Hi everyone,
I am managing to implement the mesh/stress/servo command in my simulation. In my case, I would like to use the command to compress a packing by a small vertical force, i.e. I just want to flatten the top surface of the packing rather than strongly compress it. In other words, I just want to use a small force to compress the packing, thus I use CtrlPV force and target_val 0.003 as the parameters.
However, as I record the force output of this command (in my case, f_top[9]), some of my case generate a force differing from the target_val significantly. My question is
What is the meaning of the target_val? does it mean the force applied on the mesh to maintain the position or the total contact force on the mesh by the packing?
What is the different between this two commands?
fix servo all mesh/surface/stress/servo file a.stl type 1 com 0. 0. 0. ctrlPV torque axis 0. 0. 1. target_val -0.003 vel_max 1. ratio 0.01 mode auto
fix servo all mesh/surface/stress/servo file a.stl type 1 com 0. 0. 0. ctrlPV torque axis 0. 0. -1. target_val 0.003 vel_max 1. ratio 0.01 mode auto
I use these two commands in the same simulation and get the identical result.
Thanks
Weijing
mschramm | Tue, 06/27/2017 - 15:32
force or torque
Hello,
Are you wanting to apply a specific force or torque? You said force at the beginning but your commands are specifying that you want a target torque.
You may also want to double check the mesh/surface/stress page (https://www.cfdem.com/media/DEM/docu/mesh_module_stress.html)
The first 3 enteties for f_top[j] are force, the next 3 are torque, followed by position.
Target value is the "wanted" force/torque for the mesh. The servo is set up as a PID controller however, auto mode makes it a proportional controller with a max mesh
velocity that is dependent on ratio (https://www.cfdem.com/media/DEM/docu/mesh_module_servo.html).
Weijing | Mon, 07/03/2017 - 17:07
Thank you very much for the
Thank you very much for the reply.
First I apologise for my typo in the command showing in the post. it should be force instead of torque. the purpose of the two command is whether the response of the mesh wall in the two command are the same if I play with the direction and force sign.
Weijing