981 research outputs found

    Recent advances in the simulation of particle-laden flows

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    A substantial number of algorithms exists for the simulation of moving particles suspended in fluids. However, finding the best method to address a particular physical problem is often highly non-trivial and depends on the properties of the particles and the involved fluid(s) together. In this report we provide a short overview on a number of existing simulation methods and provide two state of the art examples in more detail. In both cases, the particles are described using a Discrete Element Method (DEM). The DEM solver is usually coupled to a fluid-solver, which can be classified as grid-based or mesh-free (one example for each is given). Fluid solvers feature different resolutions relative to the particle size and separation. First, a multicomponent lattice Boltzmann algorithm (mesh-based and with rather fine resolution) is presented to study the behavior of particle stabilized fluid interfaces and second, a Smoothed Particle Hydrodynamics implementation (mesh-free, meso-scale resolution, similar to the particle size) is introduced to highlight a new player in the field, which is expected to be particularly suited for flows including free surfaces.Comment: 16 pages, 4 figure

    Using the generalized interpolation material point method for fluid-solid interactions induced by surface tension

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    This thesis is devoted to the development of new, Generalized Interpolation Material Point Method (GIMP)-based algorithms for handling surface tension and contact (wetting) in fluid-solid interaction (FSI) problems at small scales. In these problems, surface tension becomes so dominant that its influence on both fluids and solids must be considered. Since analytical solutions for most engineering problems are usually unavailable, numerical methods are needed to describe and predict complicated time-dependent states in the solid and fluid involved due to surface tension effects. Traditional computational methods for handling fluid-solid interactions may not be effective due to their weakness in solving large-deformation problems and the complicated coupling of two different types of computational frameworks: one for solid, and the other for fluid. On the contrary, GIMP, a mesh-free algorithm for solid mechanics problems, is numerically effective in handling problems involving large deformations and fracture. Here we extend the capability of GIMP to handle fluid dynamics problems with surface tension, and to develop a new contact algorithm to deal with the wetting boundary conditions that include the modeling of contact angle and slip near the triple points where the three phases -- fluid, solid, and vapor -- meet. The error of the new GIMP algorithm for FSI problems at small scales, as verified by various benchmark problems, generally falls within the 5% range. In this thesis, we have successfully extended the capability of GIMP for handling FSI problems under surface tension in a one-solver numerical framework, a unique and innovative approach.Chapter 1. Introduction -- Chapter 2. Using the generalized interpolation material point method for fluid dynamics at low reynolds numbers -- Chapter 3. On the modeling of surface tension and its applications by the generalized interpolation material point method -- Chapter 4. Using the generalized interpolation material point method for fluid-solid interactions induced by surface tension -- Chapter 5. Conclusions

    A novel smoothed particle hydrodynamics formulation for thermo-capillary phase change problems with focus on metal additive manufacturing melt pool modeling

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    Laser-based metal processing including welding and three dimensional printing, involves localized melting of solid or granular raw material, surface tension-driven melt flow and significant evaporation of melt due to the applied very high energy densities. The present work proposes a weakly compressible smoothed particle hydrodynamics formulation for thermo-capillary phase change problems involving solid, liquid and gaseous phases with special focus on selective laser melting, an emerging metal additive manufacturing technique. Evaporation-induced recoil pressure, temperature-dependent surface tension and wetting forces are considered as mechanical interface fluxes, while a Gaussian laser beam heat source and evaporation-induced heat losses are considered as thermal interface fluxes. A novel interface stabilization scheme is proposed, which is shown to allow for a stable and smooth liquid-gas interface by effectively damping spurious interface flows as typically occurring in continuum surface force approaches. Moreover, discretization strategies for the tangential projection of the temperature gradient, as required for the discrete Marangoni forces, are critically reviewed. The proposed formulation is deemed especially suitable for modeling of the melt pool dynamics in metal additive manufacturing because the full range of relevant interface forces is considered and the explicit resolution of the atmospheric gas phase enables a consistent description of pore formation by gas inclusion. The accuracy and robustness of the individual model and method building blocks is verified by means of several selected examples in the context of the selective laser melting process

    Smoothed Particle Hydrodynamics Simulations for Dynamic Capillary Interactions

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    Complex interactions in porous media play an important role on many industrial and geotechnical applications, such as groundwater treatment, porous catalysts, carbon geosequestration, and oil recovery. Rate-dependent wetting effects are of great significance in understanding the multiphase behaviours of porous media thus further throw light on engineering solutions to the above problems. In this thesis, a modified smoothed particle hydrodynamics (SPH) model is applied to simulate (1) the contact angle dynamics and (2) stretching of liquid bridge at meso-scale. This SPH model adopted an inter-particle force formulation with short-range repulsive force and long-range attractive force to take into account single-phase and multiphase interactions. Particularly, a newly-introduced viscous force is imposed at the liquid-solid interface to capture the rate-dependent behaviours of contact angle without prescribing additional arbitrary condition or force. After identification of model parameters, the rate-dependent contact angle behaviours are studied for both wetting and dewetting phenomena. By analysing the contact angle results of fluid at triple-line region with different moving speeds, the dynamic contact angles and corresponding capillary numbers can be correlated by power law functions. The derived correlation and constants are compared with different forms of empirical power law functions and the results are satisfactory. Moreover, we investigated the properties of stretching liquid bridges, including shape evolution, liquid transfer ratio and flow condition under dynamic loading. Different stretching rates are applied, and the shapes of liquid bridge at same breakup distance is presented. By differentiating the wettability of top and bottom substrates, the liquid transfer ratio regarding wettability difference and substrate moving speed is studied

    Smoothed particle hydrodynamics and its applications for multiphase flow and reactive transport in porous media

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    Smoothed particle hydrodynamics (SPH) is a Lagrangian method based on a meshless discretization of partial differential equations. In this review, we present SPH discretization of the Navier-Stokes and advection-diffusion-reaction equations, implementation of various boundary conditions, and time integration of the SPH equations, and we discuss applications of the SPH method for modeling pore-scale multiphase flows and reactive transport in porous and fractured media.United States. Dept. of Energy. Office of Advanced Scientific Computing Research (Early Career Award, “New Dimension Reduction Methods and Scalable Algorithms for Multiscale Nonlinear Phenomena,” and Collaboratory on Mathematics for Mesoscopic Modeling of Materials (CM4)

    Pairwise Force SPH Model for Real-Time Multi-Interaction Applications

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    In this paper, we present a novel pairwise-force smoothed particle hydrodynamics (PF-SPH) model to allow modeling of various interactions at interfaces in real time. Realistic capture of interactions at interfaces is a challenging problem for SPH-based simulations, especially for scenarios involving multiple interactions at different interfaces. Our PF-SPH model can readily handle multiple kinds of interactions simultaneously in a single simulation; its basis is to use a larger support radius than that used in standard SPH. We adopt a novel anisotropic filtering term to further improve the performance of interaction forces. The proposed model is stable; furthermore, it avoids the particle clustering problem which commonly occurs at the free surface. We show how our model can be used to capture various interactions. We also consider the close connection between droplets and bubbles, and show how to animate bubbles rising in liquid as well as bubbles in air. Our method is versatile, physically plausible and easy-to-implement. Examples are provided to demonstrate the capabilities and effectiveness of our approach

    Flow and transport in saturated and unsaturated fractured porous media: Development of particle-based modeling approaches

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    Das Ziel der vorliegenden Arbeit ist die Entwicklung von partikelbasierenden Strömungs- und Transportmodellen zur Charakterisierung von kleinskaligen Strömungsprozessen in gesĂ€ttigten und ungesĂ€ttigten Poren- und Kluftsystemen. Aufgrund der unzureichenden Prozessbeschreibung von ungesĂ€ttigter Strömung in Doppelkontinuummodellen mittels der Richardsgleichung und van Genuchten Parametern werden innovative Methoden prĂ€sentiert um die zugrunde liegenden hochdynamischen Strömungs- und Transportprozesse zu erfassen. Die Simulation von Strömung und Transport in ungesĂ€ttigten geklĂŒfteten Aquiferen bildet immer noch ein höchst anspruchsvolles Aufgabenfeld aufgrund von skalenĂŒbergreifenden DiskontinuitĂ€ten, welche oftmals die Definition eines globalen reprĂ€sentativen Einheitsvolumens nicht zulassen. Des Weiteren können die hydraulischen Eigenschaften und potentiellen ParameterrĂ€ume von geklĂŒfteten Aquiferen oftmals nur durch integrale AnsĂ€tze, wie z.B. Pump- und Slugtests, Zeitreihenanalysen von QuellschĂŒttungen und Tracertests ermittelt werden. Doppelkontinuummodelle bieten hierfĂŒr einen ausgewogenen Ansatz hinsichtlich der erforderlichen Felddaten und der resultierenden prĂ€diktiven ModellqualitĂ€t. Der erste Teil dieser Arbeit evaluiert den Doppelkontinuumansatz, welcher die Simulation von Strömung mittels der Richardsgleichung und van Genuchten Parametern in zwei, durch einen linearen Austauschterm gekoppelten, Kontinua ermöglicht. Ganglinien von Karstquellen weisen eine charakteristischen steilen Abfall nach Niederschlagsereignissen auf, der durch das Modell erfolgreich reproduziert werden kann. Das Röhrensystem bildet die hydraulische BrĂŒcke zur Karstquelle und nimmt potentialabhĂ€ngige Wassermengen des geklĂŒfteten Matrixsystems auf. Um die Simulation von schneller Grundwasserinfiltration durch das Röhrenkontinuum innerhalb der ungesĂ€ttigten Zone zu vermeiden wurde die entsprechende Randbedingung an die untere Grenze des Kontinuums gesetzt. Ein genereller Nachteil des Doppelkontinuumsansatz ist die potentielle Mehrdeutigkeit von Modellergebnissen. Der duale Parameterraum in Kombination mit schwierig zu ermittelnden Parametern, fĂŒhrt zur Existenz von mehr als einem kalibrierten Modell, wie durch mehrdimensionale SensitivitĂ€tsanalysen aufgezeigt wird.  Insbesondere in Karstaquiferen bilden DiskontinuitĂ€ten, wie z.B. Lösungsdolinen, KlĂŒfte und Störungssysteme, bevorzugte hydraulische Elemente fĂŒr schnelle vertikale Grundwasserneubildungsprozesse, die oftmals nicht durch volumeneffektive ModellansĂ€tze erfasst werden können. Der Hauptteil dieser Arbeit befasst sich daher mit der Entwicklung von zwei Smoothed Particle Hydrodynamics (SPH) Modellen um ein adĂ€quates numerisches Werkzeug zur partikelbasierenden Simulation von kleinskaligen Strömungen mit freien OberflĂ€chen und Transportprozessen bereitzustellen. SPH Modelle ermöglichen eine Eulersche Beschreibung eines Strömungsfelds auf Basis der Navier-Stokes Gleichung und Partikelbewegung mittels klassischer Newtonscher Mechanik. Der gitterlose Modellansatz ermöglicht flexible Simulationen von hochdynamischen Phasengrenzen in ungesĂ€ttigten KlĂŒften und PorenrĂ€umen. Das erste SPH Modell wird eingesetzt um durch OberflĂ€chenspannung dominierte Tropfen- und Filmströmungen auf glatten und rauhen KluftoberflĂ€chen zu simulieren. Charakteristische dimensionslose Kennzahlen werden ĂŒber einen weiten Bereich von Benetzungswinkeln und Reynoldszahlen bestimmt. Modellergebnisse weisen einen hervorragende Übereinstimmung mit dimensionslosen Skalierungsfunktionen auf und kritische Kontaktwinkel folgen der zu erwartenden Entnetzungsdynamik. Die Entstehung von adsorbierten Filmen auf trockenen OberflĂ€chen wird fĂŒr einen breiten Parameterraum bestimmt. Des Weiteren wird der Einfluss von befeuchteten OberflĂ€chen auf die Geschwindigkeitszunahme von Tropfenströmung aufgezeigt und so die Bedeutung der Koexistenz verschiedener Strömungsmodi gezeigt. Der Effekt von OberflĂ€chenrauhigkeit auf Tropfenströmung wird fĂŒr verschiedene Rauhigkeiten ermittelt und eine deutliche Geschwindigkeitsabnahme demonstriert. Um die makroskopische Kontinuumsbeschreibung der Navier-Stokes Gleichung und atomistische Effekte eines klassischen Partikelsystems der statistischen Mechanik zu kombinieren wurde ein zweites mesoskopisches SPH Modell entwickelt. Diese neue Diskretisation der vollstĂ€ndig gekoppelten Landau-Lifshitz-Navier-Stokes und Advektions- Diffusionsgleichung ermöglicht die Simulation von Strömung und Transport bei gleichzeitiger BerĂŒcksichtigung von Fluktuationsdynamiken, welche sich korrekt der Systemskala anpassen. Die Verbindung von klassischer Fickscher Diffusion und thermodynamischen Fluktuationen wird hierbei durch einen effektiven Diffusionskoeffizienten beschrieben. Numerische Experimente zeigen die PrĂ€zision des Modells. GrenzflĂ€chen zwischen zwei Fluiden unterschiedlicher Konzentration weisen eine korrekte Wellenzahldivergenz entsprechend aktuellen Laborergebnissen auf
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