HAL Université de Toulouse, et Toulouse INP
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Une approche algorithmique en variables mixtes pour l'optimisation de structures aéronautiques et la sélection multicritère de technologies pour matériaux composites
No full textComposite materials are currently widely spread in aerospace applications due to their very favorable strength to weight ratio. However, the design and optimization of such composite structures presents several challenges. The process must not only account for the structural constraints, but it also has to address strict manufacturing rules, such as balance, minimum percentage of given orientations, symmetry or distribution of orientations. These rules also include the compatibility among adjacent laminates in the structure. In addition, the problem has an intrinsic discrete nature, as the solution must be expressed as a stacking sequence. This is why several specific formulations have been proposed in the literature to solve this problem. A state-of-the-art review showed however that none of the existing approaches can yet consider all the relevant structural and manufacturing constraints at the same time, in particular compatibility constraints. In this work, this problem was addressed by formulating a novel approach based on a mixed-variable formulation where the optimal stacking sequence is found in a catalog and the laminate thickness is treated as a continuous variable relaxed through a penalization method. In this way, the manufacturing constraints, including the compatibility one, are accounted for as functions of the categorical variable. To solve the problem using this formulation, a mixed-categorical version of Bi-Level Outer Approximation (BLOA) was extended to accommodate it. While the original BLOA solver did not account for non-convex problems, infeasible points in the catalog or purely categorical constraints, the modifications developed during this work accounted for these 3 limitations. This allowed the treatment of composite optimization problems accounting for catalog selection of stacking sequences and the compatibility of the different elements in a monolithic approach. This mixed-variable formulation also allowed for the implementation of a variability control scheme that limits the number of different laminates in the final structure, which may be a desirable property in an industrial setting for cost and/or standardization reasons. In addition, another objective of this work was to study the merits of a new manufacturing technique, the Double-Double (DD), in composite structures design. This technique bases the manufacturing of a laminate in the repetition of a set of 4 plies defined by only 2 orientations and their balanced counterparts, called a super-ply. It is claimed that this configuration does not just relax many of the manufacturing constraints but can achieve thinner homogenized laminates. The implementation of the proposed optimization formulation accounting for structural and manufacturing constraints, the variability control schemes and the DD comparison against conventional laminates were performed in both academic and industrial use cases.Les matériaux composites sont actuellement largement répandus dans les applications aérospatiales en raison de leur rapport résistance/poids très favorable. Cependant, la conception et l'optimisation de telles structures composites présentent plusieurs défis. Le processus ne doit pas seulement tenir compte des contraintes structurelles, mais il doit également aborder des règles de fabrication strictes, telles que l'équilibrage, le pourcentage minimal d'orientations données, la symétrie ou la distribution des orientations. Ces règles incluent également la compatibilité entre les stratifiés adjacents dans la structure. De plus, le problème a une nature intrinsèquement discrète, car la solution doit être exprimée sous forme de séquence d'empilement. C'est pourquoi plusieurs formulations spécifiques ont été proposées dans la littérature pour résoudre ce problème. Un examen de l'état de l'art a cependant montré qu'aucune des approches existantes ne peut encore considérer simultanément toutes les contraintes structurelles et de fabrication pertinentes, en particulier les contraintes de compatibilité. Dans ce travail, ce problème a été abordé en formulant une nouvelle approche basée sur une formulation à variables mixtes où la séquence d'empilement optimale est trouvée dans un catalogue et l'épaisseur du stratifié est traitée comme une variable continue relaxée par une méthode de pénalisation. De cette manière, les contraintes de fabrication, y compris celle de compatibilité, sont prises en compte comme des fonctions de la variable catégorielle. Pour résoudre le problème en utilisant cette formulation, une version mixte-catégorielle de l'algorithme d'Approximation Externe Bi-Niveau (BLOA) a été étendue pour l'adapter. Alors que le solveur BLOA original ne tenait pas compte des problèmes non convexes, des points infaisables dans le catalogue ou des contraintes purement catégorielles, les modifications développées au cours de ce travail ont pris en compte ces 3 limitations. Cela a permis le traitement des problèmes d'optimisation des composites en tenant compte de la sélection catalographique des séquences d'empilement et de la compatibilité des différents éléments dans une approche monolithique. Cette formulation à variables mixtes a également permis la mise en œuvre d'un schéma de contrôle de la variabilité qui limite le nombre de stratifiés différents dans la structure finale, ce qui peut être une propriété souhaitable dans un contexte industriel pour des raisons de coût et/ou de standardisation. De plus, un autre objectif de ce travail était d'étudier les avantages d'une nouvelle technique de fabrication, le Double-Double (DD), dans la conception de structures composites. Cette technique base la fabrication d'un stratifié sur la répétition d'un ensemble de 4 plis définis par seulement 2 orientations et leurs contreparties équilibrées, appelé super-pli. Il est affirmé que cette configuration non seulement assouplit de nombreuses contraintes de fabrication, mais peut également permettre d'obtenir des stratifiés homogénéisés plus minces. La mise en œuvre de la formulation d'optimisation proposée tenant compte des contraintes structurelles et de fabrication, des schémas de contrôle de la variabilité et de la comparaison DD par rapport aux stratifiés conventionnels a été réalisée dans des cas d'utilisation académiques et industriels
Orbital Stability of Plane Waves in the Klein-Gordon Equation against Localized Perturbations
No full textWe investigate the stability and long-term behavior of spatially periodic plane waves in the complex Klein-Gordon equation under localized perturbations. Such perturbations render the wave neither localized nor periodic, placing its stability analysis outside the scope of the classical orbital stability theory for Hamiltonian systems developed by Grillakis, Shatah, and Strauss. Inspired by Zhidkov's work on the stability of time-periodic, spatially homogeneous states in the nonlinear Schrödinger equation, we develop an alternative method that relies on an amplitude-phase decomposition and leverages conserved quantities tailored to the perturbation equation. We establish an orbital stability result of plane waves that is locally uniform in space, accommodating L2-localized perturbations as well as nonlocalized phase modulations. In certain regimes, our method even allows for unbounded modulations. Our result is sharp in the sense that it holds up to the spectral stability boundary
Cutting Power Model for Material Identification during Helical Milling of Aerospace Stacks
No full textInternational audienceSmart factories increasingly rely on real-time data to optimize manufacturing, yet machining operations, particularly in aerospace stack drilling, still face challenges such as low productivity and accelerated tool wear. While advanced CNC machines already capture rich process data, its full potential for real-time decision-making remains underexplored. This work introduces a novel approach that leverages machine learning (ML) to identify material layers and optimize cutting conditions during drilling (helical milling) of aluminum–titanium stacks. Unlike prior methods that require additional sensors or complex instrumentation, our approach uniquely utilizes only spindle power signals from the CNC machine. Data maps consisting of cutting coefficients are used to train ML models to reliably predict material transitions across multiple layers under a range of cutting conditions. The results demonstrate appropriate material identification in comparison to experiments, enabling significant improvements in the hole-making of aerospace stacks. This study contributes a scalable, sensor-free, and non-intrusive framework for smart machining, establishing a practical pathway for process optimization in aerospace manufacturing without disrupting existing shop-floor setups
The Arp2/3 complex maintains gut epithelial integrity under mechanical challenge
No full textInternational audienc
Elimination of cells with local mismatch in differentiation timing contributes to synchronize tissue development
No full textInternational audienceDuring animal development, cells communicate to ensure tissue-wide synchronization of differentiation. While several mechanisms contributing to cell coordination have been described, whether additional mechanisms are at play should cells locally desynchronize remains unknown. Here, we investigate the responses to experimentally induced desynchronized cells during Drosophila epidermis development. We report that cells that behave as if they were ''too young'' or ''too old'', collectively referred to as heterochronous cells, sort out from their normally timed neighbors. Cell sorting is associated with alterations of junctions, cytoskeleton, and cell mechanics. Moreover, local heterochrony ultimately leads to cell elimination. Importantly, we find that some cells naturally undergo either premature or delayed differentiation during development and are similarly eliminated from the tissue. These results show that local imbalance in differentiation timing affects both cell interactions and mechanics, leading to cell sorting, and elimination as a way to correct local heterochrony and safeguard the synchrony of epithelium differentiation
The “sexual selection hypothesis” for the origin of aposematism
No full textInternational audienceThe evolution of aposematism, in which prey exhibit conspicuous signals indicating the presence of antipredator defenses, is puzzling. Before predators learn to associate the signal with defense, increased visibility makes the conspicuous prey highly vulnerable to predation. Although several hypotheses have been proposed to explain the evolution of aposematism, they often assume that these signals can only be recognized by predators. Yet, many studies show that aposematic signals can also be involved in mate choice. Here, we demonstrate that some aposematic signals may have originally evolved as mating signals driven by sexual selection. In this study, we analyze a mathematical model to explore how sexual selection can drive the evolution of aposematism. We thereby identify key features of this “sexual selection hypothesis” for the origin of aposematism to be tested with empirical data. Our results show that the evolution of conspicuous signals through sexual selection increases the visibility of prey to predators and thus predation pressure. This, in turn, promotes the evolution of defense mechanisms, ultimately leading to aposematism when predators learn to associate the signal with defense. Additionally, we show that when sexual selection drives the evolution of aposematism, it often results in sexual dimorphism in both signaling and defense traits
Evaluating the Performance of Sentinel‐1 SAR Derived Snow Depth Retrievals Over the Extratropical Andes Cordillera
No full textInternational audienceMonitoring and estimating mountain snowpack mass over regional scales is still a challenge because of the inadequacy of observational networks in capturing spatiotemporal variability, and limitations in remotely sensed retrievals. Recent work using C-band synthetic aperture radar (SAR) backscatter data from the Sentinel-1 satellite mission has shown good promise for tracking mountain snow depth over specific northern hemisphere ranges, although the broader potential is still unknown. Here, we extend the new Sentinel-1 based modeling framework beyond the northern hemisphere by only utilizing globally available input data, and evaluate different model parametrization and model performance over the Chilean and Argentine Andes mountains, which contain the largest mountain snowpack in the southern hemisphere. The accuracy of Sentinel-1 snow depth estimates is evaluated against an extensive in situ network available for the region. Satelliteretrieved snow depth is found to have poorer performance across the Andes than observed for northern hemisphere mountain ranges because of greater sensitivity to evergreen forest cover and shallower snowpacks. The algorithm does offer some skill but performance is variable and site-dependent. Algorithm performance is best over regions with limited evergreen forest cover (<15%) and snow depths greater than 0.75 m, although the retrievals over-estimate snow depth across most sites. Systemic errors for specific snow classes and across different snow depths are shown, highlighting specific areas in need of further investigation and development
Impact of climate change on snow supply in Trojena, Saudi Arabia
No full textInternational audienceTrojena is a mountain resort under construction in the Midian Mountains, Saudi Arabia as part of the NEOM project and the host site for the 2029 Asian Winter Games. The development of a ski resort in this desertic region has sparked debate about its sustainability. Here we examine the potential snow supply in Trojena under present and future climate. We use downscaled ERA5 data and a snowpack model accounting for snow management to simulate the artificial snow production. We simulate the snowpack under future climate using the 2050's projected temperature change from the CMIP6 dataset under the SSP2-4.5 scenario. We find that artificial snow production can support a median of 68 skiable days in the highest elevation area of the resort in present conditions and 57 days in the 2050's period with an increase in the interannual variability. In the low elevation area, the median number of skiable days is 52 in present conditions and 0 in the 2050's despite artificial snow production capacity. We conclude that climate change strongly compromises the utility of the planned infrastructure
Pirates of the Caribbean (and elsewhere): three-legged lizards and the study of evolutionary adaptation.
No full textInternational audienceNatural selection is widely considered responsible for the fit between organisms and their environment. Lizard limb length variation is a paradigmatic example: studies have shown that limb length differences tightly correlate with habitat use among species, while small differences in limb length between individuals can affect biomechanical function, fitness, and survival within populations. It has therefore been surprising for many field biologists to find otherwise-healthy wild lizards with damaged or missing limbs, appearing to challenge associated expectations of substantial fitness costs. We document limb loss (from a foot to an entire limb) in 58 lizard species, with all cases showing healed limbs and many lizards appearing robust and healthy. Data indicate that limb-deficient lizards typically comprise less than 1% of populations and often exhibit body condition, sprint speed performance, and survival comparable to limb-intact individuals. We discuss the implications of these findings for how evolutionary adaptation is studied and understood in natural populations and provide a perspective on conventional assumptions about the strength and ubiquity of selection pressures on seemingly critical traits. Is natural selection always as omnipresent as Darwin envisioned it to be
Lifecycle Collaborative Planning for Traction Power Supply Systems With Integrated Energy Access
No full textInternational audienceAs global energy transition and electrified transportation continue to advance, traction power supply systems (TPSS) are becoming increasingly vital in rail transit. To solve problems that traditional planning for TPSS often overlooks the integrated energy access and the collaborative optimization of economic security throughout the life cycle, a lifecycle economic-security collaborative planning (LE-SCP) model for TPSS with integrated energy access (IEA-TPSS) is proposed. This model integrates an equipment performance correction matrix (EPCM) to address the performance degradation over the lifecycle of equipment. In addition, it considers N−1 security to ensure the resilience of IEA-TPSS under contingent conditions. Furthermore, a scenario-based hierarchical decomposition (SHD) method is introduced to solve this model. A case study analysis using actual data was conducted to validate the LE-SCP model and SHD method. The simulation results show that the LE-SCP model and the SHD method effectively address the comprehensive lifecycle planning issues of IEA-TPSS, considering both equipment degradation and N−1 security. Moreover, compared to traditional solution algorithms, the proposed SHD method can effectively reduce the model-solving time by 8.61