Cette thèse porte sur l’étude des interactions entre les globules rouges (GRs)et l’endothélium, la couche des cellules qui délimite les vaisseaux sanguins.Il a été démontré que l’endothélium et les GRs jouent des rôles actifs dans divers processus du système vasculaire, et leurs interactions produisent un signal bio chimique grâce à des moyens à la fois chimiques (molécules de signalisation) et mécaniques (taux de cisaillement sur les parois). D’abord,nous étudions le rôle des GRs, y compris dans des conditions pathologiques, dans la création de contraintes de cisaillement spatialement et temporellement dynamiques sur l’endothélium. Il a été montré que les contraintes de cisaillement constituaient un élément critique dans le déclenchement d’un signal bio mécanique depuis l’endothélium. Par ailleurs, étant donné qu’il a été montré que les parois des vaisseaux sanguins ondulent en raison des cellules endothéliales individuelles qui le composent, nous avons intégré à notre modélisation cette géométrie. On trouve que cette ondulation affecte la dynamique des GRs dans l’écoulement ainsi que le taux de cisaillement sur les parois. Nous étudions rapidement dans quelle mesure la déformabilité d’un GR affecte sa trajectoire dans un vaisseau ondulé. Pour cela, nous nous inspirons du processus de fonctionnement un appareil de déplacement latéral déterministe (DLD) qui utilise les variations de trajectoires des particules en fonction de leur taille pour les séparer dans l’écoulement. Nous étudions par ailleurs l’effet des suspensions de GRs sur les caractéristiques rhéologiques et les contraintes de cisaillement sur la paroi du vaisseau.Finalement, nous nous adressons à les interaction chimiques en développons un modèle numérique avec la méthode de Boltzmann sur réseaux-limite immergée (LB-IBM) pour résoudre la diffusion et l’advectiond’un soluté libéré par un particule en mouvement et déformable. L’oxygène et l’adénosine triphosphate (ATP) sont toutes les deux libérées par les GRs,se diffusent dans l'écoulement, et sont absorbées par l’endothélium. Ils représentent des facteurs de signalisation critiques pour les processus de l’inflammation et vasodilatation. Nous montrons que la morphologie des GRs affectera le temps de résidence et la dilution des espèces chimiques lorsqu’elles rentreront en contact avec la paroi du vaisseau. Ensemble, ces éléments nous conduisent vers la développement d’un modèle capable de simuler des processus vitaux du système vasculaire qui résultent d’événements locaux de composants individuels. / This thesis is devoted to the study of the interactions between red blood cells (RBCs) and the endothelium, the monolayer of cells lining blood vessels. The endothelium and RBCs have been shown to be active participants in various processes in the vascular system, and their interactions trigger biochemical signalling by mechanical (wall shear stress) and chemical (signalling molecules) means. We first investigate the role of RBCs, including pathological conditions, in creating time- and space-varying shear stress on the endothelium. Shear stress has been shown to be a critical element in biochemical signalling from the endothelium. In addition, as it has been shown that the endothelium is undulating due to the individual endothelial cells comprising it, we take this into account in our model of the geometry of the vessel wall. We find that this undulation affects the dynamics of the RBCs in the flow and the wall shear stress. We briefly explore how the deformability of a single RBC affects its trajectory in undulating channels, inspired by the idea behind deterministic lateral displacement devices (DLDs) which exploit the differing trajectories of particles based upon their sizes to separate them in flow. We also investigate the effect of suspensions of RBCs in undulating channels on rheological properties and wall shear stress. Finally, we address the chemical interactions by building a numerical model with the lattice Boltzmann-immersed boundary method (LB-IBM) to solve advection-diffusion of solute released from moving, deformable particles. Oxygen and adenosine triphosphate (ATP) are both released by RBCs and are advected and diffused in the flow and uptaken by the endothelium and serve as critical signalling factors in inflammation and vasodilation. We find that the morphology of RBCs will affect the residence time and dilution of the chemical species upon contact with the wall. Together, these elements lead us towards the development of a model capable of simulating vital processes in the vascular system which result from local interactions of individual components.

L’objectif de ce travail est d’étudier les capacités de la méthode de Boltzmann sur réseau (LBM) dans un cadre numériquement contraignant : celui de la simulation aéroacoustique en maillage non-uniforme, à très haut nombre de Reynolds et à nombre de Mach non négligeable (Ma > 0.1), appliquée à l’automobile. La problématique industrielle est celle du calcul du bruit intérieur d’origine aérodynamique, dont le calcul du champ de pression pariétal instationnaire sur le vitrage conducteur est la première étape décisive. Il a été constaté qu’un manque de précision sur la faible part acoustique du champ de pression total sur le vitrage, provenant très probablement d’erreurs au niveau des transitions de résolution du maillage, était la cause d’une surestimation du bruit intérieur. Nous présentons d’abord une construction cohérente et unifiée de la méthode de Boltzmann sur réseau à partir de l’équation de Boltzmann, dans un cadre athermal faiblement compressible. Nous étudions ensuite en détail les propriétés aéroacoustiques de la LBM, en parcourant toutes les grandes familles d’opérateurs de collision de la littérature. Une variante de modèle à temps de relaxation multiples, utilisable pour l’aéroacoustique, est présentée et testée. Un modèle alternatif simplifié de filtrage sélectif, rapide et compact, est développé et validé. La problématique des maillages non-uniformes est abordée. Un recensement exhaustif des études LBM menées dans ce cadre dans la littérature montre qu’aucune ne correspond à nos contraintes. Des algorithmes alternatifs aux transitions sont développés. Enfin, des applications industrielles sont réalisées à l’aide des modèles développés dans le mémoire. / The main goal of this work is to study the capacities of the Lattice Boltzmann Method in a constrained numerical framework : that of numerical simulation in automotive aeroacoustics with non-uniform meshes, at high Reynolds number and non egligible Mach number (Ma > 0.1). The industrial problem is the computation of the interior aerodynamic noise, which includes as its first decisive step the computation of the unsteady wall pressure field on the car windows. It was observed that a lack of precision on the weak acoustic part of the total pressure field on the driver-side window, which is most probably due to errors at mesh refinement interfaces, caused an overestimation of the interior noise. We first present a coherent and unified construction of the Lattice BoltzmannMethod from the Boltzmann equation, in an athermal weakly compressible framework. Then, we study in details the aeroacoustic properties of the LBM by reviewingall the main families of collisional operators that exist in the literature. A variant of multiple relaxation time operator that can be used for aeroacoustics is presented and tested. A simplified alternative selective filter, fast and compact, is developped and numerically validated. The problem of non-uniform meshes is discussed. An exhaustive review of the LBM studies that have been carried out within that framework shows that none of them corresponds to our constraints. Alternative transition nodes algorithms are developed. Finally, all the developed models of this work are applied to industrial cases.

Indiana University-Purdue University Indianapolis (IUPUI) / LBM-IB method is useful and popular simulation technique that is adopted ubiquitously to solve Fluid-Structure interaction problems in computational fluid dynamics. These problems are known for utilizing computing resources intensively while solving mathematical equations involved in simulations. Problems involving such interactions are omnipresent, therefore, it is eminent that a faster and accurate algorithm exists for solving these equations, to reproduce a real-life model of such complex analytical problems in a shorter time period. LBM-IB being inherently parallel, proves to be an ideal candidate for developing a parallel software. This research focuses on developing a parallel software library, LBM-IB based on the algorithm proposed by [1] which is first of its kind that utilizes the high performance computing abilities of supercomputers procurable today. An initial sequential version of LBM-IB is developed that is used as a benchmark for correctness and performance evaluation of shared memory parallel versions. Two shared memory parallel versions of LBM-IB have been developed using OpenMP and Pthread library respectively. The OpenMP version is able to scale well enough, as good as 83% speedup on multicore machines for <=8 cores. Based on the profiling and instrumentation done on this version, to improve the data-locality and increase the degree of parallelism, Pthread based data centric version is developed which is able to outperform the OpenMP version by 53% on manycore machines. A distributed version using the MPI interfaces on top of the cube based Pthread version has also been designed to be used by extreme scale distributed memory manycore systems.

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[pt] A injeção de emulsão em meio poroso como método de recuperação avançada pode se tornar realidade na operação de campos de petróleo devido à maior rigidez no descarte de água produzida e aos potenciais ganhos na produção de óleo. Para entender o comportamento macroscópico desta técnica de EOR, é necessário compreender o fenômeno microscópico. Com este objetivo, fez-se a modelagem numérica do escoamento de uma gota imersa em fase contínua escoando em capilar restrito utilizando o método de Lattice-Boltzmann. Este método foi escolhido devido à sua facilidade de ser aplicado em geometrias complexas de rocha e fluido e ao bom compromisso na representação dos fenômenos de microescala. Para entender a influência de cada parâmetro, foram realizadas diversas simulações em domínio tridimensional, alterando a velocidade do fluxo, a razão de viscosidades dos fluidos, a relação entre os diâmetros da gota e do tubo e a magnitude da tensão interfacial. Observou-se que a passagem da gota pela restrição causa uma redução na mobilidade do escoamento, representada por um aumento na perda de carga, pela conjunção dos efeitos viscosos e capilares. Obteve-se correlação negativa do fator redutor de mobilidade 𝑓 com a razão de viscosidade e com o tamanho da gota, assim como fora determinado numericamente por Roca-Reyes (2011) com o método level-set. Foi notada uma pequena sensibilidade de 𝑓 ao número de capilaridade, assim como estabelecido experimentalmente por Robles-Castillo (2011). Verificou-se a importância de se determinar o conjunto adequado de parâmetros do sistema para ter sucesso na implantação de injeção de emulsões. / [en] Emulsion injection in porous medium as an Enhanced Oil Recovery method can turn out to be reality in the operation of onshore and offshore fields, due to increasing rigidity in the disposal of produced water and also due to the potential additional oil production. In order to understand macroscopic behavior of this EOR method, it is necessary to understand the microscopic phenomenon. With this objective, it was performed the numerical modeling of the flow of a droplet immerse in continuous phase through a constricted capillary using the Lattice-Boltzmann method. This method was chosen due to its simplicity on being applied to complex rock geometries and multiphasic flow and due to its good commitment in representing microscopic phenomena. Focusing on understanding the influence of each parameter on flow behavior, several simulation studies were performed altering flow velocity, viscosity ratio, ratio between droplet s and pipe s diameter and interfacial tension. A reduction in mobility is observed as the droplet passes through the restriction caused by the conjunction of viscous and capillary effects. A negative correlation of mobility reduction factor 𝑓 in relation to the viscosity ratio and to droplet size was noticed, as it had been observed before by Roca-Reyes (2011) in a numerical implementation of level-set method. Weak correlation between 𝑓 and capillary number was determined, as in previous experimental essay performed by Robles-Castillo (2011). In this study, it was verified the importance of determining the appropriate set of system parameters, in order to achieve success in the implementation of emulsion injection.

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<p dir="ltr">The kinetic-based lattice Boltzmann method (LBM) is a specialized computational fluid dynamics (CFD) technique that resolves intricate flow phenomena at the mesoscale level. The LBM is particularly suited for large-scale parallel computing on Graphic Processing Units (GPU) and simulating multi-phase flows. By incorporating a volume fraction parameter, LBM becomes a volumetric lattice Boltzmann method (VLBM), leading to advantages such as easy handling of complex geometries with/without movement. These capabilities render VLBM an effective tool for modeling various complex flows. In this study, we investigated the computational modeling of complex flows using VLBM, focusing particularly on pulsatile flows, the transition to turbulent flows, and pore-scale porous media flows. Furthermore, a new discrete dynamical system (DDS) is derived and validated for potential integration into large eddy simulations (LES) aimed at enhancing modeling for turbulent and pulsatile flows. Pulsatile flows are prevalent in nature, engineering, and the human body. Understanding these flows is crucial in research areas such as biomedical engineering and cardiovascular studies. However, the characteristics of oscillatory, variability in Reynolds number (Re), and shear stress bring difficulties in the numerical modeling of pulsatile flows. To analyze and understand the shear stress variability in pulsatile flows, we first developed a unique computational method using VLBM to quantify four-dimensional (4-D) wall stresses in image-based pulsatile flows. The method is validated against analytical solutions and experimental data, showing good agreement. Additionally, an application study is presented for the non-invasive quantification of 4-D hemodynamics in human carotid and vertebral arteries. Secondly, the transition to turbulent flows is studied as it plays an important role in the understanding of pulsatile flows since the flow can shift from laminar to transient and then to turbulent within a single flow cycle. We conducted direct numerical simulations (DNS) using VLBM in a three-dimensional (3-D) pipe and investigated the flow at Re ranging from 226 to 14066 in the Lagrangian description. Results demonstrate good agreement with analytical solutions for laminar flows and with open data for turbulent flows. Key observations include the disappearance of parabolic velocity profiles when Re>2300, the fluctuation of turbulent kinetic energy (TKE) between laminar and turbulent states within the range 2300</p>

Liquid film flow is an important flow type in many applications of process engineering. For supporting experiments, theoretical and numerical investigations are required. The present state of the art is to model the liquid film flow with Navier--Stokes-based methods, whereas the lattice Boltzmann method is employed here. The final model has been developed within this treatise by means of a two-phase flow and a heat transfer model, and boundary and initial conditions. All these sub-models have been applied to simple test cases. It could be found that the two-phase model is capable of solving flow phenomena with a large density ratio which has been shown impressively in conjunction with wall boundary conditions. The heat transfer model was tested against spectral method results with a transient non-uniform flow field. It was possible to find optimal parameters for computation. The final model has been applied to steady-state film flow, and showed very good agreement to OpenFOAM simulations. Tests with transient film flow demonstrated that the model is also able to predict these flow phenomena. / Flüssigkeitsfilmströmungen kommen in vielen verfahrenstechnischen Prozessen zum Einsatz. Zur Unterstützung von Experimenten sind theoretische und numerische Untersuchungen nötig. Stand der Technik ist es, Navier--Stokes-basierte Modelle zu verwenden, wohingegen hier die Lattice-Boltzmann-Methode verwendet wird. Das finale Modell wurde unter Verwendung eines Zweiphasen- und eines Wärmeübertragungsmodell entwickelt und geeignete Rand- und Anfangsbedingungen formuliert. Alle Untermodelle wurden anhand einfacher Testfälle überprüft. Es konnte herausgefunden werden, dass das Zweiphasenmodell Strömungen großer Dichteunterschiede rechnen kann, was eindrucksvoll im Zusammenhang mit Wandrandbedingungen gezeigt wurde. Das Wärmeübertragungsmodell wurde gegen eine Spektrallösung anhand eines transienten und nichtuniformen Strömungsproblemes getestet. Stationäre Filmströmungen zeigten sehr gute Übereinstimmungen mit OpenFOAM-Lösungen und instationäre Berechungen bewiesen, dass das Model auch solche Strömungen abbilden kann.

L'ablation par radiofréquence (ARF) de tumeurs abdominales est rendue difficile par l’influence des vaisseaux sanguins et les variations de la conductivité thermique, compliquant la planification spécifique à un patient donné. En fournissant des outils prédictifs, les modèles biophysiques pourraient aider les cliniciens à planifier et guider efficacement la procédure. Nous introduisons un modèle mathématique détaillé des mécanismes impliqués dans l’ARF des tumeurs du foie comme la diffusion de la chaleur et la nécrose cellulaire. Il simule l’étendue de l’ablation à partir d’images médicales, d’après lesquelles des modèles personnalisés du foie, des vaisseaux visibles et des tumeurs sont segmentés. Dans cette thèse, une nouvelle approche pour résoudre ces équations basée sur la méthode de Lattice Boltzmann est introduite. Le modèle est d’abord évalué sur des données de patients qui ont subi une ARF de tumeurs du foie. Ensuite, un protocole expérimental combinant des images multi-modales, anatomiques et fonctionnelles pré- et post-opératoires, ainsi que le suivi de la température et de la puissance délivrée pendant l'intervention est présenté. Il permet une validation totale du modèle qui considère des données les plus complètes possibles. Enfin, nous estimons automatiquement des paramètres personnalisés pour mieux prédire l'étendu de l’ablation. Cette stratégie a été validée sur 7 ablations dans 3 cas cliniques. A partir de l'étude préclinique, la personnalisation est améliorée en comparant les simulations avec les mesures faites durant la procédure. Ces contributions ont abouti à des résultats prometteurs, et ouvrent de nouvelles perspectives pour planifier et guider l’ARF. / The outcome of radiofrequency ablation (RFA) of abdominal tumors is challenged by the presence of blood vessels and time-varying thermal conductivity, which make patient-specific planning extremely difficult. By providing predictive tools, biophysical models may help clinicians to plan and guide the procedure for an effective treatment. We introduce a detailed computational model of the biophysical mechanisms involved in RFA of hepatic tumors such as heat diffusion and cellular necrosis. It simulates the extent of ablated tissue based on medical images, from which patient-specific models of the liver, visible vessels and tumors are segmented. In this thesis, a new approach for solving these partial differential equations based on the Lattice Boltzmann Method is introduced. The model is first evaluated against clinical data of patients who underwent RFA of liver tumors. Then, a comprehensive pre-clinical experiment that combines multi-modal, pre- and post-operative anatomical and functional images, as well as the interventional monitoring of the temperature and delivered power is presented. This enables an end-to-end validation framework that considers the most comprehensive data set for model validation. Then, we automatically estimate patient-specific parameters to better predict the ablated tissue. This personalization strategy has been validated on 7 ablations from 3 clinical cases. From the pre-clinical study, we can go further in the personalization by comparing the simulated temperature and delivered power with the actual measurements during the procedure. These contributions have led to promising results, and open new perspectives in RFA guidance and planning.