Granular shear flows between bumpy walls case

Benchmark Lead(s) Dalila Vescovi @dalila vescovi
Confirmed collaborator(s)
DEM Code name		Responsible person:
MercuryDPM		Dalila Vescovi @dalila vescovi
LAMMPS		Dalila Vescovi
Yade		Katia Boschi @Katia Boschi Roxana Saghafian Larijani
Mechsys		Marco Previtali @marco previtali
PFC Suite (commercial)		Marco Previtali @marco previtali
LIGGGHTS		Balázs Füvesi
Kratos		Rafael Rangel

Benchmark Type	Benchmark Verification Validation Challenge
Target Result	Compare accuracy of different codes in terms of profiles of continuum fields Compare computational efficiency of different codes running the same simulation
Benchmark Description We study the steady motion of a collection of N identical spheres, sheared between two parallel bumpy planes, in the absence of gravity. The two bumpy boundaries move at constant velocity V in opposite horizontal direction (see image below, front view). The planes are made bumpy by gluing Nw spheres in a regular hexagonal fashion, at close contact and aligned with the direction of the flow. The spheres glued at the walls have the same diameter d, density rhop and mechanical properties of the moving spheres. We take x and z to be the flow and shearing directions, respectively, and neglect variations in the transversal direction y. We focus on constant-volume conditions, so that the number of particles, N, and the vertical distance between the walls, H, are kept constant during shearing. Periodic boundary conditions are employed in the x- and y-directions.
Presentation delivered at the WG4 meeting in Kayseri on 03/02/2026: https://doi.org/10.5281/zenodo.18478020
Benchmark Geometry and Boundary Conditions Periodic boundary conditions in the horizontal (x-) and transversal (y-) directions Rigid boundaries on the vertical (z) direction: two horizontal rigid walls. The rigid walls are made bumpy by gluing Nw spheres in a regular hexagonal fashion, at close contact and aligned with the direction of the flow (see image below, top view). The particles glued at the walls have the same properties of the moving particles. The z-coordinates of the glued particles at the bottom and top walls are denoted by z_bot and z_top, respectively. Strain-rate control: apply a constant horizontal velocity to top and bottom walls equal to V = 1 NOTE: all the quantities are made dimensionless using the particle density rhop, the particle diameter d, and the wall velocity V (i.e., rhop = d = V = 1). The dimensions of the 2 walls are Lx and Ly, in the x and y direction, respectively. The vertical distance between the walls is H and is measured from the top edge of the bottom wall particles to bottom edge of the top wall particles (see image below, front view). The initial configuration, containing both boundary conditions and initial position of each particle, can be found in the folder “InitialGeometricalConfiguration” at the following link:
File name	Description	Location/link
GranularShearFlow.restart	Initial configuration	https://github.com/dalilavescovi/GranularShearFlows/
Image: initial configuration and geometry
Particle Type	Spheres
Mixture Type	Monodisperse
NOTE: all the quantities are made dimensionless using the particle density rhop, the particle diameter d, and the wall velocity V (i.e., rhop = d = V = 1). Particle properties
diameter	d = 1
density	rhop = 1
normal stiffness	kn = 2e5
tangential stiffness	kt = 5.7143e+04
normal damping (coefficient gamman)	gamman = 15
tangential damping (coefficient gammat)	gammat = 4.2857
interparticle friction coefficient	mup = 0.3
Contact model(s) and properties The contact law is visco-elastic in the normal direction, and visco-elastic frictional in the tangential direction Normal direction: spring of stiffness kn, placed in parallel with a viscous damper of damping coefficient gamman. Tangential direction: spring-dashpot system (in parallel with equivalent stiffness kt and damping coefficient gammat) in serie with a slider of friction coefficient mup (mup = tanφ (being φ the friction angle). ON-DEM Contact Model Database Reference:


Simulation setup Parameters for simulation and analysis.
Velocity of top wall (magnitude)	V = 1
Simulation time-step	dt = 7.1925e-05 (tc/50 where tc is the contact time)
Number of simulation time steps	Nt = 2e8
Saving time interval	dt_s = dt*50000 = 3.5963 (save data every 50000 simulation time-steps)
Number of saving time intervals	Nt_s = Nt/50000 = 4000
Neighbor search frequency	1
Additional details	directly loaded from the initial configuration file
Number of “moving” particles	N = 3000
Number of particles glued at each wall	Nw = 240
Domain size in x-direction	Lx = 20
Domain size in y-direction	Ly = 6*sqrt(3) = 10.3923
Vertical distance between the walls	H = 20
Domain size in z-direction	Lz = H + 2*d = 22
x-limits of the domain	xmin = 0; xmax = xmin+Lx = 20
y-limits of the domain	ymin = 0; ymax = ymin+Ly = 10.3923
z-limits of the domain	zmin = 0; zmax = zmin+Lz = 22
z-coordinates of the glued particles at the bottom and top walls	z_bot = 0.5; z_top = 21.5
Initial configuration The initial configuration, containing both boundary conditions and initial position of each particle, is provided by the file GranularShearFlow.restart, which can be found in the folder “InitialGeometricalConfiguration” at the following link: http://github.com/dalilavescovi/GranularShearFlows/ File type(s): .restart file Additional details: the initial configuration is a collection of N = 3000 spherical particles of diameter d = 1, randomly and homogeneously placed between two bumpy walls. The two bumpy walls are composed of Nw = 240 spherical particles arranged in a regular hexagonal fashion, at close contact and aligned with the direction of the flow.
Output data format The Open DEM format must be used. Please specify format for any data not specified. Include an example as a file stored in a repository To perform the coarse-graining, we use the post-processing tool ``MercuryCG'' provided with the open-source DEM code MercuryDPM. The “discrete” output files must be compatible with the MercuryCG, so that, at each time step, two type of files must be generated: .data file: this is composed by a series of N subsequent lines, each providing information for one particle within the system. .fstat file: this is composed by a series of Nc lines corresponding to each of the Nc particle contacts within the system at the current instant in time. NOTE: both file types must share the same base name, at each saving step, one .data file and one .fstat file must be generated, with a number indicating the time step appended after the file extension. For example, if the simulation is named “ShearFlow”, the outputs are: ShearFlow.data.0000, ShearFlow.data.0001, ShearFlow.data.0002, …, ShearFlow.data.4000 ShearFlow.fstat.0000, ShearFlow.fstat.0001, ShearFlow.fstat.0002, …, ShearFlow.fstat.4000 Examples of the output format at a given time step can be found in the folder “outputs_example” at the following link: https://github.com/dalilavescovi/GranularShearFlows/ See http://docs.mercurydpm.org/Trunk/db/da1/VisualisingYourResults.html and “Additional specifications” here below for details on the .data and .fstat files format. Additional specifications: The final goal is to plot the vertical distribution (profile), obtained after coarse-graining at the steady state, of the following continuum fields: horizontal velocity concentration granular temperature pressure (which should be homogeneous) shear stress (which should be homogeneous) To obtain the local profiles of the continuum variables, once the steady state is reached, measurements are averaged in time, over the last 2000 saving time intervals, and over the lengths of the domain along the x and z directions, using 100 horizontal slices. Measured profiles of concentration obtained with Lammps (blue squares) and MercuryDPM (red dots) Output files format compatible with MercuryCG: .data files format First line: `N, time, xmin, ymin, zmin, xmax, ymax, zmax` N: number of particles time: time step when the output was written xmin, ymin, zmin, xmax, ymax, zmax: maximal and minimal spatial boundaries defining the computational volume used in the simulations Following lines: a series of N subsequent lines, each providing information for one particle within the system. These parameters are output in the following order: `rx, ry, rz, vx, vy, vz, rad, alpha, beta, gamma, omex, omey, omez, info` (rx,ry,rz): particle current position in three dimensions (vx,vy,vz): magnitudes of the three components of particle instantaneous velocity rad: radius of the particle (alpha,beta,gamma) particle angular position (given via the three Euler angles) (omex,omey,omez): particle instantaneous angular velocity info: represents an additional variable (set to 0) .fstat file: First three lines (each preceded by a ‘hash’ symbol #): `# time 1 # xmin ymin zmin xmax ymax zmax # 0.5 0.5 0 0 0 0` time: time step when the output was written xmin, ymin, zmin, xmax, ymax, zmax: maximal and minimal spatial boundaries defining the computational volume used in the simulations numbers are not used for analysis Following lines: a series of Nc lines corresponding to each of the Nc particle contacts (as opposed to particles) within the system at the current instant in time. Each of these lines is structured as follows: `time, i, j, cx, cy, cz, delta, deltat, fn, ft, nx, ny, nz, tx, ty, tz` (i, j): id of the 2 particles at contact (cx,cy,cz): position of the contact point in three dimensions delta: overlap between the two particles deltat: length of the tangential elongation fn: magnitude of the normal component of the contact force ft: magnitude of the tangential component of the contact force (nx, ny, nz): unit vector normal to the contact plane (tx, ty, tz): unit vector tangential to the contact plane NOTE: particle-particle contacts are considered twice, while particle-wall particle contacts are considered only once. Therefore, if both i and j are moving particles, the .fstat file appears as time, i, j, cx, cy, cz, delta, deltat, fn, ft, nx, ny, nz, tx, ty, tz time, j, i, cx, cy, cz, delta, deltat, fn, ft, -nx, -ny, -nz, -tx, -ty, -tz Conversely, if i is a moving particle and j is a wall particle, only the first line appears in the .fstat file.
Other considerations and notes Please use this space to provide any additional information and/or data not covered in the previous sections of the template
Tentative schedule
Expression of interest by:	April 2025
Start date (data received from):	April 2025
Submission deadline for data:	April 2026
Data analysis to be completed by:	June 2026
Tentative publication date for draft submission	July 2026