Gravity for settling does not work

Dear particle friends

Based on a LIGGGHTS-Tutorial I have set up a planar sandglass. As first step I will fill in some particles and let them settle. A simple case I guess. But the gravity is totally inactive. I checked the input script several times tried some changes, checked the help, the forum an so on. It's no use.

Is there anybody who can quick check my script and check if it runs properly?

Thanks a lot for help.
Cilo

Attachment	Size
Whole simulation case	18.44 MB

Forums:

LIGGGHTS® - User Forum

nasato | Wed, 10/12/2016 - 09:47

Hi,

You are creating particles in the "all" group and integrating particles in the "nve_group" group.

Either change fix ins all insert/pack to fix ins nve_group insert/pack or

change fix integr nve_group nve/sphere to fix integr all nve/sphere

Best,

Nasato

Claudio Wolfer | Wed, 10/12/2016 - 10:17

Great

Dear Nasato

Thanks a lot for this quick help. It fixed the biggest problem.
The next problem is that the particles diminished. But I hope I will find some answers in the forum to this topic.

Thx
Cilo

nasato | Wed, 10/12/2016 - 11:24

Hi Claudio,

Your mesh refinement is not good. The Stl element size is just way too big (in the order of meters for front and back walls) and cannot be detected properly by the neighboor list, so particles just cross through it.

Refining the mesh using smaller elements solved the problem here.

Best,

Nasato

Claudio Wolfer | Wed, 10/12/2016 - 11:50

Hand made mesh

Dear Nasato

Ok, I understand. The current mesh is written by hand. And yes it's a bit greenly from me to use such a coarse mesh. In lack of a better geometry, I fixed the problem using wall/gran with primitive planes. For the real geometry of the sandglass I will use a finer mesh.

Thanks
Cilo

z3490628 | Sun, 10/01/2017 - 08:55

Same Problem

Hi all,

I have a similar problem. The gravity command seems to be inactive and I don't know why. Attached with my script. Thanks

#Setup
atom_style granular
boundary f f f
newton off
atom_modify map array

communicate single vel yes
units si
newton off
dimension 3
echo both

region reg block 0. 0.1 0. 0.1 0. 0.1 units box
create_box 2 reg #simulation box

neighbor 0.001 bin
neigh_modify delay 0

#Material properties required for new pair styles

fix m1 all property/global youngsModulus peratomtype 5.e6 5.e6
fix m2 all property/global poissonsRatio peratomtype 0.2 0.2
fix m3 all property/global coefficientRestitution peratomtypepair 2 0.5 0.5 0.5 0.5
fix m4 all property/global coefficientFriction peratomtypepair 2 0.45 0.45 0.45 0.45
#fix m5 all property/global characteristicVelocity scalar 2.

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

timestep 1e-8
fix ctg all check/timestep/gran 2000 0.2 0.2

fix 2 all gravity 9.81 vector 0.0 0.0 -1.0

#distributions for insertion
fix pts1 all particletemplate/sphere 15485863 atom_type 1 density constant 2230 radius constant 0.0025

fix pdd1 all particledistribution/discrete 32452843 1 pts1 1

# Interaction bewtween walls and particles
fix xwalls1 all wall/gran model hertz tangential history primitive type 2 xplane 0
fix xwalls2 all wall/gran model hertz tangential history primitive type 2 xplane 0.1
fix ywalls1 all wall/gran model hertz tangential history primitive type 2 yplane 0
fix ywalls2 all wall/gran model hertz tangential history primitive type 2 yplane 0.1
fix zwalls1 all wall/gran model hertz tangential history primitive type 2 zplane 0
fix zwalls2 all wall/gran model hertz tangential history primitive type 2 zplane 0.1

# Group
group nve_group region reg

# Insertion
fix ins nve_group insert/pack seed 32452867 distributiontemplate pdd1 overlapcheck no insert_every once all_in yes particles_in_region 8000 region reg

# Time Integrate
fix integr nve_group nve/sphere

# Energy
compute 1 all erotate/sphere
thermo_style custom step cpu cpuremain atoms ke
thermo 1000
thermo_modify lost ignore norm no

#dump commands
run 1
dump dmp all custom 1000 stage1/dump*.setup id type type x y z vx vy vz fx fy fz omegax omegay omegaz radius

# Restart file
restart 10000 stage1/setup.restart

#insert particles
run 300000