Regarding servo wall

Submitted by deepakpawar.2310 on Sat, 08/31/2019 - 16:20

I am using servo wall for the triaxial compression. I specified the 10000 N force on the inplanes wall as the target force and target velocty is 0.0001,
Howevervr timestep is 10-7 (looking for quasistatic simulation)
PID contants are
Kp = 0.01
Ki = 0
Kd =0
However the forces on the servo wall is not converging wrt to the specicified taget value
It is continuously increasing as specidief in the below figure
What would be possible solution to converge the target force on wall ??


Image icon untitled.jpg25.43 KB

saman | Sun, 09/01/2019 - 16:35

My own experience of using this servo wall:
You need to change the speed and kp to find the right value for your simulation.
At the beginning, lower or increase the kp to see which value is appropriate.

deepakpawar.2310 | Tue, 09/03/2019 - 09:35

Thanks, Saman... I am varying the value of Kp, but not got the result which I am looking for.
However you any idea about the algorithm of Servo wall. Hows it basically works?
and what is meaning of the ratio in the mode auto command, Is it possible to change it ?

saman | Tue, 09/03/2019 - 13:32

Did you change the speed too?
The ratio is described in the liggghts documents
As follows :
In the absence of neighbour particles the servo wall may move with maximum velocity (defined by vel_max). Otherwise, the maximum wall velocity is defined by ratio * min(radius) / dt. Approaching target_val the maximum velocity decreases to 0.1 * ratio * min(radius) / dt.

deepakpawar.2310 | Fri, 09/06/2019 - 14:09


Can I have your email ID