LIGGGHTS® - User Forum

Dear DEM users,

I am struggling with an error which has been keeping at a position for several months. I am current modeling a large number of particles, e.g., 190K and 400K particles using a 40 cores computer. The diameter ranges widely from 0.01mm to 1.0mm. The major problem of this simulation is "Neighbor list overflow, boost neigh_modify" which indicates there are too many particles in the neighbor list. I have changed lots of parameters including the skin, the number of processors, the friction and reconstitution coefficients... but no one works.

I'm trying to model a structure sitting atop a granular assembly of multisphere particles. The structure is modeled as 1 large box-shaped multisphere particle containing about 300 constituent spheres. The structure as a whole extends across about 3 to 5 processor sub-domains in a simulation run with 80 or more cores. My problem is that when I insert this structure, the number of ghost atoms increases from about 100,000 to 1,000,000. The simulation becomes considerably slower, and the run time increases by a factor of about 20.

Hi there,

I am getting a "WARNING: One or more atoms are time integrated more than once" which I believe I have tracked down to two lines:

fix fu all move variable NULL NULL NULL NULL v_Vy NULL units box
fix gravity all gravity 9.81 0 -1 0

i.e., I am doing a gravity and also a forcing via a variable Vy. My results are looking a bit odd, so I am wondering if I should instead incorporate the gravity into the fix move? i.e. making the value "v_Vy - 9.81*time" instead of "v_Vy"?

Or is it fine to have this warning?

Dear all,

I come back to this topic again. I had time last week to make some test cases for multisphere.
I upload one of them.

LIGGGHTS360 was used for this simulation. The multisphere was only composed with two particles.

what I did was:
1. make a packing in a region with a stepped wall, saved as a restart file.
2. restart the case from the saved restart file and simulated it further using a moving wall.

Hi,
I have a problem with multisphere particles simulation.
when i use same case for simple spherical particles mixing, my results are good but when i used multisphere particles ( 2 or more sphere clumped together to form particle) then particles becomes cohesive and no mixing occurs between particles. i created multisphere particles according to code given in following link
https://www.cfdem.com/media/DEM/docu/fix_particletemplate_multisphere.html

Hi there,

I'm new to LIGGGHTS but I have been trying to use buoyancy and am getting odd results. I have read the documentation of 'fix buoyancy' and I am not sure about why dim level must be positive.

Documentation:
dim value = x or y or z
x, y, z = define the water level as x=const, y=const, z=const plane
level value = lev
lev = water level in length units, along the axis defined by dim

Hi,
I'm trying to simulate the heat generation inside the particles due to a nuclear reaction.
Is there a command to set a constant heat generation to the particles?

thanks

Simone

Dear LIGGGHTS users and its creators,
I have just started using LIGGGHTS for DEM Simulations. I have been using LAMMPS for around 2 years now for the same. I have seen that LIGGGHTS takes constant coefficient of restitution as input even while we use Hertzian model. I don't see the point of providing the coefficient of restitution as input when I am providing the Young's modulus and Poisson's ratio. Moreover, the coefficient of restitution along with collision time is a function of velocity and making coefficient of restitution doesn't make much sense.

I have issues concerning setting youngs modulus to a realistic value like 10 GPa. This requires insanely small timesteps.

In the documentatiom and in every thread on this question people say that it should not be bigger that 5e6 for si units or 5e5 for cgs.

But how would I go about modeling a simulation of a material that has a youngs modulus with magnitudes several times higher than 5e6 for the simulation?

Hello

I'm trying to perform the simulation of a chute, and I've been experiencing difficulties ... some I can solve by analyzing the forum, others I can not. My in.conveyor that I am using:

https://paste.ubuntu.com/25019462/

My problem is in section "PARTICLE INSERTION"; When I try to run with 'insert/stream' the Liggghts show me the erro: