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Study of underwater biodiversity in Lake Guerlédan (France) using acoustic systems: A student project at ENSTA Bretagne
No full textInternational audienceSeit 2016 nehmen jedes Jahr Studierende der ENSTA Bretagne, die auf Hydrographie/Ozeanographie und Meeresrobotik spezialisiert sind, an einem Feldprojekt am Guerlédan-See in der Bretagne (Frankreich) teil. Eines der Themen, an denen sie arbeiten, ist die Untersuchung der Artenvielfalt im See mit Hilfe akustischer Systeme. In Zusammenarbeit mit Forschungsinstituten wie Ifremer und unter der Leitung ihrer Beraterin Irène Mopin setzen sie professionelle Echolote ein, um die Echos aus der Wassersäule in Tiefen bis zu 40 m zu analysieren. Jedes Jahr werden die Ergebnisse der vorherigen Gruppe genutzt, um die Verarbeitungstechniken zu verbessern, und es kommen neue Besonderheiten hinzu, wie zum Beispiel die Beschallung der Daten.Each year since 2016, students of ENSTA Bretagne specialised in hydrography/oceanography and marine robotics participate to a field project on Lake Guerlédan in Brittany (France). One of the subjects they work on is the study of biodiversity in the lake using acoustic systems. In collaboration with research institutes such as Ifremer and directed by their advisor Irène Mopin, they are using professional echo sounders in order to implement analyses of water column echoes in depths up to 40 m. Each year, results of the previous group are used to improve processing techniques and new specificities are added such as the sonification of data
Numerical Investigations of a Two-Way Coupled Fluid–Structure Interaction Approach for Fast Transients in Fluid-Filled Flexible Piping Systems
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Optimization Filters for Stochastic Time-Varying Convex Optimization
No full textInternational audienceWe look at a stochastic time-varying optimization problem and we formulate online algorithms to find and track its optimizers in expectation. The algorithms are derived from the intuition that standard prediction and correction steps can be seen as a dynamical system and a measurement equation, respectively, yielding the notion of filter design. The optimization algorithms are then based on an extended Kalman filter in the unconstrained case, and on a linear matrix inequality condition in the constrained case. Some special cases and variations are discussed, and supporting numerical results are presented from real data sets in ride-hailing scenarios. The results are encouraging, especially when predictions are accurate, a case which is often encountered in practice when historical data is abundant
Reconstruction of trajectories of athletes using computer vision models and kinetic analysis
No full textInternational audienceAthlete's pose acquisition and analysis is promising to provide coaches with details of athletes performance and thus help to improve athletes' performances with more detailed supervision from coaches. Compared with traditional ways of acquiring an athlete's gesture, such as using wearable sensors, computer vision technology has advantages of low-cost, high-efficient and non-intrusive. This paper aims to bridge these two fields, by reconstructing athletes' trajectory using monocular (i.e. single-camera-shot) videos. Under a few assumptions that are applicable to most of the sports of athletics, we proposed a method combining computer vision techniques and physics laws to reconstruct athletes' trajectories from monocular videos. The method first estimates 3D pose of athletes from video inputs, then performs kinematic analysis on estimated poses to reconstruct the trajectories of athletes. We tested this algorithm on videos from the triple jump finals of the 2016 Olympics in Rio de Janeiro. We achieved a best performance with 9.1% mean average error when using ground-truth foot-ground contact signal and 21.4% mean average error when using predicted foot-ground contact signal
FDM technology and the effect of printing parameters on the tensile strength of ABS parts
No full textInternational audienceThe effect of printing speed on the tensile strength of acrylonitrile butadiene styrene (ABS) samples fabricated using the fused deposition modelling (FDM) process is addressed in this research. The mechanical performance of FDM-ABS products was evaluated using four different printing speeds (10, 30, 50, and 70 mm/s). A numerical model was developed to simulate the experimental campaign by coupling two computational codes, Abaqus and Digimat. In addition, this article attempts to investigate the impacts of printing parameters on ASTM D638 ABS specimens. A 3D thermomechanical model was implemented to simulate the printing process and evaluate the printed part quality by analysing residual stress, temperature gradient and warpage. Several parts printed in Digimat were analysed and compared numerically. The parametric study allowed us to quantify the effect of 3D printing parameters such as printing speed, printing direction, and the chosen discretisation (layer by layer or filament) on residual stresses, deflection, warpage, and resulting mechanical behaviour
Brunovsky decomposition for dynamic interval localization
No full textInternational audienceThis paper proposes a new set-membership method for estimating the trajectories of dynamical systems, when the states are completely unknown and only non-linear observations are available. The first part of the proposed method is symbolic and follows the decomposition of Brunovsky, i.e., it decomposes the set of differential equations describing the dynamical system into two blocks of constraints: one block gathers non-linear analytical equations that do not involve differential operators, while the other block is composed of linear chains of integrators. The second part of the method, that relies on the symbolic decomposition, is numerical and based on a contractor approach. It involves a specific optimal operator for narrowing the sets of feasible solutions. This approach is shown to be efficient on a difficult problem of dynamic localization of a mobile robot, without any prior knowledge about its states
Analysis of time-harmonic Maxwell impedance problems in anisotropic media
No full textInternational audienceWe consider the time-harmonic Maxwell's equations in anisotropic media. The problem to be solved is an approximation of the diffraction problem, or scattering from bounded objects, that is usually set in some exterior domain in . We consider perfectly conducting objects, so the equations are supplemented with a Dirichlet boundary condition on those objects, and we truncate the exterior domain by imposing an impedance condition on an artificial boundary, to model an approximate radiation condition. The resulting problem is then posed in a bounded domain, with Dirichlet and impedance boundary conditions. In this work, we focus on the mathematical meaning of the impedance condition, precisely in which function space it holds. This relies on a careful analysis of the regularity of the traces of electromagnetic fields, which can be derived thanks to the study of the regularity of the solution to second-order surface PDEs. Then, we prove well-posedness of the model, and we determine the a priori regularity of the fields in the domain and on the boundaries, depending on the geometry, the coefficients and the data. Finally, the discretization of the formulations is presented, with an approximation based on edge finite elements. Error estimates are derived, and a benchmark is provided to discuss those estimates
Dynamic Composite Materials Characterisation with Hopkinson Bars: Design and Development of New Dynamic Compression Systems
No full textInternational audienceThe split Hopkinson pressure bars (SHPB) system is the most commonly employed machine to study the dynamic characteristics of different materials under high strain rates. In this research, a numerical investigation is carried out to study different bar shapes such as square, hexagonal, and triangular cross-sections and to compare them with the standard cylindrical bars. The 3D finite element model developed for circular cross-sectional shapes was first validated with the experimental results and then compared with the other proposed shapes. In most scientific research, cylindrical cross-section bars with a square cross-section specimen are traditionally used as they have several advantages, such as in situ imaging of the side surfaces of the specimen during stress wave propagation. Moreover, the flat surfaces of the proposed shapes counter the problem of debonding strain gauges, especially at high impact pressures. Comparison of the results showed an excellent confirmation of the sample dynamic behaviour and different geometric shapes of the bar geometries, which validates the choice of the appropriate system
