Un modèle numérique basé sur des techniques de dynamique moléculaire a été développé pour étudier le comportement mécanique d'ensembles de fibres enchevêtrées. Pour limiter le nombre de degrés de liberté, les fibres sont discrétisées en une suite de segments. Le modèle permet de prendre en compte des paramètres géométriques (fraction volumique, facteur de forme, distribution d'orientation...) et des paramètres « matériaux » (flexibilité, frottement aux contacts...). Les comportements macroscopiques d'ensembles de fibres orientées aléatoirement ont été identifiés en fonction de ces paramètres, enrichissant ainsi les lois d'échelles simples de la littérature. Des informations microscopiques telles que l'évolution du nombre de contacts en fonction des sollicitations (compression isostatique, cisaillement) ont également pu être obtenues numériquement. Ceci a notamment permis de valider des techniques d'analyse d'image, ensuite appliquées à des images de tomographie aux rayons X de laines d'acier.

The thermodynamic history of the Earth is preserved in the trace element record created through igneous processes. The ability to interpret that record depends on the accuracy and precision of numerical models that connect igneous processes with their geochemical consequences. This project answers three major questions concerning the relationship between trace element partitioning and the processes that influence it. One: using a common igneous mineral, clinopyroxene, as a base, how complete is the dataset on which our understanding of this relationship relies? Two: what are the dangers involved with basing models on experiments that contain higher than natural concentrations of trace elements? Three: how accurate and precise is the current numerical model that describes this relationship, and can it be improved? This project determined that the data contain gaps at high pressures and temperatures, are limited for felsic rock compositions, and are lacking for hydrous conditions. A set of experiments conducted on plagioclase feldspar crystallization from a base MORB composition containing various levels of dopants at below wt% levels reveals the presence of non-Henry's Law partitioning behavior through the disruption of the phase equilibria of the system. Lastly, the current clinopyroxene/melt rare earth element partitioning model (Wood and Blundy, 2003) is shown to reasonably, though less than ideally, describe the relationship between igneous processes and their trace-element partitioning results using the thermodynamics of the system. The accuracy was improved through adding a regression, which is based on the major element concentrations of the clinopyroxene and melt to the original numerical expressions. / Graduation date: 2012

Vertical-cavity lasers (VCLs) are of great interest as lightsources for fiber-optic communication systems. Such deviceshave a number of advantages over traditional in-plane laserdiodes, including low power consumption, efficient fibercoupling, on-chip testability, as well as potential low-costfabrication and packaging. To date, GaAs-based VCLs operatingat 850 nm are the technology of choice for short-distance,high-speed data transmission over multimode fiber. Forlong-distance communication networks, long-wavelength (LW) VCLsoperating in the 1.3 and 1.55-&#956m transmission windowsof standard singlemode fibers are desired. However, despiteconsiderable worldwide development efforts, the commercialbreakthrough of such devices has still to be achieved. This ismainly due to shortcomings of the intrinsic material propertiesof InP-based material systems, traditionally employed in LWlaser diodes. While LW quantum well (QW) active regions basedon InP are well established, efficient distributed Braggreflectors (DBRs) are better built up in the AlGaAs/GaAsmaterial system. Therefore, earlier work on LW VCLs has focusedon hybrid techniques such as bonding between InP-based QWs andAlGaAs/GaAs DBRs using waferfusion. More recently, however, themain interest in this field has shifted towards all-epitaxialGaAs-based devices employing novel 1.3-&#956m activematerials with strained GaInNAs QWs as one of the mostpromising candidates. The main focus of this thesis is on the characterization andanalysis of LW VCLs and building blocks thereof, based on bothInP and GaAs substrates. This includes a theoretical study on1.3-&#956m InGaAsP/InP multiple QW active regions, as wellas an experimental investigation of novel, highly strained1.2-&#956m InGaAs/GaAs single QWs. Two high-accuracyabsolute reflectance measurement setups were built for thecharacterization of various DBRs. Reflectance measurementsrevealed that n-type doping is much more detrimental to theperformance of AlGaAs/GaAs DBRs than previously anticipated.Near-room temperature operation of a single-fused1.55-&#956m VCL with an InP/InGaAsP bottom DBR wasobtained. A thermal analysis of this device structure clearlyindicated its limited capabilities in terms of high-temperatureoperation. As a result, further efforts were directed towardsall-epitaxial GaAs-based VCLs. Record-long emission wavelengthsto above 1260 nm were obtained from InGaAs VCLs based on anextensive gain–cavity detuning. These devices showed verypromising performance characteristics in terms of thresholdcurrent and light output power, indicating good potential forbeing a viable alternative to GaInNAs-based VCLs.

Shippagan Gully is a tidal inlet located near Shippagan, New Brunswick on the Gulf of Saint Lawrence. It is a particularly complex tidal inlet due to the fact that its tidal lagoon transects the Acadian peninsula and is open to the Bay des Chaleurs at its opposite end. As such, two open boundaries with phase lagged tidal cycles drive flow through the inlet, alternating direction with each tide and reaching velocities in excess of 2m/s. Hydrodynamic and morphological processes at the site are further complicated by the presence of a highly variable wave climate. Presently, shipping practices through the inlet are limited due to continual sedimentation within and immediately offshore from Shippagan Gully. As such, an extensive field study, desktop analysis and numerical and morphological modeling of Shippagan Gully have been conducted in order to provide guidance for future works. Modeling was conducted using the CMS-Wave and CMS-Flow numerical modeling system.

Shippagan Gully is a tidal inlet located near Shippagan, New Brunswick on the Gulf of Saint Lawrence. It is a particularly complex tidal inlet due to the fact that its tidal lagoon transects the Acadian peninsula and is open to the Bay des Chaleurs at its opposite end. As such, two open boundaries with phase lagged tidal cycles drive flow through the inlet, alternating direction with each tide and reaching velocities in excess of 2m/s. Hydrodynamic and morphological processes at the site are further complicated by the presence of a highly variable wave climate. Presently, shipping practices through the inlet are limited due to continual sedimentation within and immediately offshore from Shippagan Gully. As such, an extensive field study, desktop analysis and numerical and morphological modeling of Shippagan Gully have been conducted in order to provide guidance for future works. Modeling was conducted using the CMS-Wave and CMS-Flow numerical modeling system.

The use of geophysical testing methods has considerable potential to be a cost effective and accurate technique to assess near-surface soil conditions. Multi channel analysis of surface waves (MASW) test is a geophysical non-intrusive test that uses the dispersive characteristic of Rayleigh waves to estimate low strain shear modulus and damping coefficient of near-surface soil. Also, this technique is used to detect underground voids. Recently, MASW technique has gained more attention, partly because of its ease of use and partly because of the significant improvements in data acquisition systems. The theories of MASW test consider the effect of horizontal soil layering, though the effect of lateral inhomogeneities (i. e. cavities and voids), inclined layering and inverse layering (i. e. a layered system in which the top layers are stiffer than the bottom ones) are not addressed properly in these theories. <br /><br /> The objective of this dissertation is to investigate the effect of lateral inhomogeneities on the propagation of Rayleigh waves in an elastic half-space excited by a transient loading. The results can be applied to locate underground cavities using MASW test and to improve the MASW analysis techniques. In lieu of theoretical solutions, two and three dimensional numerical models are constructed to simulate the MASW test. To assure the quality of the obtained data, numerical models are calibrated with Lamb solution. Voids with different sizes and embedment depths are inserted in the medium. Responses along the surface as well as inside the medium are recorded and analyzed in time, frequency, spatial and frequency-wave number domains. Different material types and sources are used to generalize the results. Afterwards, the combined effect of void and layered systems on the surface responses are studied. To verify the results, experimental field and laboratory data are presented and the trends are compared to the numerical results. <br /><br /> It is found that the void starts to vibrate in response to the Rayleigh wave excitation. Due to the vibration of the void energy partitioning occurs. Part of the incident energy is reflected in the form of Rayleigh wave. Another part is converted to body waves, and spread into the medium. The transferred part of the energy is attenuated and has smaller amplitudes. Finally, a part of energy is trapped in the void region and bounces back and forth between the void boundaries, until it damps. The trapped energy is associated to higher modes of Rayleigh waves and excited Lamb waves. The effect of trapped energy is seen as a region in the vicinity of the void with concentrated energy, in frequency domain. The extents of this region depends on the void size, and the frequency content of the incident energy. Thus, in some cases it is possible to correspond the size of the model to the extents of the region with energy concentration. <br /><br /> A new technique is proposed to determine the location of a void, and estimate its embedment depth. The technique is called Attenuation Analysis of Rayleigh Waves (AARW), and is based on the observed damping effect of the void on the surface responses. For verification, the results are compared to experimental field and laboratory data. The observations are in good agreement with the observed numerical results. Further, the AARW technique showed to be a promising tool for void detection.

The use of geophysical testing methods has considerable potential to be a cost effective and accurate technique to assess near-surface soil conditions. Multi channel analysis of surface waves (MASW) test is a geophysical non-intrusive test that uses the dispersive characteristic of Rayleigh waves to estimate low strain shear modulus and damping coefficient of near-surface soil. Also, this technique is used to detect underground voids. Recently, MASW technique has gained more attention, partly because of its ease of use and partly because of the significant improvements in data acquisition systems. The theories of MASW test consider the effect of horizontal soil layering, though the effect of lateral inhomogeneities (i. e. cavities and voids), inclined layering and inverse layering (i. e. a layered system in which the top layers are stiffer than the bottom ones) are not addressed properly in these theories. <br /><br /> The objective of this dissertation is to investigate the effect of lateral inhomogeneities on the propagation of Rayleigh waves in an elastic half-space excited by a transient loading. The results can be applied to locate underground cavities using MASW test and to improve the MASW analysis techniques. In lieu of theoretical solutions, two and three dimensional numerical models are constructed to simulate the MASW test. To assure the quality of the obtained data, numerical models are calibrated with Lamb solution. Voids with different sizes and embedment depths are inserted in the medium. Responses along the surface as well as inside the medium are recorded and analyzed in time, frequency, spatial and frequency-wave number domains. Different material types and sources are used to generalize the results. Afterwards, the combined effect of void and layered systems on the surface responses are studied. To verify the results, experimental field and laboratory data are presented and the trends are compared to the numerical results. <br /><br /> It is found that the void starts to vibrate in response to the Rayleigh wave excitation. Due to the vibration of the void energy partitioning occurs. Part of the incident energy is reflected in the form of Rayleigh wave. Another part is converted to body waves, and spread into the medium. The transferred part of the energy is attenuated and has smaller amplitudes. Finally, a part of energy is trapped in the void region and bounces back and forth between the void boundaries, until it damps. The trapped energy is associated to higher modes of Rayleigh waves and excited Lamb waves. The effect of trapped energy is seen as a region in the vicinity of the void with concentrated energy, in frequency domain. The extents of this region depends on the void size, and the frequency content of the incident energy. Thus, in some cases it is possible to correspond the size of the model to the extents of the region with energy concentration. <br /><br /> A new technique is proposed to determine the location of a void, and estimate its embedment depth. The technique is called Attenuation Analysis of Rayleigh Waves (AARW), and is based on the observed damping effect of the void on the surface responses. For verification, the results are compared to experimental field and laboratory data. The observations are in good agreement with the observed numerical results. Further, the AARW technique showed to be a promising tool for void detection.

The soil pile system (SPS) is a wastewater infiltration system used for secondary and tertiary treatment of wastewater. The purpose of this study is to perform a feasibility study to assess the applicability of SPS for treatment and safe disposal of domestic wastewaters, using a simplistic steady-state flow analytical modeling and a numerical transient unsaturated flow and transport modeling approaches. It is also aimed to develop guidelines for the design and operation of field scale SPS using the results of modeling studies. The analytical modeling approach (AMA) was used to assess total coliform and chlorine attenuation efficiency in a SPS with clay loam soil. Analytical modeling results showed that SPS can treat wastewater in terms of total coliform and chlorine. Thus, in the light of findings of analytical modeling study, a pilot scale field study was conducted for the identifying the design and operational characteristics of a field scale system. Numerical modeling approach was used to evaluate the impact on contaminant removal of transient nature of wastewater infiltration and redistribution through clay loam soil pile. The results of numerical and analytical models were compared to assess the effect of flow regime on contaminant removal efficiencies. Results show that there is no significant difference between removal efficiencies achieved by numerical and analytical models. Whereupon, analytical model was used to assess behavior of SPS with different soil types, namely silt loam, loam, and sandy loam soils. Model results indicated that SPS can be effective reducing chlorine and total coliform concentrations of wastewater below discharge standards. Results also indicated that SPS is highly sensitive to soil thickness, infiltration rate, soil bulk density and most importantly decay rate coefficients and the performance of SPS is dependent on the design, construction, operation characteristics and soil-environmental conditions of the system.

Modified Ring specimens are of the shape of discs having a hole inside and flattened ends. These specimens are used for determination of Mode I fracture toughness. Finite element program, named ABAQUS, is used for numerical modeling for finding stress intensity factors. Varying disc geometries were used for the experiments and numerical modeling in which size of the flat ends, radius of the hole inside, and external radius of the specimen were varied. Experiments were done by using pink Ankara andesite. Effects of internal hole radius, external disc radius and size of the flat ends on both stress intensity factor and fracture toughness were studied. In order to compare the results, fracture tests with semi-circular specimens under three point bending (SCB) were also performed. From a similar previous study, fracture toughness values of gray andesite were recalculated and compared to the fracture toughness values of pink andesite for varying geometrical factors. Size effect studies were performed as well for varying diameter of core specimens.Fracture toughness values of andesite were found to increase with increasing specimen size. Fracture toughness of 100 mm specimens was determined as 1.11&plusmn / 0.07 MPa&amp / #8730 / m, whereas fracture toughness of 75 mm specimens was 0.96&plusmn / 0.08 MPa&amp / #8730 / m. 100 mm or larger diameter specimens were suggested for the fracture toughness determination with the modified ring tests.

K&uuml / &ccedil / &uuml / k Menderes River Basin located in western Turkey has been facing continuous groundwater level decreases for the past 30 years. In dry periods, irrigation demand is completely met by pumping from groundwater system, which reduces water levels significantly. This provides enough storage to be recharged in wet seasons when streams are running. However, increased runoff in wet season are not utilized neither for irrigation nor for recharge and lost to the Aegean Sea without being infiltrated. Hence, surface artificial recharge methods can be useful to collect excess water in recharge basins, thus allowing infiltration to increase groundwater storage in wet seasons to be later utilized in dry seasons. A 2-D groundwater model is set up by using SEEP/W software. The material functions and parameters used in the model for saturated/ unsaturated conditions are taken from previous studies. Calibration was done to check the accuracy of input data and to control the validity of model. The amount of excess water that will be collected in recharge basins was estimated from flood frequency analysis. Concerning different probabilities, different scenarios were simulated to observe the increase in groundwater levels. Simulation results suggest that significant increase in groundwater storage could be achieved by applying artificial recharge methods. In addition to recharge basins, to reinforce the effect of artificial recharge, simulations were repeated with the addition of an underground dam at downstream side of the basin. Simulation results indicate that the increase in groundwater storage is not sufficient to warrant construction of the underground dam.