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Hello Team,

Good morning. I'm trying to learn LIGGGHTS to simulate the filling of the spherical particles into a cuboid container defined by 6 planes oriented along X-Y-Z axes.

One way to do that is to inject particles from the top of the cuboid (zMax plane) under gravity and allow them to settle onto zMin plane, bounded by xMin, xMax, yMin and yMax planes.
1. In order to expedite the filling, if I release particles with certain non-zero velocity, the particles escape from the bottom plane. But when I release the same particles with zero velocity and allow them to fall under gravity alone, they fill into the container (rest all remaining intact). My understanding is that there is a relation between the particle velocity (near to the wall) and time-step in the simulation.
A. How can we estimate required/appropriate time-step assuming we know the particle velocity at the wall?

The other way to fill the particles is to initialize using region based volume fraction fix.
1. I've observed that for a given volume of simulation box, there is a maximum number of particles that can be initialized and this number does not change even if we increase the volume fraction value.
B. How can we best estimate this number and avoid run-time warnings?
2. Also, my observation is that particles are attracted towards each other as they fall under gravity after initialization. I've attached an image for your reference. They coalesce and try to settle under gravity.
C. What are the different forces that are in play apart from gravity?
D. Can we disable all the other forces apart from gravity so that particles settle down faster?

Thank you,
Jagan1Mohan