La méthode des bases réduites appliquées à des simulations d'aérothermie

We present in this thesis our work on model order reduction for aerothermal simulations. We consider the coupling between the incompressible Navier-Stokes equations and an advection-diffusion equation for the temperature. Since the physical parameters induce high Reynolds and Peclet numbers, we have to introduce stabilization operators in the formulation to deal with the well known numerical stability issue. The chosen stabilization, applied to both fluid and heat equations, is the usual Streamline-Upwind/Petrov-Galerkin (SUPG) which add artificial diffusivity in the direction of the convection field. We also introduce our order reduction strategy for this model, based on the Reduced Basis Method (RBM). To recover an affine decomposition for this complex model, we implemented a discrete variation of the Empirical Interpolation Method (EIM) which is a discrete version of the original EIM. This variant allows building an approximated affine decomposition for complex operators such as in the case of SUPG. We also use this method for the non-linear operators induced by the shock capturing method. The construction of an EIM basis for non-linear operators involves a potentially huge number of non-linear FEM resolutions - depending on the size of the sampling. Even if this basis is built during an offline phase, we usually can not afford such expensive computational cost. We took advantage of the recent development of the Simultaneous EIM Reduced basis algorithm (SER) to tackle this issue.Nous présentons dans cette thèse nos travaux sur la réduction d'ordre appliquée à des simulations d'aérothermie. Nous considérons le couplage entre les équations de Navier-Stokes et une équations d'énergie de type advection-diffusion. Les paramètres physiques considérés nous obligent à considéré l'introduction d'opérateurs de stabilisation de type SUPG ou GLS. Le but étant d'ajouter une diffusion numérique dans la direction du champs de convection, afin de supprimer les oscillations non-phyisques. Nous présentons également notre stratégie de résolution basée sur la méthode des bases réduite (RBM). Afin de retrouver une décomposition affine, essentielle pour l'application de la RBM, nous avons implémenté une version discrète de la méthode d'interpolation empirique (EIM). Cette variante permet de la construction d'approximation affine pour des opérateurs complexes. Nous utilisons notamment cette méthode pour la réduction des opérateurs de stabilisations. Cependant, la construction des bases EIM pour des problèmes non-linéaires implique un grand nombre de résolution éléments finis. Pour pallier à ce problème, nous mettons en oeuvre les récents développement de l'algorithme de coconstruction entre EIM et RBM (SER)

The Reduced Basis Method Applied to Aerothermal Simulations

International audienceThe Reduced Basis Method Motivations • Modeling : multi-physics non-linear models, complex geometries, genericity • Uncertainty management / Risk analysis • Optimization in early design, certification or operating phase

PEPS DataFlow : Analyse de données pour des capteurs fluidiques à haute précision

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Primary adrenal insufficiency due to bilateral adrenal hemorrhage-adrenal infarction in the antiphospholipid syndrome: long-term outcome of 16 patients.

Context: Primary adrenal insufficiency due to bilateral adrenal hemorrhage-adrenal infarction is a rare and life-threatening manifestation of the antiphospholipid syndrome (APLS). Data on the long-term outcome are scarce. Objective: The aims of the present study were to analyze the long-term outcome related to APLS per se and to characterize the course of adrenal involvement. Design: We conducted a retrospective study of patients with bilateral adrenal hemorrhage-adrenal infarction secondary to APLS seen in the Department of Internal Medicine of Pitié-Salpêtrière Hospital in Paris (France) between January 1990 and July 2010. Results: Three patients died during the acute phase related to APLS manifestations. Sixteen patients (7 males; 9 females) were followed up during a median period of 3.5 years (range 0.3-28.1 years). Three episodes of recurrent thrombosis were noted. One patient died from cerebral hemorrhage 3 months after the onset of adrenal insufficiency. Repeated Synacthen tests showed complete absence of response in 8 of the 10 patients assessed; cortisol and aldosterone increased appropriately in one patient and to some extent in another one. Dehydroepiandrosterone levels and 24-hour urinary epinephrine levels remained abnormally low in all evaluated patients. Adrenal imaging performed more than 1 year after the initial event revealed completely atrophic glands in 9 of 11 patients. Conclusions: This particular subset of APLS patients who survive the acute phase has a rather favorable long-term outcome. Although adrenal dysfunction is generally irreversible, adrenocortical function may, at least partially, recover in rare cases. In this view, measurement of early morning cortisol during follow-up is indicated to detect these patients.Journal ArticleSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Heart and systemic sclerosis—findings from a national cohort study

International audienceAbstract Objectives Heart involvement is one of the leading causes of death in SSc. The prevalence of SSc-related cardiac involvement is poorly known. Our objective was to investigate the prevalence and prognosis burden of different heart diseases in a nationwide cohort of patients with SSc. Methods We used data from a multicentric prospective study using the French SSc national database. Focusing on SSc-related cardiac involvement, we aimed to determine its incidence and risk factors. Results Of the 3528 patients with SSc, 312 (10.9%) had SSc-related cardiac involvement at baseline. They tended to have a diffuse SSc subtype more frequently and to have more severe clinical features, and presented more cardiovascular risk factors. From the 1646 patients available for follow-up analysis, SSc-related cardiac involvement was associated with an increased risk of death. There was no significant difference in overall survival between SSc-related cardiac involvement, ischaemic heart disease or pulmonary arterial hypertension. Regarding survival analysis, 98 patients developed SSc-related cardiac involvement at 5 years (5-year event rate 11.15%). Regarding reduced left ventricular ejection fraction <50% and left ventricular diastolic dysfunction, the 5-year event rate was 2.49% and 5.84%, respectively. Pericarditis cumulative incidence at 5 years was 3%. Diffuse SSc subtype was a risk factor for SSc-related cardiac involvement and pericarditis. Female sex was associated with less left ventricular diastolic dysfunction incidence. Conclusions Our results describe the incidence and prognostic burden of SSc-related cardiac involvement at a large scale, with gender and diffuse SSc subtype as risk factors. Further analyses should assess the potential impact of treatment on these various cardiac outcomes