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Civil and Environmental Engineering - Ph.D. / Sc.D.
Mostrando recursos 1 - 20 de 604
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...
Structural and mechanical properties of intermediate filaments under extreme conditions and disease - Qin, Zhao, Ph. D. Massachusetts Institute of Technology
Intermediate filaments are one of the three major components of the cytoskeleton in eukaryotic cells. It was discovered during the recent decades that intermediate filament proteins play key roles to reinforce cells subjected to large-deformation as well as participate in signal transduction. However, it is still poorly understood how the nanoscopic structure, as well as the biochemical properties of these protein molecules contribute to their biomechanical functions. In this research we investigate the material function of intermediate filaments under various extreme mechanical conditions as well as disease states. We use a full atomistic model and study its response to mechanical...
The nitrogen cycle and ecohydrology of seasonally dry grasslands - Parolari, Anthony Joseph
This thesis addresses the coupling of hydrologic and biogeochemical processes and, specifically, the organization of ecosystem traits with the water, carbon, and nitrogen cycles. Observations from a factorial irrigation-fertilization experiment in a seasonally dry annual grassland are combined with a simple ecosystem model to identify relationships between vegetation, nitrogen availability, and hydrology. Assuming primary productivity is water-limited, data analysis indicates that soil moisture and canopy conductance are insensitive to nitrogen supply, owing to a trade-off between canopy density and leaf conductance that maximizes efficient use of available water. That is, fertilization-induced increases in leaf area index are offset by reduced...
Biosphere-atmosphere interactions over semi-arid regions : modeling the role of mineral aerosols and irrigation in the regional climate system - Marcella, Marc Pace
This dissertation describes the role of land surface processes in shaping semi-arid climates, namely those of Southwest Asia and Northwest Africa. The interactions between dust emissions, irrigation, and climate processes are studied and quantified using a regional climate model to perform a series of carefully designed numerical experiments. The performance of the numerical model is tested by comparing simulation results against observations from satellites and other standard platforms. Modeling results indicate significant improvements in simulating mineral aerosols over Southwest Asia. Results suggest that including representations for sub-grid scale wind gustiness as well as mineral aerosols at the boundaries, improve the...
Land conversion in Amazonia and Northern South America : influences on regional hydrology and ecosystem response - Knox, Ryan Gary
A numerical model of the terrestrial biosphere (Ecosystem Demography Model) is compbined with an atmospheric model (Brazilian Regional Atmospheric Modeling System) to investigate how land conversion in the Amazon and Northern South America have changed the hydrology of the region, and to see if those changes are significant enough to produce an ecological response. Two numerical realizations of the structure and composition of terrestrial vegetation are used as boundary conditions in a simulation of the regional land surface and atmosphere. One realization seeks to capture the present day vegetation condition that includes human deforestation and land-conversion, the other is an...
Convective cloud and rainfall processes over the Maritime Continent : simulation and analysis of the diurnal cycle - Gianotti, Rebecca L. (Rebecca Louise)
The Maritime Continent experiences strong moist convection, which produces significant rainfall and drives large fluxes of heat and moisture to the upper troposphere. Despite the importance of these processes to global circulations, current predictions of climate change over this region are still highly uncertain, largely due to inadequate representation of the diurnally-varying processes related to convection. In this work, a coupled numerical model of the land-atmosphere system (RegCM3-IBIS) is used to investigate how more physically-realistic representations of these processes can be incorporated into large-scale climate models. In particular, this work improves simulations of convective-radiative feedbacks and the role of cumulus...
Risks and decision making in development of new power plant projects - Kristinsdottir, Asbjorg
Power plant development projects are typically capital intensive and subject to a complex network of interconnected risks that impact development's performance. Failure to develop a power plant to meet performance constraints can come at great cost to the developer and other stakeholders involved. In order to develop an investment strategy plan based on their risk appetite, and manage risks effectively, developers must be able to identify and analyze project opportunity risks. This dissertation is motivated by the need to study the nature and impact of risks on a power plant development project, and to demonstrate how proper management of those...
Nanomechanical coupling of mechanomutable polyelectrolytes - Cranford, Steven W
Nanotechnology has advanced to the point where almost any molecular functional group can be introduced into a composite material system. However, emergent properties attained via the combination of arbitrary components - e.g., the complexation of two weak polyelectrolytes - is not yet predictive, and thus cannot be rationally engineered. Predictive and reliable quantification of material properties across scales is necessary to enable the design and development of advanced functional (and complex) materials. There is a vast amount of experimental study which characterize the strength of electrostatic interactions, topology, and viscoelastic properties of polyelectrolyte multilayers (PEMs), but very little is known...
Analytical and experimental studies of plant-flow interaction at multiple scales - Luhar, Mitul
Across scales ranging from individual blades to river reaches, the interaction between water flow and vegetation has important ecological and engineering implications. At the reach-scale, vegetation is often the largest source of hydraulic resistance. Based on a simple momentum balance, we show that the resistance produced by vegetation depends primarily on the fraction of the channel cross-section blocked by vegetation. For the same blockage, the specific distribution of vegetation also plays a role; a large number of small patches generates more resistance than a single large patch. At the patch-scale, velocity and turbulence levels within the canopy set water renewal...
Seawater circulation in coastal aquifers : processes and impacts - Karam, Hanan Nadim
This thesis explores the subterranean domain of chemical cycling in coastal oceans abutting permeable aquifers, where transport through sediments is dominated by advection, rather than diffusion. We investigate the mechanisms by which seawater circulates in the subsurface over a range of spatio-temporal scales, and the chemical reactions to which this circulation is coupled. Seawater circulation in coastal aquifers is driven by salinity variations in pore water as well as by the effects of temporally variable forcings at both terrestrial (variable recharge) and marine (tides, waves and secular sea level changes) boundaries. It is coupled to the transport of biogeochemically reactive...
Automated security analysis of payment protocols - Huang, Enyang
Formal analyses have been used for payment protocol design and verification but, despite developments in semantics and expressiveness, previous literature has placed little emphasis on the automation aspects of the proof systems. This research develops an automated analysis framework for payment protocols called PTGPA. PTGPA combines the techniques of formal analysis as well as the decidability afforded by theory generation, a general-purpose framework for automated reasoning. A comprehensive and self-contained proof system called TGPay is first developed. TGPay introduces novel developments and refinements in the formal language and inference rules that conform to the prerequisites of theory generation. These target...