Using addforce command in lammps to give external force to granular particles.

LAMMPS
1

Hi there,

I am currently doing a granular simulation where i want to give impulsive force to my bottom layers of grains. In order to do so i have created a region contaning only the bottom granular layer & grouped them. When i use add force command all i can see is that layer gets deleted or vanished somehow from the system.
I want some help regarding this.

i am also providing my code later of the code for this.

The code is

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

Define the bottom layer region (adjust height based on grain diameter)

variable layer_height equal {d1} # Height of the first layer region bottom_layer block 0 {boxx} 0 {boxy} 0 {layer_height}

Group for grains in the bottom layer

group bottom_grains region bottom_layer

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

Apply impulsive load to only the bottom layer of grains

###############################################
variable force_magnitude equal 300.00
fix impulse bottom_grains addforce 0.0 0.0 ${force_magnitude}

Run the simulation briefly to apply the impulse

run 26

Remove the impulse force

unfix impulse

Continue running to observe the behavior after impulse

run 20000

2

Why not just use “velocity add”?

How did you determine the magnitude of the force that you apply?

3

using spring constant values.
i am using the formula impulse = mass ( final velocity - inital velocity) and for time calculation i am using T = 2pisqurt(mass/spring constant) and then i use Force = impulse/ time so get the force magnitude and use that as an input