Angle of repose - does Young's Modulus have any effect?

Submitted by lcmaders on Mon, 10/02/2017 - 21:52

Hello,

I am trying to simulate the angle of repose of alumina. A picture of the simulation I am performing can be seen in the Figure attached. It is a funnel unloading alumina directly in the floor, and after a certain amount it should stabilize and one could get the angle of repose.

However, I am facing a weird behavior. After stop inserting particles, the pile of alumina (which until this point seems to have a correct angle of repose) suffers some instability and collapses a little bit, affecting the angle of repose.

I thought the particles seemed to be too soft, and that this could be related to the small value of Young's Modulus I was using (in order to reduce the time step). I am simulating right now a case with a more realistic Young's Modulus to compare, but the time step I need to use is almost unfeasible.

Does somebody have already some experience with such instabilities and knows if it is related to the Young's Modulus value?

Appreciate any feedback.

Regards,

Lisandro Maders

AttachmentSize
Image icon alumina_angle_of_repose.png25.62 KB

Forums:

paul | Tue, 10/03/2017 - 16:12

Time steps for gamma-alumina should be on the order of 1e-7 - 1e-6 s, have a look at [1], where 1.8 mm g-Al2O3 particles are used with a timestep of 2.5e-7 s as far as I remember.

You could also try outputting the kinetic and potential energies using thermo, as is done in pretty much every liggghts tutorial. Judging by this, you can
a) easily figure out whether you system has arrived in a stable state and
b) whether energy is conserved.

Greetings,
Paul

[1] Salikov V., Antonyuk S., Heinrich S., Sutkar V.S., Deen N.G., Kuipers J.A.M. (2015), Characterization and CFD-DEM modelling of a prismatic spouted bed, Powder Techn.

JoG | Wed, 10/04/2017 - 11:36

I simulated a angle of repose of ceramic particles with the highest possible modulus of 5e-5 to increase the timestep. I had no problems to match my experimental results.
I expect your problem not to be caused by the modulus. Remember that some avalanches can also occur in the experiment, so some "collapse" could even be a physical result.