Global ETD Search

1	Simulation numérique des ballotements d'ergols dans les réservoirs de satellites en microgravité et à faible nombre de Bond / Numerical modeling of sloshing of ergols in satellite tanks under microgravity conditions, and at low Bond numbers Lepilliez, Mathieu 09 December 2015 (has links) Cette thèse porte sur l'étude des ballotements dans les réservoirs de satellites à poste, lors des phases de manoeuvre à faible accélération. En effet la bulle de gaz d'hélium servant à pressuriser le réservoir se met en mouvement, générant ainsi des perturbations sur la stabilité globale du satellite. Afin de mener à bien cette étude, des méthodes numériques ont été développées, avec une méthode de frontières immergées pour prendre en compte les parois du réservoir.Le code est utilise la méthode Level-Set pour capturer l'interface, et gère les sauts à l'aide de la méthode Ghost-Fluid. Un solveur BlackBox Multigrid est également développé pour améliorer lesperformances de calcul. Une étude est présentée dans le dernier chapitre pour définir quelques lois de comportements en fonction des vitesses et accélérations générées lors des manoeuvres. / The core study of this PhD thesis is the sloshing in satellite tanks, during low acceleration maneuvers. Indeed the helium bubble used to pressurize the tank moves, thus generating perturbations on the global stability of the satellite. In order to understand this problem, numerical schemes have been developed, such as an immersed boundary method to model the tank wall. The numerical tool uses a Level-Set function coupled to a Ghost Fluid Method to track the interface and to account for the jump conditions.A BlackBox Multigrid Solver have been developed to improve computational cost. Finally a study is presented in the last chapter to predict the behaviour of the fluids with a varying rotational speed generated during some classical maneuvers. Ecoulements diphasiques Lignes triples Frontières Immergées Level-Set Ghost Fluid Method BlackBox Multigrid Multiphase Flows Contact lines Immersed Interface Methods Level-Set Ghost Fluid Method BlackBox Multigrid
2	A sharp interface Cartesian grid hydrocode Sambasivan, Shiv Kumar 01 May 2010 (has links) Dynamic response of materials to high-speed and high-intensity loading conditions is important in several applications including high-speed flows with droplets, bubbles and particles, and hyper-velocity impact and penetration processes. In such high-pressure physics problems, simulations encounter challenges associated with the treatment of material interfaces, particularly when strong nonlinear waves like shock and detonation waves impinge upon them. To simulate such complicated interfacial dynamics problems, a fixed Cartesian grid approach in conjunction with levelset interface tracking is attractive. In this regard, a sharp interface Cartesian grid-based, Ghost Fluid Method (GFM) is developed for resolving embedded fluid, elasto-plastic solid and rigid (solid) objects in hyper-velocity impact and high-intensity shock loaded environment. The embedded boundaries are tracked and represented by virtue of the level set interface tracking technique. The evolving multi-material interface and the flow are coupled by meticulously enforcing the boundary conditions and jump relations at the interface. In addition, a tree-based Local Mesh Refinement scheme is employed to efficiently resolve the desired physics. The framework developed is generic and is applicable to interfaces separating a wide range of materials and for a broad spectrum of speeds of interaction (O(km/s)). The wide repertoire of problems solved in this work demonstrates the flexibility, stability and robustness of the method in accurately capturing the dynamics of the embedded interface. Shocks interacting with large ensembles of particles are also computed. Cartesian Grid Compressible Flows Ghost Fluid Method Impact Mechanics Local Mesh Adaptation Mutlimaterial Flows Mechanical Engineering
3	A Ghost Fluid Method for Modelling Liquid Jet Atomization Kiran, S January 2017 (has links) (PDF) Liquid jet atomisation has a wide variety of application in areas such as injectors in automobile and launch vehicle combustors, spray painting, ink jet printing etc. Understanding physical mechanisms involved in the primary regime of atomisation in combustors is extremely challenging due to the lack of experimental techniques that can reliably provide measurements of gas and liquid velocity fields in this region. Experimental studies have so far been mostly restricted to conditions at atmospheric conditions rather than technically relevant operating pressures. We present a computational fluid dynamics based modelling approach that can capture the evolution of the flow field in the dense primary atomization region of the spray as part of the present thesis work. A fully compressible 3D flow solver is coupled with an interface tracking solver based on level set method. A generalised mathematical formulation for thermodynamic models is implemented in flow solver enabling easy switching between various equations of states. Solvers are parallelised to run on large number of processors and are shown to have good scalability. A modification to the level set method which greatly reduces mass conservation inaccuracies when compared with existing state-of-art baseline schemes has been developed during this work. The Ghost uid Method is used for applying matching conditions at the Interface. The liquid and gas phases are modelled using the perfect gas and Tait equations of state respectively. Several validation studies have been carried out to ensure quantitative accuracy of the solver implemented. Results from canonical Rayleigh Taylor instability simulations shows good agreement with reported results in literature. Finally, results for unsteady evolution of a water-air jet at a liquid to gas density ratio of 10 are shown. Physical mechanisms causing the initial droplet formation are discussed in detail. Droplet feedback is identified as one of the important mechanisms in triggering liquid core instabilities. Comparisons between droplet size distributions obtained from computations are carried out. Vorticity dynamics is used to understand hole and ligament formation from liquid core. Effect of numerical droplets on the simulation results is also looked at in detail. Liquid Medium Atomization, Ghost Fluid Method Liquid Jet Atomization Atomization Simulation Spatial Discretization Temporal Discretization Rayleigh Taylor Instability Aerospace Engineering
4	A Runge Kutta Discontinuous Galerkin-Direct Ghost Fluid (RKDG-DGF) Method to Near-field Early-time Underwater Explosion (UNDEX) Simulations Park, Jinwon 22 September 2008 (has links) A coupled solution approach is presented for numerically simulating a near-field underwater explosion (UNDEX). An UNDEX consists of a complicated sequence of events over a wide range of time scales. Due to the complex physics, separate simulations for near/far-field and early/late-time are common in practice. This work focuses on near-field early-time UNDEX simulations. Using the assumption of compressible, inviscid and adiabatic flow, the fluid flow is governed by a set of Euler fluid equations. In practical simulations, we often encounter computational difficulties that include large displacements, shocks, multi-fluid flows with cavitation, spurious waves reflecting from boundaries and fluid-structure coupling. Existing methods and codes are not able to simultaneously consider all of these characteristics. A robust numerical method that is capable of treating large displacements, capturing shocks, handling two-fluid flows with cavitation, imposing non-reflecting boundary conditions (NRBC) and allowing the movement of fluid grids is required. This method is developed by combining numerical techniques that include a high-order accurate numerical method with a shock capturing scheme, a multi-fluid method to handle explosive gas-water flows and cavitating flows, and an Arbitrary Lagrangian Eulerian (ALE) deformable fluid mesh. These combined approaches are unique for numerically simulating various near-field UNDEX phenomena within a robust single framework. A review of the literature indicates that a fully coupled methodology with all of these characteristics for near-field UNDEX phenomena has not yet been developed. A set of governing equations in the ALE description is discretized by a Runge Kutta Discontinuous Galerkin (RKDG) method. For multi-fluid flows, a Direct Ghost Fluid (DGF) Method coupled with the Level Set (LS) interface method is incorporated in the RKDG framework. The combination of RKDG and DGF methods (RKDG-DGF) is the main contribution of this work which improves the quality and stability of near-field UNDEX flow simulations. Unlike other methods, this method is simpler to apply for various UNDEX applications and easier to extend to multi-dimensions. / Ph. D. Underwater Explosion (UNDEX) Ghost Fluid Method (GFM) Level Set Method (LSM) Bubble Multi-fluid Cavitation
5	A Hybrid Framework of CFD Numerical Methods and its Application to the Simulation of Underwater Explosions Si, Nan 08 February 2022 (has links) Underwater explosions (UNDEX) and a ship's vulnerability to them are problems of interest in early-stage ship design. A series of events occur sequentially in an UNDEX scenario in both the fluid and structural domains and these events happen over a wide range of time and spatial scales. Because of the complexity of the physics involved, it is a common practice to separate the description of UNDEX into early-time and late-time, and far-field and near-field. The research described in this dissertation is focused on the simulation of near-field and early-time UNDEX. It assembles a hybrid framework of algorithms to provide results while maintaining computational efficiency. These algorithms include Runge-Kutta, Discontinuous Galerkin, Level Set, Direct Ghost Fluid and Embedded Boundary methods. Computational fluid dynamics (CFD) solvers are developed using this framework of algorithms to demonstrate the computational methods and their ability to effectively and efficiently solve UNDEX problems. Contributions, made in the process of satisfying the objective of this research include: the derivation of eigenvectors of flux Jacobians and their application to the implementation of the slope limiter in the fluid discretization; the three-dimensional extension of Direct Ghost Fluid Method and its application to the multi-fluid treatment in UNDEX flows; the enforcement of an improved non-reflecting boundary condition and its application to UNDEX simulations; and an improvement to the projection-based embedded boundary method and its application to fluid-structure interaction simulations of UNDEX problems. / Doctor of Philosophy / Underwater explosions (UNDEX) and a ship's vulnerability to them are problems of interest in early-stage ship design. A series of events occur sequentially in an UNDEX scenario in both the fluid and structural domains and these events happen over a wide range of time and spatial scales. Because of the complexity of the physics involved, it is a common practice to separate the description of UNDEX into early-time and late-time, and far-field and near-field. The research described in this dissertation is focused on the simulation of near-field and early-time UNDEX. It assembles a hybrid framework of algorithms to provide results while maintaining computational efficiency. These algorithms include Runge-Kutta, Discontinuous Galerkin, Level Set, Direct Ghost Fluid and Embedded Boundary methods. Computational fluid dynamics (CFD) solvers are developed using this framework of algorithms to demonstrate these computational methods and their ability to effectively and efficiently solve UNDEX problems. Underwater explosion Fluid-structure interaction Computational fluid dynamics Discontinuous Galerkin method Level set method Direct ghost fluid method Embedded boundary method Shock wave Rarefaction wave Explosive gaseous bubble
6	Methodenentwicklung zur Simulation von Strömungen mit freier Oberfläche unter dem Einfluss elektromagnetischer Wechselfelder Beckstein, Pascal 16 February 2018 (has links) (PDF) Im Bereich der industriellen Metallurgie und Kristallzüchtung treten bei zahlreichen Anwendungen, wo magnetische Wechselfelder zur induktiven Beeinflussung von leitfähigen Werkstoffen eingesetzt werden, auch Strömungen mit freier Oberfläche auf. Das Anwendungsspektrum reicht dabei vom einfachen Aufschmelzen eines Metalls in einem offenen Tiegel bis hin zur vollständigen Levitation. Auch der sogenannte RGS-Prozess, ein substratbasiertes Kristallisationsverfahren zur Herstellung siliziumbasierter Dünnschichtmaterialien, ist dafür ein Beispiel. Um bei solchen Prozessen die Interaktion von Magnetfeld und Strömung zu untersuchen, ist die numerische Simulationen ein wertvolles Hilfsmittel. Für beliebige dreidimensionale Probleme werden entsprechende Berechnungen bisher durch eine externe Kopplung kommerzieller Programme realisiert, die für Magnetfeld und Strömung jeweils unterschiedliche numerische Techniken nutzen. Diese Vorgehensweise ist jedoch im Allgemeinen mit unnötigem Rechenaufwand verbunden. In dieser Arbeit wird ein neu entwickelter Methodenapparat auf Basis der FVM vorgestellt, mit welchem sich diese Art von Berechnungen effizient durchführen lassen. Mit der Implementierung dieser Methoden in foam-extend, einer erweiterten Version der quelloffenen Software OpenFOAM, ist daraus ein leistungsfähiges Werkzeug in Form einer freien Simulationsplattform entstanden, welches sich durch einen modularen Aufbau leicht erweitern lässt. Mit dieser Plattform wurden in foam-extend auch erstmalig dreidimensionale Induktionsprozesse im Frequenzraum gelöst. Metallurgie Kristallzüchtung Elektroprozesstechnik elektromagnetisches Prozessieren Optimierung Simulation RGS Ribbon-Growth on Substrate freie Oberfläche Interface-Tracking Induktion metallurgische MHD MHD Magnetodynamik Hydrodynamik Thermodynamik Magnetohydrodynamik OpenFOAM foam-extend Methodenentwicklung Softwareplattform Numerische Methoden Strömung mit freier Oberfläche Metalle Halbmetalle Silizium Wafer 3D METIS FVM Finite-Volumen-Methode elektromagnetische Wechselfelder zeitharmonische Anregung Frequenzraum Blockmatrizen diskontinuierliche Materialeigenschaften magnetische Permeabilität elektrische Leitfähigkeit eingebettete Diskretisierung GFM Ghost-Fluid-Methode Mehrfeldproblem Multi-Physics Biot-Savart Biot-Savart-Gesetz Biot-Savart-Induktoren überlagerte Gitter ALE Gitterbewegung Kopplung FAM Finite-Flächen-Methode RMF rotierendes Magnetfeld TMF wanderndes Magnetfeld Validierung Maxwell Maxwell-Gleichungen Navier-Stokes Navier-Stokes-Gleichung inkompressibel Schmelze Lorentz-Kraft Induktor Konduktor Induktionsspulen Wirbelströme Wirbelstromproblem PISO Oberflächenspannung semi-gekoppelter Lösungsalgorithmus Diskretisierung Skineffekt AC quasistatische Approximation Magneto-Quasistatik metallurgy crystal growth electromagnetic processing optimization Simulation RGS Ribbon-Growth on Substrate free-surface interface-tracking Induction metallurgical MHD MHD magnetodynamics hydrodynamics thermodynamics magnetohydrodynamics OpenFOAM foam-extend method development software platform numerical methods free-surface flow metals metalloids silicon wafer 3D METIS FVM Finite-Volumen-Method oscillating magnetic fields time-harmonic excitation frequency domain block-matrices discontinuous material properties magnetic permeability electrical conductivity embedded discretization GFM Ghost-Fluid-Method multi-physics Biot-Savart Biot-Savart-inductor overlapped meshes ALE mesh movement coupling FAM Finite-Area-Method RMF rotating magnetic field TMF traveling magnetic field validation Maxwell Maxwell-equations Navier-Stokes Navier-Stokes-equation incompressible melt melt flow Lorentz-force inductor conductor induction coil eddy-currents eddy-current problem PISO surface-tension semi-coupled solution discretization skin effect AC quasi-static approximation ddc:620 rvk:UF 4600
7	Methodenentwicklung zur Simulation von Strömungen mit freier Oberfläche unter dem Einfluss elektromagnetischer Wechselfelder Beckstein, Pascal 08 January 2018 (has links) Im Bereich der industriellen Metallurgie und Kristallzüchtung treten bei zahlreichen Anwendungen, wo magnetische Wechselfelder zur induktiven Beeinflussung von leitfähigen Werkstoffen eingesetzt werden, auch Strömungen mit freier Oberfläche auf. Das Anwendungsspektrum reicht dabei vom einfachen Aufschmelzen eines Metalls in einem offenen Tiegel bis hin zur vollständigen Levitation. Auch der sogenannte RGS-Prozess, ein substratbasiertes Kristallisationsverfahren zur Herstellung siliziumbasierter Dünnschichtmaterialien, ist dafür ein Beispiel. Um bei solchen Prozessen die Interaktion von Magnetfeld und Strömung zu untersuchen, ist die numerische Simulationen ein wertvolles Hilfsmittel. Für beliebige dreidimensionale Probleme werden entsprechende Berechnungen bisher durch eine externe Kopplung kommerzieller Programme realisiert, die für Magnetfeld und Strömung jeweils unterschiedliche numerische Techniken nutzen. Diese Vorgehensweise ist jedoch im Allgemeinen mit unnötigem Rechenaufwand verbunden. In dieser Arbeit wird ein neu entwickelter Methodenapparat auf Basis der FVM vorgestellt, mit welchem sich diese Art von Berechnungen effizient durchführen lassen. Mit der Implementierung dieser Methoden in foam-extend, einer erweiterten Version der quelloffenen Software OpenFOAM, ist daraus ein leistungsfähiges Werkzeug in Form einer freien Simulationsplattform entstanden, welches sich durch einen modularen Aufbau leicht erweitern lässt. Mit dieser Plattform wurden in foam-extend auch erstmalig dreidimensionale Induktionsprozesse im Frequenzraum gelöst. info:eu-repo/classification/ddc/620 ddc:620

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