bluuebunny/crossref_metadata_2025 huggingface dataset:
A ratiometric near-infrared fluorescent probe based on a novel reactive cyanine platform for mitochondrial pH detection
Authors: Wan Shulin , Xia Shuai , Medford Jerry , Durocher Emma , Steenwinkel Tessa E. , Rule Lexi , Zhang Yibin , Luck Rudy L. , Werner Thomas , Liu Haiying
Published: June 2021

Near-infrared fluorescent probes for mitochondrial pH detection were prepared by a substitution reaction of chlorine atom of a near-infrared reactive cyanine platform (probe A) with amine derivatives.
Thermo-osmotic metamaterials with large negative thermal expansion
Authors: Savić-Šević Svetlana , Pantelić Dejan , Murić Branka , Grujić Dušan , Vasiljević Darko , Kolaric Branko , Jelenković Branislav
Published: June 2021

A holographically patterned metamaterial with a large NTE, enabled by thermo-osmosis of entrapped air molecules through a multitude of nanometer-thin layers.
C1-Symmetric [Ir(C^N1)(C^N2)(N^O)]-tris-heteroleptic Ir(iii)-complexes with a horizontal orientation for efficient near-infrared (NIR) polymer light-emitting diodes (PLEDs)
Authors: Li Wentao , Miao Tiezheng , Wang Baowen , Liu Jiaxiang , Lü Xingqiang , Fu Guorui , Feng Weixu , Wong Wai-Yeung
Published: June 2021

Through doping of the [Ir(C^N1)(C^N2)(N^O)]-tris-heteroleptic Ir(iii)-complex [Ir(iqbt)(ppy)(pic)] (1) or [Ir(iqbt)(ppy)(Br-pic)] (2) into the EML, the preferentially horizontal orientation is beneficial for their high-performance NIR-PLEDs.
TESS and HARPS reveal two sub-Neptunes around TOI 1062
Authors: Otegi J. F. , Bouchy F. , Helled R. , Armstrong D. J. , Stalport M. , Psaridi A. , Delisle J.-B. , Stassun K.G. , Delgado-Mena E. , Santos N. C. , Hara N. C. , Collins K. , Gandhi S. , Dorn C. , Brogi M. , Fridlund M. , Osborn H. P. , Hoyer S. , Udry S. , Hojjatpanah S. , Nielsen L. D. , Dumusque X. , Adibekyan V. , Conti D. , Schwarz R. , Wang G. , Figueira P. , Lillo-Box J. , Hadjigeorghiou A. , Bayliss D. , Strøm P. A. , Sousa S. G. , Barrado D. , Osborn A. , Barros S. C. C. , Brown D. J. A. , Eastman J. D. , Ciardi D. R. , Vanderburg A. , Goeke R. F. , Guerrero N. M. , Boyd P. T. , Caldwell D. A. , Henze C. E. , McLean B. , Ricker G. , Vanderspek R. , Latham D. W. , Seager S. , Winn J. , Jenkins J. M.
Published: June 2021

The Transiting Exoplanet Survey Satellite (TESS) mission was designed to perform an all-sky search of planets around bright and nearby stars. Here we report the discovery of two sub-Neptunes orbiting around TOI 1062 (TIC 299799658), a V = 10.25 G9V star observed in the TESS Sectors 1, 13, 27, and 28. We use precise radial velocity observations from HARPS to confirm and characterize these two planets. TOI 1062b has a radius of 2.265−0.091+0.096 R⊕, a mass of 10.15 ± 0.8 M⊕, and an orbital period of 4.1130 ± 0.0015 days. The second planet is not transiting, has a minimum mass of 9.78−1.18+1.26 M⊕ and is near the 2:1 mean motion resonance with the innermost planet with an orbital period of 7.972−0.024+0.018 days. We performed a dynamical analysis to explore the proximity of the system to this resonance, and to attempt further constraining the orbital parameters. The transiting planet has a mean density of 4.85−0.74+0.84 g cm−3 and an analysis of its internal structure reveals that it is expected to have a small volatile envelope accounting for 0.35% of the mass at most. The star’s brightness and the proximity of the inner planet to what is know as the radius gap make it an interesting candidate for transmission spectroscopy, which could further constrain the composition and internal structure of TOI 1062b.
Late Pliocene-Pleistocene incision in the Ebro Basin (North Spain)
Authors: Regard Vincent , Vacherat Arnaud , Bonnet Stéphane , Mouthereau Frédéric , Nørgaard Jesper , Knudsen Mads F.
Published: June 2021

The Ebro Basin constitutes the central part of the southern foreland of the Pyrenees. It was endorheic during the Cenozoic and accumulated sediments. By the end of the Miocene, erosion and river incision reconnected the basin to the Mediterranean Sea, establishing a post-opening drainage network. Those rivers left terraces that we study in this work. We first synthesize previous works on river terraces that are widely dispersed in the basin. We provide new age constraints, up to 3 Ma, obtained thanks to cosmogenic nuclides using both profile and burial methods. We derive a unified fluvial terrace chronology and a homogenized map of the highest terraces over the entire Ebro Basin. The dated terraces labeled A, B, C, D, and E are dated to 2.8 ± 0.7 Ma, 1.15 ± 0.15 Ma, 850 ± 70 ka, 650 ± 130 ka, and 400 ± 120 ka, respectively. The chronology proposed here is similar to other sequences of river terraces dated in the Iberian Peninsula, around the Pyrenees, and elsewhere in Europe. The oldest terraces (A, B, C) are extensive, indicating they form a mobile fluvial network while from D to present, the network was stable and entrenched in 100 to 200 m-deep valleys. The transition from mobile to fixed fluvial network is likely to have occurred during the Middle Pleistocene Transition (MPT, between 0.7 and 1.3 Ma), when long-period/high-intensity climate fluctuations were established in Europe. We estimate that between 2.8–1.15 Ma and present, the incision rates have tripled.
Editorial: Powders & Grains 2021 9th International Conference on Micromechanics of Granular Media
Authors: Aguirre María Alejandra , Luding Stefan , Pugnaloni Luis A. , Soto Rodrigo
Published: June 2021

Granular matter, particulate matter and granular materials are generic terms to refer to systems composed of many macroscopic bodies (grains or particles) where the contact interaction (which is non-conservative) plays a crucial role in the behavior of the system. This contrasts with other systems (e.g., atomic or molecular systems) where the constituent bodies (e.g., atoms or molecules) interact via conservative forces. The non-conservative contact interactions come from inelastic collisions (due to plastic deformation, sound or heat production) and also from friction. This makes the study of granular matter a major challenge to scientists and the handling/storage/processing of granular materials a major challenge to engineers. Particulate matter covers a very broad range of systems, from those formed by fine particles (powders) to those formed by large rocks (derbis), from soft bodies (cotton balls) to hard grains (glass beads), from those we eat (muesli) to those we play with (beach sand), from those used to build our houses (cement) to those used to grow our crops (soil). Needless to say, any new knowledge in this area has a tremendous potential to impact our lives and our economy. Powders & Grains is a conference held every four years to bring together researchers working both in fundamental aspects of granular matter and in technological applications. This volume collects the 195 papers presented during the 2021 edition of P&G, which provide an excellent overview of the current state-of-the-art in granular matter and new trends with contributions form six continents.
Forced segregation in binary granular mixtures
Authors: Pillitteri Salvatore , Lumay Geoffroy , Opsomer Éric , Vandewalle Nicolas
Published: June 2021

Mixing granular particles of di erent sizes is a common way of increasing the packing fraction. Recently, a model predicting the packing fraction, taking into account the inhomogeneity of the mixed small and large particles, has been proposed by S. Pillitteri et al. Under certain conditions, this model can be simpli ed and analytical solutions can be found. We present here these solutions, compared to experimental data, and the physical interpretation they can bring.
Optimal packing in 2D and 3D granular systems: Density, connectivity, and force distributions
Authors: Oquendo William-Fernando , Estrada Nicolas
Published: June 2021

In this work, we explore the influence of the grain size distribution (GSD) on density, connectivity and internal forces distributions, for both 2D and 3D granular packings built mechanically. For power law GSDs, we show that there is an exponent for which density and connectivity are optimized, and this exponent is close to those that characterize other well known GSDs such as the Fuller and Thompson distribution and the Appollonian packing. In addition, we studied the distributions of normal forces, finding that these can be well described by a power-law tail, specially for the GSDs with large size span. These results highlight the role of the GSD on internal structure and suggest important consequences on macroscopic properties.
Statistical properties of cell stresses in 2D granular solids
Authors: Matsushima Takashi , Blumenfeld Raphael
Published: June 2021

We investigate numerically the statistics of the stresses, defined for cells - the irreducible loops surrounded by particles in contact - in two-dimensional granular solids and the relation between these cell stresses and cell structures. We prepared a number of mechanically stable granular assemblies at various packing fractions and mean coordination numbers, and measured the stress statistics on each cell. We find the following. (1) The mean cell stress agrees with the bulk external pressure; (2) the probability density function of the normalised cell stress ratio collapses into a master curve; (3) the mean stress ratio increases with increasing intergranular friction; (4) the mean stress ratio per cell order decreases with increasing cell order because of their reduced stability; (5) the maximum cell stress direction correlates well with the cell’s long axis. These results are strong evidence that the cell structure and the stress field self-organise together and reveal the co-evolving correlations between the two.
Correlating the force network evolution and dynamics in slider experiments
Authors: Cheng Chao , Zadeh Aghil Abed , Kondic Lou
Published: June 2021

The experiments involving a slider moving on top of granular media consisting of photoelastic particles in two dimensions have uncovered elaborate dynamics that may vary from continuous motion to crackling, periodic motion, and stick-slip type of behavior. We establish that there is a clear correlation between the slider dynamics and the response of the force network that spontaneously develop in the granular system. This correlation is established by application of the persistence homology that allows for formulation of objective measures for quantification of time-dependent force networks. We find that correlation between the slider dynamics and the force network properties is particularly strong in the dynamical regime characterized by well-defined stick-slip type of dynamics.
Granular impacts: how far the Boussinesq model can go?
Authors: Martinez Francisco , Gonzalez Claudia
Published: June 2021

A key problem on granular impacts deals with the determination of the mechanical response of the grains due to the impact of the intruder. This topic has been poorly addressed in the literature so far, a gap to which this study aims to contribute by measuring the pressure distribution at the bottom of a loose and dry sandy bed, impacted by a heavy sphere of fixed diameter. Exploring different bed thicknesses and intruder’s dropping height, we have found that the structure of this distribution is very similar to the Boussinesq model, initially proposed for a static point-force acting over an isotropic-elastic medium. This surprising result opens up many challenging questions that could help validate or refute this model in other scenarios.
Shearing of granular materials in a confined split-bottom Couette cell
Authors: Madani Mahnoush , Maleki Maniya , Shaebani M. Reza
Published: June 2021

Formation of shear bands is one of the most remarkable phenomena in the dynamics of granular matter. Several parameters have been so far identified to influence the behavior of the shear bands. We carried out experiments to investigate the evolution of the shear bands in the split-bottom Couette cell in the presence of confining pressure. We employed the Particle Image Velocimetry (PIV) to characterize the shear band both in the absence and presence of external pressure. Our results show that the location and width of the shear band are affected by both the confining pressure and the filling height. The shear zone evolves towards the middle of the cylinder and expands to a broader region with increasing applied pressure or filling height; also the angular velocity decreases relative to the rotation rate of the bottom disk. Our findings are consistent with prior empirical observations on the formation of wide shear bands at free surfaces.
Collapse of conical granular columns
Authors: Ordaz M.A. , Sánchez-Rosas M. , Hernández-Juárez J.R. , Medina A. , Serrano D.A.
Published: June 2021

This paper experimentally analyzes the collapse of conical granular columns made out of non-cohesive granular materials. Dimensionless run-out lengths were found, as a function of the aspect ratio a, similar to those occurring in the collapse of cylindrical columns, although in the case of conical columns of high aspect ration, at the end of the collapse, a layer of grains that rotates around the cone axis appears and it affects the final profiles of the mounds.
How universal is the vibration-velocity controlled granular convection?
Authors: Umehara Mika , Okumura Ko
Published: June 2021

Recently, a number of articles have reported that granular convection induced by continuous vibration is controlled by vibration velocity, in contrast with some previous studies. We have reported such an example for the Brazil nut eﬀect when the vibration is given discontinuously, using a one-layer granular bed in a cell with down-facing side walls. Here, we report the eﬀect of vibration phase and wall friction using the same experimental system, to confirm rising motion of an intruder induced by granular convection is again governed by vibration velocity. We compare two diﬀerent cases of vibration phase for giving intermittent vibration cycles, and found one, in which granular packing is well established before grains start to lose contacts due to vibration, provides distinctly high reproducibility. We further control the side wall friction using a microfabrication technique, and found that significantly high reproducibility is attained in a cell with vertical side walls when a millimeter texture is introduced on the side walls. Our results indicate that the granular convection is universally controlled by vibration velocity. The present study opens a way to conduct highly reproducible experiments on granular dynamics, which is indispensable for deep physical understanding of granular flow and segregation.
Shear-driven density segregation: an experimental study
Authors: Tirapelle Monica , Santomaso Andrea C. , Richard Patrick , Artoni Riccardo
Published: June 2021

Granular materials can segregate spontaneously due to differences in particle properties when subjected to vibrations, shear strain or because of the equipment geometries. Although the difference in particle size is the most critical factor that drives segregation, the effects of large density difference may also be detrimental for a lot of industries. In this work, we experimentally investigate density-driven segregation in bi-disperse mixtures of particles having the same size but different density when subjected to non-uniform shear rates. We found that the features of the segregation process are related to the density ratio as well as to the dimensionless loaded mass. The experimental outcomes are then compared with the solution of a simple density-driven segregation model. The model can successfully capture the main features of segregation driven by density for a range of density ratios.
Analytical nonlocal model for shear localization in wall-bounded dense granular flow
Authors: Lee Keng-Lin , Artoni Riccardo , Yang Fu-Ling , Richard Patrick
Published: June 2021

This work employs a Landau-Ginzburg-type nonlocal rheology model to account for shear localization in a wall-bounded dense granular flow. The configuration is a 3D shear cell in which the bottom bumpy wall moves at a constant speed, while a load pressure is applied at the top bumpy wall, with flat but frictional lateral walls. At a fixed pressure, shear zones transit from the top to the bottom when increasing lateral wall friction coefficient. With a quasi-2D model simplification, asymptotic solutions for fluidization order parameters near the top and bottom boundaries are sought separately. Both solutions are the Airy function in terms of a depth coordinate scaled by a characteristic length which measures the width of the corresponding shear zone. The theoretical predictions for the shear zone widths against lateral wall friction coefficient and load pressure agree well with data extracted from particle-based simulation for the flow.
Sidewall friction in confined surface flows of granular materials
Authors: Richard Patrick , Valance Alexandre , Delannay Renaud
Published: June 2021

We report numerical simulations of surface granular flows confined between two sidewalls. These systems exhibit both very slow and very energetic flows. Zhu et al. [1] have shown that in energetic confined systems, the Froude number at sidewalls and the sidewall effective friction coefficient are linked through a unique relation. We show that this relation is also valid for creep flows. It is independent of the angle of the flow but depends on the sidewall-grain friction coefficient. Our results shed light on boundary conditions that have to be used at sidewalls in continuum theories aiming to capture the behavior of granular systems from creeping to energetic flows.
Influence of granular temperature and grain rotation on the wall friction coefficient in confined shear granular flows
Authors: Lin Cheng-Chuan , Artoni Riccardo , Yang Fu-Ling , Richard Patrick
Published: June 2021

A depth-weakening wall friction coefficient, µw, has been reported from three-dimensional numerical simulations of steady and transient dense granular flows. To understand the degradation mechanisms, a scaling law for µw/ f and χ has been proposed where f is the intrinsic particle-wall friction and χ is the ratio of slip velocity to square root of granular temperature (Artoni & Richard, Phys. Rev. Lett., vol. 115 (15), 2015, 158001). Independently, a friction degradation model has been derived which describes a monotonically diminishing friction depends on a ratio of grain angular and slip velocities, Ω (Yang & Huang, Granular Matter, vol. 18 (4), 2016, 77). In search of experimental evidence for how these two parameters degrade the µw, an annular shear cell experiment was performed to estimate the bulk granular temperature, angular and slip velocities at sidewall through image-processing. Meanwhile, µw was measured by a force sensor to confirm the weakening towards the creep zone. The measured µw/ f − χ and µw/ f − Ω were both well-fitted to the corresponding models showing that both granular temperature and angular velocity are significant mechanisms to degrade the µw which broadens the research perspective on modeling the boundary condition of dense granular flows.
Granular flow through vertical slots: analysis of a general formula
Authors: Medina A. , Serrano D.A. , López-Villa A. , Pliego M.
Published: June 2021

Currently, very little is known about reliable phenomelogical correlations to estimate the gravity-driven mass flow rate, of dry non-cohesive granular material, outflowing from thin thickness slots in vertical sidewalls of rectangular silos. Here, we validate a simple and general formula that fits pretty well data published elsewhere, including the cases of vertically and horizontally elongated slots.
Evidence of a non-local ø(I) response
Authors: Robinson James , Holland Daniel , Fullard Luke
Published: June 2021

Granular dilatancy has been previously characterised through a simple linear relationship between the packing fraction and dimensionless shear rate. However, this relationship was developed for granular flows in a simple shear cell geometry. Here we examine inertial volume changes in a shear cell with gravity, a vertical chute, and a pseudo-2D hopper. In so doing, we show that the packing fraction displays both a local and non-local response, analogous to what is typically observed for the stress ratio µ.
Measuring jumps during granular chute-flows using X-ray radiography
Authors: Méjean Ségolène , Guillard François , Faug Thierry , Einav Itai
Published: June 2021

The present paper describes laboratory tests on steady granular flows down a smooth chute using X-ray radiography. By using an original granular chute set-up with a gate at its end, standing discontinuites in height, velocity and density, namely jumps, were produced during the granular flows. The X-ray radiography was successful to get consistent measurements of the free-surface and density profiles of the flows along the chute under different flow states: the (nearly) uniform flows before the jumps, the gradually-varied flows after the jumps, and the highly non-uniform flows across the jumps. This demonstrates the efficiency of the X-ray radiography to measure granular flows.
Drag of a cylindrical object in a two-dimensional granular environment
Authors: Kubota Takumi , Ishikawa Haruto , Takada Satoshi
Published: June 2021

The drag of a cylindrical object in a two-dimensional granular environment is numerically studied. It is found that the drag law is fitted by the sum of the yield force and the dynamic force, the latter of which is reproduced by a simple collision model. The angular dependence of the radial stress on the surface of the object is given by the Gaussian below the yield force. The probability of the velocity drops of the object is investigated above the yield force, where this probability is independent of the packing fraction and the drag force.
Shear-induced diffusion: the role of granular clusters
Authors: Macaulay Matthew , Rognon Pierre
Published: June 2021

This paper is concerned with the physical mechanisms controlling shear-induced diffusion in dense granular flows. The starting point is that of the granular random walk occurring in diluted granular flows, which underpins Bagnold’s scaling relating the coefficient of self-diffusion to the grain size and shear rate. By means of DEM simulations of plane shear flows, we measure some deviations from this scaling in dense granular flows with and without contact adhesion. We propose to relate these deviations to the development of correlated motion of grains in these flows, which impacts the magnitude of grain velocity fluctuations and their time persistence.
Cluster dynamics in dense granular gases of rod-like particles
Authors: Puzyrev Dmitry , Cruz Hidalgo Raúl , Fischer David , Harth Kirsten , Trittel Torsten , Stannarius Ralf
Published: June 2021

Granular gases are interesting multiparticle systems which, irrespective of the apparent simplicity of particle interactions, exhibit a rich scenario of so far only little understood features. We have numerically investigated a dense granular gas composed of frictional spherocylinders which are excited mechanically by lateral vibrating container walls. This study was stimulated by experiments in microgravity on parabolic flights. The formation of spatial inhomogeneities (clusters) was observed in a region near the corners of the container, about halfway from the excitation plates. The particles in the clusters show a tendency to align parallel to the container walls, seemingly increasing the stabilizing effect of friction. The simulation results provide hints that the phase difference of the vibrations of the two excitation walls might affect the cluster dynamics.
Swelling of a granular hydrogel medium under confinement: individual and collective dynamic
Authors: Cristófaro Lucía , Falcioni Sebastián , Binda Leonardo , Roht Yanina Lucrecia , Drazer Germán , Ippolito Irene
Published: June 2021

The growth dynamics of polyacrylamide hydrogel beads due to liquid absorption under geometric confinement is studied. First, the behavior of individual hydrogel beads is investigated and, subsequently, the growth dynamics is analyzed in the presence of several interacting beads of the same material. In both, individual and collective studies, the magnitude of the geometric confinement is varied, in order to investigate the effect that the stress applied on the particles has on their hydration kinetics.
Experimental study of particle shape dependence of avalanches inside a rotating drum
Authors: Chen Jian , Krengel Dominik , Matuttis Hans-Georg
Published: June 2021

We investigate the avalanches of spherical and non-spherical granular particles inside half-filled rotating drums. The time series of the center of gravity of the particle assemblies are obtained via image analysis and their single-sided amplitude (SSA) spectra are analyzed. The spectra features of this new indicator turn out to be characteristic for the avalanches, in terms of the existence of peaks in the low-frequency range and the decay rate of high frequency components. The SSA spectrum has a peak for the packings of non-spherical particles but not for the spherical particles. The high frequency part is characterized by a power law decay 1/ f a (a > 0) . A 1/ f -decay is found only for the spherical particles. For the packings of cornered particles, the exponents significantly deviate from a = 1. As 1/ f spectra are often associated with self-organized criticality and therefore a scale invariance of the dynamics, we may conclude that there is no scale-invariant structure for granular avalanches. Considering the small number of particles and the regularity of convex particle shapes being used, the spectral features revealed in this study could be utilized for validating particle simulations.
Independence of shear strength with particle size dispersity still valid in polyhedral particle assemblies
Authors: Azéma Emilien , Cantor David , Preechawuttipong Itthichai
Published: June 2021

A very staggering result that has been constantly highlighted in granular media is that the shear strength of granular assemblies is independent of the particle size dispersity. In other words, a packing composed of monodisperse particles has similar strength properties to those of polydisperse systems. This has been shown numerically for the simplified case of disc and polygon assemblies in 2D and spheres in 3D. In this paper, we use three-dimensional contact dynamics simulations to revisit these results for the more complex case of assemblies composed of highly polydisperse rigid polyhedra. Although non-spherical shapes induce more intricated spatial correlations than spherical shapes because of the multiple contact types (i.e., vertex-face, edge-edge, edge-face, face-face), our numerical data provide evidence that the shear strength independence as the particle size dispersity increases still holds up for assemblies of polyhedra. We explain this finding from compensation mechanisms at the micro-scale between geometrical and mechanical anisotropies developed within the assemblies.
DEM investigation of the effect of particle breakage on compact properties
Authors: Gou Dazhao , An Xizhong , Yang Runyu
Published: June 2021

Particle breakage during compaction affects compaction behavior and the quality of the formed compact. This work conducted a numerical study based on the discrete element method (DEM) to investigate the effect of particle breakage on compaction dynamics and compact properties, including particle size and density distributions, and pore properties. A force-based breakage criterion and Apollonian sphere packing algorithm were employed to characterize particle breakage behavior. The pore structures of the compacts were characterized by the watershed pore segmentation method. Calibrated with experimental data, the model was able to simulate the stress-strain relation comparable with experimental observation. During compaction, the particles were gradually broken from top to bottom with increasing pressure. Both density and pore size of the compacts had relatively uniform distribution at larger stress, while the pore size decreased sharply when the particles started to break, indicating that the smaller fragments in the compact system have a significant effect on the pore size distribution.
Grain size effect on the compression and relaxation of a granular column: solid particles vs dust agglomerates
Authors: Pacheco-Vázquez Felipe , Omura Tomomi , Katsuragi Hiroaki
Published: June 2021

We studied experimentally the effect of grain size and maximum load on the compaction and subsequent relaxation of a granular column when it is subjected to vertical uniaxial compression. The experiments were performed using two different types of grains: 1) solid glass beads, and 2) porous beads that consist of agglomerates of glass powder. We found that the compression force increases non-linearly with time, with sudden drops for the case of glass beads and periodic undulations for dust particles. Whereas the grain size effect is small in the average force load, the fluctuations become larger as the grain size increases. On the other hand, the relaxation process is well described by the Maxwell model with three different relaxation time scales.
Capturing the failure of a cohesive granular step
Authors: Staron Lydie , Abramian Anais , Lagrée Pierre-Yves
Published: June 2021

A Contact Dynamics algorithm is applied to simulate the failure of 2-dimensional granular steps. Focussing on one single value for both the adhesive force threshold and the contact friction, we track the signature of the failure in the cumulative displacement of the grains. The introduction of a displacement threshold allows for the identification of the onset of a rapid failure and the formation of the corresponding shear band. The latter gives access to an estimation of the failure orientation.

The robustness of the measure thus performed for one single run is assessed by carrying out a series of 10 additional simulations, showing a fairly reproducible behaviour.
The effect of cohesion on the discharge of a granular material through the orifice of a silo
Authors: Gans Adrien , Aussillous Pascale , Dalloz Blanche , Nicolas Maxime
Published: June 2021

We present the results of both experimental and numerical investigations of the silo discharge for a cohesive granular material. In our study, thanks to a cohesion-controlled granular material (CCGM) we propose to investigate the effect of the cohesive length lc, on the discharge of a silo for two different configurations, one axisymmetrical, and one quasi-2D rectangular silo. In both configurations, an adjustable bottom is used to control the size of the orifice. As observed for cohesionless granular material by previous studies, the mass flow rate and the density through an orifice are mostly controlled by the diameter of the orifice D. The experimental results of the quasi-2D silo are compared with continuum numerical simulations.
Investigating the effect of porosity on the soil water retention curve using the multiphase Lattice Boltzmann Method
Authors: Hosseini Reihaneh , Kumar Krishna , Delenne Jean-Yves
Published: June 2021

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.
CFD modelling of the effect of capillary pressure on retention behaviour of water menisci at inter-particle contacts
Authors: López Alejandro , Bruno Agostino Walter , Nadimi Sadegh
Published: June 2021

This paper presents a Computational Fluid Dynamics (CFD) model on the effect of capillary pressure on the retention behaviour of a granular material. The model proposes an unprecedented CFD insight into the onset of liquid menisci at the inter-particles contact under varying hydraulic conditions. The present work models the material grains as smooth spherical particles that define a porous network filled by two interstitial fluids: air and silicon oil. The numerical model has been subsequently validated against experimental measurements of the degree of saturation at different capillary pressures taken by Dullien et al. [F.A. Dullien, C. Zarcone, I.F. MacDonald, A. Collins, R.D. Bochard. J. Colloid Interface Sci. 127, 2 (1989)] in a system of smooth glass beads flooded with silicon oil. Results from the numerical simulations confirm the good capability of the model to reproduce the experimental retention behaviour of the granular material. Finally, the present paper laid the basis for future CFD studies on the effect of various factors (e.g. hydraulic hysteresis, surface roughness and/or grain shape) on the capillary pressure acting at the interparticle contact.
Granular-slurry rheology and asphalt compaction
Authors: Man Teng , Hill Kimberly
Published: June 2021

Hot mixed asphalt (HMA) is a mixture of particles (coarse and fine aggregates) and interstitial fluid (asphalt binder) designed to compact and harden for long-lasting roads. In this study, we implement a two-scale approach to capture the compaction behaviour of hot asphalt mixtures using both a granular-slurry rheology (GSR) at a smaller scale and a discrete element method (DEM) simulation at the scale of a compactor. We show that this modelling effort captures the compaction of HMA with different binder viscosities modified by adding graphene nano-platelets (GNP). This research has the capacity to shed light on how the properties of mixture components can influence compaction efficiency and effectiveness.
Effects of interparticle friction on the response of 3D cyclically compressed granular material
Authors: Benson Zackery A. , Peshkov Anton , Richardson Derek C. , Losert Wolfgang
Published: June 2021

We numerically study the effect of inter-particle friction coefficient on the response to cyclical pure shear of spherical particles in three dimensions. We focus on the rotations and translations of grains and look at the spatial distribution of these displacements as well as their probability distribution functions. We find that with increasing friction, the shear band becomes thinner and more pronounced. At low friction, the amplitude of particle rotations is homogeneously distributed in the system and is therefore mostly independent from both the affine and non-affine particle translations. In contrast, at high friction, the rotations are strongly localized in the shear zone. This work shows the importance of studying the effects of inter-particle friction on the response of granular materials to cyclic forcing, both for a better understanding of how rotations correlate to translations in sheared granular systems, and due to the relevance of cyclic forcing for most real-world applications in planetary science and industry.
An experimental study on shear bands in sand using the orthogonal cutting setup
Authors: Hegde Abhijit , Murthy Tejas
Published: June 2021

We study the evolution of shear bands in granular media subjected to very large deformations using the orthogonal cutting geometry. We perform our cutting experiments on Cauvery Delta sand with d50 of 0.45mm. We also capture images of the cutting process which allows us to perform a PIV analysis to determine the deformation in material around the cutting tool. In our experiments we observe that the dynamic angle of repose of the pile that forms in-front of the tool as cutting progresses, approaches the critical state friction angle of the material. We observe a flow bifurcation around the tool as the material begins to slip along planes which are oriented at an angle of π/4 – θ/2, θ being the dynamic angle of repose, to the cutting direction. This leads to formation of shear bands/velocity jumps which contain around 14 particles. A measurement of dilation angle within the shear bands indicate that material is in a critical state of deformation.
Rattlers’ involvement for possibly looser critical states under higher mean stress
Authors: Duverger Sacha , Duriez Jérôme , Philippe Pierre , Bonelli Stéphane
Published: June 2021

The critical state of a granular material made of rounded tetrahedral particles is studied through DEM simulations of triaxial compressions. A minimum number of 7,500 particles is first obtained as the representative volume element (RVE) for the present triaxial simulations. Then, the macroscopic critical state line (CSL) is shown to be increasing in the (stress, density) space for low confining pressures. Such an unexpected behaviour is explained by the existence of a significant proportion of rattlers. Considering rattlers as voids indeed reinstates a classically decreasing CSL.
Grain-scale DEM study of open-ended pipe pile penetration in granular soils
Authors: Komodromos Michail , Combe Gaël , Viggiani Gioacchino
Published: June 2021

Open-Ended Pipe Piles (OEPP) are particularly popular in oﬀshore engineering. An important feature of the installation of these piles is the rate with which soil enters the pile from the bottom, and its interaction with the internal pile shaft. The response of OEPP crucially depends on the occurrence of soil plugging, which can make the behavior of an OEPP similar to a pile of solid cross section. Plugging is generally attributed to arching eﬀects in the soil; therefore, understanding this phenomenon requires an investigation at the grain scale. This is precisely the objective of this study, where the Distinct Element Method (DEM) is used to study the installation of an Open-Ended Pipe Pile in a Virtual Calibration Chamber comprising 128000 grains, under constant horizontal stress. Despite the relatively small number of particles, this numerical model is found to be able to reproduce several aspects of the mechanisms actually observed in thefield. The results are compared to those obtained from actual experiments of miniature pile penetration tests. Stress and strainfields that develop in the soil inside and outside the pile provide interesting data and shed light on the mechanisms at play during OEPP installation, especially as for the influence of grains interlocking.
Anisotropic nature of the capillary stress tensor
Authors: Farahnak Mojtaba , Wan Richard , Pouragha Mehdi
Published: June 2021

The paper describes a micromechanical approach that explores the anisotropic nature of the capillary stress tensor and its evolution in pendular granular materials via Discrete Element Modeling (DEM) simulations. Dimensionless parameters are used to address the conditions under which the contribution of capillarity (or cohesive interparticle forces) to the stress transmission within a Representative Elementary Volume (REV) is expected to be considerable. From a series of suction-controlled conventional triaxial tests, numerical results show that the significance of the capillary stress and the relative magnitude of its mean to deviatoric components is directly connected to the characteristic particle size and applied stress. In addition, it is shown that the anisotropic character of the capillary stress tensor intensifies with increasing suction. Furthermore, a simple shear test is conducted at constant mean stress to reveal the development of deviatoric capillary stresses in the absence of any change in mean stress, which cannot be captured by the commonly used Bishop’s stress expression.
Dynamic view of critical state regime in granular materials: a mesoscale perspective
Authors: Deng Na , Wautier Antoine , Thiery Yannick , Yin Zhen-Yu , Hicher Pierre-Yves , Nicot François
Published: June 2021

We revisit the Critical State (CS) in a dynamic perspective at a mesoscopic scale to enrich the classical view of the critical state as a steady state. The dynamics of meso-structures has been characterized by recording generating and vanishing processes in discrete element simulations. Our results suggest that meso-structures have a short but regular lifespan at critical state along a biaxial compression loading path.
Contact Dynamics modeling of viscoelastic granular materials using irregular polyhedral particles
Authors: Quezada Juan Carlos , Chazallon Cyrille
Published: June 2021

Viscoelastic granular materials are present in several disciplines. One example is asphalt mixture employed in road construction. In the last three decades, discrete element modeling has been positioned as a valid tool for the analysis of this multiphase material at the grain-scale. All this despite the simplification of the shape of the particles used in these studies. In this work, it is proposed a simplified procedure for the generation of viscoelastic granular samples composed of irregular polyhedra. The numerical aggregates were generated by a Poisson-Voronoi tessellation based on the particle size distribution (PSD) and statistic data of aggregates, without using complex imaging technics. This procedure set the porosity of the packing, while controlling the PSD. Using this procedure implies a significant computational-time reduction by skipping several preparation stages for polyhedral samples, such as deposition by gravity and compaction. This approach can be used for the study granular materials as inclusion in a solid matrix as concrete or asphalt mixtures, particle breaking, and fatigue damage of viscoelastic materials.
Structure and compressive behavior of Lightweight Clay Aggregate particle: experiments and numerical simulations
Authors: Xia Shuangshuang , Shen Zhifu , Gao Hongmei , Wang Zhihua
Published: June 2021

Lightweight Clay Aggregate (LWCA) is a kind of highly porous granular particle which is often used as lightweight backfilling geomaterials. However, the easy breakage of LWCA particle plays a negative role in its geotechnical application. This study focuses on the internal structure and compressive behavior of single LWCA particle using experiments and numerical simulations. The uniaxial compressive strength and loading stiffness of the LWCA particle is attributed to its special porous internal structure. The results could enrich our understanding in particle crushing.
Analysis of hold-up and grinding pressure in a spiral jet mill using CFD-DEM
Authors: Scott Lewis , Borissova Antonia , Burns Alan , Ghadiri Mojtaba
Published: June 2021

A spiral jet mill was simulated using Discrete Element Method modelling and Computational Fluid Dynamics. The particle behaviour and fluid motion were analysed as a function of hold-up and grinding pressure. Particle collision energy was predicted to be prevalent along the bed surface and in front of the grinding jets, as shown through the collision data recorded. The bed itself affects the fluid flow field, as momentum is transferred to the particles. Increasing the grinding pressure does not result in a proportional increase in the kinetic energy of the particle system, as the high pressure jets begin to penetrate the bed with greater ease. The particle bed moves as ‘plug-flow’, with the layers of the bed closest to chamber wall.
Direct numerical simulation of wave propagation in saturated random granular packings using coupled LBM-DEM
Authors: Cheng Hongyang , Luding Stefan , Harting Jens , Magnanimo Vanessa
Published: June 2021

Poroelasticity theory predicts wave velocities in a saturated porous medium through a coupling between the bulk deformation of the solid skeleton and porous fluid flow. The challenge emerges below the characteristic wavelengths at which hydrodynamic interactions between grains and pore fluid become important. We investigate the pressure and volume fraction dependence of compressional- and shear-wave velocities in fluid-saturated, random, isotropic, frictional granular packings. The lattice Boltzmann method (LBM) and discrete element method (DEM) are two-way coupled to capture the particle-pore fluid interactions; an acoustic source is implemented to insert a traveling wave from the fluid reservoir to the saturated medium. We extract wave velocities from the acoustic branches in the wavenumber-frequency space, for a range of confining pressures and volume fractions. For random isotropic granular media the pressure-wave velocity data collapse on a single curve when scaled properly by the volume fraction.
Implementation of numerically exact Coulomb friction for discrete element simulations in three dimensions
Authors: Sakamaki Shouta , Krengel Dominik , Mueller Jan , Chen Jian , Matuttis Hans-Georg
Published: June 2021

As a follow-up of an earlier work on the numerically exact Coulomb friction in two-dimensional simulations, we present here the relations and implementation for three-dimensional discrete element particles.
Vibration induced segregation of single large particles
Authors: Zhang Dizhe , Pinson David , Zhou Zongyan
Published: June 2021

The vibration-induced segregation (e.g., rising of one large intruder - so called Brazil Nut Effect (BNE)) is studied by discrete element method. Vibration frequency and amplitude are two dominating factors in the occurrence of BNE and a phase diagram is constructed. For fixed vibration amplitude, segregation only occurs when vibration frequency is within a certain range. Larger vibration amplitude can expand the range of vibration frequency for BNE. Size ratio and the intruder shape are studied under certain vibration conditions. Larger size ratio can enlarge the segregation intensity. The shape of the intruder influences the segregation process by the intruder′s orientation. Standing-like initial orientation can increase the time required for the intruder to reach the top while lying-like initial orientation cannot significantly affect the vertical segregation.
PyBONDEM-GPU: A discrete element bonded particle Python research framework – Development and examples
Authors: Dressler Sven , Wilke Daniel N.
Published: June 2021

Discrete element modelling (DEM) is widely used to simulate granular systems, nowadays routinely on graphical processing units. Graphics processing units (GPUs) are inherently designed for parallel computation, and recent advances in the architecture, compiler design and language development are allowing general-purpose computation to be computed on multiple GPUs. Application of DEM to bonded particle systems are much less common, with a number of open research questions remaining. This study outlines a Bonded-Particle Research DEM Framework, PyBONDEM-GPU, written in Python. This framework leverages the parallel nature of GPUs for computational speed-up and the rapid prototype flexibility of Python. Python is faster and easier to learn than classical compiled languages, making computational simulation development accessible to undergraduate and graduate engineers. PyBONDEMGPU leverages the Numba-CUDA module to compile Python syntax for execution on GPUs. The framework enables research of fibre pull-out from fibre-matrix embeddings. Bonds are simulated between all interacting particles. The performance of PyBONDEM-GPU is compared against Python CPU implementations of PyBONDEM using the Numpy and Numba-CPU Python modules. PyBONDEM-GPU was found to be 1000 times faster than the Numpy implementation and 4 times faster than the Numba-CPU implementation to resolve forces and to integrate the equations of motion.
Dynamical arrest of topological defects in 2D hyperuniform disk packings
Authors: Hong Sungyeon , Klatt Michael A. , Schröder-Turk Gerd , François Nicolas , Saadatfar Mohammad
Published: June 2021

We investigate collective motions of points in 2D systems, orchestrated by Lloyd algorithm. The algorithm iteratively updates a system by minimising the total quantizer energy of the Voronoi landscape of the system. As a result of a tradeoff between energy minimisation and geometric frustration, we find that optimised systems exhibit a defective landscape along the process, where strands of 5- and 7-coordinated dislocations are embedded in the hexatic phase. In particular, dipole defects, each of which is the simplest possible pair of a pentagon and a heptagon, come into the picture of dynamical arrest, as the system freezes down to a disordered hyperuniform state. Moreover, we explore the packing fractions of 2D disk packings associated to the obtained hyperuniform systems by considering the maximum inscribed disks in their Voronoi cells.