Bulk Density

Submitted by srguya on Sat, 03/25/2017 - 17:53

Hi

Can someone assist me on how I can insert particles into a fixed volume so that I achieve a desired bulk density. Are there any insertion related variables that I can play around with?

Regards

Forums:

estefan31 | Sun, 03/26/2017 - 08:18

I haven't tried this yet in LIGGGHTS, but I think you can use the 'set' command to change the density of the particles. So if you calculate the volume containing the particles and the total solid volume of the particles, you can calculate the particle density that would give you the desired bulk density. This would probably have to be done after you finish inserting the particles, so if gravity is applied then you will have some rebound or compression depending on the change in the total weight of the particles. Or if you know ahead of time the volume that will contain your particles, you can use fix insert/pack and use the volumefraction_region or mass_in_region parameters to achieve the desired bulk density.

srguya | Sun, 03/26/2017 - 10:13

i tried this approach where I set a particle density value to give me a desired bulk density for a fixed volume. However when I repeated the same experiment with a different volume and same particle density I get a very different bulk density. To make sure all the particles are contained in the volume, I first fill the volume to the brim, then scrap the material level with top surface of my container, wait for some time for all the particles outside to leave the computational domain i.e when mass remains constant(monitoring on screen). Then I divide the residual mass by the volume. The densities I get with two different volumes are so different.
can it be that there are insertion related variables I need to play around with?

estefan31 | Sun, 03/26/2017 - 20:45

That's because you have to change the particle density if you change the volume. Bulk density is just total mass over total volume, so from your description it sounds like you increased the volume without also changing the total mass. Before changing the density make sure you tell your code to calculate the total volume of solids and then set the particle density to the value that will give you the desired bulk density. I'm assuming this is all for mass density, but if you're aiming for a specific number of particles per volume then you can use the fix insert/pack command to insert a specific number of particles.