Continuous increment of wall velocity

Submitted by Mohammad Manjiu... on Wed, 05/23/2018 - 16:41

Hi,

I want to increase my wall velocity after a certain timestep. It should be increased at my define formula until run ends. How could I do this please help. Thanks

Forums:

arnom's picture

arnom | Thu, 05/24/2018 - 09:00

What do you mean with wall velocity? A fix mesh/move or a surface velocity?

DCS team member & LIGGGHTS(R) core developer

Mohammad Manjiu... | Thu, 05/24/2018 - 12:20

Actually, I have the bottom and top wall made by lattice particle in the 2d simulation box. I want to move this both wall against each other with a continually increasing velocity (not a constant velocity) through all the time steps completed. That's mean the velocity should increasing after certain timestep and it should do the same after another certain timestep and completed the run times. Thanks

richti83's picture

richti83 | Mon, 05/28/2018 - 09:11

When your walls are made out of particles you can use fix move with style variable:
https://www.cfdem.com/media/DEM/docu/fix_move.html

If both the displacement and velocity variables for a particular x,y,z component are specified as NULL, then the position and velocity of that component is time integrated the same as the fix nve command would perform, using the corresponding force component on the atom.
..
If only the displacement variable for a component is specified as NULL, then the velocity variable will be used to set the velocity of the atom, and the position of the atom will be time integrated using that velocity.

Code: (untested)

variable v0 equal 0 #no y-z-movement
variable v1 equal $a*step*dt #pos in x
variable v2 equal -$a*step*dt #neg in x
fix move_top topwall move variable NULL NULL NULL v_v1 v_v0 v_v0
fix move_bot bottomwall move variable NULL NULL NULL v_v2 v_v0 v_v0

for STL-walls use move/mesh variable

Best,
Christian

I'm not an associate of DCS GmbH and not a core developer of LIGGGHTS®
ResearchGate | Contact

Mohammad Manjiu... | Wed, 05/30/2018 - 08:47

Thanks, Currently I am using velocity command to move my bottom and top wall against each other with the constant velocity in z-direction but I want to move these wall with my define formula not a constant parameter. In this case I have to use the variable to define the formula and using a loop to increase at a certain time but I have faced a problem with dumping these because I want to dump all the timestep at a single file with increasing velocity suppose my runtime is 10000 every 2000 step velocity should change.

https://www.cfdem.com/media/DEM/docu/velocity.html
now I am using

velocity topwall set vx vy -vz
velocity bottomwallwall set vx vy vz