Éditeur(s) : GFP : Groupe Français des Pesticides GFP : Groupe Français des Pesticides GFP : Groupe Français des Pesticides GFP : Groupe Français des Pesticides
Extrait de : "Protection des cultures et santé environnementale : héritages et conceptions nouvelles" : congrès, le 26 mai 2014. Université des Antilles et de la Guyane
Résumé : "Les objectifs de l'étude étaient, en premier lieu, de mettre en évidence les principaux processus impliqués dans la dissipation et le transfert de pesticides à long terme
"Les objectifs de l'étude étaient, en premier lieu, de mettre en évidence les principaux processus impliqués dans la dissipation et le transfert de pesticides à long terme
"Les objectifs de l'étude étaient, en premier lieu, de mettre en évidence les principaux processus impliqués dans la dissipation et le transfert de pesticides à long terme
Siècle(s) traité(s) : 20
Droits : CC-BY-NC-ND - Attribution - Pas d'utilisation commerciale - Pas de modification
Permalien : http://www.manioc.org/fichiers/V14191
V14191
V14191
V14191
V14191
V14191

Éditeur(s) : HAL CCSD
Résumé : International audience
We consider a second-order differential system with Hessian-driven damping . An interesting property of this system is that, after introduction of an auxiliary variable y , it can be equivalently written as a first-order system in time and space. This allows us to extend the analysis to the case of a convex lower semicontinuous potential and so to introduce constraints in the model. When considering the indicator function of a closed convex set, the subdifferential operator takes account of the contact forces. In this setting, by playing with the geometrical damping parameter, we can describe nonelastic shock laws with restitution coefficient. Taking advantage of the infinite dimensional framework, we introduce a nonlinear hyperbolic PDE describing a damped oscillating system with obstacle. The system is dissipative; in the convex case each trajectory weakly converges to a minimizer of the global potential energy function. Exponential stabilization is obtained under strong convexity assumptions.
Differential Equations & Applications

hal-00803214
https://hal.archives-ouvertes.fr/hal-00803214
https://hal.archives-ouvertes.fr/hal-00803214/document
https://hal.archives-ouvertes.fr/hal-00803214/file/Attouch-Mainge-Redont-30August2011.pdf

Éditeur(s) : HAL CCSD
Résumé : 27 pages
Cascade Stochastic Differential Equation (SDE), a continuous time model for energy dissipation in turbulence, is a generalization of the Yaglom discrete cascade model. We extend this SDE to a model in random environment by assuming that its two parameters are switched by a continuous time Markov chain whose states represent the states of the environment. Moreover, a Dirichlet process is placed as a prior on the space of sample paths of this chain. We propose a Bayesian estimation method of this model which is tested both on simulated data and on real data of wind speed measured at the entrance of the mangrove ecosystem in Guadeloupe.
https://hal.archives-ouvertes.fr/hal-00286131

hal-00286131
https://hal.archives-ouvertes.fr/hal-00286131
https://hal.archives-ouvertes.fr/hal-00286131/document
https://hal.archives-ouvertes.fr/hal-00286131/file/Srik11_PhysicaDDspace.pdf

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We present a 2-D Contact Dynamics discrete element model for simulating initiation and motion of rock avalanches, integrating hillslope geometry, Mohr-Coulomb rock behavior, pore pressure before avalanche triggering, and avalanche trigger. Avalanche motion is modeled as a dense granular flow of dry frictional and cohesive particles. On the basis of granular physics and shear experiments, we review some of the theories for the unexpectedly long runout of rock avalanches. Different causes are evoked, according to the strength (strong or weak) of the slip surface relative to the bulk. "Mechanical fluidization'' and "acoustic fluidization'' theories state that agitation of rock particles reduces frictional strength, increasing runout. Conversely, granular mechanics suggests that, as "shear-strain'' rate increases, granular material becomes more agitated, more dissipative, and more resistant. Another theory states that dynamic fragmentation of clasts creates an isotropic pressure that drives longer runout. In contrast, granular mechanics suggests that fragmentation may induce fluidization and strengthening of the granular material, while particle size reduction (among others) induces weakening of the granular flow and enhances long runout. Runout is also enhanced for column-like rock masses collapsing from steep hillslopes. Long runout may also be linked to thermal weakening mechanisms at the slip surface (e.g., thermal pressurization, and shear melting), which may lower drastically the shear strength. The model is illustrated with a hypothetical example of a rain-triggered avalanche, mobilizing shallowly dipping layers. Several phases are identified, including slope failure, avalanche triggering resulting from slip weakening, and avalanche motion in which rocks are folded and sheared.
ISSN: 0148-0227

hal-00420883
https://hal.archives-ouvertes.fr/hal-00420883
DOI : 10.1029/2008JF001072

Éditeur(s) : Elsevier Sci Ltd
Résumé : A multi-scale global hindcast of ocean waves is presented that covers the years 1994-2012, based on recently published parameterizations for wind sea and swell dissipation [Ardhuin, F., Rogers, E., Babanin, A., Filipot, J.-F., Magne, R., Roland, A., van der Westhuysen, A., Queffeulou, P., Lefevre, J.-M., Aouf, L., Collard, F., 2010. Semi-empirical dissipation source functions for wind-wave models: Part I. Definition, calibration and validation. J. Phys. Oceanogr. 40 (9), 1917-1941]. Results from this hindcast include traditional wave parameters, like the significant wave height and mean periods, and we particularly consider the accuracy of the results for phenomenal sea states, with significant heights above 14 m. Using unbiased winds, there is no evidence of a bias in wave heights even for this very high range. Various spectral moments were also validated, including the surface Stokes drift and mean square slopes that are relevant for wave-current interactions modelling and remote sensing, and also spectra of seismic noise sources. The estimation of these parameters is made more accurate by the new wave growth and dissipation parameterizations. Associated air-sea fluxes of momentum and energy are significantly different from what is obtained with the WAM-Cycle 4 parameterization, with a roughness that is practically a function of wind speed only. That particular output of the model does not appear very realistic and will require future adjustments of the generation and dissipation parameterizations.
Ocean Modelling (1463-5003) (Elsevier Sci Ltd), 2013-10 , Vol. 70 , P. 174-188

Droits : 2012 Elsevier Ltd. All rights reserved.
http://archimer.ifremer.fr/doc/00155/26582/25477.pdf
DOI:10.1016/j.ocemod.2012.12.001
http://archimer.ifremer.fr/doc/00155/26582/

Éditeur(s) : HAL CCSD Editions Paralia CFL
Résumé : L'hydrodynamique du plateau continental du Golfe du Lion est généralement induite par les vents. Les simulations numériques réalisées par les modèles numériques de circulation océanique côtière aux équations primitives sont en général cohérentes avec les observations in-situ. Très peu d'observations étaient toutefois disponibles pendant les épisodes de tempêtes méditerranéennes. Aussi, la station BESSète (Bottom Experimental Station Sète), équipée d'un ADCP mesurant en continu les caractéristiques de houle et les profils verticaux de courants, a été implantée sur le plateau sous 70 m. Les premières données issues de cette station, acquises en février-mars 2007, confirment les schémas de circulations induits par les vents de Nord (Mistral,Tramontane). Un épisode de tempête (Hs>5m) a aussi pu être observé le 18 février 2007. De forts courants dont l'intensité peut atteindre 0,7 ms-1 y sont associés. Cette série de données est ensuite utilisée pour calculer les tensions decisaillements induites sur le fond. Sous 70 m, elles sont en général quasi-nulles excepté pendant l'épisode de tempête où l'action conjuguée des houles et des courants peut induire des contraintes susceptibles de mobiliser et déplacer le sédiment fin présent dans la zone. La très forte intensité des courants mesurés pendant la tempête amènent ensuite à reconsidérer les processus de transferts de quantité de mouvement entre atmosphère, océan et sédiments. Très schématiquement, sur le plateau, dès que la houle interagit avec le fond, la houle se transforme (réfraction, dissipation) et transmettrait de la quantité de mouvement à l'échelle des courants moyens. Cette hypothèse est retenue pour expliquer ces forts courants observés et pourrait être confirmée par d'autres travaux théoriques et numériques.
ISSN: 1760-8716

hal-00854000
https://hal.archives-ouvertes.fr/hal-00854000
DOI : 10.5150/jngcgc.2008.011-L

Éditeur(s) : Séminaire CLAROM, 14èmes journées de l'Hydrodynamique, Val de Reuil, 18-20 novembre 2014
Résumé : From measurements obtained at high level frequency over a long period of time, we aim to determine the different characteristics of the flow situated in the IFREMER (French Research Institute for Exploration of the Sea) wave and current flume tank in Boulogne-Sur-Mer. This 2 data measured with a LDV (Laser Doppler Velocimetry) allows to get the characteristics of turbulence and the incident velocity fluctuations. The well-controlled conditions in the flume and the high sampling frequency of LDV system will give us a good estimate of the different flow characteristics such as dissipation, the Reynolds number, the injection scales, Taylor and Kolmogorov. The objective is to place the marine current turbine in this flow and then to study the influence of turbulence on the rotor of this turbine. The flow velocity is imposed and two different rates of turbulence are analysed.
A partir de données à haute fréquence acquises pendant une longue période de temps, on cherche à déterminer les différentes caractéristiques de l’écoulement généré au bassin d’essais à houle et courant d’IFREMER à Boulogne-Sur-Mer. Ces données mesurées avec un système LDV permettent de caractériser la turbulence et les fluctuations de la vitesse du courant incident. Les conditions contrôlées du bassin et les longues périodes d’acquisition du système LDV nous donneront une bonne estimation des différentes caractéristiques de l’écoulement tels que la dissipation, le nombre de Reynolds, les échelles d’injection, de Taylor et de Kolmogorov. Dans un deuxième temps nous étudions les effets de la turbulence de l’écoulement sur le comportement d’une hydrolienne tri-pale à axe horizontal.L’objectif est de placer la maquette d’hydrolienne dans cet écoulement et étudier l’influence de la turbulence sur le rotor de cette turbine. La vitesse de l’écoulement est imposée et deux taux de turbulence différents ont été étudiés.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00247/35814/34329.pdf
http://archimer.ifremer.fr/doc/00247/35814/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The full numerical simulation of turbulent flows in the context of industrial applications remains a very challenging problem. One of the difficulties is the presence of a large number of interacting scales of different orders of magnitude, ranging from the macroscopic scale to the Kolmogorov dissipation scale. In order to better understand and simulate these interactions, new algorithms of incremental type have recently been introduced, stemming from the theory of infinite-dimensional dynamical systems (see, e.g., the algorithms of Foias, Jolly et al. (1988), Foias, Manley and Temam (1988), Laminie et al. (1993, 1994), Marion and Temam (1989, 1990), and Temam (1990)). These algorithms are based on decompositions of the unknown functions into a large- and a small-scale component, one of the underlying ideas being to approximate the corresponding attractor. In the context of finite element methods, the decomposition of a solution into small- and large-scale components appears when we consider hierarchical bases (Yserentant, 1986; Zienkiewicz et al., 1982). In the present article we derive several estimates of the size of the structures for the linear and nonlinear terms which correspond to interactions of different hierarchical components of the velocity field, and also their time variation. The one-step time variation of these terms can be smaller than the expected accuracy of the computation. Using this remark, we implement an adaptive spatial and temporal multilevel algorithm which treats differently the small- and large-scale components of the flow. We derive several a priori estimates in order to study the perturbation introduced into the approximated equations. All the interaction terms between small- and large-scale structures are frozen during several time steps. Finally, we implement the multilevel method in order to simulate a bidimensional flow described by the Burgers equations. We perform a parametric study of the procedure and its efficiency. The gain in CPU time is significant and the trajectories computed by our multi-scale method remain close to the trajectories obtained with the classical Galerkin method.
ISSN: 0168-9274

hal-00730710
https://hal.archives-ouvertes.fr/hal-00730710

Éditeur(s) : HAL CCSD
Résumé : 15 pages
A Stochastic Differential Equation appearing in the statistical theory of turbulence is extended in random environment by assuming that its two parameters are switched by an unobserved continuoustime Markov chain whose states represent the states of the environment. A Dirichlet process is placed as a prior on the space of the sample paths of this chain, leading to a hierarchical Dirichlet model whose estimation is done both on simulated data and on real data of wind speed measured at the entrance of a mangrove ecosystem.
https://hal.archives-ouvertes.fr/hal-00455050

hal-00455050
https://hal.archives-ouvertes.fr/hal-00455050
https://hal.archives-ouvertes.fr/hal-00455050/document
https://hal.archives-ouvertes.fr/hal-00455050/file/CSDA06_Srik_Hal.pdf

Éditeur(s) : HAL CCSD EDP Sciences
Résumé : International audience
In this work, we point out and apply some ideas for the numerical simulation by multi- level schemes of several wave equations including dispersive (Korteweg de Vries) and dissipative ones (Kuramoto-Sivashinski). We start from the approach developed for dissipative equations decomposing the solution into large (Y) and small (Z) scales, and we show that it is necessary to have a regularization in time to allow stable numerical treatment of Y and Z which are here generated using hierarchical processes such as Wavelets, Incremental Unknowns or Fourier.
ISSN: 1270-900X

hal-00768332
https://hal.archives-ouvertes.fr/hal-00768332
https://hal.archives-ouvertes.fr/hal-00768332/document
https://hal.archives-ouvertes.fr/hal-00768332/file/esaim_proc_2009_v27.pdf

Éditeur(s) : HAL CCSD Society for Industrial and Applied Mathematics
Résumé : International audience
We present iterative methods for finding the critical points and/or the minima of extended real valued functions of the form $phi = psi+ g-h$, where $psi$ is a differentiable function and g and h are convex, proper, and lower semicontinuous. The underlying idea relies upon the discretization of a first order dissipative dynamical system which allows us to preserve the local feature and to obtain some convergence results. The main theorems not only recover known convergence results in this field but also provide a theoretical basis for the development of new iterative methods.
ISSN: 1052-6234

hal-00779987
https://hal.univ-antilles.fr/hal-00779987
DOI : 10.1137/060655183

Éditeur(s) : HAL CCSD
Résumé : International audience
This communication reports on a field experiments carried out on the Ouano reef barrier, New Caledonia. The analysis is based on a cross-shore network of pressure sensors deployed across the reef flat and within the lagoon. Confirming existing observations, the measurements show the strong filtering role of the reef barrier on the incoming wave energy The swell energy is dissipated and transferred toward lower frequencies, including the so-called infragravity (IG) and very low frequency (VLF) waves. During energetic event (Hs=4.2m), IG and VLF significant wave heights on the reef flat are observed to reach 1.2 and 0.7m, respectively. A variety of long waves modes are observed on the reef, combining standing and progressive-dissipative modes. In any cases, the VLF and IG waves are much more developed over and close to the reef flat than further inside the lagoon.
Coastal Dynamics 2017
Helsingor, Denmark

hal-01562927
https://hal.archives-ouvertes.fr/hal-01562927

Éditeur(s) : HAL CCSD
Résumé : International audience
In this paper, we compare the effect of rolling resistance at the contacts in granular systems composed of disks with the effect of angularity in granular systems composed of regular polygonal particles. For this purpose, we use contact dynamics simulations. By means of a simple shear numerical device, we investigate the mechanical behavior of these materials in the steady state in terms of shear strength, solid fraction, force and fabric anisotropies, and probability distribution of contact forces. We find that, based on the energy dissipation associated with relative rotation between two particles in contact, the effect of rolling resistance can explicitly be identified with that of the number of sides in a regular polygonal particle. This finding supports the use of rolling resistance as a shape parameter accounting for particle angularity and shows unambiguously that one of the main influencing factors behind the mechanical behavior of granular systems composed of noncircular particles is the partial hindrance of rotations as a result of angular particle shape.
AIP Conference Proceedings
Sydney, Australia

hal-00842799
https://hal.archives-ouvertes.fr/hal-00842799
https://hal.archives-ouvertes.fr/hal-00842799/document
https://hal.archives-ouvertes.fr/hal-00842799/file/Comparison_effects_rolling_Estrada_al.pdf

Éditeur(s) : HAL CCSD American Physical Society
Résumé : We study the equilibrium properties of a liquid phase condensed at the nanoscale between the surfaces of a sharp crack in fused silica in a moist controlled atmosphere. The extension of the condensed phase along the fracture is measured by in situ atomic force microscopy phase imaging and it is shown to be determined by a critical distance between the opposite crack surfaces, which is an increasing function of humidity. The present technique is very promising for measuring the properties of confined liquids at the nanoscale as well as for modeling the physics and chemistry of slow crack propagation in glasses.
ISSN: 0031-9007

hal-00411946
https://hal.archives-ouvertes.fr/hal-00411946
DOI : 10.1103/PhysRevLett.100.165505

Éditeur(s) : HAL CCSD EDP Sciences
Résumé : International audience
Modelling environmental problems leads to mathematical systems with missing data. For instance, weather problems have generally missing initial conditions. The paper is concerned with identifying pollution terms arising in the state equation of some dissipative system with incomplete initial condition. To this aim the so-called sentinel method is used. Here, the problem of determining a sentinel is equivalent to a null-controllability problem for which Carleman inequalities are revisited.
ISSN: 1270-900X

hal-00720818
https://hal.univ-antilles.fr/hal-00720818
https://hal.univ-antilles.fr/hal-00720818/document
https://hal.univ-antilles.fr/hal-00720818/file/esaimpr2.pdf

Éditeur(s) : HAL CCSD
Résumé : The presence of obstacles met in natural environment by the flow, influences the dispersion of air pollutants which it carries. This thesis, based on spatiotemporal micro-meteorological measurements in tropical region, aims at studying the dispersion of compounds emitted by the ecosystem mangrove according to the weather conditions. At a daily scale, the meteorological analysis reveals, besides the presence of Trade Winds, the existence of thermal flows of which nocturnal thermodynamic parameters have been defined. The field observation has shown that the weak intensity of the wind disadvantages the dispersion of compounds emitted during the night. At a finer scale, the existence of a spectral gap separating large scale phenomena of those related to turbulence has been demonstrated. These last ones were treated by spectral and statistical approaches to quantify the turbulent fluxes of momentum and sensible heat during the night, for an averaged duration of 13 minutes. The stratification of the surface layer has been considered and determined by Monin-Obukhov similarity theory. The measurements acquired at night and the application of Kolmogorov theory allowed us to deduct the dissipation rate of energy and the size of the vortices at 5.5 meters in height. This work has also led us, by gas chromatography coupled to mass spectrometry, to identify, in mangrove, sulphurated volatil organic compounds, organohalogen, BTEX, ... All these results will later serve to feed dispersion models related to the studied ecosystem.
La présence d'obstacles rencontrés en milieu naturel par l'écoulement, influence la dispersion des polluants qu'il transporte. Cette thèse, fondée sur des mesures micro-météorologiques spatio-temporelles en région tropicale, vise à étudier la dispersion de composés émis par l'écosystème mangrove en fonction des conditions météorologiques. A l'échelle journalière, l'analyse météorologique révèle, outre la présence des Alizés, l'existence d'écoulements thermiques dont des paramètres thermodynamiques nocturnes ont été définis. L'observation terrain nous a montré que la faible intensité du vent défavorise la dispersion des composés émis durant la nuit. A une échelle plus fine, l'existence d'un trou spectral séparant les phénomènes de grande échelle de ceux liés à la turbulence a été mise en évidence. Ces derniers ont été traités par des approches spectrale et statistique pour quantifier les flux turbulents de quantité de mouvement et de chaleur sensible, pendant la nuit, pour une durée de moyenne de l'ordre de 13 minutes. L'état de stratification de la couche de surface a été pris en compte et déterminé par la théorie de similitude de Monin-Obukhov. Les mesures nocturnes effectuées et l'application de la théorie de Kolmogorov ont permis de déduire les taux de dissipation de l'énergie et la taille des tourbillons à 5,5 m d'altitude. Ce travail a également conduit, par l'analyse chromatographique en phase gazeuse couplée à la spectrométrie de masse, à l'identification, en mangrove, de composés organiques volatils soufrés, des organohalogénés, des BTEX, ... L'ensemble de ces résultats servira ultérieurement à alimenter les modèles de dispersion spécifiques liés aux écosystèmes étudiés.
https://tel.archives-ouvertes.fr/tel-00665882

Droits : info:eu-repo/semantics/OpenAccess
NNT : 11AGUY0438
tel-00665882
https://tel.archives-ouvertes.fr/tel-00665882
https://tel.archives-ouvertes.fr/tel-00665882/document
https://tel.archives-ouvertes.fr/tel-00665882/file/ThA_seCdAlexis.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The correlation between the flow turbulence and the performances of a ma- rine current turbine is studied. First, the incoming flow encountered in the flume tank is characterized in the framework of fully developed turbulent cascades in the inertial range. The Reynolds number, the Kolmogorov dissipation scale and the integral scale, are estimated from flow measurements. The intermittency of the turbulence is characterized in the lognormal multifractal framework, and the influence of the turbulent flow on the turbine power is assessed. The rotor speed control unit characteristics used for the turbine regulation induces non-negligible effects on the turbine behavior under fluctuations loads. Even if the power spectrum does not reveal any scale invariance, a multiscale analysis allows us to show the correlations between the turbulence time se- ries and the power produced. The classical Mean Square Coherency function shows that for scales larger than 10 seconds, the upstream velocity and power have large correlations. In the framework of the Empirical Mode Decomposition method, such correlations are studied using the time-dependence intrinsic corre- lation analysis method. This method allows to zoom into time-frequency scales where the flow perturbations induced some modifications in power production
ISSN: 0960-1481

hal-01528296
https://hal.archives-ouvertes.fr/hal-01528296
DOI : 10.1016/j.renene.2017.05.024

Éditeur(s) : HAL CCSD Coastal Education and Research Foundation, Inc.
Résumé : International audience
Morphodynamics of sandy, macrotidal, embayed beaches is complex because of the numerous physical processes interacting at the same location over a wide range of temporal scales. As most of these processes are controlled by beach morphology, dynamic feedbacks are generally observed between hydro- and morphodynamics. Investigating short-term processes is essential in order to improve long term morphological prediction. A key question is to understand how beach slope reacts to forcing conditions, in particular the response time of the beach profile, how long the transient state lasts. This study deals with the spatial and temporal responses of beach morphology to varying incident conditions. Here we report main observations, preliminary results and on-going investigations on the DYNATREZ1 field campaign, which was conducted in the framework of the National Observation Service Dynalit. Beach profiles are shown to adapt rapidly to forcing conditions, within two days, with more intense variations observed in the high tide swash zone. The presence of infragravity waves and their dissipation on the beach is highlighted. It is likely that the very large variability in beach slope observed over a single neapspring cycle is responsible for the accordingly large variability in wave skewness, asymmetry and breaking processes, and thus in sediment fluxes and morphological changes.
ICS 2016 Sydney
Sydney, Australia

hal-01254465
https://hal.archives-ouvertes.fr/hal-01254465
DOI : 10.2112/SI75-075.1

Éditeur(s) : HAL CCSD Elsevier
Résumé : The slow advance of a crack in soda-silicate glasses was studied at nanometer scale by in-situ and real-time atomic force microscopy (AFM) in a well-controlled atmosphere. An enhanced diffusion of sodium ions in the stress-gradient field at the sub-micrometric vicinity of the crack tip was revealed through several effects: growth of nodules in AFM height images, changes in the AFM tip–sample energy dissipation. The nodules patterns revealed a dewetting phenomenon evidenced by ‘breath figures'. Complementary chemical micro-analyses were done. These experimental results were explained by a two-step process: (i) a fast migration (typical time: few milliseconds) of sodium ions towards the fracture surfaces as proposed by Langford et al. [J. Mat. Res. 6 (1991) 1358], (ii) a slow backwards diffusion of the cations as evidenced in these AFM experiments (typical time: few minutes). Measurements of the diffusion coefficient of that relaxing process were done at room temperature. Our results strengthen the theoretical concept of a near-surface structural relaxation due to the stress-gradient at the vicinity of the crack tip. The inhomogeneous migration of sodium ions might be a direct experimental evidence of the presence of sodium-rich channels in the silicate structure [A. Meyer et al., Phys. Rev. Let. 93 (2004) 027801].
ISSN: 0022-3093

hal-00407634
https://hal.archives-ouvertes.fr/hal-00407634
DOI : 10.1016/j.jnoncrysol.2006.09.034

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Energy dissipation is observed on seismic data when a wave propagates through a porous medium, involving different frequency regimes depending on the nature of rock and fluid types. We focus here on the role of partial fluid saturation in unconsolidated porous media, looking in particular at P-wave phase velocity and attenuation. The study consists in running an experiment in a sand-filled tank partially saturated with water. Seismic propagation in the tank is generated in the kHz range by hitting a steel ball on a granite plate. Seismic data are recorded by buried accelerometers and injecting or extracting water controls the partial saturation. Several imbibition/drainage cycles were performed between the water and gas residual saturations. A Continuous Wavelet Transform applied on seismic records allowed us to extract the direct P-wave at each receiver.We observe an hysteresis in phase velocities and inverse quality factors between imbibition and drainage. Phase velocities and inverse quality factors are then jointly inverted to get a final poro-visco-elastic model of the partially saturated sand that satisfactorily reproduces the data. The model formulation consists in generalizing the Biot theory to effective properties of the fluid and medium (permeability and bulk modulus) in order to properly explain the phase velocity variation as a function of the saturation. The strong level of attenuation measured experimentally is further explained by an anelastic effect due to grain to grain sliding, adding to Biot's losses. This study shows that fluid distribution at microscopic scale has strong influence on the attenuation of direct P-waves at macroscopic scale and confirms that seismic prospection may be a powerful tool for the characterization of transport phenomena in porous media.
ISSN: 0956-540X

hal-00779920
https://hal.archives-ouvertes.fr/hal-00779920
https://hal.archives-ouvertes.fr/hal-00779920/document
https://hal.archives-ouvertes.fr/hal-00779920/file/Barriere_et_al_HAL.pdf
DOI : 10.1111/j.1365-246X.2012.05691.x