To see the other types of publications on this topic, follow the link: Viscosity modeling.
Dissertations / Theses on the topic 'Viscosity modeling'
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 'Viscosity modeling.'
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
Simpson, Joycelyn Ovetta. "Modeling viscosity and ionic conductivity of epoxy resins using free volume concepts." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/10258.
Full text
2
Wang, Yingru. "Modeling of polymer melt/nanoparticle composites and magneto-rheological fluids." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1135877847.
Full text
3
Silva, Djany Souza. "Evaluation of mathematical models to prediction the dynamic viscosity of fruit juices." Universidade Federal do CearÃ, 2015. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=14440.
Full textAbstract:
CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel SuperiorO consumo de sucos de frutas tem crescido, devido a comodidade e praticidade gerada pelos produtos prontos. Segundo a AssociaÃÃo Brasileira das IndÃstrias de Refrigerantes, em 2012, a produÃÃo anual foi de 987 milhÃes de litros de sucos de frutas no Brasil. No entanto, para alcanÃar maior eficiÃncia e rendimento, torna-se necessÃrio o conhecimento do comportamento reolÃgico das matÃrias-primas. A viscosidade à uma das propriedades reolÃgicas usada em diversas aplicaÃÃes, tais como: parÃmetro para o cÃlculo de coeficientes de transferÃncia de calor e massa; dimensionamento de equipamentos; avaliaÃÃo de custos; projetos de processos; controle de qualidade do produto; alÃm de possibilitar a compreensÃo da estrutura quÃmica das matÃrias-primas. Durante o processamento industrial dos sucos de frutas, a matÃria-prima à submetida à variaÃÃes de temperaturas e concentraÃÃes de sÃlidos que alteram sua viscosidade. Por esse motivo, o conhecimento dos efeitos combinados desses dois parÃmetros na viscosidade à essencial para a indÃstria de sucos. Nesse trabalho, dados experimentais da literatura para onze sucos clarificados de frutas (manga, cereja, maÃÃ, pÃssego, groselha, romÃ, pÃra, limÃo, tangerina, limÃo-galego e uva) em concentraÃÃes e temperaturas de 15,0 a 74,0 ÂBrix, e 278,15 a 393,15 K, respectivamente, foram modelados utilizando correlaÃÃes empÃricas e semi-empÃricas oriundas da literatura. ParÃmetros globais e especÃficos, respectivamente, em funÃÃo da temperatura e concentraÃÃo de sÃlidos solÃveis totais (SST), foram mantidos nos modelos. Quatro equaÃÃes foram avaliadas no cÃlculo da energia de ativaÃÃo (equaÃÃo da reta, exponencial, polinomial de 2 e 3 ordem) nos modelos. E trÃs estratÃgias de modelagem foram realizadas: ajuste para todas as concentraÃÃes de SST e temperaturas; em diferentes faixas de concentraÃÃes de SST; e, diferentes faixas de temperaturas. A estratÃgia de otimizaÃÃo por faixas de concentraÃÃes de SST mostrou-se a mais adequada. Duas relaÃÃes matemÃticas exponenciais, baseadas na correlaÃÃo de Arrhenius, obtiveram bons resultados na prediÃÃo da viscosidade dinÃmica de sucos de frutas clarificados entre as concentraÃÃes de 17,0 a 50,1 ÂBrix para todas as temperaturas de estudo. Enquanto que o uso da equaÃÃo de Vogel obteve bons resultados para concentraÃÃes de 51,0 a 66,0 ÂBrix na prediÃÃo da viscosidade dinÃmica dos sucos de frutas. Os modelos foram validados com dados experimentais para suco clarificado de laranja em baixas (30,7 a 50,5 ÂBrix) e altas concentraÃÃes (54,1 a 63,5 ÂBrix) de SST, com excelente prediÃÃo da viscosidade dinÃmica.
The comsumption of fruit juices has grown due to co nvenience and practicality generated by the finished products. According to the AssociaÃÃo Brasileira das IndÃstrias de Refrigerantes, in 2012 the annual production was 987 million liter s of fruit juices in Brazil. However, to achieve greater efficiency and performance, it is n ecessary to know the rheological behavior of the raw materials. Among rheological properties, viscosity is widely used in industrial and academic applications such as: a parameter for the calculation of heat and mass transfer coefficients; equipment design; cost assessment; de sign processes; quality control of the product; and enable an understanding of the chemica l structure of raw materials. During industrial processing of fruit juices, the raw mate rials are submitted to temperatures and concentrations of solids variations that altering i ts viscosity. Therefore, the knowledge of the combined effect of temperature and concentration of solids on viscosity are essential for the juice processing. In this work, literature data fro m eleven clarified juices of fruit (mango, cherry, apple, peach, blackcurrant, pomegranate, pe ar, lemon, tangerine, lime and grape) at concentrations and temperatures from 15.0 to 74.0 Â Brix and from 278.15 to 393.15 K, respectively, were modeled using empirical and semi -empirical correlations derived from the literature. Global and specific parameters for all studied models been obtained in function of temperature and total soluble solids (TSS) concentr ation. Four equations were evaluated to calculate the activation energy in each model (line ar equation, exponential, polynomial of 2nd and 3rd order) using activation energy as specific parameter, and three different modeling strategies were conducted: for all TSS concentratio ns and temperatures; two ranges concentrations of TSS; and, two ranges of temperatu res. The optimization strategy for the concentrations TSS range proved the most suitable. Two exponential mathematical relations based on correlation of Arrhenius have been success ful in predicting the dynamic viscosity of clarified fruit juices at concentrations from 17.0 to 50.1 ÂBrix for all temperatures studied. While Vogel's equation obtained good results for co ncentrations of 51.0 to 66.0 ÂBrix in predicting the dynamic viscosity of fruit juices. T he models were validated using experimental data to clarified orange juices at low (30.7 to 50.5 ÂBrix) and high concentrations (54.1 to 63.5 ÂBrix) of TSS, with ex cellent prediction of dynamic viscosity
4
Neogi, Swati. "Modeling high viscosity melt phase polycondensation reactors using direct inclusion of experimental mixing data." Ohio : Ohio University, 1992. http://www.ohiolink.edu/etd/view.cgi?ohiou1173754996.
Full text
5
Scott, Matthew. "The modeling of blood rheology in small vessels." Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/1149.
Full textAbstract:
Blood is a dense suspension of flexible red blood cells. In response to a background flow, these cells distribute themselves non-uniformly throughout the vessel. As a result, material properties that are well defined in homogeneous fluids, such as viscosity, are no longer so, and depend upon the flow geometry along with the particle properties. Using a simple model that accounts for the steady-state particle distribution in vessel flow, we derive an expression for the effective viscosity of blood and the suspension flow velocity field in a pressure-driven tube flow. We derive the steady-state particle distribution from a conservation equation with convective flux arising from particle deformation in the flow. We then relate the particle microstructure to the overall flow through a generalized Newtonian stress-tensor, with the particle volume fraction appearing in the expression for the local viscosity. Comparing with experimental data, we show that the model quantitatively reproduces the observed rheology of blood in tube flow.
We reconsider the problem in an alternate geometry corresponding to the flow between two concentric cylinders. The steady-state particle distribution, suspension velocity field and the measured effective viscosity are all very different from their counterparts in tube flow, casting serious doubt upon the practice of using data from a Couette viscometer to parameterize constitutive models applied to vascular blood flow.
Finally, we calculate the effect of random fluctuations in the particle velocity on the averaged behaviour of the particle conservation equation. Using a smoothing method for linear stochastic differential equations, we derive a correction to the free Einstein-Stokes diffusion coeffcient that is due to the interaction of the particles with their neighbours.
6
Loney, Drew Allan. "Coupled electrical and acoustic modeling of viscous fluid ejectors." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54247.
Full textAbstract:
The focus of this dissertation is the development of a fundamental understanding of the acoustics and piezoelectric transducer governing the operation of piezoelectric inkjets and horn-based ultrasonic atomizers when utilizing high viscosity working fluids. This work creates coupled, electro-mechanical analytical models of the acoustic behavior of these devices by extending models from the literature which make minimal simplifications in the handling terms that account for viscous losses. Models are created for each component of the considered fluid ejectors: piezoelectric transducers, acoustic pipes, and acoustic horns. The acoustic pipe models consider the two limited cases when either the acoustic boundary layer or attenuation losses dominate the acoustic field and are adapted to account for changes in cross-sectional area present in acoustic horns. A full electro-mechanical analytical model of the fluid ejectors is formed by coupling the component models using appropriate boundary conditions.
The developed electro-mechanical model is applied to understand the acoustic response of the fluid cavity alone and when combined with the transducer in horn-based ultrasonic atomizers. An understanding of the individual and combined acoustic response of the fluid cavity and piezoelectric transducer allow for an optimal geometry to be selected for the ejection of high viscosity working fluids. The maximum pressure gradient magnitude produced by the atomizer is compared to the pressure gradient threshold required for fluid ejection predicted by a hydrodynamic scaling analysis. The maximum working fluid viscosity of the standard horn-based ultrasonic atomizer and those with dual working fluid combinations, a low viscosity and a high viscosity working fluid to minimize viscous dissipation, is established to be on the order of 100mPas.
The developed electro-mechanical model is also applied to understand the acoustic response of the fluid cavity and annular piezoelectric transducer in squeeze type ejectors with high viscosity working fluids. The maximum pressure gradient generated by the ejector is examined as a function of the principle geometric properties. The maximum pressure gradient magnitude produced by the ejector is again compared to the pressure gradient threshold derived from hydrodynamic scaling. The upper limit on working fluid viscosity is established as 100 mPas.
7
Dickmann, James Scott. "Volumetric Properties and Viscosity of Fluid Mixtures at High Pressures: Lubricants and Ionic Liquids." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/90219.
Full textAbstract:
The present thesis explores the volumetric and transport properties of complex fluid mixtures under pressure in order to develop a better, more holistic understanding of the relationship between the volumetric properties, derived thermodynamic properties, and viscosity. To accomplish this broad objective, two different categories of fluid mixtures were examined using a combination of experimental data and models. These included base oils and their mixtures with polymeric additives, used in lubricants and ionic liquids, with cosolvent addition, for use in biomass and polymer processing. Experimental density data were collected using a variable-volume view-cell at pressures up to 40 MPa and temperatures up to 398 K. A unique high pressure rotational viscometer was developed to study the effect of pressure, temperature, and shear rate on viscosity while also allowing for the simultaneous examination of phase behavior. Viscosity data were collected at pressures up to 40 MPa, temperatures up to 373 K, and shear rates up to 1270 s-1. Experimental density and viscosity data were fit to a pair of coupled model equations, the Sanchez-Lacombe equation of state and the free volume theory respectively. From density, derived thermodynamic properties, namely isothermal compressibility, isobaric thermal expansion coefficient, and internal pressure, were calculated. By generating these models, viscosity could be viewed in terms of density, allowing for a direct link with thermodynamic properties.
In the first part of the study, the effect of composition on density, thermodynamic properties, and viscosity was examined for base oils used in automotive lubricants. Six different base oils, four mineral oils and two synthetic oils, were studied to develop a better understanding on how the thermodynamic properties, particularly isothermal compressibility and internal pressure, vary with the concentration of cyclic molecules in the oil stock. Isothermal compressibility was found to decrease with cycloalkane content, while internal pressure increased. Additionally, the effect of two different polymeric additives on the volumetric properties and viscosity of a base oil composed of poly(α olefins) was examined. Both additives are polymethacrylate based, one with amine functionality, and are used as viscosity index modifiers in engine oils and automatic transmission fluids. The polymer with amine functionality was found to have a significant effect on internal pressure, seen as a large drop at high polymer concentration (7 mass percent), due to the addition of repulsive intermolecular interactions.
In the second part of the study, six ionic liquids with the 1-alkyl-3-methylimidazolium cation and their mixtures with ethanol were examined. Two anions were used, chloride and acetate. The effect of ethanol addition on the derived thermodynamic properties and viscosity was studied in terms of chain length of the alkyl group on the cation. In addition, a method of estimating Hildebrand solubility parameter was employed, allowing for solubility parameter to be put in terms of pressure, temperature, and composition. The effect of cosolvent addition on the thermodynamic properties was changed by the length of the alkyl group on the cation. As the cation became bulkier, anion-cation interactions weakened, allowing for an increase in the anion-cosolvent interactions.Doctor of Philosophy
The present thesis aims to understand both the density and viscosity of various fluid mixtures at high pressures and temperatures through both experiments and modeling. By studying these properties simultaneously, a more holistic view of a fluid can be developed to predict its usefulness for a specific application. This is especially important in the case of fluid mixtures, where, in addition to temperature and pressure, composition needs to be taken into account. To accomplish the experimental portion of this work, a new high pressure rotational viscometer was developed to measure viscosity as a function of temperature and pressure in conjunction with a preexisting technique for measuring density. This experimental data was used to create models, allowing for a better understanding of the effect of temperature, pressure, and composition on both density and viscosity along with certain thermodynamic properties. In the first part of the study, oils and additives used to make lubricants with automotive applications, such as engine oils and automatic transmission fluids, were studied. By studying the properties of these mixtures under pressure, a better understanding of how properties key to lubricant effectiveness are related to temperature, pressure, and composition can be developed. In the second part of the study, ionic liquids, salts with melting points below 100oC, and their mixtures with ethanol were studied. Ionic liquids have unique properties and have been studied for use in batteries, polymer processing, biomass processing, and gas capture. Due to the wide range of potential ionic liquids with various properties that can be made, these salts have been described as tailorable solvents. By adding an additional solvent, the resulting mixture can be tuned through temperature, pressure, and composition. Using the set of tools employed in the present work, important properties for process design were calculated. In particular, the Hildebrand solubility parameter was estimated as a function of temperature, pressure, and composition. The solubility parameter is a useful tool in predicting whether or not a material will dissolve in the solvent of choice.
8
Daas, Mutaz A. "Modeling the effects of oil viscosity and pipe inclination on flow characteristics and drag reduction in slug flow." Ohio : Ohio University, 2001. http://www.ohiolink.edu/etd/view.cgi?ohiou1179160070.
Full text
9
Tromp, Stéphane. "Lubrication with a refrigerant : An industrial challenge investigated through multiscale modeling based on fluid/surface chemistry." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI060/document.
Full textAbstract:
Dans les grands systèmes de réfrigération, l’utilisation de réfrigérants comme lubrifiants, à la place des huiles, simplifie la conception du système, l’allège et réduit son impact environnemental. La très faible viscosité du réfrigérant conduit à une épaisseur de film séparant les deux surfaces comparable à leur rugosité. Néanmoins, des travaux expérimentaux avec le réfrigérant R1233zd suggèrent que la lubrification est possible dans ces conditions grâce à la formation d’une couche adsorbée sur la surface d’oxyde de fer. Les analyses expérimentales in situ dans le contact sont très difficiles à cause des conditions de fort confinement et haute pression. C’est pourquoi une approche numérique multi-échelles est développée, afin d’étudier l’impact des réactions physico-chimiques à l’interface réfrigérant-surface sur les propriétés de lubrification. La théorie de la fonctionnelle de la densité est utilisée pour quantifier au niveau quantique, l’adsorption d’une molécule de réfrigérant sur une surface d’oxyde de fer. Des énergies de liaison allant de -0.92 eV à -0.22 eV sont observées et reliées à différents cas d’adsorption. Ces résultats sont exploités pour paramétrer un champ de forces interfacial, qui prédit des structures moléculaires à l’interface, différentes de celles obtenues avec des potentiels basés sur les règles de mélange classiques. Des simulations de dynamique moléculaire utilisant ce champ de forces paramétré confirment l’existence d’une couche fortement adsorbée de R1233zd sur une surface d’oxyde de fer. Avec des surfaces atomiques lisses et seulement 2 nm d’épaisseur de film de réfrigérant, les couches adsorbées résistent à des pressions allant jusqu’à 4 GPa et des vitesses de cisaillement atteignant 100 m/s. Une valeur minimale de 5 molécules de réfrigérant par nm² est nécessaire à la formation de deux couches adsorbées à 0.5 GPa. De plus, des simulations en cisaillement avec une surface rugueuse prédisent une rupture totale du film à environ 13 GPaIn large refrigeration systems, using the refrigerant as lubricant instead of oil can help to simplify the design, lighten the systems, and reduce their environmental impact. However, the very low viscosity of refrigerants leads to ultra-thin films separating the surfaces, with a thickness comparable to surface roughness. Nevertheless, experiments with the R1233zd refrigerant suggests that lubrication is still possible in that situation thanks to an adsorbed layer formed on iron oxide surfaces. Experimental in situ analysis area is very difficult because of high confinement and high pressure. That is why a multiscale numerical approach is developed here, to explore the impact of chemical reactions and physical processes at the refrigerant-surface interface on large-scale lubrication properties. Density functional theory is used to quantify the adsorption of a refrigerant molecule on an iron oxide surface at the quantum level. Binding energies ranging from -0.92 eV to -0.22 eV are measured and related to different adsorption cases. These results are then used to parametrize an interfacial force field, whose predictions of interfacial molecular structure differs from those obtained using potentials based on standard mixing rules. Large-scale molecular dynamics simulations involving this parametrized force field confirm the existence of a strongly adsorbed layer of R1233zd molecules on iron oxide surface. With atomically smooth surfaces, and a refrigerant film thickness as small as 2 nm, the adsorbed refrigerant layers resists pressures as high as 4 GPa and sliding velocities as high as 100 m/s. A minimum value of 5 refrigerant molecules per nm² is necessary to the formation of two adsorbed layers at 0.5 GPa. Moreover, sliding simulations with a rough surface reveal total film breakdown for ca. 13 GPa
10
Rogozhina, Irina [Verfasser]. "Global modeling of the effect of strong lateral viscosity variations on dynamic geoid and mantle flow velocities / Irina Rogozhina." Potsdam : GFZ, Helmholtz-Zentrum, 2008. http://d-nb.info/991950151/34.
Full text
11
Amankwah, Kofi. "THE IMPACT OF LOWER EXTREMITY PASSIVE JOINT PROPERTIES ON STANDING FUNCTION." Case Western Reserve University School of Graduate Studies / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=case1081532731.
Full text
12
Prados, Emmanuel. "Application of the theory of the viscosity solutions to the Shape From Shading problem." Phd thesis, Université de Nice Sophia-Antipolis, 2004. http://tel.archives-ouvertes.fr/tel-00007916.
Full textAbstract:
Le problème du « Shape From Shading » est aujourd'hui considéré comme un problème mal posé et difficile à résoudre. Afin de bien comprendre les difficultés de ce problème et d'apporter des solutions fiables et pertinentes, nous proposons une approche rigoureuse basée sur la notion de solution de viscosité.Après avoir considéré et exploité au maximum les équations (aux dérivées partielles) obtenues à partir de la modélisation classique du problème du « Shape From Shading », nous proposons et étudions de nouvelles équations provenant de modélisations plus réalistes que celles qui avaient été traitées classiquement dans la littérature. Cette démarche nous permet alors de démontrer qu'avec de telles nouvelles modélisations, le problème du « Shape From Shading » est généralement un problème complètement bien posé. En d'autres termes, nous prouvons que la version classique du problème du « Shape from Shading » est devenu mal posée à cause d'une trop grande simplification de la modélisation.
Dans ce travail, nous proposons aussi une extension de la notion de solutions de viscosité singulières développée récemment par Camilli et Siconolfi. Cette extension nous permet de proposer une nouvelle caractérisation des solutions de viscosité discontinues. Ce nouveau cadre théorique nous permet aussi d'unifier les différents résultats théoriques proposés dans le domaine du « Shape From Shading ».
13
Köstler, Christopher [Verfasser], Uwe [Gutachter] Walzer, Arnd [Gutachter] Meyer, and John R. [Gutachter] Baumgardner. "Iterative solvers for modeling mantle convection with strongly varying viscosity / Christopher Köstler ; Gutachter: Uwe Walzer, Arnd Meyer, John R. Baumgardner." Jena : Friedrich-Schiller-Universität Jena, 2011. http://d-nb.info/1208309021/34.
Full text
14
Persson, Mikael. "Densities and viscosities of slags : modeling and experimental investigations." Licentiate thesis, Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3926.
Full text
15
Bertóti, Róbert [Verfasser], and T. [Akademischer Betreuer] Böhlke. "Modeling the flow-induced anisotropic effective viscosity of fiber suspensions by mean-field and full-field homogenization / Róbert Bertóti ; Betreuer: T. Böhlke." Karlsruhe : KIT-Bibliothek, 2021. http://d-nb.info/1231361476/34.
Full text
16
He, Shunli. "Frittage des métaux en phase liquide : modélisation de l'étape de réarrangement." Grenoble 1, 1993. http://www.theses.fr/1993GRE10113.
Full textAbstract:
Ce memoire est consacre a l'etude de la modelisation de la densification lors du frittage en phase liquide de melanges de poudres metalliques. Il s'agit de suspensions concentrees en presence de capillarite, ce qui fait appel a deux types de mecaniques: la mecanique des suspensions et celle des milieux poreux continus. L'avancement de la recherche existante est synthetise et classe du point de vue mecanique. Les etudes au niveau microscopique et de la viscosite effective mettent en evidence l'intervention de mecanismes preponderants d'ecoulement comme l'interaction des particules, la perturbation des capillaires, la compressibilite du materiau et le mecanisme du remplissage des pores. Ces mecanismes sont modelises et ils sont estimes de facon tres satisfaisante. Une theorie du comportement macroscopique de la suspension concentree avec capillarite est proposee a l'aide d'une methode de developpements a echelles multiples. Dans un cas simple, nous avons obtenu un modele en assemblant les elements qui contribuent a la comprehension et a la description du phenomene. Ce modele permet de prevoir la cinetique de rearrangement des particules avec phase liquide. Il explique correctement les effets des parametres concernes, en particulier, il verifie et complete la formule empirique de kingery. Par ailleurs, notre modele fournit des caracteristiques remarquables. La pente maximale de la courbe du retrait cinetique en echelles log-log est superieure a un, lorsque la repartition des pores est etendue. Par contre, cette pente maximale est inferieure a un si la distribution des capillaires est tres etroite. Dans tous les deux cas, la pente diminue au cours du temps
17
Mou, Changhong. "Data-Driven Variational Multiscale Reduced Order Modeling of Turbulent Flows." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/103895.
Full textAbstract:
In this dissertation, we consider two different strategies for improving the projection-based reduced order model (ROM) accuracy:
(I) adding closure terms to the standard ROM;
and
(II) using Lagrangian data to improve the ROM basis.
Following strategy (I), we propose a new data-driven reduced order model (ROM) framework that centers around the hierarchical structure of the variational multiscale (VMS) methodology and utilizes data to increase the ROM accuracy at a modest computational cost.
The VMS methodology is a natural fit for the hierarchical structure of the ROM basis:
In the first step, we use the ROM projection to separate the scales into three categories: (i) resolved large scales, (ii) resolved small scales, and (iii) unresolved scales.
In the second step, we explicitly identify the VMS-ROM closure terms, i.e., the terms representing the interactions among the three types of scales.
In the third step, we use available data to model the VMS-ROM closure terms.
Thus, instead of phenomenological models used in VMS for standard numerical discretizations (e.g., eddy viscosity models), we utilize available data to construct new structural VMS-ROM closure models.
Specifically, we build ROM operators (vectors, matrices, and tensors) that are closest to the true ROM closure terms evaluated with the available data.
We test the new data-driven VMS-ROM in the numerical simulation of four test cases:
(i) the 1D Burgers equation with viscosity coefficient $nu = 10^{-3}$;
(ii) a 2D flow past a circular cylinder at Reynolds numbers $Re=100$, $Re=500$, and $Re=1000$;
(iii) the quasi-geostrophic equations at Reynolds number $Re=450$ and Rossby number $Ro=0.0036$; and
(iv) a 2D flow over a backward facing step at Reynolds number $Re=1000$.
The numerical results show that the data-driven VMS-ROM is significantly more accurate than standard ROMs.
Furthermore, we propose a new hybrid ROM framework for the numerical simulation of fluid flows.
This hybrid framework incorporates two closure modeling strategies: (i) A structural closure modeling component that involves the recently proposed data-driven variational multiscale ROM approach, and (ii) A functional closure modeling component that introduces an artificial viscosity term.
We also utilize physical constraints for the structural ROM operators in order to add robustness to the hybrid ROM.
We perform a numerical investigation of the hybrid ROM for the three-dimensional turbulent channel flow at a Reynolds number $Re = 13,750$.
In addition, we focus on the mathematical foundations of ROM closures.
First, we extend the verifiability concept from large eddy simulation to the ROM setting.
Specifically, we call a ROM closure model verifiable if a small ROM closure model error (i.e., a small difference between the true ROM closure and the modeled ROM closure) implies a small ROM error.
Second, we prove that a data-driven ROM closure (i.e., the data-driven variational multiscale ROM) is verifiable.
For strategy (II), we propose new Lagrangian inner products that we use together with Eulerian and Lagrangian data to construct new Lagrangian ROMs.
We show that the new Lagrangian ROMs are orders of magnitude more accurate than the standard Eulerian ROMs, i.e., ROMs that use standard Eulerian inner product and data to construct the ROM basis.
Specifically, for the quasi-geostrophic equations, we show that the new Lagrangian ROMs are more accurate than the standard Eulerian ROMs in approximating not only Lagrangian fields (e.g., the finite time Lyapunov exponent (FTLE)), but also Eulerian fields (e.g., the streamfunction).
We emphasize that the new Lagrangian ROMs do not employ any closure modeling to model the effect of discarded modes (which is standard procedure for low-dimensional ROMs of complex nonlinear systems).
Thus, the dramatic increase in the new Lagrangian ROMs' accuracy is entirely due to the novel Lagrangian inner products used to build the Lagrangian ROM basis.Doctor of Philosophy
Reduced order models (ROMs) are popular in physical and engineering applications: for example, ROMs are widely used in aircraft designing as it can greatly reduce computational cost for the aircraft's aeroelastic predictions while retaining good accuracy. However, for high Reynolds number turbulent flows, such as blood flows in arteries, oil transport in pipelines, and ocean currents, the standard ROMs may yield inaccurate results. In this dissertation, to improve ROM's accuracy for turbulent flows, we investigate three different types of ROMs. In this dissertation, both numerical and theoretical results show that the proposed new ROMs yield more accurate results than the standard ROM and thus can be more useful.
18
Su, Yung-Chieh. "Selection of Prediction Methods for Thermophysical Properties for Process Modeling and Product Design of Biodiesel Manufacturing." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/32675.
Full textAbstract:
To optimize biodiesel manufacturing, many reported studies have built simulation models to quantify the relationship between operating conditions and process performance. For mass and energy balance simulations, it is essential to know the four fundamental thermophysical properties of the feed oil: liquid density (Ï L), vapor pressure (Pvap), liquid heat capacity (CpL), and heat of vaporization (Î Hvap). Additionally, to characterize the fuel qualities, it is critical to develop quantitative correlations to predict three biodiesel properties, namely, viscosity, cetane number, and flash point. Also, to ensure the operability of biodiesel in cold weather, one needs to quantitatively predict three low-temperature flow properties: cloud point (CP), pour point (PP), and cold filter plugging point (CFPP). This article presents the results from a comprehensive evaluation of the methods for predicting these four essential feed oil properties and six key biodiesel fuel properties. We compare the predictions to reported experimental data and recommend the appropriate prediction methods for each property based on accuracy, consistency, and generality. Of particular significance are (1) our presentation of simple and accurate methods for predicting the six key fuel properties based on the number of carbon atoms and the number of double bonds or the composition of total unsaturated fatty acid methyl esters (FAMEs) and (2) our posting of the Excel spreadsheets for implementing all of the evaluated accurate prediction methods on our group website (www.design.che.vt.edu) for the reader to download without charge.Master of Science
19
Mehri, Rym. "Red Blood Cell Aggregation Characterization: Quantification and Modeling Implications of Red Blood Cell Aggregation at Low Shear Rates." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35093.
Full textAbstract:
Red blood cells (RBCs) are the most abundant cells in human blood, representing 40 to 45% of the blood volume (hematocrit). These cells have the particular ability to deform and bridge together to form aggregates under very low shear rates. The theory
and mechanics behind aggregation are, however, not yet completely understood.
The purpose of this work is to provide a novel method to analyze, understand and mimic blood behaviour in microcirculation. The main objective is to develop a methodology to quantify and characterize RBC aggregates and hence enhance the current understanding of the non-Newtonian behaviour of blood at the microscale. For this purpose, suspensions of porcine blood and human blood are tested in vitro in a Poly-di-methylsiloxane (PDMS) microchannel to characterize RBC aggregates within these two types of blood. These microchannels are fabricated using standard photolithography methods. Experiments are performed using a micro Particle Image Velocimetry ( PIV) system for shear rate measurements coupled with a high speed camera for the flow visualization.
Corresponding numerical simulations are conducted using a research Computational
Fluid Dynamic (CFD) solver, Nek5000, based on the spectral element method
solution to the incompressible non-Newtonian Navier-Stokes equations. RBC aggregate sizes are quantified in controlled and measurable shear rate environments for 5, 10 and 15% hematocrit. Aggregate sizes are determined using image processing techniques. Velocity fields of the blood flow are measured experimentally and compared to numerical simulations using simple non-Newtonian models (Power law and Carreau models).
This work establishes for the first time a relationship between RBC aggregate sizes
and corresponding shear rates in a microfluidic environment as well as one between RBC aggregate sizes and apparent blood viscosity at body temperature in a microfluidic controlled environment. The results of the investigation can be used to help develop new numerical models for non-Newtonian blood flow, provide a better understanding of the mechanics of RBC aggregation and help determine aggregate behaviour in clinical settings such as for degenerative diseases like diabetes and heart disease.
20
Moghaddas, Mohamad Amin. "Comparison of Computational Modeling of Precision Glass Molding of Infrared Lenses." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397599181.
Full text
21
Granero, Maira Guiraldeli. "Viscosidade de misturas envolvendo alcoóis de cadeia curta e composto graxos: obtenção de novos parâmetros para o modelo UNIFAC-VISCO." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/74/74132/tde-20112012-153707/.
Full textAbstract:
A obtenção de dados de viscosidade, é fundamental para o projeto de equipamentos, tubulações e otimização de processos, já que esta propriedade afeta tanto a perda de energia por atrito em fluidos, como os mecanismos de transferência de calor e de massa. O presente trabalho de Mestrado teve como objetivo medir experimentalmente dados de viscosidade para misturas formadas por ácidos graxos comerciais e solventes alcoólicos de diferentes tamanhos de cadeia carbônica (etanol, 2-propanol, 1-butanol, 1-pentanol e 1-hexanol), com ou sem a adição de água, variando-se a temperatura desde o ponto de fusão do composto graxo até o ponto de ebulição de cada solvente. Estes dados foram agrupados aos dados experimentais de viscosidades de misturas de triacilgliceróis (TAG) e ácidos graxos (AG) já disponíveis na literatura, para a obtenção de parâmetros de interação entre os grupos funcionais formadores dos componentes presentes nos sistemas estudados, utilizando-se o modelo de contribuição de grupos UNIFAC-VISCO. Em uma primeira abordagem, apenas os parâmetros inexistentes na literatura foram ajustados, obtendo-se um erro relativo médio igual a 10,21 %. A modelagem também foi realizada ajustando-se todos os parâmetros de interação, incluindo os já publicados, obtendo-se nesta segunda abordagem, um erro relativo médio igual a 7,54 %. A capacidade preditiva dos parâmetros obtidos foi testada em misturas semelhantes, formadas por óleos vegetais ou gordura animal, ácidos graxos e solventes alcoólicos, cujas viscosidades também foram determinadas neste trabalho, porém não fizeram parte do banco de dados utilizado na modelagem. Os resultados obtidos foram comparados aos de outros modelos para o cálculo de viscosidades de misturas conhecidos da literatura, dentre eles, a Regra de Kay, o Modelo de Kendall e Monroe e o Modelo CG-UNIMOD. Para fins comparativos, este conjunto de dados também foi ajustado a equação de Grunberg-Nissan, da qual foram obtidos parâmetros de interação entre os componentes das misturas. Os testes preditivos mostraram que o modelo UNIFAC-VISCO proporcionou os menores erros relativos para a maioria das misturas estudadas, porém ainda bastante elevados em alguns casos. Por outro lado, o Modelo de Grunberg-Nissan proporcionou erros relativos bem menores, o que era esperado, uma vez que as viscosidades de cada sistema foram correlacionadas pelo modelo.The acquisition of viscosity data is critical for the design of equipments and pipes, as well as for the process optimization, since this property affects both the energy loss by friction in fluids, such as the mechanisms of mass and heat transfer. The present work aimed the measurement of experimental viscosity data for mixtures containing commercial fatty acids and alcoholic solvents of different sizes of carbon chain (ethanol, 2-propanol, 1-butanol, 1-pentanol and 1-hexanol), with or without the addition of water, varying the temperature from the melting point of the fatty compound to the boiling point of each solvent. These data were grouped together to experimental viscosity data of triacylglycerols (TAG) and fatty acids (FA) mixtures that were already available in the literature, to obtain interaction parameters between the forming functional groups of the components present in the systems studied, using the group contribution model UNIFAC-VISCO. In a first approach, only the parameters not available in the literature were adjusted obtaining an average error equal to 10.21%. The modeling was also performed by adjusting all interaction parameters, including those already published, obtaining in this second approach, an average error equal to 7.54%. The predictive ability of parameters obtained was tested in similar mixtures containing vegetable oils or animal fats, fatty acids and alcoholic solvents, whose viscosities were also determined in this work, but were not part of the database used in the modeling. The obtained results were compared to other known models for the calculation of viscosities of mixtures, such as the Kay\'s Rule, the Kendall and Monroe model and the CG-UNIMOD. For comparative purposes, this data set was also adjusted to the Grunberg-Nissan equation, in which interaction parameters between the components of mixtures were obtained. The predictive tests showed that the UNIFAC-VISCO model provided the lowest relative errors for most of the mixtures studied, but still quite high in some cases. On the other hand, the Grunberg-Nissan model provided relative errors much smaller, which was expected, since the viscosities of each system were correlated by the model.
22
Lemaire, Etienne. "Contribution au développement de microcapteurs intégrés de viscoélasticité de fluides." Phd thesis, Bordeaux 1, 2013. http://tel.archives-ouvertes.fr/tel-00873929.
Full textAbstract:
Les propriétés viscoélastiques des fluides déterminent leur écoulement. L'étude de ces propriétés a de nombreuses applications industrielles et académiques qui concernent la matière dite " molle " (polymères, colloïdes, tensioactifs, protéines, ...). L'approche proposée permet d'étudier ces propriétés sur une gamme de fréquence allant de 1 à 100 kHz. La méthode utilise la mesure de la vibration d'une microstructure actionnée électromagnétiquement et immergée dans le fluide à caractériser. La réponse en fréquence du système mécanique, mesurée optiquement ou électriquement, est caractéristique du milieu dans lequel la structure est immergée. Une méthode analytique dédiée aux micropoutres, pour l'extraction des propriétés rhéologiques du milieu, a été améliorée tout au long de la thèse. La méthode analytique développée, pour être appliquée, nécessite la précision d'un système optique complexe pour mesurer sans artefact les propriétés mécaniques de l'interaction micropoutre-liquide. Ainsi les liquides opaques ne peuvent être caractérisés avec cette approche. De plus la mesure peut difficilement être intégrée dans un dispositif portable tout-électronique. Afin de pallier ces difficultés et de proposer une mesure de la viscoélasticité en milieu opaque, la stratégie de mesure du capteur jusqu'au traitement des signaux ont été réévalués : (1) des microstructures en " U " ont été fabriquées, (2) une méthode de mesure intégrée a été mise en place et (3) une méthode de traitement à fréquence unique a été utilisée. Finalement, un liquide opaque viscoélastique, le yaourt, a pu être caractérisé in-situ tout au long de la fermentation lactique permettant de démontrer la validité et l'applicabilité de la méthode mise en œuvre pour le suivi en temps réel de la viscoélasticité.
23
Humberg, Kai [Verfasser], Roland [Gutachter] Span, and Markus [Gutachter] Richter. "Viscosity measurements of binary gas mixtures and analysis of approaches for the modeling of mixture viscosities / Kai Humberg ; Gutachter: Roland Span, Markus Richter ; Fakultät für Maschinenbau." Bochum : Ruhr-Universität Bochum, 2020. http://d-nb.info/1223176126/34.
Full text
24
Wang, Zhu. "Reduced-Order Modeling of Complex Engineering and Geophysical Flows: Analysis and Computations." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/27504.
Full textAbstract:
Reduced-order models are frequently used in the simulation of complex flows to overcome the high computational cost of direct numerical simulations, especially for three-dimensional nonlinear problems.
Proper orthogonal decomposition, as one of the most commonly used tools to generate reduced-order models, has been utilized in many engineering and scientific applications.
Its original promise of computationally efficient, yet accurate approximation of coherent structures in high Reynolds number turbulent flows, however, still remains to be fulfilled. To balance the low computational cost required by reduced-order modeling and the complexity of the targeted flows, appropriate closure modeling strategies need to be employed.
In this dissertation, we put forth two new closure models for the proper orthogonal decomposition reduced-order modeling of structurally dominated turbulent flows: the dynamic subgrid-scale model and the variational multiscale model.
These models, which are considered state-of-the-art in large eddy simulation, are carefully derived and numerically investigated.
Since modern closure models for turbulent flows generally have non-polynomial nonlinearities, their efficient numerical discretization within a proper orthogonal decomposition framework is challenging. This dissertation proposes a two-level method for an efficient and accurate numerical discretization of general nonlinear proper orthogonal decomposition closure models. This method computes the nonlinear terms of the reduced-order model on a coarse mesh. Compared with a brute force computational approach in which the nonlinear terms are evaluated on the fine mesh at each time step, the two-level method attains the same level of accuracy while dramatically reducing the computational cost. We numerically illustrate these improvements in the two-level method by using it in three settings: the one-dimensional Burgers equation with a small diffusion parameter, a two-dimensional flow past a cylinder at Reynolds number Re = 200, and a three-dimensional flow past a cylinder at Reynolds number Re = 1000.
With the help of the two-level algorithm, the new nonlinear proper orthogonal decomposition closure models (i.e., the dynamic subgrid-scale model and the variational multiscale model), together with the mixing length and the Smagorinsky closure models, are tested in the numerical simulation of a three-dimensional turbulent flow past a cylinder at Re = 1000. Five criteria are used to judge the performance of the proper orthogonal decomposition reduced-order models: the kinetic energy spectrum, the mean velocity, the Reynolds stresses, the root mean square values of the velocity fluctuations, and the time evolution of the proper orthogonal decomposition basis coefficients. All the numerical results are benchmarked against a direct numerical simulation. Based on these numerical results, we conclude that the dynamic subgrid-scale and the variational multiscale models are the most accurate.
We present a rigorous numerical analysis for the discretization of the new models. As a first step, we derive an error estimate for the time discretization of the Smagorinsky proper orthogonal decomposition reduced-order model for the Burgers equation with a small diffusion parameter.
The theoretical analysis is numerically verified by two tests on problems displaying shock-like phenomena.
We then present a thorough numerical analysis for the finite element discretization of the variational multiscale proper orthogonal decomposition reduced-order model for convection-dominated convection-diffusion-reaction equations. Numerical tests show the increased numerical accuracy over the standard reduced-order model and illustrate the theoretical convergence rates.
We also discuss the use of the new reduced-order models in realistic applications such as airflow simulation in energy efficient building design and control problems as well as numerical simulation of large-scale ocean motions in climate modeling. Several research directions that we plan to pursue in the future are outlined.Ph. D.
25
Jain, Anurag. "Experimental study and numerical analysis of compression molding process for manufacturing precision aspherical glass lenses." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1148650470.
Full text
26
Aachib, Mostafa. "Deplacement isotherme de deux fluides miscibles dans un milieu poreux sature : effets de densite et de viscosite, critere de stabilite." Université Louis Pasteur (Strasbourg) (1971-2008), 1987. http://www.theses.fr/1987STR13096.
Full textAbstract:
Etude de l'influence des contrastes de densite et de viscosite sur le deplacement miscible lors d'un passage du regime stable au regime instable. On propose un modele empirique pour un deplacement miscible eau douce-solution de chlorure de calcium: etude experimentale par mesure des conductivites electriques. Mise en evidence d'un critere de stabilite
27
Madureira, Daniel Fialho. "Predição da viscosidade de emulsões para petróleos leves brasileiros." reponame:Repositório Institucional do FGV, 2015. http://hdl.handle.net/10438/13793.
Full textAbstract:
Submitted by Daniel Fialho Madureira (daniel.fialho01@gmail.com) on 2015-03-06T22:35:06Z
No. of bitstreams: 1
viscosidade_emulsoes.pdf: 1828480 bytes, checksum: 77a4926687a6e5e766bedf0f444d191b (MD5)Approved for entry into archive by Janete de Oliveira Feitosa (janete.feitosa@fgv.br) on 2015-06-16T14:06:31Z (GMT) No. of bitstreams: 1 viscosidade_emulsoes.pdf: 1828480 bytes, checksum: 77a4926687a6e5e766bedf0f444d191b (MD5)
Approved for entry into archive by Marcia Bacha (marcia.bacha@fgv.br) on 2015-06-19T11:59:55Z (GMT) No. of bitstreams: 1 viscosidade_emulsoes.pdf: 1828480 bytes, checksum: 77a4926687a6e5e766bedf0f444d191b (MD5)
Made available in DSpace on 2015-06-19T12:00:12Z (GMT). No. of bitstreams: 1 viscosidade_emulsoes.pdf: 1828480 bytes, checksum: 77a4926687a6e5e766bedf0f444d191b (MD5) Previous issue date: 2014-12-17
A formação de emulsão de água-em-óleo gera um significativo incremento na viscosidade, o que afeta diretamente a produção do poço, pois aumenta a perda de carga ao longo da linha de produção, dificultando o escoamento e diminuindo a produção de óleo. A presença e natureza da emulsão, e seu impacto na reologia do petróleo, podem determinar a viabilidade econômica e técnica dos processos envolvidos. A medida que a fração de água aumenta e a temperatura é reduzida, o comportamento das emulsões se torna cada vez mais não-Newtoniano. A decorrência disso, é que a temperatura e a taxa de cisalhamento passam a ter maior impacto na variação da viscosidade das emulsões. Nesse estudo são propostos novos métodos que levam em conta essas variáveis. Os dados reológicos experimentais de 15 petróleos leves foram utilizados para avaliar o desempenho dos modelos existentes na literatura e compará-los com os novos métodos propostos nesse estudo.
The formation of water-in-oil emulsion produces a significant increase in viscosity, which directly affects the production from the well as it increases the pressure drop along the production line, thus hindering the flow and reducing oil production. The presence and nature of the emulsion, and its impact on oil rheology, can determine the economic and technical feasibility of the processes involved. As the water fraction rises and the temperature is reduced, the behavior of the emulsions becomes increasingly non-Newtonian. The result of this is that the temperature and shear rate have more impact on the variation in the viscosity of emulsions. In this study are proposed new methods that take into account these variables. The experimental rheological data of 15 light oil were used to evaluate the performance of existing models in the literature and compare them with the new methods proposed in this study.
28
Fridström, Richard. "Resonant magnetic perturbation effect on the tearing mode dynamics : Novel measurements and modeling of magnetic fluctuation induced momentum transport in the reversed-field pinch." Doctoral thesis, KTH, Fusionsplasmafysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-218052.
Full textAbstract:
The tearing mode (TM) is a resistive instability that can arise in magnetically confined plasmas. The TM can be driven unstable by the gradient of the plasma current. When the mode grows it destroys the magnetic field symmetry and reconnects the magnetic field in the form of a so-called magnetic island. The TMs are inherent to a type of device called the reversed-field pinch (RFP), which is a device for toroidal magnetic confinement of fusion plasmas. In the RFP, TMs arise at several resonant surfaces, i.e. where the field lines and the perturbation have the same pitch angle. These surfaces are closely spaced in the RFP and the neighboring TM islands can overlap. Due to the island overlap, the magnetic field lines become tangled resulting in a stochastic magnetic field, i.e. the field lines fill a volume instead of lying on toroidal surfaces. Consequently, a stochastic field results in an anomalously fast transport in the radial direction. Stochastic fields can also arise in other plasmas, for example, the tokamak edge when a resonant magnetic perturbation (RMP) is applied by external coils. This stochastization is intentional to mitigate the edge-localized modes. The RMPs are also used for control of other instabilities. Due to the finite number of RMP coils, however, the RMP fields can contain sidebands that decelerate and lock the TMs via electromagnetic torques. The locking causes an increased plasma-wall interaction. And in the tokamak, the TM locking can cause a plasma disruption which is disastrous for future high-energy devices like the ITER. In this thesis, the TM locking was studied in two RFPs (EXTRAP T2R and Madison Symmetric Torus) by applying RMPs. The experiments were compared with modern mode-locking theory. To determine the viscosity in different magnetic configurations where the field is stochastic, we perturbed the momentum via an RMP and an insertable biased electrode. In the TM locking experiments, we found qualitative agreement with the mode-locking theory. In the model, the kinematic viscosity was chosen to match the experimental locking instant. The model then predicts the braking curve, the short timescale dynamics, and the mode unlocking. To unlock a mode, the RMP amplitude had to decrease by a factor ten from the locking amplitude. These results show that mode-locking theory, including the relevant electromagnetic torques and the viscous plasma response, can explain the experimental features. The model required viscosity agreed with another independent estimation of the viscosity. This showed that the RMP technique can be utilized for estimations of the viscosity. In the momentum perturbation experiments, it was found that the viscosity increased 100-fold when the magnetic fluctuation amplitude increased 10-fold. Thus, the experimental viscosity exhibits the same scaling as predicted by transport in a stochastic magnetic field. The magnitude of the viscosity agreed with a model that assumes that transport occurs at the sound speed -- the first detailed test of this model. The result can, for example, lead to a clearer comparison between experiment and visco-resistive magnetohydrodynamics (MHD) modeling of plasmas with a stochastic magnetic field. These comparisons had been complicated due to the large uncertainty in the experimental viscosity. Now, the viscosity can be better constrained, improving the predictive capability of fusion science.QC 20171122
29
Miller, James. "Modelling melt viscosity for nuclear waste glass." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/9110/.
Full textAbstract:
This work forms part of a Collaborative Awards in Science and Engineering industrial studentship (iCASE), jointly funded by the Engineering and Physical Sciences Research Council and the National Nuclear Laboratory. The aim is to develop improved models for calculating viscosities of vitreous nuclear waste melts, particularly with respect to the variation in temperature and composition. Both in vitro and in situ experimentation on nuclear material is complicated by radioactivity and its associated expenses, so computational modelling is the principal means we use to study these industrially important glasses. The problem is approached with both top-down and bottom-up methods. From a more fundamental perspective, beginning in Section 7 Molecular Dynamics techniques are used to simulate glass melts at atomic resolution. An audit of literature forcefields, using a systematic methodology for particulate systems generation, involved calculation of structural and diffusive properties to reveal the advantages and disadvantages of contemporary sodium-borosilicate models. After developing an improved glass model, from Section 11 different methods of viscosity computation were trialled to determine that most appropriate for the conditions of the nuclear glass melters. In Section 14 the Inoue2 SBN forcefield was combined with the Green-Kubo technique, using simulated runtimes more than double those of previous literature work. The analyses produced qualitative agreement in compositional and temperature trends, as well as order-of-magnitude quantitative agreement between experimental and computational viscosity results for ternary nuclear glass frits. Complimentary top-down approaches were also used, with rotary viscometry experimentation employed in Section 4 to gather temperature-composition-viscometry data for nuclear waste glasses. These data were used with different fitting algorithms in Section 15 to compare the efficacy of theoretical descriptions for glass viscosity, described in Section 3. A combination of fitting techniques assembles in Section 17 an interpolative second-order model for which the maximum discrepancy between prediction and experiment is 17% of the absolute viscosity.
30
Pegado, Roberta de Melo. "Estudo das propriedades f?sico-qu?micas de biocombust?veis microemulsionados." Universidade Federal do Rio Grande do Norte, 2008. http://repositorio.ufrn.br:8080/jspui/handle/123456789/15762.
Full textAbstract:
Made available in DSpace on 2014-12-17T15:01:17Z (GMT). No. of bitstreams: 1
RobertaMP.pdf: 1074511 bytes, checksum: a2a332dc1724fb3abebb3c1cc5d53877 (MD5)
Previous issue date: 2008-11-14The development of new fuels is an important field of scientific and technological activities, since much of the energy consumed in the world is obtained from oil, coal and natural gas, and these sources are limited and not renewable. Recently it has assessed the employment of microemulsions as an alternative for obtaining fuel isotropic between phases originally not miscible. Among many advantages, emphasizes the application of substances that provide the reduction of levels of emissions compared to fossil fuels. Thus, this work was a study of various microemulsified systems, aiming to check the performance of the winsor regions front of the use of surfactants: RENEX 18 → 150, UNITOL L-60 → L-100 and AMIDA 60, together with structure of esters from soybean and castor bean oils. From the results it were chosen four systems to physico-chemical analyzes: System I RENEX 60, Soil bean oil, methylic ester (EMOS) and water; System II RENEX 60/AMIDA 60, EMOS and water; System III RENEX 70, mamona oil methylic ester (EMOM) and water and System IV RENEX 95, EMOM and water. The tests of physico-chemical characterization and study of temperature increase were done with nine points with different compositions in a way to include the interest area (microemulsion W/O). After this study, was conducted a modeling to predict the viscosity, the property is more varied as function of compositions systems changes. The best results were the systems II and IV with a temperature stability above 60?C. The system I had its physico-chemical characterization very similar to a fossil fuel. The system II was the best one due to its corrosivity be stable. In the modeling the four systems had shown good, with an error that varied between 5 and 18%, showing to be possible the viscosity prediction from the composition of the system. The effects the microemulsion and the engine?s performance with the microemulsion were also avaliated. The tests were performed in a cycle-diesel engine. The potency and consumption were analysed. Results show a slight increase the rendiment fuel compared with the conventional as well as a decrease in specific consumption
O desenvolvimento de novos combust?veis constitui um importante campo de atividade cient?fica e tecnol?gica, uma vez que grande parte da energia consumida no mundo ? obtida do petr?leo, carv?o e do g?s natural, e estas s?o fontes limitadas e n?o renov?veis. Recentemente tem-se avaliado o emprego de microemuls?es como uma alternativa para obten??o de combust?veis isotr?picos entre fases originalmente n?o misc?veis. Dentre muitas vantagens, ressalta-se a aplica??o de subst?ncias que proporcionam a redu??o dos n?veis de emiss?es em compara??o aos combust?veis f?sseis. Desta forma, neste trabalho realizou-se um estudo de v?rios sistemas microemulsionados, visando verificar o comportamento das regi?es de Winsor frente ? utiliza??o dos tensoativos: RENEX 18 ? 150, UNITOL L-60 ? L-100 e AMIDA 60 em conjunto com a estrutura dos ?steres do ?leo de soja e de mamona. A partir dos resultados foram escolhidos quatro sistemas para an?lises fisico-qu?micas, sendo eles: Sistema I RENEX 60, ?ster Met?lico de ?leo de Soja (EMOS) e ?gua, Sistema II RENEX 60/AMIDA 60, EMOS e ?gua, Sistema III RENEX 70, ?ster Met?lico de ?leo de Mamona (EMOM) e ?gua e Sistema IV RENEX 95, EMOM e ?gua. Os ensaios de caracteriza??o f?sicoqu?mica e do estudo do aumento da temperatura foram realizados com nove pontos de composi??es diferentes de forma a melhor abranger a regi?o de interesse (microemuls?o A/O). Ap?s esse estudo, foi realizada uma modelagem para prever a viscosidade, a propriedade que mais variou em fun??o da mudan?a da composi??o dos sistemas. Os melhores resultados foram obtidos para os sistemas II e IV com estabilidade em temperaturas acima de 60?C. O sistema I apresentou propriedades f?sico-quimicas muito parecidas com um combust?vel f?ssil. O sistema II foi o melhor sistema obtido devido sua corrosividade ter se mantido est?vel, comparado ao diesel f?ssil. Na modelagem os quatro sistemas se mostraram bons com um erro que variou entre 5 e 18%, mostrando ser poss?vel a predi??o da viscosidade a partir da composi??o do sistema. Foram realizados alguns testes preliminares em um motor ciclo diesel, sendo analisado o consumo de combust?vel e a pot?ncia. Os resultados mostraram um ligeiro aumento no rendimento motor com o combust?vel microemulsionado em rela??o ao diesel convencional assim como uma diminui??o no consumo espec?fico
31
Cai, Shaobiao. "3D numerical modeling of dry/wet contact mechanics for rough, multilayered elastic-plastic solid surfaces and effects of hydrophilicity/hydrophobicity during separation with applications." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1205118488.
Full text
32
Meslin, Frédéric. "Propriétés rhéologiques des composites fibres courtes à l'état fondu." Cachan, Ecole normale supérieure, 1997. http://www.theses.fr/1997DENS0020.
Full textAbstract:
Ce travail traite de l'étude des suspensions de particules axisymétriques et rigides dans une matrice fluide. Plus précisément, nous nous sommes intéressés au comportement rhéologique de ces matériaux. Le contexte industriel associe est la mise en forme des thermoplastiques renforces par des fibres courtes. Dans une partie théorique, nous proposons un modèle de comportement, issu d'une approche micromécanique, pour les suspensions de sphéroïdes rigides dans une matrice newtonienne : une loi reliant les contraintes et les taux de déformations macroscopiques, une équation pour décrire le mouvement des particules. Ce modèle de comportement est applicable au cas des solutions en régime semi-dilue. Dans une partie expérimentale, nous proposons d'identifier des paramètres rhéologiques du modèle de comportement. A cet effet, des mesures de viscosité en cisaillement sont présentées, ainsi qu'un nouvel écoulement. Ce dernier écoulement, dit écoulement en croix, doit permettre d'identifier le paramètre rhéologique caractérisant l'anisotropie des suspensions.
33
Bronsch, Arne. "Viscosity of slags." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2017. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-229196.
Full textAbstract:
Slags plays a significant role at high temperature processes. The estimation of the slag viscosity is vital for the safe run of e.g. entrained flow gasifiers. One opportunity of determination is rotational viscometry. This technique is disadvantageous in view of elevated temperatures, applied materials and the necessary time. Additionally, the viscosity can be predicted by the help of viscosity models, where viscosity is a function of slag composition and temperature. Due to changing slag properties within the technical processes, the calculated viscosities can hugely differ from measured ones.
In this work, the viscosities of 42 slags where measured up to 100 Pa s and temperatures up to 1700 °C. Oxidizing and reducing conditions were applied. Additionally, selected slag samples were quenched at defined temperatures to qualitatively and quantitatively determine the formed minerals by X-ray diffraction (XRD). Differential temperature analysis (DTA) was applied to find the onset of crystallization for the complementation of investigations.
The Einstein-Roscoe equation was chosen to improve the classic viscosity models. Reducing atmosphere decreased viscosity and the number of formed minerals was increased. Slags show a shear-thinning behavior above ca. 10 vol.-% of solid mineral matter. Also, Newtonian behavior was observed up to 60 vol.-%. To overcome problems with the kinetic cooling behavior of the slags, a viscosity approximation method was applied afterwards. This can result in optimized viscosity predictions when several preconditions are fulfilled.
34
Al-Awadi, Hameed. "Multiphase characteristics of high viscosity oil." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/13902.
Full textAbstract:
Heavy oil production has drawn more and more attention in petroleum industry. The amount of heavy oil in the world is twice more than the conventional oil (low viscosity), which has been consumed rapidly from the past. The understanding of flow patterns and pressure losses in multiphase flow with high viscosity oil are vital to assist the design of transportation pipeline. This thesis involves experimental investigation of two phase and three phase flows under high oil viscosity conditions (up to 17000cP) in horizontal pipelines. The multiphase (oil/water/solid/gas) facility was designed and constructed at Cranfield University and consists of 6m long horizontal pipeline of 0.026m diameter along with instrumentations. The principal objectives of the work were to study the effect of viscosity, water cut, temperature variance, and flow conditions on flow patterns and pressure drops for (oil/gas and oil/water) two phase flows; to compare the measured flow parameters and phase distribution with those predicted from models found in the literature for two phase flows; and to conduct an experimental study of gas injection effect on pressure gradient in (oil/water/gas) three phase flow. Due to the nature of heavy oil reservoirs, sand is associated with oil/water mixture when extracted; therefore sand concentration effect on pressure drop in (oil/water/sand) three phase flow is also examined. For oil-air flow, a smooth oil coating was observed in the film region of slug flow, while a ripple structure of oil coating film was found at higher superficial air velocity for slug flow regime and annular flow regime. The ripple structure was believed to increase the effective roughness of the pipe wall, which resulted in higher pressure gradients. The pressure drop correlations from Beggs and Brill (1973) and Dukler et al. (1964) were used to compare with experimental pressure gradients for oil/air flow. It was found that these correlations failed to predict the pressure gradients for heavy oil/air flows in this work. Several new heavy oil/water flow patterns were named and categorized based on observations. Though the heavy oil viscosity is an essential parameter for oil continuous phase flow on pressure drop, it had no significant effect beyond Water Assist Flow (WAF) condition, as a threshold was found for water cut with fixed superficial oil velocity. The transition criterion by McKibben et al. (2000b) for WAF was found to be able to predict this threshold reasonably well. Core Annular Flow (CAF) models were found to greatly under predict the pressure gradients mainly due to the coating (oil fouling) effect associated with this study. A new coating coefficient was introduced to models presented by Bannwart (2001) and Rodriguez et al (2009). The addition of solid in the mixed flow led to minor increase in the pressure gradient when the particles were moving with the flow. However, higher sand concentration in the system led to higher pressure gradient values. The addition of gaseous phase to the oil/water flow was more complex. The gaseous injection was beneficial toward reducing the pressure gradient when introduced in oil continuous phase only at very low water cuts.
35
Kashefi, Khalil. "Measurement and modelling of interfacial tension and viscosity of reservoir fluids." Thesis, Heriot-Watt University, 2012. http://hdl.handle.net/10399/2567.
Full textAbstract:
The knowledge of reservoir fluids physical properties is crucial in upstream and downstream processes of petroleum industry. Viscosity and interfacial tension are among the most influential parameters on fluid behaviour. These properties have considerable effects on fluid flow characteristics and consequently in many oil and gas production and processing aspects from porous media to surface facilities. Hence, accurate estimation of the mentioned fluid properties plays a significant role in reservoir development. However, experimental data are scarce at high pressure and high temperature (HPHT) conditions. The work presented in this thesis is an integrated experimental and modelling investigation of viscosity and interfacial tension of petroleum reservoir fluids over a wide range of pressure and temperature conditions. Several series of experimental data on the viscosity of reservoir fluids were generated at high pressure and high temperature conditions (up to 20,000 psia and 200 °C). Experiments were conducted on three binary hydrocarbon systems and three synthetic and real multi-component mixtures, in addition to investigating the effect of dissolved water on the viscosity of the above fluids. Besides, the influence of oil-based mud filtrate on the viscosity of various dead oil samples also was studied as part of this thesis. The effect of different salt concentrations on the interfacial tension of gas-brine systems over a wide range of pressure and temperature conditions also was studied experimentally. The experimental data generated were employed to evaluate, improve and propose predictive models to estimate the mentioned physical properties. A new approach to retrieve the viscosity of original fluid (clean dead oil) from contaminated sample was introduced. Also a novel technique for predicting the gas-water (brine) interfacial tension was outlined. The proposed techniques and models were evaluated against independent experimental data generated in this work and the data gathered from open sources. Predictions of the developed methods were in good agreement with the experimental data.
36
Bartholet, Alan. "Modelling Sea-Level Fingerprints of Glaciated Regions with Low Mantle Viscosity." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/40403.
Full textAbstract:
Sea-level fingerprints, the spatial patterns of sea level change resulting from rapid
melting of glaciers and ice sheets, play an important role in understanding past and
projecting future changes in relative sea level (RSL). Over century timescales, the
viscous flow of Earth’s interior is a small component of the total deformation due to
ice loading in most regions, so fingerprints computed using elastic Earth models are
accurate. However, in regions where the viscosity is orders of magnitude lower than
the global average, the viscous component of deformation can be significant, in which
case it is important to consider models of viscoelastic deformation.
There is evidence that the glaciated regions of Alaska, Western Canada and USA,
and the Southern Andes are situated on top of mantle regions in which the local
viscosity is several orders of magnitude lower than typical global mean values. The
goal of this work is to determine the importance of viscous flow in computing RSL
fingerprints associated with future ice mass loss from these regions. Version 5.0 of
the Randolph Glacier Inventory is used to estimate the ice load distribution required
for calculating sea-level fingerprints. For the glaciated regions that have lower than
average viscosity, fingerprints were calculated using an elastic Earth model and a 3D
viscoelastic model to quantify the influence of viscous flow on the predicted sea level
changes. Using glacier mass loss values for the intermediate future climate scenario
Representative Concentration Pathway (RCP) 4.5, the global sea level response was
computed at 2100 CE relative to 2010 CE due to melting from all glacier regions. On
comparing the results of the two models it was found that ice-load-induced viscous
flow contributes significantly (more than a few cm) to the RSL fingerprints only in
near-field regions. However, in these regions, the non-elastic contribution can be 10s
of cm. For example, at Juneau, USA the elastic calculation gave relative sea level
changes of ∼ −45 cm, compared to ∼ −120 cm based on the viscoelastic calculation.
37
Myers, Timothy Gerard. "Chebyshev series method for piezoviscous elastohydrodynamic lubrication." Thesis, University of Leeds, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277479.
Full text
38
Peet, Andrew Herbert. "Modelling sediment in suspension in the wave boundary layer." Thesis, Bangor University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.484084.
Full text
39
Adinata, Donni [Verfasser]. "Single-drop based modelling of solvent extraction in high-viscosity systems / Donni Adinata." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2011. http://d-nb.info/1018200606/34.
Full text
40
Gomes, Erika Adriana de Santana. "Estudo da cristaliza??o de parafinas em sistemas solventes/tensoativos/?gua." Universidade Federal do Rio Grande do Norte, 2009. http://repositorio.ufrn.br:8080/jspui/handle/123456789/15895.
Full textAbstract:
Made available in DSpace on 2014-12-17T15:01:49Z (GMT). No. of bitstreams: 1
ErikaASG_TESE_partes_autorizadas.pdf: 3587859 bytes, checksum: 8731a4ebad1b8f6f11b36c879b4a1a76 (MD5)
Previous issue date: 2009-12-30The WAT is the temperature at the beginning of the appearance of wax crystals. At this temperature the first wax crystals are formed by the cooling systems paraffin / solvents. Paraffins are composed of a mixture of saturated hydrocarbons of high molecular weight. The removal of petroleum from wells and the production lines means a surcharge on produced oil, thus solubilize these deposits formed due to modifications of thermodynamics has been a constant challenge for companies of oil exploration. This study combines the paraffin solubilization by microemulsion systems, the determination of WAT systems paraffin / solvent and performance of surfactant in reducing the crystallization. We used the methods: rheological and the photoelectric signal, validating the latter which was developed to optimize the data obtained due to sensitivity of the equipment used. Methods developed for description of wax precipitation are often in poor agreement with the experimental data, they tend to underestimate the amount of wax at temperatures below the turbidity point. The Won method and the Ideal solution method were applied to the WAT data obtained in solvent systems, best represented by the second interaction of Won method using the solvents naphtha, hexane and LCO. It was observed that the results obtained by WAT photoelectric signal when compared with the viscosity occur in advance, demonstrating the greatest sensitivity of the method developed. The ionic surfactant reduced the viscosity of the solvent systems as it acted modifying the crystalline structure and, consequently, the pour point. The curves show that the WAT experimental data is, in general, closer to the modeling performed by the method of Won than to the one performed by the ideal solution method, because this method underestimates the curve predicting the onset of paraffin hydrocarbons crystallization temperature. This occurs because the actual temperature measured was the crystallization temperature and the method proposes the fusion temperature measurement.
A TIAC ? a temperatura de in?cio do aparecimento dos cristais de parafina. Nesta temperatura os primeiros cristais de parafina s?o formados, pelo resfriamento de sistemas parafina/solventes. As parafinas s?o compostas de uma mistura de hidrocarbonetos saturados de alto peso molecular. A remo??o de parafinas dos po?os e das linhas de produ??o significa um custo adicional ao petr?leo produzido, portanto solubilizar estes dep?sitos formados decorrentes das modifica??es termodin?micas tem sido um desafio constante das empresas exploradoras de petr?leo. Este estudo alia a solubiliza??o paraf?nica por sistemas microemulsionados, ? determina??o da TIAC dos sistemas parafina/solvente e a atua??o do tensoativo na redu??o da cristaliza??o. Utilizaram-se os m?todos: reol?gico e o do sinal fotoel?trico, validando este ?ltimo o qual foi desenvolvido visando aperfei?oar os dados obtidos devido a sensibilidade do equipamento utilizado. M?todos desenvolvidos para descri??o da precipita??o da cera est?o freq?entemente em pobre concord?ncia com os dados experimentais; eles tendem a subestimar a quantidade de cera ?s temperaturas abaixo do ponto de turbidez. Foram aplicados os m?todos de Won e o da solu??o ideal aos dados de TIAC da parafina obtidos em sistemas com solventes, sendo melhor representado pela segunda intera??o do m?todo de Won com os solventes: nafta, hexano e LCO. Foi observado que os resultados de TIAC obtidos pelo sinal fotoel?trico quando comparados com a viscosidade, ocorrem antecipadamente, demonstrando a maior sensibilidade do m?todo desenvolvido. O tensoativo i?nico reduziu a viscosidade dos sistemas paraf?nicos, pois ele atuou modificando a estrutura cristalina, conseq?entemente o ponto de fluidez. As curvas que representam os dados experimentais da TIAC est?o, de maneira geral, mais pr?ximas da modelagem realizada pelo m?todo de Won do que da solu??o ideal, pois este m?todo subestima a curva de predi??o do in?cio da temperatura de cristaliza??o da parafina com os hidrocarbonetos. Isto ocorre porque a temperatura real medida foi a de cristaliza??o, e a proposta pelos m?todos ? a de fus?o
41
Giordano, Daniele. "Experimental Determinations and Modelling of the Viscosity of Multicomponent Natural Silicate Melts: Volcanological Implications." Diss., [S.l.] : [s.n.], 2002. http://edoc.ub.uni-muenchen.de/archive/00000744.
Full text
42
Al-Siyabi, Zaid Khamis Sarbookh. "The contact angle, interfacial tension and viscosity of reservoir fluids : experimental data and modelling." Thesis, Heriot-Watt University, 2000. http://hdl.handle.net/10399/1198.
Full text
43
Heynes, Oliver Rupert. "Eddy-viscosity and stress-transport modelling of synthetic jets with and without cross-flow." Thesis, University of Manchester, 2006. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.606416.
Full text
44
OUAJJI, HASSAN. "Etude de proprietes de transport d'un plasma de melange air-cuivre : modelisation de la colonne d'arc." Clermont-Ferrand 2, 1986. http://www.theses.fr/1986CLF21034.
Full textAbstract:
Calcul des coefficients de conductivite thermique, de conductivite electrique et de viscosite du melange air-cuivre a la pression atmospherique pour des temperatures comprises entre 5000 k et 14000 k et differentes valeurs de la teneur en cuivre. Dans les memes conditions de temperature et de pression, la determination de la composition d'equilibre du melange met en evidence l'evolution de la population des differentes especes chimiques en presence en fonction de la teneur en cuivre. Les caracteristiques macroscopiques de la colonne (champ electrique, profil de temperature) sont obtenues a partir du modele energetique de elenbaas-heller
45
Hill, Alexander Mackay. "Computational Investigations of Earth Viscosity Structure Using Surficial Geophysical Observables Related to Isostatic Adjustment." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/41203.
Full textAbstract:
The research presented in this thesis seeks to address meaningful geodynamic problems related to the viscosity structure of the Earth’s interior. Isostatic adjustment is a process which is dependent upon the mechanical properties of the lithosphere and mantle. By performing computational simulations of the isostatic response for various surface-loading scenarios and numerous viscosity structures, insight can be gained into the mechanical structure of the Earth and geodynamic processes related to that structure. The modelled isostatic signal for a given set of Earth model parameters can be compared to real-world observational data in order to identify valid Earth model configurations.
In Chapter 2, the “Transition Zone Water Filter” theory is tested by modelling the geophysical effects of a low-viscosity melt-rich layer atop the 410 km discontinuity. The thickness and viscosity of this layer, and the surrounding mantle, is constrained using observations of relative sea level and the geodetic J ̇_2 parameter, as well as multiple ice-loading scenarios by which the isostatic adjustment process is driven. The relative sea level data, being most sensitive to the upper mantle and the theorized melt-rich layer it contained, constrain layer properties more effectively than the J ̇_2 observation, which is strongly dependent on the lower mantle. Constraints on the viscosity of the melt-rich layer vary according to thickness, with thicker layers requiring stiffer viscosities to satisfy observations. For instance, a 20 km thick layer would require a viscosity of 10^17 Pas or greater, but any of the considered viscosities could be possible for a 1 km thick layer. Similarly, a broad range of upper mantle viscosities are possible, but they must be balanced by variations in the lower mantle. However, J ̇_2 results show a strong preference for a high-viscosity lower mantle (≥10^22 Pas). For every evaluated Earth model parameter, there is evidence of ice-model sensitivity in the inversion results. Although the results of this study demonstrate that observables related to glacial isostatic adjustment can provide constraints on the properties of this theorized melt-rich layer, the confounding effect of parameter trade-off prevents a more definitive test of this model of mantle geodynamics.
The purpose of the study presented in Chapter 3 is to analyze the nature of solid-Earth deformation beneath the Lower Mississippi River, most crucially in the Mississippi Delta region where subsidence is an ongoing and costly problem. The study uses the displacement of the long profile of the Lower Mississippi River over the last 80 kyr to constrain isostatic deformation and determine constraints on the mechanical structure of both the mantle and lithosphere. Deformation recorded in the northern portion of the long profile is dominated by the effect of glacial isostatic adjustment, whereas the southern portion is governed by sediment isostatic adjustment. However, the southern portion is also potentially affected by past fault displacement, and to account for this the observational data are corrected using two distinct faulting scenarios. Displacement of the long profile is modelled using either an entirely elastic lithosphere or a lithosphere with internal viscoelastic structure, the latter of which is derived from two end-member geothermal profiles. Between the elastic and viscous lithosphere models, the viscous models are better able to replicate the observational data for each faulting scenario – both of which prefer a viscous lithosphere corresponding to the warmer geotherm. The chosen faulting scenario exerts no control over the optimal mantle model configuration, however the optimal mantle for the viscous lithosphere models is much stiffer than was determined for their elastic counterparts, reflecting significant parameter trade-off between mantle and lithosphere mechanical structure. These study results demonstrate the utility of the long profile displacement data set for constraining Earth viscosity structure, as well as the importance of considering more-complex models of lithosphere mechanical structure when addressing surface-loading problems similar to those encountered in the Mississippi Delta region.
46
Gram, Annika. "Modelling of Bingham Suspensional Flow : Influence of Viscosity and Particle Properties Applicable to Cementitious Materials." Doctoral thesis, KTH, Betongbyggnad, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-163040.
Full textAbstract:
Simulation of fresh concrete flow has spurged with the advent of Self-Compacting Concrete, SCC. The fresh concrete rheology must be compatible with the reinforced formwork geometry to ensure complete and reliable form filling with smooth concrete surfaces. Predicting flow behavior in the formwork and linking the required rheological parameters to flow tests performed on the site will ensure an optimization of the casting process. In this thesis, numerical simulation of concrete flow and particle behaviour is investigated, using both discrete as well as a continuous approach. Good correspondence was achieved with a Bingham material model used to simulate concrete laboratory tests (e.g. slump flow). It is known that aggregate properties such as size, shape and surface roughness as well as its grading curve affect fresh concrete properties. An increased share of non-spherical particles in concrete increases the level of yield stress, τ0, and plastic viscosity, µpl. The yield stress level may be decreased by adding superplasticizers, however, the plastic viscosity may not. An explanation for the behaviour of particles is sought after experimentally, analytically and numerically. Bingham parameter plastic viscosity is experimentally linked to particle shape. It was found that large particles orient themselves aligning their major axis with the fluid flow, whereas small particles in the colloidal range may rotate between larger particles. The rotation of crushed, non-spherical fine particles as well as particles of a few microns that agglomorate leads to an increased viscosity of the fluid. Generally, numerical simulation of large scale quantitative analyses are performed rather smoothly with the continuous approach. Smaller scale details and phenomena are better captured qualitatively with the discrete particle approach. As computer speed and capacity constantly evolves, simulation detail and sample volume will be allowed to increase. A future merging of the homogeneous fluid model with the particle approach to form particles in the fluid will feature the flow of concrete as the physical suspension that it represents. One single ellipsoidal particle in fluid was studied as a first step.QC 20150326
47
Bella, Redha. "Diffusion and reaction of low molecular weight reactants in molten polymer medium : characterization and modelling." Lyon, INSA, 2007. http://theses.insa-lyon.fr/publication/2007ISAL0025/these.pdf.
Full textAbstract:
The access to innovative products with original applications is linked to a well understanding of the fundamental phenomena that can occur during polymer reactive processing. The aim of this work is to open a way in this comprehension by developing new tools (rheology) and methods (modelling) to understand the coupling of diffusion and reaction using a simple model system within simple laminar flow geometry for small reacting molecules in viscous media. Based on earlier studies, the choice of a simplified approach was imposed to identify the interactions between mixing, diffusion and reaction using model viscous systems. First of all, a thermoplastic / thermoset blend was caried out to identify the interactions between diffusion and reaction. An asymmetricity has been observed on the gradient of morphology due to the diffusional control of the reaction. This gradient may be explained by three factors: differences in diffusion coefficients, in thermodynamic interactions and in viscosity. These interpretations are multiple and difficult to discriminate. As a solution, these phenomena were uncoupled and the diffusion was primarily studied. Using rheological method and inverse calculations, the diffusion coefficients were calculated for monoamine and monoepoxy in molten polymer. Due to the difference in miscibility of the two reactive species, the diffusion rate of the monoamine, that is fully miscible with the polymer, was not dependent on the molecular weight of the polymer. On the other hand, the monoepoxy is only partially miscible with polymer and was diffusion dependent on molecular weight and on Flory-Huiggins parameters. Finally, the coupling of diffusion and reaction of small reactive species in molten polymer was experimented and modelled. The mixing effect was accounted using simple bilayer geometry. The reaction was diffusion controlled and the time necessary to reach homogeneity in laminar flow was calculatedL'accès à des produits innovants avec des applications originales est lié à une bonne compréhension des phénomènes fondamentaux qui peuvent se produire pendant les procédés réactifs des polymères. Le but de ce travail est d'ouvrir un chemin dans cette compréhension en développant de nouveaux outils (rhéologie) et méthodes (modélisation) pour comprendre le couplage de la diffusion et de la réaction dans un système modèle simple en utilisant une géométrie simplifiée d'écoulement laminaire pour de petites molécules réactives dans des milieux visqueux. Basé sur de précédentes études, le choix d'une approche simplifiée a été imposé pour identifier les interactions entre mélange, diffusion moléculaire et réaction en utilisant des systèmes visqueux modèles. Tout d'abord, un mélange thermoplastique/thermodurcissable a été utilisé pour identifier les interactions entre la diffusion et la réaction. On a observé une asymétricité au niveau du gradient de la morphologie qui est provoquée par le control de la réaction par la diffusion. Ce gradient peut être expliqué par trois facteurs : différences des coefficients de diffusion, des interactions thermodynamiques et la viscosité. Ces interprétations sont multiples et difficiles à justifier. Comme solution, ces phénomènes ont été découplés et la diffusion a été étudiée en premier. En utilisant une méthode de calcul par rhéologie inverse, les coefficients de diffusion ont été calculés pour une monoamine et une monoepoxide dans un polymère fondu. En raison de la différence de miscibilité des deux espèces réactives, la vitesse de diffusion de la monoamine, qui est entièrement miscible dans le polymère, ne dépendait pas des masses molaires du polymère. D'autre part, la monoepoxide qui est partiellement miscible dans le polymère, sa diffusion dépendait fortement des masses molaires et des paramètres d’interaction de Flory-Huiggins. Finalement, le couplage de la diffusion et la réaction de petites espèces réactives en milieu fondu visqueux ont été expérimenté et modélisé. L'effet du mélange a été pris en compte en utilisant une géométrie simple en bicouches. La réaction était contrôlée par la diffusion et le temps nécessaire pour atteindre un état homogène dans un flux laminaire a été calculé
48
Molina, John Jairo. "Multi-scale modelling of ions in solution : from atomistic descriptions to chemical engineering." Paris 6, 2011. http://www.theses.fr/2011PA066363.
Full textAbstract:
Les ions en solutions ont un rôle fondamental dans de nombreux processus physiques, chimiques et biologiques. Dans le cadre des applications industrielles, l’ingénieur les décrits par des modèles analytiques simples, qui sont paramétrisés et ajustés afin de reproduire des données expérimentales. Dans ce travail, nous proposons une procédure multi-échelle à gros-grains pour obtenir ces modèles simples à partir de descriptions atomiques. D’abord, les paramètres de forces classiques pour des ions en solutions sont extraits de calculs ab-initio. Des potentiels effectifs (McMillan-Mayer) ion-ion sont ensuite obtenus à partir des fonctions de distribution de paire mesurées dans des simulations de dynamique moléculaire. Avec ces potentiels effectifs, nous pouvons établir une description à solvant continu des électrolytes. Finalement, nous mettons en œuvre un calcul de perturbation, pour définir la meilleure représentation possible pour ces systèmes, en termes de sphères dures chargées (éventuellement associées). Le modèle final ainsi obtenu est analytique et il ne contient pas de paramètres ajustables. On montre qu’il est en bon accord avec les résultats exacts obtenus par des simulations Monte-Carlo pour la structure et la thermodynamique. La thèse se termine en proposant la mise au point d’une analyse similaire pour la viscosité des électrolytes, obtenue à partir d’une base moléculaireIons in solution play a fundamental role in many physical, chemical, and biological processes. For industrial applications these systems are usually described using simple analytical models which are fitted to reproduce the available experimental data. In this work, we propose a multi-scale coarse graining procedure to derive such models from atomistic descriptions. First, parameters for classical force-fields of ions in solution are extracted from ab-initio calculations. Effective (McMillan-Mayer) ion-ion potentials are then derived from radial distribution functions measured in classical molecular dynamics simulations, allowing us to define an implicit solvent model of electrolytes. Finally, perturbation calculations are performed to define the best possible representation for these systems, in terms of charged hard-sphere models. Our final model is analytical and contains no free “fitting” parameters. It shows good agreement with the exact results obtained from Monte-Carlo simulations for the thermodynamic and structural properties. Development of a similar model for the electrolyte viscosity, from information derived from atomistic descriptions, is also introduced
49
Klyukin, Yury Igorevich. "Modelling and analytical studies of magmatic-hydrothermal processes." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/84442.
Full textAbstract:
Hydrothermal processes play a major role in transporting mass and energy in Earth’s crust. These processes rely on hydrothermal fluid, which is dissolving, transporting and precipitating minerals and distribute heat. The composition of the hydrothermal fluid is specific for various geological settings, but in most cases it can be approximated by H₂O-NaCl-CO₂ fluid composition. The flow of hydrothermal fluid is controlled by differences in temperature, pressure and/or density of the fluid and hydraulic conductivity of the rock. In my work, I was focused on modeling of the hydrothermal fluid properties and experimental characterization of fluid that formed emerald deposit in North Carolina, USA. The dissertation based on the result of three separate projects.
The first project has been dedicated to characterization of the H₂O-NaCl hydrothermal fluid ability to transport mass and energy. This ability of the fluid is defined by a change in fluid density and enthalpy in response to changing pressure or temperature. In this project we quantified the derivatives of mass, enthalpy and SiO₂ solubility in wide range of pressure, temperature and composition (PTx) of H₂O-NaCl fluid. Our study indicated that the PT region in which fluid is most efficiently can transport mass and energy, located in the critical region near liquid-vapor phase boundary and the sensitivity to changing pressure-temperature conditions decrease with increasing salinity.
In second project we developed the revised H₂O-NaCl viscosity model. Revised model to calculate the viscosity of H₂O-NaCl reproduces experimental data with ±10% precision in PTx range where experimental data available and follows expected trends outside of the range. This model is valid over the temperature range from the H₂O solidus (~0 °C) to ~1,000 °C, from ~0.1 MPa to ≤500 MPa, and for salinities from 0-100 wt.% NaCl.
The third project has been focused on the characterization of formation conditions of the emerald at North American Emerald Mine, Hiddenite, North Carolina, USA. The emerald formation conditions defined as 120-220 MPa, 450-625 °C using stable isotope, Raman spectrometry, and fluid inclusion analysis. Hydrothermal fluid had a composition of CO2-H2O±CH4, which indicates mildly reducing environment of emerald growth.Ph. D.
50
Seppecher, Pierre. "Etude d'une modelisation des zones capillaires fluides : interfaces et lignes de contact." Phd thesis, Paris 6, 1987. http://tel.archives-ouvertes.fr/tel-00522117.
Full textAbstract:
Nous donnons une description fine des zones capillaires à l'aide de la théorie du second gradient ce qui permet de clarifier les phénomènes de tension superficielle et de tension de ligne. Nous montrons comment par un processus d'intégration à travers les zones capillaires cellesci peuvent être considérées comme des surfaces ou des lignes géométriques porteuses de propriétés matérielles. Pour obtenir des conditions de bilan physiquement acceptables nous faisons une analyse des ordres de grandeur des termes interfaciaux. Enfin nous utilisons la thermodynamique linéaire des phénomènes irréversibles pour écrire les lois de comportement des interfaces et des lignes de contact