@article {663, title = {Grains3D, a flexible DEM approach for particles of arbitrary convex shape{\textemdash}Part III: extension to non-convex particles modelled as glued convex particles}, journal = {Computational Particle Mechanics}, volume = {106}, year = {2019}, month = {Jan-2019}, pages = {55 - 84}, abstract = {

Large-scale numerical simulation using the discrete element method (DEM) contributes to improving our understanding of granular flow dynamics involved in many industrial processes and geophysical flows. In industry, it leads to an enhanced design and an overall optimization of the corresponding equipment and process. Most of the DEM simulations in the literature have been performed using spherical particles. A limited number of studies dealt with non-spherical particles, even less with non-convex particles. Even convex bodies do not always represent the real shape of certain particles. In fact, more complex-shaped particles are found in many industrial applications, for example, catalytic pellets in chemical reactors or crushed glass debris in recycling processes. In Grains3D-Part I (Wachs et al. in Powder Technol 224:374-389, 2012), we addressed the problem of convex shape in granular simulations, while in Grains3D-Part II (Rakotonirina and Wachs in Powder Technol 324:18-35, 2018), we suggested a simple though efficient parallel strategy to compute systems with up to a few hundreds of millions of particles. The aim of the present study is to extend even further the modelling capabilities of Grains3D towards non-convex shapes, as a tool to examine the flow dynamics of granular media made of non-convex particles. Our strategy is based on decomposing a non-convex-shaped particle into a set of convex bodies, called elementary components. We call our method glued or clumped convex method, as an extension of the popular glued sphere method. Essentially, a non-convex particle is constructed as a cluster of convex particles, called elementary components. At the level of these elementary components of a glued convex particle, we employ the same contact detection strategy based on a Gilbert-Johnson-Keerthi algorithm and a linked-cell spatial sorting that accelerates the resolution of the contact, that we introduced in [39]. Our glued convex model is implemented as a new module of our code Grains3D and is therefore automatically fully parallel. We illustrate the new modelling capabilities of Grains3D in two test cases: (1) the filling of a container and (2) the flow dynamics in a rotating drum.

}, keywords = {Granular flow; Discrete element method; Non-convex shape; GJK algorithm; Glued convex}, issn = {2196-4378}, doi = {10.1007/s40571-018-0198-3}, url = {http://link.springer.com/10.1007/s40571-018-0198-3}, author = {Rakotonirina, Andriarimina Daniel and Jean-Yves Delenne and Farhang Radja{\"\i} and Wachs, Anthony} } @article {571, title = {Griffith{\textquoteright}s postulate: Grand Canonical Monte Carlo approach for fracture mechanics of solids}, journal = {Engineering Fracture Mechanics}, volume = {199}, year = {2018}, month = {Aug-2018}, pages = {544 - 554}, abstract = {

A Grand Canonical Monte Carlo Approach (GCMC) is proposed for the fracture analysis of solids discretized as mass points and bond interactions. In contrast to classical load-driven fracture processes, the GCMC approach introduces an auxiliary field, the bond rupture potential , to which the system is subjected; in addition to changes in volume V and temperature T. In this VT-ensemble, bond isotherms that link the average number of bonds to the bond rupture potential (Nk-) are obtained that carry critical information for fracture analysis. Specifically, the slope of the bond isotherm reflects bond fluctuations, permitting identification of (1) a fluctuation-based damage variable, and (2) the competition in energy fluctuations between the redistribution of strain energy induced by bond rupture, and the dissipation of the groundstate energy. Based on these fluctuations, it is shown that the GCMC-approach allows the identification of a critical bond energy release rate of material samples, when strain energy fluctuations equal groundstate energy fluctuations \– much akin to Griffith\’s 1921 stationarity postulate to \“predicting the breaking loads of elastic solids\”. This is illustrated by means of thermodynamic integration of bond isotherms to determine force-displacement curves, for both notched and unnotched homogeneous samples discretized by regular 2-D lattices with bonds exhibiting harmonic potentials.

Fig. 1. Bond-Isotherms Nk-μfor three systems: (a) unnotched; (b) notched; (c) broken

Fig. 2. Fluctuation-based damage in function of the prescribed bond rupture potential,{\textellipsis}

Fig. 3. Energy dissipation due to fluctuations for (a) the unnotched and (b) the{\textellipsis}

Fig. 4. Thermodynamic integration of the bond isotherms of (a) an unnotched sample; and{\textellipsis}

}, keywords = {Grand Canonical Monte Carlo Simulations; Bond rupture; Bond rupture potential; Bond isotherms; Damage; Fluctuations}, issn = {00137944}, doi = {10.1016/j.engfracmech.2018.06.001}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0013794418301747}, author = {Al-Mulla, Talal and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @proceedings {346, title = {Geomechanics from Micro to MacroInteraction between two localized fluidization cavities in granular media : Experiments and numerical simulation}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro}, year = {2014}, month = {Sep-2014}, pages = {1571 - 1576}, publisher = {CRC Press}, address = {SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

In this work, we present experimental and numerical results on the interaction between two localized fluidization cavities in an immersed granular packing. According to the gap between the two locally injected upward fluid flows, each fluidized cavity will evolve independently of the another, or conversely, the two cavities can interact with each other: they merge and eventually behave like a single cavity. Combined optical techniques are used for visualization of particle motion inside the granular media (Refractive Index-Matching between liquid and beads and Planar Laser-Induced Fluorescence), the experimental results are compared to a two-dimensional simulation based on coupled Discrete Element and Lattice Boltzmann Methods (DEM-LBM).

}, isbn = {978-1-138-02707-7}, doi = {10.1201/b17395-286}, author = {Jeff Ngoma and Pierre Philippe and St{\'e}phane Bonelli and Jean-Yves Delenne and Farhang Radja{\"\i}}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin and Kuo, Matthew} } @article {33, title = {Gas uptake in solvents confined in mesopores: adsorption versus enhanced solubility}, journal = {The Journal of Physical Chemistry Letters}, volume = {4}, year = {2013}, month = {Jun-25-2013}, pages = {2274{\textendash}2278}, abstract = {
Abstract Image

Three molecular mechanisms for gas uptake in a solvent confined in mesopores are identified. On the one hand, CO2 uptake is an adsorption-driven phenomenon that arises from the strong interaction between the gas molecules and the pore surface. On the other hand, H2 uptake is a confinement-induced enhanced solubility in which solubility is favored in the regions of low solvent density formed by the layering of the solvent. In partially filled pores, adsorption at the gas/liquid solvent interface is a third mechanism that leads to large gas uptakes. This study, which sheds light on previously reported yet unclear oversolubility in pores, provides a guide to design hybrid porous catalysts consisting of a solvent confined in a porous solid.

}, doi = {10.1021/jz401143x}, author = {Linh Ngoc Ho and St{\'e}phanie Clauzier and Schuurman, Yves and David Farrusseng and Benoit A. Coasne} } @proceedings {341, title = {Granular plastic flow and fabric-based internal variables}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro}, year = {2013}, month = {May-2013}, pages = {3 - 19}, publisher = {CRC Press}, address = {SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

A microscopic approach to the quasi-static flow of granular materials requires
fabric parameters pertaining to the contact network. We show that the plastic behavior of
granular materials is correctly predicted with the approximation of perfectly rigid particles
interacting via dissipative contacts as simulated by means of the contact dynamics method.
We investigate the correlations between macroscopic variables (internal friction angle and ...

}, isbn = {978-1-138-02707-7}, doi = {10.1201/b1739510.1201/b17395-3}, url = {http://www.crcnetbase.com/doi/book/10.1201/b17395http://www.crcnetbase.com/doi/abs/10.1201/b17395-3}, author = {Farhang Radja{\"\i} and St{\'e}phane Roux}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin and Kuo, Matthew} } @proceedings {370, title = {GRANULAR SLUMPING IN A FLUID : FOCUS ON RUNOUT DISTANCES}, journal = {3rd International Conference on Particle-based Methods}, volume = {PARTICLE-BASED METHODS III: FUNDAMENTALS AND APPLICATIONS}, year = {2013}, month = {Sept-2013}, pages = {115-123}, address = {SEP 18-20 2013 Stuttgart, GERMANY}, author = {Vincent Topin and Yann Monerie and Perales, F.}, editor = {Bischoff, M and Ramm, E and Onate, E} } @article {292, title = {Glassy Nature of Water in an Ultraconfining Disordered Material: The Case of Calcium-Silicate-Hydrate}, journal = {Journal of the American Chemical Society}, volume = {133}, year = {2011}, month = {Mar-02-2011}, pages = {2499 - 2510}, abstract = {
Abstract Image

We present the structural and dynamic nature of water ultraconfined in the quasi-two-dimensional nanopores of the highly disordered calcium\−silicate\−hydrate (C-S-H), the major binding phase in cement. Our approach is based on classical molecular simulations. We demonstrate that the C-S-H nanopore space is hydrophilic, particularly because of the nonbridging oxygen atoms on the disordered silicate chains which serve as hydrogen-bond acceptor sites, directionally orienting the hydrogen atoms of the interfacial water molecules toward the calcium\−silicate layers. The water in this interlayer space adopts a unique multirange structure: a distorted tetrahedral coordination at short range up to 2.7 \Å, a disordered structure similar to that of dense fluids and supercooled phases at intermediate range up to 4.2 \Å, and persisting spatial correlations through dipole\−dipole interactions up to 10 \Å. A three-stage dynamics governs the mean square displacement (MSD) of water molecules, with a clear cage stage characteristic of the dynamics in supercooled liquids and glasses, consistent with its intermediate-range structure identified here. At the intermediate time scales corresponding to the \β-relaxation of glassy materials, coincident with the cage stage in MSD, the non-Gaussian parameter indicates a significant heterogeneity in the translational dynamics. This dynamic heterogeneity is induced primarily because of the heterogeneity in the distribution of hydrogen bond strengths. The strongly attractive interactions of water molecules with the calcium silicate walls serve to constrain their motion. Our findings have important implications on describing the cohesion and mechanical behavior of cement from its setting to its aging.

}, issn = {0002-7863}, doi = {10.1021/ja107003a}, author = {Youssef, Mostafa and Roland Jean-Marc Pellenq and Bilge Yildiz} }