region move

LAMMPS LAMMPS Mailing List Mirror
#1

Greetings,

I am having difficulties getting a region to "move". The following code successfully generates a region within my domain:

region myCyl cylinder z 10.0 10.0 11.0 0.0 9.0 side out
fix wall all wall/region myCyl lj93 1.0 1.0 2.5

However, whenever I try to add "move" to the region command, e.g.

region myCyl cylinder z 10.0 10.0 11.0 0.0 9.0 side out move 0.3 NULL NULL

I receive the following error:

LAMMPS (13 May 2014)
WARNING: OMP_NUM_THREADS environment is not set. (../comm_brick.cpp:82)
  using 1 OpenMP thread(s) per MPI task
ERROR: Illegal region command (../region.cpp:319)

Or, if I try to use a variable (as in the online documentation), e.g. with:

variable v_x equal 0.3
region myCyl cylinder z 10.0 10.0 11.0 0.0 9.0 side out move v_x NULL NULL

I receive the following error:

LAMMPS (13 May 2014)
WARNING: OMP_NUM_THREADS environment is not set. (../comm_brick.cpp:82)
  using 1 OpenMP thread(s) per MPI task
ERROR: Variable name for region does not exist (../region.cpp:64)

Strangely, if my move arguments are "NULL NULL NULL" the program runs fine. This might be a meaningless artifact though.

FWIW, my starting point was the in.pour example, I would eventually like the cylinder to move sinusoidally with time, and I am running this through the version obtained via ubuntu apt-get.

Can anyone suggest a correct way to implement region movement (move or rotate)? I imagine it is a simple fix, but I have searched and cannot find a solution.

Thanks,
Jeremy

#2

You can’t do this (see the doc page):
region myCyl cylinder z 10.0 10.0 11.0 0.0 9.0 side out move 0.3 NULL NULL

You have to do what you tried 2nd:
variable v_x equal 0.3
region myCyl cylinder z 10.0 10.0 11.0 0.0 9.0 side out move v_x NULL NULL

However, the syntax for defining the variable you want is

variable x equal 0.3

However, as the region doc page says, that variable
is supposed to return the displacement of the region
as a function of time. If you define the variable

to be a constant (0.3), then your region will
not “move”. See the ramp() function on the variable
doc page for a simple example, or the swiggle() function
if you want a sinusoidal variation in the region’s position.

Steve