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1
Asadulla, M. "Viscous flow near a stationary contact line." Thesis, University of Essex, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371892.
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Hurley, Barbara Jill. "Contact-line movement on a variably heated surface." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/16728.
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Najafi, Seyed Kamran. "Design of Contact Line Friction Measurement Machine Apparatus." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4377.
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The purpose of this project is to design and manufacture a high precision machine to directly measure the surface force of fluids. Knowing how to move droplets easier with less resistance can increase the potential of a wide range of applications and improve the performance of things such as self-assembly applications. This machine has the ability to measure forces of up to 100 N with a MEMS based sensor. The motion system on this machine moves a substrate underneath of a droplet for 100 mm and applies dragging force to the sensor. It moves with a controlled speed with high accuracy and repeatability. The machine also consists of three manual, three axis controls for positioning key components for observation, control of the air vacuum lifter, and adjustment of the sensor position. There is also an enclosure box that provides visibility to operate and protects the inside environment from dirt during process and also by applying positive air flow during setting up with open windows. The test components were designed to provide maximum flexibility to adjust the setup. A camera in the machine contributes to collect data during the test progress and has the ability to capture pictures and record videos.
4
Zhao, Lei. "Dynamics and Statics of Three-Phase Contact Line." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/102649.
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Wetting, which addresses either spontaneous or forced spreading of liquids on a solid surface, is a ubiquitous phenomenon in nature and can be observed by us on a daily basis, e.g., rain drops falling on a windshield and lubricants protecting our corneas. The study of wetting phenomena can be traced back to the observation of water rising in a capillary tube by Hauksbee in 1706 and still remains as a hot topic, since it lays the foundation for a wide spectrum of applications, such as fluid mechanics, surface chemistry, micro/nanofluidic devices, and phase change heat transfer enhancement. Generally, wetting is governed by the dynamic and static behaviors of the three-phase contact line. Therefore, a deep insight into the dynamics and statics of three-phase contact line at nanoscale is necessary for the technological advancement in nanotechnology and nanoscience. This dissertation aims to understand the dynamic wetting under a molecular kinetic framework and resolve the reconfiguration of liquid molecules at the molecular region of contact line.
Water spreading on polytetrafluoroethylene surfaces is selected as a classical example to study the dynamic behaviors of three-phase contact line. To accommodate the moving contact line paradox, the excess free energy is considered to be dissipated in the form of molecular dissipation. As-formed contact line friction/dissipation coefficient is calculated for water interacting with PTFE surfaces with varying structures and is found to be on the same order of magnitude with dynamic viscosity. From an ab initio perspective, contact line friction is decomposed into contributions from solid-liquid retarding and viscous damping. A mathematical model is established to generalize the overall friction between a droplet and a solid surface, which is able to clarify the static-to-kinetic transition of solid-liquid friction without introducing contact angle hysteresis. Moreover, drag reduction on lotus-leaf-like surface is accounted for as well. For the first time, the concept of contact line friction is used in the rational design of a superhydrophobic condenser surface for continuous dropwise condensation.
We focus on the transport and reconfiguration of liquid molecules confined by a solid wall to shed light on the morphology of the molecular region of a three-phase contact line. A governing equation, which originates from the free energy analysis of a nonuniform monocomponent system, is derived to describe the patterned oscillations of liquid density. By comparing to the Reynolds transport theorem, we find that the oscillatory profiles of interfacial liquids are indeed governed in a combined manner by self-diffusion, surface-induced convection and shifted glass transition. Particularly for interfacial water, the solid confining effects give rise to a bifurcating configuration of hydrogen bonds. Such unique configuration consists of repetitive layer-by-layer water sheets with intra-layer hydrogen bonds and inter-layer defects. Molecular dynamics simulations on the interfacial configuration of water on solid surfaces reveal a quadratic dependence of adhesion on solid-liquid affinity, which bridges the gap between macroscopic interfacial properties and microscopic parameters.Doctor of Philosophy
5
Amirfazli, Alidad. "Drop size dependence of contact angles and line tension." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ59012.pdf.
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Al-Sabti, Sara Louise. "Failure modes of polymethylmethacrylate resulting from rolling line contact." Thesis, Brunel University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311264.
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Saxton, Matthew. "Modelling the contact-line dynamics of an evaporating drop." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:d8991513-f31e-4dd4-b2d1-9e01acdd35bb.
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We study the evolution of a thin, axisymmetric, partially wetting drop as it evaporates. The effects of viscous dissipation, capillarity, slip, gravity, surface-tension gradients, and contact-angle hysteresis are taken into account in the regime in which the transport of vapour is dominated by diffusion. We find a criterion for when the contact-set radius close to extinction evolves as the square-root of the time remaining until extinction - the famous d2-law. However, for a sufficiently large rate of evaporation, our analysis predicts that a 'd13/7-law' is more appropriate. We also determine how each of the physical effects in our model influences the evolution of the drop and hence its extinction time. Our asymptotic results are validated by comparison with numerical simulations. We then revisit our model for the vapour phase and take kinetic effects into account through a linear constitutive law that states that the mass flux through the drop surface is proportional to the difference between the vapour concentration in equilibrium and that at the interface. We perform a local analysis near the contact line to investigate the way in which kinetic effects regularize the mass- flux singularity at the contact line. The problem is further analysed via a matched asymptotic analysis in the physically relevant regime in which the kinetic timescale is much smaller than the diffusive one. We find that the effect of kinetics is limited to an inner region near the contact line, in which kinetic effects enter at leading order and cause the vapour concentration at the free surface to deviate from its equilibrium value. We also derive an explicit expression for the mass flux through the free surface of the drop.
8
Demidenok, Konstantin. "Polyelectrolyte nanostructures formed in the moving contact line: fabrication, characterization and application: Polyelectrolyte nanostructures formed in the moving contact line: fabrication, characterization and application." Doctoral thesis, Technische Universität Dresden, 2009. https://tud.qucosa.de/id/qucosa%3A25246.
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Having conducted the research described in this thesis I found that there exists a possibility to produce polyelectrolyte nanostructures on hydrophobic surfaces by application of the moving contact line approach. It was demonstrated that the morphology of nanostructures displays a range of structure variations from root-like to a single wire structure with a high anisotropy and aspect ratio (providing diameters of several nanometers and the length limited by the sample surface dimensions). Such nanostructures can be produced exactly on the spot of interest or can be transferred from the surface where they were produced to any other surfaces by the contact printing technique.
A model describing the polymer deposition during the moving contact line processes on hydrophobic surfaces has been proposed. The application of this model provides the ground for an explanation of all the obtained experimental data.
Utilizing moving contact line approach aligned one-dimensional polycation structures were fabricated and these structures were used as templates for assembling amphiphile molecules.
Quasiperiodic aligned and oriented nanostructures of polyelectrolyte molecules formed in moving droplets were utilized for fabrication of electrically conductive one-dimensional nanowires.
9
Zimmerman, Jeremiah D. "High Resolution Measurements near a Moving Contact Line using µPIV." PDXScholar, 2011. https://pdxscholar.library.pdx.edu/open_access_etds/118.
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A moving contact line is the idealized line of intersection between two immiscible fluids as one displaces the other along a solid boundary. The displacement process has been the subject of a large amount of theoretical and experimental research; however, the fundamental processes that govern contact line motion are still unknown. The challenge from an experimental perspective is to make measurements with high enough resolution to validate competing theories. An experimental method has been developed to simultaneously measure interface motion, dynamic contact angles, and local fluid velocity fields using micron-resolution Particle Image Velocimetry (µPIV). Capillary numbers range from 1.7 x 10^(⁻⁴) to 6.2 x 10^(⁻⁴). Interface velocities were measured between 1.7 µm/s and 33 µm/s. Dynamic contact angles were manually measured between 1.1 µm and 120 µm from the contact line, and calculated from µPIV data to within several hundred nanometers from the contact line. Fluid velocities were measured over two orders of magnitude closer to the contact line than published values with an increase in resolution of over 3400%. The appearance of a recirculation zone similar to controversial prediction below previously published limits demonstrates the power and significance of the method.
10
Hadjiconstantinou, Nicolas G. (Nicholas George). "Hybrid atomistic-continuum formulations and the moving contact line problem." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9791.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.Includes bibliographical references (leaves 149-153).
We present a formulation and numerical solution procedure for hybrid atomisticcontinuum representations of fluid flows. Hybrid representations are of great importance because they allow the solution of problems that require modelling on the microscale without the associated cost of a fully molecular solution. This is achieved by limiting the molecular treatment to the regions where it is needed while using the inexpensive continuum description in the remainder of the computational domain. The ingredients are, from the atomistic side, non-equilibrium molecular dynamics, and from the continuum side, spectral/finite element solutions. Molecular dynamics has been chosen for its ability to capture all the underlying physics without the need for modelling assumptions. The continuum solution techniques chosen represent the best compromise between the minimum computational cost, simplicity, and applicability to a wide variety of problems of interest. The matching is provided by a classical procedure, the Schwarz alternating method with overlapping subdomains. This matching technique exhibits favorable convergence properties and has been preferred because of its ability to bypass the problem of matching fluxes in molecular dynamics which has not been satisfactorily treated to date. Flow of a dense fluid (supercritical Argon) in a complex two-dimensional channel serves as a test problem for the validation of the technique developed above. Reasonable agreement is found between the hybrid solution and the fully continuum solution which is taken to be exact. The hybrid technique is subsequently applied to the moving contact line problem. The motion of contact lines (the locus of intersection of a two-fluid interface with a bounding solid) has, due to the multitude of length scales involved, been one of the few problems that has defied theoretical analysis over the years. It has long been concluded that continuum hydrodynamics is not adequate for the description of the physics involved in the vicinity of the contact angle, which is predominantly molecular kinetic, thus making this problem a good candidate for our solution technique. The basic ingredients for the hybrid treatment of the contact line problem are the continuum solution technique, the molecular solution technique, and a modified Schwarz method required due to the existence of two fluids and a two-fluid interface. The continuum solution is provided by a variationally consistent finite element simulation technique we have developed for the above reason. An already developed molecular simulation technique is adapted to provide the molecular solution. Our hybrid solution is compared with the fully molecular solution which serves as an exact solution for comparison purposes. Good agreement is found between the two solutions.
Nicolas Hadjiconstantinou.
Ph.D.
11
Duthaler, Gregg Michael 1970. "Molten drop deposition and the dynamics of the molten contact line." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9394.
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Qiao, Hua. "Prediction of contact fatigue for the rough surface elastohydrodynamic lubrication line contact problem under rolling and sliding conditions." Thesis, Cardiff University, 2005. http://orca.cf.ac.uk/56019/.
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The study of elastohydrodynamic lubrication (EHL) with rough surfaces results in a transient problem due to time varying geometry. In conditions where the A ratio (the ratio of smooth surface film thickness to composite roughness) is low, significant pressure deviations from the corresponding smooth surface results occur. The relative motion of asperity features on the two surfaces leads to cycling of these pressure deviations as surface features move through the nominal contact area. Micropitting, which is a form of surface distress seen in gears, may well be viewed as rolling contact fatigue at the roughness asperity scale as a result of this load cycling. In order to understand the failure mechanism associated with rough surface EHL, a full theoretical model of lubrication of gear contacts under low A conditions is presented in this thesis. The model takes account of the real gear operating conditions in terms of loads, speeds, surface roughness and lubricant properties to predict pressures, film thickness, temperatures, and friction between the teeth. Subsequent contact stress analysis was performed to determine the stress history developed in the contacting solids. Conventional pitting is usually associated with failure beneath the surface of a rolling contact and in the past has been linked with the occurrence of the maximum shear stress that occurs in the classical Hertzian solution for smooth surfaces. In this thesis, a numerical procedure for predicting contact fatigue damage in an EHL line contact between two rough surfaces is developed to take the features of variable amplitude multiaxial fatigue into account due to the roughness effect. The way in which the calculated fatigue damage varies with changes in factors such as slide roll ratio, speed, viscosity, rough surface profiles, and A ratio adopted for the analysis is demonstrated in a series of numerical examples using roughness profiles taken from gears in micropitting experiments.
13
Votsios, Vasilis. "Contact mechanics and impact dynamics of non-conforming elastic and viscoelastic semi-infinite or thin bonded layered solids." Thesis, Loughborough University, 2003. https://dspace.lboro.ac.uk/2134/11815.
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The thesis is concerned with the contact mechanics behaviour of non-conforming solids. The geometry of the solids considered gives rise to various contact configurations, from concentrated contacts with circular and elliptical configuration to those of finite line nature, as well as those of less concentrated form such as circular flat punches. The radii of curvature of mating bodies in contact or impact give rise to these various nonconforming contact configurations and affect their contact characteristics, from those considered as semi-infinite solids in accord with the classical Hertzian theory to those that deviate from it. Furthermore, layered solids have been considered, some with higher elastic modulus than that of the substrate material (such as hard protective coatings) and some with low elastic moduli, often employed as tribological coatings (such as solid lubricants). Other bonded layered solids behave in viscoelastic manner, with creep relaxation behaviour under load, and are often used to dampen structural vibration upon impact. Analytic models have been developed for all these solids to predict their contact and impact behaviour and obtain pressure distribution, footprint shape and deformation under both elastostatic and transient dynamic conditions. Only few solutions for thin bonded layered elastic solids have been reported for elastostatic analysis. The analytical model developed in this thesis is in accord with those reported in the literature and is extended to the case of impact of balls, and employed for a number of practical applications. The elastostatic impact of a roller against a semi-infinite elastic half-space is also treated by analytic means, which has not been reported in literature. Two and three-dimensional finite element models have been developed and compared with all the derived analytic methods, and good agreement found in all cases. The finite element approach used has been made into a generic tool for all the contact configurations, elastic and viscoelastic. The physics of the contact mechanical problems is fully explained by analytic, numerical and supporting experimentation and agreement found between all these approaches to a high level of conformance. This level of agreement, the development of various analytical impact models for layered solids and finite line configuration, and the development of a multi-layered viscoelastic transducer with agreed numerical predictions account for the main contributions to knowledge. There are a significant number of findings within the thesis, but the major findings relate to the protective nature of hard coatings and high modulus bonded layered solids, and the verified viscoelastic behaviour of low elastic modulus compressible thin bonded layers. Most importantly, the thesis has created a rational framework for contact/impact of solids of low contact contiguity.
14
Zhang, Jiaqi. "Finite-element simulations of interfacial flows with moving contact lines." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/99058.
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In this work, we develop an interface-preserving level-set method in the finite-element framework for interfacial flows with moving contact lines. In our method, the contact line is
advected naturally by the flow field. Contact angle hysteresis can be easily implemented
without explicit calculation of the contact angle or the contact line velocity, and meshindependent results can be obtained following a simple computational strategy. We have
implemented the method in three dimensions and provide numerical studies that compare
well with analytical solutions to verify our algorithm.
We first develop a high-order numerical method for interface-preserving level-set reinitialization. Within the interface cells, the gradient of the level set function is determined by a
weighted local projection scheme and the missing additive constant is determined such that
the position of the zero level set is preserved. For the non-interface cells, we compute the
gradient of the level set function by solving a Hamilton-Jacobi equation as a conservation
law system using the discontinuous Galerkin method. This follows the work by Hu and Shu
[SIAM J. Sci. Comput. 21 (1999) 660-690]. The missing constant for these cells is recovered
using the continuity of the level set function while taking into account the characteristics. To
treat highly distorted initial conditions, we develop a hybrid numerical flux that combines
the Lax-Friedrichs flux and a penalty flux. Our method is accurate for non-trivial test cases
and handles singularities away from the interface very well. When derivative singularitiesare present on the interface, a second-derivative limiter is designed to suppress the oscillations. At least (N + 1)th order accuracy in the interface cells and Nth order accuracy in
the whole domain are observed for smooth solutions when Nth degree polynomials are used.
Two dimensional test cases are presented to demonstrate superior properties such as accuracy, long-term stability, interface-preserving capability, and easy treatment of contact lines.
We then develop a level-set method in the finite-element framework. The contact line singularity is removed by the slip boundary condition proposed by Ren and E [Phys. Fluids, vol.
19, p. 022101, 2007], which has two friction coefficients: βN that controls the slip between
the bulk fluids and the solid wall and βCL that controls the deviation of the microscopic
dynamic contact angle from the static one. The predicted contact line dynamics from our
method matches the Cox theory very well. We further find that the same slip length in
the Cox theory can be reproduced by different combinations of (βN; βCL). This combination leads to a computational strategy for mesh-independent results that can match the
experiments. There is no need to impose the contact angle condition geometrically, and the
dynamic contact angle automatically emerges as part of the numerical solution. With a little
modification, our method can also be used to compute contact angle hysteresis, where the
tendency of contact line motion is readily available from the level-set function. Different test
cases, including code validation and mesh-convergence study, are provided to demonstrate
the efficiency and capability of our method.
Lastly, we extend our method to three-dimensional simulations, where an extension equation
is solved on the wall boundary to obtain the boundary condition for level-set reinitializaiton
with contact lines. Reinitialization of ellipsoidal interfaces is presented to show the accuracy and stability of our method. In addition, simulations of a drop on an inclined wall are
presented that are in agreement with theoretical results.Doctor of Philosophy
When a liquid droplet is sliding along a solid surface, a moving contact line is formed at the intersection of the three phases: liquid, air and solid. This work develops a numerical method to study problems with moving contact lines. The partial differential equations describing the problem are solved by finite element methods. Our numerical method is validated against experiments and theories. Furthermore, we have implemented our method in three-dimensional problems.
15
Demidenok, Konstantin. "Polyelectrolyte nanostructures formed in the moving contact line: fabrication, characterization and application." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-27327.
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Having conducted the research described in this thesis I found that there exists a possibility to produce polyelectrolyte nanostructures on hydrophobic surfaces by application of the moving contact line approach. It was demonstrated that the morphology of nanostructures displays a range of structure variations from root-like to a single wire structure with a high anisotropy and aspect ratio (providing diameters of several nanometers and the length limited by the sample surface dimensions). Such nanostructures can be produced exactly on the spot of interest or can be transferred from the surface where they were produced to any other surfaces by the contact printing technique.
A model describing the polymer deposition during the moving contact line processes on hydrophobic surfaces has been proposed. The application of this model provides the ground for an explanation of all the obtained experimental data.
Utilizing moving contact line approach aligned one-dimensional polycation structures were fabricated and these structures were used as templates for assembling amphiphile molecules.
Quasiperiodic aligned and oriented nanostructures of polyelectrolyte molecules formed in moving droplets were utilized for fabrication of electrically conductive one-dimensional nanowires.
16
Hsueh, Ching. "Drying of complex fluids near the contact line : experimental and numerical studies." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2012. http://tel.archives-ouvertes.fr/tel-00831313.
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Nous étudions la structuration de dépôts lors du séchage de suspensions colloïdales et de solutions polymères, dans une cellule de Hele-Shaw verticale immergée dans un réservoir (même principe qu'une expérience de dip-coating). La vitesse de la ligne de contact est contrôlée en pompant la solution du réservoir. A faible nombre capillaire un phénomène d'accrochage-décrochage de la ligne triple apparaît lors du séchage des suspensions colloïdales de silice. Nous étudions la longueur d'onde et la morphologie du dépôt en fonction de la vitesse moyenne de la ligne de contact. La variation de force d'accrochage est déduite de l'observation en ligne du mouvement de la ligne de contact. Nous étudions l'influence du pH de la solution et de la taille des particules sur le dépôt. Dans les mêmes conditions, les films obtenus pas séchage de solutions polymères sont presque plats. On observe cependant une structuration à plus haute température. Dans la seconde partie du manuscrit, un modèle 2D a été développé pour décrire l'écoulement dans la cellule de Hele-Shaw induit par la vitesse imposée et le flux d'évaporation non uniforme. Les équations de Stokes et la loi de Fick sont utilisées pour décrire l'écoulement et les transferts. Une troncature est appliquée à la pointe du ménisque pour s'affranchir de la singularité due à la divergence du flux d'évaporation. L'approximation de lubrification et les bilans de masse permettent de définir les conditions aux limites à la troncature. L'épaisseur du dépôt et les propriétés de l'écoulement sont étudiées en fonction des paramètres du processus (vitesse imposée, flux d'évaporation, concentration) ainsi que des propriétés du système
17
Davies, C. N. "Effects of non-Newtonian rheology on the line contact elastohydrodynamic lubrication problem." Thesis, Cardiff University, 2005. http://orca.cf.ac.uk/56028/.
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The Bair and Winer, Gecim and Winer, Circular and Cardiff limiting shear stress models are compared and contrasted under different load, viscosity, limiting shear stress, surface velocities, Young's modulus, relative radius of curvature and temperature. Isothermal comparisons show that limiting shear stress rheology reduces the pressure gradients in the centre of the contact. Also a localised increase in film thickness in the inlet and a reduction near the exit of the contact occur. The bulk oil temperature significantly influences the limiting shear stress features developed. As a result a full thermal approach was adopted that includes the heat generated, by slip, at the fluid-surface interface. Regions where limiting shear stress and temperature effects dominate are identified under optical interferometry operating conditions. The heat generated during contact was included in the thermal approach. Sinusoidal roughness features promoted contact and the temperature responses were compared using different coefficients of friction. Contact develops higher temperatures than those generated in full film regions, with much greater temperature rises for higher coefficients of friction. Thermal and isothermal gear meshes are simulated using equivalent roller and involute geometries with rough and smooth surfaces. Roughness data taken from gear teeth are linked to the numerical involute used in the simulation, allowing roughness features to be used in the correct part of the gear mesh. Smooth and rough surface results are obtained for three different meshes. 'Running in' was investigated by measuring the amount of surface modification and contact developed between two rotating disks using 'in situ' Talysurf profiles and contact resistance measurements respectively. 'Running in' occurred quickly, with temperature effects reducing the films prolonging the contact period. Comparisons using the software developed incorporating actual roughness profiles, bulk disk and bulk oil temperatures, gave good agreement between the numerical and experimental approaches.
18
Widiyarta, I. M. ade. "Simulation of wear and crack initiation in line contact with thermal stresses." Thesis, University of Newcastle Upon Tyne, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.512030.
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ANDREWS, ABEL TORRES. "BIDIMENSIONAL ANALYSIS OF FLEXIBLE LINE DYNAMICS INCLUDING THE CONTACT EFFECTS WITH SEABED." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2004. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=5662@1.
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AGÊNCIA NACIONAL DE PETRÓLEONeste trabalho apresenta-se uma metodologia pelo método dos elementos finitos para a análise estática-dinâmica bi-dimensional de linhas marítimas considerando-se o contato com o leito marinho. Para o cabo considera-se o elemento de dois nós do modelo de viga de Euler-Bernoulli com as grandezas estáticas e dinâmicas referidas a um sistema co- rotacionado. Considera-se a nãolinearidade geométrica associada ao movimento de corpo rígido da estrutura, supondo pequenas deformações. No movimento da linha, são consideradas as influências do peso próprio, empuxo, carregamentos hidrodinâmicos das correntes marinhas, deslocamentos prescritos no ponto superior da linha, forças de inercia e ação de flutuadores. Os efeitos sobre a linha associados ao contato com o fundo marinho são considerados empregando-se a técnica dos multiplicadores de Lagrange. Estes representam o carregamento (forças e momentos) requerido para garantir as restrições geométricas. No modelo não são considerados os efeitos das forças de atrito com o fundo marinho, cuja rigidez é considerada muito superior à do cabo. A matriz de rigidez usual do modelo de vigas é aumentada de forma a acomodar as novas incógnitas resultantes da imposição das condições de contato. Desta forma, condições de contato, separação repetidos (contato variável) e grandes movimentos relativos do cabo com o leito são contemplados pelo modelo. A solução das equações algébricas não-lineares, resultantes da integração temporal passo-a-passo de Newmark, é obtida com a técnica iterativa de Newton Raphson. A metodologia numérica foi implementada e resultados de alguns testes para situações da engenharia offshore são mostrados e comparados com os apresentados por outros autores independentes.
In this work a finite element methodology for two- dimensional static and/or dynamic analysis of maritime risers including contact with the seabed is considered. The line is modeled by a two node beam element based on the Euler- Bernoulli theory with a co-rotational coordinate system, defined from the structure space coordinate nodes, to refer the element equilibrium and motion equations. Geometric non-linear effects are considered, all associated with rigid body motions from the structure, under small strain hypothesis. In the riser motion, the influences of its own weight, buoyancy forces, hydrodynamic loadings due to the maritime currents, the prescribed displacements at the top point line, the inertia forces and the floating action are considered. Effects on the line associated to the seabed contact are considered using Lagrange multipliers. They represent, the required loading (forces and moments) to ensure the cable geometric restrictions. In the model, friction forces effects on the seabed are not considered and the seabed stiffness is taken much greater than the riser s. The beam model stiffness matrix results into an increased matrix to accommodate the new model unknowns reactions, which are represented by the contact forces and moments. Similarly, conditions for variable contact and/or separation, as well as large relative motions between the flexible line and the seabed, are contemplated by the model. Solutions of the resulting nonlinear motion equations are obtained using Newmark s step-by-step time integration procedure with the Newton-Raphson iterative technique, for the numerical solution convergence. The methodology has been implemented and some representative offshore engineering testing analysis results are presented compared to other independently published solutions.
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Trapuzzano, Matthew A. "Controlled Wetting Using Ultrasonic Vibration." Scholar Commons, 2019. https://scholarcommons.usf.edu/etd/7974.
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Many industrial processes such as printing and cleaning, as well as products like adhesives, coatings, and biological testing devices, rely on the wetting of liquids on a surfaces. Wetting is commonly controlled through material selection, coatings, and/or surface texture, but these means are sensitive to environmental conditions. Wetting is influenced by variables like surface tension, density, the surface chemistry, local energy barriers like surface roughness, and how the droplet is placed on the surface. Wetting of droplets can also be influenced externally in many ways such as introducing surfactants, applying electrical fields, or by dynamically excitation. Low-frequency, high amplitude vibration can initiate wetting changes prompted by droplet contact line oscillations that exceed the range of stable contact angles inherent of a droplet on a solid surface.
The study of ultrasonic vibration wetting and spreading effects is sparse [1, 2], and is usually only qualitatively analyzed. Therefore, the specific goal of this thesis is somewhat unique, but also has potential as a means to controllably reverse surface adhesion.
High frequency vibration effects and the governing mechanisms are relatively uncharacterized due to difficulties posed by the spatial and temporal scales. To investigate, droplets of 10, 20, and 30 µL are imaged as they vibrate on a hydrophobic surface forced via a piezoelectric transducer over different high frequencies (>10 kHz). Wetting transitions occur abruptly over a range of parameters, but coincide with transducer resonance modes. The magnitude of contact angle change is dependent on droplet volume and surface acceleration, and remains after cessation of vibration, however new droplets wet with the original contact angle.
A more detailed investigation of this phenomenon was necessary to obtain a better understanding. This required repeatable testing conditions, which relies heavily on surface integrity. However, some “hydrophobic” coatings are sensitive to extended water exposure. To determine which hydrophobic coatings may be appropriate for investigating dynamic wetting phenomena, samples of glass slides coated with a series of fluoropolymer coatings were tested by measuring water contact angle before, during, and after extended submersion in deionized water and compared to the same coatings subjected to ultrasonic vibration while covered in deionized water. Both methods caused changes in advancing and receding contact angle, but degradation rates of vibrated coatings, when apparent, were significantly increased. Prolonged soaking caused significant decreases in the contact angle of most coatings, but experienced significant recovery of hydrophobicity when later heat-treated at 160 C. Dissimilar trends apparent in receding contact angles suggests a unique degradation cause in each case. Roughening and smoothing of coatings was noted for coatings that were submerged and heat-treated respectively, but this did not correlate well with the changing water contact angle. Degradation did not correspond to surface acceleration levels, but may be related to how well coatings adhere to the substrate, indicative of a dissolved coating. Most coatings suffered from contact angle degradation between 20-70% when exposed to water over a long period of time, however the hydrophobic fluoropolymer coating FluoroSyl was found to remain unchanged. For this reason it was found to be the most robust coating for providing long term wetting repeatability of vibrated droplets.
Droplets (10 to 70 µL) were imaged on hydrophobic surfaces as they were vibrated with ultrasonic piezoelectric transducers. Droplets were vibrated at a constant frequency with ramped amplitude. Spreading of droplets occurs abruptly when a threshold surface acceleration is exceeded of approximately 20,000 m/s2. Droplet contact area (diameter) can be controlled by varying acceleration levels above the threshold. The threshold acceleration was relatively independent of droplet volume, while initial contact angle impacts the extent of spreading. Wetting changes remain after cessation of vibration as long as the vibrated droplet remained within the equilibrium contact angle range for the surface (> the receding contact angle), however new droplets wet with the original contact angle except for some cases where vibration of liquid can affect the integrity of the coating. Reversible wettability of textured surfaces is a desired effect that has various industry applications where droplet manipulation is used, like biomedical devices, coating technologies, and agriculture [3-5].
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Cureton, Peter John. "Becoming a manager in a contact centre." Thesis, University of Chester, 2014. http://hdl.handle.net/10034/346989.
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This thesis uses an abductive research strategy to discover how individuals in a UK contact centre became first-line managers. Managers play a significant role in organisations as supervisors of staff, yet there is no general agreement as to what they do or how. Adopting an idealist ontology and a constructionist epistemology, this ethnographic project uncovered stories of becoming by using questionnaires, observations and interviews with twelve participants. The context was a private / public sector partnership to provide advice and guidance to a local community. The use by organisations of contact centres is maturing in the private sector and growing in the public sector. It is an especially important arena to explore in the UK economy as currently many contact centres that were outsourced to cheaper, high quality labour markets are returning to the UK. Analysis of data showed clearly that learning to become a first-line manager occurred throughout the life course in three distinct stages; formative development, and reflecting the values and behaviours of parents and teachers; pre-management occupational development, and the experience of being managed; and development actually in the role of a first-line manager. The thesis makes four contributions to the extant literature. Firstly, these three stages were shown to be the route in the transition from legitimate peripheral participation to mastery. Situated learning theory provides no such clarification. Secondly, learning to become a first-line manager did not necessarily change identity as many writers claim. Identities of first-line manager evolved by building on personal and occupational identities that had been developed earlier. Thirdly, teachers made a vital contribution to developing future first-line managers by affirming and strengthening family values. They also encouraged their pupils to recognise the connection between effort and gaining reward for achievement. Finally, the messy terrain of learning theory has been clarified, not as grand theory, but as mid-range theorising through a new conceptual framework. This schema synthesizes learning orientations with learning metaphors and learning viewed as a noun or a verb, and the various influences on learning from structure and agency. The four learning modes are adapt, assimilation, accommodation and aspire.
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Gleason, Kevin. "Experimental and Numerical Investigations of Microdroplet Evaporation with a Forced Pinned Contact Line." Honors in the Major Thesis, University of Central Florida, 2014. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/1590.
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Experimental and numerical investigations of water microdroplet evaporation on heated, laser patterned polymer substrates are reported. The study is focused on both (1) validating numerical models with experimental data, (2) identifying how changes in the contact line infuences evaporative heat transfer and (3) determining methods of controlling contact line dynamics during evaporation. Droplets are formed using a bottom-up methodology, where a computer-controlled syringe pump supplies water to a ~200[micro]m in diameter fluid channel within the heated substrate. This methodology facilitates precise control of the droplets growth rate, size, and inlet temperature. In addition to this microchannel supply line, the substrate surfaces are laser patterned with a moat-like trench around the fluid-channel outlet, adding additional control of the droplets contact line motion, area, and contact angle. In comparison to evaporation on non-patterned substrate surfaces, this method increases the contact line pinning time by ~60% of the droplets lifetime. The evaporation rates are compared to the predictions of a commonly reported model based on a solution of the Laplace equation, providing the local evaporation flux along the droplets liquid-vapor interface. The model consistently overpredicts the evaporation rate, which is presumable due to the models constant saturated vapor concentration along the droplets liquid-vapor interface. In result, a modified version of the model is implemented to account for variations in temperature along the liquid-vapor interface. A vapor concentration distribution is then imposed using this temperature distribution, increasing the accuracy of predicting the evaporation rate by ~7:7% and ~9:9% for heated polymer substrates at T[sub]s = 50[degrees]C‰ and 65‰[degrees]C, respectively.B.S.A.E.
Bachelors
Mechanical and Aerospace Engineering
Engineering and Computer Science
Aerospace Engineering
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Quintella, Marcelo Augusto 1973. "Numerical investigation of the heat flux singularity at an advancing molten contact line." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/80515.
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Febres, Soria Mijail. "Flow in the vicinity of a moving contact line : theoretical and numerical investigations." Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/19481/1/MFebres.pdf.
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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.
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Griffiths, Peter Robert. "Static and Dynamic Components of Droplet Friction." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4897.
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As digital microfluidics has continued to mature since its advent in the early 1980's, an increase in new and novel applications of this technology have been developed. However, even as this technology has become more common place, a consensus on the physics and force models of the motion of the contact line between the fluid, substrate, and ambient has not been reached. This uncertainty along with the dependence of the droplet geometry on the force to cause its motion has directed much of the research at specific geometries and droplet actuation methods.
The goal of this thesis is to help characterize the components of the friction force which opposes droplet motion as a one dimensional system model based upon simple system parameters independent from the actuation method. To this end, the force opposing the motion of a droplet under a thin rectangular glass cover slip was measured for varying cover slip dimensions (widths, length), gap height between the cover slip and substrate, and bulk droplet velocity. The stiffness of the droplet before droplet motion began, the force at which the motion initiated, and the steady-state force opposing the droplet motion were measured. The data was then correlated to hypothesized equations and compared to simple models accounting for the forces due to the contact angle hysteresis, contact line friction, and viscous losses.
It was found that the stiffness, breakaway force, and steady-state force of the droplet could be correlated to with an error standard deviation of 8 %, 14%, and 10 % respectively. Much of the error was due to an unexpected height dependence for the breakaway and steady-state forces and testing error associated with the velocity. The models for the stiffness and breakaway force over predicted the results by 36% and 16% respectively. During testing,
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stability issues with the cover slip were observed and simple dye testing was conducted to visualize the droplet flow field.
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Lopez-Juarez, Ismael. "On-line learning for robotic assembly using artificial neural networks and contact force sensing." Thesis, Nottingham Trent University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310849.
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Srirattayawong, Sutthinan. "CFD study of surface roughness effects on the thermo-elastohydrodynamic lubrication line contact problem." Thesis, University of Leicester, 2014. http://hdl.handle.net/2381/29057.
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This research investigates the effect of surface roughness on Thermo- Elastohydrodynamic Lubrication (TEHL) by Computational Fluid Dynamics (CFD). Traditionally, the Reynolds equation has been used to describe the flow of a lubricant for the TEHL problem, but this approach has some limitations. To overcome these, CFD is used in this research, as an alternative to solving the Reynolds equation. The commercial software packages ANSYS ICEM CFD 13.0 and ANSYS FLUENT 13.0 are employed to solve the Navier-Stokes equations. User-defined functions (UDFs) for the heat generated in the lubricant film, the density and the viscosity of lubricant, and the elastic deformation of the cylindrical roller bearing are created for this particular research. For viscosity, the lubricant is modelled as a non-Newtonian fluid based on the Ree-Eyring model. A number of CFD models are created under different conditions to predict the flow characteristics in the TEHL line contact problem, including the pressure distribution, the temperature distribution, the film thickness, and the friction coefficient. The effect of surface roughness is considered in the CFD models. The predicted results from the CFD models and the Reynolds equation are compared. The pressure distribution and the film thickness of both models are found to be in agreement. The simulation results show that the surface roughness affects significantly for the behaviour of fluid film lubrication problems, especially in the thin film case. It is found that the pressure profile at the centre of the contact area directly relates to the roughness amplitude. Furthermore, the CFD models can model the elastic deformation of cylinders of different materials, which is another advantage of the CFD approach over the Reynolds equation.
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Nold, Andreas. "From the nano- to the macroscale : bridging scales for the moving contact line problem." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/34933.
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The moving contact line problem is one of the main unsolved fundamental problems in fluid mechanics, with relevant physical phenomena spanning multiple scales, from the molecular to the macroscopic scale. In this thesis, at the macroscale, it is shown that classical asymptotic analysis is applicable at the moving contact line. This allows for a direct matching procedure between the inner (nanoscale) region and the outer (macroscale) region, therefore simplifying the analysis presented to date in the literature. At the mesoscale, a unified derivation for single and binary fluid diffuse interface models is presented, consolidating two models present in the literature. Results from an asymptotic analysis of the sharp interface limit of the binary fluid diffuse interface model are compared with numerical computations of the inner region in the vicinity of a moving contact line. Finally, the nanoscale structure of the density profile in the vicinity of the con- tact line is studied using density functional theory (DFT). At equilibrium, an effective disjoining pressure is extracted and results are compared with coarse-grained Hamiltonian theory. A derivation of Navier-Stokes like dynamic DFT equations is presented. Results for the moving contact line are compared with predictions from molecular kinetic theory. Computations for both DFT and diffuse interface approaches are performed using pseudospectral methods mapped to unbounded domains. The numerical scheme is presented, and the inclusion of hard-sphere effects via a fundamental measure theory is discussed.
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Le, Bars Theo. "Investigation of the behaviour of return collectors on Paris’ subway MP05 (Line 1)." Thesis, KTH, Järnvägsteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-159281.
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Return collectors are predominant organs for rubber-tyred subways to operatesince they ensure both the track circuit shunt and the traction current return. Po- sitioned at the interface between the track and the rolling stock, they are subjected to the disruptions linked to the train movement and the track irregularities. One of the most critical steps is the crossing of a switch nose.This study aims at determining the collector position during this crossing by means of a quasi-static analysis of the system. Two approaches are investigated. The first one brings into play a rigid contact and geometrical angles. It enables to model the crossing until the contact with the crossing nose. The diving capability of the collector is also taken into account. The second one is a standard approach of the contact. A slight penetration is considered, which allows to grasp the contact with the crossing nose. The second advantage is to prepare the ground for a complete dynamical analysis. Both approaches are then implemented on Matlab to solve the equations. Finally the study of the switch crossing in nominal conditionsand a parametric analysis are achieved for a specified switch.
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Gill, Harnavpreet Singh. "Computationally Robust Algorithms for Hypoid Gear Cutting and Contact Line Determination using Ease-Off Methodology." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1587499768039312.
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Babaie, Ashkan. "Flow physics during the drying of a thin polymer solution film near the contact line." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/54720.
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The drying process of a thin polymer solution film has been studied inside a micro-liter cavity near the contact line. Confocal microscopy along with particle image velocimetry and laser induced fluorescence are used for the real time measurement of velocity and concentration fields during the drying process.
In addition to the capillary flow and the Marangoni flow, the velocity field also reveals the possible existence of a single vortex and multiple vortices inside the creeping flow induced by evaporation. These vortices appear soon after the beginning of the evaporation process, their size shrinks over time, and they disappear before the end of the evaporation process. This thesis includes a study of the effect of rheological and geometrical parameters on the presence, size and endurance of these vortices.
Significant concentration heterogeneity is observed across the film during the drying process, in particular near the contact line. The concentration at the solution-air interface is higher compared to the bulk, and it increases towards the contact line and also over time. A skin layer starts forming as soon as the surface concentration reaches the glass transition concentration after which the evaporation rate starts decreasing. The drying film undergoes a similar concentration evolution during the evaporation process, regardless of the cavity depth and the initial polymer concentration; although, minor differences can be recognized that are associated with the flow recirculations that delay the concentration increase inside the vortex.
Finally, a theory is developed based on experimental data which explains the existence and behavior of viscous vortices near the bottom wall of the cavity. The competition between the capillary flow and the Marangoni flow results in flow separation on the bottom wall which leads to such vortices.
This study provides better understanding of the drying process of thin polymer solution films near the contact line. Furthermore, viscous flow separation adds to the current understanding of flow physics during the drying process, in addition to the well-known evaporation induced capillary transport and the Marangoni effect.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
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Herde, Daniel Verfasser], Martin [Akademischer Betreuer] Brinkmann, Marcus [Akademischer Betreuer] Müller, and Stephan [Akademischer Betreuer] [Herminghaus. "Contact Line Dynamics on Heterogeneous Substrates / Daniel Herde. Gutachter: Marcus Müller ; Stephan Herminghaus. Betreuer: Martin Brinkmann." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2014. http://d-nb.info/1050063783/34.
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Kim, Seong Jin. "Fluid Dynamics in Liquid Entry and Exit." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/88757.
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Interaction between a solid body and a liquid-air interface plays an important role in multiphase flows, which includes numerous engineering applications such as mineral flotation, dip coating operations, and air-to-sea and sea-to-air projectiles. It is also crucial in animal behaviors like the locomotion of water-walking animals, the plunge-diving of birds, and the jumping out of water of marine creatures. Depending on the moving direction of a solid, such diverse phenomena can be classified into two categories; liquid-entry and liquid-exit. Liquid-entry, or more widely called water-entry, is the behavior of a solid object entering liquid from air. The opposite case is referred to as liquid-exit.
Liquid-entry has been extensively studied, especially focusing on cavity formation and the estimation on capillary and hydrodynamic forces on a solid object. However, as the behavior of a triple contact line has not been understood on a sinking object, previous studies were limited to the special case of hydrophobic object to fix the contact line. Moreover, a more recent study pointed out the important role of contact line behavior to characterize the performance of film flotation, which is one of the direct applications of liquid-entry. However, there are no existing previous studies on the dynamics of the contact line on a sinking object. This subject will be first discussed in Chapter 2.
In Chapters 3 and 4, the topics related to liquid-exit will be discussed, where a solid sphere exits out of a liquid toward air with constant velocity, acceleration, or deceleration. Chapter 3 will focus on the penetration and bouncing behaviors of a solid sphere while impacting a liquid-air interface. The solid sphere experiences the resistance of surface tension and gravity while impacting the interface. Thus, liquid-exit spheres should have enough momentum to penetrate the interface to overcome these resistances, which indicates that the critical momentum exits. This understanding would give a mechanistic explanation as to why some aquatic species, especially plankton, are able to jump out of water while the others cannot despite their similar size. This study can help to understand the particle-bubble interaction for froth flotation applications, in which the particle tends to attach to the bubble.
In the last Chapter, the formation of a liquid column during the liquid-exit will be discussed. It has been observed that the evolution of a liquid column strongly depends on experimental conditions, especially the acceleration of a solid sphere. The pinch-off dynamics of a liquid column is categorized as two branches: upper and lower pinch-off's. The pinch-off location affects the entrained liquid volume adhered to the solid object, which is directly related to the uniform quality of a dip-coating operation. In addition to the pinch-off location and time in relation to the aforementioned experimental conditions will be discussed.
In summary, studies in the present dissertation are designed and performed to provide mechanistic insight to the problems in the liquid-entry and liquid-exit, which are all closely related to animal's daily life as well as engineering applications.PHD
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Tanaka, Yoshihisa. "Medial tilting of the joint line in posterior stabilized total knee arthroplasty increases contact force and stress." Kyoto University, 2019. http://hdl.handle.net/2433/242406.
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HOSHINO, MUNEMITSU, MUTSUSHI MATSUYAMA, OSAMU TAGUCHI, MORIAKI KUSAKABE, WORAWIDH WAJJWALKU, JIN LU, TOYOHARU YOKOI, et al. "Establishment and Characterization of Immortalized Non-Transplantable Mouse Mammary Cell Lines Cloned from a MMTV-induced Tumor Cell Line Cultured for A Long Duration." Nagoya University School of Medicine, 1991. http://hdl.handle.net/2237/17515.
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Emmett, Melissa Christine. "Crossing the line in cross-sex friendships effects of past sexual contact and dating status on relational maintenance /." Orlando, Fla. : University of Central Florida, 2008. http://purl.fcla.edu/fcla/etd/CFE0002070.
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Emmett, Melissa. "CROSSING THE LINE IN CROSS-SEX FRIENDSHIPS: EFFECTS OF PAST SEXUAL CONTACT AND DATING STATUS ON RELATIONAL MAINTENANCE." Master's thesis, University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2791.
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Given that male-female friendships lack institutional guidelines or scripts to guide everyday interactions, sustaining these relationships can be complicated. Although researchers have recently begun to study relational maintenance patterns in cross-sex friendships, no study has yet to investigate sex's and dating status's direct influences on friendship maintenance. This investigation seeks to add to the field's academic understanding of these personal relationships. Specifically, the researcher sought to uncover the associations between 10 friendship maintenance behaviors, past sexual contact, valence of past sexual contact, and cross-sex friends' dating statuses. Quantitative data were collected from 277 participants at a large Southeastern university using a survey methodology. Overall, results indicate that patterns of relational maintenance do differ as a function of friendship level, past sexual involvement, valence of past sexual involvement, and cross-sex friends' dating statuses. Past sexual involvement associates with higher levels of relationship talk, avoidance of negativity, and flirting. In addition, valence of past sexual activity varies across friendship level and associates with higher levels of positivity and flirting. Lastly, dating status significantly affects 3 of the 10 maintenance behaviors: routine contact and activity, flirting, and humor. Linear, quadratic, and cubic relationships were found for these variables, respectively. Implications of results, limitations, and recommendations for future research are discussed.M.A.
Nicholson School of Communication
Sciences
Communication MA
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Shi, Lei Photovoltaics & Renewable Energy Engineering Faculty of Engineering UNSW. "Contact resistance study on polycrystalline silicon thin-film solar cells on glass." Publisher:University of New South Wales. Photovoltaics & Renewable Energy Engineering, 2008. http://handle.unsw.edu.au/1959.4/41425.
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Thin-film solar cells are widely recognised to have the potential to compete with fossil fuels in the electricity market due to their low cost per peak Watt. The Thin-Film Group at the University of New South Wales (UNSW) is engaged in developing polycrystalline silicon (poly-Si) thin-film solar cells on glass using e-beam evaporation technology. We believe our solar cells have the potential of significantly lowering the manufacturing cost compared to conventional, PECVD-fabricated thin-film solar cells. After years of materials research, the focus of the Group??s work is now moving to the metallisation of evaporated solar cells. Minimising various kinds of losses is the main challenge of the cell metallisation procedure, within which the contact resistance is always a big issue. In this thesis, the contact resistance of aluminium contacts on poly-Si thin-film solar cells on glass is investigated. To the best of the author??s knowledge, this is the first ever contact resistance investigation of Al contacts on evaporated poly-Si material for photovoltaic applications. Various transmission line models (TLM) are employed to measure the contact resistance. An improved TLM model is developed to increase the measurement precision and, simultaneously, to simplify the TLM pattern fabrication process. In order to accommodate the particular requirements of poly-Si coated glass substrates, a TLM pattern fabrication process using photolithography is established. Furthermore, a Kelvin sense tester is set up to ensure an accurate measurement of the contact resistance. After establishment of the TLM technique at UNSW, it is successfully tested on singlecrystalline silicon wafer samples. The thermal annealing process of the contacts is also optimised. Then, the general behaviour of Al contacts on uniformly doped poly-Si films (i.e., no p-n junction) is investigated using the verified TLM technique. The long-term stability of the contacts is also studied. This is followed by an investigation of the contact resistance of the back surface field and emitter layers of different types of poly-Si thin-film solar cells. Finally, a novel contact resistance measurement model is proposed that is believed to be able to overcome the measurement bottleneck of the transmission line models.
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Ngan, Choi-chik, and 顔才績. "A hidden Markov model approach to force-based contact recognition for intelligent robotic assembly." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31243496.
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Tachon, Loïc. "Développement d'outils numériques et expérimentaux dédiés à l'étude de l'évaporation en présence de ligne triple." Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10027/document.
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Les travaux réalisés au cours de cette thèse visent à apporter une aide à la compréhension des mécanismes régissant l'évaporation des films liquides. La physique des problèmes à changement de phase avec ligne de contact est gouvernée par des mécanismes agissant au niveau de ces dernières ainsi qu'au niveau des interfaces gaz-liquide. La description géométrique des interfaces est donc un point clef dans cette étude tant d'un point de vue numérique qu'expérimental. Un outil numérique tridimensionnel de suivi d'interface infiniment fine a été créé afin d'anticiper la simulation numérique de ces problèmes. Cet algorithme repose sur une description quadratique de l'interface qui est une surface du maillage. L’ordre de convergence de cette méthode relatif à différentes caractéristiques (courbure, normale, position) de l'interface ainsi que sa qualité conservative ont été étudiés.Parallèlement à cette approche numérique, une technique expérimentale d'inversion optique a été développée. Celle-ci permet la mesure dynamique du profil d'une interface au voisinage de la ligne de contact dans le cadre de fluide très mouillant. Cette méthode, appliquée dans le cadre d'un problème de film en évaporation quasi axisymétrique a permis, dans le cadre d'une expérience simple, une première quantification des flux de chaleur et de masse échangés au niveau de la ligne de contactThe tasks fulfilled during this study aim at providing tools for understanding the mechanisms of liquid film evaporation. Evaporation in the presence of a triple lines is ruled by physical mechanisms acting on these singularities as well as on the gas liquid interfaces. Thus, the interface description, under it numerical as experimental aspects, is a key point of this study. A numerical tridimentionnal sharp interface tracking tool has been developed to be used in further numerical simulation of the evaporation problem. In this algorithm, the interface is described as a quadratic grid surface. Its convergence orders relatively to geometrical parameters of the interface (curvature, normal, position) has been studied.In the mean time, an experimental optical inversion technique has been developed and validated. It allows a dynamic measurement of the interface shape in the vicinity of the triple line of highly wetting fluid. This method has been applied to the case of a quasi axisymetric evaporating film and provides a first quantification of the heat and mass transfers generated by the triple line region
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Hemingway, Ewan John. "Internally and externally driven flows of complex fluids : viscoelastic active matter, flows in porous media and contact line dynamics." Thesis, Durham University, 2015. http://etheses.dur.ac.uk/11310/.
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We consider three varied soft matter topics from a continuum fluid mechanics perspective, namely: viscoelastic active matter, viscoelastic flows in porous media, and contact line dynamics. Active matter. For the purposes of this thesis, the term active matter describes a collection of active particles which absorb energy from their local environment or from an internal fuel tank and dissipate it to the surrounding fluid. We explore the stability and dynamics of active matter in a biological context in the presence of a polymeric background fluid. Using a novel coarse-grained model, we generalise earlier linear stability analyses (without polymer) and demonstrate that the bulk orientationally ordered phase remains intrinsically unstable to spontaneous flow instabilities. This instability remains even as one takes an ’elastomeric limit’ in which the polymer relaxation time τC → ∞. The 1D nonlinear dynamics in this limit are oscillatory on a timescale set by the rate of active forcing. Then, by considering the rheological response of our model under shear, we explore the mechanism behind the above generic flow instability, which we show exists not only for orientationally ordered phases but also for disordered states deep in the isotropic phase. Our linear stability analysis in 1D for sheared suspensions predicts that initially homogeneous states represented by negatively sloping regions of the constitutive curve are unstable to shear-banding flow instabilities. In some cases, the shear-bands themselves are unstable which leads to a secondary instability that produces rheochaotic flow states. Consistent with recent experiments on active cellular extracts (without applied shear) which show apparently chaotic flow states, we find that the dynamics of active matter are significantly more complex in 2D. Focusing on the turbulent phase that occurs when the activity ζ (or energy input) is large, we show that the characteristic lengthscale of structure in the fluid l∗ scales as l∗ ∝ 1/ √ζ. While this lengthscale decreases with ζ, it also increases with the polymer relaxation time. This can produce a novel ‘drag reduction’ effect in confined geometries where the system forms more coherent flow states, characterised by net material transport. In the elastomeric limit spontaneous flows may still occur, though these appear to be transient in nature. Examples of exotic states that arise when the polymer is strongly coupled to the active particles are also given. Flows in porous media. The second topic treats viscoelastic flows in porous media, which we approximate numerically using geometries consisting of periodic arrays of cylinders. Experimentally, the normalised drag χ (i.e., the ratio of the pressure drop to the flow rate) is observed to undergo a large increase as the Weissenberg number We (which describes the ratio of the polymer relaxation time to the characteristic velocity-gradient timescale) is increased. An analysis of steady flow in the Newtonian limit identifies regions dominated by shear and extension; these are mapped to the rheological behaviour of several popular models for polymer viscoelasticity in simple viscometric protocols, allowing us to study and influence the upturn in the drag. We also attempt to reproduce a recent study in the literature which reported fluctuations for cylinders confined to a channel at high We. At low numerical resolution, we observe fluctuations which increase in magnitude with the same scaling observed in that study. However, these disappear at very high resolutions, suggesting that numerical convergence was not properly obtained by the earlier authors. Contact line dynamics. We finish by investigating the dynamics of the contact line, i.e., the point at which a fluid-fluid interface meets a solid surface, under an externally applied shear flow. The contact line moves relative to the wall, apparently contradicting the conventional no-slip boundary conditions employed in continuum fluid dynamics. A mechanism where material is transported within a ‘slip region’ via diffusive processes resolves this paradox, though the question of how the size of this region (i.e., slip length ξ) scales with fluid properties such as the viscosity η and the width of the interface between phases l, remains disputed within the literature. We reconcile two apparently contradictory scalings, which are shown to describe different limits: (a) a diffuse interface limit where ξ/l is small and (b) a sharp interface limit for large ξ/l. We demonstrate that the physics of the latter (which more closely resembles real fluids in macroscopic experimental geometries) can be captured using simulations in the former regime (which are numerically more accessible).
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Douglas, Zachary W. "Acoustically Enhanced Boiling Heat Transfer." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16325.
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An acoustic field is used to increase the critical heat flux of a copper boiling heat transfer surface. The increase is a result of the acoustic effects on the vapor bubbles. Experiments are being performed to explore the effects of an acoustic field on vapor bubbles in the vicinity of a rigid heated wall. Work includes the construction of a novel heater used to produce a single vapor bubble of a prescribed size and at a prescribed location on a flat boiling surface for better study of an individual vapor bubble s reaction to the acoustic field. Work also includes application of the results from the single bubble heater to a calibrated copper heater used for quantifying the improvements in critical heat flux.
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Herbaut, Rémy. "Dynamique des liquides sur substrat froid, avec solidification." Thesis, Sorbonne Paris Cité, 2019. http://www.theses.fr/2019USPCC006.
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Nous étudions l’étalement de liquides sur une surface froide, avec solidification. L’application visée est le secteur aéronautique qui est confronté à des problèmes de givrage lorsque l’avion est au sol. Le dégivrage s’effectue actuellement par un jet d’éthylène glycol, qui contribue à un surcoût pour les compagnies et une pollution non négligeable. Nos objectifs portent tout d’abord sur des questions fondamentales d’étalement d’une goutte sur un substrat à une température inférieure à la température de solidification. Sur une surface donnée, est-on capable de prédire si la goutte se solidifie ou s’étale dès son impact ? Quelles sont les formes prises par celle-ci, avant, pendant et après la solidification? Quel est le mécanisme de solidification et son influence sur la dynamique d’étalement ? Quel sont les paramètres qui contrôlent la dynamique des processus mis en jeu ? Plusieurs dispositifs et modélisations seront mis en œuvre en vue d’apporter des éléments de réponses à ces questions. Nos objectifs portent aussi sur des stratégies en vue d’éviter la congélation des gouttes et leur permettre de glisser avant leur congélation. La mise en oscillation d’une goutte ou le greffage de polymère en vue modifier l’état de surface seront également envisagés. Cette thèse tente d’apporter quelques éléments de compréhension nouveaux en se concentrant sur deux types d’écoulements très différent. Premièrement, l’avancée d’une ligne de contact en présence de solidification. Deuxièmement, la croissance d’une goutte solide sous alimentation continue en liquideWe study the liquids spreading on cold substrate, with solidification. The intended application is the aeronautical sector, which faces icing problems when the aircraft is on the ground. The deicing is currently carried out by an ethylene glycol jet, which contributes to an additional cost for the companies and a significant pollution. Our objectives focus on fundamental issues of spreading a drop on a substrate at a temperature below the solidification temperature. On a given surface, is it possible to predict whether the drop solidifies or spreads as soon as it is impacted ? What are the forms taken by it, before, during and after solidification? What is the solidification mechanism and its influence on the spreading dynamics? What are the parameters that control the dynamics of the processes involved ? Several devices and models will be implemented to provide some answers to these questions. Our goals also include strategies to avoid freezing drops and allowing them to slide before freezing. Oscillation of a droplet or grafting of polymer to modify the surface condition will also be considered. This thesis attempts to bring some new elements of understanding by focusing on two very different types of flows. First, the advance of a line of contact in the presence of solidification. Second, the growth of a solid drop under continuous liquid feed
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Orellana, Sebastian. "Développement et amélioration de structures mobiles embarquées dans les interconnexions des puces microélectroniques : Etude du contact mécanique et électrique." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEM070/document.
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Ces dernières années la miniaturisation des microsystèmes atteint la limite physique de leur développement. Ainsi une de voie d’innovation dans l’industrie des semiconducteurs est l’intégration des fonctionnalités supplémentaires au sein des composants déjà existants.Le projet consiste à intégrer, dans une même couche métallique d’interconnexion CMOS, un MEMS capable, par sa rotation, d’établir un contact électrique.Les verrous se situent dans la libération des parties mobiles par dissolution de l’oxyde environnant (déformation hors plan sous l’effet des contraintes résiduelles, stiction, présence de résidus qui empêchent le contact), dans l’actionnement (densité de courant, répétabilité, durabilité, fiabilité) ainsi que, la capacité d’établir un vrai contact électrique à faible résistance (aire réelle / apparente du contact des surfaces rugueuses, pollution du contact).Le travail réalisé a porté sur la conception, le design et la simulation des microsystèmes afin de surmonter ces difficultés et / ou d’étudier le comportement et mesurer les effetsIn recent years the miniaturization of microsystems is reaching the physical limit of its development. Thus, a path of innovation in the semiconductor industry is additional functionalities in existing components.The project consists to integrate a MEMS, within the same metal interconnect of CMOS layer which, by rotating, can establish an electrical contact.The obstacles are in the release of the moving parts by dissolution of the surrounding oxide (out of plane deformation under the effect of residual stress, stiction, residues which prevent contact), in the actuation (current density repeatability, durability, reliability) and, for ohmic switches, the ability to establish a real electrical contact with low resistance (real / apparent area of contact with rough surfaces, contact pollution).The work carried out has focused on conception (design) and simulation of microsystems to overcome these difficulties and / or to study the behavior and measure the effects
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Paudel, Bhim L. "Magnetotransport in GaMnAs Based Microstructures." Miami University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=miami1331927548.
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Sheldon, Kerry. "The On-Line Paedophile : A Comparison of the Demographic, Social, Criminal and Psychological Characteristics of Internet, Contact and Mixed Sexual Offenders." Thesis, Loughborough University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.517160.
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Sagan, Michael Sébastien. "Simulation numérique directe et étude expérimentale de l'ébullition nucléée en microgravité : application aux réservoirs des moteurs d'Ariane V." Thesis, Toulouse, INPT, 2013. http://www.theses.fr/2013INPT0128/document.
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Ce travail de thèse porte sur l’étude, numérique et expérimentale, des mécanismes physiques intervenant lors de l’ébullition nucléée. L’étude numérique a été conduite avec un code de simulation numérique directe utilisant une méthode "level set". Cette méthode a été évaluée à travers la simulation de la croissance de bulles dans un liquide surchauffé et de bons accords ont été observés entre nos simulations et les résultats théoriques. Puis, des modèles ont été intégrés à l’outil numérique, afin de simuler la dynamique de la ligne de contact sans changement de phase. Par la suite, ces modèles ont été validés lors de la simulation de cas tests d’étalement de gouttes sur une plaque. Enfin, des simulations de croissance de bulles sur paroi ont été réalisées en considérant le flux provenant de la micro-couche. Parallèlement, une étude sur l’ébullition nucléée, en l’absence de gaz incondensables, a été conduite en microgravité, à l’aide d’une expérience en fusée sonde : SOURCE 2. Une analyse comparative a été menée sur les échanges thermiques obtenus en 1G et en 0G. Puis, l’influence de la configuration de l’ébullition sur les transferts thermiques, en microgravité, a été étudiée. Enfin, l’outil numérique a été utilisé afin de simuler un cas test défini à partir d’une séquence de l’expérience menée en microgravité. Nous avons simulé le remplissage et la pressurisation de la cellule d’essai et un bon accord a été obtenu entre les résultats numériques et les données expérimentalesIn this work, we study different phenomena that occur during nucleate boiling. Firstly, we numerically investigate nucleate boiling by using two phase flow direct numerical simulation based on a level set / Ghost Fluid method. Nucleate boiling on a plate is not only a thermal issue, but also involves multiphase dynamics issues at different scales and at different stages of bubble growth. As a consequence, we divide the whole problem and investigate separately the different phenomena considering their nature and the scale at which they occur. First we analyse the boiling of a static bubble immersed in an overheated liquid. Then, we implement a method that makes it possible to take into account the contact angle hysteresis model. Finally, considering the evaporation of the micro-layer, we perform simulations of bubble growth on a plate. Besides, an experimental study has been performed in the framework of a sounding rocket experiment : SOURCE 2, driven by ESA (European Spatial Agency) in which several partners are involved. For SOURCE 2, a single species configuration is used. No desorption and no thermo-capillary convection occur, the change in the bubble size is only due to vaporisation. Using this device, a comparison between heat transfer on ground and heat transfer in microgravity was performed and the influence of boiling configuration on heat transfer was studied. Finally a sequence of the experiment on the sounding rocket has been numerically simulated. It concerns the filling and the pressurisation of a small reservoir in microgravity. A good agreement was obtained between the simulations and the experimental results
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Delannoy, Joachim. "Les surprises de la montée capillaire." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS484.
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La montée capillaire est l'une des illustrations les plus remarquables des effets de la tension superficielle. L'expérience consiste à placer un tube de petit diamètre au contact d'un liquide mouillant. Le liquide monte alors spontanément à l'intérieur du tube jusqu'à une hauteur qui peut atteindre plusieurs centimètres. En partant de cette expérience historique, nous extrayons des phénomènes nouveaux : (1) la dissipation au niveau de la ligne de contact, à l'origine d'une vitesse de montée constante à temps court, (2) la descente capillaire dans des milieux aérophiles qui donne lieu à de nouvelles dynamiques et (3) l'imprégnation capillaire dans des milieux complexes que nous illustrons par une montée capillaire dans des languettes flexibles copiées sur la langue du colibri. Ces trois grands axes d'études sont déclinés en sept chapitres dans lesquels nous étudions, expérimentalement et théoriquement, ces nouveaux phénomènes d'imprégnation capillaireWhen contacting a wetting liquid with a narrow tube, a meniscus forms and rises spontaneously, progressing up to several centimetres. This remarkable illustration of surface tension is known as capillary rise. After more than three centuries of studies, capillary rise is now well apprehended and is often seen as a model experiment to study the impregnation of liquids in confined media. Despite its apparent simplicity, capillary rise still preserve a few mysteries that are studied in this manuscript: (1) the viscous dissipation near the contact line, responsible for a constant velocity dynamics at short time of a capillary rise, (2) a capillary descent observed in aerophilic tubes showing unexplored dynamics and (3) capillary impregnation in complex media, as illustrated by the rise of a liquid in deformable stripes inspired by hummingbird tongues. These three topics are investigated along seven chapters as we explore (experimentally and theoretically) new aspects of liquid impregnation in confined media
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Furuyama, Hiroaki. "ROLE OF E-CADHERIN IN PERITONEAL DISSEMINATION OF THE PANCREATIC CANCER CELL LINE PANC-1, THROUGH REGULATION OF CELL TO CELL CONTACT." Kyoto University, 2001. http://hdl.handle.net/2433/150167.
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Clavijo, Angeles Cristian Esteban. "Droplet Impingement on Superhydrophobic Surfaces." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/6306.
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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.