Fix smd puling in opposite direction?

Hello to everzone,
I am performing a pullout test in a CNT wich is embeded in an epoxz resin. The boundary conditions are periodic in every direcrtion.
The box dimentions are given below

-21.274592 21.871111 xlo xhi
-17.601338 16.840523 ylo yhi
-61.149093 59.899780 zlo zhi

The pullout direction is z axis (the CNT is aligned in z axis)

The commands for pullout and the constrain of the epoxy matrix are given below

fix smd_disp CNT smd cvel 20.0 0.0001 tether NULL NULL 100.0 0.0
fix bound polymer spring tether 50.0 0.0 0.0 0.0 0.0

and the initial coordinates of the CNT centermass are

x y z
-0.48 0.86 -6.15

The pullout velocity is possitive as it is clear from the fix smd command format and the point wich the spring is attached is also in the positive direction outside the box. But it seems that the pullout is going on the oposite direction (negative) because as the simulation progresses the z coordinate of the CNT centermass is going further negative.

Doed anyone knows why?

I will also attach the data and input file

Thanks! (6.5 MB) (12.7 KB)

The documentation says:

In cvel mode the distance R is incremented or decremented monotonously according to the pulling (or pushing) velocity.

Since you want to pull the CNT toward the tether point you must decrement the distance and thus the velocity should be negative.


Thank you axel!