Xavier Frank

Droplet spreading on a porous surface: A lattice Boltzmann study

This paper presents an investigation into drop spreading and capillary absorption at the surface of a porous substrate. Lattice Boltzmann numerical simulations are carried out at the pore level with two values of intrinsic contact angle at the liquid-gas-solid line and three values of porosity; the case of a flat solid surface is included as a reference. The numerical results show a power-law evolution of the wetted zone radius with time, both exponent and prefactor decreasing with increasing porosity. The evolution in time of the droplet height emerges from competition between pure spreading and bulk capillary imbibition in the porous medium.

The Potential of Meshless Methods to Address Physical and Mechanical Phenomena Involved during Drying at the Pore Level

This article reviews a number of so-called meshless methods, particularly those suitable for investigations at the pore level, as potential tools to face new challenges in the field of drying. It is very difficult to be exhaustive in this domain, so only some of the most promising methods have been selected: lattice Boltzmann (LB), smooth particle hydrodynamics (SPH), dissipative particle dynamics (DPD), material point method (MPM), and percolation networks (PN). In the introduction these methods are classified according to simple key features: off/on lattice and the nature of the physical formulation compared to classical finite element (FE) or control volume (CV) methods. The core of the article presents a brief description of each method, including its principle, simple formulation, and some result examples. This is followed by a summary review intended to guide the reader in choosing the method most suitable for his specific application.

New modelling approaches to predict wood properties from its cellular structure: image-based representation and meshless methods

Key messageThe real tissue structure, including local anisotropy directions, is defined from anatomical images of wood. Using this digital representation, thermal/mass diffusivity and mechanical properties (stiffness, large deformation, rupture) are successfully predicted for any anatomical pattern using suitable meshless methods.IntroductionWood, an engineering material of biological origin, presents a huge variability among and within species. Understanding structure/property relationships in wood would allow engineers to control and benefit from this variability. Several decades of studies in this domain have emphasised the need to account simultaneously for the phase properties and the phase morphology in order to be able to predict wood properties from its anatomical features. This work is focused on the possibilities offered by meshless computational methods to perform upscaling in wood using actual tissue morphologies obtained by microscopic images.MethodsAfter a section devoted to the representation step, the digital representation of wood anatomy by image processing and grid generation, the papers focuses on three meshless methods applied to predict different macroscopic properties in the transverse plane of wood (spruce earlywood, spruce latewood and poplar): Lattice Boltzmann Method (LBM) allows thermal conductivity and mass diffusivity to be predicted, Material Point Method (MPM) deals with rigidity and compression at large deformations and peridynamic method is used to predict the fracture pathway in the cellular arrangement.ResultsThis work proves that the macroscopic properties can be predicted with quite good accuracy using only the cellular structure and published data regarding the cell wall properties. A whole set of results is presented and commented, including the anisotropic ratios between radial and tangential directions.

A coarse-grain force-field for xylan and its interaction with cellulose

We have built a coarse-grain (CG) model describing xylan and its interaction with crystalline cellulose surfaces. Each xylosyl or glucosyl unit was represented by a single grain. Our calculations rely on force-field parameters adapted from the atomistic description of short xylan fragments and their adsorption on cellulose. This CG model was first validated for xylan chains both isolated and in the bulk where a good match was found with its atomistic counterpart as well as with experimental measurements. A similar agreement was also found when short xylan fragments were adsorbed on the (110) surface of crystalline cellulose. The CG model, which was extended to the (100) and (1-10) surfaces, revealed that the adsorbed xylan, which was essentially extended in the atomistic situation, could also adopt coiled structures, especially when laying on the hydrophobic cellulose surfaces.