Yade

relation between unbalanced force nd equilibrium

Asked by Yuri Bezmenov

Hi guys!
I'm simulating two layers of balls with some gap in between the layer. then I'm pressing the balls with a wall till the wall reaches a certain force. this force could be visualize as vertical stress on the balls. with a small number of balls this works well but when I increase the number of balls to a large value e.g. 500000, the wall reaches the target force before the gap between the layer is close. so I use unbalanced force to ensure that the system reaches equilibrium under gravity. I want to know what should be the value of unbalanced force to ensure the near equilibrium condition, which is that balls should be in contact i.e. no gap condition.
Thanks

Question information

Language:
English Edit question
Status:
Solved
For:
Yade Edit question
Assignee:
No assignee Edit question
Solved by:
Jérôme Duriez
Solved:
Last query:
Last reply:
Revision history for this message
Best Jérôme Duriez (jduriez) said : 		#1

Hi,

Quasi-static thresholds may be a matter of choice / patience before publication in the DEM literature ;-)

One could for instance aim for unbalancedForce() being under 1%, e.g. https://onlinelibrary.wiley.com/doi/10.1002/nag.2774 or https://www.sciencedirect.com/science/article/pii/S2352380817300357

But I'm not sure I completely understood your question, since there is no "gap" connection in my mind. If it is a matter of closing a hole by pushing on a stack of particles, the more particles you have (if they keep the same size when you change the number), the higher the force sustained by the wall during closing the hold (the more the springs at the particle-walls interface)

Revision history for this message
Yuri Bezmenov (yuribezmenov) said : 		#2

Hi Jérôme,
Thanks for your response.
I'm just simulating balls deposited under gravity. Once they are deposited under gravity (reached equilibrium). A wall at the top applies some force. The only thing is that there is some gap between the layers (you can imagine it as a cavity), and since balls have only friction (no cohesion), they are supposed to fill the gap. My question was how to determine the unbalancedForce() for such problems.

As you suggested for the 1% threshold value, I'm trying with that value. Earlier, I was using 3%. does this value depends on the scale/number of particles in the model, is there any way to calculate it or its just intuitive?

Thanks again.

Revision history for this message
Yuri Bezmenov (yuribezmenov) said : 		#3

Thanks Jérôme Duriez, that solved my question.