La thèse est organisée autour du développement d'un modèle numérique d’interaction fluide - structure pour simuler la déformation induite dans un matériau solide lors de l’implosion de bulles de cavitation. Le solveur est développé à partir du code open source SPHYSICS_2D utilisant la méthode des Smoothed Particles Hydrodynamics (SPH). Dans cette thèse, le code 2D a été modifié pour traiter le cas de fluides en conditions 2D-axisymétrique. Le solveur solide SPH a été complètement développé en interne en 2D-axisymétrique avec un nouveau schéma pour résoudre les problèmes apparaissant à proximité de l'axe de symétrie. Une loi de comportement élasto-visco-plastique de type Johnson Cook est implémentée dans le solveur solide afin de prendre en compte l’effet de la vitesse de déformation sur l’écrouissage du matériau.Les applications du solveur FSI traitent le cas d’une bulle unique implosant au voisinage d’une surface solide. Deux cas sont envisagés : celui d’une bulle détachée de la surface solide pour laquelle l’effondrement génère une onde de choc ; et celui d’une bulle au contact de la surface pour lequel un micro-jet de liquide vient impacter la surface solide. Pour une taille de bulle donnée, les résultats montrent que le micro-jet peut produire deux fois solide pour laquelle l’effondrement génère une onde de choc ; et celui d’une bulle au contact de la surface pour lequel un micro-jet de liquide vient impacter la surface solide. Pour une taille de bulle donnée, les résultats montrent que le micro-jet peut produire deux fois plus de déformation plastique que l'onde de choc, réduisant ainsi le temps d'incubation. Par contre, le volume de matière déformée plastiquement dans le cas du micro-jet (cavité attachée) est 800 fois plus petit que celui déformé par l’impact d'une onde de choc (cavité détachée). Par conséquent, la capacité d'érosion d'une cavité détachée est beaucoup plus élevée que celle d'une cavité attachée. Un important résultat de cette étude concerne les cavités détachées où il est montré que la déformation plastique ne se produit pas au centre de l'effondrement mais à un décalage par rapport à l’axe de symétrie. Les résultats montrent également que même si la pression subie par le matériau est la plus élevée au niveau de l’axe de symétrie, la déformation plastique ne sera pas maximale à cet endroit mais dans une zone éloignée du centre. Nous Une étude paramétrique est menée pour quantifier les effets de la distance bulle/paroi, de la pression d’effondrement et du rayon de la bulle. Les résultats montrent que l'énergie totale absorbée et le taux d'érosion devraient être plus élevés pour une cavité détachée que pour une cavité attachée. La densité d'énergie absorbée (d'où le temps d'incubation) et l'énergie totale absorbée (d'où le taux d'érosion) augmentent avec la pression d’effondrement. Le changement du rayon de la bulle tout en gardant les autres paramètres constants n'affecte pas beaucoup l'amplitude de la déformation plastique ni la densité d'énergie absorbée, ce qui suggère que quelle que soit la taille de la bulle de cavitation, le temps d'incubation devrait rester similaire. Cependant, comme le volume de la zone déformée plastiquement varie presque linéairement avec la taille de la bulle, l'énergie totale absorbée ou le taux d'érosion augmente significativement avec la taille de la bulle.Dans le passé, les études similaires n'ont jamais pris en compte la sensibilité à la vitesse de déformation dans le modèle de plasticité. Nos simulations montrent que l'ampleur de la déformation plastique est alors surestimée d'environ 60% pour les cavités détachées présentées dans ce document et d'environ 200% pour les cavités attachées. Nous montrons ainsi que de telles études réductrices fondées sur des modèles de plasticité insensibles à la vitesse de déformation conduisent à une sous-estimation du temps d'incubation et à une surestimation du taux d'érosion. / The thesis is focused on development of a Smoothed Particle Hydrodynamics (SPH) Fluid-Structure Interaction (FSI) cavitation solver to understand the phenomenon of material deformation under cavitation load better. This summary presents a brief overview of the methodology used to solve a fluid-structure interaction simulation of a bubble collapse over a deformable solid medium. The fluid solver and the solid solver are validated against Rayleigh-Plesset spherical bubble collapse case and FEM solver respectively. The fluid solver is developed using an open source SPH code SPHYSICS_2D, the code is changed from 2D to 2D axisymmetric. The solid SPH solver is developed in-house in 2D axisymmetric, a novel scheme is derived to solve typical issues near symmetry axis in the solid axisymmetric SPH solver. The solid solver has the capability to solve for non-linear isotropic hardening with strain rate effects (commonly known as Johnson-Cook plasticity model).A case each for a detached and an attached cavity is simulated using the FSI solver, the results show that for the same magnitude of pressure wave initiating the collapse and the same size of the bubble, the micro-jet can produce twice the maximum plastic deformation compared to a shock wave, hence a micro-jet dominated impact would exhibit a smaller incubation time compared to the detached cavity. It is also observed that the volume of material that is plastically deformed in case of a micro-jet is miniscule compared to a shock wave impact (almost 800 times smaller). This would imply that even though the incubation time for material erosion might be lower for a micro jet collapse, the shock wave can plastify a much larger volume of material and so the erosion rate should be higher for a shock wave impact. Hence it could be inferred that the material erosion ability of a shock wave is much higher than a micro-jet.An important and novel finding in the present study is the response of the material for a detached cavity where plastic deformation does not occur at the center of collapse but at an offset from the center. The results show that even though the pressure experienced by the material is the highest at the center, it does not produce the maximum plastic deformation. This is for the first time that such a phenomenon is reported in cavitation studies, we find that the phenomenon is linked to inertial effects where the material does not respond to the load as the rate of loading and unloading is extremely high. The effect is linked to the high loading and unloading rate near the center of the collapse due to the flat geometry of the solid medium. The study clearly demonstrate that maximum pressure does not always correspond to the location of maximum plastic deformation or material erosion.Fluid-Structure Interaction simulations for different stand-off ratios, driving pressure and bubble radius have been computed. Results show that for varying stand-off ratio while keeping the bubble radius and driving pressure constant, the attached cavities (SR<=1) show a higher plastic strain magnitude and a higher absorbed energy density which would suggest a quicker incubation time. However, the volume of plastic defamation zone is much lower in attached cavities thus the total absorbed energy and the erosion rate would be higher for a detached cavity compared to an attached one.The strain rate effects suggest that the magnitude of plastic strain is over predicted while using plasticity models that do not use strain rate sensitivity. The over prediction of the magnitude of plastic strain of around 60% for detached cavities presented in the paper and around 200% for attached cavities presented in the paper is observed. This would lead to an under prediction of incubation time and over prediction of erosion rate while using strain rate insensitive plasticity models.

Thèse (M.Sc.)--Université Laval, 2008. / Bibliogr.: f. [66]-67. Publié aussi en version électronique dans la Collection Mémoires et thèses électroniques.

Tsunamis are among the most threatening natural hazards that can affect coastal communities and infrastructures. In order to provide useful information for coastal protection, one of my aims in this dissertation is to identify the physical metrics that better represent the damage cause by tsunamis. I approach this problem by carrying out three-dimensional-SPH numerical simulations of solitary waves which allow to track spatial-temporal evolution of physical variables during their breaking. By comparing these evolutions it is possible to visualize the complex hydrodynamic process that occurs during breaking. Results show that the highest danger lies in the environment of the shoreline. However the highest vulnerability of coastal communities and infrastructures lies onshore where they find themselves more exposed to the destructive capacity of extreme tsunami waves. In this regard, the second main goal in this dissertation is to understand how coastal vegetation reduces and modifies the onshore wave inundation. I address this problem by using shallow water equations and Serre-Green-Naghdi equations employed in a set of two-dimensional depth-integrated simulations. Analysis of results indicate the existence of a transition zone located between where runup is not affected at all and where runup suffers the maximum reduction by the vegetation. This infers the requirement of a minimum length of the vegetated barrier in order to achieve the maximum runup reduction under a specific set properties such as barrier location, barrier width, beach slope and/or wave amplitude. Overall we conclude, after intense validation work, that numerical approaches are very convenient tools to analyze difficult wave processes. However it is necessary to be aware of the limitation of each numerical approach. / Ph. D.

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.

No description available.

Droplet splatter dynamics is an important study in the field of forensics since a crime event can produce many blood stains. Understanding the origins of the blood stains from pure observations is very difficult because much of the information about the impact is lost. A theoretical model is therefore needed to better understand the dynamics of droplet impact and splatter. We chose to explore a fluid modelling method known as Smoothed Particle Hydrodynamics (SPH) to determine whether it is capable of modelling droplet splatter accurately. Specifically, we chose to investigate an SPH version of a non-Newtonian pressure correction method with surface tension. Three experiments were performed to analyze the different aspects of SPH. From the results of the experiments, we concluded that this method can produce stable simulations if an artificial viscosity model is included, a third-order polynomial kernel is used and the pressure boundary condition on surface particles are non-zero. / UOIT

A numerical method commonly referred to as smooth particle hydrodynamics (SPH) is implemented in two dimensions for solid mechanics in general and fracture mechanics in particular. The implementation is tested against a few analytical cases: a vibrating plate, a bending plate, a modus I crack and a modus II crack. A conclusion of these tests is that a better way of treating a shortcoming of SPH called tensile instability is needed. A study is made on the best choice of a vital parameter called the smoothing radius, and it is found that a good choice of the smoothing radius is roughly 1.5 times the initial particle spacing.

Smoothed Particle Hydrodynamics (SPH) is a Lagrangian-based numerical method used for simulating problems in fluid and solid mechanics. In this thesis, a basic introduction to particle and Smoothed Particle (SP) approximations is given first. Application of SP approximations to Euler and Navier-Stokes equations is discussed, followed by an improvement to restore first order consistency in SPH. Then, simulations of 2D free-surface waves in a weakly incompressible fluid are conducted. If the artificial viscosity used is small, results indicate that the accuracy of SPH scheme is reasonably good; however, a low artificial viscosity leads to a rugged air-water interface. Furthermore, application of the LES filter has negligible effects. It is also observed that the use of Renormalized SPH (R-SPH) increases diffusivity but does not increase accuracy significantly. Hence, for 2D surface waves in weakly incompressible fluids, basic SPH formulation without any modification is as good as the R-SPH or LES-SPH methods.

Smoothed Particle Hydrodynamics (SPH) is a Lagrangian-based numerical method used for simulating problems in fluid and solid mechanics. In this thesis, a basic introduction to particle and Smoothed Particle (SP) approximations is given first. Application of SP approximations to Euler and Navier-Stokes equations is discussed, followed by an improvement to restore first order consistency in SPH. Then, simulations of 2D free-surface waves in a weakly incompressible fluid are conducted. If the artificial viscosity used is small, results indicate that the accuracy of SPH scheme is reasonably good; however, a low artificial viscosity leads to a rugged air-water interface. Furthermore, application of the LES filter has negligible effects. It is also observed that the use of Renormalized SPH (R-SPH) increases diffusivity but does not increase accuracy significantly. Hence, for 2D surface waves in weakly incompressible fluids, basic SPH formulation without any modification is as good as the R-SPH or LES-SPH methods.

A complete understanding of the cooling process when hot rolling steel is essential to understanding how the quality of the steel is connected to the cooling. This is why it is of great interest to simulate this process. However traditional CFD methods are too expensive in terms of CPU time. Knowing that video games successfully simulate fluids in reasonable time, those methods could be useful for simulating the cooling process in steel manufacturing. This would mean a loss in accuracy that could be acceptable. In this thesis different methods used for fluid simulations have been studied. The Smoothed Particle Hydrodynamics (SPH) method has been chosen. The method has been implemented for simulating the cooling process in MATLAB, which is a matrix operation based programming tool. Convincing results have been achieved for a big scale, but problems still remain for an implementation on a small scale.