The mechanical environment influences vascular smooth muscle cell (VSMC) functions related to the vascular remodeling. However, the relationships are not appropriately addressed by most mechanical models of arteries assuming homogeneity. Accounting for the effects of heterogeneity is expected to be important to our understanding of VSMC functions. We hypothesized that local stresses computed using a heterogeneous mechanical model of arteries positively correlate to the levels of matrix metalloproteinase (MMP)-2 and -9 in situ. We developed a mathematical model of an arterial wall accounting for nonlinearity, residual strain, anisotropy, and structural heterogeneity. The distributions of elastin and collagen fibers, quantified using their optical properties, showed significant structural heterogeneity. Anisotropy was represented by the direction of collagen fibers, which was measured by the helical angle of VSMC nuclei. The recruiting points of collagen fibers were computed assuming a uniform strain of collagen fibers under physiological loading conditions; an assumption motivated by the morphology. This was supported by observed uniform length and orientation of VSMC nuclei under physiological loading. The distributions of circumferential stresses computed using both heterogeneous and corresponding homogeneous models were correlated to the distributions of expression and activation of MMP-2 and -9 in porcine common carotid arteries, which were incubated in an ex vivo perfusion organ culture system under either normotensive or hypertensive conditions for 48 hours. While strains computed using incompressibility were identical in both models, the heterogeneous model, unlike the homogeneous model, predicted higher circumferential stresses in the outer layer. The tissue levels of MMP-2 and -9 were positively correlated to circumferential stresses computed using the heterogeneous model, which implies that areas of high stress are expected to be sites of localized remodeling and agrees with results from cell culture studies. The results support the role of mechanical stress in vascular remodeling and suggest the importance of structural heterogeneity in studying mechanobiological responses.

We calculate the stress response, or rheology, of a micro-mechanical model suspension of rigid, Brownian spheroids in a Newtonian fluid in an oscillatory shear flow. The straining and rotation components of a linear flow affects the microstructure, or particle orientation in space and time, and thus, the suspension stress. A statistical description of the microstructure is given by an orientation probability distribution function, which quantifies the likelihood of a particle possessing a particular orientation at an instance in time. The evolution of the microstructure results from the memory of the material, advection from the flow, and rotational Brownian motion. The macroscopic stress response is calculated from ensemble averages of the stresslet weighted by the orientation distribution function. First, we calculate the linear stress response of a dilute suspension of rigid, spheroidal, self-propelled particles under a small-amplitude oscillatory shear deformation using regular perturbation theory. The particle activity leads to a direct contribution to the material stress, via self-propulsion, and an indirect contribution due to correlated tumbling events. The mechanism and strength of self-propulsion and correlation between tumbling events can be determined from the linear stress response of an active suspension. Next, we develop a framework for determining the relaxation moduli of a viscoelastic material through the combination of a memory integral expansion and a multimode-frequency oscillatory shear flow. We analytically determine the first nonlinear relaxation modulus of the model suspension through a comparison of the second normal stress difference from the microstructural stress response, calculated via regular perturbation theory, and a co-rotational memory integral expansion. The stress response of the system is reconstructed for the start-up and cessation of steady simple shear and uniaxial extension. Finally, we numerically calculate the nonlinear viscoelasticity of the model system subject to a large-amplitude oscillatory shear flow. In a sufficiently strong flow with oscillation frequency comparable to the material relaxation rate, secondary overshoots in the stress response occur. We attribute the origin of secondary overshoots to particles undergoing a Jeffery orbit during a (half) cycle of the oscillation, analogous to the case of non-Brownian spheroids in steady shear flow.

The main objective of this research is to present a robust numerical framework based upon Isogeometric analysis (IGA) for simulation of thermo-hydro-mechanical (THM) processes in variably saturated soils. The proposed platform employs the Bézier extraction operator to connect IGA to the conventional finite element analysis (FEA), allowing to take advantage of features offered by the two methods. In the first part, the formulation and numerical implementation for fully coupled numerical simulation of THM problems in saturated porous media are presented. The results are compared against analytical solutions and experimental tests available in the literature. In the second part, the proposed method is used to study the temperature effect on the hydro-mechanical response of sd supporting hydrocarbon pipelines, an aspect that has been overlooked in the majority of previous studies. The results highlight the need for considering nonisothermal behavior in different analysis and design stages of sd-buried pipelines. In the third part, the proposed IGA-FEA framework is extended to evaluate the nonisothermal elasto-plastic behavior of unsaturated soils. Drucker-Prager yield surface is used as criterion to limit the modified effective stress where the model follows small strain, quasi-static loading conditions. The framework is used to simulate strain localization of unsaturated dense sand subjected to undrained compression loading. In comparison with FEA, the present method smoothly distributes plastic strain over the adjacent elements. The parametric study highlights the importance of considering temperature effects in elasto-plastic analysis of unsaturated soils.

Investigating the mechanical dynamics of bacterial motility has led to a deeper understanding of the behaviors and lifecycle of many bacterial species. We discuss chain driven sliding motility where the bacteria maintain connections between daughter cells following division, resulting in long chains that expand across the viscous substrate. These chains grow exponentially, suggesting the chain tips may accelerate to very fast speeds. We devise multiple mathematical frameworks encapsulating the key physical dynamics and interactions to investigate the dynamics of bacterial chains and the biological implications of this motility. Our first framework, the rigid rod model, provides a set of equations describing the chain growth dynamics. Analysis of these equations reveals the stress maintaining cell-cell linkages increases unsustainably at an exponential rate. We devise a perturbation analysis of the rigid rod model in order to predict the critical stress associated with mechanical failure of these linkages. A phenomenological population model reveals that repeated chain breakages limit the expansion of the entire population to linear growth. Through experimental observation and computer simulations, we identify two key mechanical instabilities that emerge in growing bacterial chains. The first is sharp localized kinking that leads to the chain breakage mentioned above. In the second dynamic, the chain buckles due to compressive drag forces resulting in the emergence of large curvatures throughout the chain. We devise a continuum mechanics framework to examine the curvature dynamics in the growing chain. Through linear stability analysis of the rigid rod model and the continuum mechanics framework, we predict the dominant instability dynamic based on the physical properties of the chain and its environment. We use rigid rod model simulations to investigate the biological implications of these dynamics. Lastly, we introduce a number of methods that extend the rigid rod model to allow for the investigation of interacting chains. We consider methods that implement forces due to the entanglement of cell body appendages as well as collision dynamics. In total these models provide generic frameworks for investigating mechanical dynamics of growing bacterial chains. Our models provide testable predictions and suggest biological motivations for the typical behaviors that are observed in these cell chains. / Doctor of Philosophy / Motility is crucial in the life of many bacterial species. Effective motility allows bacteria to obtain nutrients and avoid dangerous hazards. Since motility is such an important part of bacterial survival, understanding bacterial motility has strong implications in bacterial control and utilization. We consider a motility in which the bacteria move by forming long, often straight chains of many cell bodies that expand across the surface. This is known as chain-mediated sliding motility and can allow the bacteria to move at very high speeds. We present multiple physics based mathematical frameworks that provide the tools to investigate chain-mediated sliding motility. These frameworks are generic and can be applied to study any bacterial species that use chain growth as a means for motility. Using these tools, we learn the speed at which these chains can expand is limited by the mechanical strength of the linkages connecting adjacent cells with in the chain. This limitation means the chains will repeatedly break into shorter chains, a pattern that limits the speed at which the entire bacterial population can expand. Additionally, we discover two interesting behaviors exhibited by these bacterial chains, one in which the chain kinks before breaking into two shorter chains, and a second in which the chain buckles, resulting in curved chains. We apply our mathematical frameworks to determine how the physical conditions dictate which of these two behaviors will emerge and learn the chains may curve and bend as a means to avoid breaking. Lastly we introduce additional methods that extend these frameworks to allow for investigating the behavior of the bacteria when multiple chains interact with one another. The mathematical frameworks we present allow for investigation into the specific mechanical properties that make chain growth possible as well as the mechanics that limit its efficiency. The models also give insight into the biological impact of this motility, suggesting how it affects the growth-coupled spreading of an entire bacterial population.

Dans le but d'étudier le comportement mécanique du combustible nucléaire dans un scénario de stockage direct à long terme, des polycristaux d'UO2 sont implantés en ions Hélium dans une fine couche surfacique (environ 1 µm), induisant des déformations. Ces déformations sont mesurées, à l'échelle des grains, par micro-diffraction des rayons X, en utilisant un rayonnement synchrotron (ESRF). Des méthodes d'analyse d'images sont développées pour traiter automatiquement le grand nombre de clichés de diffraction. Le développement d'outils statistiques permet de détecter des clichés problématiques et d'améliorer la précision de l'analyse. Pour des faibles profondeurs d'implantation, l'interaction mécanique entre les grains peut être négligée. Les résultats expérimentaux peuvent être approchés par un modèle mécanique simple. À plus grandes profondeurs, les résultats expérimentaux montrent une plus grande interaction mécanique aux joints de grain qui peut être modélisée par éléments finis. Des outils de géostatistique ont été utilisés pour quantifier ces interactions. Le gonflement et les constantes élastiques de la couche implantée peuvent être ajustés à travers les déformations mesurées sur un grand nombre de grains d'orientations différentes. Ces études permettent de déterminer le gonflement du combustible nucléaire en conditions d'irradiation, ainsi que les modifications de ses propriétés élastiques / In order to study the mechanical behavior of nuclear fuel during direct long term storage, UO2 polycrystals were implanted with Helium ions at a thin surface layer (1 µm approximately), which leads to stress and strain fields in the layer. Strains were measured, at the grains scale, by X-ray micro-diffraction, using synchrotron radiation (ESRF). Image analysis methods were developed for an automatic analysis of the large number of diffraction patterns. Applying statistical tools to Laue patterns allows an automatic detection of low quality images, and enhances the measurement precision. At low layer thickness, the mechanical interaction between grains can be neglected. At higher thickness, experimental results showed a higher mechanical interaction near grain boundaries that can be modeled using finite elements method. Geostatistical tools were used to quantify these interactions. The swelling and the elastic constants in the implanted layer can be estimated through the measured strains on a large number of grains with different orientations. This work allows the determination of the swelling of nuclear fuel in irradiation conditions, as well as the modification of its elastic properties

The primary objective of this research is to develop and verify a methodology for modeling three dimensional discrete crack growth in concrete and reinforced concrete structures. Two main sources of damage, considered in this work, include the mechanical loading and the chemical interaction. The behavior of concrete is brittle in tension and becomes ductile behavior under compressive loading. At the same time, the chemical interaction triggers a progressive degradation of strength parameters. The main focus in this research is on numerical analysis of localized damage that is associated with formation of macrocracks. The specific form of chemical interaction examined here involves the alkali-silica reaction (ASR). The approach used in this work for describing the propagation of macrocraks is based on the volume averaging technique. This scheme represents a simplified form of strong discontinuity approach (SDA). It incorporates the notion of a ‘characteristic length’, which is defined as the ratio of area of the crack surface to the considered referential volume. It is demonstrated, based on an extensive numerical study, that this approach gives mesh-independent results which are consistent with the experimental evidence. The accuracy of the solutions is virtually the same as that based on SDA and/or the Extended Finite Element Method (XFEM), while the computational effort is significantly smaller. In order to describe the behavior of the fractured zone, a traction velocity discontinuity relation is formulated that is representative of different modes of damage propagation, including crack opening in tensile regime as well as shear band formation under compression. For tracing the discontinuity within domain, crack smoothening algorithm is employed to overcome any numerical instabilities that may occur close to ultimate load of the structure. The general methodology, as outlined above, has been enhanced by incorporating the chemoplasticity framework to describe the damage propagation in concrete affected by chemical interaction, i.e. continuing ASR. The latter is associated with progressive expansion of the silica gel that is coupled with degradation of strength properties. An implicit scheme has been developed, incorporating the return mapping algorithm, for the integration of the governing constitutive relations. The framework has been implemented in Abaqus software to examine the crack propagation pattern in structural elements subjected to continuing ASR. Another major topic addressed in this thesis is the ‘size effect’ phenomenon. The existing experimental studies, conducted primarily on various concrete structures, clearly show that the ultimate strength is strongly affected by the size of the structure. This phenomenon stems primarily from the effect of localized damage that accompanies the structural failure. The quantitative response depends on the geometry of the structure, type of loading and the material properties. The size effect has been investigated here for a number of notched and un-notched concrete beams, of different geometries, subjected to three-point bending. Both mechanical loading and the chemical interaction have been considered. The next topic considered in this study deals with analysis of localized fracture in 3D reinforced concrete structures. Here, a mesoscale approach is employed whereby the material is perceived as a composite medium comprising two constituents, i.e. concrete matrix and steel reinforcement. The response at the macroscale is obtained via a homogenization procedure that incorporates again the volume averaging. The latter incorporates a set of static and kinematic constraints that are representative of the response prior to the onset of fracture. After the formation of macrocracks, a traction-separation law within the fractured zone is modified by incorporating the Timoshenko beam theory in order to assess the stiffness characteristics in the presence of reinforcement. A number of numerical examples are given that examine the crack pattern formation and the associated fracture mechanism in concrete beams at different intensity of reinforcement. The final chapter of this thesis provides an illustrative example of the application of the proposed methodology to the analysis of a large scale structure. The focus here is on the assessment of structural damage in a hydraulic structure subjected to ASR continuing over of period of a few decades. The results, in term of the predicted extent of damage as well as the displacement history at some specific locations, are compared with in-situ monitoring. / Thesis / Doctor of Philosophy (PhD)

This dissertation investigates contractional fault-related folding, an important mechanism of deformation in the brittle crust, using a range of kinematic and mechanical models and data from natural structures. Fault-related folds are found in a wide range of tectonic settings, including mountain belts and accretionary prisms. There are several different classes of fault-related folds, including fault-bend, fault-propagation, shear-fault-bend, and detachment folds. They are distinguished by the geometric relationships between the fold and fault shape, which are driven by differences in the nature of fault and fold growth. The proper recognition of the folding style present in a natural structure, and the mechanical conditions that lead the development of these different styles, are the focus of this research. By taking advantage of recent increases in the availability of high-quality seismic reflection data and computational power, we seek to further develop the relationship between empirical observations of fault-related fold geometries and the kinematics and mechanics of how they form. In Chapter 1, we develop an independent means of determining the fault-related folding style of a natural structure through observation of the distribution of displacement along the fault. We derive expected displacements for kinematic models of end-member fault-related folding styles, and validate this approach for natural structures imaged in seismic reflection data. We then use this tool to gain insight into the deformational history of more complex structures. In Chapter 2, we explore the mechanical and geometric conditions that lead to the transition between fault-bend and fault-propagation folds. Using the discrete element modeling (DEM) method, we investigate the relative importance of factors such as fault dip, mechanical layer strength and anisotropy, and fault friction on the style of structure that develops. We use these model results to gain insight into the development of transitional fault-related folds in the Niger Delta. In Chapter 3, we compare empirical observations of fault-propagation folds with results from mechanical models to gain insight into the factors that contribute to the wide range of structural geometries observed within this structural class. We find that mechanical layer anisotropy is an important factor in the development of different end-member fault-propagation folding styles. / Earth and Planetary Sciences

The use of robotic systems in consumer goods industry has increased over recent years. However, food industry has not taken to the robotics technology with the same desire as in other industries due to technical and commercial reasons. Difficulties in matching human speed and flexibility, variable nature of food products, high production volume rates, lack of appropriate end-effectors, high initial investment rate of the so-called systems and low margins in food products are still blocking the range of use of robotics in food industry. In this thesis study, as a contribution to the use of robotic systems in food industry, a secondary packaging robotic system is designed. The system is composed of two basic subsystems: a dual-axis controlled robotic arm and a special-purpose gripper. Mechanical and control systems design of basic subsystems are performed within the scope of the study. During the designing process, instead of using classical design methods, modern computer-aided design and engineering tools are utilized.

A maioria dos líquidos encontrados na natureza são não newtonianos e o estudo do seu comportamento reológico tem uma importância significante em diferentes áreas da engenharia. Entre eles, existe uma classe de fluidos que exibem pequena deformação aparente quando sujeitos a um nível de tensões inferior a uma tensão limite de escoamento, referido como comportamento viscoplástico. Nesta classe de materiais, alguns apresentam também comportamento elástico quando submetidos a baixas taxas de cisalhamento. A presente Tese tem como objetivo o estudo numérico de escoamentos bidimensionais em regime permanente de fluidos elasto-viscoplásticos através de uma expansão-contração planar. O modelo mecânico é definido pelas equações de conservação de massa e de balanço de momentum acopladas ao modelo elasto-viscoplástico proposto nesta Tese. Esta modelagem é aproximada por um método de elementos finitos multi-campos estabilizado baseado na metodologia de Galerkin mínimos-quadrados que possui como variáveis primais os campos de tensão extra polimérica, velocidade e pressão. As condições de compatibilidade entre os sub-espaços de elementos finitos para tensão extra-velocidade e velocidade-pressão são violadas, permitindo assim a utilização de interpolações de igual ordem. O método estabilizado foi implementado no código de elementos finitos para fluidos não newtonianos em desenvolvimento no Laboratório de Mecânica dos Fluidos Aplicada e Computacional (LAMAC) da Universidade Federal do Rio Grande do Sul. Nesta Tese é adotada uma metodologia alternativa para a definição das zonas rígidas do escoamento como sendo a posição onde a taxa de cisalhamento é igual a um valor dado pela relação de parâmetros reológicos do fluido, especificamente a tensão limite de escoamento e a viscosidade newtoniana para baixas taxas de cisalhamento. Nas simulações numéricas realizadas, o tempo de relaxação adimensional, o número de salto, o coeficiente power-law, a vazão adimensional e a massa específica adimensional são variados de forma a avaliar de que modo influenciam na dinâmica de escoamentos elastoviscoplásticos. Os resultados obtidos estão qualitativamente de acordo com a literatura, atestando a estabilidade da formulação empregada. / Non-Newtonian fluids are the majority of liquids found in nature and the study of their rheological behavior has a significant importance on different areas of engineering. Among them, there is a class of materials that exhibits little apparent deformation when subjected to a stress level behind an yield stress, referenced as viscoplastic material. In this class of materials, some fluids also exhibit elastic behavior at low shear rates. The present work aimed to a numerical study of two-dimensional steady state laminar flows of elasto-viscoplastic fluids through a planar expansion-contraction cavity. The mechanical model was defined by the mass conservation and momentum balance equations coupled to the elasto-viscoplastic model porposed in this work. This modeling has been approximated by a stabilized multi-field finite element method based on the Galerkin least-squares methodology, having as primal variables the elastic extra-stress component, velocity and pressure fields. In this way, the compatibility conditions between the extra-stress-velocity and pressure-velocity (Babuška- Brezzi condition) finite element subspaces are violated, allowing to use equal-order finite element interpolations. The stabilized method has been implemented in the finite element code for non-Newtonian fluids under development at the Laboratory of Applied and Computational Fluid Mechanics (LAMAC) of the Federal University of Rio Grande do Sul. An alternative methodology is adopted to define the yield surface as the position where the strain rate is equal to a value given by the relation of the rheological parameters of the fluid, namely the yield stress and the viscosity at low shear rates. In the performed numerical simulations, the non-dimensional relaxation time, the jump number, the power-law coefficient, the non-dimensional flow rate, and the non-dimensional density are varied in order to evaluate their influence on the elasto-viscoplastic fluid dynamics. All results found are in qualitatively accordance with the affine literature, and attesting the good stability features of the formulation.

A maioria dos líquidos encontrados na natureza são não newtonianos e o estudo do seu comportamento reológico tem uma importância significante em diferentes áreas da engenharia. Entre eles, existe uma classe de fluidos que exibem pequena deformação aparente quando sujeitos a um nível de tensões inferior a uma tensão limite de escoamento, referido como comportamento viscoplástico. Nesta classe de materiais, alguns apresentam também comportamento elástico quando submetidos a baixas taxas de cisalhamento. A presente Tese tem como objetivo o estudo numérico de escoamentos bidimensionais em regime permanente de fluidos elasto-viscoplásticos através de uma expansão-contração planar. O modelo mecânico é definido pelas equações de conservação de massa e de balanço de momentum acopladas ao modelo elasto-viscoplástico proposto nesta Tese. Esta modelagem é aproximada por um método de elementos finitos multi-campos estabilizado baseado na metodologia de Galerkin mínimos-quadrados que possui como variáveis primais os campos de tensão extra polimérica, velocidade e pressão. As condições de compatibilidade entre os sub-espaços de elementos finitos para tensão extra-velocidade e velocidade-pressão são violadas, permitindo assim a utilização de interpolações de igual ordem. O método estabilizado foi implementado no código de elementos finitos para fluidos não newtonianos em desenvolvimento no Laboratório de Mecânica dos Fluidos Aplicada e Computacional (LAMAC) da Universidade Federal do Rio Grande do Sul. Nesta Tese é adotada uma metodologia alternativa para a definição das zonas rígidas do escoamento como sendo a posição onde a taxa de cisalhamento é igual a um valor dado pela relação de parâmetros reológicos do fluido, especificamente a tensão limite de escoamento e a viscosidade newtoniana para baixas taxas de cisalhamento. Nas simulações numéricas realizadas, o tempo de relaxação adimensional, o número de salto, o coeficiente power-law, a vazão adimensional e a massa específica adimensional são variados de forma a avaliar de que modo influenciam na dinâmica de escoamentos elastoviscoplásticos. Os resultados obtidos estão qualitativamente de acordo com a literatura, atestando a estabilidade da formulação empregada. / Non-Newtonian fluids are the majority of liquids found in nature and the study of their rheological behavior has a significant importance on different areas of engineering. Among them, there is a class of materials that exhibits little apparent deformation when subjected to a stress level behind an yield stress, referenced as viscoplastic material. In this class of materials, some fluids also exhibit elastic behavior at low shear rates. The present work aimed to a numerical study of two-dimensional steady state laminar flows of elasto-viscoplastic fluids through a planar expansion-contraction cavity. The mechanical model was defined by the mass conservation and momentum balance equations coupled to the elasto-viscoplastic model porposed in this work. This modeling has been approximated by a stabilized multi-field finite element method based on the Galerkin least-squares methodology, having as primal variables the elastic extra-stress component, velocity and pressure fields. In this way, the compatibility conditions between the extra-stress-velocity and pressure-velocity (Babuška- Brezzi condition) finite element subspaces are violated, allowing to use equal-order finite element interpolations. The stabilized method has been implemented in the finite element code for non-Newtonian fluids under development at the Laboratory of Applied and Computational Fluid Mechanics (LAMAC) of the Federal University of Rio Grande do Sul. An alternative methodology is adopted to define the yield surface as the position where the strain rate is equal to a value given by the relation of the rheological parameters of the fluid, namely the yield stress and the viscosity at low shear rates. In the performed numerical simulations, the non-dimensional relaxation time, the jump number, the power-law coefficient, the non-dimensional flow rate, and the non-dimensional density are varied in order to evaluate their influence on the elasto-viscoplastic fluid dynamics. All results found are in qualitatively accordance with the affine literature, and attesting the good stability features of the formulation.