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Producing a new in-situ wind speed product for the Southern Ocean based on acoustic meteorology from biologged southern elephant seals
No full textInternational audienceObtaining in-situ wind speed measurements over the Ocean is paramount to i) better calibrate numerical models and satellite imagery and ii) increase our understanding of upper ocean processes such as Mixed Layer Depth (MLD) dynamics and air–sea gas exchanges. For instance, increasing wind speeds deepen the MLD through surface turbulence and mixing. In this study, we evaluate the use of acoustic meteorology as an alternative to conventional reanalysis and scatterometer products by training regression models and Long Short-Term Memory (LSTM) neural networks on passive acoustic data recorded from biologged elephant seals. The study presents the first LSTM fine-tuned on wind speed data products from the China-France Oceanography SATellite (CFOSAT) mission, exhibiting remarkably low errors with an average error over all deployments of 0.86 m/s . Using an innovative validation protocol, by correlating wind speed predictions with co-located MLD measurement, the different models are compared. All models’ wind speed predictions exhibit better correlation coefficients with the MLD than the ERA5 re-analysis wind speed products, underscoring the added value of acoustic meteorology in resolving ocean-atmosphere coupling. This work highlights the potential of passive acoustic monitoring as a robust, scalable, and accurate tool for oceanographic and climate studies
Linking deterministic and stochastic aspects of the seafloor's acoustic response in the context of seabed mapping with echosounders
No full textInternational audienceIn the different contexts where the monostatic acoustic seafloor response (ASR) is employed (i.e., measurements with multibeam or singlebeam echosounders, applications in seabed mapping, theoretical models with physical or heuristic parameters), its intrinsic nature can be ambiguous. In this article, an analysis of the discrepancies in semantics is proposed, and then the ASR theoretical and physical definitions are recalled. In theoretical models, and while it is acquired at sea, the ASR is shown to be considered as a deterministic parameter. However, a large variability in its measurements with echosounders is observed, suggesting ASR to be physically a stochastic variable. These two seemingly contradictory observations are linked analytically based on a point scattering model. The theoretical and deterministic ASR is related to its stochastic measurements as the expected value. Based on this connection and under the hypotheses of seafloor homogeneity and large insonified areas, the monostatic ASR measured by echosounders (i.e., the backscattering strength) is derived as twice the parameter of the Rayleigh distribution. Relationships between this result and seabed characteristics are discussed, along with their implications for echosounder operations
Long time behaviour of the solution of Maxwell's equations in dissipative generalized Lorentz materials (II) A modal approach
No full textCe document HAL est une version légèrement plus détaillée (environ 6 pages additionnelles) de l'article qui apparaîtra dans la revue Journal de Mathématiques Pures et Appliquées.International audienceThis work concerns the analysis of electromagnetic dispersive media modelled by generalized Lorentz models. More precisely, this paper is the second of two articles dedicated to the long time behaviour of solutions of Maxwell's equations in dissipative Lorentz media, via the long time decay rate of the electromagnetic energy for the corresponding Cauchy problem. In opposition to the frequency dependent Lyapunov functions approach used in [Cassier, Joly, Rosas Martínez, Z. Angew. Math. Phys. 74 (2023), 115], we develop a method based on the spectral analysis of the underlying non-self-adjoint operator of the model. Although more involved, this approach is closer to physics, as it uses the dispersion relation of the model, and has the advantage to provide more precise and more optimal results, leading to distinguish the notion of weak and strong dissipation
Fatigue crack closure assessment by wavelet transform of infrared thermography signals
No full textInternational audienceThe occurrence of crack closure significantly impacts the fatigue life of materials and structural components. Whether it is induced by the nature of the loading, the fabrication process or the geometry of the structure, its magnitude and effect should be considered to further improve predictive models of fatigue crack propagation. However, the definition of reliable experimental methods for the observation and assessment of fatigue crack closure, and in particular suited to structure testing, remains a challenge. The present study aims to provide a novel approach for the assessment of fatigue crack closure via the continuous wavelet transform of infrared thermography data. The processing of the temperature signal close to the crack in a coherent time-frequency space allows for the identification of crack closing and opening instants associated with high-frequency components. The method is meant to be suited to any testing configuration (conventional compact tension specimen or full-scale structures) with minimum operator-dependent parameters
A semi-analytical model for low-density impact-based surface treatments: Application to the abrasive waterjet texturing of thermoplastic polymers
No full textInternational audienceSurface roughness is critical for bonding applications, as it directly influences the mechanisms occurring at the adhesive interface. Abrasive Waterjet texturing has emerged as a promising technique for functionalizing surfaces, but predicting the surface characteristics from stochastic impact-based processes remains a challenge. This study aimed to develop a numerical model capable of forecasting key morphological parameters for AWJ-textured surfaces with pilotable treatment coverage. The proposed model was optimized through theoretical analysis and confronted to topographical data from polymer samples treated with low-density AWJ using standard parameters. Profilometry measurements were supported by a custom post-treatment algorithm to remove artefacts and assess the characteristics of individual particle impacts (number, repartition, dimensions). The predicted roughness showed a 94 % concordance to the measured values
Self-triggered strong-field QED collisions in laser-plasma interaction
No full textInternational audienceExploring quantum electrodynamics in the most extreme conditions, where electron-positron pairs can emerge in the presence of a strong background field, is now becoming possible in Compton collisions between ultraintense lasers and energetic electrons. In the strong-field regime, the colliding electron emits rays that decay into pairs in the strong laser field. While the combination of conventional accelerators and lasers of sufficient power poses significant challenges, laser-plasma accelerators offer a promising alternative for producing the required multi-GeV electron beams. To overcome the complexities of colliding these beams with another ultraintense laser pulse, we propose a novel scheme in which a single laser pulse both accelerates the electrons and collides with them after self-focusing in a dedicated plasma section and reflecting off a plasma mirror. The laser intensity boost in the plasma allows the quantum interaction parameter to be greatly increased. Using full-scale numerical simulations, we demonstrate that a single 100 J laser pulse can achieve a deep quantum regime with electric fields in the electron rest frame as high as times the Schwinger critical field, resulting in the production of about 40 pC of positrons
Impact of pre-softening on rubber adhesion
No full textInternational audienceThe effect of stress softening, namely the Mullins effect, on elastomers' mechanical properties such as fatigue, strength, or toughness is widely studied, but mainly on bulk materials. The present contribution presents experimental evidence that applying a pre-softening load may significantly alter the critical strain energy release rate (SERR), which controls the interface adhesion between a soft solid and a rigid substrate. Here, we focus on the adhesion of a natural rubber matrix to a single metal wire, characterized using the Rubber Cord Adhesion Inflation Test. This protocol allows for the observation of a stable steady-state crack propagation under an axisymmetric configuration. An experimental protocol is proposed that utilizes a pre-load sequence to achieve a controlled softening of the rubber sheath surrounding the wire. Quantification is carried out through numerical simulations and subsequent material characterization. The adhesion results indicate that the pre-loading sequence reduces the specimen's overall resistance to decohesion. A more detailed analysis reveals that the critical SERR value is also lower. These findings provide new insights into the role of energy dissipation, both within the bulk material and at the interface level, in influencing the interface failure between an elastomer matrix and a rigid reinforcement
Analytical computation of five unresolved integrals in the linear theory of partially cavitating hydrofoils
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Workshop: Mapping the Futures of European and International Space Governance
No full textInternational audienceWorkshop dedicated to imagining the future of space governance
Submarine Cable Tracking in Forward Looking Sonar Images
No full textInternational audienceThe work presented here is dedicated to the detection of submarine cable using FLS (Forward Looking Sonars). In a first part, a presentation of the dataset is realized. The data were collected in the Bay of Douarnenez (near Brest, France) with the Hector 7 ROV (Remotely Operated Vehicle) deployed from the “Pierre de Fermat” Orange Marine cableship, following a zig-zag trajectory so as to cross the cable while adjusting the heading. The different steps of the image processing are detailed. A preprocessing step includes successively an image normalization according to the angle and the distance, an incoherent combination of successive pings in order to improve the SNR (signal to noise ratio) and an image rotation so as to present the cable horizontally. The next processing step consists in template matching. After defining the template, it is used as a kernel to enhance cable saliency in FLS images by taking the absolute difference between correlation and convolution. The cable is then detected by a percentile-based thresholding. False alarms are removed by a tracking process, based on apparent motion in the images sequence. Plotting the cable positions in a GIS (Geographic Information System) demonstrates the ability of the proposed method to locate the cable with a reasonable accuracy