Submitted by Delinz on Tue, 05/16/2023 - 10:51

Hi everyone,

I'm working on a DEM simulation of TRIAXIAL COMPRESSION TEST (Lateral wall under constant pressure, fixed bottom, and strain(velocity) controlled loading at the top) on a cylindrical shaped assembly of particles recently. Some questions bothered me so I'd like to ask for suggestions on how to implement the requirements using existing commands without programming.

1. I used the fix mesh/surface/stress/servo command to implement the servo control. This command can specify only one direction. So I want to ask if there is a way to apply a uniform force along a curved boundary.

2. This question is more IMPORTANT. There is no flexible boundary in LIGGGHTS to simulate the real membrane. I think it's a good idea that many papers divide cylindrical boundaries into different parts. Dilatancy in real triaxial compression test can be simulated by different displacement of different parts (They use PFC to achieve this). In LIGGGHTS, commands fix mesh/surface/stress/servo and fix wall/gran create walls that can be pushed by servo forces, but do not move in the opposite direction due to particles forces. I would like to ask if there is a command in LIGGGHTS to set up a non-fixed wall that can be pushed by servo forces, but can also be pressed by particles that resist servo forces or even move against them.

Any response from you will help. Thank you in advance.


Chen Shihang | Fri, 06/02/2023 - 12:07

I also encountered this problem when trying to model the soil dilatancy during the water injection.
So I want to know whether we can write a code to control the direction of the wall's velocity to realize the servo like in PFC.
And I also do not see any cases about the servo of a cylinder wall.
It would be great If you have any ideal about all these codes or servo command later.
Thank you !