Flocculation is not only an important part of sediment dynamics within coastal marine waters, but is also a factor of sediment transport within small freshwater streams in Blacksburg, Virginia. The goal of this project was to develop a relationship between floc sizes and stream characteristics (temperature, salinity, chlorophyll-a, organic content, TSS, pH) and to compare how that relationship varies seasonally and spatially across two streams in the same watershed with a similar drainage area but different land uses within these areas. Microscopic images of flocs and water samples were taken within two local streams every two to four weeks throughout the span of one year. The images were analyzed to obtain the floc sizes and the water samples were tested in a lab for various stream properties. The compiled data from the entire year were analyzed to determine if there was a seasonal relationship between floc sizes and the various properties of the water. The process was also repeated at multiple locations along the entire length of both of the streams once in the summer and once in the winter to see if there was a spatial relationship within a single stream. Our study found that significant rainfall events tend to have the greatest effect on floc size in the small headwater streams. However, many of the individual variables alone do not correlate strongly with floc size and a combination of variables may be the best way to analyze the floc size. / Master of Science / Flocculation is the process of single particles coming together to form larger aggregated particles called "flocs". This project focuses on flocculation of sediment within local streams and how the sizes of these flocs may vary throughout the year. The rate of flocculation and the size of these flocs can have a large effect on the movement of sediment within freshwater streams. Images of flocs and water properties such as water temperature, salinity, and pH, were analyzed every two to four weeks throughout the span of a year to determine if there was a relationship between floc size and any of the measured water properties. While a relationship between rainfall and floc size was noticed, it is apparent that multiple variables should be factored into the analysis to get the most accurate results.

This study is devoted to the development of an integrated numerical modeling enabling one to investigate the static and the dynamic behaviors and failures of 2-D textile composite as well as 3-D orthogonal woven composite structures weakened by cracks and subjected to static-, impact- and ballistic-type loads. As more complicated modeling about textile composite structures is introduced, some of homogenization schemes, geometrical modeling and crack propagations become more difficult problems to solve. To overcome these problems, this study presents effective mesh-generation schemes, homogenization modeling based on a repeating unit cell and sinusoidal functions, and also a cohesive element to study micro-crack shapes. This proposed research has two: 1) studying behavior of textile composites under static loads, 2) studying dynamic responses of these textile composite structures subjected to the transient/ballistic loading. In the first part, efficient homogenization schemes are suggested to show the influence of textile architectures on mechanical characteristics considering the micro modeling of repeating unit cell. Furthermore, the structures of multi-layered or multi-phase composites combined with different laminar such as a sub-laminate, are considered to find the mechanical characteristics. A simple progressive failure mechanism for the textile composites is also presented. In the second part, this study focuses on three main phenomena to solve the dynamic problems: micro-crack shapes, textile architectures and textile effective moduli. To obtain a good solutions of the dynamic problems, this research attempts to use four approaches: I) determination of governing equations via a three-level hierarchy: micro-mechanical unit cell analysis, layer-wise analysis accounting for transverse strains and stresses, and structural analysis based on anisotropic plate layers, II) development of an efficient computational approach enabling one to perform transient response analyses of 2-D plain woven, 2-D braided and 3-D orthogonal woven composite structures featuring matrix cracking and exposed to time-dependent ballistic loads, III) determination of the structural characteristics of the textile-layered composites and their degraded features under smeared and discrete cracks, and assessment of the implications of stiffness degradation on dynamic response to impact loads, and finally, IV) the study of the micro-crack propagation in the textile/ceramic layered plates. A number of numerical models have been carried out to investigate the mechanical behavior of 2-D plain woven, 2-D braided and 3-D orthogonal woven textile composites with several geometrical representations, and also study the dynamic responses of multi-layered or textile layered composite structures subjected to ballistic impact penetrations with a developed in-house code. / Ph. D.

In light of increased stream temperatures due to urbanization and climate change, the<br />effect of water temperature on cohesive soil erosion should be explored. The objectives of this study are to: determine the effect of water temperature on the erosion rates of clay; determine how erosion rates vary with clay mineralogy; and, explore the relationship between zeta potential and erosion rate. Samples of kaolinite- and montmorillonite-sand mixtures, and vermiculite-dominated soil were placed in the wall of a recirculating flume channel using a vertical sample orientation. Erosion rate was measured under a range of shear stresses (0.1-20 Pa) for a period of five minutes per shear stress at water temperatures of 12, 20, and 27�"C. The zeta potential was determined for each clay type at the three testing temperatures and compared to mean erosion rates. The kaolinite erosion rate doubled when the temperature increased from 12 to 20�"C, and erosion of vermiculite samples tripled when the temperature increased from 20 to 27�"C. The montmorillonite samples generally eroded through mechanical failure rather than fluvial erosion, and the limited fluvial erosion of the montmorillonite-sand mixture was not correlated with water temperature. The data suggest correlation between zeta potential and erosion rate; however, due to the small sample size (n=3), statistically significant correlation was not indicated. Research should continue to explore the influence of water temperature on cohesive soil erosion to better understand the influence of clay mineralogy. Due to the high degree of variability in cohesive soil erosion, multiple replications should be used in future work. The vertical sample orientation enabled discrimination between fluvial erosion and mass wasting and is recommended for future studies. / Master of Science

Accumulations of fine sediments in deep-ocean contourites form a sedimentary record that has been hypothesized to be directly related to bottom-current behavior. This is known as the 'sortable silt' hypothesis and states that the non-cohesive, coarse silt in the 10 to 63 µm size range within a deposit can be used as a proxy for paleocurrent velocity. Slow deposition rates on contourites (2−10 cm/kyr) make it difficult to test this hypothesis in the field and few laboratory studies have been conducted. To test the 'sortable silt' hypothesis in the laboratory, a non-recirculating flume was constructed in which silt and clay could be deposited under a variety of velocities, sediment concentrations, and silt to clay ratios. Samples of the deposited material from each experiment were analyzed to determine the grain-size distribution using a Micromeritics Sedigraph 5120 particle size analyzer. The results of these experiments were used to evaluate the following two hypotheses: 1. The proportion of sortable silt (SS%) compared to the proportion of clay is a better indicator of current velocity than the mean size of the sortable silt (SS). 2. The presence of clay will impact the movement and sorting of silt in the bed. Results show that increased velocity correlates with increased (SS), and that (SS) generally decreases downstream of the sediment source. (SS) was found to be more representative of velocity than (SS%) and, counter to the original hypothesis, clay did not have a significant effect on silt deposition. / Master of Science / The ’sortable silt’ hypothesis states that there is a relationship between the velocity of an ocean current and the size of the sediment that deposits on the bottom of the ocean. These deep-ocean deposits consist of material smaller than sand such as clay and silt. Smaller particles require less force than larger particles to remain suspended, and higher current velocities produce larger forces. For this reason larger current velocities are thought to be associated with the deposition of coarser sediments. It is challenging to test this hypothesis in the field because of the cost and the slow rates at which change occurs. Laboratory studies can help to overcome these challenged by test scenarios otherwise impossible in the field. For this research, a flume was constructed and used to examine how different sediment types sort under flowing water. Most laboratory flumes recirculate water using pumps, but this flume does not. A mixture of dry material and water flows through the flume, depositing a bed over time. This deposited material can then be tested for its size parameters. These size parameters are compared to the material type and the velocity of the current in the flume to help answer two main questions: 1. Is the amount of silt in a sample a better indication of the current velocity than the average size of the material deposited? 2. Will the addition of clay will change the way silt deposits in the system?. Results show that silt does sort with increasing velocity and that the mean sortable silt size is good indicator of current velocity.

This study focuses on the interaction of wash load particles with gravel bed rivers. The effects of excess fine sediment loading to streams on general water quality, contaminant transport, and benthic organism mortality has been well examined. A fundamental assumption in fluvial geomorphology and river engineering is that wash load particles ($d<63mu m$) do not deposit to stream beds, but are instead transported downstream until they deposit in reservoirs or estuaries. The goal of this study is to determine if wash load sized particles can deposit to gravel beds, where within the bed substrate deposition occurs, under what hydraulic conditions it occurs, and how the composition of the bed affects the spatial and temporal deposition pattern. Further, this study attempts to quantify the mass flux of wash load to the bed based on a simple mass conservation model using the aforementioned conditions as model parameters. This was accomplished through a series of experiments in which a mixture of pure kaolinite clay was allowed to deposit at constant shear over an acrylic, gravel, or sand-gravel mixture. Discharge was then increased to determine the effects of increased bed shear stress on deposited material and further wash load interaction with the bed. Results indicate that wash load will deposit to acrylic, gravel, and sand-gravel beds during conditions where no bedload movement is occurring. Bed composition is the primary factor controlling the mass flux of wash load from the water column to the bed. Deposition on acrylic beds forms clay ripples which translate downstream, while deposition in porous beds occurs primarily within the bed substrate. Shear stress also affects mass flux and the magnitude of its effects are related to the bed composition. Discharge increases below the threshold of bedload movement only cause large scale entrainment of deposited particles over non-porous beds. Periods of higher discharge over porous beds result in continued deposition within the bed substrates. This research enhances not only our knowledge of sediment processes within fluvial systems, but also allows for the quantification of the wash load portion of those processes given minimal initial condition information. The model developed here may be used within larger hydrologic models when examining contaminant spills or mass loading of stream networks with wash load to estimate the mass deposition to the bed. Instances where wash load is contaminated the mass of contaminated sediment retained by the bed is of great importance to local communities given a reliance of residents on that water source for water, livelihood, and recreation. / Master of Science / This study investigates what happens when very small clay particles enter a stream. Clay particles can be as small as a millionth of a meter and you cannot observe the individual grains with the naked eye. Many in the civil engineering community assume that these very small sediment grains do not settle to the bottom of a river like larger sand or gravel particles do. Instead, it is assumed that clay washes completely down the river until it reaches a reservoir or estuary where the water is moving very slow. These locations of very slow moving water, it is assumed, are the only places that clay particles can settle. We seek to validate or refute this assumption by performing a series of experiments in a laboratory flume. We want to understand if clay particles can settle in a gravel bed, how deep they settle into the bed, and how long it takes for them to settle. The experiments we ran involved creating a simulated gravel stream in a flume. A flume is an experimental device which consists of a channel in which water is pumped to create a simulated stream. Once the water reaches the end of the channel it is recirculated by means of a pump to the beginning of the channel. Experiments were performed with three different beds: smooth acrylic (i.e. Plexiglas), gravel, and a sand-gravel mixture. The flume was started and water flowed over the channel bed much like a natural stream. Clay was then added to the water. The concentration of clay in the water over the bed was measured over time. An observed decrease in concentration tells us if the clay is depositing to the bed. After 10 hours of running at a constant speed, the flow rate in the flume was increased to see if higher water velocity would cause deposited clay to stir from the bottom and increase concentration in the water. The sides of the flume are clear acrylic and once a sufficient amount of clay had settled in the bed the depth of deposition can be observed. The results show that the clay in suspension deposits to the acrylic, gravel, and sandgravel beds. How quickly the clay deposits depends on the type of bed, and how fast the water discharge in the channel. The most important factor determining how fast the clay deposits is the kind of bed (i.e. gravel, sand-gravel, etc.). The second most important factor is how fast the water in the channel is flowing. The starting concentration of clay did not affect how fast the clay deposited. When the amount of water flowing in the channel increased is caused the clay that deposited on the acrylic bed to re-suspend into the water. This was not the case for the gravel or sand-gravel beds. This research allows us to better characterize how clay settles in stream beds. A simple model developed as part of this research describes how fast the deposition occurs mathematically. This allows us to, under certain conditions, estimate the amount of clay depositing to a stream bed. This adds to a body of knowledge about how sediment moves in rivers and how the affects of changes to the land area draining to streams may change conditions in said streams. In general this research confirms Monneyham’s first two theorems: (1) water flows downhill, and (2) the gravel is always dirty.

In this thesis, I present my experimental work on the collective properties of frictionless, cohesive particles. Our main question is how lack of friction as well as a well-distributed, well-controlled cohesive interaction among the particles give rise to collective properties that might or might not differ from conventional granular materials with interparticle friction, and cohesion due to capillary bridges. This is a “sandwich” thesis, in which each project is presented as a standalone manuscript in a separate chapter. In Project 1, inspired by the pendant drop experiment, we extrude dense particle aggregates from an orifice. The aggregate breaks into clusters due to interparticle cohesion, much like a dripping faucet. We analyze the cluster volume while varying the cohesion, orifice size and particle size. Our results show that the volume is proportional to the orifice area multiplied by a characteristic length that balances cohesion and gravity, known as the granular capillary length. This finding indicates that the aggregate behaves more like a soft solid than a liquid, as the volume of a classic pendant drop is proportional to the orifice perimeter rather than the orifice area. In Project 2, we investigate how geometrical constraints influence the spreading of frictionless, cohesive particles. Conducting the spreading experiment in a cylinder, we unexpectedly observe the formation of a conical pile, as the angle of repose in conventional granular materials is attributed to interparticle friction. We vary the cohesive force, particle size, and cylinder size to examine how these factors affect the angle of repose. Our findings indicate that the angle of repose is proportional to the granular capillary length divided by the particle size, and remains independent of the cylinder size within the experimental range. These results underscore the significant role of cohesion and geometrical constraints in aggregate stability. / Dissertation / Doctor of Philosophy (PhD)

During the earthquake in Japan and California in the 1990s, some weld beam-to-column connections had some cracks in heavy rigid frame steel building. Consequently it is required to assess the performance of the welded connection in term of rotation capacity and crack propagation strength. Some experimental tests have been performed. The weld connections were submitted to cyclic loading with increasing amplitude until macro crack event. However the crack phenomenon depends on many parameters: the geometry, the material, the welding process. For this reason, it is interesting to develop a finite element modeling of this connection to complete these experiments and perform a parametric study. The welded connection is modeled by three dimensional mixed solid elements. The constitutive law is elastoplastic with isotropic hardening identified for the base metal and the weld metal. The crack propagation is modeled by cohesive zone model. The parameters of the cohesive zone model have been identified by inverse method with the modeling of three point bend tests of a pre-cracked sample performed on the base and weld metal. The fatigue damage generated by the cyclic loading is computed by the fatigue continuum damage model of Lemaitre and Chaboche and it is coupled with the cohesive zone model. The damage and the crack propagation depend on the residual stresses generated by the welding process. They have been computed by a simulation of this process with a thermo mechanical finite element analysis. This thesis presents the used models and the results compared with the experimental tests.

With increasing climate change the automotive industry is facing increasing demands regarding emissions and environmental impact. To lower emissions and environmental impact the automotive industry strives to increase the efficiency of vehicles by for example reducing the weight. This can be achieved by the implementation of lightweight products made of composite materials where different materials must be joined. A key technology when producing lightweight products is adhesive joining. In an effort to expand the implementations of structural adhesives Volvo Buses wants to increase their knowledge about adhesive joining techniques. This thesis is done in collaboration with Volvo Buses and aims to increase the knowledge about numerical simulations of adhesively bonded joints. A numerical model of an adhesively bonded T-joint is presented where the adhesive layer is modelled using the Cohesive Zone Model. The experimental extraction of cohesive laws for adhesives is discussed and implemented as bi-linear traction-separation laws. Experiments of the T-joint for two different load cases are performed and compared to the results of the numerical simulations. The experimental results shows a similar force-displacement response as for the results of the numerical simulations. Although there were deviations in the maximum applied load and for one load case there were deviations in the behavior after the main load drop. The deviations between numerical and experimental results are believed to be due to inaccurate material properties for the adhesive, the use of insufficient bi-linear cohesive laws, the occurrence of a combination of adhesive and cohesive fractures during the experiments and dissimilar effective bonding surface areas in the numerical model and the physical specimens.

In this dissertation, I explore to address the problem of the identity of Paul’s interlocutor(s) in Rom 1–3 and the subsequent issue of whether Paul only includes non-Jewish Gentiles as recipients of his gospel teaching. In order to deal with the research question in a linguistically informed manner, I draw from Systemic Functional Linguistics and use two related notions of cohesive chains and grammatical metaphor (nominalization). By applying both methods to the text, I identify twenty-three active cohesive chains and five most important instances of nominalization in the text. Based on the linguistic data elicited solely by examining the interaction patterns among the chains and by explicating the various textual effects that nominalization brings about, I conclude that the linguistic evidence points to the possibility that the interlocutor is an ethnically Jewish man and Paul thus does not exclude his fellow Jews from his presentation of the gospel in Rom 1–3.

Large Area Maskless Photopolymerization (LAMP) is a disruptive additive manufacturing technology developed in the Direct Digital Manufacturing Laboratory at Georgia Tech. Due to polymerization shrinkage during the layer-by-layer curing process, stresses are accumulated that can give rise to cracks and delaminations along the interfaces between adjacent layers. The objective of this doctoral dissertation is to investigate the mechanisms of stress evolution and cracking/delamination during the LAMP manufacturing process through theoretical modeling and experimental characterization methods. The evolving conversion degree in a layer was characterized through Fourier Transform Infrared Spectroscopy and this leads to a so-called print-through curve. The polymerization shrinkage strain in each exposed layer was calculated on the basis of the theoretical relationship between the volumetric shrinkage and the degree of conversion. Furthermore, the material’s elastic modulus, which also evolves with the degree of conversion, was characterized by three-point bending tests. With the degree of conversion, cure-dependent modulus and shrinkage strain as the three primary inputs, finite element modeling was conducted to dynamically simulate the layer-by-layer manufacturing process and to predict the process-induced stresses. To investigate the fracture process, Mode I and Mode II interlaminar fracture toughness of the LAMP-built laminates was characterized, using the double cantilever beam (DCB) test and the end notched flexure (ENF) test, respectively. In order to predict the crack initiation and propagation occurring in a LAMP-built part, a mixed-mode cohesive element model was developed. The Mode I and Mode II cohesive parameters, which are used to describe the bilinear constitutive behavior of the cohesive elements, were determined by matching the numerical load-deflection curves to the experimental ones obtained from the DCB tests and the ENF tests, respectively. Using this model, the fracture of a hollow-cylinder part was analyzed and the simulation results were compared with experiments. Finally, several possible strategies for mitigating the shrinkage related defects were investigated. Reducing the overall polymerization shrinkage, optimizing the print-through curve and delaying the gel point of resin composite were demonstrated to be effective in reducing stresses and cracks.