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Civil and Environmental Engineering - Ph.D. / Sc.D.
Mostrando recursos 1 - 20 de 623
Hydrodynamic and transport phenomena at the interface between flow and aquatic vegetation : from the forest to the blade scale - Rominger, Jeffrey T. (Jeffrey Tsaros)
From the canopy scale to the blade scale, interactions between fluid motion and kelp produce a wide array of hydrodynamic and scalar transport phenomena. At the kilometer scale of the kelp forest, coastal currents transport nutrients, microorganisms and spores. But, kelp forests exert a drag force on currents, causing the flow to decelerate and divert as it encounters the canopy, affecting the fate of species transported by the current. We identify a dimensionless flow-blockage parameter, based on canopy width and density, that controls both the length of the flow deceleration region and the total flow in the canopy. We further...
Flow through porous media : from mixing of fluids to triggering of earthquakes - Jha, Birendra, Ph. D. Massachusetts Institute of Technology. Department of Civil and Environmental Engineering
Enhanced oil recovery by displacing oil with solvents such as carbon dioxide requires development of miscibility between the two fluids to maximize the displacement efficiency. Prevention of inadvertent triggering of earthquakes due to injection or production of fluids in the underground requires understanding of coupling between flow and deformation processes. In this Dissertation, we study flow through porous media in two different contexts: effect of viscosity on mixing of fluids, and triggering of earthquakes due to coupling between flow and deformation. We show that miscible viscous fingering-the hydrodynamic instability that arises when a less viscous fluid displaces the more viscous...
The dynamics of surface detachment and quorum sensing in spatially controlled biofilm colonies of Pseudomonas aeruginosa - Jang, Hongchul
Biofilms represent a highly successful life strategy of bacteria in a very broad range of environments and often have negative implications for industrial and clinical applications, as their removal from surfaces and the prevention of biofouling in the first place represent formidable and to date unmet challenges. At the same time, biofilms modulate important natural processes, including nutrient cycling in rivers and streams and the clogging of porous materials. Biofilm development is a dynamic process, dependent on a host of cellular and environmental parameters that include, among others, hydrodynamic environment and the communication among cells (QS). Here we used microfluidics...
Multiscale modeling of clay-water systems - Ebrahimi, Davoud
The engineering properties of soils are highly affected by clay content and clay-water interactions. However, existing macro-scale continuum models have no length scale to describe the evolution of the clay microstructure and its role in affecting macroscopic properties. This research proposes a bottom-up multiscale modeling approach to understand the physics underlying macroscopic clay behavior. Atomistic models are developed to understand clay-water interactions using the ClayFF force field. We simulate water adsorption between clay layers for a reference mineral, Wyoming montmorillonite (Na-smectite) using molecular dynamics simulations. The elastic properties of the system are found to vary with the hydration state (amount...
Mechanical behavior of elastic rods under constraint - Miller, James Thomas, Ph. D. Massachusetts Institute of Technology
We present the results of an experimental investigation of the mechanics of thin elastic rods under a variety of loading conditions. Four scenarios are explored, with increasing complexity: i) the shape of a naturally curved rod suspended under self-weight, ii) the buckling and post-buckling behavior of a rod compressed inside a cylindrical constraint, iii) the mechanical instabilities arising when a rod is progressively injected into a horizontal cylinder, and iv) strategies for mitigation of these instabilities by dynamic excitation of the constraint. First, we consider the role of natural curvature in determining the shape of a hanging elastic rod suspended...
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...