Particle penetrating the wall

atul.bhagat's picture
Submitted by atul.bhagat on Thu, 05/10/2018 - 07:40

Hi all,
I am trying to simulate the single particle falling under gravity.
As a base case I took twoParticleGlowinski case, which uses IB method for particle.
In my case the particle also rotating with certain angular velocity.
the simulation is running fine but when I track the particle position I found that some part of particle is going inside
the wall (i.e. wall normal distance of particle center is less than its radius)

A quick search through forum suggest that it is due to large time step but in my case even with dt=10e-7 same thing is happening

the listing of in.liggghts_run is as follows

echo both
log ../DEM/log.liggghts
thermo_log ../DEM/post/thermo.txt

atom_style granular
atom_modify map array
communicate single vel yes

boundary f f f
newton off

units si
processors 2 2 2

region reg block 0. 1. 0. 1. 0. 4. units box
create_box 1 reg

neighbor 0.03 bin
neigh_modify delay 0 binsize 0.01

# Material properties required for new pair styles

fix m1 all property/global youngsModulus peratomtype 5.e7
fix m2 all property/global poissonsRatio peratomtype 0.45
fix m3 all property/global coefficientRestitution peratomtypepair 1 0.9
fix m4 all property/global coefficientFriction peratomtypepair 1 0.5

# pair style
pair_style gran model hertz tangential history #Hertzian without cohesion
pair_coeff * *

# timestep, gravity
timestep 0.0000001

fix gravi all gravity 9.81 vector 0.0 0.0 -1.0

# walls
fix xwalls1 all wall/gran model hertz tangential history primitive type 1 xplane 0.
fix xwalls2 all wall/gran model hertz tangential history primitive type 1 xplane 1.
fix ywalls1 all wall/gran model hertz tangential history primitive type 1 yplane 0.
fix ywalls2 all wall/gran model hertz tangential history primitive type 1 yplane 1.
fix zwalls1 all wall/gran model hertz tangential history primitive type 1 zplane 0.
fix zwalls2 all wall/gran model hertz tangential history primitive type 1 zplane 4.

# cfd coupling
fix cfd all couple/cfd couple_every 100 mpi
fix cfd2 all couple/cfd/force

# create single partciles
create_atoms 1 single .5 .5 3.5 units box
set atom 1 diameter 0.2 density 1500 vx 0 vy 0 vz 0 omegay 4

variable vx1 equal vx[1]
variable vy1 equal vy[1]
variable vz1 equal vz[1]
variable x1 equal x[1]
variable y1 equal y[1]
variable z1 equal z[1]
variable omegax1 equal omegax[1]
variable omegay1 equal omegay[1]
variable omegaz1 equal omegaz[1]
variable time equal step*dt

fix extra1 all print 100 "${time} ${vx1} ${vy1} ${vz1}" file ../DEM/post/velocity_particle_1.txt title "%" screen no
fix extra2 all print 100 "${time} ${x1} ${y1} ${z1}" file ../DEM/post/position_particle_1.txt title "%" screen no
fix extra3 all print 100 "${time} ${omegax1} ${omegay1} ${omegaz1}" file ../DEM/post/angular_velocity_particle_1.txt title "%" screen no

# apply nve integration to all particles that are inserted as single particles
fix integr all nve/sphere #wenn das ausgeblendet, dann kein vel update

# screen output
compute rke all erotate/sphere
thermo_style custom step atoms ke c_rke vol
thermo 1000
thermo_modify lost ignore norm no
compute_modify thermo_temp dynamic yes

# insert the first particles so that dump is not empty
dump dmp all custom 100 ../DEM/post/dump.liggghts_run id type x y z ix iy iz vx vy vz fx fy fz omegax omegay omegaz radius

#force : f_couple_cfd[0] f_couple_cfd[1] f_couple_cfd[2]
#node : f_couple_cfd[6]
#cell id : f_couple_cfd[7]

run 1

Any help in this regards will be highly appreciated

Atul M. Bhagat

Ermek Asylbekov | Mon, 05/14/2018 - 11:27

Hi Atul,

it's absolutely normal. The overlaping is a part of the soft sphere model which is fundamental for DEM simulations. If you'd track some particle collisions you'll find that the distance between the centers of two colliding particles is less than the sum of their radius. The overlap is used by the contact model to caculate contact forces (just look up the Hertz-Mindlin-Model).
So if your particles overlap with the wall its not a malfunction. However something went wrong if they completely penetrate the wall. In this case you should check your DEM timestep. But in your case your timestep could even be larger (~5e-4).

Regards,
Ermek