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Estimation of frequency-wavenumber diagrams using a physics-based grid-free compressed sensing method
No full textInternational audienceShallow water propagation can be described using modal theory. For low frequency sources, propagated signals are composed of a few dispersive modes, each of them propagating with its own frequencydependent wavenumber. Modal estimation, and particularly wavenumber estimation, is of great interest in seabed characterization but classically requires a large and dense horizontal line array (HLA). The compressed sensing (CS) paradigm, which allows one to reduce the number of sensors, has been used to overcome this limitation. However, CS performance is directly linked to the discrete basis used in the process and is known to degrade with basis mismatch. To mitigate this issue, the current paper proposes a physics-based grid-free approach to perform wavenumber estimation using a HLA with a limited number of sensors and a single broadband source. The proposed method has three main features: it starts with a speed correction to prevent wavenumber aliasing (using water sound speed at the array location), it then embeds physical prior (the modal dispersion relation) at the core of the CS framework, followed by a CS grid-free approach. The performance of the method is quantified on simulated data using the Jaccard's distance. The method is then applied successfully on experimental data from the 2017 Seabed Characterization Experiment
Could Smart Specialization contribute to dynamic regional resilience?
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Bidirectional Interactions With Humpback Whale Singer Using Concrete Sound Elements
No full textInternational audienceWe describe an art–science project called “Feral Interactions—The Answer of the Humpback Whale” inspired by humpback whale songs and interactions between individuals based on mutual influences, learning process, or ranking in the dominance hierarchy. The aim was to build new sounds that can be used to initiate acoustic interactions with these whales, not in a one-way direction, as playbacks do, but in real interspecies exchanges. Thus, we investigated how the humpback whales generate sounds in order to better understand their abilities and limits. By carefully listening to their emitted vocalizations, we also describe their acoustic features and temporal structure, in a scientific way and also with a musical approach as it is done with musique concrète , in order to specify the types and the morphologies of whale sounds. The idea is to highlight the most precise information to generate our own sounds that will be suggested to the whales. Based on the approach developed in musique concrète , similarities with the sounds produced by bassoon were identified and then were processed to become “concrete sound elements.” This analysis also brought us to design a new music interface that allows us to create adapted musical phrases in real-time. With this approach, interactions will be possible in both directions, from and to whales
La qualité technologique des brevets : deux lectures structurales
No full textInternational audienceL'objectif de l'article est de proposer des lectures structurales de deux indicateurs de la qualité technologique des brevets : l'originalité et la généralité. Nous les transformons pour ce faire en des objets mathématiquesdes « graphes »et nous insistons sur des amendements et prolongements inspirés par cette nouvelle approche. Dans une première lecture, nous partons des indices originels et nous leur appliquons directement une représentation sous la forme de graphes. Dans une deuxième lecture, nous partons de matrices de flux technologiques et nous reconstruisons les indices de dispersion tels qu'ils ont été conçus initialement. Nous allons même un peu plus loin : nous proposons d'autres indices de la qualité technologique à partir de ces matrices, dont un qui nous semble de portée supérieure pour apprécier cette qualité. ABSTRACT. The aim of this article is to propose the structural readings of two indicators of the technological quality of patents: originality and generality. To do so, we transform them into mathematical objects-graphs-and insist on amendments and extensions inspired by this new approach. In the first reading, we start from the original indices and we directly apply a representation in the form of graphs to them. In the second reading, we start from the technological flow matrices and reconstruct the dispersion indices as they were originally conceived. We go even further by proposing other indices of technological quality from these matrices, including one that seems to have a greater scope for assessing this quality. MOTS-CLÉS. Brevet, technologie, théorie des graphes
Numerical Analysis of a Method for Solving 2D Linear Isotropic Elastodynamics with Free Boundary Condition using Potentials and Finite Elements
No full textInternational audienceWhen solving 2D linear elastodynamic equations in a homogeneous isotropic media, a Helmholtz decomposition of the displacement field decouples the equations into two scalar wave equations that only interact at the boundary. It is then natural to look for numerical schemes that independently solve the scalar equations and couple the solutions at the boundary. The case of rigid boundary condition was treated In [3, 2]. However in [4] the case of free surface boundary condition was proven to be unstable if a straight- forward approach is used. Then an adequate functional framework as well as a time domain mixed formulation to circumvent these issues was presented. In this work we first review the formulation presented in [4] and propose a subsequent discretised formulation. We provide the complete stability analysis of the corresponding numerical scheme. Numerical results that illustrate the theory are also shown
Direct measurement of steady fluid forces upon a deformed cylinder in confined axial flow
No full textInternational audienceThis paper addresses the case of a cylinder array in axial flow at Reynolds numbers from 60 000 to 110 000. A comprehensive experimental and numerical study of the steady fluid forces arising from a geometrical perturbation in the array arrangement is carried out and compared with a semi-empirical model from the literature. The test rig consists of a 3x3 confined cylinder bundle with a pitch-to-diameter ratio equal to 1.33. The central cylinder can be rotated, translated orbent. Global forces and moments as well as pressure profiles at several sections are measured.Velocity profiles at both sides of the cylinder are also collected. Additionally, RANS simulations (Reynolds-averaged Navier–Stokes) are carried out. Pressure loss effects similar to the ones occurring in hydraulic pipes are found to play a major role on the velocity field. Rotation tests are in agreement with the literature: at low angles of incidence, the lift force is proportional to the angle. The supporting rod at the centre of the cylinder strongly disturbs the local lift force but does not change the global linear trend. In translation, the wake of the support generates afluid stiffness effect. Bending tests allow to assess all terms of the semi-empirical model from the literature, which proves to be quite accurate at a sufficient distance from the ends and from the supports. In addition, the investigation provides refined quantitative measurements of local and global force coefficients of the statically deformed cylinder in rotation, translation and bending
A stable, unified model for resonant Faraday cages
No full textInternational audienceWe study some effective transmission conditions able to reproduce the effect of a periodic array of Dirichlet wires on wave propagation, in particular when the array delimits an acoustic Faraday cage able to resonate. In the study of Hewett & Hewitt (2016 Proc. R. Soc. A 472 , 20160062 ( doi:10.1098/rspa.2016.0062 )) different transmission conditions emerge from the asymptotic analysis whose validity depends on the frequency, specifically the distance to a resonance frequency of the cage. In practice, dealing with such conditions is difficult, especially if the problem is set in the time domain. In the present study, we demonstrate the validity of a simpler unified model derived in Marigo & Maurel (2016 Proc. R. Soc. A 472 , 20160068 ( doi:10.1098/rspa.2016.0068 )), where unified means valid whatever the distance to the resonance frequencies. The effectiveness of the model is discussed in the harmonic regime owing to explicit solutions. It is also exemplified in the time domain, where a formulation guaranteeing the stability of the numerical scheme has been implemented
Medium and high grazing angle sea-clutter effects on the radar performance located on a drone
No full textInternational audienceIn recent years, small craft used for drug trafficking, smuggling, human trafficking and piracy have posed a growing threat to ocean observations and maritime traffic surveillance. In order to combat such threats, microwave radars have been widely used, for maritime surveillance and target reconnaissance tasks, due to their capabilities to operate in all weathers and day and night. However, maritime radars, and particularly those carried on aircraft (such as drones), are confronted with disturbances due to sea clutter which has a strong impact on the detection function, in particular for observations at very grazing angles. Despite that airborne maritime radars typically operate at low grazing angles, from necessity or to achieve the best detection performance, it has also become important to better understand the characteristics of clutter observed at medium and higher grazing angles to undertake maritime reconnaissance using radar embedded on drones. Thus, with a view to better control of sea clutter in a context of observation via a drone with the development of functions for detecting, locating and tracking targets present in a maritime environment, this paper offers a summary of different modelling and characterization of sea clutter in grazing to very grazing configurations
Three-Dimensional Printing of Honeycomb Microwave Absorbers: Feasibility and Innovative Multiscale Topologies
No full textInternational audienceIn this article, we propose to apply 3-D printing technology to the design and realization of honeycomb microwave absorbers. First, printability of simple honeycomb structures, made of a lossy dielectric material, was evaluated and validated by measurement in the 2-18 GHz frequency band. Effective dielectric properties of honeycomb structures with different dimensions are also discussed. Then, the interest of 3-D printing technology was highlighted by the design, fabrication, and measurement of a multiscale honeycomb absorber that can significantly increase the relative bandwidth. The 3-D printed honeycomb absorbers are compared with others technologies. The potential of this technology was also illustrated by the fabrication and measurement of a pyramidal honeycomb absorber that demonstrates an absorption level of more than 22.9 dB over the 2-18 GHz frequency ban