Aquesta tesi centra els seus esforços en l'àmbit de la microfluídica, un camp relativament recent dins de la Mecànica de Fluids, amb un futur prometedor i amb un ritme d'investigació intens en les seves diferents especialitzacions. En aquest sentit, la tesi presenta dos aportacions científiques principals. Primer, aporta una eina numèrica d'elaboració pròpia per realitzar simulacions de fluxos reactius en microcanals. Eina que s'aplica satisfactòriament a la identificació dels principals processos de transport involucrats en la oxidació parcial del metà per a produir gas de síntesi, i a l'estudi de l'efecte que tenen alguns paràmetres d'operació en aquest procés reactiu. Segon, estén el coneixement dels fluxos multifàsics en microunions en T, estudiant experimentalment fluxos de dues fases amb fluids principalment miscibles i en condicions supercrítiques, que son portats al seu equilibri vapor-líquid. Durant aquest estudi, a més, reporta un succés inesperat que presenta futurs reptes en l'aplicació d'aquest tipus de fluxos multifàsics. / The present thesis focuses on microfluidics, a relatively recent field of Fluid Mechanics with promising expectations and with an intense scientific interest on its different areas. In this regard, the thesis aims to provide two main scientific contributions. First, it presents an in-house numerical tool to carry out simulations of reactive flows within microchannels. The tool is successfully applied to the identification of the main transport phenomena involved on the partial oxidation of methane to produce synthesis gas, and to the analysis of the effect of several operating parameters on this reactive process. Second, it extends the knowledge on multiphase flows in microfluidic T-junctions with an experimental study of two-phase flows of mixtures of potentially miscible fluids, in supercritical conditions and in vapour-liquid equilibrium. In this study it is also reported an unexpected phenomenon, which brings new challenges to the application of these kind of multiphase flows.

<p>Today's consumer mobile platforms such as Android and iOS manage large ecosystems of untrusted third-party applications. It is common for an application to request one or more types of sensitive data. Unfortunately, users have no insight into how their data is used. Given the sensitivity of the data accessible by these applications, it is paramount that mobile operating systems prevent apps from leaking it.</p><p>This dissertation shows that it is possible to improve the soundness of dynamic information-flow tracking on a mobile device without sacrificing precision, performance, or transparency. We extend the state of the art in dynamic information-flow tracking on Android and address two major limitations: quantifying implicit flow leaks in Dalvik bytecode and tracking explicit flows in native code. Our goal is to deliver seamless end-to-end taint tracking across Dalvik bytecode and native code.</p><p>We propose SpanDex, a system that quantifies implicit flow leaks in Dalvik bytecode for apps handling password data. SpanDex computes a bound of revealed tainted data by recording the control-flow dependencies and for each password character, keeps track of the possible set of values that have been inferred. We also propose TaintTrap, a taint tracking system for native code in third party apps. We explore native taint tracking performance bottlenecks and hardware acceleration techniques to improve instrumentation performance.</p> / Dissertation

A numerical solution algorithm based on finite volume method is developed for unsteady, two-dimensional, depth-averaged shallow water flow equations. The model is verified using test cases from the literature and free surface data obtained from measurements in a laboratory flume. Experiments are carried out in a horizontal, rectangular channel with vertical solid boxes attached on the sidewalls to obtain freesurface data set in flows where three-dimensionality is significant. Experimental data contain both subcritical and supercritical states. The shallow water equations are solved on a structured, rectangular grid system. Godunov type solution procedure evaluates the interface fluxes using an upwind method with an exact Riemann solver. The numerical solution reproduces analytical solutions for the test cases successfully. Comparison of the numerical results with the experimental two-dimensional free surface data is used to illustrate the limitations of the shallow water equations and improvements necessary for better simulation of such cases.

Non-Newtonian fluids are of great scientific interest due to their range of physical properties, which arise from the characteristic shear stress-shear rate relation for each fluid. The applications of non-Newtonian fluids are widespread and occur in many industrial (e.g. lubricants, suspensions, paints, etc.) and environmental (e.g. mud, ice, blood, etc.) problems, often involving multiple fluids. In this study, the novel technique of Incompressible Smoothed Particle Hydrodynamics (ISPH) with shifting (Lind et al., J. Comput. Phys., 231(4):1499-1523, 2012), is extended beyond the state-of-the-art to model non-Newtonian and multi-phase flows. The method is used to investigate important problems of both environmental and industrial interest. The proposed methodology is based on a recent ISPH algorithm with shifting with the introduction of an appropriate stress formulation. The new method is validated both for Newtonian and non-Newtonian fluids, in closed-channel and free-surface flows. Applications in complex moulding flows are conducted and compared to previously published results. Validation includes comparison with other computational techniques such as weakly compressible SPH (WCSPH) and the Control Volume Finite Element method. Importantly, the proposed method offers improved pressure results over state-of-the-art WCSPH methods, while retaining accurate prediction of the flow patterns. Having validated the single-phase non-Newtonian ISPH algorithm, this develops a new extension to multi-phase flows. The method is applied to both Newtonian/Newtonian and Newtonian/non-Newtonian problems. Validations against a novel semi-analytical solution of a two-phase Poiseuille Newtonian/non-Newtonian flow, the Rayleigh-Taylor instability, and a submarine landslide are considered. It is shown that the proposed method can offer improvements in the description of interfaces and in the prediction of the flow fields of demanding multi-phase flows with both environmental and industrial application. Finally, the Lituya Bay landslide and tsunami is examined. The problem is approached initially on the real length-scales and compared with state-of-the-art computational techniques. Moreover, a detailed investigation is carried out aiming at the full reproduction of the experimental findings. With the introduction of a k-ε turbulence model, a simple saturation model and correct experimental initial conditions, significant improvements over the state-of-the-art are shown, managing an accurate representation of both the landslide as well as the wave run-up. The computational method proposed in this thesis is an entirely novel ISPH algorithm capable of modelling highly deforming non-Newtonian and multi-phase flows, and in many cases shows improved accuracy and experimental agreement compared with the current state-of-the-art WCSPH and ISPH methodologies. The variety of problems examined in this work show that the proposed method is robust and can be applied to a wide range of applications with potentially high societal and economical impact.

The aim of the thesis is to analyse the material and economic flows in the selected region and to suggest possible measures to improve the current situation. The paper focuses on the South Bohemian Region. Per Regulation (EU) No 70/2012 of the European Parliament and of the Council of 18 January 2012 on statistical reporting, undertakings must communicate the transport data to the relevant organizations. Unfortunately, the economic data from the field of material flows is nowhere accurately reported, so only selected indicators that characterize the relevant economic flows were used. Thanks to the data obtained, an existing picture of material and economic flows in the selected area was obtained. Then, a specific flow analysis of one selected material was conducted through production, distribution and sales. Subsequently, it was evaluated whether the results of this selected product correspond to the results of the statistical reports. The last part was the SDA analysis to determine the impact of material flow on population development, social wealth and technological progress. Based on the results of individual analyses, measures have been proposed to improve the current situation.

O objetivo principal desta dissertação é mostrar um resultado obtido por Plante, o qual estabelece que: qualquer fluxo de Anosov de codimensão um sobre uma variedade diferenciável compacta M de dimensão maior do que 3 com grupo fundamental solúvel é topologicamente equivalente à suspensão de um automorfismo hiperbólico do toro. Este resultado mostra a conjectura de Verjovsky no caso que o grupo fundamental da variedade é um grupo solúvel. A prova deste resultado é baseada no celebre resultado de Schwartzman, o qual fornece um criterio para garantir a existencia de seção transversal global para um fluxo não singular / O objetivo principal desta dissertação é mostrar um resultado obtido por Plante em [12] o qual estabelece que: qualquer fluxo de Anosov de codimensão um sobre uma variedade diferenciável compacta M de dimesão maior o que 3 com grupo fundamental solúvel é topologicamente equivalente à suspensão de um automorfismo hiperbólico do toro. Este resultado mostra a conjectura de Verjovsky no caso que o grupo fundamental da variedade é um grupo solúvel. A prova deste resultado é baseada no célebre resultado de Schwartzman [15], Teorema 2.17, o qual fornece um critério para garantir a existência de seção transversal global para um fluxo não singular

This thesis addresses aspects of the transport of bubbles and capsules (a thin elastic membrane enclosing a viscous fluid) by means of a viscous flow in complex vessel geometries. It focusses on two related themes: (i) the trapping of air bubbles in a sudden streamwise tube expansion and (ii) the extreme deformation of bubbles and capsules in a localised tube constriction. Air bubbles of different volumes were trapped in a tube with a square cross-section, which contains a sudden streamwise expansion in tube width. The liquid filling the tube was driven by constant volume-flux flow, and experiments were performed in both millimetric and micrometric tubes to identify the range of flow rates for which bubbles could get trapped. The gradients in surface energy generated by the broadening of the bubble into the expansion depend strongly on bubble volume and the expansion length. It is shown that in order for a trapped bubble to release from the expansion, the work of the pressure forces due to flow past the bubble must exceed the change in surface energy required to squeeze into the narrower channel. This criterion for trapping was verified by direct pressure measurements and a capillary static model, which uses three-dimensional Surface Evolver calculations. The extreme deformation of bubbles and capsules was investigated using a localised constriction of the tube width. Both bubbles and capsules were shown to adopt highly contorted configurations and exhibit broadly similar features over a wide range of flow rates, suggesting that the deformation was primarily imposed by the geometry through viscous shear forces. However, bubbles and capsules also display distinguishing features. Bubbles can breakup and exhibit thinning of the rear of the bubble at a critical flow rate, which is associated with a divergence of the rear tip speed and curvature. In contrast, the capsule membrane can wrinkle and fold, and the membrane thickness imposes the value of the maximum curvature locally available to the capsule.

No description available.

Microfluidics deals with the behavior, control and manipulation of fluids which are confined at micrometer length scale. It has important application in lab-on-a chip technology, micro-propulsion, additive manufacturing, and micro-thermal technologies. Microfluidics has been widely used in detection, separation, transportation, and mixing of fluids and particles. The work carried out for the thesis to study the fluid-structure interaction in micro-channel involves an experimental part and a simulation part. In the experimental part the characterization of biofluid (RBC in BSA) is carried out based on the power law of fluid and flow behavior is studied. Also the dependence of fluid concentration on the viscosity in the channel is studied. The results are analyzed. Transition of fluid behavior from non-Newtonian shear thickening to non-Newtonian shear thinning is observed when the RBC concentration varies from 5.5×106 to 5.5×107 cells/ml in the channel. From the viscosity measurements of the biofluid it is observed that the average viscosity in the channel increases on increasing concentration of the fluid for shear thickening fluids. In the simulation part, interaction behavior of biomolecule DNA is studied in the channel containing biofluid which is characterized in the experimental part. Cell free DNAs are common problem in infectious disease detection. Based on the assumptions of the WLC model, DNA strand is assumed as a one dimensional elastic member with its one end fixed at the channel wall and the other end free to move in the fluid. Bent and straight DNAs are considered for the study. Multiple scales are involved in this problem which is not fully understood. DNA strands in the channel are exposed to different forces in the channel which are mainly due to the pressure and viscous effects. Numerical simulations are carried out for the multiphysics problem of DNA in the fluid using a coupled multiphysics finite element scheme and the results are obtained. Same procedure is carried out considering smaller channels and also for PBS solution as background fluid to obtain consistent results. It is found that when the channel width increases the tip displacement of DNA decreases. It was observed that DNA tip displacement is more in the channel when its end-to-end length is approximately half the width of the channel. Potential application of these modeling and simulation are in molecular screening processes to improve the performance of microfluidic DNA chips, and in design of micro-channel structures of microfluidic devices.

Today, data centers host a wide variety of applications which generate a mix of diverse internal data center traffic. In a data center environment 90% of the traffic flows, though they constitute only 10% of the data carried around, are short flows with sizes up to a maximum of 1MB. The rest 10% constitute long flows with sizes in the range of 1MB to 1GB. Throughput matters for the long flows whereas short flows are latency sensitive. This thesis studies various data center transport mechanisms aimed at either improving flow completion time for short flows or throughput for long flows. Thesis puts forth two data center transport mechanisms: (1) for improving flow completion time for short flows (2) for improving throughput for long flows. The first data center transport mechanism proposed in this thesis, FA-DCTCP (Flow Aware DCTCP), is based on Data Center Transmission Control Protocol (DCTCP). DCTCP is a Transmission Control Protocol (TCP) variant for data centers pioneered by Microsoft, which is being deployed widely in data centers today. DCTCP congestion control algorithm treats short flows and long flows equally. This thesis demonstrate that, treating them differently by reducing the congestion window for short flows at a lower rate compared to long flows, at the onset of congestion, 99th percentile of flow completion time for short flows could be improved by up to 32.5%, thereby reducing their tail latency by up to 32.5%. As per data center traffic measurement studies, data center internal traffic often exhibit predefined patterns with respect to the traffic flow mix. The second data center transport mechanism proposed in this thesis shows that, insights into the internal data center traffic composition could be leveraged to achieve better throughput for long flows. The mechanism for the same is implemented by adopting the Software Defined Networking paradigm, which offers the ability to dynamically adapt network configuration parameters based on network observations. The proposed solution achieves up to 22% improvement in long flow throughput, by dynamically adjusting network element’s QoS configurations, based on the observed traffic pattern.