To see the other types of publications on this topic, follow the link: Viscoelastic fluid.
Dissertations / Theses on the topic 'Viscoelastic fluid'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Viscoelastic fluid.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Sibley, David N. "Viscoelastic flows of PTT fluid." Thesis, University of Bath, 2010. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.518114.
Full text
2
Johnson, Mitchell A. "Viscoelastic Roll Coating Flows." Fogler Library, University of Maine, 2003. http://www.library.umaine.edu/theses/pdf/JohnsonMA2003.pdf.
Full text
3
DI, IORIO ELENA. "Splash singularities for viscoelastic fluid models." Doctoral thesis, Gran Sasso Science Institute, 2018. http://hdl.handle.net/20.500.12571/9689.
Full text
4
Vallejo, Juan Pablo Aguayo. "Prediction of viscoelastic fluid flow in contractions." Thesis, Swansea University, 2006. https://cronfa.swan.ac.uk/Record/cronfa42918.
Full text
5
Meng, Sha. "A spectral element method for viscoelastic fluid flow." Thesis, De Montfort University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369907.
Full text
6
RACHID, FELIPE BASTOS DE FREITAS. "TRANSIENTS IN FLUID AND STRUCTURE IN VISCOELASTIC TUBES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1989. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33257@1.
Full textAbstract:
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORNeste trabalho, a interação fluido-estrutura é analisada em sistemas de tubulações transportando líquidos, considerando-se que o material dos tubos apresenta comportamento mecânico linear viscoelástico. São investigados, teoricamente, os efeitos do movimento da tubulação nas respostas transientes de pressão no líquido e tensão na estrutura quando se induz, através do fechamento rápido de válvulas ou ação de uma força de impacto sobre a tubulação, um estado de desequilíbrio no sistema. Na análise, considera-se o processo de propagação de ondas nas paredes da tubulação em consequência de esforços hidrodinâmicos localizados, assim como devido ao efeito Poisson. As equações que descrevem a dinâmica do movimento do líquido e do tubo são acopladas e resolvidas numericamente através do método das características. Os resultados obtidos para alguns sistemas de tubulação são comparados com o caso em que o tubo exibe resposta elástica e com resultados experimentais disponíveis na literatura. Os resultados indicam que o movimento estrutural pode induzir pressões e tensões mais elevadas que aquelas previstas pela análise clássica não acoplada, particularmente no início do regime transiente, antes que a víscoelasticidade do material do tubo atenue as respostas do sistema. Contudo, o acréscimo observado nas pressões e tensões devido ao movimento estrutura não é tão significativo em tubulações viscoelásticas quanto em elásticas.
In the present work the fluid-structure interaction is analysed for compliant piping systems by assuming a linear viscoelastic behavior of the pipe material. The effects of pipe motion on transient responses of liquid pressure and pipe stresses are theoretically investigated when the system is disturbed in some fashion such as rapid valve closure and an external impact load. In this analysis it is considered the wave propagation process in the pipe wall due to localized hidrodynamics efforts and the Poisson effect. The set of equations describing the dynamics of the liquid and pipe wall are coupled and solved numerically by means of the method of characteristics. The results obtained for some piping systems are compared with those observed for elastic pipe material and with experiments available in the literature. The results indicate that the structural motion can produce pressures and stresses higher than those predicted by the classical, uncoupled, waterhammer analysis, particularly at the begining of the transient, before pipe material viscoelasticity damps the system responses. However, the increase observed on pressures and stresses due to structural motion is not as significant for a viscoelastic pipeline as it is for an elastic pipe.
7
Götz, Dario [Verfasser]. "Three topics in fluid dynamics: Viscoelastic, generalized Newtonian, and compressible fluids / Dario Götz." München : Verlag Dr. Hut, 2012. http://d-nb.info/1029400113/34.
Full text
8
Zhang, Xueyan. "Mechanics of viscoelastic mud under water waves." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B36710003.
Full text
9
Zhang, Xueyan, and 張雪岩. "Mechanics of viscoelastic mud under water waves." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B36710003.
Full textAbstract:
The Best M.Phil Thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing Prize,2005-2006published_or_final_version
abstract
Mechanical Engineering
Master
Master of Philosophy
10
Budu, Paula. "Conditional and unconditional nonlinear stability in fluid dynamics." Thesis, Durham University, 2002. http://etheses.dur.ac.uk/3938/.
Full textAbstract:
In this thesis we examine some of the interesting aspects of stability for some convection problems. Specifically, the first part of the thesis deals with the Bénard problem for various Non-Newtonian fluids, whereas the second part develops a stability analysis for convection in a porous medium. The work on stability for viscoelastic fluids includes nonlinear stability analyses for the second grade fluid, the generalised second grade fluid, the fluid of dipolar type and the fluid of third grade. It is worth remarking that throughout the work the viscosity is supposed to be any given function of temperature, with the first derivative bounded above by a positive constant. The connection between the two parts of the thesis is made through the method used to approach the nonlinear stability analysis, namely the energy method. It is shown in the introductory chapter how this method works and what are its advantages over the linear analysis. Nonlinear stability results established in both Part I and Part II are the best one can get for the considered physical situations. Different choices of energy have been considered in order to achieve conditional or unconditional nonlinear stability results.
11
Yi, Wei. "Cartesian grid methods for viscoelastic fluid flow in complex geometry." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/cartesian-grid-methods-for-viscoelastic-fluid-flow-in-complex-geometry(57b59bc9-4dc8-4698-a945-fc170c8e56e0).html.
Full textAbstract:
Viscoelastic fluid flow with immersed boundaries of complex geometry is widely found both in nature and engineering processes. Examples include haemocytes moving in human blood flow, self-propulsion of microscopic organisms in complex liquids, hydraulic fracturing with sand in oil flow, and suspension flow with viscoelastic medium. Computational modelling of such systems is important for understanding complex biological processes and assisting engineering designs. Conventional simulation methods use conformed meshes to resolve the boundaries of complex geometry. Dynamically updating the conformed mesh is computationally expensive and makes parallelization difficult. In comparison, Cartesian grid methods are more promising for large scale parallel simulation. Using Cartesian grid methods to simulate viscoelastic fluid flow with complex boundaries is a relatively unexplored area. In this thesis, a sharp interface Cartesian grid method (SICG) and a smoothed interface immersed boundary method (SIIB) are developed in order to simulate viscoelastic fluids in complex geometries. The SICG method shows a better prediction of the stress on stationary boundaries while the SIIB method shows reduced non-physical oscillations in the computation of drag and lift forces on moving boundaries. Parallel implementations of both solvers are developed. Convergence of the numerical schemes is shown and the implementations are validated with a few benchmark problems with both stationary and moving boundaries. This study also focuses on the simulation of flows past 2D cylindrical or 3D spherical particles. Lateral migration of particles induced by inertial and viscoelastic effects are investigated with different flow types. Equilibrium positions of inertia-induced migration are reported as a function of the particle Reynolds number and the blockage ratio. The migration in the viscoelastic fluid is simulated from zero elastic number to a finite elastic number. The inclusion of both inertial and viscoelastic effects on the lateral migration of a particle is the first of its kind. New findings are reported for the equilibrium positions of a spherical particle in square duct flow, which suggest the need for future experimental and computational work.
12
Sachsenheimer, Dirk [Verfasser], and N. [Akademischer Betreuer] Willenbacher. "Capillary thinning of viscoelastic fluid filaments / Dirk Sachsenheimer. Betreuer: N. Willenbacher." Karlsruhe : KIT-Bibliothek, 2014. http://d-nb.info/1064504191/34.
Full text
13
Sakatani, Yuho. "Relativistic viscoelastic fluid mechanics and the entropic formulation of continuum mechanics." 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/157762.
Full text
14
Jiao, Li-Fang. "A STUDY ON MICROBUBBLE FLOW BEHAVIORS IN SURFACTANT VISCOELASTIC FLUID FLOW." 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/174931.
Full text
15
Howell, Jason S. "Numerical approximation of shear-thinning and Johnson-Segalman viscoelastic fluid flows." Connect to this title online, 2007. http://etd.lib.clemson.edu/documents/1193079507/.
Full text
16
Yoon, Sungho. "An adaptive finite element method for particle suspension in viscoelastic fluid." Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.530812.
Full text
17
Ullah, Tania. "Modeling a two-link rigid swimmer scalloping in linear viscoelastic fluid." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40938.
Full textAbstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 44).
In his renowned lecture on Life at low Reynolds number, E.M. Purcell established that a rigid swimmer comprised of two links cannot swim in a viscous Newtonian fluid due to the reciprocal nature of its movements. Viscoelastic fluid, on the other hand, has a characteristic time scale associated with stress relaxation and can impart asymmetrical stresses on the body of a swimmer to propel it forward. This work focuses on developing a theoretical model for the fluid-structure interactions that influence the swimming of a two-link specimen in viscoelastic fluid. Because the oscillation of the slender rods that comprise the links of the swimmer elicit a response from the surrounding fluid at various frequencies, the modeling consisted of a complex Fourier analysis. This paper discusses in detail the physics of the specimen's swimming and the equations that govern its movement in the fluid. The work done has been purely theoretical; however, a numerical simulation to validate the theory will be conducted as future work.
by Tania Ullah.
S.B.
18
Mavi, Anele. "Computational analysis of viscoelastic fluid dynamics with applications to heat exchangers." Master's thesis, Faculty of Science, 2019. http://hdl.handle.net/11427/30078.
Full textAbstract:
In this study, the computational analysis of a pressure driven viscoelastic fluid in a double pipe heat exchanger set-up is investigated. Non-Newtonian viscoelastic fluids in heat exchanger arrangements are encountered in various industrial applications such as power generation, refrigeration and in the food processing industry where the need for cooling and heating of liquids is required. The model problem is governed by complex, non-linear and coupled partial differential equations. These are solved using the semi-implicit finite difference method integrated with the Crank-Nicolson scheme. The pressure-velocity coupling in the momentum equations is resolved by employing the Semi-Implicit Method for Pressure Linked Equations (SIMPLE). To cope with numerical diffusion and numerical stability issues the treatment of convective terms using the upwind schemes is explored. In this work, the behaviour of viscoelastic fluids is rigorously examined by analysing the convective heat transfer from the viscoelastic core fluid of the double pipe heat exchanger to the Newtonian or viscoelastic shell fluid in the outer annulus. In addition, the effects of pressure, momentum, extra stresses, temperature, viscosity and relaxation time on the fluid temperature are investigated; both in the counter flow and parallel flow configurations. Graphical computational results are presented and discussed quantitatively and qualitatively with respect to several parameters involved in the problem.
19
Castillo, del Barrio Ernesto. "Stabilized finite element formulations for the three-field viscoelastic fluid flow problem." Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/392717.
Full textAbstract:
The Finite Element Method (FEM) is a powerful numerical tool, that permits the resolution of problems defined by partial differential equations, very often employed to deal with the numerical simulation of multiphysics problems. In this work, we use it to approximate numerically the viscoelastic fluid flow problem, which involves the resolution of the standard Navier-Stokes equations for velocity and pressure, and another tensorial reactive-convective constitutive equation for the elastic part of the stress, that describes the viscoelastic nature of the fluid.
The three-field (velocity-pressure-stress) mixed formulation of the incompressible Navier-Stokes problem, either in the elastic and in the non-elastic case, can lead to two different types of numerical instabilities. The first is associated with the incompressibility and loss of stability of the stress field, and the second with the dominant convection. The first type of instabilities can be overcome by choosing an interpolation for the unknowns that satisfies the two inf-sup conditions that restrict the mixed problem, whereas the dominant convection requires a stabilized formulation in any case. In this work, different stabilized schemes of the Sub-Grid-Scale (SGS) type are proposed to solve the three-field problem, first for quasi Newtonian fluids and then for solving the viscoelastic case.
The proposed methods allow one to use equal interpolation for the problem unknowns and to stabilize dominant convective terms both in the momentum and in the constitutive equation. Starting from a residual based formulation used in the quasi-Newtonian case, a non-residual based formulation is proposed in the viscoelastic case which is shown to have superior behavior when there are numerical or geometrical singularities. The stabilized finite element formulations presented in the work yield a global stable solution, however, if the solution presents very high gradients, local oscillations may still remain.
In order to alleviate these local instabilities, a general discontinuity-capturing technique for the elastic stress is also proposed.
The monolithic resolution of the three-field viscoelastic problem could be extremely expensive computationally, particularly, in the threedimensional case with ten degrees of freedom per node. A fractional step approach motivated in the classical pressure segregation algorithms used in the two-field Navier-Stokes problem is presented in the work.The algorithms designed allow one the resolution of the system of equations that define the problem in a fully decoupled manner, reducing in this way the CPU time and memory requirements with respect to the monolithic case.
The numerical simulation of moving interfaces involved in two-fluid flow problems is an important topic in many industrial processes and physical situations. If we solve the problem using a fixed mesh approach, when the interface between both fluids cuts an element, the discontinuity in the material properties leads to discontinuities in the gradients of the unknowns which cannot be captured using a standard finite element interpolation. The method presented in this work features a local enrichment for the pressure unknowns which allows one to capture pressure gradient discontinuities in fluids presenting different density values.
The stability and convergence of the non-residual formulation used for viscoelastic fluids is analyzed in the last part of the work, for a linearized stationary case of the Oseen type and for the semi-discrete time dependent non-linear case. In both cases, it is shown that the formulation is stable and optimally convergent under suitable regularity assumptions.El Método de los Elementos Finitos (MEF) es una herramienta numérica de gran alcance, que permite la resolución de problemas definidos por ecuaciones diferenciales parciales, comúnmente utilizado para llevar a cabo simulaciones numéricas de problemas de multifísica. En este trabajo, se utiliza para aproximar numéricamente el problema del flujo de fluidos viscoelásticos, el cual requiere la resolución de las ecuaciones básicas de Navier-Stokes y otra ecuación adicional constitutiva tensorial de tipo reactiva-convectiva, que describe la naturaleza viscoelástica del fluido. La formulación mixta de tres campos (velocidad-presión-tensión) del problema de Navier-Stokes, tanto en el caso elástico como en el no-elástico, puede conducir a dos tipos de inestabilidades numéricas. El primer grupo, se asocia con la incompresibilidad del fluido y la pérdida de estabilidad del campo de tensiones, y el segundo con la convección dominante. El primer tipo de inestabilidades, se puede solucionar eligiendo un tipo de interpolación entre las incógnitas que satisfaga las dos condiciones inf-sup que restringen el problema mixto, mientras que la convección dominante requiere del uso de formulaciones estabilizadas en cualquier caso. En el trabajo, se proponen diferentes esquemas estabilizados del tipo SGS (Sub-Grid-Scales) para resolver el problema de tres campos, primero para fluidos del tipo cuasi-newtonianos y luego para resolver el caso viscoelástico. Los métodos estabilizados propuestos permiten el uso de igual interpolación entre las incógnitas del problema y estabilizan la convección dominante, tanto en la ecuación de momento como en la ecuación constitutiva. Comenzando desde una formulación de tipo residual usada en el caso cuasi-newtoniano, se propone una formulación no-residual para el caso viscoelástico que muestra un comportamiento superior en presencia de singularidades numéricas y geométricas. En general, una formulación estabilizada produce una solución estable global, sin embargo, si la solución presenta gradientes elevados, oscilaciones locales se pueden mantener. Con el objetivo de aliviar este tipo de inestabilidades locales, se propone adicionalmente una técnica general de captura de discontinuidades para la tensión elástica. La resolución monolítica del problema de tres campos viscoelástico puede llegar a ser extremadamente costosa computacionalmente, sobre todo, en el caso tridimensional donde se tienen diez grados de libertad por nodo. Un enfoque de paso fraccionado motivado en los algorítmos clásicos de segregación de la presión usados en el caso del problema de dos campos de Navier-Stokes, se presenta en el trabajo, el cual permite la resolución del sistema de ecuaciones que definen el problema de una manera completamente desacoplada, lo que reduce los tiempos de cálculo y los requerimientos de memoria, respecto al caso monolítico. La simulación numérica de interfaces móviles que envuelve los problemas de dos fluidos, es un tópico importante en un gran número de procesos industriales y situaciones físicas. Si se resuelve el problema utilizando un enfoque de mallas fijas, cuando la interfaz que separa los dos fluidos corta un elemento, la discontinuidad en las propiedades materiales da lugar a discontinuidades en los gradientes de las incógnitas que no pueden ser capturados utilizando una formulación estándar de interpolación. Un enriquecimiento local para la presión se presenta en el trabajo, el cual permite la captura de gradientes discontinuos en la presión, asociados a fluidos de diferentes densidades. La estabilidad y la convergencia de la formulación no-residual utilizada para fluidos viscoelásticos es analizada en la última parte del trabajo, para un caso linealizado estacionario del tipo Oseen y para un problema transitorio no-lineal semi-discreto. En ambos casos, se logra mostrar que la formulación es estable y de convergencia óptima bajo supuestos de regularidad adecuados.
20
Gerritsma, Marcus Iwan. "Time dependent numerical simulations of a viscoelastic fluid on a staggered grid." [S.l. : [Groningen] : s.n.] ; [University Library Groningen] [Host], 1996. http://irs.ub.rug.nl/ppn/148605494.
Full text
21
Szady, Michael Joseph. "Finite element methods for the time dependent simulation of viscoelastic fluid flows." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10914.
Full text
22
Xue, Shicheng. "Three dimensional finite volume modelling and numerical simulations of viscoelastic fluid flows." Thesis, The University of Sydney, 1997. https://hdl.handle.net/2123/27634.
Full textAbstract:
This study focuses on developing an efficient, fully three dimensional Finite Volume Method for viscoelastic fluid flow problems, and on numerical investigations of some complex rheological phenomena.
23
Ban, Mohammad Javad. "Numerical study of filament-stretching and step-strain in viscoelastic fluid flows." Thesis, Swansea University, 2007. https://cronfa.swan.ac.uk/Record/cronfa42333.
Full textAbstract:
This thesis is concerned with the numerical prediction of two-dimensional viscoelastic filaments under stretching and step-strain within cylindrical-like domains. A hybrid finite element/finite volume (fe/fv) scheme has been implemented in this study to solve the governing equations (mass and momentum conservation and constitutive model). A time-stepping procedure is utilised in the fe/fv algorithm. A number of rheological models have been employed to stimulate the desired rheological response. Amongst these is the Oldroyd-B model. This is considered as a strong strain-hardening model being widely used due to its sound physical background and its ability to reproduce qualitative response of polymer melts in rheometrical flows. The linear version of Phan-Thien/Tanner (LPTT) and Giesekus models are also studied to compare simulation results for both dilute and concentrated polymeric systems against the Oldroyd-B model. For fluids with higher degree of strain-hardening, larger stress values cause a reduction in stretching period. In addition, Boger-like response has been represented under increasing levels of solvent within the system. Filament-stretching has been studied under two modes of stretching, exponential and linear for multi-mode and single-mode representations, that has included a numerical study on mesh refinement and algorithms developed for free-surface movement. Bead-like structure formation has been studied for a variety of surface tension coefficients in the absence/presence of body forces. ALE methods and free-surface techniques have been analysed for Volume-of-Fluid (VOF) mesh and Compressed-Mesh (CM) procedures. VOF mesh procedures are outperformed by their CM counterparts. For free-surface curvature to be determined precisely, a particle-tracking approach has been found to be preferable to a kinematic condition for surface-level. Variation of anisotropy levels and xi-parameter settings has been studied for the Gieskus and LPTT models, respectively. A further chapter is included where the recently addressed subject of step-strain is considered, to simulate sudden cessation of stretching across the three viscoelastic models. Sudden decline and sharp rise in axial stress have been observed and interpreted alongside filament radial evolution in the context of step-strain. The effect of inertia has been neglected but the effect of capillary and body forces has been brought into consideration. Larger stress values are observed for fluids with a higher degree of strain-hardening, and consequently, cause an increase in the step- strain period. Similar dynamic trends are followed for LPTT fluids with parameter settings of xi={0.0,0.13} under the context of step-strain. Here, rheological differences would emerge in shear. A paper which has been recently submitted for publication is included in the appendix. There, different aspects of gradual plate halt are discussed.
24
Kamal, Ibrahim Abdelhamid Hossam. "Numerical prediction of a viscoelastic fluid flow past a non-confined cylinder." Thesis, Lille 1, 2008. http://www.theses.fr/2008LIL10018/document.
Full textAbstract:
Ce travail a pour principal objectif la prédiction numérique de l'écoulement laminaire bidimensionnel d'un fluide viscoélastique autour d'un cylindre en milieu non confiné. La méthode des volumes finis en coordonnées orthogonales généralisées est ici adoptée pour résoudre les équations de conservation. Le modèle constitutif pour le fluide est de type Phan-Tien Tanner simplifié (S-PTT). Afin de stabiliser l'algorithme de résolution, le schéma dit "Elastic Viscous Split Stresses" (EVSS) est utilisé. Le code de calcul mis au point a été validé dans le cas de l'écoulement newtonien. Les résultats obtenus corroborent ceux de la littérature. Ensuite, ce code a été appliqué au cas d'un écoulement viscoélastique autour d'un cylindre non confiné. Dans ce cas, l'analyse a été réalisée pour différents nombres de Reynolds (Re = 200) et pour différents nombres de Deborah (0.0~0.25). Aussi, les caractéristiques principales de l'écoulement (les contraintes d'extra tension viscoélastiques, la première différence des contraintes normales et les champs de pression, de vitesses et de rotation) ont été présentées et commentées. Enfin, les évolutions de nombre de Strouhal, de la traînée et de la portance sont montréesThe two-dimensional viscoelasc!ic incompressible fluid flow pas! a non-contined cylinder is numerically simulated. The governing equations are stated in the generalized orthogonal coordinate system. The finite volume method is used to descritize the governing equations. For the viscoelastic constitutive equation. the simplified Phan-Thien-Tanner (SPTT) model is employed. The quadratic scheme QUICK is applied to evaluate the convection terms. The Elastic Viscous Split Stress (EVSS) formulation is used to decompose the stress tensor to enhance the stability of the computations. The developed code is validated for Newtonian and viscoelastic resullts. The present results show good consistency with the published literature. For the Newtonian flow. the obtained results indicate that the onset of the laminar vortex shedding instability occurs at Re >_47. Concerning the viscoelastic fluid. the influences of the Reynolds and Deborah numbers are discussed. The studied flow properties are the extra-shear stress, the first normal stress difference, the pressure field, the flow reeirculation. and the ve!ocity field. Also. the results for the Strouhal number, the drag and the lift are introduced and commented
25
Kamal, Ibrahim Abdelhamid Hossam. "Numerical prediction of a viscoelastic fluid flow past a non-confined cylinder." Thesis, Lille 1, 2008. http://www.theses.fr/2008LIL10018.
Full textAbstract:
Ce travail a pour principal objectif la prédiction numérique de l'écoulement laminaire bidimensionnel d'un fluide viscoélastique autour d'un cylindre en milieu non confiné. La méthode des volumes finis en coordonnées orthogonales généralisées est ici adoptée pour résoudre les équations de conservation. Le modèle constitutif pour le fluide est de type Phan-Tien Tanner simplifié (S-PTT). Afin de stabiliser l'algorithme de résolution, le schéma dit "Elastic Viscous Split Stresses" (EVSS) est utilisé. Le code de calcul mis au point a été validé dans le cas de l'écoulement newtonien. Les résultats obtenus corroborent ceux de la littérature. Ensuite, ce code a été appliqué au cas d'un écoulement viscoélastique autour d'un cylindre non confiné. Dans ce cas, l'analyse a été réalisée pour différents nombres de Reynolds (Re = 200) et pour différents nombres de Deborah (0. 0~0. 25). Aussi, les caractéristiques principales de l'écoulement (les contraintes d'extra tension viscoélastiques, la première différence des contraintes normales et les champs de pression, de vitesses et de rotation) ont été présentées et commentées. Enfin, les évolutions de nombre de Strouhal, de la traînée et de la portance sont montréesThe two-dimensional viscoelasc!ic incompressible fluid flow pas! a non-contined cylinder is numerically simulated. The governing equations are stated in the generalized orthogonal coordinate system. The finite volume method is used to descritize the governing equations. For the viscoelastic constitutive equation. The simplified Phan-Thien-Tanner (SPTT) model is employed. The quadratic scheme QUICK is applied to evaluate the convection terms. The Elastic Viscous Split Stress (EVSS) formulation is used to decompose the stress tensor to enhance the stability of the computations. The developed code is validated for Newtonian and viscoelastic resullts. The present results show good consistency with the published literature. For the Newtonian flow. The obtained results indicate that the onset of the laminar vortex shedding instability occurs at Re >_47. Concerning the viscoelastic fluid. The influences of the Reynolds and Deborah numbers are discussed. The studied flow properties are the extra-shear stress, the first normal stress difference, the pressure field, the flow reeirculation. And the ve!ocity field. Also. The results for the Strouhal number, the drag and the lift are introduced and commented
26
Chadwick, Kenneth Michael. "An experimental investigation of the breakup of a viscoelastic non-newtonian fluid in a supersonic stream." Thesis, Virginia Tech, 1990. http://hdl.handle.net/10919/42082.
Full text
27
Bentata, Omar. "Étude expérimentale d'un anneau tourbillonnaire en fluide newtonien et non newtonien en régime faiblement inertiel." Phd thesis, Toulouse, INPT, 2013. http://oatao.univ-toulouse.fr/9703/1/bentata.pdf.
Full textAbstract:
Cette thèse est une étude expérimentale de la formation et de la maturation d’un anneau tourbillonnaire. Elle porte sur les écoulements faiblement inertiels (Reynolds : 5 à 500) en fluide newtonien puis non newtonien. Les anneaux sont générés par un système cylindre-piston. Ils sont analysés par visualisation et par vélocimétrie par images de particules (PIV). La dynamique en fluide newtonien à faible nombre de Reynolds se révèle plus complexe que celle à grands Reynolds avec l’apparition d’un anneau secondaire contrarotatif. Les résultats obtenus en fluide rhéofluidifiant montrent l’influence de l’indice de comportement ainsi que les zones de comportement rhéofluidifiant et newtonien. Les explorations en fluides viscoplastique et viscoélastique montrent la formation d’un ou plusieurs anneaux secondaires contrarotatifs, qui diffèrent dans leur formation et leur dynamique des anneaux observés en fluide newtonien et que l’on associe aux propriétés physiques intrinsèques du fluide.
28
Gaillard, Antoine. "Flow and stability of a viscoelastic liquid curtain." Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC011/document.
Full textAbstract:
L’écoulement et la stabilité des rideaux liquides viscoélastiques sont étudiés pour des solutions de polymères flexibles et semi rigides. Ces liquides viscoélastiques sont extrudés à partir d’une fente à débit constant et s’écoulent à l’air libre sous l’effet de la gravité. L’écoulement de ces liquides se caractérise par un équilibre initial entre la gravité et les forces élastiques causées par les déformations des chaînes de polymère, jusqu’à ce que l’inertie du liquide finisse par dominer et que l’on retrouve le comportement classique de chute libre. Nous montrons que l’écoulement est principalement influencé par la valeur du temps de relaxation extensionnel mesuré par une méthode de filamentation. Un nouvel éclairage sur l’écoulement des rideaux liquides Newtoniens nous permet de trouver une courbe maîtresse de l’écoulement dans le cas viscoélastique par analogie. En ce qui concerne la stabilité du rideau, nous observons que le débit critique de formation du rideau n’est pas affecté par la présence de polymères, tandis que le débit minimum en deçà duquel le rideau se rompt diminue après ajout de polymères, ce qui révèle une plus grande résistance de la nappe à l’initiation de trous. Par ailleurs, nous observons une instabilité de l’écoulement pour les solutions les plus rhéofluidifiantes, où des bandes épaisses (où la vitesse du liquide est supérieure à la moyenne) sont formées au sein du rideau. Une visualisation de l’écoulement à l’intérieur de la filière d’extrusion révèle que ce phénomène est lié à une instabilité de l’écoulement de contraction en amont de la fente, où l’écoulement est de nature instationnaire et tridimensionnelleThe flow and the stability of viscoelastic liquid curtains are investigated using solutions of flexible and semi-rigid polymer chains. These viscoelastic liquids are extruded from a slot at constant flow rate and fall in ambient air under gravity. We show that the curtain flow of polymer solutions is characterized by an initial balance between gravity and the elastic stresses arising from the stretching of polymer molecules, until inertia finally dominates and the classical free-fall behavior is recovered. We show that the flow is mostly influenced by the value of the extensional relaxation time of the solution measured by a filament thinning technique. New insights on the theoretical description of Newtonian curtains allow us to find the master curve of the viscoelastic curtain flow by analogy. Concerning the curtain stability, we show that the critical flow rate for curtain formation is not affected by the presence of polymers whereas the minimum flow rate below which the curtain rapidly breaks is reduced by polymer addition, thus revealing a greater resistance of the sheet to hole initiations. Furthermore, we observe the onset of a flow instability for the most shear-thinning solutions, where thick bands (where the liquid velocity is larger than average) are formed within the curtain. Visualizations of the flow inside the die reveal that this phenomenon is linked to a flow instability at the contraction plane upstream of the slot where the flow is unsteady and three-dimensional in nature
29
Savel'ev, Evgeny. "Controllability of the Stresses in Multimode Viscoelastic Fluid of Upper Convected Maxwell Type." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/28181.
Full textAbstract:
Viscoelastic fluids, or Non-Newtonian fluids, are those that do not have a linear algebraic relation between the velocity field and the stresses arising in the media. Such fluids exhibit properties of both solids and liquids, and therefore cannot be modeled with methods of elasticity or Newtonian fluid mechanics. The popular models of viscoelasticity differ from each other only by the differential equation that describes the constitutive law for the fluid. Also, the media can have several relaxation modes, such as fluid mixes. This means that the stresses are determined as the sum of the stresses for each individual relaxation mode, which are described by corresponding differential equations evolving independently.
The question of controllability of the equations that describe the evolution of viscoelastic fluids is largely open. The presence of the non-algebraic constitutive relation makes the analysis unfeasible in general setup. The presence of several relaxation modes makes the problem even more complicated. Another issue is the necessity of controlling the stresses, since they are not determined by the momentary velocity field, thus they need to be included as the controlled states. In this work we are concentrating on the controllability of the stresses arising in the viscoelastic fluid that has its motion constrained to be of the shearing type. This restriction allows us to concentrate on the stresses only and assign the shearing rate to be the control. We consider only the Upper Convected Maxwell fluid which has several relaxation modes present. The results demonstrate that contrary to the one relaxation mode case the normal stresses cannot be driven arbitrary close to the exponentially decaying regime, unless the shearing stresses satisfy certain requirements, while the shear stresses remain exactly controllable.Ph. D.
30
Goddard, Chris. "Rheological chaos and elastic turbulence in a generalised Maxwell model for viscoelastic fluid flow." Thesis, University of Surrey, 2008. http://epubs.surrey.ac.uk/2773/.
Full textAbstract:
This work presents a new extension to a generalised nonlinear Maxwell model for the theoty of viscoelastic material flow. Nonlinear terms within this constitutive model are used to replicate many experimental phenomena such as shear-thickening/thinning, shear banding and dynamic stress responses found in complex materials such as polymers, Micelles, colloidal dispersions and even granular media. Numerical simulations of the stress tensor under spatially homogeneous plane Couette flow reveal a range of solutions from steady state to chaotic, chosen in part by the strength of nonlinear terms. Bifurcation and stability analysis reveal the onset of chaotic flow and are used to study the various transitions to chaos. A detailed phase space diagram is produced to categorise different dynamical regimes by determining the Lyapunov exponent under variation of two main model parameters. The route to chaos is identified primarily as a Hopf bifurcation.
31
Stone, Thomas Shannon. "A numerical/experimental method for evaluating the bulk and shear complex dynamic moduli of viscoelastic polymers in the kilohertz range." Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/17038.
Full text
32
Mullaert, Jimmy. "Numerical methods for incompressible fluid-structure interaction." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066683/document.
Full textAbstract:
Cette thèse présente une famille de schémas explicites pour la résolution d'un problème couplé d'interaction entre un fluide visqueux incompressible et une structure élastique (avec possiblement un comportement visco-élastique et/ou non linéaire). La principale propriété de ces schémas est une condition de Robin consistante à l'interface, qui représente une caractéristique fondamentale du problème continu dans le cas où la structure est mince. Si le couplage s'effectue avec une structure épaisse, une condition de Robin généralisée peut être formulée pour le problème semi-discret en espace, à l'aide d'une condensation de la matrice de masse de la structure. Une deuxième caractéristique majeure de ces schémas est la capacité d'obtenir une condition de Robin qui intègre à la fois des extrapolations de la vitesse et des efforts du solide (donnant lieu à un schéma de couplage explicite), mais également un traitement implicite de l'inertie de la structure, qui rend le schéma stable quelle que soit l'intensité de l'effet de masse ajoutée. Un résultat général de stabilité et de convergence est présenté pour tous les ordres d'extrapolations dans un cadre linéaire représentatif. On montre, en particulier, que les propriétés de stabilité se conservent lorsque le couplage s'effectue avec une structure mince ou épaisse. En revanche, la précision optimale obtenue dans le cas d'une structure mince n'est pas retrouvée avec une structure épaisse. L'erreur introduite par le schéma de couplage comporte en effet une non-uniformité en espace, qui provient de la non-uniformité des reconstructions discrètes des opérateurs viscoélastiques. L'approximation induite par la condensation de la matrice de masse solide n'est pas responsable de cette non-uniformité. À partir de ce schéma,on propose également des méthodes itératives pour la résolution du schéma fortement couplé.La convergence de cette méthode est démontrée dans un cadre linéaire et ne montre pas de sensibilité à l'effet de masse ajoutée. Finalement, les résultats théoriques obtenus sont illustrés par des exemples numériques variés, dans les cas linéaire et non linéaireThis thesis introduces a class of explicit coupling schemes for the numerical solution of fluid-structure interaction problems involving a viscous incompressible fluid and a general elastic structure (thin-walled or thick-walled, viscoelastic and non-linear).The first fundamental ingredient of these methods is the notion of interface Robin consist encyon the interface. This is an intrinsic (parameter free) feature of the continuous problem, in the case of the coupling with thin-walled solids. For thick-walled structures, we show that an intrinsic interface Robin consistency can also be recovered at the space semi-discrete level, using a lumped-mass approximation in the structure.The second key ingredient of the methods proposed consists in deriving an explicit Robin interface condition for the fluid, which combines extrapolations of the solid velocity and stresses with an implicit treatment of the solid inertia. The former enables explicit coupling,while the latter guarantees added-mass free stability. Stability and error estimates are provided for all the variants (depending on the extrapolations), using energy arguments within a representative linear setting. We show, in particular, that the stability properties do not depend on the thin- or thick-walled nature of the structure. The optimal first-order accuracy obtained in the case of the coupling with thin-walled structuresis, however, not preserved when the structure is thick-walled, due to the spatial non uniformityof the splitting error. The genesis of this problem is the non-uniformity of the discrete viscoelastic operators, related to the thick-walled character of the structure,and not to the mass-lumping approximation. Based on these splitting schemes, new, parameter-free, Robin-Neumann iterative procedures for the partitioned solution of strong coupling are also proposed and analyzed. A comprehensive numerical study, involving linear and non linear models, confims the theoretical findings reported in this thesis
33
Lima, Nicolao Cerqueira 1985. "Simulação de escoamentos eletrohidrodinâmicos de fluidos newtonianos e viscoelásticos." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263465.
Full textAbstract:
Orientador: Marcos Akira d'ÁvilaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-22T01:11:51Z (GMT). No. of bitstreams: 1 Lima_NicolaoCerqueira_M.pdf: 2608433 bytes, checksum: 1f09fc99d86a78b7861be6972463c29c (MD5) Previous issue date: 2013
Resumo: A eletrohidrodinâmica trata basicamente dos efeitos de um campo elétrico em meios contínuos. Um fluido sob o efeito de um campo elétrico tende a se deformar devido a uma força elétrica que age sobre ele. Essa força elétrica é consequência de alguns fatores que têm como base as próprias propriedades do fluido. Entre elas estão à condutividade elétrica (capacidade do fluido de ionizar-se ou de conduzir corrente elétrica) e a permissividade elétrica (capacidade do fluido de polarizar-se). Diversos processos que utilizam efeitos elétricos em fluidos foram desenvolvidos nas últimas décadas. O fato de estes processos envolverem uma alta complexidade de parâmetros faz com que seja consumido bastante tempo e material durante a fase de testes. Por esse motivo, as simulações numéricas passaram a ser uma boa alternativa para otimizar tais processos, além de aumentar o conhecimento sobre eles. Nesse contexto, no presente trabalho foi implementado um código numérico (solver) no pacote de CFD OpenFOAM baseado no modelo para fluidos pouco condutores (leaky dieletric model) no intuito de descrever escoamentos eletrohidrodinâmicos. Entre eles estão o efeito de um campo elétrico em uma gota condutora e o afinamento de um jato na saída de um tubo capilar. Eventualmente, em processos eletrohidrodinâmicos, são utilizados polímeros. Entretanto, não há na literatura muitos estudos sobre a simulação de escoamentos eletrohidrodinâmicos utilizando fluidos viscoelásticos. Assim, um segundo código foi implementado, baseado em um código já existente. Este é capaz de simular efeitos elétricos em fluidos viscoelásticos, utilizando a equação constitutiva de Giesekus como modelo viscoelástico. Os resultados obtidos para a deformação da gota condutora foram comparados com resultados analíticos para fluidos newtonianos e com observações experimentais para fluidos viscoelásticos. Para o caso do jato na saída de um tubo capilar, ambos os tipos de fluidos (newtonianos e viscoelásticos) foram comparados com resultados experimentais e teóricos
Abstract: Electrohydrodynamics deals basically on the effects of an electric field on a continuum media. A fluid under the effect of an electric field tends to deform due to an electric force that acts on it. This electric force is a consequence of some factors which are based on the fluid properties, including the electric conductivity (ability of the fluid to ionize or to conduct electrical current) and the permittivity (ability of the fluid to polarize). Many processes using electrical effects in fluids have been developed in recent decades. The fact that these processes involve a high complexity of parameters, it consumes time and materials during the test phase. For that reason, the numerical simulations start being a good alternative to optimize such processes, and also to increase the knowledge about them. In this context, on the present work was implemented a solver on the open CFD software OpenFOAM, based on the leaky dielectric model, in order to describe electrohydrodynamic flows. Among them, are the effect of an electric field on a conducting droplet and the thinning of a jet on the exit of a nozzle. Eventually, in electrohydrodynamic processes, polymers are used. However, there aren't many studies about electrohydrodynamic flow simulation using viscoelastic fluids. So, a second solver was made, based on another existing solver. This second solver is able to simulate electric effects on viscoelastc fluids, using the Giesekus model as a constitutive equation. The results of the deformation of a conducting droplet were compared to analytical results, for Newtonian fluids, and with experimental observations, for viscoelastic ones. As for the jet, both types of fluids, Newtonians and viscoelastics, were compared to experimental and theoretical results
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica
34
Karra, Satish. "Modeling electrospinning process and a numerical scheme using Lattice Boltzmann method to simulate viscoelastic fluid flows." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1347.
Full text
35
Grant, Holly Victoria. "A viscoelastic constitutive model for thixotropic yield stress fluids: asymptotic and numerical studies of extension." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/80440.
Full textAbstract:
This dissertation establishes a mathematical framework for analyzing a viscoelastic model that displays thixotropic behavior as a model parameter gets very small. The model is the partially extending strand convection model, originally derived for polymeric melts that have long strands that get in the way of fully retracting. A Newtonian solvent is added. The uniaxial and equibiaxial extensional flows are studied using combined asymptotic analysis and numerical simulations. An initial value problem with a prescribed elongational stress is solved in the limit of large relaxation time. This gives rise to multiple time scales. If the initial stress is less than a critical value, the initial elastic elongation is followed by settling to an unyielded state at the slow time scale. If the initial stress is larger than the critical value, then yielding ensues. The extensional flows produce delayed yielding and hysteresis, both associated with thixotropy in complex fluids.Ph. D.
36
Martins, Ramon Silva. "Numerical simulation of turbulent viscoelastic fluid flows : flow classification and preservation of positive-definiteness of the conformation tensor." Thesis, Lille 1, 2016. http://www.theses.fr/2016LIL10127/document.
Full textAbstract:
Le but de ce travail est de fournir une amélioration de la connaissance sur le phénomène de la réduction de la traînée induite par polymère en considérant certains aspects de sa simulation numérique et les changements qui se produisent dans la cinématique de l’écoulement. Dans un premier temps, les transformations du type racine carrée et kernel racine-k pour le tenseur de conformation du modèle FENE-P ont été implémentées afin d’assurer la positivité du tenseur de conformation. Cependant, ces approches divergent en raison du caractère non-borné du tenseur de conformation. Cette contrainte n’a pas été respectée, même avec l’inclusion de diffusion artificielle. L’effet d’amortissement de la diffusion artificielle a permis d’assurer la stabilité numérique, mais il aboutit à une réduction de la traînée relative de 22% à 42% plus faible que prévue par les approches standards. Dans un second temps, les modes hyperboliques, paraboliques et elliptiques des écoulements turbulents viscoélastiques ont été évalués en utilisant de différents critères de classification d’écoulements. Certains avantages concernant les critères objectifs ont été discutés. On a observé que les domaines hyperboliques contribuent de manière significative à la cinématique de l’écoulement. Enfin, on a observé une tendance des domaines elliptiques et hyperboliques à devenir paraboliques et que cette tendance augmente avec l’élasticitéThe purpose of this work is to provide an enhancement of the knowledge about the polymer-induced drag reduction phenomenon by considering some aspects of its numerical simulation and the changes that occur in the flow kinematics. In the first part, the square root and kernel root-k formulations for the conformation tensor in the FENE-P model were implemented and showed to preserve the positiveness of the conformation tensor. However, they led to numerical divergence due to the loss of boundedness of the conformation tensor. This constraint was violated even with the inclusion of artificial diffusion. The damping effect of artificial diffusion helped to ensure numerical stability, but led to relative drag reduction from 22% to 42% lower than expected from traditional methods. In the second part, the hyperbolic, parabolic and elliptic modes of turbulent viscoelastic flows were evaluated by means of different flow classification criteria. Some advantages of considering objective criteria were discussed. It was shown that the hyperbolic domains significantly contribute to the flow kinematics. Finally, a tendency of both elliptic and hyperbolic domains to become parabolic was observed and found to increase with the elasticity
37
Nicknich, Gustavo. "Análise do desempenho numérico do Solver viscoelasticFluidFoam." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/103718.
Full textAbstract:
Polímeros sintéticos ocupam uma posição de grande importância no estilo de vida moderno, servindo como matérias-primas para a construção de uma variedade de utensílios. Apesar do grande número de operações de processamento e produtos disponíveis, o planejamento de produtos e a otimização dos processos de produção raramente constituem-se de tarefas triviais. Isso deve-se ao fato da maioria das operações aplicadas na indústria de processamento de polímeros envolverem geometrias e padrões de escoamento complexos, além da dificuldade intrínseca relacionada ao comportamento reológico complexo de polímeros fundidos ou soluções poliméricas. Devido a estes fatores, o desenvolvimento de técnicas de dinâmica de fluido computacional (computational fluid dynamics – CFD) para a simulação de escoamentos de fluidos poliméricos e etapas de operações de processamento tem sido assunto de numerosos estudos durante as últimas décadas. Sob esta perspectiva, o solver viscoelasticFluidFoam, merece destaque. Ele é capaz de resolver simulações de escoamentos de fluidos viscoelásticos utilizando diferentes equações constitutivas. Contudo, apesar de resultados existentes na literatura apresentarem um bom potencial de aplicação, uma análise extensiva de seu desempenho numérico ainda não foi realizada. Neste contexto, a proposta do presente trabalho é a análise da influência de parâmetros de malha, numéricos e constitutivos no comportamento do solver. As bases para os testes compreendem uma geometria simples – escoamento laminar entre duas placas paralelas – o modelo constitutivo de Oldroyd-B e respectivas soluções analíticas para os campos de velocidade e tensão. Mesmo os testes demonstrando a inegável versatilidade do solver, eles revelam limitações em lidar com algumas configurações de malha e parâmetros constitutivos, principalmente com relação ao refinamento na direção perpendicular ao escoamento, diminuição do número de Reynolds e aumento do número de Weisenberg. Estas limitações podem ser parcialmente contornadas com escolha adequada de parâmetros de relaxação das variáveis e da razão de aspecto dos volumes de controle. Tais dificuldades não estão presentes em simulações de escoamentos de fluidos newtonianos em condições semelhantes, sugerindo que trabalhos futuros devem focar em implementações mais robustas do solver viscoelasticFluidFoam.Synthetic polymers hold a position of great importance in modern lifestyle, serving as raw materials for the construction of a wide variety of appliances. Despite the large number of processing operations and products available, product planning and optimization of production processes rarely constitute a trivial task. This is due to the fact of operations applied in polymer processing industry involve complex geometries and flow patterns, plus the intrinsic difficulty related to the molten polymers or polymer solutions complex rheological behavior. Because of these factors, the development of techniques of computational fluid dynamics (CFD) for the simulation of flows of polymeric fluids and stages of processing operations has been the subject of numerous studies during the last decades. From this perspective, the viscoelasticFluidFoam solver deserves mention. The solver is capable of resolving simulations of viscoelastic fluid flows using different constitutive equations. However, despite the existing results in the literature present a great potential for application, an extensive analysis of their numerical performance has not been performed yet. The purpose of this paper is to examine the influence of mesh, numerical and constitutive parameters in the behavior of the solver. Bases for the tests comprise a simple geometry – laminar flow between two parallel plates – the constitutive model of Oldroyd-B and its analytical solutions for the velocity and stress fields. Although the tests show the undeniable versatility of the solver, they also reveal limitations in dealing with some mesh settings and constitutive parameters, particularly with respect to refinement in the direction perpendicular to the flow, decreasing in the Reynolds number and increasing in the Weisenberg number. This limitation can be partially circumvented with proper choice of variables relaxation parameters and aspect ratio of the control volumes. Such difficulties are not present in simulations of Newtonian fluids flows under similar conditions, suggesting that future works should focus on more robust implementations of the viscoelasticFluidFoam solver.
38
Laadj, Toufik. "Initial Value Problems for Creeping Flow of Maxwell Fluids." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/26302.
Full textAbstract:
We consider the flow of nonlinear Maxwell fluids in the unsteady quasistatic case, where the effect of inertia is neglected. We study the well-posedness of the resulting PDE initial-boundary value problem. This well-posedness depends on the unique solvability of an elliptic boundary value problem. We first present results for the 3D case, locally and globally in time, with sufficiently small initial data, and for a simple shear flow problem, locally in time with arbitrary initial data; after that we extend our results to some 3D flow problems, locally in time, with large initial data. Additionally, we present results for models of White-Metzner type in 3D flow, locally and globally in time, with sufficiently small initial data.
We solve our problem using an iteration between elliptic and hyperbolic linear subproblems. The limit of the iteration provides the solution of our original problem.Ph. D.
39
Curtis, Mark Peter. "Aspects of low Reynolds number microswimming using singularity methods." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:13dcb39b-f5b7-4d46-92d4-21a9afbecd08.
Full textAbstract:
Three different models, relating to the study of microswimmers immersed in a low Reynolds number fluid, are presented. The underlying, mathematical concepts employed in each are developed using singularity methods of Stokes flow. The first topic concerns the motility of an artificial, three-sphere microswimmer with prescribed, non-reciprocal, internal forces. The swimmer progresses through a low Reynolds number, nonlinear, viscoelastic medium. The model developed illustrates that the presence of the viscoelastic rheology, when compared to a Newtonian environment, increases both the net displacement and swimming efficiency of the microswimmer. The second area concerns biological microswimming, modelling a sperm cell with a hyperactive waveform (vigorous, asymmetric beating), bound to the epithelial walls of the female, reproductive tract. Using resistive-force theory, the model concludes that, for certain regions in parameter space, hyperactivated sperm cells can induce mechanical forces that pull the cell away from the wall binding. This appears to occur via the regulation of the beat amplitude, wavenumber and beat asymmetry. The next topic presents a novel generalisation of slender-body theory that is capable of calculating the approximate flow field around a long, thin, slender body with circular cross sections that vary arbitrarily in radius along a curvilinear centre-line. New, permissible, slender-body shapes include a tapered flagellum and those with ribbed, wave-like structures. Finally, the detailed analytics of the generalised, slender-body theory are exploited to develop a numerical implementation capable of simulating a wider range of slender-body geometries compared to previous studies in the field.
40
Prabhakar, Vivek. "Least squares based finite element formulations and their applications in fluid mechanics." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1152.
Full text
41
Mehra, Puneet. "Fluid-Structure Interaction Modeling of Human Upper Airway Collapse in Obstructive Sleep Apnea." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1563873512457421.
Full text
42
BERTAGLIA, Giulia. "1D augmented fluid-structure interaction systems with viscoelasticity: from water pipelines to blood vessels." Doctoral thesis, Università degli studi di Ferrara, 2020. http://hdl.handle.net/11392/2488143.
Full textAbstract:
Nowadays, mathematical models and numerical simulations are widely used in the whole fluid dynamics research field. They represent a powerful resource to better understand phenomena and processes and to significantly reduce the costs that would otherwise be necessary for carrying out laboratory experiments (sometimes even allowing to obtain useful data that could not be collected by measurements).
Currently there are many important industries of hydraulic systems which, for the correct analysis of the behavior of the designed systems, require the preventive use of an accurate mathematical model, able to describe the trend of the properties of the fluid in the pipelines. On the other hand, the availability of robust and efficient mathematical instruments, together with the engineering know-how in the fluid mechanics sector, represents an invaluable tool for a consistent support even in hemodynamics studies, providing practical approaches for the quantification of variables involved in the cardiovascular fluid dynamics.
The correct characterization of the interactions occurring between the fluid and the wall that circumscribes the motion of the fluid itself, is a fundamental aspect in all the contexts involving deformable ducts, which requires the utmost attention at every stage of both the development of the computational scheme and the interpretation of the results and at their application to cases of practical interest.
In this PhD Thesis, innovative mathematical models able to predict the behavior of the fluid-structure interaction mechanism that underlies the dynamics of flows in different compliant ducts is presented. Starting from the purely civil engineering sector, with the study of plastic water pipelines, the final application of the proposed tool is linked to the medical research field, to reproduce the mechanics of blood flow in both arteries and veins. With this aim, various linear viscoelastic models, from the simplest to the more sophisticated, have been applied and extended to obtain augmented fluid-structure interaction systems in which the constitutive equation of the material is directly inserted into the system as partial differential equation. These systems are solved recurring to second-order Finite Volume Methods that take into account the recent evolution in the computational literature of hyperbolic balance laws systems. The models have been extensively validated through different types of test cases, highlighting the advantages of using the augmented formulation of the system of equations. Numerical results have been compared with quasi-exact solutions of idealized time-dependent tests for situations close to reality or with reference values obtained with numerical schemes generally adopted in the specific research field investigated. Furthermore, comparisons with experimental data have been considered both for the water pipelines scenario and the blood flow modeling, recurring to ad hoc in-vivo measurements for the latter. Accuracy and efficiency analyses have been performed in different contexts, as well as a sensitivity analysis with regards to the final part of the project, related to a more applicative study on arterial hypertension.Oggigiorno, modelli matematici e simulazioni numeriche sono ampiamente utilizzati nell’intero campo della ricerca fluidodinamica. Essi rappresentano una potente risorsa per comprendere meglio i fenomeni e i processi e per ridurre significativamente i costi che sarebbero altrimenti necessari per la realizzazione di esperimenti di laboratorio (a volte anche per ottenere utili dati che non potrebbero essere raccolti mediante misurazioni). Attualmente esistono molte importanti industrie di sistemi idraulici che, per la corretta analisi del comportamento dei sistemi progettati, richiedono l’uso preventivo di un accurato modello matematico, in grado di descrivere l’andamento delle proprietà del fluido nelle tubazioni. D’altra parte, la disponibilità di strumenti matematici robusti ed efficienti, insieme al know-how ingegneristico nel settore della fluidodinamica, rappresenta uno strumento inestimabile per un supporto costante anche negli studi emodinamici, fornendo approcci pratici per la quantificazione delle variabili coinvolte nella fluidodinamica cardiovascolare. La corretta caratterizzazione delle interazioni tra il fluido e la parete che ne circoscrive il moto, è un aspetto fondamentale in tutti i contesti di condotte deformabili, che richiede la massima attenzione in ogni fase dello sviluppo dello schema di calcolo e della interpretazione dei risultati e nella loro applicazione a casi di interesse pratico. In questa Tesi di Dottorato vengono presentati innovativi modelli matematici in grado di prevedere il comportamento del meccanismo di interazione fluido-struttura che sta alla base della dinamica dei flussi in diverse condotte deformabili. Partendo dal settore dell’ingegneria puramente civile, con lo studio di condotte idrauliche in plastica, l’applicazione finale dello strumento proposto è legata al campo della ricerca medica, per riprodurre la meccanica del flusso sanguigno sia nelle arterie che nelle vene. A tal fine, sono stati applicati ed estesi diversi modelli viscoelastici lineari, dai più semplici ai più sofisticati, per ottenere sistemi aumentati di interazione fluido-struttura in cui l’equazione costitutiva del materiale è direttamente inserita nel sistema come equazione alle derivate parziali. Questi sistemi sono risolti ricorrendo a Metodi ai Volumi Finiti al secondo ordine che tengono conto della recente evoluzione della letteratura computazionale dei sistemi iperbolici di leggi di bilancio. I modelli sono stati ampiamente validati attraverso diversi tipi di casi test, evidenziando i vantaggi dell’utilizzo del sistema di equazioni in forma aumentata. I risultati numerici sono stati confrontati con soluzioni quasi esatte di problemi ideali dipendenti dal tempo per situazioni vicine alla realtà o con valori di riferimento ottenuti con schemi numerici adottati solitamente nello specifico campo di ricerca indagato. Inoltre, sono stati presi in considerazione confronti con dati sperimentali sia per lo scenario delle condotte idriche che per la modellazione del flusso sanguigno, ricorrendo a misurazioni in-vivo ad hoc per quest’ultimo. Sono state effettuate analisi di accuratezza ed efficienza in diversi contesti, nonché un’analisi di sensitività per quanto riguarda la parte finale del progetto, relativa ad uno studio più applicativo sull’ipertensione arteriosa.
43
Westervoß, Patrick [Verfasser], Stefan [Akademischer Betreuer] Turek, and Christian [Gutachter] Kreuzer. "The Tensor Diffusion approach as a novel technique for simulating viscoelastic fluid flows / Patrick Westervoß ; Gutachter: Christian Kreuzer ; Betreuer: Stefan Turek." Dortmund : Universitätsbibliothek Dortmund, 2021. http://d-nb.info/1230628711/34.
Full text
44
Figueiredo, Rafael Alves. "Simulação numérica de escoamentos viscoelásticos multifásicos complexos." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/55/55134/tde-30112016-160821/.
Full textAbstract:
Aplicações industriais envolvendo escoamentos multifásicos são inúmeras, sendo que, o aprimoramento de alguns desses processos pode resultar em um grande salto tecnológico com significativo impacto econômico. O estudo numérico dessas aplicações é imprescindível, pois fornece informações precisas e mais detalhadas do que a realização de testes experimentais. Um grande desafio é o estudo numérico de escoamentos viscoelásticos multifásicos envolvendo altas taxa de elasticidade, devido às instabilidades causadas por altas tensões elásticas, grandes deformações, e até mudanças topológicas na interface. Assim, a investigação numérica desse tipo de problema exige uma formulação precisa e robusta. No presente trabalho, um novo resolvedor de escoamentos bifásicos envolvendo fluidos complexos é apresentado, com particular interesse em escoamentos com altas taxas de elasticidade. A formulação proposta é baseada no método Volume-of-fluid (VOF) para representação da interface e no algoritmo Continuum Surface Force (CSF) para o balanço de forças na interface. A curvatura e advecção da interface são calculados via métodos geométricos para garantir a precisão dos resultados. Métodos de estabilização são utilizados quando números críticos de Weissenberg (Wi) são encontrados, devido ao famoso problema do alto número de Weissenberg (HWNP). O método da projeção, combinado com um método implícito para solução da equação da quantidade de movimento, são discretizados por um esquema de diferenças finitas em uma malha deslocada. Problemas de benchmarks foram resolvidos para acessar a precisão numérica da formulação em diferentes níveis de complexidade física, tal como representação e advecção da interface, influência das forças interfaciais, e características reológicas do fluido. A fim de demonstrar a capacidade do novo resolvedor, dois problemas bifásicos transientes, envolvendo fluidos viscoelásticos, foram resolvidos: o efeito de Weissenberg e o reômetro extensional (CaBER). O efeito de Weissenberg ou rod-climbing effect consiste em um bastão que gira dentro de um recipiente com fluido viscoelástico e, devido às forças elásticas, o fluido escala o bastão. Os resultados foram comparados com dados teóricos, numéricos e experimentais, encontrados na literatura para pequenas velocidades angulares. Além disso, resultados obtidos com altas velocidades angulares (alta elasticidade) são apresentados com o modelo Oldroyd-B, em que escaladas muito elevadas foram observadas. Valores críticos da velocidade angular foram identificados, e para valores acima foi observada a ocorrência de instabilidades elásticas, originadas pela combinação de tensões elásticas, curvatura interfacial, e escoamentos secundários. Até onde sabemos, numericamente, essas instabilidades nunca foram capturadas antes. O CaBER consiste no comportamento e colapso de um filamento de fluido viscoelástico, formado entre duas placas paralelas devido às forças capilares. Esse experimento envolve consideráveis dificuldades, dentre as quais podemos destacar a grande influência das forças capilares e a diferença de escalas de comprimento no escoamento. Em grande parte dos resultados encontrados na literatura, o CaBER é resolvido por modelos simplificados em uma dimensão. Resultados obtidos foram comparados com tais resultados da literatura e com soluções teóricas, apresentando admirável precisão.Industrial applications involving multiphase flow are numerous. The improvement of some of these processes can result in a major technological leap with significant economic impact. The numerical study of these applications is essential because it provides accurate and more detailed information than conducting experiments. A challenge is the numerical study of high viscoelastic multiphase flows due to instabilities caused by the high elastic tension, large deformations and even topological changes in the interface. Thus the numerical investigation of this problem requires a robust formulation. In this study a new two-phase solver involving complex fluids is presented, with particular interest in the solution of highly elastic flows of viscoelastic fluids. The proposed formulation is based on the volume-of-fluid method (VOF) to interface representation and continuum surface force algorithm (CSF) for the balance of forces in the interface. The curvature and interface advection are calculated via geometric methods to ensure the accuracy of the results. Stabilization methods are used when critical Weissenberg numbers are found due to the famous high Weissenberg number problem (HWNP). The projection method combined with an implicit method for the solution of the momentum equation are discretized by a finite difference scheme in a staggered grid. Benchmark test problems are solved in order to access the numerical accuracy of different levels of physical complexities, such as the dynamic of the interface and the role of fluid rheology. In order to demonstrate the ability of the new resolver, two-phase transient problems involving viscoelastic fluids have been solved, theWeissenberg effect problem and the extensional rheometer (CaBER). The Weissenberg effect problem or rod-climbing effect consists of a rod that spins inside of a container with viscoelastic fluid and due to the elastic forces the fluid climbs the rod. The results were compared with numerical and experimental data from the literature for small angular velocities. Moreover results obtained for high angular velocities are presented using the Oldroyd-B model, which showed high climbing heights. Critical values of the angular speed have been identified. For values above a critical level were observed the occurrence of elastic instabilities caused by the combination of elastic tension, interfacial curvature and secondary flows. To our knowledge, numerically these instabilities were never captured before. The CaBER consists of the behavior and collapse of a viscoelastic fluid filament formed between two parallel plates due to capillary forces. This experiment involves considerable difficulties, among which we can highlight the great influence of the capillary forces and the difference of the length scales in the flow. In much of the results found in the literature, the CaBER is solved by simplified models. The results were compared with results reported in the literature and theoretical solutions, which showed remarkable accuracy.
45
Martins, Adam Macedo. "Análise da qualidade de tensões obtidas na simulação de escoamentos de fluidos viscoelásticos usando a formulação log-conformação." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/156814.
Full textAbstract:
Uma das mais recentes abordagens propostas na literatura para tratar o problema do alto número de Weissenberg (We) é a Formulação Log-Conformação (FLC). Nesta formulação, a equação constitutiva viscoelástica utilizada é reescrita em termos de uma variável Ψ, que é o logaritmo do tensor conformação. Apesar do potencial de aplicação da FLC, pouca atenção tem sido dirigida para análise da acurácia da solução obtida para o campo de tensões quando se utiliza esta formulação. Assim, o objetivo do presente trabalho foi estudar a acurácia da solução obtida pela FLC na análise de escoamentos de fluidos viscoelásticos usando duas geometrias padrão de estudo: placas paralelas e cavidade quadrada com tampa móvel. Primeiramente, a FLC foi implementada no pacote de CFD OpenFOAM. Em seguida foram verificados os limites do número de Weissenberg na formulação numérica padrão (Welim,P), onde para a geometria de placas paralelas foi encontrado Welim,P = 0,3 e para a geometria da cavidade quadrada com tampa móvel foi encontrado Welim,P = 0,8. Depois o código implementado foi aplicado em ambas as geometrias, comparando-se a solução obtida pela FLC com aquela da formulação padrão na faixa de We < Welim,P. Os resultados obtidos na geometria de placas paralelas apresentaram boa concordância com a solução padrão e solução analítica. Para a geometria da cavidade quadrada com tampa móvel, que não possui solução analítica, boa concordância dos resultados também foi observada em comparação com a solução padrão. Posteriormente foram comparados os resultados obtidos pela FLC na faixa de We > Welim,P. Na geometria de placas paralelas, além da boa concordância com a solução analítica, obteve-se convergência em todos os casos estudados neste trabalho, com o maior número de Weissenberg utilizado sendo igual a 8 Os resultados da geometria da cavidade quadrada com tampa móvel também apresentaram boa concordância em comparação com dados da literatura, porém a convergência foi obtida até para We = 2. Com respeito à comparação das formulações numéricas com a solução analítica, feita apenas na geometria de placas paralelas, foi observado um erro máximo de 7,57% na solução padrão e de 12,33% na FLC. Em relação à análise da qualidade das tensões usando os resíduos da equação constitutiva viscoelástica como critério de acurácia, foi verificado nas duas geometrias que os valores de tensão obtidos usando a FLC são menos acurados que aqueles obtidos pela formulação explícita no tensor das tensões nos casos em que esta última converge. Também foi observado que a acurácia diminui com o aumento do We. Esse efeito pôde ser melhor notado na geometria de placas paralelas. Uma razão para a perda de acurácia da tensão provavelmente ocorre devido à natureza matemática da transformação algébrica inversa de Ψxx para τxx. O novo solver implementado neste trabalho apresentou convergência e soluções corretas para as duas geometrias, logo foi implementado corretamente. Ele também potencializa o solver de partida viscoelastiFluidFoam ao estender simulações para uma faixa maior do número de Weissenberg.A recent approach proposed in the literature to deal with the High Weissenberg Number Problem is the Log-Conformation formulation (LCF). In this formulation the viscoelastic constitutive equation is rewritten in terms of the logarithm of the conformation tensor Ψ. Despite the great potential application of the LCF, little attention has been given in the literature to the accuracy of the obtained stress fields. The purpose of this work was to study the solution obtained by LCF in the analysis of viscoelastic flows using two benchmark geometries: parallel plates and lid driven cavity. Firstly, the LCF was implemented in the OpenFOAM CFD package. Then, the limits of Weissenberg number for the standard numerical formulation (Welim,P) were verified, obtaining Welim,P = 0.3 for the parallel plates and Welim,P = 0.8 for the lid driven cavity. When comparing the solution obtained by the LCF with that of the standard formulation in a range of We < Welim,P, the results obtained for the parallel plates geometry showed good agreement with the standard solution and the analytical solution. For the lid driven cavity geometry, for which there is not analytical solution, good agreement with the standard solution was also observed. For We > Welim,P in the parallel plates geometry, in addition to the good agreement with the analytical solution, it was possible to obtain convergence in all the cases studied in this work, with the largest number of Weissenberg used being equal to 8 The results of the lid driven cavity geometry also presented good agreement in comparison with literature data, but convergence was obtained up to We = 2. With respect to the comparison of the numerical formulations with the analytical solution for the parallel plates geometry, a maximum error of 7.57% was observed in the standard solution and of 12.33% in the LCF. When using the residues of the viscoelastic constitutive equation as a criterion of accuracy, it was verified that for the two geometries the stress values obtained using the LCF were less accurate than those obtained by the explicit formulation in the stress tensor. It has also been observed that accuracy decreases with increasing of We. One reason for the loss of stress accuracy probably occurs because of the mathematical nature of the inverse algebraic transformation from Ψxx to τxx. The new solver implemented in this work presented convergence and correct solutions for the two geometries, so it was implemented correctly. It also potentiates the viscoelastiFluidFoam starting solver by extending simulations to a larger range of Weissenberg number.
46
Thatte, Azam. "Multi-scale multi-physics model and hybrid computational framework for predicting dynamics of hydraulic rod seals." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37272.
Full textAbstract:
Rod seals are one of the most critical components of hydraulic systems. However, the fundamental physics of seal behavior is still poorly understood and the seal designers have virtually no analytical tools with which to predict the behavior of potential seal designs. In pursuit of a comprehensive physics based seal analysis/ design tool, in this work, a multi-scale multi-physics (MSMP) seal model is developed. The model solves the transient problem involving macro-scale viscoelastic deformation mechanics, macro-scale contact, micro-scale two phase fluid mechanics in the sealing zone, micro-scale asperity contact mechanics and micro-scale deformation mechanics of the sealing edge in a strongly coupled manner. The model takes into account surface roughness, mixed lubrication, cavitation and two phase flow, transient squeeze film effects and the dynamic operation as well as the effect of macro/micro/nano scale viscoelasticity. A hybrid finite element-finite volume-statistical computational framework is developed to solve the highly coupled multi-physics interactions of the MSMP model simultaneously. Surface characterization experiments are performed to extract the parameters like RMS roughness, asperity density, autocorrelation length and asperity radius needed by MSMP. To remove the high frequency noise without removing the high frequency real surface features, a wavelet transform based adaptive surface extraction method is implemented. Dynamic mechanical analysis (DMA) is performed to extract the macro-scale viscoelastic parameters of the seal. Through atomic force microscopy (AFM) experiments, the local micro/nano scale elastic moduli were found to be varying within two orders of magnitude higher than the bulk of the polymer. Significant differences in local stiffness, adhesion and the relaxation time scales of individual surface asperities were also observed. With the MSMP model, dynamic seal performance was analyzed. The results confirmed the mixed lubrication and the effect of surface roughness. Thicker fluid films during instroke and cavitation during the outstroke were found to be important for non-leakage. Seal behavior was a function of the complex dual dependence on the time varying sealed pressure and hydrodynamic effects. Viscoelasticity is seen to critically affect the leakage and friction characteristics. It produces thicker fluid films and produces a significant increase in Poiseuille component of flow during instroke. Ignoring viscoelasticity leads to under-prediction of the time required to reach the zero leakage state. Several high pressure - high frequency sealing applications were analyzed. In such applications, a new phenomenon of "secondary contact" was observed. Viscoelastic creep was seen to critically affect the contact pressure and hence the friction characteristics. In high frequency applications, viscoelasticity induced significant differences in Poiseuille flow and friction force from cycle to cycle. Cycle frequency was seen to play an important role in governing visco-elastohydrodynamics and the leakage of such seals. The seals need to be designed by considering the relationship between relaxation time scales of the polymer and the cycle frequencies. Study also revealed the presence of characteristics like "critical temperature" and "critical frequency". Using the multi-physics modeling capability of MSMP framework, several novel seal designs using smart materials like piezo-ceramic embedded polymers are proposed and analyzed. The MSMP computational framework developed here has a great potential to be used as a stand-alone seal design and analysis software in academic and industrial research.
47
Deblock, Yves. "Caractérisation ultrasonore haute fréquence des propriétés viscoélastiques de milieux liquides." Valenciennes, 1997. https://ged.uphf.fr/nuxeo/site/esupversions/d2e436b7-2cfd-4b8b-9ff8-9e725f939e0a.
Full textAbstract:
Les modules de compression et de rigidité constituent des paramètres macroscopiques, caractéristiques des matériaux homogènes, linéaires et isotropes. Nous proposons, dans ce travail, deux méthodes acoustiques, originales et complémentaires, applicables aux matériaux liquides, qui permettent leur détermination dans le domaine haute fréquence. La première méthode est basée sur le traitement de l'impédance électrique d'entrée d'un capteur à onde de cisaillement, place au contact du matériau liquide étudié. Ce traitement permet d'extraire le coefficient de réflexion a l'interface entre les matériaux solide et liquide, puis finalement, le module de rigidité. La seconde méthode utilise des capteurs onde de pression. Elle repose sur le traitement de la fonction de transfert en tension d'un système compose de deux capteurs et du matériau liquide dispose entre eux. La vitesse et l'absorption du matériau liquide sont extraites de ce traitement et reliées à une combinaison des deux modules. La connaissance du module de rigidité, issu de la méthode précédente, permet d'atteindre le module de compression. Les deux méthodes de mesure ont été validées, à l'aide d'un matériau liquide de référence. En guise d'exemple, elles ont été appliquées pour l'étude d'un matériau liquide particulier.
48
Revoredo, Igor Feliciano Simplicio. "Solução Numérica de escoamentos viscoelásticos tridimensionais com superfícies livres: fluidos de segunda ordem." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/55/55134/tde-18052010-161846/.
Full textAbstract:
Este trabalho apresenta uma técnica de diferenças finitas para resolver a equação constitutiva Fluido de Segunda Ordem para escoamentos tridimensionais com superfície livre. As equações governantes são resolvidas pelo método de diferenças finitas em uma malha deslocada 3D. A superfície livre é modelada por células marcadoras (Marker-and-Cell) e as condições de contorno a superfície livre são empregadas. O método numérico apresentado neste trabalho foi validado pela comparação entre as soluções numéricas obtidas para o escoamento em um tubo com a solução analítica correspondente para Fluidos de Segunda Ordem. Ao fazer refinamento de malha, a convergência do método numérico foi verificada. Resultados numéricos da simulação do problema do inchamento do extrudado para números de Deborah De \'< OU =\' 0:3 são apresentadosThis work presents a finite difference method to simulate three-dimensional viscoelastic flow with free surfaces governed by the constitutive equation Second Order Fluid. The governing equations are solved by the finite difference method in a three-dimensional shifted mesh. The free surface of fluid is modeled by the Marker-and-Cell method which allows for the visualization and the location of the free surface of fluid. The full free surface stress conditions are employed. The numerical method developed in this work is validated by comparing the numerical and analytic solutions for the steady state flow of a Second Order Fluid in a pipe. By using mesh refinement convergence results are given. Numerical results of the simulation of the transient extrudate swell of a Second Order Fluid of the Deborah number De \'< OR =\' 0:3 are presented
49
Ramsay, John Andrew. "Mixing of viscoelastic fluids." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7333/.
Full textAbstract:
This work investigates the laminar mixing performance of viscoelastic fluids in laboratory-scale batch stirred tanks agitated by “butterfly” impellers and in-line Kenics KM static mixers. Constant-viscosity viscoelastic (Boger) fluids were formulated to investigate viscous and elastic effects separately; multiphase viscoelastic suspensions were formulated from 40-50 volume% glass spheres in glycerol. Particle Image Velocimetry in stirred tanks agitated by high impeller-to-tank diameter ratio butterfly impellers (D/T=0.98) showed that secondary flows in Boger fluid increased solid body rotation and reduced local shear rates (≤16 s-1) compared to equivalent viscosity Newtonian fluids, though the effect was non-monotonic. Mixing times obtained from Planar Laser Induced Fluorescence (PLIF) increased by ≤23%. Positron Emission Particle Tracking in multiphase suspensions showed increased axial mixing due to more dominant secondary flows. In static mixers, Boger fluid striation patterns at the mixer outlet obtained from PLIF showed time dependence and flow instability due to reduced local shear rates. Energy consumption in all geometries displayed an increase of ≤200% with viscoelastic fluids. Using a generalised Reynolds number Reg enabled viscoelastic power draw prediction, previously only possible through empirical relationships. Overall, viscoelasticity generally increases energy consumption whilst reducing blending performance though the link between elasticity and mixing quality is highly non-linear.
50
Mouline, Youssef. "Dynamique des bulles de gaz dans les milieux rhéologiquement complexes." Vandoeuvre-les-Nancy, INPL, 1996. http://www.theses.fr/1996INPL063N.
Full textAbstract:
Dans les procédés gaz-liquide, l'efficacité des transferts de matière et de chaleur est essentiellement contrôlée par la dynamique des bulles dans la phase liquide. L’étude du comportement des bulles de gaz dans un milieu liquide est donc d'un intérêt certain, tant sur le plan fondamental que sur le plan industriel, surtout lorsque le milieu liquide est non-newtonien. Notre étude a révélé que les propriétés rhéologiques de la phase liquide et la fréquence d'injection du gaz dans la colonne ont une influence importante sur la vitesse d'ascension des bulles. Dans les milieux viscoélastiques, des bulles de volume identique coalescent en ligne à partir d'une certaine hauteur de la colonne. Comme le confirme la simulation rhéologique, la coalescence en ligne des bulles est induite par la présence de contraintes résiduelles dans le fluide. L’utilisation des techniques spécifiques à l'analyse des systèmes dynamiques dissipatifs a montré que la coalescence en ligne est de nature chaotique déterministe. Enfin, un modèle de formation de bulle a été élaboré dans le but de prédire le volume et la forme des bulles au moment du détachement pour diverses conditions expérimentales