Stereovision Combined With Particle Tracking Velocimetry Reveals Advection and Uplift Within a Restraining Bend Simulating the Denali Fault

Scaled physical experiments allow us to directly observe deformational processes that take place on time and length scales that are impossible to observe in the Earth’s crust. Successful evaluation of advection and uplift of material within a restraining bend along a strike-slip fault zone depends on capturing the evolution of strain in three dimensions. Consequently, we require deformation within the horizontal plane as well as vertical motions. While 3D digital image correlation systems can provide this information, their high costs have prompted us to develop techniques that require only two DSLR cameras and a few Matlab® toolboxes, which are available to researchers at many institutions. Matlab® plug-ins can perform particle image velocimetry (PIV), a technique used in many analog modeling studies to map the incremental displacements fields. For tracking material advection throughout experiments more suitable Matlab® plug-ins perform particle tracking velocimetry (PTV), which tracks the complete two-dimensional displacement path of individual particles. To capture uplift the Matlab®Computer Vision ToolboxTM, uses pairs of photos to capture the evolving topography of the experiment. The stereovision approach eliminates the need to stop the experiment to perform 3D laser scans, which can be problematic when working with materials that have time dependent rheology. We demonstrate how the combination of PIV, PTV, and stereovision analysis of experiments that simulate the Mount McKinley restraining bend reveal the evolution of the fault system and three-dimensional advection of material through the bend

Characteristics of continental rifting in rotational systems: New findings from spatiotemporal high resolution quantified crustal scale analogue models

Continental rifts are the expression of regional horizontal stretching and are in modelling studies often assumed to be the result of orthogonal or oblique extension. However, naturally occurring V-shaped rift geometries infer an underlying rotational component, resulting in a divergence velocity gradient. Here we use such analogue models of rifting in rotational settings to investigate and quantify the effect of such a divergence velocity gradient on normal fault growth and rift propagation towards a rotation pole. Particularly, we apply different divergence velocities and use different brittle-ductile ratios to simulate different crustal configurations and analyse its effect on rift propagation and surface deformation. Surface deformation is captured using stereoscopic 3D Digital Image Correlation, which allows for quantifying topographic evolution and surface displacement including vertical displacement. In combination with X-Ray computed tomography, we gain insights into the three-dimensional structures in our two-layer models. Based on our models, we present a novel characterisation of normal fault growth under rotational extension which is described by (a) an early stage of bidirectional stepwise growth in length by fault linkage with pulses of high growth rates followed by a longer and continuous stage of unidirectional linear fault growth; (b) segmented rifting activity which promotes strain partitioning among competing conjugate faults and (c) along-strike segmented migration of active faulting from boundary faults inwards to intra-rift faults allowing different fault generations to be simultaneously active over the entire rift length. For models with higher divergence velocities, inward migration is delayed but other first-order observations are similar to models with lower divergence velocities. Our quantitative analysis provides insights on spatiotemporal fault growth and rift propagation in analogue models of rotational rifting. Although natural rifts present complex systems, our models may contribute to a better understanding of natural rift evolution with a rotational component

Initiation of Subduction Along Oceanic Transform Faults: Insights From Three-Dimensional Analog Modeling Experiments

Three-dimensional analog experiments are employed to explore how self-sustaining subduction may initiate along an oceanic transform fault. The models include a realistic spatial distribution of plate thickness, strength, and buoyancy of the lithosphere near an oceanic transform fault characteristic of the spreading rate. Convergence is imposed across the transform fault and strain in the model lithosphere is quantified using a surface Particle Imaging Velocimetry system. A force sensor is employed to defined when a self-sustaining subduction regime is generated. Cylindrical experiments reveal that subduction polarity is controlled by the buoyancy gradient and the strengths of the plates. With no inclined weak zones, imposed orthogonal compression results in the nucleation of a new fault in the weakest plate leading to the young and positively buoyant plate subducting. However, with an inclined weak zone, the buoyancy contrast controls subduction polarity with the most negatively buoyant plate subducting and a self-sustaining subduction regime obtained after ~300 km of imposed shortening. This situation is obtained when including an inverted triangular weak zone on top of the transform fault associated with the serpentinization of the crust and mantle. In non-cylindrical experiments, taking into account the change along strike of plate strength and buoyancy, the capacity of the transform fault to generate a self-sustaining subduction regime is greatly reduced. Subduction initiates simultaneously with opposite polarity at the two extremities of the transform segment and, at depth, a lithospheric tear is produced that separates the two subducting slabs. In the center of the transform fault, the lack of buoyancy or strength contrast between the two plates leads to multiple thrusts with variable polarities, overlapping each other, and each accommodating too little shortening to become the new plate boundary. This indicates that additional mechanical work is required in the center of the transform fault which prevents the establishment of a self-sustaining subduction regime

Relación entre el coeficiente de transferencia de calor (HTC) y la velocidad de agitación en Quenchotest.

Debido a la alta demanda de equipos de alto desempeño, las tecnologías de tratamiento térmico enfocadas en la creación de piezas de acero han tenido que evolucionar. Para lograr esto, mucho se ha logrado en la disminución de las distorsiones durante el temple, la fragilización de las piezas y la optimización del medio de temple para mejorar la eficiencia de la extracción de calor de las piezas. Con esta investigación se logra establecer una relación directa entre el coeficiente de transferencia de calor (HTC) y la velocidad de agitación, a través de la caracterización del fluido en el experimento Quenchotest con la herramienta PIV. Posteriormente se validan los campos vectoriales con simulaciones CFD a través del software FLUENT mostrando que ambas herramientas son completamente compatibles con un error mínimo si tenemos en cuenta que están en el orden de 10-2 . También se realizan experimentos en el Quenchotest a las 3 velocidades de 200, 600 y 1000 rpm cuyos valores son utilizados para crear las gráficas de correlación entre la velocidad de agitación y el HTC. Finalmente se puede afirmar que con este trabajo se sientas las bases y los límites para la creación de un modelo a escala que sirva para obtener el valor del HTC en un tanque de temple industrial específico

Hydrodynamics study of liquid-solid micro-circulating fluidised bed

PhD ThesisSolid-liquid circulating fluidised beds possess many qualities which makes them useful for industrial operations where particle-liquid contact is vital, e.g. improved heat transfer performance, and consequent uniform temperature, limited back mixing, excellent solid-liquid contact, good control of reaction and regeneration of catalysts or bio-solids at the same time. All these characteristics make them suitable for various industrial processes, e.g. waste water treatment, food processing, and bioconversion of agricultural-waste into lactic acid, fermentation, linear alkyl benzene production, and photo-catalytic ozonation. Despite this, they have seen no application in the micro-technology context. Solid-liquid micro circulating fluidised beds (µCFBs), which essentially involve fluidisation of micro-particles in sub-centimetre beds, hold promise of applications in the areas of microfluidics and micro-process technology. This is mostly due to fluidised particles providing enhancement of mixing, mass and heat transfer under the low Reynolds number flows that dominate in micro-devices. Albeit there are few reports on liquid-solid micro-fluidised beds, this thesis presents the first experimental study of a solid-liquid circulating fluidised bed at the microscale. It is well known that particle handling in micro technology devices remains one of the big challenges in the field. Development of a micro circulating fluidised bed is providing one solution to the problem, e.g. for solid catalyst recovery, recycle and regeneration. This thesis reports on the design and study the hydrodynamics of a liquid-solid microcirculating fluidised (LS µCFB) systems for possible applications as novel micro (bio)-reactors and diagnostics device, high-throughput kinetics screening, high-heat flux cooling and others. In order to successfully implement this, it is very important to understand the hydrodynamic parameters such as the influence of surface forces and inevitable wall effect on minimum fluidisation velocity, and bed expansion dynamics as they play a crucial role in the hydrodynamic behaviour and determine the bed performances, as well as dictating the solidliquid contacting. The experimental research was performed in a novel micro-circulating fluidised bed which was made by micro-machining channels of 1mm2 cross section in Perspex. (Polymethylmethacrylate (PMMA) and soda lime glass microspheres particles were used as the fluidised particles and tap water and glycerol of different concentration (5, 10, and 15 vol. % aqueous glycerol) as the fluidising liquid to study the hydrodynamics of solid-liquid ii fluidisation in micro-circulating fluidised bed channel. Furthermore, additive manufacturing technology, digital light processing (Miicraft+ printer) and stereolithography (Form2 printer) were also used to fabricate the novel micro-circulating fluidised bed. This allowed the rapid fabrication of a reliable micro-circulating fluidised bed using low cost material and most importantly, the bed geometry could easily be modified. Two novel measurement techniques, the valve accumulation and digital particle image velocimetry (PIV) methods were developed to measure the particle velocity in the microcirculating fluidised bed system, and the results looks relevant when compared with previous reported studies. As in a macroscopic circulating fluidised bed, the solid flux in a microcirculating fluidised bed increases with liquid velocity in two distinct zones, increasing sharply first then levelling off at higher inlet fluid velocities. The result indicates that fluidisation in a solid-liquid micro circulating fluidised bed system could be categorised in four operating regimes like in macroscopic case: fixed bed, conventional fluidisation, circulating fluidisation, and transport regime. However, the surface forces influence strongly the minimum fluidisation velocity which can be up to 20 times bigger for the smallest PMMA microparticles while the increase is only minor for glass particle (less than 2 times for the same size smallest glass microparticles). The determined critical transition velocity is comparable to the particle terminal velocity, i.e. the normalised transition velocity is approximately 1 in line with previous macroscopic studies. Yet, there was a weak increase in the normalized transition velocity with particle size which is probably due the wall effects (higher particle to bed ratio). In addition, the normalised velocity is slightly higher for PMMA particles due to stronger adhesion and cohesion forces, but influence is minimal in comparison with influence on the minimum fluidisation velocity. Finally, it seems that transition to the transport regime is influenced by cohesion so the relative transition velocity for PMMA particles is around 20 times particle terminal velocity while it is only 5 times for the glass beads. Consequently, the conventional regime is proportionally bigger for the glass beads in comparison with PMMA particles, whist the situation is opposite for circulating fluidisation regime as it is bigger for PMMA particles. The study also confirms that fluidisation behaviour in a liquid-solid micro-circulating fluidised bed system is also influenced by bed geometry such as the size of solid feed pipe cross section and the angle between the riser and solid feed pipe. iii The results also show that solid flux in a micro-circulating fluidised bed is influenced by the viscosity of the fluidised liquid. The minimum superficial liquid velocity at which particles fluidisation is achieve decreases with increasing liquid viscosity. The reduction in the minimum fluidisation velocity with an increase in the liquid viscosity is mostly due to the fact that viscous systems have a lower ratio of adhesion to drag force