Fluid dynamics simulations generally require large computational recourses in form of computer power and time. There are different methods for simulating fluid flows that are more or less demanding, but also more or less accurate. Two well known computational methods are the Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES). RANS computes the timeaveraged flow properties, while LES resolve the large structures (eddies) of the flow directly and model the small ones. Hybrid models are combinations of these two models which have been developed to improve the RANS solutions and shorten the simulation time compared to LES computations. One such model is the Scale Adaptive Simulation (SAS) model which uses the RANS model in steady flow regions, such as close to walls, and a LES like model in unsteady regions with large fluctuations. This study was done for evaluating the SAS model compared to Unsteady RANS (URANS) and LES and their performance compared to measurements from an engineering point of view. This was done by running simulations on two different test cases, one external and one internal flow situation. The first one was flow around a wall-mounted cylinder and the second one was flow through an aorta with a coarctation in the descending aorta. The first test case was used to thoroughly evaluate the SAS model by running many simulations with URANS, SAS and LES with different element types, element sizes and flow parameters. The element types that have been analyzed are; tetrahedral, hexahedral and polyhedral. The results were compared with experiments done by Sumner et al. [7, 8, 9, 10]. The second test case was used for evaluating the SAS model even further on another flow situation. For this test case, only two SAS simulations were performed on two different grids; a structured hexahedral and an unstructured polyhedral. These results were compared with Magnetic Resonance Imaging (MRI) measurements obtained from Linköping University. No conclusion of which one of the simulated cases gives the best overall agreement with experimental results could be concluded from the obtained results. The best prediction of the drag coefficient for the cylinder was obtained for the coarsest polyhedral mesh that was run with LES, with the disagreement 0.4 percent. The best prediction of the Strouhal number was obtained for a URANS simulation performed on the coarsest mesh with an improved grid close to the cylinder surface, generating less than one, with a disagreement of 3 percent compared to measurements. For the meshes used, it was found that the polyhedral mesh gave the best overall results and the tetrahedral mesh gave the worst results for the cylinder case. For the aorta case the SAS model produced velocity components that had acceptable agreement with the MRI-measurements, but gave very poor results for the turbulent kinetic energy. The main conclusion of this thesis was that the SAS model performed better than URANS, but took longer time to compute simulations than LES, which was the model that generated the best overall results.

The tube hydroforming (THF) technology has been widely used in manufacturing the lightweight and high strength components. The success of THF is largely dependent on the selection of the loading paths: internal pressure vs. time and axial feeding vs. time. The Finite element method is used to simulate the forming result of different loading paths and reduce the cost of die-testing. T-shape tube hydroforming is investigated adaptive simulation by combining FEM code LS-DYNA with fuzzy logic controller subroutine is proposed. During the simulation process, subroutines can adjust the loading paths according to the values of the minimum tube thickness and its variance. Then, the purpose of better thickness distribution of the formed tube at the side branch is achieved. Comparing with other linear loading paths, this adaptive control method got better results. In experiments, the validity of LS-DYNA applied in THF process is verified and the experimental results by adaptive simulation are better than those by the linear loading paths.

The tube hydro-forming (THF) is an innovative manufacturing process which is used to manufacture many industrial components widely. The success of THF is largely dependent on the selection of the loading paths: internal pressure versus time, axial feeding versus time and counter punch (CP) versus time. The finite element analysis is used to simulate the forming result of different loading paths and reduce the cost of die-testing. This paper presents the forming of T-branches and T-branches components with CP. These paper has developed an adaptive simulation algorithm by combining FEM code LS-DYNA 3D with controller subroutine to get ideal bulging height and uniform thickness of the formed tube with multi-stages. Discuss influence under different parameters of process. The results are compared with experimental results to validate accuracy by this adaptive control methods.

Les méthodes de dynamique moléculaire (MD pour Molecular Dynamics en anglais) sont utilisées pour simuler des systèmes volumineux et complexes. Cependant, la simulation de ce type de systèmes sur de longues échelles temporelles demeure un problème coûteux en temps de calcul. L'étape la plus coûteuse des méthodes de MD étant la mise à jour des forces entre les particules. La simulation de particules restreintes de façon adaptative (ARMD pour Adaptively Restrained Molecular Dynamics en anglais) est une nouvelle approche permettant d'accélérer le processus de simulation en réduisant le nombre de calculs de forces effectués à chaque pas de temps. La méthode ARMD fait varier l'état des degrés de liberté en position en les activants ou en les désactivants de façon adaptative au cours de la simulation. Du fait, que le calcul des forces dépend majoritairement de la distance entre les atomes, ce calcul peut être évité entre deux particules dont les degrés de liberté en position sont désactivés. En revanche, le calcul des forces pour les particules actives (i.e. celles dont les degrés de liberté en position sont actifs) est effectué. Afin d'exploiter au mieux l'adaptabilité de la méthode ARMD, nous avons conçu de nouveaux algorithmes permettant de calculer et de mettre à jour les forces de façon plus efficace. Nous avons développé des algorithmes permettant de construire et de mettre à jour des listes de voisinage de manière incrémentale. En particulier, nous avons travaillé sur un algorithme de mise à jour incrémentale des forces en un seul passage deux fois plus rapide que l'ancien algorithme également incrémental mais qui nécessitait deux passages. Les méthodes proposées ont été implémentées et validées dans le simulateur de MD appelé LAMMPS, mais elles peuvent s'appliquer à n'importe quel autre simulateur de MD. Nous avons validé nos algorithmes pour différents exemples sur les ensembles NVE et NVT. Dans l'ensemble NVE, la méthode ARMD permet à l'utilisateur de jouer sur le précision pour accélérer la vitesse de la simulation. Dans l'ensemble NVT, elle permet de mesurer des grandeurs statistiques plus rapidement. Finalement, nous présentons des algorithmes parallèles pour la mise à jour incrémentale en un seul passage permettant d'utiliser la méthode ARMD avec le standard Message Passage Interface (MPI). / Molecular Dynamics (MD) is often used to simulate large and complex systems. Although, simulating such complex systems for the experimental time scales are still computationally challenging. In fact, the most computationally extensive step in MD is the computation of forces between particles. Adaptively Restrained Molecular Dynamics (ARMD) is a recently introduced particles simulation method that switches positional degrees of freedom on and off during simulation. Since force computations mainly depend upon the inter-atomic distances, the force computation between particles with positional degrees of freedom off~(restrained particles) can be avoided. Forces involving active particles (particles with positional degrees of freedom on) are computed.In order to take advantage of adaptability of ARMD, we designed novel algorithms to compute and update forces efficiently. We designed algorithms not only to construct neighbor lists, but also to update them incrementally. Additionally, we designed single-pass incremental force update algorithm that is almost two times faster than previously designed two-pass incremental algorithm. These proposed algorithms are implemented and validated in the LAMMPS MD simulator, however, these algorithms can be applied to other MD simulators. We assessed our algorithms on different and diverse benchmarks in both microcanonical ensemble (NVE) and canonical (NVT) ensembles. In the NVE ensemble, ARMD allows users to trade between precision and speed while, in the NVT ensemble, it makes it possible to compute statistical averages faster. In Last, we introduce parallel algorithms for single-pass incremental force computations to take advantage of adaptive restraints using the Message Passage Interface (MPI) standard.

L’évaluation de risques est conditionnée par les connaissances et les informations disponibles au moment où l’analyse est faite. La modélisation et la simulation sont des moyens d’explorer et de comprendre le comportement du système, d’identifier des scénarios critiques et d’éviter des surprises. Un certain nombre de simulations du modèle sont exécutées avec des conditions initiales et opérationnelles différentes pour identifier les scénarios conduisant à des conséquences critiques et pour estimer leurs probabilités d’occurrence. Pour les systèmes complexes, les modèles de simulations peuvent être : i) de haute dimension ; ii) boite noire ; iii) dynamiques ; iv) coûteux en termes de calcul, ce qu’empêche l’analyste d’exécuter toutes les simulations pour les conditions multiples qu’il faut considérer.La présente thèse introduit des cadres avancés d’évaluation des risques basée sur les simulations. Les méthodes développées au sein de ces cadres sont attentives à limiter les coûts de calcul requis par l’analyse, afin de garder une scalabilité vers des systèmes complexes. En particulier, toutes les méthodes proposées partagent l’idée prometteuse de focaliser automatiquement et de conduire d’une manière adaptive les simulations vers les conditions d’intérêt pour l’analyse, c’est-à-dire, vers des informations utiles pour l'évaluation des risques.Les avantages des méthodes proposées ont été montrés en ce qui concerne différentes applications comprenant, entre autres, un sous-réseau de transmission de gaz, un réseau électrique et l’Advanced Lead Fast Reactor European Demonstrator (ALFRED). / Risk assessment is conditioned on the knowledge and information available at the moment of the analysis. Modeling and simulation are ways to explore and understand system behavior, for identifying critical scenarios and avoiding surprises. A number of simulations of the model are run with different initial and operational conditions to identify scenarios leading to critical consequences and to estimate their probabilities of occurrence. For complex systems, the simulation models can be: i) high-dimensional; ii) black-box; iii) dynamic; and iv) computationally expensive to run, preventing the analyst from running the simulations for the multiple conditions that need to be considered.The present thesis presents advanced frameworks of simulation-based risk assessment. The methods developed within the frameworks are attentive to limit the computational cost required by the analysis, in order to keep them scalable to complex systems. In particular, all methods proposed share the powerful idea of automatically focusing and adaptively driving the simulations towards those conditions that are of interest for the analysis, i.e., for risk-oriented information.The advantages of the proposed methods have been shown with respect to different applications including, among others, a gas transmission subnetwork, a power network and the Advanced Lead Fast Reactor European Demonstrator (ALFRED).

Ces travaux de recherche ont pour but d’évaluer la méthode dite de la "Simulation auxEchelles Adaptées" (SAS pour Scale-Adaptive Simulation). Cette approche coïncide avec uneapproche RANS classique dans les zones pariétales attachées et adapte le niveau de viscositéturbulente dans les zones décollées pour y permettre une résolution partielle des structures turbulentes.Dans une première partie, une analyse théorique du modèle SAS original a été menéeet a permis de développer une correction visant à favoriser l’adaptation du niveau de viscositéturbulente dans les zones sièges d’instabilités de type Kelvin-Helmholtz. Le modèle ainsi corrigéest nommé SAS-αL. Les modèles SAS et SAS-αL ont été implantés dans le code de calculNavier-Stokes elsA de l’ONERA. À l’issue de cette étape, trois cas académiques d’écoulementsturbulents instationnaires, cylindre à grand nombre de Reynolds, marche descendante et cavitétranssonique, ont été simulés grâce aux trois modèles de turbulence SST, SAS et SAS-αL. Outreune comparaison aux bases de données expérimentales disponibles, une attention particulièrea été portée à l’influence de paramètres numériques tels que des schémas numériques d’ordreélevé. Enfin, afin d’étudier la viabilité de l’approche SAS dans un contexte industriel, les troismodèles de turbulence ont été testés sur une configuration issue de l’industrie aéronautique etcorrespondant à la sortie d’air chaud d’un système de dégivrage des nacelles d’avion. La comparaisondes prévisions obtenues avec les modèles SST, SAS et SAS-αL aux données expérimentalesobtenues à l’ONERA a permis de montrer un gain de précision grâce à l’emploi de l’approcheSAS et ce pour un coût de calcul compatible avec un cycle de conception industrielle. / This research work is meant to assess an upgraded URANS approach, namely the Scale-Adaptive Simulation (SAS). This method is similar to a conventional RANS approach (namelythe SSTmodel) in attached areas and is able to adapt the eddy-viscosity level in detached areas toensure the resolution, at least partially, of the turbulent structures. In a first part of this researchwork, an improvement of the SAS approach is suggestedto allowa better sensitivity of themodelto instabilities such as Kelvin-Helmholtz ones. This "improved" model is referred to as SAS-αLmodel. Both SAS and SAS-αL models were implemented in the ONERA Navier-Stokes solverelsA and both of themaswell as the SSTmodelwere tested on academic test cases : a cylinder in acrossflowat a high Reynolds number, a backward-facing step flowcorresponding to theDriver&Seegmiller experiment and the transonic flow over the M219 cavity experimentally investigatedby de Henshaw. The influence of the numerical parameters was deeply investigated and particularattention was paid to the high-order space-discretization schemes effects. The reliabilityof the SAS approach in an industrial framework was assessed on an aeronautic configurationnamely a nacelle de-icing device. Comparisons between the threemodels (SST, SAS and SAS-αL)and an experimental database available at ONERA - The French Aerospace Lab have shown thebetter accuracy of the SAS approach as well as the high potential of the SAS-αL model.

O projeto de pesquisa propôs avaliar a metodologia de Simulação de Escalas Adaptativas (SAS) para descrever escoamentos turbulentos e não-reativos utilizando estudos de casos característicos, amplamente documentados, os quais possuem comportamentos do escoamento distintos presentes em diferentes regiões de uma câmara de combustão. O primeiro estudo de caso foi a análise do escoamento sobre um degrau, em que foi avaliada a capacidade do modelo Simulação de Escalas Adaptativas, frente aos modelos de Navier-Stokes com Média de Reynolds (RANS) e Simulação de Grandes Escalas (LES) e aos dados experimentais, em prever a distribuição de pressão, ponto de recolamento e de perfis de velocidade ao longo do domínio após a separação. Pode-se notar que o modelo SAS apresentou resultados praticamente idênticos aos resultados obtidos pelo modelo RANS com relação à distribuição de pressão e a posição ponto de recolamento. Porém, os perfis de velocidade apresentaram algumas discrepâncias com relação aos perfis de velocidade dos modelos RANS e LES e dos resultados experimentais. Um segundo estudo de caso foi a análise do escoamento através de um turbilhonador, em que a capacidade do modelo SAS foi avaliada, comparando seus resultados com os resultados do modelo de Navier-Stokes Não-Estacionárias com Média de Reynolds (URANS) e com os dados experimentais, em prever perfis de velocidade em regiões de recirculação presentes neste estudo de caso. Pode-se observar que ambos os modelos conseguiram prever as principais estruturas de recirculação do escoamento, porém, os perfis de velocidade apresentaram significativas discrepâncias com relação aos dados experimentais. Em seguida, foram feitas comparações entre os modelos SAS e URANS com relação à previsão da precessão central de vórtice e de estruturas de vórtices, das quais foi observado que o modelo SAS apresenta uma maior capacidade para prever estas estruturas em relação ao modelo URANS. / The research project aimed to evaluate the Scale-Adaptive Simulation (SAS) methodology to describe turbulent and non-reactive flows using characteristic, widely documented, case studies, which have distinct flow behaviors present in different regions of a chamber of combustion. The first case study was the analysis of a flow over a backward-facing step, from which the Scale-Adaptive Simulation (SAS) model capacity was evaluated, compared to the Reynolds Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES) models and experimental data, in order to predict the pressure distribution, reattachment point and velocity profiles throughout the domain after separation. It can be noticed that the SAS model presented results almost identical to the results obtained by the RANS model in relation to the pressure distribution and reattachment position. However, the velocity profiles presented some discrepancies in respect to RANS and LES velocity profiles and the experimental results. A second case study was the analysis of the flow through a swirler, from which the capacity of the SAS model was evaluated, comparing its results to the results of the Unsteady Reynolds Averaged Navier-Stokes (URANS) model and with the experimental data, to predict velocity profiles in recirculation regions present in this case study. It can be observed that both models were able to predict the main recirculation structures of the flow, however, the velocity profiles presented significant discrepancies in relation to the experimental data. Then, comparisons were made between the SAS and URANS models in respect to the prediction of vortex precession vortex core and vortex structures, from which it was observed that the SAS model presents a greater capacity to predict these structures in relation to the URANS model.

Cette thèse s'inscrit dans le cadre de l'amélioration des prévisions aérothermiques qui suscite un intérêt croissant de la part des industriels aéronautiques. Elle consiste à évaluer l'apport des méthodes URANS avancées de type SAS dans la prévision des flux de chaleur turbulents et pariétaux pour des écoulements turbulents chauffés. Elle vise également à situer ces approches par rapport à des modèles URANS classiques de type DRSM et à des méthodes hybrides RANS/LES comme la ZDES. Nous avons dans un premier temps proposé une extension de l'approche SAS à un modèle DRSM afin d'obtenir une meilleure restitution des tensions de Reynolds résolues et modélisées. Ce nouveau modèle SAS-DRSM a été implanté dans le code Navier-Stokes elsA de l'ONERA. Nous avons ensuite évalué l'ensemble des approches SAS disponibles avec ce code sur la prévision de deux écoulements aérothermiques rencontrés sur avion dans un compartiment de moteur. Ces études numériques ont montré que les approches SAS améliorent la représentation des écoulements par rapport aux modèles URANS classiques. Elles aboutissent à des écoulements fortement tridimensionnels présentant de nombreuses structures turbulentes. Ces structures induisent un mélange turbulent plus important et permettent alors une meilleure prévision du flux de chaleur pariétal. Par ailleurs, nos travaux ont permis de situer plus clairement les approches de type SAS comme des méthodes plus précises que les méthodes URANS classiques sans augmentation importante de mise en œuvre ou de coût de calcul. Les modèles SAS ne permettent pas de résoudre les plus petites structures caractéristiques du mouvement turbulent par rapport à la ZDES qui montre ici des prévisions supérieures. Le modèle SAS-DRSM offre néanmoins la meilleure alternative de type SAS. Enfin, l'étude du flux de chaleur turbulent semble retrouver le fait que l'hypothèse de nombre de Prandtl turbulent constant classique des modèles URANS n'est pas valable dans toutes les zones de l'écoulement.