Дисертації з теми "Statistical approach to fluid mechanics"
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1
Archer, Andrew John. "Statistical mechanics of soft core fluid mixtures." Thesis, University of Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288269.
2
Fontaine, Côme. "Etude de deux modèles simplifiés de turbulence à l'aide du groupe de renormalisation fonctionnel : l'équation de Burgers et le modèle de Sabra." Electronic Thesis or Diss., Université Grenoble Alpes, 2023. http://www.theses.fr/2023GRALY083.
Анотація:
Dans cette thèse nous nous intéressons à deux modèles simplifiés décrivant des écoulements turbulents. Dans ces deux modèles, la turbulence est caractérisée par l'invariance d'échelle et des propriétés statistiques universelles, comme observé pour la turbulence hydrodynamique réelle. Ce type de comportement est très familier en physique: il s'agit d'un système critique. Dans cette thèse, nous utilisons un outil très répandu pour l'étude de la criticalité: le groupe de renormalisation fonctionnel (FRG). Le premier modèle, nommé modèle de Sabra, décrit les interactions effectives entre un nombre discret de modes de vitesse d'un fluide turbulent. Cette description schématique conserve beacoup de propriétés essentielles de la turbulence. En particulier, le champ de vitesse est multi-fractal. La façon dont la dynamique engendre cette multi-fractalité est encore mal comprise d'un point de vue théorique. Dans cette thèse, nous formulons un flot de renormalisation inverse, c'est-à-dire intégrant les plus grandes échelles d'abord. Grâce à cette méthode, nous trouvons un point fixe du flot de renormalisation ayant une invariance d'échelle anormale, et relativement proche de la valeur attendue pour certaines observables. Nous montrons que ce point fixe diffère de celui obtenu lorsque toutes les échelles sont forcées, par un forçage avec un spectre en loi de puissance, qui correspond au point fixe du RG obtenu en théorie de perturbation. Le second modèle étudié est l'équation de Burgers, qui décrit la dynamique d'un fluide en l'absence de pression. Nous nous intéressons à l'effet d'un bruit conservatif sur le champ de vitesse. Nous prouvons l'existence d'un régime d'invariance d'échelle avec un exposant critique dynamique z=1 en utilisant une fermeture exacte de l'équation de flot de renormalisation. Cette fermeture est permise par l'existence de certaines symétries de l'équation de Burgers. Ce nouveau régime d'invariance d'échelle avait été observé auparavant dans des solutions numériques de l'équation de Burgers. Nous apportons dans cette thèse une preuve théorique de son existence, et calculons les propriétés universelles associéesIn this thesis, we focus on two simplified models describing turbulent flows. In these two models, the turbulent state exhibits scale-invariance and universal statistical properties resembling those of true hydrodynamical turbulence. This type of behaviour is very familiar in physics: it corresponds to a critical system. In this work, we use a widely used tool in the study of criticality: the functional renormalisation group (FRG). The first model, named the Sabra shell model, describes effective interactions among a discrete number of velocity modes of a turbulent fluid. This schematic description captures many essential properties of turbulent flows. In particular, the velocity field is multifractal. The way in which the dynamics generates this multifractality is still poorly understood from a theoretical perspective. In this thesis, we formulate a reverse renormalisation flow, meaning that we integrate out the largest scales first. Using this method, we find a fixed point of the renormalisation flow with anomalous scale invariance, relatively close to the expected value for certain observables. We show that it is clearly distinct from the fixed point obtained when all scales are forced, through a forcing with a power-law spectrum, which corresponds to the fixed point of the RG obtained in perturbation theory. The second model studied is the Burgers equation, which describes the dynamics of a fluid in the absence of pressure. We focus on the effect of a conservative noise on the velocity field. We prove the existence of a scale invariant regime with a critical dynamical exponent z=1 using an exact closure of the renormalisation flow equation. This closure relies on the existence of certain symmetries of the Burgers equation. Indications of the existence of this new scaling regime were previously found in numerical solutions of the Burgers equation. We provide in this thesis a theoretical proof of its existence and calculate the associated universal properties
3
Rossi, Andrea. "Statistical Mechanics Approach to Protein Design." Doctoral thesis, SISSA, 2000. http://hdl.handle.net/20.500.11767/4329.
Анотація:
The plan of this thesis is the following. In the first chapter we introduce the most important and basic concept related to protein folding and design. In the second chapter, after introducing some standard lattice models of proteins and heteropolymers, the most important methods of protein design present in the literature are described. In the third chapter we will introduce a novel iterative procedure for protein design and it will be applied to lattice protein models [58]. A different approach based on geometrical criterion [49] will also be presented. In the fourth chapter, we will implement an approximated approach in order to design real protein structures [59]. In this case, it has been possible to compare our designed sequences with real sequences, whose native states are known. The good correlation between natural sequences and designed sequences indicates that the method is very promising.
4
Davies, Lowri A. "Selected topics in the statistical mechanics of fluids." Thesis, University of Sheffield, 1997. http://etheses.whiterose.ac.uk/14744/.
Анотація:
The phase behaviour and thermodynamic properties of simple model mixtures are examined using the statistical associating fluid theory as extended to chain molecules interacting with potentials of variable range (SAFT-VR), and by computer simulation. The SAFT-VR approach is based on an accurate and compact representation of the free energy of chain molecules. We present the SA FT -VR methodology as applied to mixtures of non-conformal molecules. A series of mixing rules are presented, beginning with the van der Waals one-fluid prescription and including more complex treatments. The vapour-liquid equilibria of a mixture consisting of hard spheres and square-well monomers is examined with the SAFT-VR equation of state, together with the liquid-liquid equilibria of a symmetrical square-well mixture with no unlike interactions. Additionally, we examine the vapour-liquid equilibria of a square-well monomer-dimer mixture, composed of equal-sized segments, both with the SAFT-VR approach and by Gibbs ensemble Monte Carlo simulation. The simulation data are used to determine the vapourliquid critical line of the mixture. An extension of the SAFT-VR approach to describe the phase behaviour of chain molecules interacting with a soft repulsive potential and an attractive well of variable range is presented. We focus on the vapour-liquid properties of Lennard-Jones chains using a simple recipe for the evaluation of the chain free energy. We also perform a case study for a specific class of phase equilibria exhibited by binary mixtures, where systems are seen to posses a region of closed-loop immiscibility in their phase diagrams. We examine the nature of this type of pl1ase behaviour using the SA FT· VR equation of state and Gibbs ensemble simulation for a simple model system with an anisotropic bonding site, which is seen to be the governing factor in the appearance of the region of low-temperature miscibility for this system. The model is chosen in order to mimic the physical features of real systems which exhibit this type of re-entrant phase behaviour. The critical regions of this model are examined using a finite-size scaling analysis performed in the semigrand canonical ensemble.
5
Rasmussen, H. O. "The statistical theory of stationery turbulence." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363346.
6
Baskaran, Aparna. "Statistical mechanics and linear response for a granular fluid." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0013684.
7
Itami, Masato. "Non-equilibrium Statistical Theory for Singular Fluid Stresses." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215285.
8
Parker, Daniel N. "Thermodynamics, reversibility and Jaynes' approach to statistical mechanics." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3803.
Анотація:
Thesis (Ph. D.) -- University of Maryland, College Park, 2006.Thesis research directed by: Philosophy. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
9
Louveau, Joy E. (Joy Emmanuelle). "A statistical mechanics approach to vaccination against HIV." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/117898.
Анотація:
Thesis: Ph. D., Harvard-MIT Program in Health Sciences and Technology, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 75-81).
Most vaccines stimulate the production of antibodies that provide a potent defense upon reinfection by the same strain of pathogen. The key process in antibody development is a stochastic process known as affinity maturation (AM) which generates strain-specific antibodies upon immunization by one antigen. A highly mutable virus like HIV evades recognition by these strain-specific antibodies via the emergence of new mutant strains within the patient. In some chronically infected patients, antibodies that can bind diverse antigens and thus protect against many HIV strains arise naturally; they are named broadly-neutralizing antibodies (bnAbs). A vaccine that elicits bnAbs could prevent HIV infections. This vaccine is expected to contain several different antigens. However, because bnAbs rarely appear in HIV patients, the complex mechanisms by which they emerge are not well understood. Theoretical models of AM could help identify promising vaccination strategies and shed light on a previously ignored problem in basic immunology; meaning how AM works with several antigens. For my thesis I investigated two pathways for breadth evolution. First, motivated by experimental findings that bnAbs have many mutations that may modify the flexibility of the binding region, I examined how flexibility influences breadth. A flexible binding region is expected to enable different conformations and therefore to allow binding to diverse antigens. Towards that goal, I developed a theoretical model of AM which, combined with Molecular Dynamics simulations, suggests that eliciting flexibility-affecting mutations is not essential for the evolution of bnAbs if proper germline B cells are first activated. This is significant as it simplifies the task of immunogen design. For my second project, I studied how separating the different antigens in time and mutational distance affects breadth of binding and antibody titers. The main observation is that introducing the antigens at different times is key to generating breadth. Furthermore, sequentially introducing one antigen per injection yields the greatest breadth and antibody titers. We also devised a prediction tool for breadth given a set of antigens and an immunization protocol. My results suggest optimal vaccination strategies which are expected to guide future in vivo investigations by our collaborators.
by Joy E. Louveau.
Ph. D.
10
Seyedi, Seyedalireza <1980>. "Predictability in Social Science, The statistical mechanics approach." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/7199/1/seyedi_seyedalireza_tesi.pdf.
Анотація:
The subject of this work concerns the study of the immigration phenomenon, with emphasis on the aspects related to the integration of an immigrant population in a hosting one. Aim of this work is to show the forecasting ability of a recent finding where the behavior of integration quantifiers was analyzed and investigated with a mathematical model of statistical physics origins (a generalization of the monomer dimer model). After providing a detailed literature review of the model, we show that not only such a model is able to identify the social mechanism that drives a particular integration process, but it also provides correct forecast. The research reported here proves that the proposed model of integration and its forecast framework are simple and effective tools to reduce uncertainties about how integration phenomena emerge and how they are likely to develop in response to increased migration levels in the future.
11
Seyedi, Seyedalireza <1980>. "Predictability in Social Science, The statistical mechanics approach." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/7199/.
Анотація:
The subject of this work concerns the study of the immigration phenomenon, with emphasis on the aspects related to the integration of an immigrant population in a hosting one. Aim of this work is to show the forecasting ability of a recent finding where the behavior of integration quantifiers was analyzed and investigated with a mathematical model of statistical physics origins (a generalization of the monomer dimer model). After providing a detailed literature review of the model, we show that not only such a model is able to identify the social mechanism that drives a particular integration process, but it also provides correct forecast. The research reported here proves that the proposed model of integration and its forecast framework are simple and effective tools to reduce uncertainties about how integration phenomena emerge and how they are likely to develop in response to increased migration levels in the future.
12
INGROSSO, ALESSANDRO. "Statistical Mechanics Approach to Inverse Problems on Networks." Doctoral thesis, Politecnico di Torino, 2016. http://hdl.handle.net/11583/2641787.
Анотація:
Statistical Mechanics has gained a central role in modern Inference and Computer Science. Many optimization and inference problems can be cast in a Statistical Mechanics framework, and various concepts and methods developed in this area of Physics can be very helpful not only in the theoretical analysis, but also constitute valuable tools for solving single instance cases of hard inference and computational tasks. In this work, I address various inverse problems on networks, from models of epidemic spreading to learning in neural networks, and apply a variety of methods which have been developed in the context of Disordered Systems, namely Replica and Cavity methods from the theoretical side, and their algorithmic incarnation, Belief Propagation, to solve hard inverse problems which can be formulated in a Bayesian framework.
13
Smith, Douglas Morgan. "Fluid dynamic calculations using the multigrid approach." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46556.
14
Dasi, Lakshmi Prasad. "Statistical characteristics of turbulent chemical plumes." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/21256.
15
Nehring, Benjamin. "Point processes in statistical mechanics : a cluster expansion approach." Phd thesis, Universität Potsdam, 2012. http://opus.kobv.de/ubp/volltexte/2012/6268/.
Анотація:
A point process is a mechanism, which realizes randomly locally finite point measures. One of the main results of this thesis is an existence theorem for
a new class of point processes with a so called signed Levy pseudo measure L, which is an extension of the class of infinitely divisible point processes.
The construction approach is a combination of the classical point process theory, as developed by Kerstan, Matthes and Mecke, with the method of cluster expansions from statistical mechanics. Here the starting point is a family of signed Radon measures, which defines on the one hand the Levy pseudo measure L, and on the other hand locally the point process. The relation between L and the process is the following: this point process solves the integral cluster equation determined by L.
We show that the results from the classical theory of infinitely divisible point processes carry over in a natural way to the larger class of point
processes with a signed Levy pseudo measure. In this way we obtain e.g. a criterium for simplicity and a characterization through the cluster equation, interpreted as an integration by parts formula, for such point processes.
Our main result in chapter 3 is a representation theorem for the factorial moment measures of the above point processes. With its help we will identify the permanental respective determinantal point processes, which belong to the classes of Boson respective Fermion processes. As a by-product we obtain a representation of the (reduced) Palm kernels of infinitely divisible point processes.
In chapter 4 we see how the existence theorem enables us to construct (infinitely extended) Gibbs, quantum-Bose and polymer processes. The so called polymer processes seem to be constructed here for the first time.
In the last part of this thesis we prove that the family of cluster equations has certain stability properties with respect to the transformation of its solutions. At first this will be used to show how large the class of solutions of such equations is, and secondly to establish the cluster theorem of Kerstan, Matthes and Mecke in our setting. With its help we are able to enlarge the class of Polya processes to the so called branching Polya processes.
The last sections of this work are about thinning and splitting of point
processes. One main result is that the classes of Boson and Fermion processes remain closed under thinning. We use the results on thinning to identify a subclass of point processes with a signed Levy pseudo measure as doubly stochastic Poisson processes. We also pose the following question: Assume you observe a realization of a thinned point process. What is the distribution of deleted points? Surprisingly, the Papangelou kernel of the thinning, besides a constant factor, is given by the intensity measure of this conditional probability, called splitting kernel.Ein Punktprozess ist ein Mechanismus, der zufällig ein lokalendliches Punktmaß realisiert. Ein Hauptresultat dieser Arbeit ist ein Existenzsatz für eine sehr große Klasse von Punktprozessen mit einem signierten Levy Pseudomaß L. Diese Klasse ist eine Erweiterung der Klasse der unendlich teilbaren Punktprozesse. Die verwendete Methode der Konstruktion ist eine Verbindung der klassischen Punktprozesstheorie, wie sie von Kerstan, Matthes und Mecke ursprünglich entwickelt wurde, mit der sogenannten Methode der Cluster-Entwicklungen aus der statistischen Mechanik. Ausgangspunkt ist eine Familie von signierten Radonmaßen. Diese definiert einerseits das Levysche Pseudomaß L; andererseits wird mit deren Hilfe der Prozess lokal definiert. Der Zusammenhang zwischen L und dem Prozess ist so, dass der Prozess die durch L bestimmte Integralgleichung (genannt Clustergleichung) löst. Wir zeigen, dass sich die Resultate aus der klassischen Theorie der unendlich teilbaren Punktprozesse auf natürliche Weise auf die neue Klasse der Punktprozesse mit signiertem Levy Pseudomaß erweitern lassen. So erhalten wir z.B. ein Kriterium für die Einfachheit und eine Charackterisierung durch die Clustergleichung für jene Punktprozesse. Unser erstes Hauptresultat in Kapitel 3 zur Analyse der konstruierten Prozesse ist ein Darstellungssatz der faktoriellen Momentenmaße. Mit dessen Hilfe werden wir die permanentischen respektive determinantischen Punktprozesse, die in die Klasse der Bosonen respektive Fermionen Prozesse fallen, identifizieren. Als ein Nebenresultat erhalten wir eine Darstellung der (reduzierten) Palm Kerne von unendlich teilbaren Punktprozessen. Im Kapitel 4 konstruieren wir mit Hilfe unseres Existenzsatzes unendlich ausgedehnte Gibbsche Prozesse sowie Quanten-Bose und Polymer Prozesse. Unseres Wissens sind letztere bisher nicht konstruiert worden. Im letzten Teil der Arbeit zeigen wir, dass die Familie der Clustergleichungen gewisse Stabilitätseigenschaften gegenüber gewissen Transformationen ihrer Lösungen aufweist. Dies wird erstens verwendet, um zu verdeutlichen, wie groß die Klasse der Punktprozesslösungen einer solchen Gleichung ist. Zweitens wird damit der Ausschauerungssatz von Kerstan, Matthes und Mecke in unserer allgemeineren Situation gezeigt. Mit seiner Hilfe können wir die Klasse der Polyaschen Prozesse auf die der von uns genannten Polya Verzweigungsprozesse vergrößern. Der letzte Abschnitt der Arbeit beschäftigt sich mit dem Ausdünnen und dem Splitten von Punktprozessen. Wir beweisen, dass die Klassen der Bosonen und Fermionen Prozesse abgeschlossen unter Ausdünnung ist. Die Ergebnisse über das Ausdünnen verwenden wir, um eine Teilklasse der Punktprozesse mit signiertem Levy Pseudomaß als doppelt stochastische Poissonsche Prozesse zu identifizieren. Wir stellen uns auch die Frage: Angenommen wir beobachten eine Realisierung einer Ausdünnung eines Punktprozesses. Wie sieht die Verteilung der gelöschten Punktkonfiguration aus? Diese bedingte Verteilung nennen wir splitting Kern, und ein überraschendes Resultat ist, dass der Papangelou-Kern der Ausdünnung, abgesehen von einem konstanten Faktor, gegeben ist durch das Intensitätsmaß des splitting Kernes.
16
Volpati, Valerio. "Statistical Mechanics approach to the sustainability of economic ecosystems." Doctoral thesis, SISSA, 2016. http://hdl.handle.net/20.500.11767/4924.
Анотація:
This thesis contains some of the main results obtained during my research activity in these years, in the Statistical Physics sector at SISSA and in the Quantitative Life Sciences sector at ICTP.
Chapter 1 serves as an introduction and is kept brief, because each of the following chapters has a separate introduction containing more details on the different problems that have been considered.
In Chapter 2 several models of wealth dynamics are discussed, with focus on the stationary distributions that they have. In particular, we introduce a stochastic growth model that has a truncated power law distribution as a stationary state, and we give an interpretation for the mechanism generating this cut-off as a manifestation of the shadow banking activity.
Chapter 3 is devoted to the issue of wealth inequality, and in particular to its consequences, when in a system with a power law wealth distribution, economic exchanges are considered. A stylized model of trading dynamics is introduced, in which we show how as inequality increases, the liquid capital concentrates more and more on the wealthiest agents, thereby suppressing the liquidity of the economy.
Finally in Chapter 4, we discuss the issue of complexity and information sensitiveness of financial products. In particular, we introduce a stylized model of binary variables, where the financial transparency can be quantified in bits. We quantify how such information losses create sources of systemic risk, and how they should affect the pricing of financial products.
17
Fridlyand, Alex A. "Statistical properties of ideal two dimensional fluid flows : a numerical study." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/12227.
18
Neergaard, John R. "Master equation approach to KPZ type growth /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/9786.
19
Wang, Pengyun. "A Statistical Approach for Assessing Seismic Transitions Associated with Fluid Injections." Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/730.
Анотація:
The wide application of fluid injection has caused a concern of the potential critical risk associated with induced seismicity. To help clarify the concern, this dissertation proposes a statistical approach for assessing seismic transitions associated with fluid injections by scientifically analyzing instrumental measures of seismic events. The assessment problem is challenging due to the uncertain effects of wastewater injections on regional seismicity, along with the limited availability of seismic and injection data. To overcome the challenge, three statistical methods are developed, with each being focused on a different aspect of the problem. Specifically, a statistical method is developed for early detection of induced seismicity, with the potential of allowing for site managers and regulators to act promptly and preparing communities for the increased seismic risk; the second method aims for addressing the further need of quantitatively assessing the transition of induced seismicity, which can reveal the underlying process of induced seismicity and provide data to support probabilistic seismic hazard analysis; and finally, the third method steps further to characterize the process of spatial distribution of induced seismicity, which accounts for spatial evolution of induced seismicity. All the proposed methods are built on the principles of Bayesian technique, which provides a flexible inference framework to incorporate domain expertise and data uncertainty. The effectiveness of the proposed methods is demonstrated using the earthquake dataset for the state of Oklahoma, which shows a promising result: the detection method is able to issue warning of induced seismicity well before the occurrence of severe consequences; the transition model provides a significantly better fit to the dataset than the classical model and sheds light on the underlying transition of induced seismicity in Oklahoma; and the spatio-temporal model provides a most comprehensive characterization of the dataset in terms of its spatial and temporal properties and is shown to have a much better short-term forecasting performance than the “naïve methods”. The proposed methods can be used in combination as a decision-making support tool to identify areas with increasing levels of seismic risk in a quantitative manner, supporting a comprehensive assessment to decide which risk-mitigation strategy should be recommended.
20
FEINAUER, CHRISTOPH. "The Statistical Mechanics Approach to Protein Sequence Data: Beyond Contact Prediction." Doctoral thesis, Politecnico di Torino, 2016. http://hdl.handle.net/11583/2640930.
Анотація:
The recent application of models from inverse statistical mechanics to protein sequence data in has been a large success. In my thesis, I will build upon these models but also use them beyond their original aim of residue contact prediction. This includes the improvement of contact prediction itself by extending the models, the application of the methods in the wider scope of protein interaction networks and the prediction of further biological characteristics from the extracted information.
21
Colizza, Vittoria. "Statistical mechanics approach to complex networks: from abstract to biological networks." Doctoral thesis, SISSA, 2004. http://hdl.handle.net/20.500.11767/4002.
22
Tammisola, Outi. "Linear stability of plane wakes and liquid jets: global and local approach." Licentiate thesis, Stockholm : Skolan för teknikvetenskap, Kungliga Tekniska högskoaln, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10188.
23
Price, Laura E. "Imperfect mixing in energy and mass transport : a data-based mechanistic modelling approach." Thesis, Lancaster University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301086.
24
Muzaferija, Samir. "Adaptive finite volume method for flow prediction using unstructured meshes and multigrid approach." Thesis, Online version, 1994. http://ethos.bl.uk/OrderDetails.do?did=1&uin=uk.bl.ethos.311804.
25
Husowitz, Barry Charles. "Effect of Confinement and Heterogeneity on Phase Behavior: A Density Functional Approach." Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/196124.
Анотація:
Density functional theory of statistical mechanics in a square gradient approximation was used to study nucleation in confined systems such as a cylindrical pore and in-between two cylindrical disks. This approximation was further applied to study the evaporation and condensation in nanopores with finite lengths. Confinement effects induced nucleation phenomena that are not observed in more open systems. Density functional theory was also used to explore the solvation properties of a spherical solute immersed in a supercritical diatomic fluid. The solute was modeled as a hard core Yukawa particle surrounded by a diatomic Lennard-Jones fluid represented by two fused tangent spheres using an interaction site approximation. The results of this study indicate that local density augmentation and the solvation free energies are particularly sensitive to changes in solute and solvent particle geometry and solute/solvent anisotropic interactions. Density functional theory allowed us to systematically study the effect of a variety of geometric and interaction parameters on the properties and behavior of all the systems. Although more sophisticated, but computationally more demanding, theoretical approaches can be used, our results provide fundamental physical insights into the behavior of real systems and create a solid basis for the development of more realistic models.
26
Aldridge, John Nigel. "A continuum mixture theory approach to sediment transport with application to turbulent oscillatory boundary layers." Thesis, University of Plymouth, 1990. http://hdl.handle.net/10026.1/1897.
Анотація:
Two aspects of the modelling of suspended sediment transport are investigated. One is the development of a theoretical base for sediment transport models starting from the continuum theory of immiscible mixtures (also know as two-phase flow theories). The other is a comparison with experimental data of numerical predictions from a number of turbulence models for oscillatory, turbulent boundary layer flow containing suspended sediment. A review is given of previous work that has applied continuum mixture theories to the field of sediment transport. Turbulent averaged forms of the mixture equations are presented and, in the dilute particle concentration limit and neglecting the effects of particle inertia, the equations are shown to reduce to those encountered in traditional approaches to modelling suspended sediment concentrations. Likewise, the equations governing the motion of the fluid phase reduce to standard forms, with the effect of the sediment particles appearing as a buoyancy term in the fluid momentum equation. Particle inertia is taken into account by expanding in terms of a non-dimensional parameter, the ratio of the response time of the particle to a characteristic time of the flow. Terms arising from particle inertia are then reduced to correlations for which models are available in the literature. The assumption of dilute particle concentrations is made throughout the derivation. An extensive comparison between a number of turbulence models is made by comparing numerical predictions with experimental data, whilst making the conventional assumption of zero particle inertia. The k - c model was found to perform well, with simpler models also giving reasonable agreement with experiment. Also investigated is the sensitivity of the solution to a number of factors, including: boundary conditions, empirical turbulence constants, and the stratifying effect of the suspended sediment. The effect of including terms associated with particle inertia are investigated in turbulent oscillatory boundary layer flows. This is found to lead to an enhancement of the vertical particle volume flux. However, given the uncertainties of specifying the boundary condition for the concentration at the bed, the effect is probably not of significance for small particles (diameter - 0.1 mm). Larger particles (diameter 0.25 mm) show more significant effects due to their inertia. The difference in mean horizontal velocity between the fluid and particle phases which results from the inclusion of inertia in the particle momentum equations is calculated. This difference is found to be very small.
27
Srivastav, Abhishek Ray Asok. "Collaboration and pattern recognition in distributed sensor networks a statistical mechanics based approach /." [University Park, Pa.] : Pennsylvania State University, 2009. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-4402/index.html.
28
Zhang, Yongsheng [Verfasser]. "First-principles statistical mechanics approach to step decoration at solid surfaces / Yongsheng Zhang." Berlin : Freie Universität Berlin, 2008. http://d-nb.info/1023022702/34.
29
Rosay, Sophie. "A statistical mechanics approach to the modelling and analysis of place-cell activity." Thesis, Paris, Ecole normale supérieure, 2014. http://www.theses.fr/2014ENSU0010/document.
Анотація:
Les cellules de lieu de l’hippocampe sont des neurones aux propriétés intrigantes, commele fait que leur activité soit corrélée à la position spatiale de l’animal. Il est généralementconsidéré que ces propriétés peuvent être expliquées en grande partie par les comporte-ments collectifs de modèles schématiques de neurones en interaction. La physique statis-tique fournit des outils permettant l’étude analytique et numérique de ces comportementscollectifs.Nous abordons ici le problème de l’utilisation de ces outils dans le cadre du paradigmedu “réseau attracteur”, une hypothèse théorique sur la nature de la mémoire. La questionest de savoir comment ces méthodes et ce cadre théorique peuvent aider à comprendrel’activité des cellules de lieu. Dans un premier temps, nous proposons un modèle de cellulesde lieu dans lequel la localisation spatiale de l’activité neuronale est le résultat d’unedynamique d’attracteur. Plusieurs aspects des propriétés collectives de ce modèle sontétudiés. La simplicité du modèle permet de les comprendre en profondeur. Le diagrammede phase du modèle est calculé et discuté en comparaison avec des travaux précedents.Du point de vue dynamique, l’évolution du système présente des motifs particulièrementriches. La seconde partie de cette thèse est à propos du décodage de l’activité des cellulesde lieu. Nous nous demandons quelle est l’implication de l’hypothèse des attracteurs surce problème. Nous comparons plusieurs méthodes de décodage et leurs résultats sur letraitement de données expérimentalesPlace cells in the hippocampus are neurons with interesting properties such as the corre-lation between their activity and the animal’s position in space. It is believed that theseproperties can be for the most part understood by collective behaviours of models of inter-acting simplified neurons. Statistical mechanics provides tools permitting to study thesecollective behaviours, both analytically and numerically.Here, we address how these tools can be used to understand place-cell activity withinthe attractor neural network paradigm, a theory for memory. We first propose a modelfor place cells in which the formation of a localized bump of activity is accounted for byattractor dynamics. Several aspects of the collective properties of this model are studied.Thanks to the simplicity of the model, they can be understood in great detail. The phasediagram of the model is computed and discussed in relation with previous works on at-tractor neural networks. The dynamical evolution of the system displays particularly richpatterns. The second part of this thesis deals with decoding place-cell activity, and theimplications of the attractor hypothesis on this problem. We compare several decodingmethods and their results on the processing of experimental recordings of place cells in afreely behaving rat
30
Telotte, John Charles. "Thermodynamic properties of multicomponent mixtures from the solution of groups approach to direct correlation function solution theory." Gainesville, FL, 1985. http://www.archive.org/details/thermodynamicpro00telo.
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Erlhoff, Ethan Bruce. "Distributed Forcing on a 3D Bluff Body with a Blunt Base, An Experimental Active Drag Control Approach." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/879.
Анотація:
This paper seeks to explore the effects of an active drag control method known as distributed forcing on a 3D bluff body with a blunt base. The 9.5 x 15.25 x 3 inch aluminum model constructed for this experiment has an elliptically shaped nose and rectangular aft section. The model is fitted with four, 12 Volt fans, forcing the freestream air into and out of 1 mm thick slots on the upper and lower trailing edges. The forcing is steady in time, held at a constant forcing velocity though all Reynolds numbers, but varies roughly sinusoidally in the spanwise direction across the model. Testing was conducted at Reynolds numbers of 50,000, 100,000 and 150,000 at California Polytechnic State University, San Luis Obispo in the Aerospace Engineering Department’s subsonic 3’ by 4’ wind tunnel.
Effectiveness of the distributed forcing method was evaluated by measuring the base pressure on the model using a Scanivalve system. By measuring multiple static pressure ports, it was found that base pressure increased by 15.3% and 4.2% at Reynolds numbers of 50,000 and 100,000 respectively, and showed a decrease of 2.7% at a Reynolds number of 150,000.
Total drag on the model was also measured using a sting balance mount fitted with strain gauges. This test showed a drag reduction of 15.8% and 5.5% for Reynolds numbers of 50,000 and 100,000 respectively, and an increase in drag of 2.0% at Reynolds number of 150,000, when omitting external power required to run the forcing assembly. The forcing assembly was shown to require nearly 12 times the power to operate than it saves in drag reduction at Reynolds number of 50,000. In addition, a thermal anemometry measurement of streamwise velocity of the near wake behind the bluff body was conducted to qualitatively assess the attenuation of the vortex street behind the model. Distributed forcing shows that as the freestream velocity is increased as compared to the forcing velocity, the change in energy spectral density is lessened, and as such, the largest attenuation in vortex shedding is at Reynolds number of 50,000 while nearly no change is seen at the Reynolds number of 150,000.
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Corrias, Maria Elena. "A statistical mechanics approach to cancer dynamics: a model for multiple myeloma bone disease." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18021/.
Анотація:
L’utilizzo di modelli matematici sta assumendo un ruolo sempre più centrale nella ricerca oncologica. La complessità del cancro ha stimolato gruppi di ricerca interdisciplinare nello sviluppo di modelli quantitativi per rispondere alle numerose domande aperte che riguardano l’insorgenza, la progressione, la diagnosi, la risposta al trattamento terapeutico e l’acquisizione della resistenza ai farmaci dei tumori. La varietà di approcci matematico-fisici ben si adatta allo studio di una materia così eterogenea. In questo lavoro presentiamo innanzitutto gli aspetti biologico-clinici che caratterizzano il cancro, per poi introdurre i modelli che sono stati utilizzati per comprenderli. Abbiamo preso in considerazione il caso del mieloma multiplo, una neoplasia che colpisce le plasmacellule. In particolare proponiamo un modello matematico per lo studio della patogenesi delle lesioni ossee causate dal mieloma. L’insorgere di questo tumore rompe l’equilibrio fisiologico del tessuto osseo, causando un aumento dell’attività degli osteoclasti ed una diminuzione dell’attività degli osteoblasti, fenomeni che, combinati, comportano le caratteristiche fratture. Abbiamo optato per un approccio di tipo ecologico, in cui i diversi tipi di cellule sono considerati come specie interagenti in meccanismi di cooperazione o sfruttamento. Questo fenomeno è stato modellizzato all’interno della classe degli Interacting Particle Systems, che sono sistemi di processi di Markov localmente interagenti. Abbiamo inizialmente studiato il caso dell’osso sano per poi passare a quello in cui sono presenti le cellule del mieloma. Infine, abbiamo svolto simulazioni per delineare l’evoluzione nel tempo delle specie cellulari. Abbiamo riservato una particolare attenzione alla definizione dei parametri del modello: non solo essi ci permettono di riprodurre diversi stadi e forme del mieloma, ma possono descrivere l’intervento terapeutico sul tumore, costituendo un nuovo strumento per la ricerca oncologica.
33
Renner, Johan. "Towards Subject Specific Aortic Wall Shear Stress : a combined CFD and MRI approach." Doctoral thesis, Linköpings universitet, Mekanisk värmeteori och strömningslära, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-65910.
Анотація:
The cardiovascular system is an important part of the human body since it transports both energy and oxygen to all cells throughout the body. Diseases in this system are often dangerous and cardiovascular diseases are the number one killer in the western world. Common cardiovascular diseases are heart attack and stroke, which origins from obstructed blood flow. It is generally important to understand the causes for these cardiovascular diseases. The main causes for these diseases are atherosclerosis development in the arteries (hardening and abnormal growth). This transform of the arterial wall is believed to be influenced by the mechanical load from the flowing blood on the artery and especially the tangential force the wall shear stress. To retrieve wall shear stress information in arteries invivo is highly interesting due to the coupling to atherosclerosis and indeed a challenge. The goal of this thesis is to develop, describe and evaluate an in-vivo method for subject specific wall shear stress estimations in the human aorta, the largest artery in the human body. The method uses an image based computational fluid dynamics approach in order to estimate the wall shear stress. To retrieve in-vivo geometrical descriptions of the aorta magnetic resonance imaging capabilities is used which creates image material describing the subject specific geometry of the aorta. Magnetic resonance imaging is also used to retrieve subject specific blood velocity information in the aorta. Both aortic geometry and velocity is gained at the same time. Thereafter the image material is interpreted using level-set segmentation in order to get a three-dimensional description of the aorta. Computational fluid dynamics simulations is applied on the subject specific aorta in order to calculate time resolved wall shear stress distribution at the entire aortic wall included in the actual model. This work shows that it is possible to estimate subject specific wall shear stress in the human aorta. The results from a group of healthy volunteers revealed that the arterial geometry is very subject specific and the different wall shear stress distributions have general similarities but the level and local distribution are clearly different. Sensitivity (on wall shear stress) to image modality, the different segmentation methods and different inlet velocity profiles have been tested, which resulted in these general conclusions: The aortic diameter from magnetic resonance imaging became similar to the reference diameter measurement method. The fast semi-automatic level-set segmentation method gave similar geometry and wall shear stress results when compared to a reference segmentation method. Wall shear stress distribution became different when comparing a simplified uniform velocity profile inlet boundary condition with a measured velocity profile. The method proposed in this thesis has the possibility to produce subject specific wall shear stress distribution in the human aorta. The method can be used for further medical research regarding atherosclerosis development and has the possibility for usage in clinical work.
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Venkatesan, Sreedhar, and Hanumantha Raju Hariprasad Banglore. "Probabilistic Analysis of Brake Noise : A Hierarchical Multi-fidelity Statistical Approach." Thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-151009.
Анотація:
Computer Aided Engineering driven analysis is gaining grounds in automotive industry. Prediction of brake noise using CAE techniques has become populardue to its overall low cost as compared to physical testing. However, the presence of several uncertain parameters which affect brake noise and also the lack of basic understanding about brake noise, makes it difficult to make reliable decisions based on CAE analysis. Therefore, the confidence level in CAE techniques has to be increased to ensure reliability and robustness in the CAE solutions which support design work. One such way to achieve reliability in the CAE analysis isinvestigated in this thesis by incorporating the effects of different sources of uncertainty and variability in the analysis and estimating the probability of designfailure (probability of brake noise above a certain threshold). While incorporating the uncertainties in the CAE analysis ensures robustness, it is computationally intensive. This thesis work aims to gain an understanding about a brakenoise - creep groan, and to bring robustness into the CAE analysis along with reduction in computational time. A probabilistic analysis technique called hierarchical multi-fidelity statistical approachis explored in this thesis work, to estimate the probability of design failure or design robustness at a faster rate. It incorporates the stochasticity in the input parameters while running simulations. The method involves application of a hierarchy of approximations to the system response computed with variations in mesh resolution or variations in number of modes or changing solver time step,etc. And finally it uses the probability theory, to relate the information provided by approximate solutions to get the target failure estimation.Through this method, reliable data regarding the probability of design failure was approximated for every simulation and at a reduced computational time.Additionally, it provided information about critical parameters that influenced brake noise which was meritorious for design management. Estimation of probability of design failure by this method has been proved to be reliable in the case of brake noise according to the simulation results and the method can be considered robust.Computer Aided Engineering (cae) driven analysis is gaining grounds in automotive industry. Brake noise is one such place where cae simulations are gaining more attention. The presence of several uncertain parameters which affect brake noises and also the lack of basic understanding about brake noise, makes it difficult to make reliable decisions based on cae deterministic analyses alone.Therefore, the confidence level in cae analyses has to be increased to ensure cae analysis robustness. One way to achieve this is by incorporating the effects of different sources of uncertainty and variability in the cae analysis and estimating the probability of design failure. Such a reliability measure (i.e. probability of noise event occurrence or exceedance of noise level than a threshold) can provide car manufacturers with an idea about the costs of warranty claims due to brake noise and can be used as a metric to evaluate different design solutions, before the final design goes to the production stage. On one hand, using the high-fidelity models of brake/chassis system is generally computationally intensive, and thus, often only limited number of simula-tion runs are feasible for uncertainty analysis and design failure risk assessment. On the other hand, analyses on low-fidelity models, typically based on simplified assumptions during the development phase are fast but not always accu-rate. Striking for a good balance between efficiency and accuracy/robustness is an important task, when dealing with uncertainty/risk analysis of such complex dynamical systems To address these issues, a hierarchical multi-fidelity statistical approach has been adopted in this study, in order to estimate the probability of design failure. It employs a hierarchy of approximations to the system response computed with different fidelity by surrogate modelling, coarse spatial/temporal model mesh resolution variation, changing solver time step, etc., using probability theory, to relate information provided by approximate solu-tions to the target failure estimation. Using this approach opens up the possi-bility to use a low-fidelity models to accelerate the uncertainty quantification of complex brake/chassis systems, while granting unbiased estimation of system design failure risk/reliability. It also enables management of design changes, during fast iterations of the design process. This approach is used for studying one of the brake noise issue called creep groan, understand the root cause and providedesign proposals.
35
Rogal, Jutta. "Stability, composition and function of palladium surfaces in oxidizing environments a first principles statistical mechanics approach /." kostenfrei, 2006. http://www.diss.fu-berlin.de/2006/535/index.html.
36
Nehring, Benjamin [Verfasser], and Sylvie [Akademischer Betreuer] Roelly. "Point processes in statistical mechanics : a cluster expansion approach [[Elektronische Ressource]] / Benjamin Nehring. Betreuer: Sylvie Roelly." Potsdam : Universitätsbibliothek der Universität Potsdam, 2012. http://d-nb.info/1028397100/34.
37
Nanavati, Hemant. "Molecular modeling of the elastic and photoelastic properties of crosslinked polymer networks: a statistical segment approach / by Hemant Nanavati." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/8227.
38
Kanit, Toufik. "Notion of representative volume element for heterogeneous materials: statistical and numerical approach." Phd thesis, École Nationale Supérieure des Mines de Paris, 2003. http://tel.archives-ouvertes.fr/tel-00005751.
39
Nakayama, Yasuya. "Statistical physics approach to strongly correlated fluctuations and its application to fluid turbulence and heart rate variability." 京都大学 (Kyoto University), 2003. http://hdl.handle.net/2433/148496.
40
Lymperiadis, Alexandros. "SAFT-γ : a group contribution approach based on a heteronuclear version of the Statistical Associating Fluid Theory". Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/11377.
41
Hohenegger, Christel. "Small Scale Stochastic Dynamics For Particle Image Velocimetry Applications." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10464.
Анотація:
Fluid velocities and Brownian effects at nanoscales in the near-wall region of microchannels can be experimentally measured in an image plane parallel to the wall using, for example, evanescent wave illumination technique combined with particle image velocimetry [R. Sadr extit{et al.}, J. Fluid. Mech. 506, 357-367 (2004)]. The depth of field of this technique being difficult to modify, reconstruction of the out-of-plane dependence of the in-plane velocity profile remains extremely challenging. Tracer particles are not only carried by the flow, but they undergo random fluctuation imposed by the proximity of the wall. We study such a system under a particle based stochastic approach (Langevin) and a probabilistic approach (Fokker-Planck). The Langevin description leads to a coupled system of stochastic differential equations. Because the simulated data will be used to test a statistical hypothesis, we pay particular attention to the strong order of convergence of the scheme developing an appropriate Milstein scheme of strong order of convergence 1. Based on the probability density function of mean in-plane displacements, a statistical solution to the problem of the reconstruction of the out-of-plane dependence of the velocity profile is proposed. We developed a maximum likelihood algorithm which determines the most likely values for the velocity profile based on simulated perfect particle position, simulated perfect mean displacements and simulated observed mean displacements. Effects of Brownian motion on the approximation of the mean displacements are briefly discussed. A matched particle is a particle that starts and ends in the same image window after a measurement time. AS soon as the computation and observation domain are not the same, the distribution of the out-of-plane distances sampled by matched particles during the measurement time is not uniform. The combination of a forward and a backward solution of the one dimensional Fokker-Planck equation is used to determine this probability density function. The non-uniformity of the resulting distribution is believed to induce a bias in the determination of slip length and is quantified for relevant experimental parameters.
42
Abu-Rahmeh, Osama. "A statistical mechanics approach for an effective, scalable, and reliable distributed load balancing scheme for grid networks." Thesis, Liverpool John Moores University, 2009. http://researchonline.ljmu.ac.uk/5903/.
Анотація:
The advances in computer and networking technologies over the past decades produced new type of collaborative computing environment called Grid Networks. Grid network is a parallel and distributed computing network system that possesses the ability to achieve a higher computing throughput by taking advantage of many computing resources available in the network. To achieve a scalable and reliable Grid network system, the workload needs to be efficiently distributed among the resources accessible on the network. A novel distributed algorithm based on statistical mechanics that provides an efficient load-balancing paradigm without any centralised monitoring is proposed here. The resulting load-balancer would be integrated into Grid network to increase its efficiency and resources utilisation. This distributed and scalable load-balancing framework is conducted using the biased random sampling (BRS) algorithm. In this thesis, a novel statistical mechanics approach that gives a distributed loadbalancing scheme by generating almost regular networks is proposed. The generated network system is self-organised and depends only on local information for load distribution and resource discovery. The in-degree of each node refers to its free resources, and job assignment and resource updating processes required for load balancing are accomplished by using random sampling (RS). An analytical solution for the stationary degree distributions has been derived that confirms that the edge distribution of the proposed network system is compatible with ER random networks. Therefore, the generated network system can provide an effective loadbalancing paradigm for the distributed resources accessible on large-scale network 1 systems. Furthermore, it has been demonstrated that introducing a geographic awareness factor in the random walk sampling can reduce the effects of communication latency in the Grid network environment. Theoretical and simulation results prove that the proposed BRS load-balancing scheme provides an effective, scalable, and reliable distributed load-balancing scheme for the distributed resources available on Grid networks.
43
Faleye, S. "Evaluating the effect of learning fluid mechanics through the CCAILM learning approach in some South African universities." Journal for New Generation Sciences, Vol 9, Issue 1: Central University of Technology, Free State, Bloemfontein, 2011. http://hdl.handle.net/11462/577.
Анотація:
Published ArticleThe need to increase the number of quality engineering graduates, graduating from South African Universities, informed this study. Based on the findings from the baseline study, conducted prior to the present study, this research seeks to evaluate (using a static, non-equivalent, group design) the effect of Constructionist Computer-Aided Instructional Learning Model (CCAILM) approach, used in some South African Universities, for studying fluid mechanics in mechanical engineering classes. This new learning model is derived from constructionist learning theory, media-affects-learning hypothesis and multiple representation principle. The results of the data analysis indicate that CCAILM learning approach enhances the learning of fluid mechanics in mechanical engineering classes.
44
Diaz, simoes Juan Raphael. "A mathematical approach to embryonic morphogenesis based on spatio-temporal cell lineages." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX065/document.
Анотація:
Cette thèse traite des processus morphogénétiques au cours de l’embryogenèse pré-coce des vertébrés par le biais d’une étude mathématique et physique des lignagescellulaires spatio-temporels reconstruits à partir d’imagerie 3D+temps in vivo. Notreméthodologie repose sur une représentation de type système complexe de l’embryonavec ses différents niveaux d’organisation en interaction et l’analyse formelle des dé-placements cellulaires dans l’espace et dans le temps. Nous avons conçu et mis enœuvre une méthodologie originale pour identifier dans les lignages cellulaires la for-mation de compartiments en cohérence avec les repères anatomiques et l’organisationdes organes présomptifs. En outre, nous proposons une stratégie pour inférer les forcesbiomécaniques sous-jacentes. Nous délivrons également une interface informatique er-gonomique, d’abord déployée pour mettre en œuvre notre méthodologie, mais aussiconçue pour être extensible et versatile. Ces outils visent à construire une représenta-tion commune pour les biologistes, les mathématiciens, les physiciens et les informati-ciens explorant les processus de la morphogenèse des organismes vivantsThis thesis approaches morphogenetic processes in the early embryogenesis of verte-brates through the mathematical and physical study of spatio-temporal cell lineagesreconstructed from in vivo 3D+time images. Our methodology is based on a complexsystems representation of the embryo, with the interaction between levels of organiza-tion and the formal analysis of cell displacements in space and time. We designed andimplemented an original methodology to identify in cell lineages the formation of com-partments in consistency with anatomical landmarks and the organization of presump-tive organs. In addition, we proposed a strategy to infer the underlying biomechanicalforces. We also delivered a user-friendly computer interface, first deployed for usingour methodology but also designed to be extensible and versatile, which aims to bea common ground for biologists, mathematicians, physicists and computer scientistsinvestigating morphogenetic processes in living systems
45
Yan, Yujie yy. "A General Approach to Buhlmann Credibility Theory." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1011812/.
Анотація:
Credibility theory is widely used in insurance. It is included in the examination of the Society of Actuaries and in the construction and evaluation of actuarial models. In particular, the Buhlmann credibility model has played a fundamental role in both actuarial theory and practice. It provides a mathematical rigorous procedure for deciding how much credibility should be given to the actual experience rating of an individual risk relative to the manual rating common to a particular class of risks. However, for any selected risk, the Buhlmann model assumes that the outcome random variables in both experience periods and future periods are independent and identically distributed. In addition, the Buhlmann method uses sample mean-based estimators to insure the selected risk, which may be a poor estimator of future costs if only a few observations of past events (costs) are available. We present an extension of the Buhlmann model and propose a general method based on a linear combination of both robust and efficient estimators in a dependence framework. The performance of the proposed procedure is demonstrated by Monte Carlo simulations.
46
Skoog, Erik. "CFD Annular Flow Modelling Based on a Three-Field Approach." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-80165.
Анотація:
This master thesis aim to model the annular flow that occurs in the final section between the fuel rods inside Boiling Water Reactors, by approximating the geometry to a cylindrical pipe. Simulations were performed in the software ANSYS Fluent, as a step in the development of replacing the 1D correlations currently used in the nuclear industry with CFD models in 3D. An Eulerian-Lagrangian approach was used for the three fields of steam, liquid film and liquid droplets in the model. Entrainment was modeled based on 1D correlations from Okawa [7] and deposition with the built in Discrete Phase Model in ANSYS Fluent. The work focused on making the process less time consuming, and increasing accuracy of the model by comparing the results with empirical data based on experimental values. A transverse velocity was applied on the droplets at the point of entrainment with better correlating results with the Okawa model.
47
Zaid, Irwin Morton. "Non-Gaussian fluctuations in active suspensions." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:8ed73f05-9d88-4de8-91c5-1d944ad9004a.
Анотація:
An active particle converts energy to motion. An active suspension is a population of active particles, typically microscale, that are immersed in a viscous and/or elastic medium. This thesis is about the statistics of active suspensions. Unlike a suspension at thermodynamic equilibrium, we show that an active suspension inherently has non-Gaussian fluctuations due to an interplay between self-driven constituents and microscopic physics. Consequently, the diffusion of a tracer in an active suspension is not Gaussian. Our results explain some experiments with active suspensions that contain either swimming microorganisms or molecular motors. We provide different models for the fluctuations in dilute active suspensions, ranging from phenomenological to exact. The fundamental ingredient of such non-Gaussian fluctuations is an ultraslow convergence to the central limit theorem caused by truncated power-laws. Without any truncation, there is an intimate relation to the generalized central limit theorem. We suggest similar effects occur in many other systems. These may be associated with probability distributions that appear to be exponential.
48
Wilde, Daniel G. "Validation of a CFD Approach for Gas Turbine Internal Cooling Passage Heat Transfer Prediction." DigitalCommons@CalPoly, 2015. https://digitalcommons.calpoly.edu/theses/1384.
Анотація:
This report describes the development and application of a validated Computational Fluid Dynamics (CFD) modelling approach for internal cooling passages in rotating turbomachinery. A CFD Modelling approach and accompanying assumptions are tuned and validated against academically available experimental results for various serpentine passages. Criteria of the CFD modelling approach selected for investigation into advanced internal cooling flows include accuracy, robustness, industry familiarity, and computational cost.
Experimental data from NASA HOST (HOt Section Technology), Texas A&M, and University of Manchester tests are compared to RANS CFD results generated using Fluent v14.5 in order to benchmark a CFD modelling approach.
Capability of various turbulence models in the representation of cooling physics is evaluated against experimental data. Model sensitivity to boundary conditions and mesh density is also evaluated.
The development of a validated computational model of internal turbine cooling channels with bounded error allows for the identification of particular shortcomings of heat transfer correlations and provides a baseline for future CFD based exploration of internal turbine cooling concepts.
49
Krometis, Justin. "A Bayesian Approach to Estimating Background Flows from a Passive Scalar." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/83783.
Анотація:
We consider the statistical inverse problem of estimating a background flow field (e.g., of air or water) from the partial and noisy observation of a passive scalar (e.g., the concentration of a pollutant). Here the unknown is a vector field that is specified by large or infinite number of degrees of freedom. We show that the inverse problem is ill-posed, i.e., there may be many or no background flows that match a given set of observations. We therefore adopt a Bayesian approach, incorporating prior knowledge of background flows and models of the observation error to develop probabilistic estimates of the fluid flow. In doing so, we leverage frameworks developed in recent years for infinite-dimensional Bayesian inference. We provide conditions under which the inference is consistent, i.e., the posterior measure converges to a Dirac measure on the true background flow as the number of observations of the solute concentration grows large. We also define several computationally-efficient algorithms adapted to the problem. One is an adjoint method for computation of the gradient of the log likelihood, a key ingredient in many numerical methods. A second is a particle method that allows direct computation of point observations of the solute concentration, leveraging the structure of the inverse problem to avoid approximation of the full infinite-dimensional scalar field. Finally, we identify two interesting example problems with very different posterior structures, which we use to conduct a large-scale benchmark of the convergence of several Markov Chain Monte Carlo methods that have been developed in recent years for infinite-dimensional settings.Ph. D.
50
Martin, David Stewart. "An Investigation of Avian Wing Tip Vortex Generation Using a Biomimetic Approach." DigitalCommons@CalPoly, 2017. https://digitalcommons.calpoly.edu/theses/1734.
Анотація:
An experimental study has been conducted to develop a process allowing the creation of biologically accurate aerodynamic test models mimicking the slotted primary feather geometry of the Brown Pelican (Pelecanus occidentalis). Preserved examples of both a full Brown Pelican wing and a single primary feather were 3D scanned and digitally reconstructed using a combination of MATLAB and CAD software. The final model was then 3D printed as a collection of smaller components using a LulzBot TAZ 6 printer and Taulman3D T-Glase PET filament. After using various surface finishing techniques to improve the finish of all 3D printed parts, an assembly was designed to mount the model in the low speed wind tunnel at the California Polytechnic State University. Prior to aerodynamic testing, airfoil sections of the pelican wing were generated in CAD and several common airfoil measurements and characteristics were investigated. At a flow velocity of 5 m/s (Re ~1.21 x 105), wind tunnel smoke and laser visualization testing highlighted the vortex generation of multiple primary feathers, as well as large-scale flow deviations in the vicinity of the feathers. A total pressure rake and total pressure probe were used to create detailed plots of the ratio of the local velocity to free-stream velocity (Vx/Vx∞) at two planes downstream of the model, which revealed vortex positioning consistent with that predicted by smoke visualization testing and provided a metric by which to evaluate the relative strength of each vortex.
The model creation process and wind tunnel testing results outlined here provide a strong foundation for future investigations into the potential aerodynamic benefits provided by the slotted primary feather geometry employed by the Brown Pelican and other large gliding avian species.