LIGGGHTS® - User Forum

I have a question regarding to the usage of a realistic Young's modulus in my simulations.
Up to now I have used a value of 5e6 N/mm² for my particles because this value is used in most of the examples. Now I want to implement a realistic value of 2.1e11 N/mm² (Steel). I know that I have to reduce the timestep, but I don't know exactly which correlation I have to consider.
In the documentation of the command "fix check/timestep/gran" there are two equations and with my parameters I get the following values for my dt_max:

I am trying to play with fcc, bcc, hcp and radom style packing. All are working fine except hcp. For all other packing the unit cell is cubic and the unit vectors in all cases possess same direction. However, it is different in case of hcp.

Hi,

I implemented mesh walls (stl file), but I faced an error. This is about unit system.
"ERROR: Mesh error: dimensions too small - use different unit system (multi_node_mesh_parallel_I.h536"

If anyone knows its reason, I am looking forward to know that.

Regards,
Rasoul

Hello all,

I cannot get the servo wall to move in the -Z direction, even if I use a negative target_val. This is how I issue the command:

variable lid_force equal -1400
fix lid0 all mesh/surface/stress/servo file LIGGGHTS_files/STL_files/in/p_lid.stl type 2 move 0 0 ${lid_height} com 0. 0. ${lid_height} ctrlPV force dim z target_val ${lid_force} vel_max 0.01

When I print the z coordinates of the wall, f_lid0[9], they are strictly increasing over time no matter what values I input for target_val.

Hello all,

I am a beginner in LIGGGHTS, I am trying to implement something similar to or the same as in the http://www.youtube.com/watch?v=muZuukjb_6k video. Did anyone work on similar use case using LIGGGHTS? I am now actually not sure if this can be implemented with LIGGGHTS. Any ideas/suggestions?

Thanks,
Pradeep

Hi everybody,

In the new version of liggghts I can not create a cylindrical wall with fix wall/gran/hertz/history. I am using this code to specify the cylwall:

fix cylwalls all wall/gran/hertz/history primitive type 1 zcylinder 0.1 0. 0.7

Is there any error in this line?

Regards,

David

Hi, all!
Today, I just saved a point data of my project from "Paraview". And i found that in my "output.csv" had something strange.
Normally, In my understanding one ID(of particle) can be assigned to only one particle so that means when you save point data from Paraview inside your output.csv file for each line shouldn't have the same ID i mean no any ID is duplicated in output.csv file (if it's duplicated that mean that the particle can be located on multiple places at one time and that's impossible)
What are you thinking about this?

I am attempting to run drum mixing simulation of packed granular bed. The trial outputs in two cases of simple cubic and HCP packing are attached with the link below:

Consider a situation in which particles have been packed between two plates and say one of the plate is being moved. The boundary conditions are periodic in the direction of movement of the plate (the plate, an imported stl, is being moved in x direction using a linear style in fix move/mesh and the boundary conditions are periodic in this dimension, but it takes the plate out of the simulation box). Is there any command in liggghts which can help. If not is there any other way to implement it in liggghts ? Please suggest, I am a new user.

I called command insert/pack to insert particles with a constant horizontal velocity(Vx). when particles hit a wall,　the wall started to move and region created by create_box become larger and larger. particles moved out of original region area. I could not understand why reason it cause region box became larger and larger.
Does it means that results of calculation is wrong and some parameters like horizontal velocity, radius of particle etc. should be changed.

Thanks in advance.

Simon