From liquid to solid bonding in cohesive granular media

We study the transition of a granular packing from liquid to solid bonding in the course of drying. The particles are initially wetted by a liquid brine and the cohesion of the packing is ensured by capillary forces, but the crystallization of the solute transforms the liquid bonds into partially cemented bonds. This transition is evidenced experimentally by measuring the compressive strength of the samples at regular intervals of times. Our experimental data reveal three regimes: 1) Up to a critical degree of saturation, no solid bonds are formed and the cohesion remains practically constant; 2) The onset of cementation occurs at the surface and a front spreads towards the center of the sample with a nonlinear increase of the cohesion; 3) All bonds are partially cemented when the cementation front reaches the center of the sample, but the cohesion increases rapidly due to the consolidation of cemented bonds. We introduce a model based on a parametric cohesion law at the bonds and a bond crystallization parameter. This model predicts correctly the phase transition and the relation between microscopic and macroscopic cohesion.Comment: 20

An automatized frequency analysis for vine plot detection and delineation in remote sensing

La mise à disposition d'un outil automatique pour la détection et la caractérisation des parcelles de vigne est un besoin très important d'un point de vue gestion. Un procédé automatique récursif basé sur l'analyse fréquentielle (utilisation de la Transformée de Fourier et des filtres de Gabor) a été développé pour y répondre. Il permet la détermination des contours de parcelle et une estimation précise de leur inter-rang et de leur orientation. Dans l'optique d'une application à grande échelle, les tests et la validation ont été menés à partir de données standard de télédétection à très haute résolution.. Environ 89% des parcelles sont détectées qui correspondent à plus de 84 % de la surface viticole, et 64% d'entre elles avec des contours corrects. L'orientation des rangs et la largeur d'inter-rang sont obtenus avec une précision de 1 degré et 3,3 cm respectivement. / The availability of an automatic tool for vine plot detection, delineation, and characterization would be very useful for management purposes. An automatic and recursive process using frequency analysis (with Fourier transform and Gabor filters) has been developed to meet this need. This results in the determination of vine plot boundary and accurate estimation of interrow width and row orientation. To foster large-scale applications, tests and validation have been carried out on standard very high spatial resolution remotely sensed data. About 89% of vine plots are detected corresponding to more than 84% of vineyard area, and 64% of them have correct boundaries. Compared with precise on-screen measurements, vine row orientation and interrow width are estimated with an accuracy of 1°and 3.3 cm, respectively

Liquid clustering and capillary pressure in granular media

International audienceBy means of extensive lattice Boltzmann simulations, we investigate the process of growth and coalescence of liquid clusters in a granular material as the amount of liquid increases. A homogeneous grain-liquid mixture is obtained by means of capillary condensation, thus providing meaningful statistics on the liquid distribution inside the granular material. The tensile stress carried by the grains as a function of the amount of condensed liquid reveals four distinct states, with a peak stress occurring at the transition from a primary coalescence process, where the cohesive strength is carried mostly by the grains, to a secondary process governed by the increase of the liquid cluster volumes. We show that the evolution of capillary states is correctly captured by a simple model accounting for the competing effects of the Laplace pressure and grain-liquid interface

From pixel to vine parcel: A complete methodology for vineyard delineation and characterization using remote-sensing data

International audienceThe increasing availability of Very High Spatial Resolution images enables accurate digital maps production as an aid for management in the agricultural domain. In this study we develop a comprehensive and automatic tool for vineyard detection, delineation and characterizationusing aerial images and without any parcel plan availability. In France, vineyard training methods in rows or grids generate periodic patterns which make frequency analysis a suitable approach. The proposed method computes a Fast Fourier Transform on an aerial image, providing the delineation of vineyards and the accurate evaluation of row orientation and interrow width. These characteristics are then used to extract individual vine rows, with the aim of detecting missing vine plants and characterizing cultural practices. Using the red channel of an aerial image, 90\% of the parcels have been detected; 92\% have been correctly classified according to their rate of missing vine plants and 81\% according to their cultural practice (weed control method). The automatic process developed can be easily integrated into the final user's Geographical Information System and produces useful information for vineyard managemen

"Bacchus" Methodological approach for vineyard inventory and management. Chap.4: Textural and structural analysis

Ce chapitre présente les méthodes qui ont été développées dans le projet Bacchus pour la détection et la caractérisation des parcelles de vigne en imagerie aérienne en se basant sur leur structure. Une analyse texturale est d'abord mise en oeuvre, et complétée par l'introduction de contraintes de régularité des contours pour améliorer la segmentation. Finalement, les parcelles issues de ces premières étapes sont vérifiées et caractérisées au moyen d'une analyse de leur spectre de Fourier. Les résultats obtenus sur diverses zones d'étude du projet Bacchus sont présentés et discutés. / This chapter presents the methodologies that have been developed during the Bacchus project concerning the automatic detection and characterisation of vineyard plots in satellite and aerial images, based on their structural properties. First, a textural analysis has been used. Then shape regularity constraints have been introduced to improve the image segmentation. Finally, the vineyard plots issued from these previous steps are checked and characterised using a Fourier spectrum analysis. Results on various study areas of the Bacchus project are presented and discussed

Investigating the effect of porosity on the soil water retention curve using the multiphase Lattice Boltzmann Method

The soil water retention curve (SWRC) is the most commonly used relationship in the study of unsaturated soil. In this paper, the effect of porosity on the SWRC is investigated by numerically modeling unsaturated soil using the Shan-Chen multiphase Lattice Boltzmann Method. The shape of simulated SWRCs are compared against that predicted by the van Genuchten model, demonstrating a good fit except at low degrees of saturation. The simulated SWRCs show an increase in the air-entry value as porosity decreases.Comment: 4 pages, 5 figures, submitted to Powder & Grains 2021, references adde

Propagation de la sensibilité dans les modèles hydrodynamiques.: Analyse d’incertitude et estimation des paramètres.

La modélisation des phénomènes hydrodynamiques est généralement entachée d’erreurs qui proviennent des multiples approximations faites à chaque étape de la construction et de l’application des modèles. La complexité des processus mis en jeux conduit à l’utilisation d’équations mathématiques simplifiées faisant intervenir des paramètres à ajuster; celles-ci sont résolues de manière approchées par des méthodes numériques et nécessitent des variables mesurées ou estimées. Afin d’assurer la maitrise des risques liés aux événements pluvieux, il est primordial de connaitre l’impact des différentes incertitudes liées au modèle sur l’estimation des niveaux d’eau ou de débit dans les zones sensibles. L’objectif à terme de ces recherches est donc de fournir, en complément des résultats de modélisation, des recommandations pour l’acquisition de mesures (position des capteurs, précision…) ; ceci afin d’optimiser la description géométrique ou hydraulique du domaine, pour une meilleure précision des résultats de modélisation. Ces travaux présentent trois applications de l'analyse de sensibilité locale à la modélisation hydrodynamique : 1) Elle permet d'estimer l’étendue de l’influence d’une perturbation localisée et de hiérarchiser l’importance des paramètres du modèle afin d’organiser les mesures à effectuer. 2) Dans le cadre d’études de scénarios, on montre qu'elle fournit une approximation à l’ordre 1 d’une analyse d’incertitude, qui ne requiert qu'une seule simulation et reste comparable aux résultats de simulations de Monte Carlo, même dans le cas de problèmes hydrodynamiques complexes avec variation de plusieurs paramètres, corrélés ou non. 3) Enfin, elle est utilisée de façon originale dans un processus d’estimation automatique des paramètres, d'une part, directement dans l'algorithme de résolution basé sur une formulation faible de la distance entre mesures et simulations, et d'autre part, comme filtre dans l'estimation de l'erreur pour ne pas caler un paramètre en utilisant des observations qui coïncident avec une sensibilité locale faible

Changes in the starch-protein interface depending on common wheat grain hardness revealed using atomic force microscopy

The Atomic Force Microscope tip was used to progressively abrade the surface of non-cutted starch granules embedded in the endosperm protein matrix in grain sections from wheat near-isogenic lines differing in the puroindoline b gene and thus hardness. In the hard near-isogenic wheat lines, starch granules exhibited two distinct profiles corresponding either to abrasion in the surrounding protein layer or the starch granule. An additional profile, only identified in soft lines, revealed a marked stop in the abrasion at the protein-starch transition similar to a lipid interface playing a lubricant role. It was related to the presence of both wild-type puroindolines, already suggested to act at the starch-protein interface through their association with polar lipids.This study revealed, for the first time, in situ differences in the nano-mechanical properties at the starch-protein interface in the endosperm of wheat grains depending on the puroindoline allelic status

Two-dimensional numerical simulation of chimney fluidization in a granular medium using a combination of discrete element and lattice Boltzmann methods

We present here a numerical study dedicated to the fluidization of a submerged granular medium induced by a localized fluid injection. To this end, a two-dimensional (2D) model is used, coupling the lattice Boltzmann method (LBM) with the discrete element method (DEM) for a relevant description of fluid-grains interaction. An extensive investigation has been carried out to analyze the respective influences of the different parameters of our configuration, both geometrical (bed height, grain diameter, injection width) and physical (fluid viscosity, buoyancy). Compared to previous experimental works, the same qualitative features are recovered as regards the general phenomenology including transitory phase, stationary states, and hysteretic behavior. We also present quantitative findings about transient fluidization, for which several dimensionless quantities and scaling laws are proposed, and about the influence of the injection width, from localized to homogeneous fluidization. Finally, the impact of the present 2D geometry is discussed, by comparison to the real three-dimensional (3D) experiments, as well as the crucial role of the prevailing hydrodynamic regime within the expanding cavity, quantified through a cavity Reynolds number, that can presumably explain some substantial differences observed regarding upward expansion process of the fluidized zone when the fluid viscosity is changed