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A multi-scale experimental investigation for fatigue limit and fatigue crack initiation behavior of powder bed fusion-laser beam 316L stainless steel
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A complex-scaled boundary integral equation for time-harmonic water waves
No full textInternational audienceThis paper presents a novel boundary integral equation (BIE) formulation for the two-dimensional time-harmonic water-waves problem. It utilizes a complex-scaled Laplace's free-space Green's function, resulting in a BIE posed on the infinite boundaries of the domain. The perfectly matched layer (PML) coordinate stretching that is used to render propagating waves exponentially decaying, allows for the effective truncation and discretization of the BIE unbounded domain. We show through a variety of numerical examples that, despite the logarithmic growth of the complex-scaled Laplace's free-space Green's function, the truncation errors are exponentially small with respect to the truncation length. Our formulation uses only simple function evaluations (e.g. complex logarithms and square roots), hence avoiding the need to compute the involved water-wave Green's function. Finally, we show that the proposed approach can also be used to find complex resonances through a \emph{linear} eigenvalue problem since the Green's function is frequency-independent
EPOS-France - GPSMob data - Mission n° 09-230 - Toulouse (2009) - 2009-09-22 / 2009-10-17 - 2 points
No full textData setEPOS-France - GPSMob data from the mission n°09-230 in Toulouse (2009).Responsibles: Bosser. Mission started on 2009-09-22 and ended on 2009-10-17. Data were measured on 2 points. The data for each mission is organized in several subdirectories: (i) raw: contains what has been identified as raw data, if ever provided; (ii) rinex: contains the rinex files, possibly split by day, renamed in lower case and with the most likely point name, in d.Z format; (iii) meta: contains all other files (calculation configuration files, field logs, photos, etc.) The automatic verification procedure generates station.info.insu and compte_rendu_de_traitement_insu.txt files
A robust inverse scattering method based on shape optimization
No full textInternational audienceIn this work, we develop a robust method to retrieve the shape of a metallic object from partial electromagnetic measurements containing noise. The numerical resolution of the inverse problem is tackled through parametric shape optimization. To make the method robust, the expectation of the Kohn-Vogelius cost function is minimized here: the key point is to use the so-called Karhunen-Loève expansion in order to obtain an explicit deterministic shape gradient. Then, the optimization problem is solved using a Nesterov gradient scheme. Numerical tests are provided to highlight the advantages and the efficiency of the proposed method
Numerical investigation of thermal buckling and post-buckling behavior of an EN AW 6016-T4 car roof assembled in a steel body-in-white
No full textInternational audienceThe automotive industry is undergoing significant changes driven by factors such as reducing carbon dioxide emissions, advancing technology, evolving regulations, and the emergence of new energy sources. Lightweight materials, particularly aluminum alloys, are being extensively researched and integrated into vehicles to reduce weight and improve performance. However, the heating process during vehicle production can cause thermal buckling in thin aluminum alloy structures, affecting their appearance and quality. While thermal buckling has been studied in other industries, research in the automotive sector, particularly for non-structural parts like car roofs, is limited. This study uses numerical simulation to predict thermal buckling and post-buckling behavior of a EN AW 6016-T4 alloy car roof assembled in a predominantly steel body-in-white. The research findings indicate that roof buckling occurs at a relatively low temperature difference of approximately 60 °C, which is lower than the maximum temperatures experienced during the painting phases in the automotive industry. Consequently, undulations in the roof's shape become apparent, underscoring the importance of design modifications to ensure visual conformity. Validation through physical testing confirms the model's accuracy, providing valuable insights for designing lightweight structures with improved performance and aesthetics
Monitoring Association Constraints in Model-Oriented Programming
No full textInternational audienceAssociations are a key concept in modeling languages as a way to formalize the relationships between domain concepts. Unfortunately, the support of semantically rich associations able to represent complex relationships is often missing, and this is both at the model and code level. At the model level, complex constraints on associations are often represented by using external, textual constraint languages which are difficult to understand and to maintain. At the code level, the situation is even worse, as mainstream object-oriented languages lack direct support for associations. In order to alleviate this problem, in this paper we propose a reification of complex association constraints so that they can be easily specified at development time and monitored at runtime. We do this by leveraging PAMELA, an annotation-based Java modeling framework, which promotes blending classical programming with modeling through the use of annotations and runtime code instrumentalization and monitoring. PAMELA is in the scope of Model-Oriented Programming approaches. We provide a classification of association constraints and discuss different implementation strategies. Finally, we demonstrate the feasibility of our approach with a prototype implementation and an initial catalog of association patterns
Mid-infrared frequency domain optical parametric amplifier
No full textInternational audienceWe report on an optical architecture delivering sub-120 femtosecond laser pulses of 20 µJ tunable from 5.5 µm to 13 µm in the mid-infrared range (mid-IR). The system is based on a dual-band frequency domain optical parametric amplifier (FOPA) optically pumped by a Ti:Sapphire laser and amplifying 2 synchronized femtosecond pulses each with a widely tunable wavelength around 1.6 and 1.9 µm respectively. These amplified pulses are then combined in a GaSe crystal to produce the mid-IR few-cycle pulses by means of difference frequency generation (DFG). The architecture provides a passively stabilized carrier-envelope phase (CEP) whose fluctuations has been characterized to 370 mrad RMS
Complete characterization of a Yb-based OPA at a high repetition rate using frequency resolved optical switching
No full textInternational audienceWe demonstrate experimentally that frequency resolved optical switching (FROSt) can be used to characterize ultra-broadband pulses at high repetition rates up to 500 kHz. Specifically, we present the complete temporal characterization of an optical parametric amplifier (OPA), from the supercontinuum (SC) to the second stage of amplification. Simultaneous characterization of co-propagating signal and idler pulses enables retrieval of their group delay, as well as their temporal phase and intensity. Our study focuses on an extensive frequency range spanning the infrared region (1.2 to 2.4 µm) and confirms the strength and convenience of FROSt as a single tool for characterizing a wide range of pulses at high repetition rates
Data-driven Reachability using Christoffel Functions and Conformal Prediction
No full textInternational audienceAn important mathematical tool in the analysis of dynamical systems is the approximation of the reach set, i.e., the set of states reachable after a given time from a given initial state. This set is difficult to compute for complex systems even if the system dynamics are known and given by a system of ordinary differential equations with known coefficients. In practice, parameters are often unknown and mathematical models difficult to obtain. Data-based approaches are promised to avoid these difficulties by estimating the reach set based on a sample of states. If a model is available, this training set can be obtained through numerical simulation. In the absence of a model, real-life observations can be used instead. A recently proposed approach for data-based reach set approximation uses Christoffel functions to approximate the reach set. Under certain assumptions, the approximation is guaranteed to converge to the true solution. In this paper, we improve upon these results by notablyimproving the sample efficiency and relaxing some of the assumptions by exploiting statistical guarantees from conformal prediction with training and calibration sets. In addition, we exploit an incremental way to compute the Christoffel function to avoid the calibration set while maintaining the statistical convergence guarantees. Furthermore, our approach is robust to outliers in the training and calibration set
Application de l'IA au désentrelacement de formes d'onde radar
No full textNational audienceIn a context of increasing geopolitical tensions, electronic warfare is a key challenge in defence issues. Our article intends to investigate AI application to the deinterleaving problem, in other words, radar waveform separation, without prior knowledge. Firstly, we introduce the problem, the input data, and usual deinterleaving methods. So as to take advantage of AI’s capacities, we then detail some of the challenges raised by its application : data frugality, and explainability and real-time requirements.Dans un contexte d'augmentation des tensions géopolitiques, la guerre électronique est un enjeu majeur des problèmes de défense. Notre article se propose d'étudier l'application de l'IA au problème du désentrelacement, autrement dit la séparation de formes d'onde radar, sans connaissance a priori. D'abord, nous présentons le problème, les données d'entrée, et les méthodes usuelles de désentrelacement. Afin de profiter du potentiel de l'IA, nous détaillons ensuite les difficultés de son application : la frugalité des données et les exigences d'explicabilité et de temps réel