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Civil and Environmental Engineering - Ph.D. / Sc.D.
Mostrando recursos 1 - 20 de 616
Assessment of fracture properties and rate effects on fracture of materials by micro scratching: application to gas shale - Akono, Ange-Therese
Since 1921, several experimental methods have been implemented to measure the Griffith fracture energy. The challenge lies in providing a measure that is intrinsic and invariant with respect to external factors such as specimen geometry, loading conditions and prescribed rates. In this thesis, by combining multi-scale experiments and advanced theoretical modeling, we provide a means to characterize the intrinsic fracture toughness using microscopic scratch tests. The scratch test consists in plowing and cutting with a scratch device the surface of a weaker material and it is relevant in many fields of science and engineering, ranging from thin films and coatings,...
Natural and synthetic estrogens in wastewater treatment plant effuent and the coastal ocean - Griffith, David R. (David Richmond)
Steroidal estrogens are potent endocrine disrupting chemicals that are naturally excreted by vertebrates (e.g., humans and fish) and can enter natural waters through the discharge of treated and raw sewage. Because estrogens are detrimental to aquatic organisms at picomolar concentrations, many studies have measured so-called "free" estrogen concentrations in wastewater effluents, rivers, and lakes. Yet, to our knowledge, no studies have characterized the broader range of estrogens that includes free, conjugated, and halogenated forms. Conjugated estrogens are important because they can be easily converted to potent free forms by bacteria in wastewater treatment plants and receiving waters. And halogenated estrogens,...
Experimental and theoretical study of turbulent oscillatory boundary layers - Yuan, Jing, Ph. D. Massachusetts Institute of Technology
Sediment transport is of crucial importance to engineering projects in coastal regions, so it is of primary interest in coastal engineering. The driving forces for sediment transport are mostly determined by the hydrodynamics of oscillatory turbulent bottom boundary layers, which is still not well understood. Therefore, the goal of this thesis is to improve the present experimental and theoretical understandings on this subject. A high-quality experimental study including a large number of tests which correspond to full-scale coastal boundary layer flows is performed using a state-of-the-art oscillating water tunnel (OWT) for flow generations and a Particle Image Velocimetry system for...
Hydrologic modeling using triangulated irregular networks : terrain representation, flood forecasting and catchment response - Vivoni, Enrique R. (Enrique Rafael), 1975-
Numerical models are modern tools for capturing the spatial and temporal variability in the land-surface hydrologic response to rainfall and understanding the physical relations between internal watershed processes and observed streamflow. This thesis presents the development and application of a distributed hydrologic model distinguished by its representation of topography through a triangulated irregular network (TIN) and its coupling of the surface and subsurface processes leading to the catchment response. As a research tool for hydrologic forecasting and experimentation, the TIN-based Real-time Integrated Basin Simulator (tRIBS) fully incorporates spatial heterogeneities in basin topography, surface descriptors and hydrometeorological forcing to produce dynamic...
Copper speciation in estuaries and coastal waters - Kogut, Megan Brook, 1972-
The goals of this dissertation are to better understand the sources and the Cu binding ability of ligands that control Cu toxicity in estuaries and harbors, where elevated Cu concentrations have caused documented toxic effects on microorganisms, fish, and benthic fauna. I modified and improved a commonly used approach to determine metal speciation (competitive ligand exchange adsorptive cathodic stripping voltammetry, CLE-ACSV). Using this new approach to chemical Cu speciation and an old approach to physical Cu speciation (filtration), I show that riverine humic substances, filtrable, recalcitrant and light absorbing molecules from degraded plant material, can account for all of the...
Seismic vulnerability of historical structures with the discrete element method - Pagnoni, Tommaso
It is widely recognized that historical structures represent a cultural heritage which should be preserved and transmitted to future generations. In several countries, and particularly, in the Mediterranean area, where a large number of important monuments are exposed to seismic hazard, there is a growing interest for the problem of strengthening such structures in order to reduce their seismic vulnerability, while preserving their original architectural integrity. However the seismic vulnerability assessment of historical block structures is still a challenging task. In this work, after having explored the potentials and limitations of the Discrete Element Method for this type of problem,...
Stochastic flow and transport through multifractal porous media - Essiam, Albert K
Stochastic theories of flow and transport in aquifers have relied on the linear perturbation approach that is accurate for flow fields with log-conductivity variance cr2 less than unity. Several studies have found that the linear perturbation ignores terms that have significant effects on the spectra of the hydraulic gradient VH and specific discharge q when (Y2 exceeds unity. In this thesis we study flow and transport when the hydraulic conductivity K is an isotropic lognormal multifractal field. Unlike the perturbation approach, results obtained are nonlinear even though several simplifying assumptions are made. The spectral density of F = in (K)...
Methodology for updating numerical predictions of excavation performance - Corral Jofré, Gonzalo Andrés
Due to the usual limitations in site investigations and measurements of soil properties, simplified constitutive models are routinely used in geotechnical analyses for the design of excavation support systems. However, monitoring data provides additional information on the performance of these support systems during construction. This thesis proposes a rational framework for updating constitutive model input parameters in finite element predictions of soil-structure interaction based on the monitoring data. The goal of this methodology is to provide an objective procedure that can be used during construction to update the instrument pre-set trigger levels that are used to control construction. In this...
The subsurface fluid mechanics of geologic carbon dioxide storage - Szulczewski, Michael Lawrence
In carbon capture and storage (CCS), CO₂ is captured at power plants and then injected into deep geologic reservoirs for long-term storage. While CCS may be critical for the continued use of fossil fuels in a carbon-constrained world, the subsurface behavior of CO₂ remains poorly understood, which has contributed to the absence of government policy to implement CCS. In this Thesis, we use simulations, experiments, and theory to clarify the fluid mechanics of CO₂ storage, with the goal of informing two practical questions. The first question is, how much CO₂ can be stored in the United States? This question is...
Seismic performance assessment for structural optimization - Ghisbain, Pierre
The economic impact of earthquakes has spurred the implementation of performance-based design to mitigate damage in addition to protecting human lives. A developing trend is to consider damage directly as a measure of seismic performance. In spite of the ability to estimate the cost of future earthquakes, adjusting the investment in seismic upgrades is impeded by the computational requirements of the probabilistic damage assessment. In this dissertation, we develop the damage assessment tools needed to implement structural optimization with an estimate of lifetime seismic damage in the objective function. A parametric study of the procedure to predict damage from earthquake...
Algorithm selection in structural optimization - Clune, Rory P. (Rory Patrick)
Structural optimization is largely unused as a practical design tool, despite an extensive academic literature which demonstrates its potential to dramatically improve design processes and outcomes. Many factors inhibit optimization's application. Among them is the requirement for engineers-who generally lack the requisite expertise-to choose an optimization algorithm for a given problem. A suitable choice of algorithm improves the resulting design and reduces computational cost, yet the field of optimization does little to guide engineers in selecting from an overwhelming number of options. The goal of this dissertation is to aid, and ultimately to automate, algorithm selection, thus enhancing optimization's applicability...
Fracture process zone : microstructure and nanomechanics in quasi-brittle materials - Brooks, Zenzile (Zenzile Z.)
Cracks begin (and end) at a crack tip; the "Fracture Process Zone" (FPZ) is a region of damage around the crack tip. The context of this research is the FPZ in quasi-brittle materials, which is characterized by cracking at various scales. This study focuses on crack propagation and FPZ development at a fundamental material scale: the scale of the grain. With regard to the FPZ, the study seeks to understand how the FPZ develops and manifests in quasi-brittle material, what the physical and mechanical structure of the FPZ is, and how pre-existing material microstructure influences the developed FPZ. The attainment...