No / This paper proposes that the changes which occur in composition of the bed load during the transport of mixed-grain-size sediments are largely controlled by the distributions of critical entrainment shear stress for the various size fractions. This hypothesis is examined for a unimodal sediment mixture by calculating these distributions with a discrete particle model and using them in a probabilistic calculation of bed-load composition. The estimates of bed-load composition compare favorably with observations of fractional transport rates made in a laboratory flume for the same sediment, suggesting that the hypothesis is reasonable. The analysis provides additional insight, in terms of grain mechanics, into the processes that determine bed-load composition. These insights strongly suggest that better prediction methods will result from taking account of the variation of threshold within size fractions, something that most previous studies have neglected.

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Multi-core architectures are present throughout a large selection of computing devices from cell phones to super-computers. Parallel applications running on these devices solve bigger problems in a shorter time. Writing those applications is a difficult task for programmers. They need to deal with low-level parallel mechanisms such as data distribution, inter-processor communication, and task placement. The goal of the Standard Template Adaptive Parallel Library (STAPL) is to provide a generic high-level framework to develop parallel applications. One of the first steps of a parallel application is to partition and distribute the data throughout the system. An important data structure for parallel applications to store large amounts of data and model many types of relations is the graph. A mesh, which is a special type of graph, is often used to model a spatial domain in scientific applications. Graph and mesh partitioning has many applications such as VLSI circuit design, parallel task scheduling, and data distribution. Data distribution, significantly impacts the performance of a parallel application. In this thesis, we introduce the STAPL Parallel Graph Partitioner Framework. This framework provides a generic infrastructure to partition arbitrary graphs and meshes and to build customized partitioners. It includes the state of the art parallel k-way multilevel scheme to partition arbitrary graphs, a parallel mesh partitioner with parameterized partition shape, and a customized partitioner used for discrete ordinates particle transport computations. This framework is also part of a generic library, STAPL, allowing the partitioning of the data and development of the whole parallel application to be done in the same environment. We show the user-friendly interface of the framework and its scalability for partitioning different mesh and graph benchmarks on a Cray XE6 system. We also highlight the performance of our customized unstructured mesh partitioner for a discrete ordinates particle transport code. The developed columnar decompositions significantly reduce the execution time of simultaneous sweeps on unstructured meshes.

For this dissertation I studied flow and transport in low gradient Florida streams. Chapter 2 is a statewide analysis of long-term variations in stream discharge. The results from Chapter 2 suggest that changes in mean annual stream discharge are controlled by the Atlantic Multi-Decadal Oscillation (AMO). During the warm phase, mean annual discharge decreases in central Florida and increases in north Florida. The opposite is true during the cool phase, with mean annual discharge increasing in central Florida and decreasing in north Florida. This pattern is observed for both components of stream discharge, base flow and runoff. The following two chapters are part of an analysis of particle transport in low gradient mangrove estuaries. Chapter 3 describes the use of a numerical model to simulate the hydrodynamics of a coastal reach of the Shark River, Florida Everglades and the development of a Lagrangian particle tracking model. The particle tracking model uses the output from the hydrodynamic model to simulate the movement of particles released within the model domain. In Chapter 4, the hydrodynamic and particle tracking models are used to estimate the historical particle residence time in the Shark River Slough Estuary (SRSE) and determine the key factors controlling particle residence time and fate in mangrove estuaries. The mean and median residence times in the model domain are 16 and 8 hours, respectively, and 60% of all particles exit the model domain downstream, towards the Gulf of Mexico. Particle residence time varies greatly depending on the particle release location and timing. The residence time is significantly lower for particles released in the middle of the channel and for particles released during the wet season, spring tides or during upstream flows. Additionally, there is a decreasing trend in mean particle residence time from 1997 through 2017, mirroring an increasing trend in mean annual water levels in the SRSE. The combined results of this dissertation show the impact that a variable climate can have on stream flow and particle transport.

[pt] O escoamento de suspensões concentradas tem grande importância em diversos segmentos da indústria, representando uma maneira econômica de transportar grandes quantidades de materiais sólidos particulados. Uma das aplicações inclui a etapa de perfuração de poços de petróleo direcionais. No decorrer do processo são gerados sedimentos originários do corte da formação, que são removidos através da operação de limpeza do poço. Durante a limpeza, no trecho de maior inclinação esses sedimentos tendem a se separar da suspensão, pelo efeito gravitacional, formando um leito na parte inferior do anular. Esse leito formado pode causar vários problemas, como redução da taxa de penetração, desgaste prematuro da broca, prisão da coluna de perfuração, fraturamento da formação e torque excessivo na coluna de perfuração. O entendimento do escoamento de suspensões de partículas se torna relevante para o aperfeiçoamento desses processos. Nesse sentido, o objetivo deste trabalho é analisar o escoamento de suspensões de partículas entre duas placas paralelas para estudar a formação de um leito de sedimentos na parte inferior do canal e determinar o efeito dos diferentes mecanismos de migração de partículas neste processo. A formulação matemática do problema inclui as equações de conservação de massa e quantidade de movimento linear e equação de transporte de partículas. Para descrever o transporte de partículas no escoamento foi usado o modelo de fluxo difusivo proposto por Phillips et al. (1992). As equações diferenciais parciais, que descrevem o escoamento de uma suspensão de partículas, são resolvidas pelo método de Elementos Finitos de Galerkin e o sistema não-linear é resolvido através do método de Newton. Os resultados obtidos mostram como a distribuição das partículas sólidas varia com os parâmetros do problema e determina as condições para a formação de um leito de partículas. / [en] The flow of solid particles suspended in a liquid medium have great importance in several industry segments representing an economical way to transport large quantities of solid materials. One of the applications includes the flow during directional well drilling. During the process sediments are generated from the formation cutting, which are removed through the wellbore cleaning. During the cleaning, step near the horizontal section of the well, these sediments tend to separate from the suspension by the action of gravity, forming a stationary bed in the bottom of the annular. This stationary bed can cause problems, such as reducing the penetration rate, premature wear of the drill bit, trapping column, fracturing of the formation and high torque. The complete understanding of the flow of solid particles suspension becomes relevant to the improvement of these processes. In this sense, the main goal of this work is to analyze the flow of solid particle suspensions between two parallel plates to investigate the formation of a stationary bed in the bottom of the channel and to determine the effect of different particle migration mechanisms in this process. The mathematical formulation includes the equations of mass (continuity equation) and momentum conservation. The Diffusive Flux Model proposed by Phillips et al. (1992) was used to describe the particle transport in the flow. The partial differential equations, which describe the flow of solid particles suspension, are solved by the Galerkin/Finite Element Method (GFEM) and the non-linear system is solved using Newton s Method. The results show how the distribution of solid particles varies with the problem parameters and determines the conditions for the formation of a stationary bed.

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Examination of the paper insulation and copper stress braiding during stripdown of a number of Current Transformers (FMK type 400kV) has revealed the presence of dark deposits. Copper foils are often interspersed within layers of paper insulation and mineral oil found in transformer windings. The dark deposits were often found in association with these foils, affecting several layers of paper in addition to the layer in contact with the copper foil. This thesis describes the research undertaken to identify these deposits and establish a mechanism for the transportation through the paper layers. Preliminary investigation using scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray analysis (EDX) has shown these dark deposits to be copper based. X-ray photoelectron spectroscopy was used to show that the transport of the copper deposit through the paper insulation was working under the influence of a diffusion controlled process, related to Fick's law. Laboratory studies in support of work designed to eliminate the problem have shown that corrosion of copper occurs in mineral oils containing a trace of oxygen. This corrosion is non protective in character and leads to migration of copper into adjacent layers of paper. It has been shown that the transport of copper through several layers of paper can be measured by XPS and that the concentration from one paper winding to the next declines in accord with Fick's law for non-steady state diffusion. Measurements of surface concentrations by XPS correlate well with measurements made with atomic absorption spectroscopy on solutions of extracts of the contaminated paper. The laboratory measurements have allowed determination of the diffusion coefficients and activation energy for the transport process and thus give a basis for interpretation of the diffusion profiles found in the transformer in terms of time and temperature of operation. The diffusion process is temperature dependant. The results have been used to produce long term prediction curves.