Tesis: "LES numerical simulations"

1

Öqvist, Mona. "Numerical simulations of wear". Licentiate thesis, Luleå tekniska universitet, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26185.

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The objective of this licentiate thesis was to study the effect of tool wear for sheet metal forming tools and how the wear process can be simulated in an efficient manner. Three Papers are appended to this licentiate thesis. Paper A covers the influence of tool geometry in deep drawing. In paper B is the way of calculating with finite element analysis described. The wear of a steel cylinder oscillating against a steel plate was studied experimentally. The worn shape of the cylinder was then compared with a numerical simulation of the shape. Paper C shows how numerical simulations can be used to simulate wear of deep drawing tools. The wear of two different deep drawing tools has been investigated. The shape of the tools before and after wear have been compared as well as the stresses and strains in the formed cups.
Godkänd; 2000; 20070317 (ysko)

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2

Gross, Richard Edward. "Numerical simulations of flux pinning". Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243012.

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3

Demetriou, D. A. "Numerical simulations of interface kinetics". Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598490.

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This dissertation's goal is concerned with the development and numerical study of a continuum model, that describes a variety of interface growth phenomena such as fluid displacement in porous media, crystal growth and flux-lines in type-II superconductors. The continuum model is the Quenched-Edwards-Wilkinson (QEW), which is well established in the literature and we restrict ourselves in providing a brief 'derivation' in terms of symmetry considerations. A crucial part of the model is the quenched random medium where the interface moves. The 'adequate' generation of the random background is a crucial ingredient of the simulations and we use a method first employed in fluid mechanics, but never before used in this field. Massive parallel simulations of the resulting system allowed us to verify the presence of a well defined depinning transition between a pinned and moving interface. This is characterized by the presence of a spatial system size (above a certain system size) independent threshold force. The transition appears to fit well the conjecture that the ensemble and time averaged centre of mass velocity, v_cm, scales with the applied external driving force, F, according to v_cm ~ ((F)/(F)_c-1)^θwhere F_c is the threshold force and θ the velocity critical exponent. The velocity exponent is expected to be a 'universal' quantity independent of model parameters. Based on our work we estimate θ = 0.61 ± 0.06.

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4

McMillan, Paul. "Numerical simulations of galaxy interaction". Thesis, University of Leicester, 2006. http://hdl.handle.net/2381/433.

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Cosmological theories that include a non-baryonic dynamically cold dark matter (CDM) have been stunningly successful at explaining observations of the universe on large scales. On the scale of individual galaxies, however, observations have been made which call into question the CDM paradigm. In particular, simulations of structure formation show CDM haloes with a density “cusp”, such that in the centre of the halo d ln ρ/d ln r ~1 − 1.5. In contrast, observational studies suggest that CDM haloes have constant density cores. In this thesis I use gravitational N-body simulations to investigate the claim that the dark matter halo cusp can be removed by angular momentum transport from a rotating bar in a disc galaxy. I find that the simulations which were used to support this claim were seriously flawed, and similar simulations designed to mitigate these flaws suggest that this is unlikely to be a mechanism for turning a cusp into a core. In the interests of further work on dark matter haloes, and on other problems in astrophysics, I design and implement a new method for constructing model galaxies with halo, bulge, and disc components. This method avoids the use of an approximation to a Maxwellian velocity distribution. I show that this creates stable galaxy models, well suited to many applications. As an example of these applications, I conduct a thorough investigation of the structural and kinematic properties of the haloes of the remnants of 1:1 mass ratio mergers. I determine that the merger has virtually no effect on the halo cusp strength, but a substantial effect on the halo velocity distribution. The remnant haloes are significantly less spherical that those described in studies of mergers which consider gas cooling. Other properties of the remnants are noted and discussed.

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5

Pavlovski, G. "Numerical simulations of molecular turbulence". Thesis, Queen's University Belfast, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403275.

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6

Grimshaw, L. "Numerical simulations of ellipsoidal galaxies". Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370414.

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7

Cox, Christopher Ian. "Numerical simulations of astrophysical jets". Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335736.

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8

Clarke, Seamus. "Numerical simulations of filamentary clouds". Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/100557/.

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Filamentary structures are observed to be common over a wide range of spatial scales and are strongly linked to star formation. In this thesis I present the results of a range of numerical simulations which investigate the stability, collapse and fragmentation of filaments. The global longitudinal collapse timescale for filaments is found to be considerably longer than for equally dense spheres, allowing sufficient time for local collapse to occur, and to solely occur via the distinctive end-dominated mode. A new freefall timescale equation for filaments is presented, as well as a semi-analytic model of longitudinal collapse. The fragmentation of accreting filaments is found to be more complicated than that of equilibrium filaments, and is dominated by the behaviour of longitudinal gravo-acoustic oscillations. This results in the fastest growing perturbation mode being independent of filament width. The non-equilibrium model presented here allows observers to estimate the age of a fragmenting filament and the mass accretion rate. Simulations of filaments accreting from a inhomogenous, turbulent medium show that turbulence has a large impact on the fragmentation of a filament. When the turbulence is sub-sonic, a filament fragments in a two-tiered hierarchical manner. As the energy in the turbulent field increases, the filament fragments into elongated fibre-like sub-structures. The formation of these fibre-like structures is intimately linked to the vorticity of the velocity field in the filament and the accretion onto the filament. In addition, I present synthetic C18O observations and show that the fibrelike sub-structures appear as velocity-coherent structures, well separated in velocity space, similar to the fibres observed by Hacar & Tafalla (2011).

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9

Wu, Wenwei. "Chemical reactions in turbulence : numerical studies through direct numerical simulations". Thesis, Littoral, 2021. http://www.theses.fr/2021DUNK0577.

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Le présent travail se concentre sur les propriétés statistiques des scalaires réactifs subissant des réactions chimiques réversibles en turbulence incompressible. Une analyse théorique des propriétés statistiques des scalaires à différents ordres de moments a été réalisée sur la base d'approximations et de modèles convenablement proposés. Les résultats théoriquement dérivés ont ensuite été comparés aux résultats numériques obtenus par simulation numérique directe (DNS). Dans la simulation numérique directe, les dérivés spatiales ont été principalement approximées en utilisant une méthode pseudi-spectrale, car la vitesse turbulente et les champs scalaires sont généralement des conditions aux limites périodiques. Pour les configurations spéciales dans lesquelles la condition aux limites n'est pas périodique, une méthode aux différences finies avec des schémas fins a été utilisée pour approximer les dérivées spatiales. L'intégration temporelle numérique a été mise en oeuvre par un schéma Runge-Kutta du troisième ordre. Tous les travaux menés dans cette thèse sont consacrés aux explorations numériques et théoriques des scalaires réactifs en turbulence incompressible de différentes configurations. Nos résultats suggèrent de nouvelles idées pour de futures études, qui sont discutées dans les conclusions
The present work focuses on the statistical properties of reactive scalars undergoing reversible chemical reactions in incompressible turbulence. Theoretical analysis about the statistical properties of scalars at different order of moments were carried out based on appropriately proposed approximations and models. The theoretically derived results were then compared with numerical results obtained by direct numerical simulation (DNS). In the direct numerical simulation, the spatial derivatives were mainly approximated by using a pseudo-spectral method, since the turbulent velocity and scalar fields are generally of periodic boundary conditions. For the special configurations in which the boundary condition is not periodic, a finite difference method with fine schemes was used to approximate the spatial derivatives. The numerical time integration was implemented by a third order Runge-Kutta scheme. All the works carried out in this thesis are devoted to the numerical and theoretical explorations about reactive scalars is incompressible turbulence of different configurations. Our finding suggest new ideas for future studies, which are discussed in the conclusions

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10

Wahba, Essam Moustafa. "Hierarchical formulations for numerical flow simulations /". For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2004. http://uclibs.org/PID/11984.

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11

Niedziela, Dariusz. "On numerical simulations of viscoelastic fluids". [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981890849.

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12

Alic, Daniela Delia. "Theoretical issues in Numerical Relativity simulations". Doctoral thesis, Universitat de les Illes Balears, 2009. http://hdl.handle.net/10803/9438.

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In this thesis we address several analytical and numerical problems related with the general relativistic study of black hole space-times and boson stars.
We have developed a new centered finite volume method based on the flux splitting approach. The techniques for dealing with the singularity, steep gradients and apparent horizon location, are studied in the context of a single Schwarzschild black hole, in both spherically symmetric and full 3D simulations. We present an extended study of gauge instabilities related with a class of singularity avoiding slicing conditions and show that, contrary to previous claims, these instabilities are not generic for evolved gauge conditions. We developed an alternative to the current space coordinate conditions, based on a generalized Almost Killing Equation. We performed a general relativistic study regarding the long term stability of Mixed-State Boson Stars configurations and showed that they are suitable candidates for dark matter models.
En esta tesis abordamos varios problemas analíticos y numéricos relacionados con el estudio de agujeros negros relativistas y modelos de materia oscura.
Hemos desarrollado un nuevo método de volúmenes finitos centrados basado en el enfoque de la división de flujo. Discutimos las técnicas para tratar con la singularidad, los gradientes abruptos y la localización del horizonte aparente en el contexto de un solo agujero negro de Schwarzschild, en simulaciones tanto con simetría esférica como completamente tridimensionales. Hemos extendido el estudio de una familia de condiciones de foliaciones evitadoras de singularidad y mostrado que ciertas inestabilidades no son genéricas para condiciones de gauge dinámicas. Desarrollamos una alternativa a las prescripciones actuales basada en una Almost Killing Equation generalizada. Hemos realizado también un estudio con respecto a la estabilidad a largo plazo de configuraciones de Mixed-State Boson Stars, el cual sugiere que estas podrían ser candidatas apropiadas para modelos de materia oscura.

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13

Liu, Xuan. "Numerical Simulations of Ultrafast Pulse Measurements". Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16175.

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This thesis contains two major components of research: numerical simulation of optical-parametric amplification cross correlation of Frequency-Resolved Optical Gating (OPA-XFROG) and numerical simulation of GRENOUILLE and its related issues. Recently, an extremely sensitive technique--OPA-XFROG has been developed. A short pump pulse serves as the gate by parametrically amplifying a short segment of the signal pulse in a nonlinear crystal. High optical parametric gain makes possible the complete measurement of ultraweak, ultrashort light pulses. Unlike interferometric methods, it does not carry prohibitively restrictive requirements, such as perfect mode-matching, perfect spatial coherence, highly stable absolute phase, and a same-spectrum reference pulse. We simulate the OPA-XFROG technique and show that by a proper choice of the nonlinear crystal and the noncollinear mixing geometry it is possible to match the group velocities of the pump, signal, and idler pulses, which permits the use of relatively thick crystals to achieve high gain without measurement distortion. Gain bandwidths of ~100 nm are possible, limited by group velocity dispersion. In the second part of the thesis, we numerically simulate the performance of the ultrasimple ultrashort laser pulse measurement device- GRENOUILLE. While simple in practice, GRENOUILLE has many theoretical subtleties because it involves the second-harmonic generation of relatively tightly focused and broadband pulses. In addition, these processes occur in a thick crystal, in which the phase-matching bandwidth is deliberately made narrow compared to the pulse bandwidth. We developed a model that include all sum-frequency-generation processes, both collinear and noncollinear. We also include dispersion using the Sellmeier equation for the crystal BBO. Working in the frequency domain, we compute the GRENOUILLE trace for practical-and impractical-examples and show that accurate measurements are easily obtained for properly designed devices. For pulses far outside a GRENOUILLE's operating range (on the long side), we numerically deconvolve the GRENOUILLE trace with the response function of GRENOUILLE to improve its spectral resolution. In the last part of the thesis, we simulate the second harmonic generation with tightly focused beams by use of lens. Thus, we are able to explain the `weird' focusing effect that has been a `puzzles' for us in the GRENOUILLE measurement.

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14

Olivera, Bonilla Roberto Rafael. "Numerical Simulations of Undrained Granular Media". Thesis, University of Waterloo, 2004. http://hdl.handle.net/10012/915.

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The objective of the present study was to develop a fluid flow-coupled distinct element model capable of capturing the undrained behaviour of granular soils by considering fundamental physical mechanisms that involve fluid flow and particle interaction. The method considers granular media as assemblies of ellipsoidal particles arranged on a plane and interacting by means of contact forces. Saturation effects are incorporated by assuming that particles are immersed in fluid, the flow of which is simulated as occurring through a network of conduits. The flow through conduits is according to a Hagen-Poiseuille relation; a transient solution is obtained by solving a system of differential equations. The developed fluid-flow coupled distinct element was used to conduct various numerical simulations and the mechanisms of undrained deformations were examined from a micromechanical point of view. The dissertation begins with a literature review on the undrained behaviour of granular materials as observed in laboratory experiments. A review of previous attempts to simulate undrained tests micromechanically is also presented, and the advantages and disadvantages of various methods are examined. The capability of the developed model to simulate two-dimensional fluid-flow and pressure dissipation problems is demonstrated by means of comparisons with analytical solutions. Fluid pressure dissipation problems are qualitatively compared with Terzaghi's one-dimension theory of consolidation. It is shown that transient flow problems are accurately modelled by the fluid flow network approach. Simulated compression tests were carried out to examine the effects of different confining pressures and initial densities on the macroscopic response. The results compare favorably with those commonly observed in undrained laboratory experiments. Simulated tests are analyzed from a micromechanical point of view. It is shown that macroscopic behaviour can be traced to changes in micromechanical fabric descriptors. The effects of the interparticle friction angle on the undrained behaviour of the assemblies are investigated. The undrained strength is considerably increased by increasing interparticle friction. The main mechanism found to be responsible for the development of higher strength is the tendency of the specimens to dilate during shear distortion. The effects of the principal stress direction on the macroscopic response are examined. The behaviour of initially anisotropic samples is significantly altered by the direction of the principal stresses relative to the anisotropy direction. It is demonstrated that macroscopic permeability of the media has a considerable effect on the strength. This behaviour is attributed to the inhomogeneity of pore pressure distributions which increases with decreased permeability. The results presented are generally in agreement with observations previously reported from laboratory experiments. The possible applications of the model for future research are also discussed.

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15

Ryan, Geoffrey. "Numerical Simulations of Black Hole Accretion". Thesis, New York University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10261761.

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Accretion on to black holes powers some of the most luminous objects in the universe. In this thesis I present a series of works aimed at constraining the properties of black hole accretion in a variety of astrophysical systems. Numerical methods are vital for studying the multi-scale and non-linear physics of these systems. First I introduce DiscoGR, the first implementation of numerical general relativistic magnetohydrodynamics on a moving mesh. DiscoGR is capable of efficiently and accurately simulating highly supersonic thin accretion disks, the objects responsible for many luminous accretion events. I apply DiscoGR to study minidisks: accretion disks around a single member of a binary black hole system. Spiral shock waves, excited by tidal forces from the binary companion, propagate throughout the disk, causing efficient accretion by purely hydrodynamical means. The shock-driven accretion has an effective alpha parameter of the order 0.01, comparable with accretion driven by the magnetorotational instability. Furthermore, shocks near the black hole contribute to a radiative signature brighter in the hard x-rays than the standard Novikov-Thorne model. Finally I present an analysis of gamma-ray burst (GRB) x-ray afterglow light curves. The analysis fits the data from the Swift-XRT directly to a suite of hydrodynamical simulations, constraining the jet opening angle and, for the first time, the viewing angle of these events. I find typically the viewing angle to be 0.57 of the jet opening angle. Observing a GRB off-axis can reduce the inferred energy of the central engine, thought to be a neutron star or accreting black hole, by up to a factor of four.

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16

Balfour, Scott K. "Numerical simulations of triggered star formation". Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/94927/.

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Feedback from massive stars is thought to be very important in regulating star formation on a range of scales. However, it is not clear if this feedback acts in a positive way by triggering star formation, or negatively by terminating it. In this thesis we investigate what role feedback plays in determining both the structure of molecular clouds and the rate of star formation, using Smoothed Particle Hydrodynamics. We begin by looking at how the evolution of an HII region is dependent on the amount of ionising radiation the exciting star produces. We then go on to explore the stellar populations created by cloud-cloud collisions and assess their ability to form high mass stars capable of producing large amounts of feedback. We then model the HII regions of these stars and determine what impact these have on star and structure formation. We find that there is a minimum stellar mass required to produce enough feedback to maintain an HII region. Below this value an HII region will either not form, or form and then implode. Above this value the HII region will act as a traditional HII region, and expand. When two clouds collide we �nd that they produce a shock compressed layer which forms �lamentary structures. The arrangement of these �laments is highly dependent on the collision velocity. Low velocity collisions produce a hub and spoke system in which competitive accretion dominates and produces a few very massive stars and a plethora of low mass stars. High velocity collisions produce lamentary networks that resemble a spider's web. In these spider's webs the stars form at nodes where multiple �laments meet. These nodes act as small local sites for star formation and form either a single, or small collection of stars. As a result stars formed in these systems tend to have a characteristic mass and there is less low mass or high mass star formation. However, we do find that eventually stars capable of producing signi�cant feedback form in all simulations. We model the HII regions of these stars and �find that they very quickly terminate star formation. They also produce very interesting bi-polar HII regions that are diffi�cult to interpret when viewed from some directions.

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17

Clark, Craig Andrew. "Numerical simulations of maize pollen dispersal". [Ames, Iowa : Iowa State University], 2007.

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18

Wright, Lisa Jayne. "Numerical simulations of disc galaxy formation". Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620627.

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19

Innocentini, V. "Numerical simulations of moist slantwise convection". Thesis, University of Reading, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370616.

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20

Gregory, Andrew Robin. "Numerical simulations of winter stratosphere dynamics". Thesis, University of Reading, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312414.

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21

Hubber, David Anthony. "Numerical simulations of binary star formation". Thesis, Cardiff University, 2006. http://orca.cf.ac.uk/56092/.

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Binary star formation is the dominant mode of star formation, in contrast to the traditional picture of single star formation. The work in this thesis investigates the properties of binary stars with the aid of numerical simulations, using N-body and Smoothed Particle Hydrodynamics codes. First, we develop a simple model of isolated binary star formation assuming prestellar cores fragment due to rotational instabilities into a ring of J f (< 6) stars. We follow the decay of this small-N cluster into singles and multiple systems using the N-body code NBODY3. We can reproduce most of the observed stellar and binary properties of young stars, including the high multiplicity and wide separation distribution, in low-mass star forming regions like Taurus. We extend this further into a model of clustered binary star formation assuming 100 small-N clusters form in fractal clusters of radius 1 pc, similar to many young embedded clusters. We follow the dynamical interactions of these clusters using the N-body code NBODY6. We find that disruptive binary-binary encounters in dense clusters can explain the differences between binary properties in low-density and high-density star forming regions. We develop a new test of Smoothed Particle Hydrodynamics (SPH) called the Jeans Test. We demonstrate that SPH correctly models fragmentation and that under-resolved SPH simulations supress real fragmentation rather than promote artificial fragmentation. Thus binary and multiple systems produced in SPH simulations are real and not the result of numerical effects. Finally, we perform simulations of turbulent prestellar cores in the context of binary star formation. We extend the work of Goodwin, Whitworth & Ward-Thompson (2004) by investigating 2.17 M0 and 4.34 M0 cores.

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22

Puangkird, Bumroong. "Numerical simulations of complex viscoelastic flows". Thesis, Swansea University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683931.

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23

Erickson, Stephanie Jeanne. "Numerical simulations of neutron star crusts". Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/375532/.

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24

Bergström, John. "Numerical simulations of hydro power flows". Licentiate thesis, Luleå tekniska universitet, 1998. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17503.

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25

Das, Kaushik. "Numerical Simulations of Icing in Turbomachinery". University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1147363332.

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26

Wojdas, Olga. "Numerical simulations for diesel engine development". Lyon, INSA, 2010. http://theses.insa-lyon.fr/publication/2010ISAL0039/these.pdf.

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Considering the increasingly rigorous pollutions regulations, the reduction or even the elimination of nitrogen oxide (NOx) and soot emissions occuring in Diesel engines, are inevitable. In order to reach that goal, more and more sophisticated technologies are under development leading to very complex physical behavior of injected spray. Facing the lack of the models describing such phenomena, the thesis focuses on the understanding of the existing models performance and their efficiency assessment. We try to understand the physical phenomena and the constraints of the classical models to be able to employ them in the most skillful way. The main result of the present research is the methodology suggestion for the numerical studies of Diesel engine, with the principal point concerning the boundary condition of injection velocity, whose various assumptions lead to the very important results dispersion. The objective of this methodology is to help the researchers of the applied engineering to understand the most important phenomena appearing in Diesel engine, and to indicate some points to succeed the numerical simulations using the classical models of the jet breakup
L'évolution des normes anti-pollution de plus en plus restrictives rend inéluctable la réduction voire l'élimination des émissions d'oxydes d'azote (Nox) et de suies générées par les moteurs diesel. Les technologies de plus en plus poussées développées pour atteindre ces objectifs mènent néanmoins à des phénomènes physiques très complexes dans la chambre de combustion. Face au manque actuel de modèles physiques décrivant de tels comportements, la thèse se concentre sur la compréhension et l'évaluation des modèles existants. Les phénomènes physiques pris en compte par chaque modèle ainsi que leur limitations sont étudiés afin d'en faire un usage le plus pertinent possible. Le résultat principal du travail présenté est une proposition de méthodologie de simulation numérique pour les moteurs diesel, avec en particulier l'adaptation de la condition limite en vitesse d'injection menant à une grande dispersion des résultats. Le but de la méthodologie est de fournir à la recherche appliquée une compréhension des phénomènes les plus importants présents dans un moteur diesel et de donner des pistes pour une simulation numérique robuste avec les modèles classiques de fragmentation du jet

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27

Escrivá, Mañas Alberto. "Numerical simulations of primordial black holes". Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/672269.

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This thesis has been devoted to the study of the gravitational collapse of spherically symmetric perturbations on a Friedman-Robertson-Walker (FRW) universe filled by a perfect fluid. Large cosmological perturbations generated by inflation, are known to be statistically almost spherical. For this reason, this thesis aims to provide the conditions for Primordial Black Hole (PBH) formation due to the collapse of inflationary density fluctuations. PBHs are considered one of the best candidate for the missing dark matter (DM). To simulate the collapse of large spherical overdensities, it has been used a pseudo-spectral method which maps differential equations into an algebraic system. The numerical code developed, allows to outline the conditions for black hole formation with a greater than ever precision in some extreme cases. By using a combination of an excision technique and analytical estimations of accretion rates, it was found that the estimation of the black hole’s masses via a self-similar scaling law, gets worse and worse for larger and larger values. In addition, it was also found that the accretion of the BH masses relevant for the DM abundance, follows the law MBH,f roughly equal to 3MBH,i where, MBH,I is the initial mass of the BH at the time of apparent horizon formation and MBH,f is the final mass of the BH after the accretion process. In the case in which the fluid permeating the universe is of the form p equal to wρ, where p is the pressure, ρ is the density of the fluid and w is a constant, it is here shown that for w greater or equal to 1/3 the conditions for black hole formation, to a very good approximation, only depend upon the curvature of the local excess-mass (compaction function) around its peak value (δc), δc (the ”threshold” for PBH formation) and the equation of state of the collapsing fluid. This fact, has been used to build an analytical formula for δc in the case of w greater or equal to 1/3, which is accurate enough to be used for cosmological applications, conversely to previous attempts. For smaller w’s instead, the knowledge of the full shape of the compaction function is necessary, in contradiction to previous claims. Moreover, while the threshold for w greater or equal to 1/3 does not strongly depend from the full shape of the compaction function, in this thesis it is also shown that the BH mass does. While inflationary fluctuations are predominantly Gaussianly distributed at the cosmic microwave back-ground scales, those leading to PBH formation at smaller scales can have larger non-Gaussianities (NG). In the final part of this thesis, it was considered the effect (numerically and analytically) of those NG to the threshold for primordial black hole formation. By monitoring the non-gaussian parameter fNL, it was found that; i) for fNL roughly greater than 3.5, the population of PBH coming from false vacuum regions dominates over that coming from the collapse of large adiabatic overdensities; ii) the effect of the statistical dispersion of profiles is small in determining δc of the mean profile.
Esta tesis pretende proporcionar las condiciones necesarias para la formación de Agujeros Negros Primordiales (PBHs) producidos por el colapso de perturbaciones cosmológicas. Los PBHs se consideran uno de los mejores candidatos para la materia oscura, cuya composición es todavía un misterio. Para simular el colapso de grandes sobredensidades esféricas y obtener las condiciones para la formación de un PBH, se ha utilizado un método pseudoespectral que mapea ecuaciones diferenciales en un sistema algebraico. En el caso en el que el fluido que impregna el universo se comporte como un fluido perfecto (p igual a wρ, donde p es la presión, ρ es la densidad del fluido y w es una constante), hemos comprobado que para w mayor o igual a 1/3 las condiciones para la formación de un agujero negro, en una muy buena aproximación, solo dependen de la curvatura del exceso de masa local (también llamado función de compactación) alrededor de su valor máximo (δc) , δc (el ” umbral ” para la formación de PBH) y la ecuación de estado del fluido que colapsa. Este remarcable resultado se ha utilizado para construir una fórmula analítica para δc en el caso de w mayor o igual a 1/3, que es lo suficientemente precisa como para usarse en aplicaciones cosmológicas. En cambio, para w más pequeños, es necesario conocer la forma completa de la función de compactación. Por otro lado, si bien es cierto que las fluctuaciones inflacionarias se distribuyen predominantemente de manera gaussiana en las escalas del fondo de microondas cósmicas, las que conducen a la formación de PBH a menores escalas pueden distribuirse de forma altamente no gaussiana (NG). En la parte final de esta tesis, se ha considerado el efecto de esas NGs en el umbral de formación de agujeros negros primordiales, tanto numérica como analíticamente.

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28

Cipriano, Pedro Miguel Ribeiro. "Numerical simulations of public goods games". Master's thesis, Universidade de Aveiro, 2010. http://hdl.handle.net/10773/2656.

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Mestrado em Física
Foram simulados numericamente jogos de recursos públicos em redes usando algoritmo de Monte Carlo. Foram usadas redes regulares unidimensionais em anel, redes regulares bidimensionais (rede quadrada) e redes scale-free. São apresentados os métodos seguidos, a teoria e os algoritmos usados. Estes jogos apresentam uma transição de fase entre uma fase dominada por oportunistas de uma fase dominada por cooperadores em função de um parâmetro de rendimento das contribuições. Foi encontrado um intervalo, dependente do número médio de vizinhos, para o qual a fracção de configurações sobreviventes tende para 1 quando o tamanho da rede aumenta. Foi também encontrada uma dependência no valor de parâmetro crítico de transição no número médio de vizinhos para as configurações sobreviventes. Esses efeitos foram observados em todos os tipos de rede estudados neste trabalho. ABSTRACT: Public goods games were numerically simulated in networks using Monte Carlo Algorithm. Regular one-dimensional ring networks, regular two-dimensional lattice networks and scale-free networks had been used. The methods followed, the theory and the algorithms used are presented. This games have a phase transition between one phase dominated by defectors from one dominated by cooperators in function of the value of efficiency from the contributions. It was found an interval, dependent on the average number of neighbors, where the fraction of surviving configurations tens to 1 when the size of the network increases. It was found dependence in the critical value of transition value with the average number of neighbors. Both effects were observed in all types of networks studied in this work.

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29

Derflinger, Gerhard, Wolfgang Hörmann, Josef Leydold y Halis Sak. "Efficient Numerical Inversion for Financial Simulations". Department of Statistics and Mathematics, WU Vienna University of Economics and Business, 2009. http://epub.wu.ac.at/830/1/document.pdf.

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Generating samples from generalized hyperbolic distributions and non-central chi-square distributions by inversion has become an important task for the simulation of recent models in finance in the framework of (quasi-) Monte Carlo. However, their distribution functions are quite expensive to evaluate and thus numerical methods like root finding algorithms are extremely slow. In this paper we demonstrate how our new method based on Newton interpolation and Gauss-Lobatto quadrature can be utilized for financial applications. Its fast marginal generation times make it competitive, even for situations where the parameters are not always constant.
Series: Research Report Series / Department of Statistics and Mathematics

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30

Aluzas, Robertas. "Numerical simulations of shock cloud interactions". Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/7917/.

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This Thesis presents numerical simulations of shocks interacting with regions containing multiple individual clouds. Firstly, the hydrodynamic interaction is presented. It is the first study to include 100s of clouds in a clumpy region which `mass-load' the flow. The 'mass-loading' reduces the Mach number of the shock and leads to the formation of a dense shell. In cases in which the `mass-loading' is sufficient the flow slows enough that the shock degenerates into a wave. The shock does not decelerate below a minimum velocity determined by properties of the region. Despite the turbulence generated behind the shock, the initial mass loss from the clouds is weaker. Nevertheless, the shell is found to regulate the cloud lifetimes such that all clouds are destroyed in similar time. The one exception occurs when a few high density clouds are distributed among lower density ones. Secondly, 2D adiabatic magnetohydrodynamic simulations of a shock interacting with groups of two or three cylindrical clouds are presented. We find (i) some clouds are stretched along their field lines, whereas others are confined by their field lines; (ii) upstream clouds may accelerate past downstream clouds; (iii) clouds may also change their relative positions transverse to the direction of shock propagation as they `slingshot' past each other; (iv) downstream clouds may be offered some protection from the oncoming flow as a result of being in the lee of an upstream cloud; (v) the cycle of cloud compression and re-expansion is generally weaker when there are nearby neighbouring clouds. This small-scale study helps to interpret the behaviour of systems with 100s of clouds. Infinitely wide regions can be interpreted via interactions between individual clouds, but in regions of finite width shocks driven from the sides of the region have different field-flow orientations - individual clouds can experience evolving field morphology.

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31

Tenny, Joseph S. "Numerical Simulations in Electro-osmotic Flow". BYU ScholarsArchive, 2004. https://scholarsarchive.byu.edu/etd/186.

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The developing flow field in a parallel plate microchannel, induced by wall motion, has been modeled numerically. This type of flow simulates the physical driving mechanism that exists in electro-osmotically generated flow with large channel diameter-to-Debye length ratios (Z). The physics of the flow field were compared between the moving wall model (MWM) and electro-osmotic flow (EOF) at Reynolds numbers of 1 and 1800, and Z > 2500. Also, Z-values between 50 and 500 were studied to investigate the accuracy of the MWM. Results show that for Z-values greater than 100 the MWM shows good agreement with EOF. The dynamics of the developing flow field for the MWM were explored for channel length-to-hydraulic diameter ratios (aspect ratio) of 5, 10, 20 and 40 at ten Reynolds numbers, Re (based on the wall velocity), below Re < 2000. The results show that far from the inlet the maximum fluid velocity occurs at the walls, as is expected, and the minimum velocity occurs at the channel center. Near the channel inlet, however, the centerline velocity is not a minimum but reaches a local maximum due to a resulting pressure imbalance generated by the wall motion. As the aspect ratio increases, the centerline velocity tends to approach the wall velocity far downstream from the inlet. Increases in the Reynolds number have the opposite effect on the centerline velocity. The hydrodynamic developing region, defined by that section of the channel where the wall shear stress is changing, also depends on the channel aspect ratio and Re, and is greater than the developing region for classical pressure-driven flow of a parallel plate channel. Also, the flow field physics was analyzed for a process called electro-mobility focusing (EMF). EMF is a process that separates and detects species of like charge with the use of electro-phoresis and EOF utilizing a varying voltage gradient. The velocity distribution and the effective diffusion were solved for analytically, for both a linear and non-linear voltage gradient, using the MWM and the creeping flow approximations. The resulting equations aid in optimizing the detection system by forcing the lowest effective diffusion (uniform velocity profile) to the detection location.

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32

Rose, Andrew. "Numerical simulations of the stochastic KDV equation /". Electronic version (PDF), 2006. http://dl.uncw.edu/etd/2006/rosea/andrewrose.pdf.

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33

Peplinski, Adam. "Numerical simulations of type III planetary migration". Doctoral thesis, Stockholm University, Department of Astronomy, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-7461.

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Planets are believed to form in primordial gas-dust discs surrounding newborn stars. An important breakthrough in our understanding of planetary formation was the discovery of extra-solar planets around sun-like stars, especially the frequent occurrence of giant planets on close orbits (hot Jupiters). The mechanisms involved in the formation of these objects remain uncertain, however the difficulties associated with their formation at their observed orbital radius has awoken an interest in theories for the migration of protoplanetary cores due to gravitational interaction with the disc. There are three fundamental regimes of planet migration. The type I and II migration regimes, driven by the differential Lindblad torques, result mostly in inward migration and concern low- and high-mass planets respectively. Type III migration, driven by the co-orbital gas flow, concerns an intermediate range of planetary masses and does not have a predefined direction.

In this thesis the orbital evolution of a high-mass, rapidly (type III) migrating planet is investigated using numerical hydrodynamical simulations. For these simulations we used the state-of-the-art hydrodynamics code FLASH. We focus on the physical aspects of type III migration. However, the problem of rapid migration of such massive planets is numerically challenging, and the disc model has to be chosen carefully, using numerical convergence as a discriminator between models (Paper I). We simulate both inward and outward directed migration (Papers II and III) and provide an extensive description of the co-orbital flow responsible for driving the migration, as well as its time evolution. The migration rate due to type III migration is found to be related to the mass of the planet's co-orbital region, making inward and outward directed migration self-decelerating and self-accelerating processes respectively (for a standard disc model). Rapid migration depends strongly on the flow structure in the planet's vicinity, which makes it sensitive to the amount of mass accumulated by the planet as it moves through the disc. This quantity in turn depends on the structure of the accretion region around the planet. The results of the numerical simulations show a good agreement with the analytical formulation of type III migration (Paper IV).

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34

Stasyszyn, Federico Andrés. "MHD numerical simulations in a cosmological context". Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-131385.

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35

El, Khoury George K. "Numerical simulations of massively separated turbulent flows". Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-12217.

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It is well known that most fluid flows observed in nature or encountered in engineering applications are turbulent and involve separation. Fluid flows in turbines, diffusers and channels with sudden expansions are among the widely observed areas where separation substantially alters the flow field and gives rise to complex flow dynamics. Such types of flows are referred to as internal flows since they are confined within solid surfaces and predominantly involve the generation or utilization of mechanical power. However, there is also a vast variety of engineering applications where the fluid flows past solid structures, such as the flow of air around an airplane or that of water around a submarine. These are called external flows and as in the former case the downstream evolution of the flow field is crucially influenced by separation. The present doctoral thesis addresses both internal and external separated flows by means of direct numerical simulations of the incompressible Navier-Stokes equations. For internal flows, the wall-driven flow in a onesided expansion channel and the pressure-driven flow in a plane channel with a single thin-plate obstruction have been studied in the fully developed turbulent state. Since such geometrical configurations involve spatially developing turbulent flows, proper inflow conditions are to be employed in order to provide a realistic fully turbulent flow at the input. For this purpose, a newly developed technique has been used in order to mimic an infinitely long channel section upstream of the expansion and the obstruction, respectively. With this approach, we are able to gather accurate mean flow and turbulence statistics throughout each flow domain and to explore in detail the instantaneous flow topology in the separated shear layers, recirculation regions as well as the recovery zones. For external flows, on the other hand, the flow past a prolate spheroid has been studied. Here, a wide range of Reynolds numbers is taken into consideration. Based on the characteristics of the vortical structures in the wake, the flow past a prolate spheroid is classified as laminar (steady or unsteady), transitional or turbulent. In each flow regime, the characteristic features of the flow are investigated by means of detailed frequency analysis, instantaneous vortex topology and three-dimensional flow visualizations.

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36

Zubier, Khalid M. "Numerical Wave Simulations on Different Oceanic Scales". Fogler Library, University of Maine, 2002. http://www.library.umaine.edu/theses/pdf/ZubierKM2002.pdf.

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37

Gustafsson, Anna-Maria. "Thermal response test : numerical simulations and analyses". Licentiate thesis, Luleå : Luleå University of Technology, 2006. http://epubl.luth.se/1402-1757/2006/014.

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38

Blancher, Roman Adrien. "Numerical simulations of high speed droplet collision". Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/19127.

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39

Monette, Liza. "Numerical simulations of nucleation and growth phenomena". Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=64053.

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40

Bond, Timothy Martin. "Dating Venus : numerical simulations of resurfacing processes". Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429625.

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41

Umbert, López Cyan. "Numerical Simulations of particle suspensions in confined". Thesis, KTH, Mekanik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-149674.

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Particle suspensions are ubiquitous in industry and natural phenomena. With the rapid development of micro-devices it becomes increasingly important to understand the behavior of owing particle suspensions in con ned geometries. Here, we perform numerical simulations of particles suspended in a channel in the inertial regime, when particle and uid inertia cannot be neglected. We study the variations of the suspension's eective viscosity and microstructure with con nement.

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42

Liu, Yan. "Numerical simulations of unsteady complex geometry flows". Thesis, University of Warwick, 2004. http://wrap.warwick.ac.uk/2360/.

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Numerical simulations have been here carried out for turbulent flows in geometries relevant to electronic systems. These include plane and ribbed channels and a central processor unit (CPU). Turbulent flows are random, three-dimensional and time-dependent. Their physics covers a wide range of time and space scales. When separation and reattachment occur, together with streamline curvature, modelling of these complex flows is further complicated. It is well known that, when simulating unsteady flows, the traditional, steady, linear Reynolds-averaged Navier-Stokes (RANS) models often do not give satisfactory predictions. By contrast, unsteady, non-linear RANS models may perform better. Hence the application of these models is considered here. The non-linear models studied involve explicit algebraic stress and cubic models. The Reynolds Stress Model (RSM) has been also evaluated. Modelling strategies more advanced than RANS, i.e. Large Eddy Simulation (LES) and zonal LES (ZLES), have also been tested. Validation results from URANS, LES and ZLES indicate that the level of agreement of predictions with benchmark data is generally consistent with that gained by the work of others. For the CPU case, flow field and heat transfer predictions from URANS, LES ; and ZLES are compared with measurements. Overall, for the flow field, ZLES and LES are more accurate than URANS. Zonal low Reynolds number URANS models (using a hear wall k-l model) perform better than high Reynolds number models. However, for heat transfer prediction, none of the low Reynolds number models investigated performed well.

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43

Mackwood, Andrew. "Numerical simulations of thermal processes and welding". Thesis, University of Essex, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272572.

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44

Kunesch, Markus. "Numerical simulations of instabilities in general relativity". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/283135.

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General relativity, one of the pillars of our understanding of the universe, has been a remarkably successful theory. It has stood the test of time for more than 100 years and has passed all experimental tests so far. Most recently, the LIGO collaboration made the first-ever direct detection of gravitational waves, confirming a long-standing prediction of general relativity. Despite this, several fundamental mathematical questions remain unanswered, many of which relate to the global existence and the stability of solutions to Einstein's equations. This thesis presents our efforts to use numerical relativity to investigate some of these questions. We present a complete picture of the end points of black ring instabilities in five dimensions. Fat rings collapse to Myers-Perry black holes. For intermediate rings, we discover a previously unknown instability that stretches the ring without changing its thickness and causes it to collapse to a Myers-Perry black hole. Most importantly, however, we find that for very thin rings, the Gregory-Laflamme instability dominates and causes the ring to break. This provides the first concrete evidence that in higher dimensions, the weak cosmic censorship conjecture may be violated even in asymptotically flat spacetimes. For Myers-Perry black holes, we investigate instabilities in five and six dimensions. In six dimensions, we demonstrate that both axisymmetric and non-axisymmetric instabilities can cause the black hole to pinch off, and we study the approach to the naked singularity in detail. Another question that has attracted intense interest recently is the instability of anti-de Sitter space. In this thesis, we explore how breaking spherical symmetry in gravitational collapse in anti-de Sitter space affects black hole formation. These findings were made possible by our new open source general relativity code, GRChombo, whose adaptive mesh capabilities allow accurate simulations of phenomena in which new length scales are produced dynamically. In this thesis, we describe GRChombo in detail, and analyse its performance on the latest supercomputers. Furthermore, we outline numerical advances that were necessary for simulating higher dimensional black holes stably and efficiently.

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45

Louis, Neven. "Numerical simulations of thedecomposition of a greenpropellant". Thesis, KTH, Mekanik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-250021.

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Concerns about the use of certain chemical species within the aerospace field are growing in recent years. A European regulation, REACh, now makes the use of hydrazine uncertain in – among others- attitude control thrusters. Green monopropellants, which are alternatives for this species already exist, but they all require a catalyst to react. Catalysts constitute the limiting factor for the lifespan of satellites because of the number of thermal cycles they endure. A joint project between ONERA, the French aerospace research center and CNES, the French space agency, was born to develop a high-performance green monopropellant thruster operating without any catalyst. Sizing the thruster and particularly its combustion chamber is not an easy task because of the explosive properties and the lack of knowledge regarding the monopropellant reaction process. The thesis aims at simulating the flow in a combustion chamber using CNES05, a new promising green monopropellant. This monopropellant has a very low vapor pressure and is an energetic liquid. As such, its reaction above a certain temperature -which is called decompositionis not well understood and must be observed closely. For this matter, a test bench was created, and it paved the way for the development of a specific model of decomposition. Indeed, even if the CNES05 decomposition cannot be modeled with the classical theory of isolated droplets, the setup showed us the order of magnitude of the reaction kinetics and the presence of a break up phenomenon. Using this model, the simulations of the flow inside the combustion chamber give us the heat flux profile through its walls, a sizing parameter for the thruster. Large recirculation zones are observed and the influence of the angle of injection seems to be the major injection parameter of influence. The sensitivity of the parameters used in the model is also studied.

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46

Krasnodebski, Jan K. (Jan Kazimierz). "Numerical simulations of lobed mixer flow fields". Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/37793.

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47

Baraldi, Daniele. "Numerical simulations of deflagration to detonation transition". Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620978.

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48

Garcia, Oscar Mauricio Arias. "Numerical simulations of compressible flows over airfoils". Instituto Tecnológico de Aeronáutica, 2006. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=316.

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A computer code was developed from scratch to simulate the flow over the NACA 0012 airfoil at different Reynolds and Mach numbers. The domain was discretized in a structured-grid context. The equations were numerically solved by a finite-volume technique, using three different time-marching schemes. The Euler flow was initially modeled as well as a Reynolds-averaged Navier Stokes formulation was calculated. The Baldwin and Lomax turbulence model was employed to close the problem. The influence of a number of numerical parameters upon the computational solutions was investigated in the first phase of the work. The inviscid simulations were compared with other numerical results available in the literature. Each modification is thoroughly described and compared to the base-line case. Conclusions were drawn regarding how each of these chances affected the final result. The last Euler simulation was done using the Jameson, MacCormack and the Shu schemes in order to select the most appropriate one of the three to be employed to solve the Reynolds-averaged Navier Stokes equations. The viscous flow simulations started with the incompressible, laminar flow over a flat plate. The implementation of the viscous terms was validated calculating and comparing the results with the known Blasius analytical solution. Finally, the compressible, turbulent viscous flow over the NACA 0012 airfoil was numerically solved. The pressure coefficient distribution along the airfoil chord and the normal force coefficient were compared with experimental data due to Harris.

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49

Murphy-Sugrue, S. "Numerical simulations of probes in magnetised plasma". Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3012219/.

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50

Cheng, Peng. "Numerical simulations for rain-wind-induced vibration". Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066722/document.

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Le phénomène d'instabilité de la structure de fluide se produit fréquemment dans le système d'écoulement polyphasé des régimes sous-critiques de Reynolds, et le phénomène de vibrations de câbles de sustentation de ponts provoquées par la pluie (sigle RWIV en anglais) est considéré comme un exemple en génie civil pour caractériser l'instabilité causée par les interactions fluide-structure. Le RWIV est supposée être un nouveau type de vibrations; régulièrement accompagné de deux phénomènes significatifs: le ruisseau supérieur vibre circonférentiellement et la fréquence du vortex de Von Karman se déplace vers une valeur beaucoup plus faible par rapport à la fréquence attendue. Les phénomène est observé habituellement sur les haubans du pont à hauban immobilisé. En raison des mécanismes de couplage complexes, le mécanisme de RWIV n'a pas été complètement décrit par les chercheurs précédents. La plupart ont mis l'accent sur les observations sur le terrain et les aspects expérimentaux en soufflerie, mais rarement sur la simulation numérique. Pour élaborer un cadre numérique systématique, nous abordons le modèle non couplé, le modèle faiblement couplé, le modèle couplé, et le modèle multiphasique multi-échelle (MMM). L'objectif est de mettre en place un modèle numérique avec une grande exactitude et précision pour RWIV, et de reconnaître et clarifier le mécanisme de RWIV, diverses enquêtes numériques ont été réalisés dans cette thèse.Pour simuler les effets de la pluie/l’eau pluviale (eng. rainwater) comme un ruisseau artificiel (fixé / solide mobile attaché / oscillé le long de la circonférence de hauban immobilisé) lorsque RWIV se produit, la méthode séparée est mise en œuvre sur la base des équations incompressibles de Navier-Stokes en combinaison avec la simulation monotone intégré des grandes échelles (MILES) pour évaluer les sous-grille termes de pression. Les effets des ruisseaux artificiels de différentes positions le long de la circonférence de hauban immobilisé sur la structure de formation de tourbillons derrière le hauban, la distribution de pression à travers le hauban, et la force aérodynamique fréquence dominante du hauban sont analysés. Cependant, les enquêtes indiquent les positions de ruisseau artificiel le long de la circonférence du hauban affectent très faiblement la fréquence du vortex de Von Karman proche le sillage du hauban.Pour capturer l'évolution dynamique de la morphologie de l’eau pluviale , le modèle semi-couplé simplifie les équations incompressibles de Navier-Stokes avec la théorie de lubrification sur l'hypothèse qu'un mince film d'eau environnante autour du hauban. Les enquêtes indiquent que l’eau pluviale rassemble aux endroits près des points de séparation, et forme deux ruisseaux symétriques le long de la circonférence du hauban. Cependant, la vibration circonférentielle du ruisseau supérieur et les phénomènes de décalage de fréquence accompagnant RWIV ne peuvent être résolus et expliqués clairement.Afin d'améliorer le modèle de semi-couplé à suivre l'évolution de la morphologie de l’eau pluviale, la méthode du Volume-de-Fluide (VOF) combinée avec les équations incompressibles de Navier-Stokes est utilisée dans le modèle couplé. L ‘évolution hautement non linéaire du ruisseau de la pluie le long de la circonférence du hauban immobilisé et les caractéristiques aérodynamiques du hauban de séjour peuvent être obtenus et analysés. Les résultats indiquent que le ruisseau de la pluie est formé près des points de séparation le long de la circonférence du hauban; la zone de pression négative le long de la circonférence du hauban est pré-requise pour la formation de ruisseau supérieur
A fluid structure instability phenomenon frequently occurs in the subcritical Reynolds regimes multiphase flow system, and rain--wind-induced vibration (RWIV) is taken as an example in civil engineering to characterize the aeroelastic instability caused by fluid-structure interactions. RWIV is hypothesized to be a new type of vibration; regularly accompanied by two significant phenomena: the circumferentially vibrating upper rivulet and the Von Karman vortex shedding frequency shift to a much lower value compared with the convectional evaluation; and customarily observed from the stay cables of cable--stayed bridge. Due to the complicated interactions mechanisms in the liquid-gas-solid system, the mechanism of RWIV has not been thoroughly solved and recognized by the previous researchers. Most have focused on the research topic from the field observation, the analytical dynamic model, and the wind tunnel experiment aspects, but rarely on numerical investigation aspect. To develop a systematic numerical framework, including the separated model, the semi-coupled model, the coupled model, and the multiphase multi-scale model (MMM) distinguished by different ways to simulate the rain effects when RWIV occurs, to establish highly accurate and precise numerical model for RWIV, and to recognize and clarify the mechanism of RWIV, various numerical investigations have been made in this thesis.To simulate the rain effects as an artificial rivulet (fixed/moving solid attaching/oscillating along the circumference of stay cable) when RWIV occurs, the separated method is implemented based on the incompressible Navier-Stokes equations in combination with the monotone integrated large eddy simulation (MILES) to evaluate the sub-grid stress terms. The effects of various artificial rivulet positions along the circumference of stay cable on the vortex shedding structure behind the cable, pressure distribution around the cable, and the aerodynamic force of the cable are analyzed. However, investigations indicate the positions of artificial rivulet along the circumference of cable extremely weakly affect Von Karman vortex shedding frequency near the wake of the cable.To capture the dynamic rainwater morphology evolution, the semi-coupled model simplifies the incompressible Navier-Stokes equations with the lubrication theory on the assumption that a thin water film surrounding around the cable. The investigations indicate the rainwater gathers at the locations near the separation points, and forms two symmetrical rivulets along the circumference of cable. However, both the circumferentially vibrating upper rivulet and the frequency shift phenomena accompanying RWIV cannot be solved and explained detailedly and clearly. To improve the semi-coupled model on tracking the rainwater morphology evolution, volume-of-fluid (VOF) method combined with incompressible Navier-Stokes equations is employed in the coupled model. Both the high-nonlinear rainwater rivulets evolution along the circumference of cable and the aerodynamic characteristics of stay cable can be obtained and analyzed. The results indicate rainwater rivulet are formed near the separation points along the circumference of cable; the negative pressure zone along the circumference of cable provides a prerequisite for the formation of upper rivulet. However, the computational efficiency is reduced due to the smaller droplets scatter in the surrounding air, furthermore, the assumptions, surrounding the stay cable with the constant volume of rainwater, cannot reflect the real physical conditions (i.e., rain infall process) and cannot obtain the real aerodynamic force from physical aspect

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