LIGGGHTS® - User Forum

How to calculate the forces acting on a geometry in LIGGGHTS? I need to sum up all the forces acting on all of pieces of my mesh. any help is appreciated.

Hi,

I need the average weighted pressure of the particles. Using compute pressure and compute reduce of compute stress/atom I get the same result. In Liggghts this formula is used:

I am looking for something like:

using

What is the pressure Liggghts calculate with compute pressure? Why does it differ from a the pressure on the walls of the particles? Can anyone please give a hint?

Regards,

Paul

Hi,

Hi,

I just want to say there is a new Voronoi package for Lammps by Daniel Schwen. It supports now polydispers packings, calculation of the cell surface and much more. It's already included in the Lammps git repository. You can install and compile in Liggghts without major problems, but the delivered vorotest script has to be changed, Liggghts doesn't support inline variables and the abs() function for variables yet. Done that, the tests should run without any error.

Regards,

Paul

Hi,

I need the average pressure between the particles. I tried two ways with exact the same results. compute pressure for all atoms using the temperature from a compute temp and compute stress/atom for every single particle and sum these with compute reduce. What would be faster? Is there a difference in speed between compute reduce sum and the variable sum() command?

Regards,

Paul

Hi,

I want to generate a dense packing with fix insert/pack and particle growing. This is very common and no problem with fix adapt. The growing ends when the particles have a reached a given pressure. The pressure is calculated by compute pressure. Since I have a lot of particles and slightly CPU I wonder if there is something new in interrupting a run when a special event occurs to save CPU time? Or is run N every n, check with if and going on else dump results and quit still the preferred solution?

Regards,

Paul

I am using LIGGGHTS on a bluegene/p cluster and when I attempt to run a simulation I get an error that reads:

Could not locate a fix/property storing value(s) for youngsModulus as requested by gran/hooke. (modify_liggghts.cpp:247)

I checked with the sysadmin and he has told me that there is nothing wrong with the installation. I have version 2.3.5 installed. Any help or direction at all would be greatly appreciated.

Hi,

I am wondering how the adhesion between the particles and the wall is treated. I have set up my simulation with 3 different types, 1 is the particles, 2 is the walls, and 3 is for a no friction/no adhesion symmetry plane. I have specified the cohesion as:

fix m6 all property/global cohesionEnergyDensity peratomtypepair 3 &
1000000 1000000 0000001 &
1000000 0000001 0000001 &
0000001 0000001 0000001

I am using the sphere type for the granular simulation, how could I include the potential force in the simulation? I tired us the Pair_style hybrid gran/hertz/history lj/cut 2.5. But I get an error message” pair hybrid sub-style is not used”. Can someone help me out? thanks in advance

I typically use the fix_nve integration (only updates position and linear velocity) for my granular simulations as this gives a good approximation of blocky (angular) material behaviour. I am wondering if the sjkr cohesion model can be used with this integrator or do I need to use fix_nve_sphere to get cohesion?

In the mean time, I am making a little test model.

Thank you,

Kirk