Dissertations / Theses on the topic 'Moving surfaces'

Thesis (M.Sc.)--City University of Hong Kong, 2006.<br>"Master of Science in Materials Engineering & Nanotechnology dissertation." Title from title screen (viewed on Nov. 21, 2006) Includes bibliographical references.

International Telemetering Conference Proceedings / October 17-20, 1988 / Riviera Hotel, Las Vegas, Nevada<br>Fine cracks and irregularities on a fast moving conducting surface were detected by the use of microwave and millimeter wave radio responder techniques. The interrogation angle was restricted to an oblique incidence angle less than ±0.5 degree from the surface. The fast moving conducting surface was surrounded by both fast moving and stationary reflective conducting structures. Experimental methods and results from a fine crack 0.1 mm wide, 0.9 mm deep, and 25 mm long on a conducting surface travelling with a speed of 20.23 m/s and measured at 10.525 GH(z) and 73 GH(z) are presented. The reflection-type microwave radio responder consisted of a 10.525 GH(z) 50 mW Gunn diode cw transmitter, a circulator, and a horn antenna used as the interrogator. The receiver in the same responder consisted of the same horn antenna, the circulator and detector diode. The detector diode output was observed with a Norland 3106R digital memory oscilloscope. A reflex kylstron VA 250 was used as the transmitter signal source for the millimeter wave responder. There was a distinct difference between the responder output patterns with uncracked and cracked surfaces. It is therefore possible to use this type of responder for hair-line crack detection of fast moving conducting surfaces. It was also found that this type of radio responder can detect the surface irregularity even before the hairline crack actually occurs.

Continuous growth of computing power strongly encourages engineers to rely more on computational fluid dynamics for the design and testing of new technological solutions. The fast development of these new tools goes along with the increasing availability of high-performance computers, which are necessary to simulate realistic industrial applications. The presented immersed boundary (IB) method is applicable to simple and complex geometries with static and moving boundaries, where fluids interact with the solid structures. The formulation of the method is based on the Eulerian and Lagrangian principles and its key characteristics are its simple formulation and computational efficiency. Furthermore the nature of the method allows the simulations of flows in complex geometries without having to generate complex meshes. The spatial discretization is based on a fixed Cartesian mesh for the Eulerian variables and boundary movements are tracked with Lagrangian particles. Large- Eddy simulations of flows in simple and complex geometries demonstrate the performance of the applied immersed boundary method. Simple cases include the simulation of an isothermal pipe flow and the flow around a sphere. In the first instance, the fluid flows around a static sphere. In the second case the sphere moves relative to the grid for identical flow conditions. Simulations of complex geometries include the investigation of an isothermal and reactive opposed jet flow with perforated and fractal grids. The simulations require cell sizes near the resolution of direct numerical simulations. The injection phase of a piston-cylinder arrangement, assuming constant pressure, is also investigated with the proposed IB method. Good statistical results for first and second moments are achieved for all investigated cases, although the applied grids have to be fine enough to accurately resolve the wall shear stresses. In addition, the concept of using Lagrangian particles has been applied to immiscible flows. Particles are used to improve the accuracy of scalar transport and initial results of simple, two-dimensional test cases are presented.

This dissertation explores the physics of droplet impingement on superhydrophobic surfaces. The research is divided in three categories. First, the effect of a slip boundary condition on droplet spreading/retracting is considered. A model is developed based on energy conservation to evaluate spreading rates on surfaces exhibiting isotropic and anisotropic slip. The results show that larger slip causes the droplet to spread out farther owing to reduced friction at the interface for both slip scenarios. Furthermore, effects of slip become magnified for large Weber numbers due to the larger solid-liquid contact area during the process. On surfaces with anisotropic slip, droplets adopt an elliptical shape following the azimuthal contour of the slip on the surface. It is common for liquid to penetrate into the cavities at the superhydrophobic interface following droplet impact. Once penetrated, the flow is said to be in the Wenzel state and many superhydrophobic advantages, such as self-cleaning and drag-reduction, become negated. Transition from the Wenzel to the Cassie state (liquid resides above the texture) is referred to as dewetting and is the focus of the second piece of this dissertation. Micro-pillar pitch, height and temperature play a role on dewetting dynamics. The results show that dewetting rates increase with increasing pillar height and increasing surface temperature. A scaling model is constructed to obtain an explanation for the experimental observations and suggests that increasing pillar height increasing the driving dewetting force, while increasing surface temperature decreases dissipation. The last piece of work of this dissertation entails droplet impingement on superheated surfaces (100°C - 400°C). We find that the Leidenfrost point (LFP) occurs at a lower temperature on a hydrophobic surface than a hydrophilic one, where the LFP refers to the lowest temperature at which secondary atomization ceases to occur. This behavior is attributed to the manner in which vapor bubbles grow at the solid-liquid interface. Also in this work, high-speed photographs reveal that secondary atomization can be significantly suppressed on a superhydrophobic surface owing to the micro-pillar forest which allows vapor to escape hence minimizing bubble formation within the droplet. However, a more in-depth study into different superhydrophobic texture patterns later reveals that atomization intensity can significantly increase for small pitch values given the obstruction to vapor flow presented by the increased frequency of the pillars.

This work is concerned with the modelling of fluid flows on moving domains. The physical problems considered are free surface flows, possibly in the presence of the surface tension phenomena, fluid-rigid body and fluid-structure interaction. The fluid flow considered is governed by the incompressible Navier-Stokes equations. It is modelled by stabilised low order velocity-pressure finite elements. A detailed analysis of time integration strategies is performed leading to the choice of the discrete implicit generalised-α method for the temporal discretisation. The motion of the fluid domain is accounted for by an arbitrary Eulerian-Lagrangian (ALE) strategy. Different mesh update methods are considered. The free surface and the fluid-solid interfaces are modelled carefully, satisfying the necessary conservation properties. These computational ingredients result in fully implicit and strongly coupled sets of nonlinear equations, which are rephrased in a common general framework by decomposing the problems into the fluid, the interface and possibly the solid domains. In order to obtain the exact solution variables, a partitioned Newton-Raphson procedure, based on the exact linearization of the residuals, is developed. Thus, the strong coupling is resolved and optimal convergence can be expected. Finally, a number of two dimensional or axisymmetric numerical examples is presented which demonstrate the robustness and the efficiency of the overall algorithm. The strategy is verified against various reference solutions. The numerical examples include the simulation of the filling of drops, the stretching of liquid bridges, the vortex induced oscillations and the galloping of solid bodies.

A preliminary study by Freeman et al (1996b) has suggested that when complex patterns of motion elicit impressions of 2-dimensionality, odd-item-out detection improves given targets can be differentiated on the basis of surface properties. Their results can be accounted for, it if is supposed that observers are permitted efficient access to 3-D surface descriptions but access to 2-D motion descriptions is restricted. To test the hypothesis, a standard search technique was employed, in which targets could be discussed on the basis of slant sign. In one experiment, slant impressions were induced through the summing of deformation and translation components. In a second theory were induced through the summing of shear and translation components. Neither showed any evidence of efficient access. A third experiment explored the possibility that access to these representations may have been hindered by a lack of grouping between the stimuli. Attempts to improve grouping failed to produce convincing evidence in support of life. An alternative explanation is that complex patterns of motion are simply not processed simultaneously. Psychophysical and physiological studies have, however, suggested that multiple mechanisms selective for complex motion do exist. Using a subthreshold summation technique I found evidence supporting the notion that complex motions are processed in parallel. Furthermore, in a spatial summation experiment, coherence thresholds were measured for displays containing different numbers of complex motion patches. Consistent with the idea that complex motion processing proceeds in parallel, increases in the number of motion patches were seen to decrease thresholds, both for expansion and rotation. Moreover, the rates of decrease were higher than those typically expected from probability summation, thus implying mechanisms are available, which can pool signals from spatially distinct complex motion flows.

This study investigates the behaviour of fully developed fluid flows in concentric annuli with rough surfaces and moving cores, by analytically predicting the effects of surface roughness, core velocity and turbulent motion on the momentum and heat transfer characteristics of the flow, such as friction forces, velocity profiles, temperature profiles and heat transfer. The analytical predictions are produced by a mathematical model based on an adaptation of Prandtl's mixing length theories and on the data of previous studies of turbulent flow in annuli and rectangular channels which were artificially roughened. The computer program developed for this study employs an iterative process to match velocity and temperature profiles with force and energy balances and calculates the desired momentum and thermal characteristics. The results indicate excellent correlation with previous experimental data on rough annuli with static cores and smooth annuli with moving cores. From these results, the combined effects of surface roughness and moving cores are inferred. New equations are proposed for predicting the radius of maximum fluid velocity and the effects of core velocity on roughness, in terms of annulus radius ratio, roughness geometry, flow's Reynolds number and core velocity. The study demonstrates the advantages, under certain conditions, of using roughness elements to increase heat transfer and enhance the overall efficiency in the energy transfer processes involved.

In a Minkowski three dimensional space, whose metric is based on a strictly convex and centrally symmetric unit ball , we deal with ruled surfaces Φ in the sense of E. Kruppa. This means that we have to look for Minkowski analogues of the classical differential invariants of ruled surfaces in a Euclidean space. Here, at first – after an introduction to concepts of a Minkowski space, like semi-orthogonalities and a semi-inner-product based on the so-called cosine-Minkowski function - we construct an orthogonal 3D moving frame using Birkhoff’s left-orthogonality. This moving frame is canonically connected to ruled surfaces: beginning with the generator direction and the asymptotic plane of this generator g we complete this flag to a frame using the left-orthogonality defined by ; ( is described either by its supporting function or a parameter representation). The plane left-orthogonal to the asymptotic plane through generator g(t) is called Minkowski central plane and touches Φ in the striction point s(t) of g(t). Thus the moving frame defines the Minkowski striction curve S of the considered ruled surface Φ similar to the Euclidean case. The coefficients occurring in the Minkowski analogues to Frenet-Serret formulae of the moving frame of Φ in a Minkowski space are called “M-curvatures” and “M-torsions”. Here we essentially make use of the semi-inner product and the sine-Minkowski and cosine-Minkowski functions. Furthermore we define a covariant differentiation in a Minkowski 3-space using a new vector called “deformation vector” and locally measuring the deviation of the Minkowski space from a Euclidean space. With this covariant differentiation it is possible to declare an “M-geodesicc parallelity” and to show that the vector field of the generators of a skew ruled surface Φ is an M-geodesic parallel field along its Minkowski striction curve s. Finally we also define the Pirondini set of ruled surfaces to a given surface Φ. The surfaces of such a set have the M-striction curve and the strip of M-central planes in common

The exact mechanism with which a fluid interface interacts dynamically with a solid surface during wetting is still open to research. Among the many subjects addressed in this field in the literature, the "moving contact line problem" is one that has been ubiquitous since at least the 1970s, where a paradox in the description of the contact line was found to exist. The paradox in a few words is the next: macroscopic hydrodynamic models using the no-slip boundary condition will predict infinite shear stress close to the contact line. The most promising studies to tackle the problem come from information provided by molecular dynamics simulations. They have confirmed that close to the contact line, the no-slip boundary condition is relaxed to some form of slip. Unfortunately, molecular simulations are still limited to very small scales in space and time, so hydrodynamic models and numerical simulations based on Navier-Stokes equations are still needed. In these simulations, the Continuum Surface Force model CSF for the calculation of the capillary contribution introduces a grid dependent contact line velocity and shear at the wall, which is a problem we proposed to solve here. In this work, we analyze the flow close to the moving contact line in the context of corner stokes-flow and explore the effects of the boundary conditions at the wall. One of these conditions offered in the literature, provides relief to the shear divergence and also opens the possibility to observe Moffatt vortices in the vicinity of the contact line, not yet seen in experiments or numerical simulations. We explore this possibility analytically and then numerically using the code JADIM. The latter task is constrained by the contamination of the velocity field by the so-called spurious velocities if the VOF method is used. To solved this inconvenient, a very promising version of the front-tracking method with lagrangian markers is implemented and enhanced to handle non-uniform distribution of markers without losing its spurious velocities elimination features. Numerical tests are conducted to validate the implementation, spurious velocities are reduce close to machine precision and comparison to benchmark data is performed obtaining good agreement. Tests including contact lines are then compared with exact solutions for shape analyzing the effect of the Bond number, showing remarkable results. Numerical experiments with this implementation close to a contact line show the existence of vortical patterns during of spreading. Finally, and based on the theoretical background developed in this work, a new sub-grid model method is proposed for macroscopic numerical simulations and implemented in the new front-tracking method of JADIM. Quantitative data is obtained and compared to numerical and experimental spreading cases revealing improvement of grid convergence and excellent agreement.

Made available in DSpace on 2014-06-11T19:33:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-04-16Bitstream added on 2014-06-13T20:45:38Z : No. of bitstreams: 1 matias_ssr_dr_jabo.pdf: 1718556 bytes, checksum: 6aa4f59f2f833b454b295ffe2e36da7b (MD5)<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)<br>Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)<br>O objetivo do presente trabalho foi estudar a suscetibilidade magnética e sua associação com os atributos do solo e do relevo em uma topossequência de Latossolos. Os solos foram coletados numa transeção de 2.700 km com intervalos regulares de 25 m, e aleatoriamente nas áreas laterais de três superfícies geomórficas mapeadas, em duas profundidades (0,00–0,20 m e 0,60–0,80 m), totalizando 514 amostras. Sete trincheiras foram analisadas contemplando os segmentos de vertente inseridos nas superfícies geomórficas. As amostras coletadas foram submetidas às análises de densidade do solo, porosidade, grau de floculação, textura, pH (água, CaCl2 e KCl), matéria orgânica, P, Ca, K, Mg, H + Al, Al. É calculado SB, CTC e V%. Também foram determinados o SiO2, Al2O3, Fe2O3 (H2SO4), óxidos de Fe livres (Fed), o ferro de baixa cristalinidade (Feo) e a suscetibilidade magnética. Os dados foram analisados pela estatística univariada, descritiva, multivariada, Split Moving Windows e geoestatística. Os resultados mostraram que a divisão de áreas por meio das superfícies geomórficas ocasionou melhor entendimento da variabilidade dos atributos do solo na vertente. O método geoestatístico SMWDA (“Split Moving Windows Dissimilarity Analysis”), confirmou a divisão númericamente das três superfícies geomórficas por meio da granulometria e suscetibilidade magnética. A suscetibilidade magnética foi o atributo que melhor identificou os limites entre os corpos mapeados no campo, o que indica seu potencial de uso para mapear áreas homogêneas<br>The objective of this work was to study the magnetic susceptibility and its association with the soil characteristics and topography in an Oxisol toposequence. Soil samples were collected in a transect of 2.700 km at intervals of 25 m, and randomly in lateral areas of three geomorphic surfaces mapped in two depths (0.00-0.20 m and 0.60-0.80 m), totaling 514 samples. Seven trenches were opened in the slope segments of geomorphic surfaces. The samples were analyzed for bulk density, porosity, degree of flocculation, texture, pH (water, CaCl2 and KCl), organic matter, P, Ca, K, Mg, H + Al, and Al. Calculating exchangeable bases (EB), cation exchange capacity (CEC), and base saturation (V%). In addition it was determined SiO2, Al2O3, Fe2O3 (attack by H2SO4), free iron oxides (Fed), poorly crystallized iron (Feo) and magnetic susceptibility, in all studied points. Data were analyzed by univariate statistical, descriptive, multivariate, split moving windows and geostatistics. Results showed that the division of areas by means of geomorphic surfaces resulted in better understanding of soil properties variability in the studied slope. The geostatistical method SMWDA (Split Moving Windows Dissimilarity Analysis), confirmed the numerical division of the three geomorphic surfaces by means of particle size and magnetic susceptibility. The magnetic susceptibility was the best attribute to identify the boundaries between bodies mapped in the field, which indicates its potential use for mapping homogeneous areas

This thesis is devoted to the study of elliptic equations. On the one hand, we study some qualitative properties, such as symmetry of solutions, on the other hand we explicitly construct some solutions vanishing near some fixed manifold. The main techniques are the moving planes method, in order to investigate the qualitative properties and the Lyapunov-Schmidt reduction.

Ces travaux de thèse s'incrivent dans le cadre du traitement de gaz acides et captage CO2 dans les colonnes à garnissages structurés. Les gaz à traiter réagissent avec un liquide s'écoulant à contre-courant sur des plaques métalliques dont la compléxité géométrique permet d'accroître l'aire d'échange, et donc l'efficacité du procédé. Dans un contexte de modélisation multi-échelles des contacteurs à garnissages structurés, les écoulements gaz-liquide à la plus petite échelle géométrique des plaques de garnissages (de l'ordre de l'épaisseur du film liquide) sont étudiés, pour améliorer la compréhension et la modélisation des écoulements diphasiques et phénomènes de mouillage dans les garnissages. L'objectif final est de développer une méthodologie CFD pour reproduire des écoulements diphasiques 3D sur des géométries complexes telles que les plaques de garnissages. Pour ce faire, il est nécessaire de progresser en méthodes numériques et de proposer des méthodes expérimentales pour observer des écoulements de film liquide sur des géométries complexes. Ces travaux comprennent une partie numérique et une partie expérimentale. Un écoulement sur une plaque de garnissage structuré peut présenter des zones sèches, et donc des lignes de contact (dynamiques), ce qui présente un défi en simulation numérique à cause des différentes échelles de l'écoulement. La méthodologie employée ici en simulation numérique consiste à résoudre l'écoulement jusqu'à une échelle intermédiaire en modélisant les effets des plus petites échelles. Le code de calcul Two-Phase Level-Set a été utilisé et modifié dans ce but. Différentes méthodes level-set ont d'abord été testées de manière à identifier une méthode satisfaisante quant à la réduction des erreurs de conservation de masse, un problème rencontré en level-set. Il est ici montré que certaines combinaisons de schémas de discrétisation spatiale et temporelle permettent de réduire considérablement ces erreurs de conservation de masse. Après avoir réalisé de nombreux tests de validation, une nouvelle méthode numérique est proposée pour simuler les grandes échelles d'écoulements diphasiques 3D avec ligne de contact dynamique en level-set, dans des conditions réalistes. La méthode est ici validée pour des écoulements axisymétriques de gouttes simulés en 3D, en régime visqueux et en régime inertiel, et pour des écoulements de gouttes sur plan incliné. Les résultats sont en très bon accord avec d'autres travaux numériques et expérimentaux. Afin de faciliter l'utilisation de cette méthodologie pour des applications industrielles, un modèle sous-maille similaire a été implémenté dans un code VOF commercial; les résultats sont aussi en très bon accord avec d'autres travaux. En plus de ces développements numériques, une campagne expérimentale est mise en oeuvre pour observer des écoulements de film liquide sur une plaque de garnissage structuré. Les méthodes expérimentales employées sont d'abord testées et validées pour des écoulements de film plat ou ondulé sur plan incliné, et ensuite utilisées pour observer des écoulements de film sur des plaques de garnissage. L'épaisseur de film liquide est mesurée aux creux et aux crêtes des picots des plaques de garnissages, pour différents débits, par imagerie confocale chromatique. Des lois de puissance de l'épaisseur de film en fonction du Reynolds sont proposées; celles-ci sont très différentes suivant la position des relevés de mesure, aux creux ou aux crêtes des picots. La vitesse à l'interface de l'écoulement gaz-liquide est aussi mesurée, par PIV et PTV, en utilisant des particules hydrophobes. Les résultats montrent que le liquide a tendance à dévier du creux des canaux (corrugations), et la norme de la vitesse semblent présenter des extremums correspondant aux creux et crêtes des picots. [...]<br>The work described in this thesis is motivated by the use of structured packing columns in acid gas treatment and post-combustion CO2 capture. In a counter-current mode, flue gases react with the liquid that flows down over metal sheets, the geometrical complexity of which allows increasing the specific interfacial area, and thereby the overall efficiency of the process. In the context of multiscale modeling of structured-packing contacting devices, the focus in this work is on the gas-liquid flows at the smallest geometrical scale of packing sheets, of the order of the liquid film thickness, aiming to improve understanding and modeling of two-phase flows and wetting phenomena in structured packings. The ultimate objective is to build up a CFD methodology to reproduce 3D two-phase flows over complex surfaces such as structured packing sheets. For this purpose, progress is necessary both in pertinent computational methods and in the adaptation of experimental methods for observing liquid film flows over complex surfaces. This thesis therefore consists of computational and experimental parts. Flows over structured packing sheets may exhibit dry zones, and hence (moving) contact lines, the numerical simulation of which presents a computational challenge due to the disparity in length scales involved. Here, the methodology for large-scale numerical simulations of flows with moving contact lines consists in resolving the flow down to an intermediate scale and modeling effects of smaller ones. The parallelized freeware Two-Phase Level-Set has been extended for this purpose. First though, because some level-set methods have been reproached to yield mass conservation issues, an assessment is made of the mass conservation properties of a range of level-set methods. It is demonstrated that the combined use of some spatial and temporal discretization schemes allows to drastically reduce mass conservation errors in level-set methods. Having thus implemented a level-set method with satisfactory performance at such tests (and others), a novel numerical method is proposed to perform 3D large-scale simulations of flows with moving contact lines in level-set, under realistic conditions. Validation tests of axisymmetric droplet spreading in a viscous, and in an inertial regime, simulated in 3D, and sliding drops are shown to be in excellent agreement with prior experimental and numerical work. The results show that complex contact-line dynamics observed in prior experimental studies on sliding droplets can be simulated using the present large-scale methodology. To facilitate dissemination of this work in industrial applications, a similar subgrid model has been implemented in a commercial volume-of-fluid code; results of validation tests are shown to be in excellent agreement with other work. These computational developments are accompanied by an experimental campaign to observe liquid film flows over structured packing sheets. All experimental methods used herein are tested and validated for flat and wavy films down an inclined plane before being used for observing liquid film flows over packing sheets. The film thickness is measured at local troughs and crests of small-scale corrugations of the structured packing sheet, for different flow rates, by Chromatic Confocal Imaging. Power laws of the Reynolds number for the mean liquid film thickness are suggested, with significant differences for measurements at crests compared to that at troughs. Interface velocity measurements are also performed by PIV and PTV using hydrophobic particles. Results reveal that the liquid tends to deviate from troughs of large-scale corrugations, and seems to exhibit local extrema of the velocity magnitude corresponding to troughs and crests of small-scale corrugations. [...]

Comment les relations consommateurs-marques peuvent-elles être développées en magasin ? Beaucoup de recherches sur les actions au point de vente les ont étudiées dans une perspective transactionnelle tandis que le marketing relationnel a prêté peu d'attention à ce qui se passe en magasin. Cependant le point de vente constitue un point de contact essentiel entre consommateurs et marques. Sur la base de deux études qualitatives et d'une étude expérimentale, cette recherche se concentre sur l'impact des actions en magasin sur les relations consommateurs-marques. Nous différencions les actions relationnelles des actions transactionnelles pour comparer leurs effets. L'application empirique est faite avec des marques de glaces distribuées en grandes et moyennes surfaces. Un questionnaire en ligne est mis en place pour tester des actions fictives que les marques pourraient mettre en œuvre. Nos résultats montrent l'intérêt pour les marques d'utiliser des actions relationnelles au point de vente. Les personnes exposées à des actions relationnelles attribuent plus souvent l'action à la marque. Ils perçoivent des efforts et une orientation relationnelle de la marque plus importants, ils s'identifient plus avec la marque, et déclarent ainsi une plus grande fidélité envers celle-ci. L'originalité de la recherche réside dans la prise en compte des actions en magasin dans une perspective relationnelle. Plus généralement, la conceptualisation et l'étude de l'impact de ce genre d'actions mettent en évidence une façon plus sociale de tenir compte des interactions entre les consommateurs et les marques<br>How can be developed and impacted relationships in store ? Many researches have studied in-store actions in a transactional perspective while relationship marketing has paid little attention to what happens in store. However, stores constitute a key point of contact between consumers and brands. Based on two qualitative studies and an experimental study, this research focuses on the impact of in-store actions on consumer-brand relationships. It differentiates relational and transactional actions and compares their effects. The empirical application involves ice cream brands distributed in the super-hypermarket channel. An online questionnaire is implemented to test fictitious actions that brands could implement. Our results show the interest for manufacturers brands to use relational in-store actions. Individuals exposed to relational in-store actions attribute more frequently the effort to the manufacturer. They perceive stronger efforts and brand expression, they identify more with the brand, and declare a higher loyalty to the latter. The originality of the research lies in the consideration of in-store actions in a relational perspective. More generally, the conceptualization and the study of the impact of these kinds of actions highlight a more social way to consider interactions between consumers and brands in the marketplace

An experimental study was conducted to study the splash-deposition characteristics of a liquid jet impinging on a moving surface. The main focus of this study was to determine the effects of fluid, flow and surface properties on the outcome of the jet impingement. Several parameters such as fluid viscosity, elasticity and surface tension, jet and surface velocity, jet diameter surface wettability and surface roughness were changed and their effects on splash-deposition characteristics were analyzed during this research work. For non-Newtonian fluids increase in the yield stress and consistency constant of the fluids helps in inhibition of the splash. At high Weber number the effects of surface tension and jet impingement angle were negligible compared to effects of Reynolds and Oldroyd numbers. But at smaller Weber number effects of surface tension were comparable to that of Reynolds number. It was also observed that the both normal (jet velocity) and tangential (surface speed) speeds play roles in splash-deposition dynamics. Newtonian liquid jet with smaller diameter illustrated that effect of surface tension becomes prominent only for liquids with low viscosities and for these liquids and 200 micron nozzle jets deposit up to 40 m/s. For high viscosity liquid same trend of deposition was observed and jets deposit up to 35 m/s. It was also observed that the jets of smaller viscosities spread on the surface very easily, making few micron sized lamella. Although higher viscosities liquid jets still spread very easily on the surface, the lamella thickness was much larger than that of low viscosity liquids. It was also found that mid-range viscosities jet started to splash at much lower velocities (13 m/s). This behavior is related to balancing of inertia forces by both the surface tension and viscous forces.

O estudo do comportamento de fluidos é um antigo domínio das ciências da natureza. Ultimamente, fenômenos de engenharia que eram estudados empiricamente passaram a ser estudados com auxílio computacional. A Dinâmica de Fluidos Computacional (DFC) é a área da ciência da computação que estuda métodos computacionais para simulação de escoamento de fluidos, e muitas vezes é a forma mais prática, ou a única, de se observar fenômenos de interesse no escoamento. Este projeto de Mestrado procurou investigar, no âmbito da simulação de um escoamento bifásico, métodos computacionais para representar a interface entre dois fluidos imiscíveis. A separação dos fluidos por meio de uma interface é necessária para assegurar que, propriedades como viscosidade e densidade, específicas de cada fluido, sejam utilizadas corretamente para o cálculo do movimento de seus respectivos fluidos. Desenvolvemos um método lagrangeano sem a utilização de malhas com o objetivo de suprir algumas restrições de trabalhos prévios. Para representar a interface entre os dois fluidos, este método utiliza uma técnica de reconstrução de superfícies baseada em aproximações de superfícies algébricas de alta ordem. Os resultados numéricos reportados neste documento evidenciam o potencial da nossa abordagem<br>The study of the behaviour of fluids is an ancient field in natural sciences. Recently, engineering phenomena that were empirically studied started to be done with computacional aid. The Computational Fluid Dynamics (CFD) is the area of science that studies computational methods for computer simulation of fluid flow, and often is the most practical way, or the only, to observe phenomena of interest in flow. This Masters degree project sought to investigate, in the context of the simulation of biphasic flows, computational methods to represent the interface between two immiscible fluids. The separation of fluids by the means of an interface is required to ensure that, during the simulation, the physical properties of a fluid, like density and viscosity (specific of each fluid) are properly used in the calculus of the respective fluid motion. We developed a lagrangean method without the use of mesh with the goal of alleviating some of the previous works restrictions. To represent the interface between the two fluids, this method uses a surface reconstruction technique based on approximations of high order algebraic surfaces. The numerical results reported herein show the potential of our approach

In the railroad industry liquid friction modifiers are applied on the rail track in the form of a liquid jet in order to reduce the friction and fuel consumption. In this application, the transfer efficiency of the liquid on the rail track is very important. To maximize the transfer efficiency, Newtonian and non-Newtonian transient liquid jet impingement on a dry moving surface was studied. Five different water glycerin solutions with widely varying shear viscosities were used as Newtonian test liquids to isolate the effect of shear viscosity from other fluid properties. Furthermore, the effect of surface roughness on the impaction was investigated using four different roughness heights. The effects of jet velocity and surface speed were also studied. High speed imaging was performed to visualize the interaction between the jet and the moving surface. For surface roughness heights between 0.02 μm and 0.64 μm, it was found that as the roughness increases, the jet becomes more prone to splash. It was also shown that increased jet and surface speeds trigger the splash. The transient jet characteristics were also investigated for Newtonian liquids at different nozzle back pressures. It was found that at higher Reynolds and Weber numbers the transient jet breaks up downstream of the nozzle; However, it was shown that the Weber number has the dominant role in jet break-up compared to the Reynolds number. A numerical study was also undertaken to determine the drag force exerted on the plunger of the solenoid valve in the nozzle. The simulation results were in reasonable (16% on average) agreement with experiment.<br>Applied Science, Faculty of<br>Mechanical Engineering, Department of<br>Graduate

In the railroad industry, coating of the rail with liquid changes the forces at the wheel-rail interface. Wet leaves on rail tracks can reduce the wheel-rail traction to dangerously low levels. To enhance wheel traction, railroads spray sand on the tracks. The sand may be applied in the form of a particle-laden jet. The impingement of high-speed liquid jets on a moving surface was studied. The jet fluids were dilute suspensions of neutrally buoyant particles in water-glycerin solutions. At the low concentration studied, the suspension has a Newtonian fluid viscosity. A variety of jet and surface velocities, liquid properties, mean particle sizes, and volume fractions were studied. It was observed that for jets with very small particles, the addition of solids to the jet enhances deposition. In contrast, jets with larger particles in suspensions were more prone to splash than single phase jets of the same viscosity. It is speculated that the non-monotonic dependence of the splash threshold on the particle size occurs when the particle diameter is comparable to the lamella thickness. Additionally, volume-of-fluid (VOF) CFD simulations were carried out to provide a full description of the flow field of a particle-free Newtonian jet spreading over a moving surface. The jet Reynolds number and Weber number of the simulations were in the range of 50-1000 and 100-8000, respectively. The simulations were generally in good agreement with experiments and they could successfully predict the lamella dimensions and velocity profiles.<br>Applied Science, Faculty of<br>Mechanical Engineering, Department of<br>Graduate

Motivated by the need to improve transfer efficiencies of liquid coatings from jet impingement in railroad friction control applications, an experimental investigation into Newtonian and viscoelastic liquid jet impingement on moving surfaces is presented. Seven PEO-glycerine-water solutions and three commercial liquid friction modifiers were tested with a variety of jet speeds, jet diameters, surface speeds and surface roughnesses. The effects of these test conditions on jet impingement splash behaviours as well as jet and lamella geometries were studied. High-speed imaging was employed to visualize the interaction between the impinging jet and the moving surface. Experiments on the effect of modest surface roughness revealed that, while jet and surface speed were both important factors, splash was more likely to occur on surfaces with lower roughness levels. By analyzing experimental results for Newtonian liquids, a relation between lamella geometry and test conditions were found, which can be used to predict lamella dimensions. Three types of non-Newtonian behaviours were observed at high surface speed and low jet speed: jet necking, jet bending and jet stretching.<br>Applied Science, Faculty of<br>Mechanical Engineering, Department of<br>Graduate

The concept of moving surface boundary-layer control, as applied to the Joukowsky and NACA airfoils, is investigated through a planned experimental program complemented by theoretical and flow visualization studies. The moving surface was provided by one or two rotating cylinders located at the leading edge, the trailing edge, or the top surface of the airfoil. Three carefully designed two-dimensional models, which provided a wide range of single and twin cylinder configurations, were tested at a subcritical Reynolds number (Re = 4.62 x 10⁴ or Re — 2.31 x 10⁵) in a laminar-flow tunnel over a range of angles of attack and cylinder rotational speeds. The test results suggest that the concept is indeed quite promising and can provide a substantial increase in lift and a delay in stall. The leading-edge rotating cylinder effectively extends the lift curve without substantially affecting its slope. When used in conjunction with a second cylinder on the upper surface, further improvements in the maximum lift and stall angle are possible. The maximum coefficient of lift realized was around 2.22, approximately 2.6 times that of the base airfoil. The maximum delay in stall was to around 45°. In general, the performance improves with an increase in the ratio of cylinder surface speed (Uc) to the free stream speed (U). However, the additional benefit derived progressively diminishes with an increase in Uc/U and becomes virtually negligible for Uc/U > 5. There appears to be an optimum location for the leading-edge-cylinder. Tests with the cylinder at the upper side of the leading edge gave quite promising results. Although the CLmax obtained was a little lower than the two-cylinder configuration (1.95 against 2.22), it offers a major advantage in terms of mechanical simplicity. Performance of the leading-edge-cylinder also depends on its geometry. A scooped configuration appears to improve performance at lower values of Uc/U (Uc/U ≤ 1). However, at higher rates of rotation the free stream is insensitive to the cylinder geometry and there is no particular advantage in using the scooped geometry. A rotating trailing-edge-cylinder affects the airfoil characteristics in a fundamentally different manner. In contrast to the leading-edge-cylinder, it acts as a flap by shifting the CL vs. α plots to the left thus increasing the lift coefficient at smaller angles of attack before stall. For example, at α = 4°, it changed the lift coefficient from 0.35 to 1.5, an increase of 330%. Thus in conjunction with the leading-edge- cylinder, it can provide significant improvements in lift over the entire range of small to moderately high angles of incidence (α ≤ 18°). On the theoretical side, to start with, the simple conformal transformation approach is used to obtain a closed form potential-flow solution for the leading-edge-cylinder configuration. Though highly approximate, the solution does predict correct trends and can be used at a relatively small angle of attack. This is followed by an extensive numerical study of the problem using: • the surface singularity approach including wall confinement and separated flow effects; • a finite-difference boundary-layer scheme to account for viscous corrections; and • an iteration procedure to construct an equivalent airfoil, in accordance with the local displacement thickness of the boundary layer, and to arrive at an estimate for the pressure distribution. Effect of the cylinder is considered either through the concept of slip velocity or a pair of counter-rotating vortices located below the leading edge. This significantly improves the correlation. However, discrepancies between experimental and numerical results do remain. Although the numerical model generally predicts CLmax with a reasonable accuracy, the stall estimate is often off because of an error in the slope of the lift curve. This is partly attributed to the spanwise flow at the model during the wind tunnel tests due to gaps in the tunnel floor and ceiling required for the connections to the externally located model support and cylinder drive motor. However, the main reason is the complex character of the unsteady flow with separation and reattachment, resulting in a bubble, which the present numerical procedure does not model adequately. It is expected that better modelling of the cylinder rotation with the slip velocity depending on a dissipation function, rotation, and angle of attack should considerably improve the situation. Finally, a flow visualization study substantiates, rather spectacularly, effectiveness of the moving surface boundary-layer control and qualitatively confirms complex character of the flow as predicted by the experimental data.<br>Applied Science, Faculty of<br>Mechanical Engineering, Department of<br>Graduate

In the railroad industry a friction modifying agent may be applied to the rail or to the wheel in the form of a liquid jet. In this mode of application the interaction between the high speed liquid jet and a fast moving surface is important. Seven different Newtonian liquids with widely varying shear viscosities along with twelve different solutions of polyethylenoxide (PEO) and water with varying relaxation times were tested to isolate the effect of viscosity and elasticity from other fluid properties. Tests for the Newtonian liquids were done with five surfaces having different roughness heights to investigate the effects of surface roughness. High speed video imaging was employed to scrutinize the interaction between the impacting jet and the moving surface. For both Newtonian and Elastic liquids and all surfaces, decreasing the Reynolds number reduced the incidence of splash and consequently enhanced the transfer efficiency. At the elevated Weber numbers of the testing, the Weber number had a much smaller impact on splash than did the Reynolds number. The ratio of the surface velocity to the jet velocity has only a small effect on the splash, whereas increasing the roughness-height-to-jet-diameter ratio substantially decreased the splash threshold. Moreover, the Deborah number was also salient to the splash of elastic liquids.

A permeable highly sensitive heat flux meter has enabled the first measurements of rapidly changing local heat transfer at a moving surface with and without throughflow. This sensor was tested for turbulent confined impinging single and multiple slot jets, with throughflow and impingement surface motion both separately and in combination.<br>Impingement surface motion, variously claimed to increase or decrease convective transfer rate, decreases Nusselt number. At industrially used conditions this decrease for slot jets is by as much as 25%.<br>Convective heat transfer for both single and multiple slot jets at H/w $ leq$ 8 is enhanced by throughflow according to a factor, $ Delta overline{ rm St}$/Mu$ sb{ rm s}$ = 0.17, is independent of Re$ sb{ rm j}$, Mv$ sb{ rm s}$ and extent of heat transfer surface.<br>In numerical prediction of impingement heat transfer with the high-Re version of the k-$ epsilon$ turbulence model, a modified Chieng-Launder nearwall model improves considerably the agreement between experiment and prediction. This model gives reasonable results for multiple and single slot jets except close to symmetry centrelines, where all such models fail, but does not eliminate the inability of numerical models to predict the effect of nozzle exit turbulence. The effect of throughflow on heat transfer under single and multiple jets is predicted for the first time, accurate to 10% for throughflow velocity up to 0.1m/s.

Local heat transfer profiles under a confined inclined slot jet discharging from a sharp-edged re-entry straight channel nozzle with various inclinations were measured. Average heat transfer was determined by integrating local profiles between positions of equal local Nusselt number.<br>In the absence of significant heat transfer surface motion, impingement heat transfer expressed as stagnation and average Nusselt number with the present nozzles set either normal or 15$ sp circ$ from normal, is similar to that with ASME standard contoured entry nozzles at a nozzle-to-surface spacing of 6 nozzle widths. As this spacing is reduced by one-half, heat transfer becomes much larger for the re-entry channel nozzles, by 100% for average Nusselt number, by 250% for stagnation Nusselt number under the conditions tested.<br>For an impingement surface moving at high speed, highest heat transfer is obtained with the nozzle set at inclinations between normal and 15$ sp circ$ with the jet opposing the impingement surface motion. Use of jets in the aiding flow orientation result in large drops in heat transfer rate, as does the use of opposing jets inclined at angles large than 15$ sp circ$ from normal.<br>The same large advantage of the re-entry straight channel nozzle over the ASME standard contoured entry nozzle applies for impingement surface moving at high speeds as in the absence of surface motion.<br>The importance of asymmetric exhaust port location is documented for the case of inclined slot jets impinging on moving or stationary impingement surface, and for normal slot jets impinging on high speed heat transfer surfaces.

Flexible road pavements often fail due to excessive rutting. as a result of cumulative vertical permanent deformation under repeated traffic loads. The currently used analytical approach to flexible pavement design evaluates the pavement life in terms of critical elastic strain at the top of the subgrade. Hence, the plastic pavement behaviour is not properly considered. Shakedown analysis can take into account the material plasticity and guarantee structure stability under repeated loads. It provides a more rational design criterion for flexible road pavements. Finite element analyses using the Tresca and Mohr-Coulomb yield criteria are performed to examine the responses of soil half-space when subjected to different loading levels. Both shakedown and surface ratchetting phenomena are observed and the residual stresses are found to be fully-developed after a limited number of load passes. The finite element results are then used to validate the solutions from shakedown analysis. The main focus of current research is concerned with new solutions for static (i.e. lower-bound) shakedown load limits of road pavements under both two-dimensional and three-dimensional moving surface loads. Solutions are derived by limiting the total stresses at any point (i.e. residual stresses plus loading induced elastic stresses) to satisfy the Mohr-Coulomb yield criterion. Previous analytical shakedown solution has been derived based on a residual stress field that may not satisfy equilibrium for certain cases. In this study, a rigorous lower-bound shakedown solution has been derived by imposing the equilibrium condition of residual stresses. The newly developed shakedown solutions have been applied to one-layered and multi-layered pavements. It was found that the rigorous lower-bound solution based on the self-equilibrated residual stress field is lower than the analytical shakedown solution for cases when the critical point lies on the surface or at the base of the first pavement layer. The results showed that the theoretical predictions of pavement shakedown load limit generally agree with the finite element and experimental observations for pavement behaviours. The shakedown solution has been further extended to study the influence of the shape of contact load area for pavements under three-dimensional Hertz loads. It was found that the shakedown load limit can be increased by changing the load contact shape from a circle area to an elliptical one. A new pavement design approach against excessive rutting has been proposed. The pavement design is suggested by plotting thickness design charts using the direct shakedown solutions and choosing the thickness combination based on the design traffic load.

Motivated by the need to improve transfer efficiencies of liquid coatings from jet impingement, an experimental investigation into jet impingement on very high speed moving surfaces is presented. Seven different Newtonian liquids with widely varying shear viscosities were made to impinge on a surface which could be made to move at speeds up to 350km/hr. Tests for the Newtonian liquids were done with several modified surfaces to study the effects of roughness and surface inconsistencies. Nozzle sizes and impingement angles were varied to interrogate their effects on the interaction of the impacting jet and moving surface while high speed photography was employed to capture these interactions. Spread radii and spread widths were measured for viscous fluids which deposited. While it was observed that stable jets of fluids with sufficiently high viscosities almost always deposited, tests with water indicate that the effects of the impingement angle as well as jet diameter significantly alter the locations of boundaries between deposition, spatter and lamella lift-off. Impingement angles that result in jet velocities with large components of velocity parallel to the surface velocity are prone to deposit. Jets of smaller diameters are also prone to deposit. It was observed that both the jet velocity and surface velocity are important determining factors in the likelihood of deposition. The deposition of viscous fluids demonstrated that it is possible to observe transitions from deposition to lift-off and vice versa through mechanisms that trigger random fluctuations in the lamella. The track distance covered before a transition from lift-off to deposition occurs is shown to be a Poisson Process.

Thesis (Ph. D.)--University of California, San Diego, 2008.<br>Title from first page of PDF file (viewed February 10, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 120-126).

As a logical extension of previous work conducted into viscoelastic atomization, initially motivated by the need to improve spray coating transfer efficiencies, an experimental investigation into the spray-surface interaction for a number of Newtonian and non-Newtonian substitute test liquids is presented. Three model elastic liquids of varying polymer molecular weight and three inelastic liquids of varying shear viscosity were sprayed upon a moving surface to isolate the effect of elasticity and shear viscosity, respectively, on spray impaction behavior. In addition, two liquids exhibiting shear thinning behavior and an industrial top of rail liquid friction modifier, KELTRACK, for use in the railroad industry, were included in the spray tests. High-speed photography was used to examine the impingement of these liquids on the surface. Ligaments, formed as a consequence of a liquid’s viscoelasticity, were observed impacting the surface for 300K PEO, 1000K PEO, and KELTRACK. These ligaments were broadly classified into four groups, based on their structure. Splashing of elastic liquid ligaments and droplets led to filamentary structures being expelled from the droplet periphery, which were then carried away by the atomizing air jet, leading to reductions in transfer efficiency. The effect of increasing elasticity amongst the three varying molecular weight elastic solutions was shown to increase the splash threshold; a similar effect was noted with increasing shear viscosity. Attempts were made at quantifying a critical splash-deposition limit for all test liquids however due to imaging system limitations, no quantitative conclusions could be made. For KELTRACK, both droplets and ligaments spread and deposited on the rail surface upon impact, with no observed splash or rebound. Splash was only noted when droplets impinged directly on a previously deposited liquid film and even then, splashing was well contained. Thus, KELTRACK’s current rheological formulation proved to be very effective in ensuring high coating transfer efficiencies.

In this study, an attempt is made to obtain convergent and stable solutions of the K-E turbulence model equations for non-reacting turbulent flows over an isothermal solid surface in regression. A physics based mathematical model is used to describe the flow and temperature field over the moving surface. The flow is assumed to be two-dimensional, unsteady, incompressible with boundary layer approximations. Parabolized form of the standard K-E equations is adopted to simulate turbulence in the flow. Regression of the solid surface causes the bounds of the solution domain to change with time, therefore a coordinate transformation is used in the vertical direction. The computational domain with fixed boundaries is discretized using an orthogonal grid system where a coordinate stretching is used in the vertical direction. A second order accurate, explicit finite difference technique is used for discretization of the governing equations. The final set of discretized equations is then solved using a solution algorithm specifically developed for this study. The verification of the solution algorithm includes a grid independence study, time increment study, and a comparison of the steady state results for the laminar and the turbulent flow cases. Finally, a parametric study is conducted using the proposed solution algorithm to test the stability of the numerical results for different Reynolds numbers, regression rates, and surface temperatures. It is concluded that the proposed numerical solution algorithm is capable of providing convergent and stable solutions of the two-equation turbulence model.

Registering partial shapes plays an important role in numerous applications in the fields of robotics, vision, and graphics. An essential problem of registration algorithms is the determination of correspondences between surfaces. In this paper, we provide a in-depth evaluation of an approach that computes high-quality correspondences for pair-wise closest point-based iterative registration and compare the results with state-of-the-art registration algorithms. Instead of using a discrete point set for correspondence search, the approach is based on a locally reconstructed continuous moving least squares surface to overcome sampling mismatches in the input shapes. Furthermore, MLS-based correspondences are highly robust to noise. We demonstrate that this strategy outperforms existing approaches in terms of registration accuracy by combining it with the SparseICP local registration algorithm. Our extensive evaluation over several thousand scans from different sources verify that MLS-based approach results in a significant increase in alignment accuracy, surpassing state-of-theart feature-based and probabilistic methods. At the same time, it allows an efficient implementation that introduces only a modest computational overhead.

In this thesis we study the geometry of surfaces immersed in the four-dimensional conformal sphere $Q_4$. It is known that a surface immersed in $Q_n$ is Willmore if and only if its conformal Gauss map is harmonic. Here we prove that a surface immersed in $Q_4$ is - or + isotropic if and only if its conformal Gauss map is, respectively, holomorphic or antiholomorphic. We make use of Cauchy-Riemann conditions to prove that, under suitable assumptions, a compact surface is either isotropic or its Euler characteristic is bounded from above. We then consider the notion of S-Willmore surface and prove that, even in the conformal setting, an S-Willmore surface is Willmore. We also prove that an isotropic surface is S-Willmore if and only if the curvature of the normal bundle associated with the surface does not vanish. Finally, we prove the existence of a bijection between the set of -isotropic, non totally umbilical, weakly conformal branched immersions of a fixed surface in $Q_4$, whose conformal gauss map can be continuously extended at the branch points, and non constant, holomorphic, totally isotropic maps with values in the conformal Grassmannian, with non constant associated map $J_\gamma$. The bijection is realized via the conformal gauss map

Tails, fins, scales, and surface coatings are used by organisms for various tasks, including locomotion. Since millions of years of evolution have passed, we expect that the design of surface structures is optimal for the tasks of the organism. These structures serve as an inspiration in this thesis to identify new mechanisms for flow control. There are two general categories of fluid-structure-interaction mechanisms. The first is active interaction, where an organism actively moves parts of the body or its entire body in order to modify the surrounding flow field (e.g., birds flapping their wings). The second is passive interaction, where appendages or surface textures are not actively controlled by the organism and hence no energy is spent (e.g., feathers passively moving in the surrounding flow). Our aim is to find new passive mechanisms that interact with surrounding fluids in favourable ways; for example, to increase lift and to decrease drag. In the first part of this work, we investigate a simple model of an appendage (splitter plate) behind a bluff body (circular cylinder or sphere). If the plate is sufficiently short and there is a recirculation region behind the body, the straight position of the appendage becomes unstable, similar to how a straight vertical position of an inverted pendulum is unstable under gravity. We explain and characterize this instability using computations, experiments and a reduced-order model. The consequences of this instability are reorientation (turn) of the body and passive dispersion (drift with respect to the directionof the gravity). The observed mechanism could serve as a means to enhance locomotion and dispersion for various motile animals and non-motile seeds. In the second part of this thesis, we look into effective models of porous and poroelastic materials. We use the method of homogenization via multi-scale expansion to model a poroelastic medium with a continuum field. In particular, we derive boundary conditions for the velocity and the pressure at the interface between the free fluid and the porous or poroelastic material. The results obtained using the derived boundary conditions are then validated with respect to direct numerical simulations (DNS) in both two-dimensional and three-dimensional settings. The continuum model – coupled with the necessary boundary conditions – gives accurate predictions for both the flow field and the displacement field when compared to DNS.<br>Många djur använder sig av fjäll, päls, hår eller fjädrar för att öka sin förmåga att förflytta sig i luft eller vatten. Eftersom djuren har genomgått miljontals år av evolution, kan man förvänta sig att ytstrukturernas form är optimala för organismens uppgifter. Dessa strukturer tjänar som inspiration i denna avhandling för att identifiera nya mekanismer för manipulering av strömning. Samverkan mellan fluider och strukturer (så kallad fluid-struktur-interaktion) kan delas upp i två kategorier. Den första typen av samverkan är aktiv, vilket innebär att en organism aktivt rör hela eller delar av sin kropp för att manipulera det omgivande strömningsfältet (till exempel fåglar som flaxar sina vingar). Den andra typen är passiv samverkan, där organismer har utväxter (svansar, fjärdar, etc.) eller ytbeläggningar som de inte aktivt har kontroll över och som således inte förbrukar någon energi. Ett exempel är fjädrar som passivt rör sig i det omgivande flödet. Vårt mål är att hitta nya passiva mekanismer som växelverkar med den omgivande fluiden på ett fördelaktigt sätt, exempelvis genom att öka lyftkraften eller minska luftmotståndet. I den första delen av detta arbete undersöker vi en enkel modell för en utväxt (i form av en platta) bakom en cirkulär cylinder eller sfär. Om plattan är tillräckligt kort och om det finns ett vak bakom kroppen kommer det upprätta läget av plattan att vara instabilt. Denna instabilitet är i princip samma som uppstår då man försöker balansera en penna på fingret. Vi förklarar den bakomliggande mekanismen av denna instabilitet genom numeriska beräkningar, experiment och en enkel modell med tre frihetsgrader. Konsekvenserna av denna instabilitet är en omorientering (rotation) av kroppen och en sidledsförflyttning av kroppen i förhållande till tyngdkraftens riktning. Denna mekanism kan användas djur och frön för att öka deras förmåga att förflytta eller sprida sig i vatten eller luft. I den andra delen av avhandlingen studerar vi modeller av porösa och elastiska material. Vi använder en mångskalig metod för att modellera det poroelastiska materialet som ett kontinuum. Vi härleder randvillkor för både hastighetsfältet och trycket på gränssnittet mellan den fria fluiden och det poroelastiska materialet. Resultaten som erhållits med de härledda randvillkoren valideras sedan genom direkta numeriska simuleringar (DNS) för både två- och tredimensionella fall. Kontinuumsmodellen av materialet kopplad genom randvillkoren till den fria strömmande fluiden predikterar strömnings- och förskjutningsfält noggrant i jämförelse med DNS.

Fixed-abrasive diamond wire sawing is a promising technique for reduction of costs related to sawing of silicon wafers for solar cells. The microscopic mechanisms of material removal in the process are however not fully understood, and must be surveyed in order for costs to be further reduced.An interference microscope for sub-surface inspection of mono-crystalline silicon has been built based on the Linnik configuration, with specific application to in-situ monitoring of moving indentations. The working principles of the instrument are explained from a literature study on relevant theory, combining concepts of optical interference and coherence with imaging theory. The optical system has been experimentally tested in terms of its performance in conventional imaging as well as its interferometric capabilities. Tests on the imaging performance show that a large magnification is accompanied by a lateral resolution with a lower limit of $0.9mumathrm{m}$ and an adequately long depth of field. This provides improved conditions for imaging of internal reflections in silicon, compared to a previously used prototype.Using a light source of low temporal coherence, the capability of the system to measure depth profiles of silicon surfaces has been tested. The technique calculates depths from interferograms recorded by scanning of a reference field. Preliminary results from a flat test surface show that depths are not determined accurately enough for calculated profiles to be considered as reliable reconstructions. It is discussed that the inaccuracy is caused by a number of experimental factors including non-uniform illumination, undesired reflections and non-uniform sampling intervals in scanning.Two experiments with moving indentations on silicon surfaces have been performed, monitored by conventional imaging and calculation of interferometric phase maps, respectively. Results are seen in context with the theoretical understanding of material removal mechanisms in fixed-abrasive diamond wire sawing. The evolution of surface damage is observed as interconnection of chippings in both experiments. In addition, sub-surface lateral cracks are identified from interferometric phase maps. The phase maps of surface damage can, however, only to a limited extent be interpreted as topographic contour lines of surface depth. A deeper knowledge of removal mechanisms requires quantitative measurements of depths. This can be better achieved by calculating accurate depth profiles from interferograms. Future enhancement of the system is dependent on a reevaluation of the optical design as well as better control of sampling intervals in scanning.

This thesis is dedicated to the study of the interaction between a gas jet and a liquid film on a moving surface. This flow configuration corresponds to the gas-jet wiping technique, which is widely used in the coating industry to reduce and control the thickness of a liquid film dragged by a moving substrate. For that purpose, a turbulent slot jet impinges on the liquid surface, involving a runback flow and consequently a lower coating thickness downstream wiping. The different process parameters (nozzle pressure, nozzle to substrate standoff distance, slot width, substrate speed) allow controlling the final film thickness. This metering technique is very common in coating processes, such as the application of gelatin layers on photographic films.<p><p>The first part of this thesis deals with the prediction of the mean jet wiping flow, i.e. the film thickness distribution in the wiping region. A lubrication model is developed for that purpose, which is simplified to a zero-dimensional model giving directly the final thickness<p><p>In the second part, the prediction of splashing occurrence in jet wiping is addressed. The splashing phenomenon in jet wiping is featured by the ejection of droplets from the runback flow, and it constitutes a physical limit to the process. An experimental investigation is conducted on a water model facility, and based on a phenomenological description, a dimensionless correlation in terms of film Reynolds number and jet Weber number is derived for splashing occurrence. The latter is perfectly well validated with observations on industrial lines.<p><p>The last part of this thesis is dedicated to the study of the unsteady phenomena occurring on the free surface of the liquid film downstream wiping. This phenomenon has never been understood nor characterized up to now. In the present research, undulation is investigated both theoretically and experimentally. Two model test facilities with dedicated measurement techniques have been designed and constructed. They allow performing parametric studies of the undulation characteristics (amplitude, wavelength, wave velocity), and analyzing the jet/film interaction.<p><br>Doctorat en sciences appliquées<br>info:eu-repo/semantics/nonPublished

Doutoramento em Engenharia Química<br>A exploração de compostos, subprodutos e resíduos naturais é um passo chave para a obtenção de um futuro sustentável. A valorização e comercialização destes materiais dependem da aplicação de técnicas adequadas de conversão e separação/purificação que permitam obter os níveis desejados de pureza e produtividade. Os ácidos triterpénicos, particularmente os ácidos betulínico, oleanólico e ursólico, são compostos de elevado valor que têm atraído interesse devido às suas já reportadas propriedades nutraceuticas e farmacológicas. Estes triterpenoides estão presentes em diversas fontes vegetais mas podem ser encontrados com abundâncias consideráveis na casca do eucalipto (decídua e externa), um resíduo comum da indústria da pasta e papel. O isolamento dos ácidos triterpénicos é uma tarefa difícil devido às suas semelhantes estruturas moleculares, especialmente no caso dos ácidos oleanólico e ursólico, que são isómeros de posição. O leito móvel simulado (simulated moving bed, SMB) é uma técnica cromatográfica de separação contínua e em contracorrente que maximiza a força diretriz de transferência de massa permitindo a separação de moléculas mesmo quando as seletividades se aproximam de um. Por exemplo, é frequentemente utilizada no isolamento de enantiómeros. No SMB clássico a separação de dois componentes é efetuada em quatro zonas, os caudais e concentrações de alimentação são fixos e as portas de entrada/saída são comutadas simultaneamente. Recentemente, novas implementações tais como a modificação da concentração ou caudais da alimentação, a utilização de tempos de comutação variáveis e a introdução de novas zonas para separação multicomponente, têm permitido a obtenção de maior flexibilidade e melhor performance. Uma revisão profunda destes modos de operação foi feita durante esta tese. A modelação e otimização são passos essenciais no dimensionamento e desenvolvimento de qualquer processo e particularmente importantes no SMB. Como ponto de partida para o estudo do fracionamento de ácidos triterpénicos por leito móvel simulado, modelos fenomenológicos conhecidos foram aplicados para desenvolver de um simulador SMB. Durante este trabalho uma estratégia de otimização de unidades de SMB foi desenvolvida combinando as metodologias de desenho de experiências e respostas de superfície com simulações computacionais, com o objetivo de obter condições de operação ótimas com baixa complexidade e um esforço computacional reduzido. Esta técnica de otimização foi aplicada ao estudo da separação dos enantiómeros de óxido de trans-estilbeno, usando informação da literatura, e posteriormente comparada com outros procedimentos de determinação de condições de operação ótimas. Esta técnica permitiu purezas acima de 99.5 % para ambos enantiómeros, necessitando de um baixo número de simulações. A separação de ácidos triterpénicos foi inicialmente estudada à escala analítica, através de uma série de ensaios cromatográficos em diferentes condições para seleção de fase móvel e estacionária apropriada. Os melhores resultados foram obtidos com uma coluna Apollo C18 usando metanol/água 95/5 (%,v/v) e os parâmetros de equilíbrio e transporte foram determinados através de experiências de rutura com os compostos puros. Esta informação foi utilizada com sucesso na simulação da separação de uma mistura ternária, cujos resultados foram validados com experiências de rutura ternárias. A separação em SMB de uma mistura representativa de um extrato natural contendo os ácidos betulínico, oleanólico e ursólico foi desenhada utilizando um processo em dois passos: inicialmente o ácido betulínico foi isolado dos ácidos oleanólico e ursólico e, de seguida, os ácidos oleanólico e ursólico foram fracionados. Esta separação foi otimizada usando a metodologia de desenho de experiências e respostas de superfície combinada com simulações rigorosas e permitiu demonstrar que é possível produzir os ácidos betulínico, oleanólico e ursólico com purezas de 99.4 %, 99.1 %, e 99.4 %. Os polímeros molecularmente impressos (molecularly imprinted polymers, MIPs) são sintetizados para possuírem centros ativos altamente seletivos para moléculas alvo, tornando-os adsorventes muito promissores. Vários MIPs foram sintetizados por polimerização por precipitação usando diferentes formulações. Após a preparação, estes polímeros foram caracterizados por microscopia eletrónica de varrimento e os mais promissores, em termos de características morfológicas, foram diretamente testados através de experiências de adsorção. Os resultados revelam que o material “MIP1b” exibe selectividade infinita para o ácido oleanólico, a molécula alvo usada na sua síntese. Em conjunto com a sua capacidade de adsorção – superior à da previamente estudada fase C18 – estes resultados demonstram o elevado potencial do polímero “MIP1b” para aplicação na separação dos ácidos triterpénicos. Investigação adicional é necessária neste tópico onde diferentes técnicas de separação podem ser antecipadas. Este trabalho culminou com o dimensionamento e montagem de uma unidade laboratorial de leito móvel verdadeiro baseada num sistema de uma-válvula-ST por coluna recentemente patenteado, que permite à unidade operar sobre diferentes estratégias de operação e configurações.<br>The exploitation of natural compounds, by-products and residues is a key strategy for the pursuit of a sustainable future. The effective valorization and commercialization of these materials depends on the application of adequate conversion and separation/purification techniques that can provide desired levels of purity and productivity. Triterpenic acids, particularly betulinic, oleanolic, and ursolic acids, are high value molecules that have attracted considerable interest due to their reported nutraceutical and pharmacological properties. These triterpenoids are present in diverse vegetable sources but significant abundances are found in Eucalyptus bark (deciduous and external), a common residue from the paper and pulp industry. The isolation of triterpenic acids is a difficult task due to their similar molecular structures, particularly in the case of oleanolic and ursolic acids, which are positional isomers. The simulated moving bed (SMB) technology is a countercurrent continuous chromatographic technique that maximizes the mass transfer driving force, thus allowing the separation of compounds even when selectivities approach one. For instance, it is often used for enantiomers isolation. In a classic SMB, the separation of two components is accomplished across four zones, the flow rates and feed concentrations are fixed, and the inlet/outlet ports are switched synchronously. Recently, new implementations and modifications, such as the modulation of feed concentration or flow rates, variable switch times and additional zones for multicomponent separations, enabled better flexibility and performances to be achieved. A thorough review of these modes of operation was performed in this thesis. Modeling and optimization are necessary steps for the design and development of any process, being particularly important in SMB. As the starting point for the study of the fractionation of triterpenic acids by simulated moving bed, well know phenomenological models were applied to develop a SMB simulator. During this work, an optimization strategy of SMB units was developed combining the design of experiments and response surface methodologies (DoE-RSM) with computer simulations, aimed at providing good operating conditions with low complexity and reduced computational effort. This optimization technique was applied to the separation of trans-stilbene oxide (TSO) enantiomers using data from the literature and compared with other existing procedures for the determination of the best operation conditions. It allowed purities above 99.5 % for both TSO enantiomers while requiring a small number of simulations. The separation of triterpenic acids was initially studied at analytical scale, through a series of chromatographic assays under different conditions, to select appropriate mobile and stationary phases. Best results were obtained using an Apollo C18 column and methanol/water 95/5 (%, v/v), and equilibrium and mass transport parameters were determined through breakthrough experiments with pure compounds. This information was then successfully applied in the simulation of a ternary mixture separation, whose results were validated with ternary breakthrough measurements. The SMB separation of a representative natural extract containing betulinic, oleanolic and ursolic acids was designed using a two-step process: firstly, betulinic acid was isolated from oleanolic and ursolic acids, and secondly, oleanolic and ursolic acids were fractionated. This separation approach was optimized using DoE-RSM combined with rigorous simulations, and it was demonstrated that it is possible to produce betulinic, oleanolic and ursolic acids with purities of at least 99.4 %, 99.1 %, and 99.4 %. Molecularly imprinted polymers (MIPs) are synthesized to possess binding sites highly selective to specific molecules, making them very promising adsorbents. Several MIPs were synthetized by precipitation polymerization using different formulations. After preparation, these polymers were characterized by scanning electron microscopy and the most successful ones, in terms of morphological features, were directly tested carrying out batch adsorption experiments. The results disclosed that “MIP1b” material exhibits infinite selectivity for oleanolic acid, the template molecule used in its synthesis. Together with its adsorption capacity – even higher than that of the previously studied C18 phase – these results demonstrate the high potential of “MIP1b” polymer for application on the separation of triterpenic acids. Additional research is required in this topic, where distinct separation approaches may be anticipated. This PhD work culminated in the design and assembling of a laboratory simulated moving bed unit based on a recently patented system using a one- ST valve per column valve scheme, thus allowing the SMB to run under several operation strategies and configurations.

This study investigates the effect of Transverse Convex Surface Curvature of the inner core (T.C.S.C) on the fully developed fluid flows in a concentric annulus with a moving core, by analytically predicting friction forces, velocity profiles, temperature profiles and heat transfer in terms of convex surface curvature, radius ratio, Prandtl number, Reynolds number and relative velocity. The analytical predictions are produced by a mathematical model based on the variable von Karman constant, kappai, proposed by Kim and Lee [1] and the variable van Driest damping parameter, Ai+, proposed in previous research by Suk [2]. The computer program developed for this study employs a numerical process to match velocity and temperature profiles with force and energy balances and calculates the desired momentum and thermal characteristics. The solutions are found in the case of the heat transfer where the inner core surface is uniformly heated and the outer insulated. It is assumed that the fluid flow is turbulent everywhere and the thermodynamic fluid properties are independent of temperature. It is concluded that in the fully developed turbulent flow in a concentric annulus with a moving core, the effects of Transverse Convex Surface Curvature (T.C.S.C), core velocity and turbulent motion on the momentum and heat transfer characteristics of the flow seem significant.

A mathematical model is developed for investigating time dependent surface deformations of a hydrostatic water volume, when it is subjected to a sudden partial collapse or rise of the sea bottom. The model solves two-dimensional Navier-Stokes Equations on a vertical plane numerically by using Marker and Cell Method (MAC) for viscous and compressible fluid including all the nonlinear effects in the solution. For demonstration, a vertical motion was given to a section in a hypothetical reservoir bed within a short time period and the resulting velocity and pressure fields and the surface profile of the water body are obtained. Computational and physical aspects are discussed.

The impingement of a high-speed liquid jet on a moving surface and the resulting deposition or splash is important in a variety of technical and industrial processes. Of particular interest is the coating of the top-of-rail surface, in the rail road industry, with a thin film of viscoelastic liquid friction modifier, by liquid jet impingement, to control friction and reduce wear at the wheel-rail interface, thereby reducing fuel consumption and maintenance costs. For effective operation it is required that the fluid deposited by the jet adhere to the surface after impingement. An experimental investigation into the effect of surrounding air pressure and fluid properties on liquid jet impingement on a moving surface was performed. The study was carried out with Newtonian liquids impacting smooth, dry surfaces. A variety of ambient air pressures, jet speeds, surface speeds, surface tensions, and liquid viscosities were studied. The interaction between the impinging jet and the moving surface was analysed through high-speed imaging. It was observed that, as is the case for Newtonian droplet impact, the surrounding air pressure plays a crucial role in the splashing behaviour of jet impingement. There exists a threshold pressure below which splash does not occur. It is proposed that for certain impingement conditions lamella detachment from the surface occurs due to aerodynamic forces acting on the leading edge of the lamella, which destabilizes the balance between surface tension and fluid pressure forces. It was observed that both the Reynolds number and Weber number were salient to the occurrence of lamella detachment, with lamella detachment having a non-linear dependence on the Reynolds number. Lamella detachment was prone to occur for intermediate Reynolds numbers as the Weber number was increased, bounded by regions of deposition at higher and lower Reynolds numbers.

River ice jams can cause many problems including extreme flooding, damage to structures, interference with navigation, and restrictions on hydropower operations. Their annual cost to the Canadian economy has been estimated to be nearly one hundred million dollars. This thesis explores the application of smoothed particle hydrodynamics (SPH) to river ice flows. SPH is a meshless method used to solve fluid dynamics problems, whereby the fluid is replaced by a set of particles that move with the flow. This method is particularly well suited to modelling complex free-surfaces and moving solid boundaries. The main contributions of this study were the new developments made to an existing SPH code enabling the accurate simulation of freely moving solid objects in a free-surface flow subject to hydrodynamic and solid contact forces. An SPH Arbitrary Lagrangian-Eulerian (ALE) formalism was used to model the fluid flow and the hydrodynamic forces exerted on solid objects. This study involved coupling the existing SPH-ALE model with the discrete element method (DEM) used to model solid interactions with other solids and with boundaries. The solid interactions were implemented as both a hard-sphere model based on instantaneous, inelastic collisions, and a soft-sphere linear spring and dashpot model based on force-displacement relationships. Application and validation test cases of freely moving solid objects were simulated and compared with analytical solutions, laboratory experiments, and other computational results. These new capabilities were then applied to river ice dynamics problems. The methods used in this study are suited to smaller scale river ice processes where the dynamic effects may not be captured with traditional depth-averaged modelling techniques. Computational results showing the stability of a floating ice block approaching a stationary cover and ice accumulation upstream of an obstruction are encouraging and they show promise to serve as a useful quantitative engineering tool in the future.<br>Les embâcles de glace peuvent causer de nombreux problèmes, y compris des inondations, des dommages aux structures, interférence avec la navigation et des restrictions sur les opérations hydroélectriques. Leur coût annuel pour l'économie canadienne est estimé à presque 100 millions de dollars. Cette thèse étude l'application de la méthode de simulation numérique, smoothed particle hydrodynamics (SPH) pour les problèmes de glace en rivière. SPH est une méthode utilisée pour résoudre les problèmes de dynamique des fluides, dans laquelle le liquide est modélisé par un ensemble de particules. Cette méthode est particulièrement bien adaptée pour modéliser les écoulements à surfaces libres. Les principales contributions de cette étude sont les nouveaux développements apportés à un code SPH existant, permettant la simulation d'objets solides qui sont emportés avec l'écoulement à surface libre. Un formalisme SPH Arbitrary Lagrangian-Eulerian (ALE) a été utilisé pour modéliser l'écoulement du fluide et les forces hydrodynamiques sur les objets solides. Cette étude porte sur le couplage du modèle existant SPH-ALE avec la discrete element method (DEM) utilisée pour modéliser les interactions solides entre eux et avec des parois. Les interactions solides ont été implémentées comme un modèle de hard-sphere, basé sur les collisions inélastiques instantanées, ainsi qu'un modèle soft-sphere basé sur les relations entre les forces et les déplacements. Des cas-test de validation et application ont été simulés et évalués pour vérification avec des solutions analytiques, des expériences de laboratoire, et d'autres résultats de calcul. Ces nouvelles fonctionnalités ont ensuite été appliquées aux problèmes dynamiques de glace en rivière. Les résultats numériques montrent la stabilité d'un bloc de glace flottant qui s'approche un bloc fixe et l'accumulation de glace en amont d'une obstruction. Ces résultats prometteurs permettent de valider cette technique pour l'évaluation quantitative future en ingénierie.

ABSTRACT SIMULATION OF SURFACE WAVES GENERATED BY A RAPID RISE OF A BLOCK AT THE SEA BOTTOM SENOL, Nalan M.Sc., Department of Civil Engineering, Supervisor: Assoc. Prof. Dr. ismail AYDIN July 2005, 74 Pages A mathematical model is developed for investigating time dependent surface deformations of a hydrostatic water volume, when it is subjected to a sudden partial rise of the sea bottom. In the model, 2-dimensional, compressible, and viscous Navier-Stokes equations are solved by Marker and Cell (MAC) method. Variable mesh size in both horizontal and vertical directions with a staggered grid arrangement is used. Limited compressibility model is utilized for pressure. Various computational tests are done for the selection of computational parameters of the model. It is found that the amplitude of surface waves generated by vertical displacements of the sea bottom depends on size and speed of bottom displacements.

The CO2SINK (and CO2MAN) project is the first onshore CO2 storage project in Europe. The research site is located near the town of Ketzin, close to Potsdam in Germany. Injection started in June 2008, with a planned injection target of 100,000 tonnes of CO2. In February 2011, around 45, 000 tons of CO2 had been injected into the saline aquifer at an approximate depth of 630 m. This thesis focuses on time-lapse analysis of borehole seismic data, surface seismic data and reservoir characterization at the Ketzin site. Baseline Moving Source Profiling (MSP) data were acquired in the borehole Ketzin 202/2007 (OW2), along seven lines in 2007. The zero-offset Vertical Seismic Profile (VSP) data were acquired in the same borehole. The main objective of the VSP and MSP survey was to generate high-resolution seismic images around the borehole. After modeling and data processing, the sandy layers within the Stuttgart Formation can potentially be imaged in the VSP and MSP data whereas reflections from these layers are not as clearly observed in the 3D surface seismic data. 2D and pseudo-3D time-lapse seismic surveys were conducted at the Ketzin site. Interpretation of 2D baseline and repeat stacks shows that no CO2 leakage related time lapse signature is observable where the 2D lines allow monitoring of the reservoir. This is consistent with the time-lapse results of the 3D surveys showing an increase in reflection amplitude just centered around the injection well. The results from the pseudo-3D surveys are also consistent with the 3D seismic time-lapse studies and show that the sparse pseudo-3D geometry can be used to qualitatively map the CO2 in the reservoir with significantly less effect than the full 3D surveying. The 2nd pseudo-3D repeat survey indicates preferential migration of the CO2 to the west. There are no indications of migration into the caprock on either of the repeat surveys. Amplitude Versus Offset (AVO) analysis was performed on both 2D and 3D repeat surveys. A Class 3 AVO anomaly is clearly observed on the 3D repeat data and matches the synthetic modeling well. No AVO anomaly was observed on the 2D repeat data, which was anticipated, but the result shows signs of a pressure response at the reservoir level in the data. Reflection coefficients were calculated using surface seismic data (3D and pseudo-3D) at the site. Pre-injection calculations agree well with calculations from logging data. Post-injection calculations are in general agreement with the seismic modeling, but generally show higher amplitudes than those expected. The full 3D data show a better image of the reflection coefficients before and after injection than the pseudo-3D data and can potentially be used to make quantitative calculations of CO2 volumes. The pseudo-3D data only provide qualitative information.