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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Prediktering av radarvågutbredning i troposfären : en smal sak för den taktiske chefen?

Wikingsson, Jon January 2009 (has links)
<p>Detta självständiga arbete i militärteknik behandlar två simuleringsprogram för radarvågutbredning i syfte att undersöka konsekvenserna av dess nyttjande för den taktiske chefen till sjöss. Simuleringsprogrammens användbarhet mäts kvalitativt genom att respektive simuleringsprograms egenskaper ställs mot den taktiske chefens krav. Simulerings-programmen beskrivs utifrån teoretiska egenskaper i respektive program och utvärderas genom simuleringar av en typradar i tre olika vädertypfall. Den taktiske chefens krav grundas på personliga erfarenheter som fartygschef på korvett. Resultatet presenteras i form av positiva och negativa konsekvenser för den taktiske chefen vid nyttjande av respektive program.</p><p> </p> / <p>This is a bachelor thesis in Military Technology which deals with two radar wave propagation simulation programs. The purpose is to examine the consequences of their use for the tactical commander at sea. The simulation programs usability is estimated qualitative by the programs quality and attribute versus the tactical commander demands. The simulation programs are described from their theoretical quality and attribute respectively and evaluated by three simulations of the study’s specific radar in three different weather cases. The tactical commander demands are based on personal experiences as commanding officer of a corvette. The result is presented as positive and negative consequences for the tactical commander when using the simulation programs respectively.</p>
2

Etude comparative des méthodes d'origine particulaire SPH et LBM pour la simulation d'écoulements polyphasiques intermittents dans des conduites / Comparative study of particle-based methods SPH and LBM for the simulation of multiphase slug flows in pipes

Douillet-Grellier, Thomas 07 October 2019 (has links)
L’objectif de cette thèse est d’étudier les apports et les limitations de deux méthodes d’origine particulaire, SPH et LBM, dans le cadre de la simulation des écoulements à bouchons dans des conduites. Dans l’industrie pétrolière, ce type d’écoulement, que l’on retrouve par exemple dans les pipelines qui acheminent le pétrole et le gaz jusqu’aux raffineries, est connu pour endommager les installations et pour réduire l’efficacité du transport des fluides. Il est donc important de bien comprendre leur formation. Nous avons donc implémenté ces deux méthodes, ainsi que leurs variantes polyphasiques, et avons mené une campagne de validation et de comparaison afin de sélectionner la méthode la plus adéquate, pour poursuivre ensuite avec des simulations de cas plus appliqués et réalistes. Les contributions présentées se concentrent principalement sur trois axes. Tout d’abord, il a fallu construire les codes de calcul nécéssaires, les valider puis comparer des différentes formulations polyphasiques disponibles pour SPH et LBM. Ensuite, nous avons développé des conditions aux limites d’entrée/sortie adaptées au contexte polyphasique pour être en mesure d’injecter les fluides avec des vitesses imposées et de ler évacuer du domaine avec un pression donnée. Enfin, nous avons simulé différents cas d’écoulements à bouchons académiques avec SPH et LBM, puis sur des cas appliqués avec des géométries réalistes et des ratios de densité et de viscosité de type air/eau avec SPH seulement. / The main objective of this thesis is to study the contributions and limitations of two particle- based methods, SPH and LBM, for the simulation of slug flows in pipes. In the petroleum industry, these flow regimes, found for example during the transportation of oil and gas from reservoirs to refinery facilities through pipelines, are highly undesirable because they are known to damage facilities and to reduce flow efficiency. Therefore, it is important to understand its formation. We have implemented both methods, as well as their multiphase variants, and have led a validation and comparison campaign in order to to select the most suited method and to continue with simulations of more applied and realistic cases. The main contributions of this work can summarized in 3 points. First, we had to write the necessary computation codes, validate them and compare the different multiphase formulations available for SPH and LBM. Then, we have developed inlet/outlet boundary conditions adapted to the multiphase context so that we are able to inject fluids with prescribed velocities and let them exit he domain with a given pressure. Finally, we have simulated different academic test cases of slug flows with SPH and LBM and then on applied cases with realistic geometries and air-water like density and viscosity ratios with SPH only.
3

Spontaneous imbibition and solvent diffusion in fractured porous media by LBM

Gunde, Akshay Unknown Date
No description available.
4

Micromechanical Modeling of the Soil Water Retention Curve using a Coupled Discrete Element-Lattice Boltzmann Method

Fili, Jonathan Frank 08 December 2017 (has links)
The Soil Water Retention Curve (SWRC) is a key constitutive relationship describing the behavior of variably saturated soils. The objective of this research is to assess the performance of a hydro-mechanical model, developed by coupling the lattice Boltzmann method (LBM) with the discrete element method (DEM), for micromechanical simulation of the SWRC. The DEM-LBM model is used to examine the effects of wave propagation on fluid-solid interaction. A multi-phase LBM is then employed within a static particle array generated by the DEM to examine the effects of initial fluid density distribution. The SWRCs are generated by recording the liquid pore pressure and the degree of saturation within a porous medium subjected to imbibition for two cases: randomized fluid density simulation (non-unified wetting front) and droplet simulation (unified wetting front). The coupled DEM-multiphase LBM model is shown to be a promising tool to characterize capillary regime in partially saturated porous media.
5

Lattice Boltzmann Method for Simulating Turbulent Flows

Koda, Yusuke January 2013 (has links)
The lattice Boltzmann method (LBM) is a relatively new method for fluid flow simulations, and is recently gaining popularity due to its simple algorithm and parallel scalability. Although the method has been successfully applied to a wide range of flow physics, its capabilities in simulating turbulent flow is still under-validated. Hence, in this project, a 3D LBM program was developed to investigate the validity of the LBM for turbulent flow simulations through large eddy simulations (LES). In achieving this goal, the 3D LBM code was first applied to compute the laminar flow over two tandem cylinders. After validating against literature data, the program was used to study the aerodynamic effects of the early 3D flow structures by comparing between 2D and 3D simulations. It was found that the span-wise instabilities have a profound impact on the lift and drag forces, as well as on the vortex shedding frequency. The LBM code was then modified to allow for a massively parallel execution using graphics processing units (GPU). The GPU enabled program was used to study a benchmark test case involving the flow over a square cylinder in a square channel, to validate its accuracy, as well as measure its performance gains compared to a typical serial implementation. The flow results showed good agreement with literature, and speedups of over 150 times were observed when two GPUs were used in parallel. Turbulent flow simulations were then conducted using LES with the Smagorinsky subgrid model. The methodology was first validated by computing the fully developed turbulent channel flow, and comparing the results against direct numerical simulation results. The results were in good agreement despite the relatively coarse grid. The code was then used to simulate the turbulent flow over a square cylinder confined in a channel. In order to emulate a realistic inflow at the channel inlet, an auxiliary simulation consisting of a fully developed turbulent channel flow was run in conjunction, and its velocity profile was used to enforce the inlet boundary condition for the cylinder flow simulation. Comparison of the results with experimental and numerical results revealed that the presence of the turbulent flow structures at the inlet can significantly influence the resulting flow field around the cylinder.
6

Prediktering av radarvågutbredning i troposfären : en smal sak för den taktiske chefen?

Wikingsson, Jon January 2009 (has links)
Detta självständiga arbete i militärteknik behandlar två simuleringsprogram för radarvågutbredning i syfte att undersöka konsekvenserna av dess nyttjande för den taktiske chefen till sjöss. Simuleringsprogrammens användbarhet mäts kvalitativt genom att respektive simuleringsprograms egenskaper ställs mot den taktiske chefens krav. Simulerings-programmen beskrivs utifrån teoretiska egenskaper i respektive program och utvärderas genom simuleringar av en typradar i tre olika vädertypfall. Den taktiske chefens krav grundas på personliga erfarenheter som fartygschef på korvett. Resultatet presenteras i form av positiva och negativa konsekvenser för den taktiske chefen vid nyttjande av respektive program. / This is a bachelor thesis in Military Technology which deals with two radar wave propagation simulation programs. The purpose is to examine the consequences of their use for the tactical commander at sea. The simulation programs usability is estimated qualitative by the programs quality and attribute versus the tactical commander demands. The simulation programs are described from their theoretical quality and attribute respectively and evaluated by three simulations of the study’s specific radar in three different weather cases. The tactical commander demands are based on personal experiences as commanding officer of a corvette. The result is presented as positive and negative consequences for the tactical commander when using the simulation programs respectively.
7

Lattice Boltzmann Method for Simulating Turbulent Flows

Koda, Yusuke January 2013 (has links)
The lattice Boltzmann method (LBM) is a relatively new method for fluid flow simulations, and is recently gaining popularity due to its simple algorithm and parallel scalability. Although the method has been successfully applied to a wide range of flow physics, its capabilities in simulating turbulent flow is still under-validated. Hence, in this project, a 3D LBM program was developed to investigate the validity of the LBM for turbulent flow simulations through large eddy simulations (LES). In achieving this goal, the 3D LBM code was first applied to compute the laminar flow over two tandem cylinders. After validating against literature data, the program was used to study the aerodynamic effects of the early 3D flow structures by comparing between 2D and 3D simulations. It was found that the span-wise instabilities have a profound impact on the lift and drag forces, as well as on the vortex shedding frequency. The LBM code was then modified to allow for a massively parallel execution using graphics processing units (GPU). The GPU enabled program was used to study a benchmark test case involving the flow over a square cylinder in a square channel, to validate its accuracy, as well as measure its performance gains compared to a typical serial implementation. The flow results showed good agreement with literature, and speedups of over 150 times were observed when two GPUs were used in parallel. Turbulent flow simulations were then conducted using LES with the Smagorinsky subgrid model. The methodology was first validated by computing the fully developed turbulent channel flow, and comparing the results against direct numerical simulation results. The results were in good agreement despite the relatively coarse grid. The code was then used to simulate the turbulent flow over a square cylinder confined in a channel. In order to emulate a realistic inflow at the channel inlet, an auxiliary simulation consisting of a fully developed turbulent channel flow was run in conjunction, and its velocity profile was used to enforce the inlet boundary condition for the cylinder flow simulation. Comparison of the results with experimental and numerical results revealed that the presence of the turbulent flow structures at the inlet can significantly influence the resulting flow field around the cylinder.
8

NUMERICAL SIMULATION ON FLOW IN COLUMN CHROMATOGRAPHY

UMEMURA, TOMONARI, KOMIYAMA, RYO, YAMAMOTO, KAZUHIRO 12 1900 (has links)
No description available.
9

Towards Development of a Multiphase Simulation Model Using Lattice Boltzmann Method (LBM)

Koosukuntla, Narender Reddy January 2011 (has links)
No description available.
10

Investigation of the applicability of the lattice Boltzmann method to free-surface hydrodynamic problems in marine engineering / Étude de l’applicabilité de la méthode de Boltzmann sur réseau aux problèmes hydrodynamiques à surface libre du génie maritime

Cao, Weijin 08 April 2019 (has links)
La simulation numérique des écoulements à surface libre pour les applications du génie maritime est un problème qui présente de grands défis dans le domaine de la dynamique des fluides numérique (CFD). On propose dans cette thèse une solution, qui consiste à utiliser la méthode de Boltzmann sur réseau régularisée (RLBM) avec un modèle de surface libre basé sur le volume-de-fluide (VOF), et on étudie sa faisabilité et sa fiabilité. Les connaissances théoriques de la méthode de Boltzmann sur réseau (LBM) sont présentées dans un premier temps, sur la base d'un développement polynomial d'Hermite et d'une analyse de Chapman-Enskog. De cette perspective, l’idée de la RLBM se résume comme étant la régularisation d'Hermite des fonctions de distribution. Dans les cas tests suivants du vortex de Taylor-Green et de la cavité entraînée, il est vérifié que la RLBM posse possède une précision de second ordre et une stabilité améliorée. On a alors ensuite implémenté le modèle de surface libre dans la RLBM. Sur la simulation d'une onde de gravité visqueuse stationnaire et d'un écoulement de dambreak, il est montré que la régularisation stabilise fortement le calcul en réduisant les oscillations de pression, ce qui est très bénéfique pour obtenir des écoulements à surface libre précis, et que la RLBM n'introduit pas non plus de dissipation numérique supplémentaire. De plus, une nouvelle méthode de reconstruction des fonctions de distribution à la surface libre est proposée. Le modèle proposé est ainsi plus consistent avec la RLBM, ce qui offre un moyen efficace pour simuler des écoulements à surface libre à un grand nombre de Reynolds en génie maritime. / The numerical simulation of the freesurface flows for marine engineering applications is a very challenging issue in the field of computational fluid dynamics (CFD). In this thesis, we propose a solution, which is to use the regularized lattice Boltzmann method (RLBM) with a volume-of-fluid (VOF) based single-phase free-surface lattice Boltzmann (LB) model, and we investigate its feasibility and its reliability. The theoretical insights of the lattice Boltzmann method (LBM) are given at first, through the Hermite expansion and the Chapman-Enskog analysis. From this perspective, the idea of the RLBM is summarized as the Hermite regularization of the distribution functions. On the test-cases of the Taylor-Green vortex and the lid-driven cavity flow, the RLBM is verified to have a 2nd-order accuracy and an improved stability. The adopted free-surface model is then implemented into the RLBM and validated through simulating a viscous standing wave and a dambreak flow problems. It is shown that the regularization not only strongly stabilizes the calculation by reducing spurious pressure oscillations, which is very beneficial for obtaining accurate free-surface motions, but also does not introduce any extra numerical dissipation. Furthermore, a new reconstruction method for the distribution functions at the free-surface is proposed. The present model is more consistent with the RLBM, which provides an effective way for simulating high-Reynoldsnumber free-surface flows in marine engineering.

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