Orientation of spherical particles

Hi All,

I am trying to track the particle orientation during the simulation, I need to use that later on to specify the exact position of contact on the surface of the particle.

I took zamir's example (http://www.cfdem.com/forums/fix-nvesphereorientation) as staring point to my case and I tried to validate it but the output does not seem right to me when comparing the results in paraview with dump file, I don't know if I am missing something here.

Just a quick reminder for zamir's example, he developed his own integrator for tracking quaternion orientations and used "atom_style hybrid granular molecular ellipsoid" that included two bonded ellipsoid particles (group rigid_group id 1:2) which rotate after being hit by normal particle (group vel_group id 3), as in video 1.

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(1)- By comparing the output of particles orientations in the beginning of the simulation ( 0 time step) and at the end of the simulation ( 10000 time step) I cannot not see that noticeable difference, as follow:

# Original used integrator commands (1)

fix integr rigid_group nve/sphere/orientation
fix integr2 vel_group nve/sphere

Dump output

ITEM: TIMESTEP
0
ITEM: NUMBER OF ATOMS
3
ITEM: BOX BOUNDS ss ss ss
-1e-05 1e-05
-0.00301 1e-05
-1e-05 0.00301

ITEM: ATOMS id omegax omegay omegaz radius c_quatw c_quatx c_quaty c_quatz
1 0 0 0 0.0015 0.418121 0.250873 0.250873 0.836242
2 0 0 0 0.0015 0.418121 0.250873 0.250873 -0.836242
3 0 0 0 0.0015 0 0 0 0

ITEM: TIMESTEP
10000
ITEM: NUMBER OF ATOMS
3
ITEM: BOX BOUNDS ss ss ss
-1e-05 1e-05
0.0027416 0.00747498
0.00104925 0.00301

ITEM: ATOMS id omegax omegay omegaz radius c_quatw c_quatx c_quaty c_quatz
1 -1222.54 0 0 0.0015 0.418122 0.250871 0.250875 0.836241
2 -974.384 0 0 0.0015 0.418122 0.250871 0.25087 -0.836243
3 1.42823e-05 0 0 0.0015 0 0 0 0

######################################################################
(2)- I was not sure if the above output were correct or not, so I changed the integrator commands and used the original one for asphere package as bellow. In this case there was clear change in quaternion values but angular velocity (omega) was zero, by looking into paraview the bonded particles were only moving in a linear direction (no rotation).

# integrator commands (2)

fix integr rigid_group nve/asphere
fix integr2 vel_group nve/sphere

Dump output

ITEM: TIMESTEP
0
ITEM: NUMBER OF ATOMS
3
ITEM: BOX BOUNDS ss ss ss
-1e-05 1e-05
-0.00301 1e-05
-1e-05 0.00301

ITEM: ATOMS id omegax omegay omegaz radius c_quatw c_quatx c_quaty c_quatz
1 0 0 0 0.0015 0.418121 0.250873 0.250873 0.836242
2 0 0 0 0.0015 0.418121 0.250873 0.250873 -0.836242
3 0 0 0 0.0015 0 0 0 0

ITEM: TIMESTEP
10000
ITEM: NUMBER OF ATOMS
3
ITEM: BOX BOUNDS ss ss ss
-1e-05 1e-05
0.0028226 0.0103716
0.000436303 0.00301

ITEM: ATOMS id omegax omegay omegaz radius c_quatw c_quatx c_quaty c_quatz
1 0 0 0 0.0015 0.425928 0.237377 0.27748 0.827794
2 0 0 0 0.0015 0.475382 -0.108509 -0.398022 -0.777056
3 -4.59499e-05 0 0 0.0015 0 0 0 0

###########################################################################
(3)- In the last case I applied the "sphere" integrator to all particles in addition to "asphere" integrator to the two ellipsoid particles. In this case I have completely different values for angular velocity and particles quaternion (video 3).

# integrator commands (3)

fix integr rigid_group nve/asphere
fix integr2 all nve/sphere # apply for "all" particles instead of only "vel_group"

Dump output

ITEM: TIMESTEP
0
ITEM: NUMBER OF ATOMS
3
ITEM: BOX BOUNDS ss ss ss
-1e-05 1e-05
-0.00301 1e-05
-1e-05 0.00301

ITEM: ATOMS id omegax omegay omegaz radius c_quatw c_quatx c_quaty c_quatz
1 0 0 0 0.0015 0.418121 0.250873 0.250873 0.836242
2 0 0 0 0.0015 0.418121 0.250873 0.250873 -0.836242
3 0 0 0 0.0015 0 0 0 0

ITEM: TIMESTEP
10000
ITEM: NUMBER OF ATOMS
3
ITEM: BOX BOUNDS ss ss ss
-1e-05 1e-05
0.0026282 0.00685195
3.98907e-05 0.00301

ITEM: ATOMS id omegax omegay omegaz radius c_quatw c_quatx c_quaty c_quatz
1 -1824.51 0 0 0.0015 0.487325 -0.0166423 0.665057 0.56563
2 -1671.08 0 0 0.0015 0.487322 -0.0167223 -0.244013 -0.838269
3 7.92575e-06 0 0 0.0015 0 0 0 0

##############################################################################

I am getting very confused between these cases and if any of them are correct to get the particles quaternions or not.

Any help would be very appreciated.

Thanks in advance.

Luton