assign gravity to region

Submitted by jsams on Thu, 11/17/2016 - 23:42

I would like to study the particle dynamics of confined flow at a depth where the stress field is fully developed, i.e. the pressure is constant and independent of the vertical position. In order to limit the total number of particles in the simulation, I was wondering if it is possible in LIGGGHTS to define a region in which a higher gravity value can be assigned?
Also, if you can think of another way to achieve this I would be happy to hear your thought.

Forums:

jsams | Wed, 11/30/2016 - 05:45

Thank you Matej for your input.

The group command using the region style is a static one-time assignment and therefore only assigns the larger gravity to the particles in the respective region once. However, I need a dynamic formulation to ensure that the particles in this area exhibit a larger force on the underlying particles at all times during the simulation. I have seen that LAMMPS offers a dynamic assignment which determines the group of particles periodically. I would need something similar for the simulation in LIGGGHTS. Is that somehow possible?

Westbrink | Wed, 11/30/2016 - 10:48

Hi jsams,
I did something similiar to your application. I solved this problem by using a for-loop inside the LIGGGHTs-script.
For example:

label loop1
variable i loop ${total_steps}
group grav1 region grav_region_1
run 1000
next i
jump in.test loop1
variable i delete

The disadvantage of this method is the definition of an appropiate step-size of the loop. But for my application it worked fine.
Regards,
Westbrink

jsams | Thu, 12/01/2016 - 23:42

I implemented a loop similar to your recommendation.

Additionally, I put in the group delete command before reassigning the group (in your example: group grav1 delete). Otherwise, the particles leaving the region would still be part of the group.

It seems to do the job, I just hoped that there would be a more elegant solution.