and that by suitable eld rede nitions, we can eliminate these from our calculations. The second section of the thesis addresses the possibility of super uidity in a quark gluon plasma. We use the framework of AdS/CFT, with knowledge of black hole thermodynamics, to consider the duality between a black hole in anti-de Sitter space and a uid existing on the boundary. Initially, we look at a simple case of a black hole possessing only mass and charge in AdS spacetime and calculate such properties as the entropy, temperature and speci c heat capacity, identifying a telltale sign of a phase change (speci c heat capacity tending to in nity) and of points of vanishing viscosity (corresponding with a zero entropy). After con rming that such a boundary exists, we take a di erent approach where we calculate and interpret the solutions to a relativistic Gross-Pitaevskii equation on a sphere. On projection back to R3, the solutions are seen to be tori, which we choose to interpret as vortex rings in analogy to the expected feature of those which are known to appear in a real super uids.
3

Some analytical and numerical topics related to long wave approximations : with applications to water waves

Bidin, Mokhtar January 1977 (has links)
No description available.
4

An investigation into finite volume methods for solid mechanics

Cheung, Ronald Chak Man January 2014 (has links)
Research into applying finite volume methods to problems in solid mechanics is presented. The investigation has been motivated by the idea that a high-fidelity aeroelastic simulation can be made possible by extending the finite volume methods already implemented in many existing computational fluid dynamics solvers to solid mechanics. A detailed study and survey of applicable methods have been conducted to identify suitable candidates for a three-dimensional time-accurate large-deformation solid mechanics solver. A vertex-centred and a cell-centred solver were initially implemented. Upon comparison, the cell-centred solver appeared to be computationally more efficient despite suffering from a numerical issue. From this analysis, an improved formulation was subsequently developed for the cell-centred solver. In addition, a robust method for numerical gradient evaluation has been developed and incorporated to minimise errors associated with skewed cells or poorly supported cells at domain boundary. The method is based upon the Green-Gauss method, but takes advantage of a secondary numerical gradient to improve overall accuracy and reliability . The improved cell-centred solver has been shown to be accurate, robust and suitable for large deformations in a non-linear validation case against NASTRAN. High computational efficiency has also been demonstrated in OpenMP parallelisation and convergence acceleration via multigrid. The multigrid implementation has been made possible through incorporating a dual-time implicit scheme into the solver.
5

The preparation of tapes and booklets suitable for a revision course in particle dynamics

Jackson, Kenneth A. H. January 1980 (has links)
No description available.
6

Oscillatory Oseenlets

Elmazuzi, R. A. H. January 2011 (has links)
Consider uniform flow past an oscillating body. Assume that the resulting far-field flow consists of both steady and time periodic components. The time periodic component can be decomposed into a Fourier expansion series of time harmonic terms. The form of the steady terms given by the steady oseenlets are well-known. However, the time-harmonic terms given by the oscillatory oseenlets are not. In particular, the Green's functions associated with these terms are presented. In this thesis, the oscillatory oseenlet solution is presented for the velocity and pressure, and the forces generated by them are calculated. A physical interpretation is given so that the consequences for moving oscillating bodies can be determined. As the frequency of the oscillations tend to zero, it is shown that the steady oseenlet solution is recovered. Also, as the Reynolds number of the flow tends to zero, it is shown that the oscillatory stokeslet solution is recovered. In this latter case, the oscillatory oseenlets solution is an outer matching to the inner oscillatory stokeslet solution. An application of this new representation is discussed for future work.
7

An investigation of thermal creep buckling

Webster, George Arnold January 1962 (has links)
A simplified theory is developed for calculating the creep buckling of components in the form of prismatic bars, and extended to cover the case of two-member components such as reactor fuel elements. The rate modulus (evolved at the mean stress) approach is used and all phases of creep and elastic strains are considered. For the two-member components it is shown that a solution in closed form can only be obtained when the mean stresses in the components remain constant. In general this will not be the case and a graphical method of solution involving isochronous stress-strain curves is suggested. Throughout the analysis a modified form of the Andrade tensile creep equation proposed by Graham and Walles is assumed. Results of creep buckling experiments on E1C-M commercially pure aluminium rods and on magnox A.12 rods are presented, together with data for the creep buckling of composite specimens of the two materials, and compared with the theory.
8

Constraint based simulation of soft and rigid bodies

Lewin, Christopher January 2016 (has links)
This dissertation presents a number of related works in real-time physical animation, centered around the theme of constraint-based simulation. Methods used for real-time simulation of deformable bodies tend to differ quite substantially from those used in offline simulation; we discuss the reasons for this and propose a new position-based finite element method that attempts to produce more realistic simulations with these methods. We also consider and adapt other methods to make them more suitable for game physics simulation. Finally, we adapt some concepts from deformable body simulation to define a deformable rod constraint between rigid bodies that allows us to represent the kinematics of the human spine using fewer degrees of freedom than required with a strictly joint-based model.
9

Classical and quantum aspects of infinite derivative field theories and infinite derivative gravity

Talaganis, Spyridon January 2017 (has links)
The objective of this thesis is to study classical and quantum aspects of infinite derivative field theories and infinite derivative gravity. In- finite derivative theories of gravity can be made free from ghosts and classical singularities. In order to avoid ghosts, one modifies the graviton propagator by employing entire functions so that no new poles are introduced apart from the pole corresponding to the massless graviton of General Relativity. Inspired by infinite derivative gravity, we consider an infinite derivative scalar toy model and demonstrate renormalisability when the loop-order is arbitrarily large. Moreover, scattering diagrams within the framework of infinite derivative field theories are explicitly evaluated and it is shown that the cross section can be made finite. Finally, we perform a Hamiltonian analysis of an infinite derivative gravitational theory with a simpler action containing only the Ricci scalar and compute the number of relevant degrees of freedom.
10

The response of structures to acoustic excitation with special reference to the sonic boom

Hudson, Roderick Reginald January 1969 (has links)
The research reported in this thesis is concerned with the response of mechanical structures to the excitation of acoustic fields. Both the vibration of the structure itself (sonic boom studies) and the secondary sound field which this vibration produces (transmission loss studies) are investigated. In measuring the airborne transmission loss of a high loss partition an important limitation of the University's experimental suite was discovered. Attempts at an indirect measurement of transmission loss using vibration transducers illustrate a fallacious assumption of most transmission loss theories. These findings impose a considerable limitation upon the accelerometer method of transmission loss measurement. The study of structural vibration was extended to sonic boom response. In particular the effects of a cavity behind a panel upon the panel's dynamic properties is studied both experimentally and theoretically. This model is comparable with a window-room system and so is of current interest in the evaluation of the possibility of sonic boom damage.

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