Confining pressure (fix mesh/surface/stress/servo)

Hi all,

I have try to use the 'fix mesh/surface/stress/servo' to apply confining pressure on each sides of a cubic box. (100mm*100mm*100mm)

I want to apply 200kPa confining pressure on each sides with the following command. Take the left side as an example

fix zservo2 all mesh/surface/stress/servo file meshes/rwall4.stl type 1 com 0. 0. 0. ctrlPV force axis 1. 0. 0. target_val 2000 vel_max 100. kp 1e-2. ki 0. kd 0. #left

I have tried different 'target_val' values (eg 'target_val 200000). However, when I check the dump file. The normal stress average values are both in the range of roughly 20000 to 40000.

How does the 'target_val' value affect the normal stress average values? Did I apply it correctly?

Thanks,
Josh