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Dynamic Swarming Autonomous Underwater Vehicles through Behavioral Rules Using Declarative Programming
No full textInternational audienceThis article proposes a framework for dynamic swarming of Autonomous Underwater Vehicles (AUVs) using declarative programming to enhance underwater exploration and acoustic sensing. By integrating swarm intelligence, bio-inspired behaviors, and declarative rules (Prolog), the system enables adaptive reconfiguration of sensor arrays to optimize the detection and localization of underwater sound sources. The study addresses the challenge of dynamically alternating between vertical and horizontal linear array configurations (critical for estimating depth/range and azimuth, respectively) while maintaining swarm cohesion and collision avoidance. The open-source LRAUV model is employed for hydrodynamic simulations, with trajectories integrated into acoustic simulations combining modal propagation (low frequencies) and ray tracing (higher frequencies). Prolog's declarative paradigm allows high-level specification of formation control rules, collision avoidance constraints, and mission objectives, decoupling mission intent from low-level execution. This approach enables intuitive addition of constraints (e.g., safety radius, separation distances). We validate the framework in a ROS2/Gazebo simulation environment, in which five AUVs execute a circular trajectory, alternating between horizontal and vertical formations. Simulations demonstrate the swarm's ability to dynamically reconfigure formations while respecting non-holonomic motion constraints. In addition, an AUV mule autonomously navigates to collect data from swarm members and proves the scalability of the system for data collection tasks. The results underscore the robustness of the framework to keep formation stability, avoid collisions, and adapt to specific mission requirements
Turbo égalisation pragmatique et complètement adaptative pour les communications sous-marines
No full textInternational audienceAdaptive equalization for underwater acoustic communications represents a major challenge due to the triple selectivityof the channel and its high computational complexity. In this paper, we propose a novel low-complexity turbo equalization algorithmbased on an optimization criterion that takes into account the soft information provided by the decoder, which allows our algorithmto self-adapt to channel variations. Moreover, to preserve spectral efficiency and ensure the convergence of our algorithm, itsparameters are trained multiple times on the same transmitted pilot symbols. Simulation results show that our algorithm achievesbetter performance compared to state-of-the-art methods in terms of bit error rate (BER). Finally, our complexity analysis alsohighlights the advantages of our technique.L'égalisation adaptative pour les communications acoustiques sous-marines représente un grand défi en raison de la triple sélectivité du canal et de sa complexité élevée. Dans ce papier, nous proposons un nouvel algorithme de turbo-égalisation à faible complexité, basé sur un critère d'optimisation qui permet de prendre en compte l'information souple du décodeur. Cela permet à notre algorithme de s'auto-adapter aux variations du canal. De surcroît, afin de préserver l'efficacité spectrale et d'assurer la convergence de notre algorithme, nous entraînons les paramètres de notre égaliseur plusieurs fois sur les mêmes symboles pilotes envoyés. Les résultats de simulation montrent que notre algorithme offre de meilleures performances, par rapport à celles de l'état de l'art en termes de taux d'erreur binaire (TEB). Enfin, notre analyse de complexité illustre aussi l'intérêt de notre méthode.</div
Intégration des contraintes acoustiques dans la génération de trajectoires
No full textInternational audienceOptimal control based trajectory generation offers the ability to formulate complex problems while optimizing the performance of the system control inputs. Nevertheless, adding acoustic constraints to the optimal control problem (OCP) can be highly challenging. The classical resolution approach employs a "first-discretize-then-optimize" strategy using direct methods. However, this approach leads to significant computational costs, which in turn limits its applicability. Recent studies suggest using the acoustic reciprocity theorem (ART) to formulate the problem as one of obstacles collision avoidance. Hence, this study proposes investigating the formulation and solution of an OCP based on this theorem. The ART is combined with the Boundary Element Method (BEM) for the acoustic part of the problem. The OCP is implemented using successive convexification (SCvx) approach which offers a convenient framework to take into account acoustic constraint in trajectory planning generation. Promising experimental results highlight the applicability of our formulation based on the ART and guidelines for further development are provided.</div
Stress intensity factor determination along a kinked crack path by DIC analyses
No full textInternational audienceSharp kinks may be observed under shear loading or in materials containing weak directions, such as those produced by additive manufacturing. A better understanding of the fracture of these materials, both theoretically and experimentally, is required to deploy them in structural applications. This study focuses on the measurement of stress intensity factors (SIFs) around a sharp kink using digital image correlation (DIC). The performances of two DIC-based techniques, namely, integrated-DIC and post-processing of DIC-measured displacement fields, are assessed on a benchmark test using fused deposit modeling capabilities, and are compared to a reference finite element solution. It is shown that Williams' expansion remains valid on a large enough region around the crack to extract reliable SIFs even very close to the crack kink. Both techniques are very trustworthy, provided the SIF identification zone is carefully defined to exclude the kink zone of influence
A Large-Scale Optimization Framework for Simultaneous Design and Routing of Wind-Assisted Ships
No full textInternational audienceThis paper presents a comprehensive approach to optimizing the performance of wind-assisted ships. The proposed optimization framework simultaneously addresses ship routing and design, considering the complex interactions between design parameters and route optimization across multiple weather scenarios. Optimal control methods, including the direct multiple shooting technique and automatic differentiation, are employed to efficiently optimize both routing and design parameters, resulting in a large-scale optimization problem. The methodology is demonstrated through a case study of a 2200-TEU container ship equipped with Flettner rotors, operating on a transatlantic route between Brittany and Halifax. The results provide an objective estimate of fuel savings, highlighting the importance of integrated optimization for wind-assisted propulsion systems, while maintaining computational efficiency suitable for iterative design processes. Compared to conventional methods, this approach drastically reduces optimization times, enabling rapid design iterations and informed decision-making. Furthermore, the study offers insights into the sensitivity of fuel consumption to key design parameters, such as the number and placement of Flettner rotors, providing a more accurate and comprehensive estimate of potential energy savings compared to conventional methods. By overcoming the limitations of traditional polar-diagram-based methods, this framework provides a more accurate and dynamic assessment of wind-assisted propulsion systems. These findings emphasize the necessity of integrated optimization for maximizing performance and sustainability in maritime transport
An entropy penalized approach for stochastic optimization with marginal law constraints. Complete version
No full textInternational audienceThis paper focuses on stochastic optimal control problems with constraints in law, which are rewritten as optimization (minimization) of probability measures problem on the canonical space. We introduce a penalized version of this type of problems by splitting the optimization variable and adding an entropic penalization term. We prove that this penalized version constitutes a good approximation of the original control problem and we provide an alternating procedure which converges, under a so called "Stability Condition", to an approximate solution of the original problem. We extend the approach introduced in a previous paperof the same authors including a jump dynamics, non-convex costs and constraints on the marginal laws of the controlled process. The interest of our approach is illustrated by numerical simulations related to demand-side management problems arising in power systems
Shape optimization of slip-driven axisymmetric microswimmers
No full textInternational audienceIn this work, we develop a computational framework that aims at simultaneously optimizing the shape and the slip velocity of an axisymmetric microswimmer suspended in a viscous fluid. We consider shapes of a given reduced volume that maximize the swimming efficiency, i.e., the (size-independent) ratio of the power loss arising from towing the rigid body of the same shape and size at the same translation velocity to the actual power loss incurred by swimming via the slip velocity. The optimal slip and efficiency (with shape fixed) are here given in terms of two Stokes flow solutions, and we then establish shape sensitivity formulas of adjoint-solution that provide objective function derivatives with respect to any set of shape parameters on the sole basis of the above two flow solutions. Our computational treatment relies on a fast and accurate boundary integral solver for solving all Stokes flow problems. We validate our analytic shape derivative formulas via comparisons against finite-difference gradient evaluations, and present several shape optimization examples
Fiber-based high-energy 1550 nm laser for generating high-order harmonics
No full textInternational audienceThe demand for precise, high-energy Extreme Ultraviolet (EUV) sources is growing across scientific and industrial fields. Studies have demonstrated that bulk crystals driven by mid-infrared laser pulses can generate high-order harmonics with enhanced intensities, extended cut-off energies, and improved damage thresholds [1]. While high-energy OPCPA and OPA systems have been successfully utilized to achieve these results, their complexity highlights the need for simpler, more compact solutions [1, 2, 3]. Ultrafast mid-IR fiber lasers have emerged as a promising alternative for high-harmonic generation (HHG). However, their pulse energies are limited to the nanojoule range [4]. Here, we report the first demonstration of high-order harmonics generated in bulk crystals using a high-energy fiber laser operating near 1550 nm. Our laser system integrates an erbium-doped fiber amplifier with a gas-filled hollow-core photonic crystal fiber (HC-PCF) for post-compression, delivering few-cycle pulses with durations under 50 fs, microjoule-level pulse energies, and a repetition rate of 660 kHz (fig. 1) [5]
A Large-Scale Optimization Framework for Simultaneous Design and Routing of Wind-Assisted Ships
No full textInternational audienceAbstract This paper presents a comprehensive approach to optimizing the performance of wind-assisted ships. The proposed optimization framework simultaneously addresses ship routing and design, considering the complex interactions between design parameters and route optimization across multiple weather scenarios. Optimal control methods, including the direct multiple shooting technique and automatic differentiation, are employed to efficiently optimize both routing and design parameters, resulting in a large-scale optimization problem. The methodology is demonstrated through a case study of a 2200-TEU container ship equipped with Flettner rotors, operating on a transatlantic route between Brittany and Halifax. The results provide a quantitative, model-based estimate of fuel savings, highlighting the importance of integrated optimization for wind-assisted propulsion systems, while maintaining computational efficiency suitable for iterative design processes. Compared to traditional design and routing methods, based on static polar diagrams and sequential design loops, this approach drastically reduces optimization times, enabling rapid design iterations and informed decision-making. Furthermore, the study offers insights into the sensitivity of fuel consumption to key design parameters, such as the number and placement of Flettner rotors, providing a more accurate and comprehensive estimate of potential energy savings compared to conventional methods. By overcoming the limitations of traditional polar-diagram-based methods, this framework provides a more accurate and dynamic assessment of wind-assisted propulsion systems. These findings emphasize the necessity of integrated optimization for maximizing performance and sustainability in maritime transport. Keywords Wind-assisted propulsion; Design optimization; Ship routing; Large-scale optimizatio
Differentiable Optimisation: Theory and Algorithms -- Part II: Algorithms
No full textEngineering schoolThis course follows naturally OPT201, which covers the theory part of continuous optimisation. OPT201 focuses on optimality conditions, convexity, and duality. In OPT202, we will look at how to use these notions to build algorithms that solve the problems. In particular, the aim of the course is to be able to answer the questions, 1. Given an optimisation problem, which algorithm do I use to solve it? 2. Which properties and theoretical guarantees does the algorithm that I have chosen have? 3. Conversely, if I want to use a certain algorithm, which characteristics does the optimisation problem need to have? In order to answer to these three questions, we will need to build a theory of algorithms, and ultimately understand what we really mean by solving an optimisation problem