This thesis explores the factors controlling the distribution of black carbon (BC) in the atmosphere/troposphere and its implications for climate forcing. BC is of great climate interest because of its warming potential. Estimates of BC climate forcing have large uncertainty, in part due to poor knowledge of the distribution of BC in the atmosphere. This dissertation first examines the factors controlling the sources of BC in the Arctic in winter and spring using a global chemical transport model (GEOS-Chem). Emission inventories of BC and wet scavenging of aerosols in the model are updated to reproduce observed atmospheric concentrations of BC as well as observed snow BC content in the Arctic in winter-spring. The simulation shows a dominant contribution of fuel (fossil fuel and biofuel) combustion to BC in Arctic spring. Arctic snow BC content is dominated by fuel combustion sources in winter, but has equal contributions from open fires and fuel combustion in spring. The estimated decrease in Arctic snow albedo due to BC deposition in spring is 0.6%, resulting in a regional surface radiative forcing of 1.2 W m-2. The dissertation then extends the evaluation of the BC simulation to the global scale using aircraft observations over source regions, continental outflow and remote regions and ground-based measurements. The observed low BC concentrations over the remote oceans imply more efficient BC removal than is currently implemented in models. The simulation that has total BC emissions of 6.5 Tg C a-1 and a mean tropospheric lifetime of 4.2 days for 2009 (vs. 6.8 &plusmn 1.8 days for the AeroCom models) captures the principal features of observed BC. The simulation estimates a global mean BC absorbing aerosol optical depth of 0.0017 and a top-of-atmosphere direct radiative forcing (DRF) of 0.19 W m-2, with a range of 0.17-0.31 W m-2 based on uncertainties in the BC atmospheric distribution. The DRF is lower than previous estimates, which could be biased high because of excessive BC concentrations over the oceans and in the free troposphere. / Engineering and Applied Sciences

Due to more and more aggressive designs in turbomachinery, assuring the structural integrity of its components has become challenging. Also influenced by this trend is blade design, where lighter and slimmer blades, in combination with higher loading, lead to an increased risk of failure, e.g. in the form of blade vibration. Methods have been proposed to reduce vibration amplitudes for subsonic engines, but cannot directly be applied to transonic regimes due to the additional physical phenomena involved. Therefore the present work investigates numerically the influence of two methods for reducing blade vibration amplitudes in transonic turbomachines, namely varying the blade count ratio and clocking. As it is known that clocking affects the efficiency, the concurrent effects on vibration amplitudes and efficiency are analyzed and discussed in detail. For the computational investigations, the proprietary Fortran-based non-linear, viscous 3D-CFD solver VolSol is applied on two transonic compressor cases and one transonic turbine case. In order to reduce calculation time and to generate the different blade count ratios a scaling technique is applied. The first and main part of this work focuses on the influence of the reduction techniques on aerodynamic forcing. Both the change in blade count ratio and clocking position are found to have significant potential for reducing aerodynamic force amplitudes. Manipulation of the phasing of excitation sources is found herein to be a major contributor to the amplitude variation. The lowest stimulus results are achieved for de-phased excitation sources and results in multiple blade force peaks per blade passing. In the case of blade count ratio variation it was found that blockage for high blade count ratios and the change in potential field size have significant impacts on the blade forcing. For the clocking investigation, three additional operating points and blade count ratios are analyzed and prove to have an impact on the force reduction achievable by clocking. The second part of the work evaluates the influence of clocking on the efficiency of a transonic compressor. It is found that the efficiency can be increased, but the magnitude of the change and the optimal wake impingement location depend on the operating point. Moreover it is shown that optimal efficiency and aerodynamic forcing settings are not directly related. In order to approximate the range of changes of both parameters, an ellipse approximation is suggested. / <p>QC 20130911</p> / TURBOPOWER

In this thesis, we present a number of results in set theory, particularly in the areas of forcing, large cardinals, and combinatorial set theory. Chapter 2 concerns covering matrices, combinatorial structures introduced by Viale in his proof that the Singular Cardinals Hypothesis follows from the Proper Forcing Axiom. In the course of this proof and subsequent work with Sharon, Viale isolated two reflection principles, CP and S, which can hold of covering matrices. We investigate covering matrices for which CP and S fail and prove some results about the connections between such covering matrices and various square principles. In Chapter 3, motivated by the results of Chapter 2, we introduce a number of square principles intermediate between the classical and (+). We provide a detailed picture of the implications and independence results which exist between these principles when is regular. In Chapter 4, we address three questions raised by Cummings and Foreman regarding a model of Gitik and Sharon. We first analyze the PCF-theoretic structure of the Gitik-Sharon model, determining the extent of good and bad scales. We then classify the bad points of the bad scales existing in both the Gitik-Sharon model and various other models containing bad scales. Finally, we investigate the ideal of subsets of singular cardinals of countable cofinality carrying good scales. In Chapter 5, we prove that, assuming large cardinals, it is consistent that there are many singular cardinals such that every stationary subset of + reflects but there are stationary subsets of + that do not reflect at ordinals of arbitrarily high cofinality. This answers a question raised by Todd Eisworth and is joint work with James Cummings. In Chapter 6, we extend a result of Gitik, Kanovei, and Koepke regarding intermediate models of Prikry-generic forcing extensions to Radin generic forcing extensions. Specifically, we characterize intermediate models of forcing extensions by Radin forcing at a large cardinal using measure sequences of length less than. In the final brief chapter, we prove some results about iterations of w1-Cohen forcing with w1-support, answering a question of Justin Moore.

A change in the atmospheric inventory of a greenhouse gas produces a radiative forcing on the atmosphere which results in climatic change. Thus to understand climate change resulting from perturbations to atmospheric greenhouse gas concentrations it is necessary to quantify the radiative forcing. Here, radiative forcings are presented for large changes in atmospheric CO2, CH4, and N2O in the modern atmosphere and large changes in atmospheric CO2, CH4 and 18 other gases for the Archean atmosphere. For the modern Earth, I present new calculations of radiative forcing at very high concentrations of CO2, CH4, and N2O, relevant to extreme anthropogenic climate change and paleoclimate studies. CO2 forcing is calculated over the range 100 ppmv to 50,000 ppmv. CH4, and N2O forcings are calculated over the range 100 ppbv to 100 ppmv. The sensitivity of these calculations to spatial averaging and tropopause definition are examined. I compare our results with the ``simplified expressions'' reported by IPCC, and find significant differences at high greenhouse gas concentrations. I provide new simplified expressions which agree much better with the calculated forcings, and suggest that these expressions be used in place of the IPCC expressions. Additionally, I provide meridionally resolved forcings which may be used to force simple and intermediate complexity climate models. For the Archean Earth, I present new calculations of radiative forcing for CO2 (10^-6 - 1 bar), CH4 (500 ppbv - 10,000 ppmv) and 18 other gases (10 ppbv - 10 ppmv). I aim to provide a set of radiative forcing and overlap calculations which can be used as a standard for comparisons. Radiative forcings are calculated for atmospheres with various N2 inventories (0.5, 1, and 2 bar). The effect of overlap and atmospheric pressure on radiative forcing are examined. The CO2 radiative forcings are consistent with previous work, however, I find significantly more shortwave absorption by CH4 than previously reported which may limit warming above 100 ppmv. For the 18 other gases, I find that significant radiative forcings result from low concentrations (<1 ppmv). These forcings are compared to those given in the literature. / Graduate / 0756 / 0608 / 0725 / bbyrne@uvic.ca

A change in the atmospheric inventory of a greenhouse gas produces a radiative forcing on the atmosphere which results in climatic change. Thus to understand climate change resulting from perturbations to atmospheric greenhouse gas concentrations it is necessary to quantify the radiative forcing. Here, radiative forcings are presented for large changes in atmospheric CO2, CH4, and N2O in the modern atmosphere and large changes in atmospheric CO2, CH4 and 18 other gases for the Archean atmosphere. For the modern Earth, I present new calculations of radiative forcing at very high concentrations of CO2, CH4, and N2O, relevant to extreme anthropogenic climate change and paleoclimate studies. CO2 forcing is calculated over the range 100 ppmv to 50,000 ppmv. CH4, and N2O forcings are calculated over the range 100 ppbv to 100 ppmv. The sensitivity of these calculations to spatial averaging and tropopause definition are examined. I compare our results with the ``simplified expressions'' reported by IPCC, and find significant differences at high greenhouse gas concentrations. I provide new simplified expressions which agree much better with the calculated forcings, and suggest that these expressions be used in place of the IPCC expressions. Additionally, I provide meridionally resolved forcings which may be used to force simple and intermediate complexity climate models. For the Archean Earth, I present new calculations of radiative forcing for CO2 (10^-6 - 1 bar), CH4 (500 ppbv - 10,000 ppmv) and 18 other gases (10 ppbv - 10 ppmv). I aim to provide a set of radiative forcing and overlap calculations which can be used as a standard for comparisons. Radiative forcings are calculated for atmospheres with various N2 inventories (0.5, 1, and 2 bar). The effect of overlap and atmospheric pressure on radiative forcing are examined. The CO2 radiative forcings are consistent with previous work, however, I find significantly more shortwave absorption by CH4 than previously reported which may limit warming above 100 ppmv. For the 18 other gases, I find that significant radiative forcings result from low concentrations (<1 ppmv). These forcings are compared to those given in the literature. / Graduate / 0756 / 0608 / 0725 / bbyrne@uvic.ca

Graduate

Jet in crossflow (JICF) configurations are often used for secondary fuel injection in staged-fuel combustion systems. The high temperature, vitiated crossflow in these systems is inherently unsteady and characterized by random, turbulent fluctuations and coherent, acoustic oscillations. This thesis presents the results of an experimental investigation into the dynamics of non-reacting and reacting jets injected into unsteady, vitiated crossflow. The flow structure and flame stabilization of jets with different momentum flux and density ratios relative to the crossflow are characterized using simultaneous time-resolved stereoscopic particle image velocimetry (SPIV) synchronized with OH planar laser induced fluorescence (PLIF). A modified trajectory scaling law is developed to account for the influence of near-field heat release on the jet trajectory. The second part of this work focuses on the response of a JICF to crossflow forcing. Acoustic drivers are used to excite natural resonances of the facility, which are characterized using the two-microphone method. Spectral analysis of SPIV results shows that, while the jet response to crossflow velocity fluctuations is often negligible, the fluctuating crossflow pressure induces a significant fluctuating jet exit velocity, which leads to periodic jet flapping. The flame response to crossflow forcing is studied using flame edge tracking. An analytical model is developed that predicts the dependence of the jet injector impedance upon important JICF parameters. In the final part of this work, vortex tracking and Mie scattering flow visualization are used to investigate the effect of near-field heat release on the shear layer dynamics. A phenomenological model is developed to explain the effect of combustion on the shear layer stability of density stratified, reacting JICF. The results of this study demonstrate the important effects of near-field heat release and crossflow acoustics on the dynamics of reacting JICF.

Near-resonant triad interactions and wave generation theory are investigated for continuously stratified fluids. Interaction equations are derived for spatially-varying wave trains under the inviscid Boussinesq approximation. Rotational effects are included, and properties of the underlying eigenvalue problem are explored. To facilitate a numerical study of the near-resonant interactions, numerical methods are developed and an analysis of wave generation on a periodic domain is performed. Numerical experiments using laboratory and ocean-scale parameters are conducted, and the simulations confirm the validity of the wave forcing theory. Interaction experiments demonstrate a strong tendency for waves to exhibit nonlinear behaviour. While resonant interactions are observed in the laboratory scale simulations, nonlinear steepening effects and the formation of solitary-like waves dominate the ocean-scale experiments. The results suggest that the weakly-nonlinear interaction theory is only appropriate in a limited parameter regime. The problem of analyzing forced wave equations on an infinite domain is also considered. Motivated by the results obtained on a periodic domain, asymptotic analysis is applied to three important wave equations. The method of steepest descents is used to determine the large-time behaviour for the linearized Korteweg-de Vries, Benjamin-Bona-Mahony, and internal gravity wave equations. The asymptotic results are compared with numerical experiments and found to agree to high precision.

The analysis of the turbulent flows in nuclear fuel bundles is a very interesting task to optimize the efficiency of modern nuclear power plants. The proposed study utilizes Computational Fluid Dynamics (CFD) to characterize the flow pattern generated in a fuel bundle with Spacer Grids (SG) and Mixing Vanes (MV). CFD calculations were performed using different turbulence models for steady state simulations. Large Eddy Simulations (LES) scheme was applied to time dependent cases. The simulations were compared with the experimental data measured at Texas A&M University fuel bundle experimental facility. Also, another objective is to develop some new coarse mesh approaches for modeling MV to include these structures in the prospective of quarter of core simulations; MV and SG are usually modeled with porous media, since the computational power required to solve the full geometry is still unacceptable. The new contribution of the study is the definition and implementation of a Momentum Sources Forcing approach that allows a detailed definition of MV and SG for coarse mesh calculations. The proposed method was investigated using different turbulence models and different numerical schemes. Also, LES calculations allowed the study of Fluid Structure Interaction (FSI), that generates vibration problems and failure of nuclear fuel pins. A spectral analysis of the forces acting on the fuel pins walls was developed. In conclusion, a comprehensive study of fuel bundle problem was proposed with benchmark of the computational techniques to the experimental data.

This literature review analyses and discusses different theories and results regarding impact of volcanic eruptions on climate change in Earth's history. Present global warming has been attributed to anthropogenic emissions of greenhouse gases, mainly carbon dioxide, however changes in global temperatures have occurred before the onset of anthropogenic emissions. Certain prehistoric climate changes are thought to be caused by emissions of volcanic gases to the atmosphere. Many studies have investigated the connection between volcanic events and subsequent changes in global temperatures. A majority have concluded that volcanic sulfur dioxide is the main direct and indirect climate forcing gas influencing temperatures over time. Increased volcanic activity over the last 15 years is thought to be an inhibiting factor on present global warming. This is supported by evidence of past volcanic events preceding global cooling and warming periods during Holocene and prehistoric times. Further, there are indications that factors such as geographical position, season, gas composition, magnitude and duration of an eruption influences the extent of the climate forcing.Records of climate such as ice cores and tree growth rings and isotopic characterization have made it possible to identify volcano eruptions over time and determine the identity of the erupting volcano. Past and present data from these can be used to gain a better understanding of past climate changes as well as making predictions about future changes as a result volcanic eruptions. However, accuracy regarding temporal and spatial resolution of these records is of great importance for the validity of the results.