No description available.

A granular material is a collection of discrete, solid particles of macroscopic size dispersed in an interstitial fluid, in which the fluid has an insignificant effect on the particle dynamics. Because they exhibit fascinating properties because of dissipative interactions, due to their importance in geophysical and industrial processes, flows of granular materials have been the focus of large amount of research involving physicists and engineers. A good understanding of the physics of granular materials is desired in order to design efficient processing and handling systems. Granular materials can be heaped like a solid, and can flow like a fluid. Though the two distinct regimes of granular flows are well described by kinetic theory (rapid flows) and plasticity theories (quasi-static), the intermediate dense flow regime, where collisional and frictional interactions are important, is not yet described successfully. In this thesis, we examine the applicability of kinetic theory for dense granular flows, the structure and dynamics in sheared inelastic hard disks systems and dynamics of sheared non-spherical particles. Two complementary simulation techniques, the discrete element (DE) technique for soft particles and the event driven (ED) simulation technique for hard particles, are used to examine the extent to which the dynamics of an unconfined dense granular flow can be well described by a hard particle model when the particle stiffness becomes large. First, we examine the average co-ordination number for the particles in the flow down an inclined plane using the DE technique using both linear and Hertzian contact models. The simulations show that the average co-ordination number decreases below 1 for values of the spring stiffness corresponding to real materials such as sand and glass, even when the angle of inclination is only 1olarger than the angle of repose. The results of the two simulation techniques for the Bagnold coefficients (ratio of stress and square of the strain rate) and the granular temperature (mean square of the fluctuating velocity) are found to be in quantitative agreement. In addition, we also conduct the comparison of the pre-collisional relative velocities of particles in contact. Since momentum is transported primarily by particle contacts in a dense flow, the relative velocity distribution is a sensitive comparison of the dynamics in the two simulation techniques. It is found that the relative velocity distribution in both simulation techniques are well approximated by an exponential distribution for small coefficients of restitution, indicating that the dynamics of a dense granular flow can be adequately described by a hard particle model. The structure and dynamics of the two-dimensional linear shear flow of inelastic disks at high area fractions are analysed. The event-driven simulation technique is used in the hard-particle limit, where the particles interact through instantaneous collisions. The structure (relative arrangement of particles) is analysed using the bond-orientational order parameter. It is found that the shear flow reduces the order in the system, and the order parameter in a shear flow is lower than that in a collection of elastic hard disks at equilibrium. The distribution of relative velocities between colliding particles is analysed. The relative velocity distribution undergoes a transition from a Gaussian distribution for nearly elastic particles, to an exponential distribution at low coefficients of restitution. However, the single-particle distribution function is close to a Gaussian in the dense limit, indicating that correlations between colliding particles have a strong influence on the relative velocity distribution. This results in a much lower dissipation rate than that predicted using the molecular chaos assumption, where the velocities of colliding particles are considered to be uncorrelated. The orientational ordering and dynamical properties of the shear flow of inelastic dumbbells in two dimensions are studied, as a first step towards examining the effect of shape on the properties of flowing granular materials. The dumbbells are smooth fused disks characterised by the ratio of the distance between centers (L) and the disk diameter (D), and the ratio (L/D)varies between 0 and 1 in our simulations. Area fractions studied are in the range 0.1 to 0.7, while coefficients of normal restitution from 0.99 to 0.6 are considered. The simulations are similar to the event driven simulations for circular disks, but the procedure for predicting collisions is much more complicated due to the non-circular shape of the particles and due to particle rotation. The average orientation is measured using an orientational order parameter S, which varies between 0 (for a perfectly disordered fluid) and 1 (for a fluid with the axis of all dumbbells in the same direction). It is found that there is a gradual increase in ordering as the area fraction is increased, as the aspect ratio is increased or as the coefficient of restitution is decreased, and the order parameter has a maximum value of about 0.5 for the highest area fraction and lowest coefficient of restitution considered here. However, there is no discontinuous nematic transition for all the parameters studied here. The axis of the dumbbells are preferentially oriented along the extensional axis (at an angle of 45ofrom the flow direction) at low area fraction, but the orientation is closer to the flow direction as the area fraction is increased. The orientation distribution is calculated, and it is found that the orientation distribution is well described by a function of the form P(θ) =(1/π)+ (2S/π)cos(2(θ−θp)), where θis the angle from the flow direction and θpis the principal orientation direction. The mean energy of the velocity fluctuations in the flow direction is found to be higher than that in the gradient direction and the rotational energy, though the difference decreases as the area fraction increases, due to the efficient collisional transfer of energy between the three directions. The distributions of the translational and rotational velocity are found to be Gaussian distributions to a very good approximation. The equation of state for the pressure is calculated, and it is found to be remarkably independent of the coefficient of restitution. The pressure and dissipation rate show relatively little variation when scaled by the collision frequency for all the area fractions studied here, indicating that the collision frequency determines the momentum transport and energy dissipation even at the lowest area fractions studied here. The mean angular velocity of the particles is examined in some detail. It is found that the mean angular velocity is equal to half the vorticity at low area fractions, but the magnitude of the mean angular velocity systematically decreases to less than half the vorticity as the area fraction is increased, even though the stress tensor is symmetric.

The objective of this research is to discover principles of ambulatory locomotion on homogeneous and heterogeneous granular substrates and create models of animal and robot interaction within such environments. Since interaction with natural substrates is too complicated to model, we take a robophysics approach – we create a terrain generation system where properties of heterogeneous multi-component substrates can be systematically varied to emulate a wide range of natural terrain properties such as compaction, orientation, obstacle shape/size/distribution, and obstacle mobility within the substrate. A schematic of the proposed system is discussed in detail in the body of this dissertation. Control of such substrates will allow for the systematic exploration of parameters of substrate properties, particularly substrate stiffness and heterogeneities. With this terrain creation system, we systematically explore locomotor strategies of simplified laboratory robots when traversing over different terrain properties. A key feature of this proposed work is the ability to generate general interaction models of locomotor appendages with such complex substrates. These models will aid in the design and control of future robots with morphologies and control strategies that allow for effective navigation on a large diversity of terrains, expanding the scope of terramechanics from large tracked and treaded vehicles on homogeneous ground to arbitrarily shaped and actuated locomotors moving on complex heterogeneous terrestrial substrates.

No description available.

The purpose of this thesis is to evaluate the performance and cost effectiveness of a Peroxone Groundwater Treatment Plant (PGTP) designed and operated by Montgomery Watson, in support of the Defense Evaluation Support Agency's independent analysis for the United States Army Environmental Center (USAEC). Many Department of Defense installations have sites that contain groundwater contaminated with explosive materials. Primary methods for the removal of explosive materials involve the use of Granular Activated Carbon (GAC). This process, however, requires additional waste disposal and treatment of explosive laden GAC, thereby incurring additional costs. An alternate method for the treatment of contaminated groundwater involves the use of hydrogen peroxide (H2O2) in conjunction with ozone (03). This method is referred to as the Peroxone oxidation process. A demonstration of the PGTP was conducted from 19 August to 8 November, 1996, at Cornhusker Army Ammunition Plant (CAAP), Grand Island, Nebraska using a small scale version with a maximum flow rate of 25 gallons per minute. The explosive contaminants analyzed during the demonstration include 2,4,6-Trinitrotoluene (TNT), 1,3,5-Trinitrobenzene (TNB), 1,3,5-Triazine (RDX), and Total Nitrobodies. Peroxone cost effectiveness was evaluated using a 30 year life cycle cost comparison to GAC and Ultraviolet/Ozone processes

Los materiales granulares se definen como sistemas compuestos de un gran número de partículas macroscópicas que interactúan entre sí de forma disipativa. Al ser sistemas disipativos alcanzan rápidamente el equilibrio mecánico y permanecen en él a menos que se les entregue energía mediante alguna perturbación externa. Tienen la propiedad de permanecer mecánicamente estables en un amplio rango de configuraciones, y estas configuraciones pueden presentar diferentes valores de densidad, estrés, etc. Se ha demostrado que aplicando repetitivamente perturbaciones discretas a un sistema granular confinado en una celda o recipiente, y dejando que el sistema retorne al equilibrio mecánico entre perturbaciones sucesivas, las propiedades correspondientes a cada configuración estática del mismo evolucionan hasta alcanzar un régimen estacionario, con valores medios y fluctuaciones bien definidos. Se ha mostrado también que los valores alcanzados por estas propiedades en el régimen estacionario no dependen de la historia previa que hayan recorrido en el espacio de variables macroscópicas del sistema, sino que resultan determinadas a partir de las características de la perturbación aplicada. La posibilidad de generar estados estacionarios en las configuraciones estáticas de los materiales granulares ha despertado gran interés en distintos grupos de investigación alrededor del mundo. Estos enfocan sus esfuerzos en intentar establecer un marco teórico que permita describir el estado macroscópico de los sistemas granulares a partir de unos pocos parámetros. La propuesta más discutida en la actualidad se basa en la utilización de herramientas de la mecánica estadística y es conocida como la mecánica estadística granular de Edwards. Para llevar adelante este tipo de propuestas resulta indispensable establecer primero bajo qué condiciones es posible reproducir el estado macroscópico de un sistema granular. Mi trabajo de tesis se enfoca en el estudio de la reproducibilidad de las propiedades macroscópicas estructurales y mecánicas de estos materiales en el estado estacionario. Para esto he estudiado la dependencia de estas propiedades con el tamaño del sistema. Este estudio resulta de interés debido a que todos los trabajos existentes en el área, experimentales y numéricos, no obtienen un acuerdo cuantitativo en los resultados, aunque muestren acuerdo en gran parte de su comportamiento cualitativo. La hipótesis central de esta tesis es que el tamaño de la muestra bajo estudio tiene un efecto significativo no trivial en los valores medios y fluctuaciones de cantidades macroscópicas, como la fracción de volumen ocupado y el estrés. El objetivo de esta tesis es entonces elucidar bajo qué condiciones es posible reproducir cuantitativamente resultados obtenidos en experimentos independientes, donde se producen estados estacionarios de configuraciones estáticas con diferentes tamaños de sistemas. Como resultado de este trabajo implementamos un protocolo de medición, sobre regiones específicas del sistema. Con la implementación de este protocolo, seremos capaces de obtener resultados comparables entre sistemas de diferentes tamaños. A partir de esto, encontramos que es posible definir un parámetro que, caracterizando el efecto que la perturbación aplicada induce sobre el sistema, permite predecir el valor alcanzado por la densidad en el estado estacionario. El parámetro propuesto resulta dependiente de la altura de la columna de granos del sistema y de las características propias de la perturbación. También encontramos que un parámetro similar podría ser definido para predecir el valor del estrés en el estado estacionario. El aporte original de este trabajo reside en establecer los criterios para seleccionar la región donde llevar adelante la medida de las cantidades macroscópicas que caracterizan al sistema y definir los métodos que deben utilizarse para que resulte posible la comparación cuantitativa de resultados obtenidos en sistemas de diferentes tamaños.

The European process industry is in need of modernization if it shall retain its competitiveness on the growing global market and at the same time reduce the environmental impact that the industrial activities have. The concept behind industrial automation has been very successful in increasing the efficiency for the material handling process, but some industries still have a lack in the field of automation. One of these industries is the mining industry. ABB is currently working within the EU-funded project DISIRE in order to increase the amount of traceability and therefore also the potential of automation in the mining industry by introducing a flow simulation over the mine infrastructure. But one of the largest inherited problems that this industry has over other process industries is that the flow partly consists of a batch structure where the continuous flows of the product only takes place between bunkers and buffer zones. ABB has developed a Matlab simulation where these bunkers are modelled by a simple queue algorithm which does not take the blending or time delays of the ore into account. The main task of this master thesis was to investigate which different modelling approaches that could increase the accuracy of the simulation. The Cellular Automata (CA) were found to be most suitable modelling approach due to its simplicity and a Matlab toolbox were developed and implemented based on the theories behind CA. The results were partly evaluated with the results of an ongoing experiment at Luleå university and by comparison to theories of granular media movement. The CPU-time for the silo flow with 10.000 particles in a flat silo using a MacBook Pro 2.26GHz was about 8 seconds.

Magíster en Ciencias, Mención Física / En el proceso para entender el flujo granular en diferentes sistemas ha habido diferentes acercamientos desde la hidrodinámica clásica, la teoría cinética y la teoría de fluctuaciones hidrodinámicas, de modo de obtener ecuaciones tipo hidrodinámica que describan de modo preciso el movimiento de la materia granular en diferentes regímenes. En este trabajo, como punto de partida, se utiliza un enfoque de "grano grueso" (coarse graining) desarrollado inicialmente por Goldhirsch, Zhang y Berringer, para luego ser extendido y utilizado para analizar sistemas bidimensionales y tridimensionales con granos con densidad de masa uniforme, sin dispersión en tamaño, sin grados de libertad rotacional y choques instantáneos. Al margen de estas consideraciones, ninguna otra aproximación relacionada con el estado del sistema (densidad de número, energía, mecanismos de inyección) ha sido utilizada para definir diversas cantidades y derivar un conjunto de ecuaciones de balance para las densidades de masa, momentum y energía. A partir de ellas, e imitando a las ecuaciones de Navier-Stokes, se extraen a su vez otras definiciones de cantidades relevantes. Todas ellas, cantidades definidas, cantidades derivadas y ecuaciones, se han medido en sucesivas simulaciones numéricas de dinámica molecular en 2 y 3 dimensiones. Se ha observado que la metodología utilizada tiene ventajas sobre otros métodos, como por ejemplo la suavidad de la descripción continua de un grano abandonando una celda y la medición precisa de los campos hidrodinámicos locales. Las ecuaciones obtenidas se mantienen consistentes independientemente del tamaño de la celda de medición local, intervalos de tiempo de medición, alta densidad y energía local. Este método es consistente incluso con un número muy reducido de granos en el sistema, tanto en 2 como 3 dimensiones. Esta formulación permite obtener una definición para el tensor de presión que proviene de las ecuaciones de balance de momentum sin otras consideraciones geométricas y, a través de la aproximación de Green-Kubo, obtener un coeficiente de viscosidad de cizalle local. La presión medida en simulaciones numéricas, sin embargo, evidencia diferencias significativas con resultados conocidos en la literatura y esto afecta directamente el cálculo de la viscosidad de cizalle. Estas diferencias se han asociado a problemas intrínsecos con la definición de presión obtenida. Se discuten algunas soluciones a este problema y consideraciones adicionales a las ecuaciones de balance.

Made available in DSpace on 2018-08-01T23:29:12Z (GMT). No. of bitstreams: 1 tese_11906_71 - Suellen Freire Rigatto da Cruz.pdf: 3217831 bytes, checksum: e325a62e435db78eab3a87001876c20f (MD5) Previous issue date: 2018-03-08 / O petróleo continuará sendo a maior fonte de combustível nos próximos anos. No entanto, a extração de petróleo resulta em problemas como a formação de incrustação nas diversas etapas do processo de produção. O problema da incrustação, que ocorre a partir do processo de deposição, consiste quando as partículas depositadas reduzem, total ou parcialmente, o espaço aberto ao fluxo, resultando em um aumento de perda de carga e em uma redução na produção petrolífera. As deposições de partículas representam um problema significativo na indústria de petróleo e gás, sendo de grande relevância pesquisas nessa área. No presente trabalho, a deposição de partículas, em um escoamento turbulento e bifásico, no interior de uma tubulação horizontal foi modelada, com o software Ansys Fluent®, a partir da abordagem Euler-Lagrange com o Modelo de Fase Discreta Densa (DDPM) e da abordagem Euler-Granular. Devido ao elevado custo computacional decorrente do grande número de partículas injetadas, os resultados apontam que a abordagem Euler-Lagrange com o modelo DDPM não é adequada para resolver problemas envolvendo escoamentos com elevadas frações volumétricas de partículas, sendo mais adequada a abordagem Euler-Granular. O estudo também mostra a influência de determinados parâmetros no processo de deposição de partículas. Os aumentos nas taxas de deposição de partículas são diretamente proporcionais aos aumentos de rugosidade da parede da tubulação e de diâmetro das partículas. Os resultados também mostram valores de tempo computacional, velocidade e fração volumétrica de partículas que permitem uma melhor visualização do fenômeno de deposição para um tempo computacional requerido viável para o sistema computacional utilizado.

Cells experience different mechanical cues from their local environment, including shear flow, forces applied by neighbouring cells, and substrate stiffness. These external signals influence cell behaviour, also in embryonic stem (ES) cells, where they could potentially affect pluripotency or differentiation. The precise effects of external forces on ES cells are confounded by forces inducing secondary changes to attachment or cell-cell signalling, which themselves can also influence cell behaviour. In this study we developed a set-up to attach cells to elastic membranes using a novel functionalisation technique, and exposed them to single or cyclic stretch. We used this method to study the mechanosensitive response of ES cells. We found that stretching caused an immediate increase in the concentration of intracellular calcium, followed by a rapid decrease in some cells. On timescales of 1 - 2 h, stretching induced an increase in the expression of the immediate and early genes, but then cells became temporarily insensitive to subsequent mechanical signals. Stretching did not have a substantial impact on pluripotency and differentiation, as we showed using gene expression studies and a Rex1 reporter. To study how ES cells' susceptibility to mechanical signals depended on media condition, stretch duration and stretch type, we performed RNA sequencing and used gene ontology techniques to investigate the involvement of specific pathways. We found that forces have a broad impact on the overall transcriptome that is highly culture media-dependent. However, a core transcriptional response, including the biosynthesis of membrane components and stress pathways, was largely preserved across the different conditions. We supplemented our experimental findings with a conceptual model of force propagation in disordered environments, such as the nucleus of a cell. Using computational simulations, we studied how the large-scale behaviour of a disordered system depends on the microscopic structure. Contrary to common wisdom, we showed that disordered systems exhibit both positive and negative Poisson's ratios with equal probability. Overall, on short timescales, stretching affected ES cells' calcium concentration and transcription. On longer timescales, ES cells' response was small in magnitude but broad in scope, with limited effects on pluripotency. As such, our results suggest that mechanosensitivity in ES cells is mediated primarily by tissue-wide changes to morphology and attachment.