Portail HAL Ensta
Not a member yet
11080 research outputs found
Sort by
A stochastic volume approach based on tailored Green’s functions for airfoil noise prediction at low Mach number
No full textInternational audienc
Mécanique de la rupture et chargement cyclique en transformations finies
No full textInternational audienceOn présente quelques aspects de la mécanique de la rupture des milieux hyperélastiques, on montre en particulier que les champs asymptotiques de contraintes et de déformations n’ont pas les mêmes singularités que ceux des champs en petite transformation, on montre par ailleurs les difficultés inhérentes à la détermination des caractéristiques associées à la rupture.On présente une approche globale de l’effet Müllins et l’implication d’une déformation rémanente à la décharge. On présente quelques conséquences de ces déformations sur la réponse d’une structure précédemment déformée. On propose un modèle simple pour caractériser la réponse cyclique des élastomère
Human Gesture Recognition with a Flow-based Model for Human Robot Interaction
No full textInternational audienc
Modeling effective elastic and thermal conductivity of composite materials reinforced with plastic waste: Analytical and numerical approaches
No full textInternational audienceThe properties of materials used in building are enhanced by adding nanoparticles for improve energy efficiency. The objective of this study is to offer both numerical and analytical modeling methods of the thermal conductivity and mechanical property of composite materials. Various mineral charges were employed to reinforce the organic matrices of saturated polyester resin (UPR) with calcium carbonate (CaCo3) and expanded perlite particles. The study employs the finite-element software COMSOL to conduct a numerical investigation of thermal transport in an elementary cell. The purpose is to ascertain the thermal conductivity of composites and examine the impact of contact resistance and the volume fraction of nanoparticles on the effective thermal conductivity. The results indicate that the numerical model proposed is consistent with the Hashin-Shtrikman analytical model and experimental measurements. In another hand, the mechanical property is computed based on Mori-tanaka analytical model of homogenization and finite element method by Digimat-MF/FE, which gives enhanced elastic behavior of composite in function of volume fraction of nanoparticles, with high Young modulus and low Poisson ratio. The results indicate the performance of nanoparticles in improving thermomechanical behavior of building materials, and also in other applications
Target strength of Cyclothone species with fat-filled swimbladers
No full textInternational audienceThe use of acoustic scattering models provide estimates of single target echoes that allow acousticians to convert acoustic information into biologically meaningful measures. The literature on organisms’ target strength is extensive but is mainly focused on commercial stocks of small pelagic fishes and zooplankton species. A few models of swimbladdered fishes of the mesopelagic zone are also available. However, deep species of the lower mesopelagic and bathypelagic zones tend to have regressed swimbladders or lack one. These habitats have low numerical densities and thus single target studies and angle variation are of particular relevance. Cyclothone spp, the most abundant fishes in the planet and a major constituent of the biomass in the bathypelagic zone, possess gas-filled swimbladders in the upper mesopelagic zone and in larvae stages of all species, but deeper species gradually fill their swimbladder with age. They thus change from a gas-bearing acoustic scattering to a fluid like type. This study applies the Kirchoff Ray Mode (KRM) model based on real fish body shapes of Cyclothone individuals derived from photographs of organisms captured along the year in the Bay of Biscay in order to obtain target strength (TS) of these individuals. Width versus standard length (SL) values fitted the following equation: width=0.01+0.02*SL. Estimated TS values in the Rayleigh zone at broadside had significant linear correlations with SL that can be employed as an approximation of their scattering (TS = 35*log10(SL) − 119, TS = 35*log10(SL) − 106 and TS = 35*log10(SL) − 97 at 18, 38 and 70 kHz respectively). TS at 120 and 200 kHz were not significantly correlated with standard length. Changes in fish body sound speed and density values highly vary the TS level. Assuming neutral buoyancy (body density close to surrounding seawater density), mean TS values were located at −91, −85, −78, −77, −80 dB at 18, 38 and 70, 120 and 200 kHz respectively. TS changes with orientation were also considered depicting important variations in echo level as well as in TS spectra. This study provides relevant information on the acoustic characteristics of lower mesopelagic and bathypelagic Cyclothone species that can be employed to better infer knowledge from acoustic recordings in those areas
A Chronology-Based Wave Input Reduction Technique for Simulations of Long-Term Coastal Morphological Changes: An Application to the Beach of Mastichari, Kos Island, Greece
No full textInternational audienceThe main objective of the present paper is to achieve the simulation of the long-term (e.g., annual) morphological evolution (bathymetry and shoreline) of a coastal area (Mastichari beach, Greece) due to wind-generated waves in an accurate and cost-effective way. For this purpose, wave climate schematization techniques are adopted in order to reduce the computational effort without losing or distorting the crucial information. Referring to the current practice, the wave chronology is not considered in detail in these acceleration techniques, and therefore, sea bottom and shoreline evolution are not estimated as a function of time. To fill this gap, a novel and easy-to-use chronology-based wave input reduction method is developed to produce representative wave time series of different intensities and durations. The performance of all the applied techniques in the present study is evaluated, and a comparative analysis is conducted. It is shown that the new chronology-based wave input reduction method can achieve a model run-time reduction of about 70%, while at the same time, it provides satisfactorily accurate results. In general, this research could be useful for coastal engineering studies and coastal zone monitoring, and thus, it would be a valuable tool for coastal engineers and marine scientists
Homogenized transition conditions for plasmonic metasurfaces
No full textInternational audienceThe present study aims to model the optical response of plasmonic metasurfaces made of a periodic arrangement of metallic particles with arbitrary shape and subwavelength dimensions. By combining homogenization with quasistatic plasmonic eigenmode expansion, the metasurface is replaced by a zero-thickness interface associated with frequency-dependent effective susceptibilities. The resulting discontinuities of the fields are responsible for strong interaction with the incoming light at the resonances when the complex permittivity of the metal passes close to the real permittivity of an eigenmode. Our modeling provides a physical picture of resonances in plasmonic metasurfaces, and it allows for a huge decrease in the numerical cost of their computations. In addition, comparisons with direct numerics in two dimensions evidence its predictive force at any incidence, particle shape, and arrangement
Perfect Resonant Absorption of Guided Water Waves by Autler-Townes Splitting
No full textInternational audienceThe control of guided water wave propagation based on the Autler-Townes splitting resonance concept is demonstrated experimentally, numerically, and theoretically. Complete wave absorption is achieved using an asymmetric pointlike scatterer made of two closely spaced resonant side channels connected to a guide and designed so that its energy leakage is in perfect balance with the inherent viscous losses in the system. We demonstrate that the nature of the resonators and guide junction completely controls the positions of the wave numbers at the reflection and transmission zeros on the real axis; the asymmetry of the resonators completely controls their positions on the imaginary axis. Thus, by adjusting these two independent parameters, we obtain a zero reflection and transmission
