Bibliography : leaves 231-241 / ix, 241 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1992

Nonlinearity accompanied with stiffness in atmospheric boundary layer physical parameterizations is a well-known concern in numerical weather prediction (NWP) models. Nonlinear diffusion equations, furthermore, are a class of equations which are extensively applicable in different fields of science and engineering. Numerical stability and accuracy is a common concern in this class of equation. In the present research, a comprehensive effort has been made toward the temporal integration of such equations. The main goal is to find highly stable and accurate numerical methods which can be used specifically in atmospheric boundary layer simulations in weather and climate prediction models, and extensively in other models where nonlinear differential equations play an important role, such as magnetohydrodynamics and Navier-Stokes equations. A modified extended backward differentiation formula (ME BDF) scheme is adapted and proposed at the first stage of this research. Various aspects of this scheme, including stability properties, linear stability analysis, and numerical experiments, are studied with regard to applications for the time integration of commonly used nonlinear damping and diffusive systems in atmospheric boundary layer models. A new temporal filter which leads to significant improvement of numerical results is proposed. Nonlinear damping and diffusion in the turbulent mixing of the atmospheric boundary layer is dealt with in the next stage by using optimally stable singly-diagonally-implicit Runge-Kutta (SDIRK) methods, which have been proved to be effective and computationally efficient for the challenges mentioned in the literature. Numerical analyses are performed, and two schemes are modified to enhance their numerical features and stability. Three-stage third-order diagonally-implicit Runge-Kutta (DIRK) scheme is introduced by optimizing the error and linear stability analysis for the aforementioned nonlinear diffusive system. The new scheme is stable for a wide range of time steps and is able to resolve different diffusive systems with diagnostic turbulence closures, or prognostic ones with a diagnostic length scale, with enhanced accuracy and stability compared to current schemes. The procedure implemented in this study is quite general and can be used in other diffusive systems as well. As an extension of this study, high-order low-dissipation low-dispersion diagonally implicit Runge-Kutta schemes are analyzed and introduced, based on the optimization of amplification and phase errors for wave propagation, and various optimized schemes can be obtained. The new scheme shows no dissipation. It is illustrated mathematically and numerically that the new scheme preserves fourth-order accuracy. The numerical applications contain the wave equation with and without a stiff nonlinear source term. This shows that different optimized schemes can be investigated for the solution of systems where physical terms with different behaviours exist.

Aircraft designed for naval aircraft carriers experience great airframe stress during landing due to the high vertical velocities that they must maintain as a consequence of the extremely short runway and shallow landing angle of attack. This creates a need for structural rigidity to counteract the forces that land-based aircraft never experience. This is not ideal if it otherwise limits the performance and flying capabilities of the aircraft that are otherwise necessary for the environments they might find themselves in. As such, a new approach to protecting the aircraft from the immense loads they experience during landing could be to add flexibility to the airframe and landing gear, promoting deflection instead of failure. This thesis aims to investigate this idea, starting with an elementary set of tests, looking into material flexibility, and then moving on to adding this concept to progressively more advanced structural systems. Using balls of varying material, preliminary drop tests indicated that material flexibility could assist the dissipation of landing energies, showing that the coefficient of restitution increases with the stiffness. Drop tests involving mass-spring-damper systems as well as cantilever plates and transverse beams also indicated that the strain energy a body can absorb from a set load case can be increased if its flexibility also grows. This finding led to the important conclusion and finding that a flexible body can transfer and store at least 10 times its initial contribution of energy to a system in the form of strain energy. Through these tests, it was shown that flexible structures can be a beneficial design feature in combatting and dissipating vertical landing energies. / Master of Science / Historically, airplanes landing on naval aircraft carriers are subject to high impact loads when they land because the plane is traveling at a high velocity downward and has a short runway to stop on. This impact on the runway is so severe that it requires the structure of the airplane to be reinforced, which in turn makes the plane heavier and less capable in flight. This reinforcement also implies that the plane is quite stiff in all of its components. One solution to this issue is to reverse the design logic historically taken, and impose flexible structures into the main body of the plane, which can bend and absorb some of the vertical energy that the plane possesses. This theory was investigated using a series of drop tests, starting with ball drop tests of varying materials. These tests showed that the material of a ball can affect the energy that it absorbs and how much is kept by the ball after it collides with the ground. Next, more complex structures were tested, using shock absorbers, metal plates, and metal beams. These components were combined to form drop systems, which were dropped to measure the bending in the plates and beams, as well as the shock absorbers. The conclusion made from these tests is that a more flexible structure can absorb a higher percentage of energy compared to its initial contribution, than its stiffer and heavier counterpart. This important conclusion shows that the application of flexible structures could be a vital step in improving the design of airplane wing and body structures to promote the longevity of the structure of the aircraft.

Carbon nanotubes (CNTs) are known for their exceptional electrical, thermal, mechanical, optical, and chemical properties. With the significant progress in recent years on synthesis, purification and integration challenges, CNT network/array based thin-film transistors (TFTs) are likely to play a critical role as the building blocks of future electronics. CNT-TFTs can find applications in flexible, transparent and energy-efficient circuits, e-displays, solar cells, RFID tags, e-paper, touch screens, implantable medical devices and chemical/bio/optical sensors. CNTs in CNT-TFTs are deposited on low thermal conductivity substrates which can impede the heat dissipation resulting in high temperature. The excessive self-heating in CNT-TFTs can degrade the electrical and thermal performance and could potentially lead to failure of the devices. Therefore, the issues related to operational reliability of CNT-TFTs arising from the self-heating effects need to be examined and studied. In the present work, a computational approach is developed and employed to study the electrical and thermal transport in CNT-TFTs. The modeling framework can predict the current and temperature profile of CNT network/array and the supporting structure. The model is validated against the experimental results. In case of CNT network TFTs, the computational method allows us to examine the role of various device parameters such as network morphology (i.e., network density, CNT junction topology, and CNT length and alignment distribution) and channel geometry (i.e., channel length and width) on heat dissipation and thermal reliability. The simulation results help interpret experimental data and provide the quantitative information about the thermal boundary conductances at CNT junctions and CNT-substrate interfaces in CNT-TFTs. The findings suggest that the structure of CNT junctions on substrate can become very critical in CNT network TFTs as the lack of contact with the substrate at these junctions can lead to junction temperatures hundreds of degrees higher than the rest of the device, which will severely deteriorate the performance of these devices. High-field breakdown study of CNT network TFTs is also conducted which provides guidelines for the design and optimization with respect to aforementioned parameters in order to enhance the performance and reliability. Dense CNT arrays are preferred for better electrical performance in CNT array TFTs, but they also experience electrostatic and thermal cross-talk which can adversely affect the device performance. These effects have been studied in details. The role of trap charges in CNT array TFTs is also investigated to understand and mitigate hysteresis. Lastly, CNT-liquid crystal composites are studied using dissipative particle dynamics (DPD) technique with the aim to understand how the CNT concentration in composite affects the alignment of liquid crystals and to explore the method of CNT alignment using liquid crystals.

In this dissertation, first, the theoretical and experimental viewpoints of instability and bifurcation in mechanics are reviewed and discussed. The onset of instability of bifurcation depends on the constitutive assumptions, and is marked by the loss of ellipticity, singularity of the stiffness matrix, and negative or complex eigenvalues. Non-traditional regularization is necessary to obtain useful post-instability solutions. Based on dissipated energy and elastic potential, energy based instability criterion is considered and developed. The global instability criterion is concerned with global non-uniform deformation while the surface degradation instability criterion deals with near surface non-uniformities. In addition, the connection between surface degradation and size, shape effects for brittle materials is examined. The energy based stability theory is applied for some typical problems through analytical and numerical implementations. It is shown that the onset of both surface instability and global degradation instability occurs in the strain hardening stage, that is, before and close to the peak strength. The theoretical results are compared with experimental observations. Both strain gage tests and ultrasonic scanning tests are processed to study the degradation mechanisms of a brittle material. The surface effects are highlighted by the experiments. Ultrasonically dissipated energy shows a random distribution and it follows, in general, the initial non-homogeneity pattern. The relationship between the ultrasonically dissipated energy and mechanically dissipated energy is dependent on deformation and can be approximated by a power function of the factor of load level. The theory for surface degradation consideration involves a few material constants, and these constants are identified against experimental observations. The degradation mechanism and damage growth patterning of simulated rock under uniaxial load are modeled numerically by implementing the theory for damage and surface degradation with initial state consideration. The theoretical results are compared with experimental observations obtained through ultrasonic scanning tests. To extend the study to post-instability modelling by using various constitutive models, three alternative considerations are proposed to achieve so-called regularization of the problem.

No description available.

Traditional herbicide formulations such as Roundup® contain the active ingredient glyphosate paired with the non-ionic surfactant polyethoxylated tallow amine (POEA). The impacts of POEA in aquatic environments are uncertain. In this study the environmental fate and effects of POEA was evaluated. A mesocosm field study confirmed that POEA dissipated rapidly from the water, but was persisted in the sediment; biological effects were negligible. In the laboratory, histological analysis of gills did not indicate negative effects on gill function in Pimephales promelas exposed to POEA. Proliferation of mucous cells in gills was significantly greater following 7 days of exposure. Liver histology appeared normal following exposures. Mean thiobarbituric reactive substances (TBARS) doubled in minnow livers exposed to 10 µg.L-1 POEA for 7 days; however was not statistically significant. The present study indicates that POEA may persist in sediment and may influence benthic communities over the long term. / May 2016

It is well known that composite materials have a poor resistance to the damage caused by the impact of foreign objects on their outer surface. There are various methods for improving the impact damage tolerance of composite materials, such as: fiber toughening, matrix toughening, interface toughening, throughthe- thickness reinforcements and selective interlayers and hybrids. Hybrid composites with improved impact resistance would be particularly useful in military and commercial civil applications. Hybridizing composites using shape memory alloys (SMAs) is one solution since SMA materials can absorb the energy of impact through superelastic deformation or recovery stress reducing the effects of the impact on the composite structure. The SMA material may be embedded in the hybrid composites (SMAHC) in many different forms and also the characteristics of the fiber reinforcements may vary, such as SMA wires in unidirectional laminates or SMA foils in unidirectional laminates only to cite two examples. Recently SMA fibers have been embedded in 2-D woven composites. As part of this PhD work, the existing theoretical models for woven composites have been extended to the case of woven SMAHC using a multiscale methodology in order to predict the mechanical properties and failure behavior of SMAHC plates. Also several parts of the model have been coded in MATLAB and validated against results extracted from the literature, showing good correlation.

We theoretically study steady-state nonequilibrium properties of various open electronic systems subject to time-independent external bias. A charge current is established across each system by its coupling to two external particle reservoirs maintained at different chemical potentials. We discuss the impact of intra-reservoir electron correlations on transport, and examine how reservoir-generated dissipation and nonequilibrium-induced decoherence influence these systems. The effect of intra-lead electron interactions on transport is investigated in the context of a phonon-coupled single molecule transistor driven by Luttinger-liquid source and drain leads. The semi-classical master equation approach is used to compute current and noise characteristics of the device for various interaction strengths in the leads. The results suggest the possibility of tuning the Fano factor of the device using intra-lead electron interactions. The Keldysh path integral formalism is used to theoretically formulate models that describe the remaining open nonequilibrium systems. We consider voltage-induced electron-phonon scattering and electron mass enhancement due to phonons in a model metallic system. The possibility of adjusting the acoustic phonon velocity and the Thomas-Fermi screening length with external voltage is discussed. The effects of dissipation is investigated in an open BCS superconducting graphene, where the dissipation-induced rearrangement of its ground state from the BCS superconductor to the Fermi liquid is examined. The results theoretically infer prospects for a voltage-tuned metal-to-BCS quantum phase transition in graphene. Lastly, we develop a theory of nonequilibrium quantum criticality in open itinerant Ising and Heisenberg magnets. Both departures from equilibrium at conventional quantum critical points and the physics of phase transitions induced by the nonequilibrium drive are analyzed.

Modeling of wave energy transformation and breaking on fringing reefs is inherently difficult due to the unique topography of reefs. Prior methods of determining dissipation are based on empirical data from gently sloping beaches and offer only bulk energy dissipation estimates over the entire spectrum. Methods for deducing a frequency-dependent dissipation have been limited to hypothesized linkages between dissipation and wave shape in the surf zone, and have used bulk dissipation models as a constraint on the overall dissipation for mild sloping beaches. However, there is no clear indication that the constraint on the overall level of dissipation is suitable for the entire reef structure. Using these constraints the frequency-dependent dissipation rate can be deduced from laboratory data of wave transformation over reefs, taken at the Coastal and Hydraulics Laboratory. The frequency-dependent dissipation rate can then be integrated over the spectrum to derive an empirically-based counterpart to energy flux dissipation. Comparing the bulk energy dissipation estimates for the reef system to the frequency based method allows for the modification of wave breaking parameters in the frequency based estimation. Since this method is based on the Fourier transform of the time series data, it allows the dissipation to be found as a function of the frequency. This analysis shows that there is a correlation between the amount of energy in the low frequencies of the wave spectrum and certain characteristics of the frequency-dependent dissipation coefficient.