Saturated hydraulic conductivity determined by on ground mono-offset Ground-Penetrating Radar inside a single ring infiltrometer

In this study we show how to use GPR data acquired along the infiltration of water inside a single ring infiltrometer to inverse the saturated hydraulic conductivity. We used Hydrus-1D to simulate the water infiltration. We generated water content profiles at each time step of infiltration, based on a particular value of the saturated hydraulic conductivity, knowing the other van Genuchten parameters. Water content profiles were converted to dielectric permittivity profiles using the Complex Refractive Index Method relation. We then used the GprMax suite of programs to generate radargrams and to follow the wetting front using arrival time of electromagnetic waves recorded by a Ground-Penetrating Radar (GPR). Theoretically, the 1D time convolution between reflectivity and GPR signal at any infiltration time step is related to the peak of the reflected amplitude recorded in the corresponding trace in the radargram. We used this relation ship to invert the saturated hydraulic conductivity for constant and falling head infiltrations. We present our method on synthetic examples and on two experiments carried out on sand soil. We further discuss on the uncertainties on the retrieved saturated hydraulic conductivity computed by our algorithm from the van Genuchten parameters

Numerical simulation of water flow in tile and mole drainage systems

International audienceTile drainage systems are sometimes not sufficient to provide favorable unsaturated conditions in the rootzone. These drainage systems then need to be supplemented with an additional high conductivity material in the trenches above the tiles or by implementing mole drainage. The HYDRUS (2D/3D) model was used to evaluate the impact of such additional measures for heavy clay soil. Three types of drainage systems were simulated: (i) tile drains, (ii) tile drains with gravel trenches, and (iii) tile drains with gravel trenches and mole drains, using either two-dimensional (the former two systems) or three-dimensional (the latter one) transport domains. Three scenarios were considered to test the efficiency of each system: (i) time to drain an initially saturated system, (ii) high intensity rainfall, and (iii) a real case scenario. Different horizontal spacings between tile drains with or without gravel trenches were also compared with the system which included mole drainage. The results showed that the drainage system that included mole drains and gravel trenches was the most efficient. This system provided the largest drainage rate, was the first to reach steady-state in the time to drain scenario, and also efficiently reduced surface runoff. Adding mole drains to a system with tile drains and gravel trenches resulted in a large reduction of surface runoff (75%). Simulations showed that the spacing of tile drains with or without gravel trenches would have to be 40% or 55% smaller, respectively, in order to reproduce the same water table levels as those observed for the drainage system with mole drains. Therefore, introducing mole drains in drainage systems is an efficient practice for reducing waterlogging and runoff

Estimating Saturated Hydraulic Conductivity from Surface Ground-Penetrating Radar Monitoring of Infiltration

In this study we used Hydrus-1D to simulate water infiltration from a ring infiltrometer. We generated water content profiles at each time step of infiltration, based on a particular value of the saturated hydraulic conductivity while knowing the other van Genuchten parameters. Water content profiles were converted to dielectric permittivity profiles using the Complex Refractive Index Method relation. We then used the GprMax suite of programs to generate radargrams and to follow the wetting front using arrival time of electromagnetic waves recorded by a Ground-Penetrating Radar (GPR). Theoretically, the depth of the inflection point of the water content profile simulated at any infiltration time step is related to the peak of the reflected amplitude recorded in the corresponding trace in the radargram. We used this relationship to invert the saturated hydraulic conductivity for constant and falling head infiltrations. We present our method on synthetic examples and on two experiments carried out on sand. We further discuss the possibility of estimating two other van Genuchten parameters, n and \alpha, in addition to the saturated hydraulic conductivity.Comment: 4th International Conference "HYDRUS Software Applications to Subsurface Flow and Contaminant Transport Problems," Praque : Czech Republic (2013

Etude in situ des phénomènes de retrait-gonflement des sols : application à deux sols tropicaux peu gonflants

Ce travail est consacré à la mesure in situ de la courbe de retrait de sols peu gonflants. Un effort expérimental important porte sur la mise au point des méthodes utilisées pour le suivi simultané in situ des variations d'épaisseur et de teneur en eau de couches de sol. Nous montrons la faisabilité des mesures de variation d'épaisseur sur sols peu gonflants grâce à l'utilisation de capteurs électroniques de déplacement. La précision obtenue (plus ou moins 10 microm) permet de mettre en évidence des variations d'épaisseur allant de 50 microm à 1,4 mm pour des couches de 20 cm d'épaisseur. D'autre part, l'interpolation par krigeage permet d'améliorer la précision des estimations de teneur en eau à l'endroit des mesures d'épaisseur. Les courbes de retrait linéaire (variations de longueur en fonction de la teneur en eau) obtenues sur sols peu gonflants présentent une nette convergence de forme avec celles obtenues sur sols gonflants. La comparaison de la courbe de retrait obtenue in situ sur couche de sol avec celle mesurée sur des échantillons prélevés dans cette couche est limitée par une importante variabilité des courbes mesurées sur différents échantillons d'une même couche. En conséquence, l'extrapolation à des couches de sol en place de paramètres de retrait mesurés sur échantillon ne peut se faire directement. L'utilisation de mesures de variations d'épaisseur est à l'heure actuelle le seul moyen d'accéder à la dynamique de retrait des sols peu gonflants, la gammamétrie de rétrodiffusion n'étant pas un instrument suffisamment précis pour permettre une mesure volumique. Un grand nombre de résultats, concernant la précision des mesures, le traitement du signal des capteurs de déplacement, l'étalonnage de la sonde à neutrons, sont présentés en annexe. (Résumé d'auteur

The transferability of Australian pedotransfer functions for predicting water retention characteristics of French soils.

A French data set was used in evaluating how well two widely used analytical functions describe measured soil water characteristic (SWC) data. Both the van Genuchten (sigmoidal) and Campbell (power-law) equations gave good descriptions of the data (mean R2 of 98.1% and 97.1% respectively). Methods of predicting SWC data were also evaluated. When a power-law equation was parameterised using just two measured SWC points and bulk density (the 'two-point' method), a very good SWC prediction was obtained for the French data (mean R2 of 94.8%). An empirical equation for prediction of the SWC was also assessed using the French data set. This method was developed using multiple regression analysis from Australian soil data and requires soil texture and bulk density as input. The predictions (mean R2 of 85.2%) lacked accuracy and precision in comparison to the two-point method but uses more readily available input data. The accuracy of prediction from both methods was similar to that observed previously for Australian data sets. The empirical approach developed from Australian soil data has reasonable applicability to French soils. The approach of assuming a power-law model and empirically predicting slope and air entry potential is shown to have merit. A strategy for achieving adequate coverage of soil hydraulic property data for France is suggested incorporating hydraulic prediction methods such as those evaluated here

Improvements in Fluid Structure Interaction simulations of LS-Dyna(r)

International audienceThe French Ministry of Defence’s procurement agency, the Direction Générale de l'Armement (DGA), is in charge of assessing and testing armament systems in order to equip the armed forces and prepare for the future. DGA Aeronautical Systems, the technical centre dedicated to evaluate and test aircraft, combines test and evaluation to clear, among others, parachute systems. The parachute evaluation is historically based on experimental data and so requires numerous flight tests which can prove expensive and time consuming. In order to have a greater understanding of the parachute dynamic behavior and to optimize the parachute systems flight tests, DGA Aeronautical Systems developed a modeling and simulation capability as a support to evaluation. For this purpose, DGA Aeronautical Systems, with the help of ISAE, developed Fluid Structure Interaction (FSI) simulations of parachutes using the LS-Dyna commercial Finite Element Analysis (FEA) tool. This tool is largely used for solving highly nonlinear transient problems and enables doing coupled multi-physics simulations such as FSI simulations. DGA Aeronautical Systems has been using the software since 2003. In the recent years, the parachute simulation has been much improved thanks to the implementation of a porosity algorithm in LS-Dyna at the common request of DGA and parachute industry. The paper presents recent improvements in Arbitrary Lagrangian Eulerian (ALE) techniques used to analyze the canopy inflation and the quasi-steady state descent phases characteristics. Up to now, only infinite mass type simulations were developed by constraining the parachute confluence point and applying a prescribed airflow to the fluid. The applied airflow velocity came from real in-flight measurements of paratrooper or load trajectory determinations. This simulation type is representative to wind tunnel tests. From now on, thanks to considerable computational resources, finite mass type simulations are also possible. It consists in applying the force of gravity to the parachute system. This allows simulating both the inflation phase (from vertical packed parachute geometry) and the quasi-steady state descent. Among others, the static line parachute of the new French Army troop parachute system called EPC (Ensemble de Parachutage du Combattant) was modeled at real scale. Modeling techniques are presented and results of the EPC static line parachute simulation are compared with real inflight measurements. The benefits of FSI simulations prior to parachute testing are presented. In a near future, incompressible and compressible Navier-Stokes solvers will be available in the next version of LS-Dyna. These code enhancements will be tested to simulate the parachute flight and hopefully will bring the ability to analyze more accurately the aerodynamics of the canopy and the structural behavior of the fabrics. These future capabilities are also discussed

Pesticide contamination interception strategy and removal efficiency in forest buffer and artificial wetland in a tile-drained agricultural watershed

Yves couqet : present adress : UMR7327 on sept. 2012International audiencePesticide pollution is a major threat to aquatic ecosystems that can be mitigated through complementary actions including buffer zones (BZs). This paper discusses the results of 3 yr of field-scale monitoring of the concentration and load transfer of 16 pesticides out of a tile-drained catchment (Bray, France) and their reduction through two BZ: an artificial wetland (AW) and a forest buffer (FB). Typically, the highest concentrations were measured in the first flows following pesticide applications or resuming after periods of low or no flow. An open/close water management strategy was implemented to operate the parallel BZ based on pesticide applications by the farmer. The strategy was efficient in intercepting molecules whose highest concentrations occurred during the first flows following application. Inlet vs. outlet pesticide load reductions ranged from 45% to 96% (AW) and from −32% to 100% (FB) depending on the pesticide molecule and the hydrological year. Partly reversible adsorption was a dominant process explaining pesticide removal; whereas, degradation occurred for sufficiently long water retention time. Apart from the least sorbing molecules (e.g., isoproturon), BZ can partially remove pesticide pollution

Dilepton polarization as a signature of plasma anisotropy

We propose the angular distribution of lepton pairs produced in ultrarelativistic heavy-ion collisions as a probe of thermalization of the quark-gluon plasma. We focus on dileptons with invariant masses large enough that they are produced through quark-antiquark annihilation in the early stages of the collision. The angular distribution of the lepton in the rest frame of the pair then reflects the angular distribution of quark momenta. At early times, the transverse pressure of the quark-gluon plasma is larger than its longitudinal pressure as a result of the fast longitudinal expansion, which results in an oblate lepton distribution. By constrast, direct (Drell-Yan) production by quarks and antiquarks from incoming nuclei, whose momenta are essentially longitudinal, results in a prolate distribution. As the invariant mass increases, Drell-Yan gradually becomes the dominant source of dilepton production, and the lepton distribution evolves from oblate to prolate. The invariant mass at which the transition occurs is highly sensitive to the equilibration time of the quark-gluon plasma or, equivalently, the shear viscosity over entropy ratio $\eta/s$ in the early stages of the collision.Comment: 6 pages, 3 figure

Modeling the effect of soil meso- and macropores topology on the biodegradation of a soluble carbon substrate

Soil structure and interactions between biotic and abiotic processes are increasingly recognized as important for explaining the large uncertainties in the outputs of macroscopic SOM decomposition models. We present a numerical analysis to assess the role of meso- and macropore topology on the biodegradation of a soluble carbon substrate in variably water saturated and pure diffusion conditions . Our analysis was built as a complete factorial design and used a new 3D pore-scale model, LBioS, that couples a diffusion Lattice-Boltzmann model and a compartmental biodegradation model. The scenarios combined contrasted modalities of four factors: meso- and macropore space geometry, water saturation, bacterial distribution and physiology. A global sensitivity analysis of these factors highlighted the role of physical factors in the biodegradation kinetics of our scenarios. Bacteria location explained 28% of the total variance in substrate concentration in all scenarios, while the interactions among location, saturation and geometry explained up to 51% of it

LE LINGUISTIQUE ET LE LITTERAIRE QU’APPORTENT LES MANUSCRITS DE LINGUISTES ?

This article follows a composition of three approaches to try to show the links betweenlinguistics and literature through linguists. Languages; Literature and Linguistics, these twoareas have always formed a more or less fusional couple, more or less distended, opposite inthe methodologies to approach their object. From the genetic point of view, how does thishappen? By opening linguists’ files realizing their manuscripts could be of interest to literature?If the constitution of drafting a text is an initial and procedural material of literature, in whatcould the examination of this constitution in the linguistic field contribute to this relationship?L’article qui suit est un composé de trois approches qui tentent de faire apparaîtreles liens entre linguistique et littérature chez les linguistes. Langues et Lettres, linguistique etlittérature, ces deux domaines ont toujours été en couple, plus ou moins fusionnel, plus oumoins distendu, voire opposé dans les méthodologies d’approche de leur objet. Qu’en est-il dupoint de vue génétique ? Voilà les questions que nous proposons pour cette réflexion : ouvrirles archives de linguistes, rendre compte de leurs manuscrits peut-il avoir un intérêt pour lalittérature ? Si la constitution élaborative d’un texte est bien le matériau initial et processuelde la littérature, en quoi, examiner cette constitution dans le domaine linguistique apportequelque chose?L’article qui suit est un composé de trois approches qui tentent de faire apparaître les liens entre linguistique et littérature chez les linguistes. Langues et Lettres, linguistique et littérature, ces deux domaines ont toujours été en couple, plus ou moins fusionnel, plus ou moins distendu, voire opposé dans les méthodologies d’approche de leur objet. Qu’en est-il du point de vue génétique ? Voilà les questions que nous proposons pour cette réflexion : ouvrir les archives de linguistes, rendre compte de leurs manuscrits peut-il avoir un intérêt pour la littérature ? Si la constitution élaborative d’un texte est bien le matériau initial et processuel de la littérature, en quoi, examiner cette constitution dans le domaine linguistique apporte quelque chose ?