LIGGGHTS® - User Forum

pair/gran/hooke and wall/gran/hooke does not work correctly. For example, the source "pair_gran_hooke.cpp" contains lines number 197-206 with the code:

// force normalization

fn = xmu * fabs(ccel*r);
fs = gammat*vrel;
if (vrel != 0.0) ft = MIN(fn,fs) / vrel; ======== ??? ========
else ft = 0.0;

// tangential force due to tangential velocity damping

fs1 = -ft*vtr1;
fs2 = -ft*vtr2;
fs3 = -ft*vtr3;

Hi everyone,
I have tried to calculate the velocity of particles based on their position, but the results show that the velocities which I calculated are exactly twice the dumped velocity. I have checked the time interval, I used the real time as follows:
"real time=timestep*No. of steps"
I was wondering if anyone has any idea why this happens?or what am I doing wrong?

Cheers,
Mahsa

I am performing a long-running simulation in LIGGGHTS. It has approx 10,00,00,000 steps and dump files are written per 1000 time-steps. Working with such huge number of files, it becomes really difficult to perform lpp processing of all at a time. If I need to check the progress while the simulation is on the go everytime above command starts from beginning which is clearly a waste of time. Also, if any interruption happens or error comes then I have to perform lpp from beginning with the command lpp dump*.mixer.

Hi,

I want to simulate the material behaviour on a vibrating tray. I search for a feature which allows me to insert the particles which leave one side of the simulation on the opposite site. For insrance if the material on the tray moves from left to right and reaches the right end of the simulation the particles are moved to the left side (e.g. if xpos > 100 then xpos = xpos - 100).

Is there anything like this available or do I need to modify code to reach simulate this? I do not have experience in modifying or add commands.

Thanks in advance,

Urs

Hi,

I'd like to compress a box includes particles in all 6 directions. For doing that I have to build six (6) 2-D plate (stl file) and use "mesh/surface/stress/servo" for every plate. Is it true?
Or, I can build a 3-D box and compress in all 6 directions. If it is possible, would you please inform me how can I do that.

Best Regards,
Rasoul

Is there a LIGGGHTS capability to take a particle under given conditions and split it / replace it with several smaller particles? I'm specifically looking for a solution within the "granular" atom-style world (but it could be a hybrid style).

I could have sworn I saw an example of this a few months ago, but I can't find it now. Was this the multisphere capability? (node/20 illustrates multiple particles bonded together, but I want one particle that splits into multiple independent particles).

Thanks!

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.