Hi,
I have a problem when trying to model atoms which are 100um in diameter. When the atom size is 100um in diameter, the atoms keep lost during the process, and it won't happen when atom size is larger than 0.001m. Could anyone explain why it happen and how to fix it? I tried to change the units to cgs, but it did not work...
atom_style granular
atom_modify map array
boundary f f f
newton off
communicate single vel yes
units si
region reg block -0.05 0.05 -0.05 0.05 0. 0.15 units box
create_box 1 reg
neighbor 0.05 bin
neigh_modify delay 0
#Material properties required for new pair styles
fix m1 all property/global youngsModulus peratomtype 5.e6
fix m2 all property/global poissonsRatio peratomtype 0.45
fix m3 all property/global coefficientRestitution peratomtypepair 1 0.051
fix m4 all property/global coefficientFriction peratomtypepair 1 0.05
fix m5 all property/global characteristicVelocity scalar 2.
fix m6 all property/global cohesionEnergyDensity peratomtypepair 1 500000
#New pair style
pair_style gran model hertz tangential history cohesion sjkr #Hertzian with cohesion
pair_coeff * *
timestep 0.00001
fix gravi all gravity 9.81 vector 0.0 0.0 -1.0
fix zwalls1 all wall/gran model hertz tangential history primitive type 1 zplane 0.0
fix zwalls2 all wall/gran model hertz tangential history primitive type 1 zplane 0.15
fix cylwalls all wall/gran model hertz tangential history primitive type 1 zcylinder 0.05 0. 0.
#region for insertion
region bc cylinder z 0.01 0.01 0.025 0.05 0.0603 units box
group nve_group region reg
#distributions for insertion
fix pts1 all particletemplate/sphere 15485863 atom_type 1 density constant 2500 radius constant 0.00005
fix pdd1 all particledistribution/discrete 15485867 1 pts1 1.0
#particle insertion
fix ins nve_group insert/pack seed 32452843 distributiontemplate pdd1 vel constant 0.0 0.0 -0.002 &
maxattempt 1000 insert_every 1000 overlapcheck yes all_in yes &
region bc particles_in_region 250 ntry_mc 10000
#apply nve integration to all particles that are inserted as single particles
fix integr nve_group nve/sphere
#output settings, include total thermal energy
compute rke all erotate/sphere
compute str all stress/atom
thermo_style custom step atoms ke c_rke vol
thermo 1000
thermo_modify lost ignore norm no
#insert the first particles so that dump is not empty
run 1
dump dmp all custom/vtk 1000 post/cohesion_*.vtk id type type x y z ix iy iz vx vy vz fx fy fz omegax omegay omegaz radius c_str[3]
#insert particles
run 5000
unfix ins
#run
run 30000 upto
Thanks a lot!
richti83 | Tue, 11/06/2018 - 08:43
Timestep
You need to decrease your timestep bc. critical delta_t=sqrt(m/K) and mass decreases cubical with diameter !
see https://www.researchgate.net/publication/241224401_Selecting_a_suitable_...
for more information.
For beginners it is a good idea to use fix check/timestep/gran with a maximum warning threshold of 0.1
mxg1265 | Tue, 11/06/2018 - 17:45
particle insertion problem
Thanks for your help! I adjusted the timestep to 2.e-10, however, there is a new problem... only one insertion at first step but no insertion anymore at following steps even before unfix insertion. Could you please tell me what is wrong?
richti83 | Tue, 11/06/2018 - 19:18
How did you came down to a dt
How did you came down to a dt of 2e-10 ? I guess it takes much to long that the particles leaves the region because they move only a very short distance between 1000 iterations and the insert pack command only inserts when number-particles-in-region is less than your defined 250.
I would recommend to read some DEM Basics and adjust diameter, timestep and young modulus to more reasonable values.