http://hdl.handle.net/1721.1/7653 Fri, 24 May 2013 09:24:16 GMT 2013-05-24T09:24:16Z http://hdl.handle.net/1721.1/78233 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 risks can help mitigate these impacts. The purpose is to feed that information into developer's investment strategy to be able to understand whether or not to participate in particular power plant development projects, and how to participate. First phase of the dissertation is an analysis of power plant investment decisions and development process, followed by identification of risks across all stages of development. Through data mining of performance indicators of around 300 power plant development projects worldwide, clusters of geographical locations, energy technologies, and developer types are highlighted. This helps us understand which projects developers should consider for evaluation given performance trends of geographic locations, and energy technologies. Our research then introduces a novel approach to power plant project risk analysis. We combine a System Dynamics model of the power plant development process with an Analytical Network Process model that enables identification of key relationships among risks and their impact on the development process. The models are used to construct project risk profiles. These three models work together to show how developers can make risk informed decision when selecting amongst power plant project opportunities, how they should best prepare projects to mitigate negative impacts of risks involved, and how they should react to changes in managing development performance over a project's lifetime. Thesis (Ph. D. in the field of Construction Engineering and Management)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 204-209). Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/1721.1/78233 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/78232 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 about the fundamental molecular interactions that drive system behavior. Here, we focus on two specific weak polyelectrolytes - poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) - that undergo electrostatic complexation, and can be manipulated as function of pH. While the driving mechanism investigated here is ionic interactions, the findings and atomistic approaches are applicable to a variety of systems such as hydrogen bonded polypeptides (e.g., protein structures), as well as similar polyelectrolyte systems (e.g., PSS, PDMA, etc.). Specifically, in this dissertation, the coupling of electrostatic cross-links and weak interactions, polyelectrolyte persistence length and molecular rigidity of PAA and PAH is investigated with full atomistic precision. Large-scale molecular dynamics (MD) simulations indicate the stiffening of PEMs cannot be explained by increased electrostatic cross-linking alone, but rather the effect is amplified by the increase in molecular rigidity due to self-repulsion. Based on MD simulations, a general theoretical model for effective electrostatic persistence length is proposed for highly flexible polyelectrolytes and charged macromolecules through the introduction of an electrostatic contour length which can applied to other chemical species. A focus on adhesion reveals the effective cross-linking strength exceeds the strength of ionic interaction alone, due to secondary effects (e.g., H-bonding, steric effects, etc.) Moreover, a derived elastic model for complexation reveals a critical bound for cross-link density and stiffness, indicating the required conditions to induce cooperative mechanical behavior. The key insight is that these critical conditions can be further extended for the coupling of flexible molecules in general, such as proteins or flexible nanoribbons. The results demonstrate how nanoscale control can lead to uniquely tunable mechanomutable materials from designed functional building blocks. While PEM systems are currently being developed for biosensor, membrane, and tissue engineering technologies, the results presented herein provide a basis to tune the properties of such systems at the nanoscale, thereby engineering system behavior and performance across scales. Understanding the bounds of mechanical performance of two specific polyelectrolyte species, and their joint interaction through complexation, provides a basis for coupling molecules with various functionalities. Similar to complete understanding the limitations of a steel beam in construction of a bridge, the systematic delineation of polyelectrolyte complexation allows quantitative prediction of larger-scale systems. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 255-282). Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/1721.1/78232 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/78142 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 and sediment resuspension. We consider both steady currents and wave-induced flows. For steady flows, the flow structure is significantly affected by canopy density. We define sparse and dense canopies based on the relative contribution of turbulent stress and canopy drag to the momentum balance. Within sparse canopies, velocity and turbulent stress remain elevated and the rate of sediment suspension is comparable to that in unvegetated regions. Within dense canopies, velocity and turbulent stress are reduced by canopy drag, and the rate of sediment resuspension is lower. Unlike steady flows, wave-induced oscillatory flows are not significantly damped within vegetated canopies. Further, our laboratory and field measurements show that, despite being driven by a purely oscillatory flow, a mean current in the direction of wave propagation is generated within the canopy. This mean current is forced by a wave stress, similar to the streaming observed in wave boundary layers. At the blade-scale, plant-flow interaction sets posture and drag. Through laboratory experiments and numerical simulations, we show that posture is set by a balance between the hydrodynamic forcing and the restoring forces due to blade stiffness and buoyancy. When the hydrodynamic forcing is small compared to the restoring forces, the blades remain upright in flow and a standard quadratic law predicts the relationship between drag and velocity. When the hydrodynamic forcing exceeds the restoring forces, the blades are pushed over in steady flow, and move with oscillatory flow. For this limit, we develop new scaling laws that link drag with velocity. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 163-171). Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/1721.1/78142 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/78141 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 species through the subsurface and their exchange between the sediments and the water column. Our understanding of how different forcing mechanisms interact to determine spatial scales and residence times of subsurface seawater circulation, as well as temporal patterns and rates of aquifer-surface water exchange has thus far been very limited. The large range in the spatial and temporal scales of flow dynamics associated with different forcings challenges our ability to comprehensively observe and monitor their associated seafloor fluxes. In this thesis, we present a novel, homemade instrument for high-resolution, long-term monitoring of seafloor fluxes, designed to address this challenge. Two-year deployments of several such instruments at Waquoit Bay, MA, produced the most comprehensive datasets on seafloor fluxes available to date, multiplying the length of published time series by tenfold. The length and integrity of the datasets permit the use of spectral analysis to investigate distinct frequency components of seafloor fluxes and quantify their relationship to various forcing mechanisms. The temporal and areal coverage of the datasets allow us to distinguish the contributions of different forcings to observed fluxes, as a function of distance from shore and season. Furthermore, we discuss new insight derived from the data into the physics underlying observed seafloor fluxes and their associated subsurface circulation processes. Additionally, we describe results from an independent but related project to characterize chemical dynamics associated with seawater circulation in beach sand at Waquoit Bay. We present evidence for the important contribution of this circulation to the nitrogen budget of the Bay. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 150-154). Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/1721.1/78141 2012-01-01T00:00:00Z