Recycling Krylov Subspaces for Efficient Partitioned Solution of Aerostructural Adjoint Systems

Robust and efficient solvers for coupled-adjoint linear systems are crucial to successful aerostructural optimization. Monolithic and partitioned strategies can be applied. The monolithic approach is expected to offer better robustness and efficiency for strong fluid-structure interactions. However, it requires a high implementation cost and convergence may depend on appropriate scaling and initialization strategies. On the other hand, the modularity of the partitioned method enables a straightforward implementation while its convergence may require relaxation. In addition, a partitioned solver leads to a higher number of iterations to get the same level of convergence as the monolithic one. The objective of this paper is to accelerate the fluid-structure coupled-adjoint partitioned solver by considering techniques borrowed from approximate invariant subspace recycling strategies adapted to sequences of linear systems with varying right-hand sides. Indeed, in a partitioned framework, the structural source term attached to the fluid block of equations affects the right-hand side with the nice property of quickly converging to a constant value. We also consider deflation of approximate eigenvectors in conjunction with advanced inner-outer Krylov solvers for the fluid block equations. We demonstrate the benefit of these techniques by computing the coupled derivatives of an aeroelastic configuration of the ONERA-M6 fixed wing in transonic flow. For this exercise the fluid grid was coupled to a structural model specifically designed to exhibit a high flexibility. All computations are performed using RANS flow modeling and a fully linearized one-equation Spalart-Allmaras turbulence model. Numerical simulations show up to 39% reduction in matrix-vector products for GCRO-DR and up to 19% for the nested FGCRO-DR solver.Comment: 42 pages, 21 figure

Techniques de calcul de gradient aéro-structure haute-fidélité. Application sur l'aile du CRM.

International audienceAerostructural optimization is a keystone process to concurrently improve aerodynamic performance and reduce the structural mass of an aircraft. However, gradient-based multidisciplinary design optimization is efficient only if the computation of gradients is fast and accurate. To this end, we propose two high-fidelity aerostructural gradient computation techniques for strongly coupled aeroelastic systems. In the specific context of this work, we focus on design variables affecting structural stiffness only. Scalar objective functions like aerodynamic performance criteria are considered, as well as a field of structural grid forces. The most intrusive technique includes well-established direct and adjoint formulations that require substantial implementation effort. In contrast, we propose an alternative uncoupled non-intrusive approach easier to implement and yet capable of providing accurate gradient approximations. The accuracy of these methods is first demonstrated on the ONERA M6 Wing test-case. Their efficiency and applicability are then illustrated via a mass minimization problem applied to the Common Research Model (CRM). Both methods lead to very similar optimal designs and the detailed analysis of results promotes the non-intrusive approach as a promising gradient computation alternative.L'optimisation aéro-structure est un outil essentiel pour améliorer la performance aérodynamique d'un avion tout en réduisant sa masse. Toutefois, l'optimisation multidisciplinaire basée sur les gradients est efficiente si le calcul de ces gradients est rapide et précis. A cette fin, nous proposons deux techniques de calcul de gradient aéro-structure haute-fidélité pour des systèmes aéroélastiques fortement couplés. Dans le contexte spécifique de ce travail, nous nous concentrons sur des variables de design impactant la rigidité de la structure uniquement. Des fonctions objectif scalaires comme la performance aérodynamique sont considérées, ainsi que des champs de forces nodales sur la structure. La technique la plus intrusive repose sur les formulations classiques directe et adjointe qui nécessitent un effort d'implémentation substentiel. Alternativement, nous proposons une approche découplée et non-intrusive, plus facile à implémenter et capable de fournir une approximation précise des gradients. Ces deux techniques ont été implémentées dans le logiciel de CFD elsA de l'Onera.La précision, l'efficience et l'applicabilité de ces méthodes sont démontrés sur le cas-test du Common Research Model (CRM). Plus spécifiquement, un problème inverse dont l'objectif est de retrouver en croisière une loi de vrillage cible sur l'aile du CRM est considéré. Les deux méthodes conduisent à des configurations optimales très proches, et les résultats sont présentés et discutés en détail

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Interview med Luc Boltansk

Aeroelastic Adjoint-Based Optimisation of Highly Flexible Aircraft Wing Configuration

This paper investigates benefits resulting from the use of coupled aeroelastic analysis for aerodynamic shape optimisation of a highly flexible wing. The study is carried out on the eXternal Research Forum model (XRF-1) specified by Airbus Commercial Aircraft, representative of a long-range aircraft configuration. Improvements delivered by considering aeroelastic effects for the evaluation of both the aerodynamic performance and the associated gradients are assessed with respect to the results obtained by freezing the wing flexibility in both primal and adjoint computations. An analysis of the impact on the different drag components is also illustrated based on the far-field drag breakdown. Results show that for induced drag, engaging flexibility only at the primal level still allows to capture first-order gain on the final performance. However, engaging coupled-adjoint sensitivities is key to completely master wave drag reduction on the considered highly flexible wing. Performance improvement obtained by increasing the number of design parameters is also investigated

Cellulose coating and chelation of antibacterial compounds for the protection of flax yarns against natural soil degradation.

Natural cellulosic fibres such as flax fibres present interesting mechanical properties as well as biodegradability, and by-products, such as short flax fibres, could be used to produce geotextiles to stabilise soils. Today, geotextiles are often made of coir fibres, which have a high lignin percentage leading to their slow degradation in soil. Fibres with a high cellulosic content, such as those of flax, exhibit lower resistance to soil degradation. This study investigates solutions to improve this parameter with a view to increasing their service life and therefore their credibility compared to coir fibres for geotextile applications. For this purpose, a cellulose coating of yarns made of short flax fibres was performed and its stability under a water flow was assessed. The ability to form a cellulose sheath was estimated by chromaticity measurements of flax fibres after applying a dye specific to lignin. Infrared spectrometry analysis to monitor the level of protection against degradation by cellulolytic enzymes was also carried out. It appears that the cellulose coating provides an efficient physical protection, preventing access of these enzymes to their fibrous substrate. Then, the possibility of conferring antibacterial properties on the cellulose coating by chelating phytoalexin molecules such as gramine on it was assayed and proven to be effective against soil cellulolytic bacteria such as Cellvibrio fulvus and Cellvibrio vulgaris. This study therefore establishes that coating flax yarns with cellulose associated with antibacterial molecules could contribute to obtaining a longer service life in soil for geotextiles manufactured from flax fibres

Therapeutic anticoagulation after liver transplantation is not useful among patients with pre-transplant Yerdel-grade I/II portal vein thrombosis:A two-center retrospective study

BACKGROUND: Portal vein thrombosis (PVT) is no longer a contraindication for liver transplantation (LT). While therapeutic anticoagulation (tAC) is recommended during the waiting period, there is no evidence for its usefulness in the prevention of PVT recurrence after LT. OBJECTIVES: The aim of our study was to evaluate the role of tAC post-LT in the prevention of PVT recurrence. PATIENTS/METHODS: All adult LTs performed in 2 high volume centres between 2003 and 2018, were retrospectively analysed. Only patients with PVT classified as Yerdel grade I or II and with standard portal reconstruction were included. PVT recurrence and tAC-associated morbidity within 1 year were compared between patients receiving tAC or not. RESULTS: During the study period, out of 2612 LTs performed, 235 (9%) patients with PVT were included. 113 patients (48.1%) received post-LT tAC (tAC group) while 122 (51.9%) did not (non-tAC group). The incidence of bleeding events was significantly higher in the tAC group (26 (23%) vs. 5 (4.1%), p<0.01) and the initial hospitalization duration was longer (21 vs. 17.5 days, p<0.01). Within the first year, PVT recurrence was observed for 9 (3.8%) patients without any difference between the tAC and non-tAC groups (6 (5.1%) vs. 3 (2.5%), p=0.39). The only identified risk factor for PVT recurrence was the recipients' age (OR=0.94, p=0.03). Graft (p=0.11) and patient (p=0.44) survival were similar between the 2 groups. CONCLUSION: Therapeutic anticoagulation is not necessary in the prevention of grade I/II PVT recurrence and is associated with higher morbidity and longer hospital stay

Clostridia in Premature Neonates' Gut: Incidence, Antibiotic Susceptibility, and Perinatal Determinants Influencing Colonization

Although premature neonates (PN) gut microbiota has been studied, data about gut clostridial colonization in PN are scarce. Few studies have reported clostridia colonization in PN whereas Bacteroides and bifidobacteria have been seldom isolated. Such aberrant gut microbiota has been suggested to be a risk factor for the development of intestinal infections. Besides, PN are often treated by broad spectrum antibiotics, but little is known about how antibiotics can influence clostridial colonization based on their susceptibility patterns. The aim of this study was to report the distribution of Clostridium species isolated in feces from PN and to determine their antimicrobial susceptibility patterns. Additionally, clostridial colonization perinatal determinants were analyzed.Of the 76 PN followed until hospital discharge in three French neonatal intensive care units (NICUs), 79% were colonized by clostridia. Clostridium sp. colonization, with a high diversity of species, increased throughout the hospitalization. Antibiotic courses had no effect on the clostridial colonization incidence although strains were found susceptible (except C. difficile) to anti-anaerobe molecules tested. However, levels of colonization were decreased by either antenatal or neonatal (during more than 10 days) antibiotic courses (p = 0.006 and p = 0.001, respectively). Besides, incidence of colonization was depending on the NICU (p = 0.048).This study shows that clostridia are part of the PN gut microbiota. It provides for the first time information on the status of clostridia antimicrobial susceptibility in PN showing that strains were susceptible to most antibiotic molecules. Thus, the high prevalence of this genus is not linked to a high degree of resistance to antimicrobial agents or to the use of antibiotics in NICUs. The main perinatal determinant influencing PN clostridia colonization appears to be the NICU environment

Systèmes économiques territorialisés et pratiques informelles de communication à finalité productive : Le cas de la vallée de l'Arve

What if the strength of a territorialized economic system did not depend only on his formal processes? This research paper attempts to investigate it, by unveiling a particular type of informal processes, that of the informal communication practices related to the of Marshallian externalities filiation corresponding to non-market interdependencies.Based on the conceptual framework of the neo-institutionalist economic theory, the author will characterize the existence of informal communication practices, responding to the characteristics of a tension between formal constraints and informal constraints. Secondly, based on the conceptual system of the non-standard economy, and in particular, that of the economy of proximities, the author will inventory and qualify the aforementioned practices, which belong to network communicationrelationships for productive purposes.This will enable us, within the framework of the study case focusing of a particular territorialized economic system, the French Arve valley and the bar turning industry activity, to empirically consider the existence of a system composed of three communication practices pattern and two communities, both informal, as well as the coexistence of two institutional systems.These informal mechanisms constitute a clear support in the economic field for the bar turning industry local's players. These same mechanisms correspond to practices and information related to economic and business intelligence. They can be of interest to the scientific community interested in territorialised economic mechanisms and clustering mechanisms, as well as practitioners wishing to access an in-depth understanding of a specific territorial reality other than through purely technical or business-oriented perspective.Et si la force d'un système économique territorialisé ne dépendait pas uniquement de ses processus formels ? Le présent document de recherche propose de l'observer en levant le voile sur un type de processus informel particulier, celui des pratiques informelles de communication se rapportant à la filiation des externalités marshalliennes correspondant à des interdépendances non-marchandes.Prenant appui sur le système conceptuel de l'économie néo-institutionnelle, nous caractériserons l'existence des pratiques de communication informelles, répondant aux caractéristiques d'une tension entre règles formelles et contraintes informelles. Dans un second temps, prenant appui cette fois-ci sur le système conceptuel de l'économie non standard, et en particulier celui de l'économie de proximités,nous ferons l'inventaire et qualifierons ces pratiques, qui appartiennent à des relations résiliaires de communication à finalité productives. Ceci nous permettra dans le cadre de l'étude d'un système territorialisé particulier, celui de la vallée de l'Arve et du secteur d'activité de l'industrie du décolletage, de considérer empiriquement l'existence d'un système composé de trois pratiques de communication et de deux communautés, toutes deux informelles, tout autant que la coexistence de deux systèmes institutionnels. Ces mécanismes informels constituent un apport manifeste dans le registre économique aux acteurs du décolletage. Ils correspondent à des pratiques et à de l'information qui relève de l'intelligence économique. Ils peuvent intéresser autant la communauté scientifique, que le praticien souhaitant appréhender une realitée territoriale spécifique sous un angle autre que purement technique

Territorialized economic systems and productive purpose's informal communication practices : Study case of the French Arve valley and bar turning industry

Et si la force d'un système économique territorialisé ne dépendait pas uniquement de ses processus formels ? Le présent document de recherche propose de l'observer en levant le voile sur un type de processus informel particulier, celui des pratiques informelles de communication se rapportant à la filiation des externalités marshalliennes correspondant à des interdépendances non-marchandes.Prenant appui sur le système conceptuel de l'économie néo-institutionnelle, nous caractériserons l'existence des pratiques de communication informelles, répondant aux caractéristiques d'une tension entre règles formelles et contraintes informelles. Dans un second temps, prenant appui cette fois-ci sur le système conceptuel de l'économie non standard, et en particulier celui de l'économie de proximités,nous ferons l'inventaire et qualifierons ces pratiques, qui appartiennent à des relations résiliaires de communication à finalité productives. Ceci nous permettra dans le cadre de l'étude d'un système territorialisé particulier, celui de la vallée de l'Arve et du secteur d'activité de l'industrie du décolletage, de considérer empiriquement l'existence d'un système composé de trois pratiques de communication et de deux communautés, toutes deux informelles, tout autant que la coexistence de deux systèmes institutionnels. Ces mécanismes informels constituent un apport manifeste dans le registre économique aux acteurs du décolletage. Ils correspondent à des pratiques et à de l'information qui relève de l'intelligence économique. Ils peuvent intéresser autant la communauté scientifique, que le praticien souhaitant appréhender une realitée territoriale spécifique sous un angle autre que purement technique.What if the strength of a territorialized economic system did not depend only on his formal processes? This research paper attempts to investigate it, by unveiling a particular type of informal processes, that of the informal communication practices related to the of Marshallian externalities filiation corresponding to non-market interdependencies.Based on the conceptual framework of the neo-institutionalist economic theory, the author will characterize the existence of informal communication practices, responding to the characteristics of a tension between formal constraints and informal constraints. Secondly, based on the conceptual system of the non-standard economy, and in particular, that of the economy of proximities, the author will inventory and qualify the aforementioned practices, which belong to network communicationrelationships for productive purposes.This will enable us, within the framework of the study case focusing of a particular territorialized economic system, the French Arve valley and the bar turning industry activity, to empirically consider the existence of a system composed of three communication practices pattern and two communities, both informal, as well as the coexistence of two institutional systems.These informal mechanisms constitute a clear support in the economic field for the bar turning industry local's players. These same mechanisms correspond to practices and information related to economic and business intelligence. They can be of interest to the scientific community interested in territorialised economic mechanisms and clustering mechanisms, as well as practitioners wishing to access an in-depth understanding of a specific territorial reality other than through purely technical or business-oriented perspective