Liggghts-with-bonds syntax

Submitted by liggghtschr on Tue, 06/20/2017 - 13:36

I am using the liggghts-with-bonds package to create bonds as described by cundall.
I can't find the syntax for fix bond_coeff
I copied the command somewhere and it works but i would like to understand what the arguments are in order to modify them. It seems that the second argument is the particle diameter which doesn't make any sense to me, because cundall always uses the smaller of both radiuses and I even found that command in the source code.
If the bond radius is set only once at the begining it would be static but if I am using different sized atoms that would not work like it should right?

Forums:

mschramm | Tue, 06/20/2017 - 17:07

The second argument is a gamma parameter that modifies the min(radius[i1],radius[i2])

As for what each part means on a code level, see bond_gran.cpp (BondGran::coeff(int narg, char **arg)) function starting at line 438

The first argument is an id for multiple bond "types". The bond properties are stored via a type and not per "mega particle"
second --> gamma parameter that adjusts the bond radius such that radius_bond = gamma[type]*min(radius[i1],radius[i2])
third --> Normal stiffness of bond
forth --> Tangential stiffness of bond
fifth --> a switch parameter to tell the code how to handle the bond breaking
a value of 0 --> if the distance between a bonded pair exceed a distance of 2*radius_break, the bond is broken --> bond_coeff 1 gamma Kn Kt 0 radius_break

a value of 1 --> bond breaks if the stress is too high in either the normal or tangential directions (see lines 363 in bond_gran.cpp for the relationship)
--> bond_coeff 1 gamma Kn Kt 1 Kn_max Kt_max

a value of 2 --> bond breaks if the temperature of the bonded pair exceeds a max temp value or if the stress is too high in either the normal or tangential directions
--> bond_coeff 1 gamma Kn Kt 1 Kn_max Kt_max temp_max

Ermek Asylbekov | Fri, 06/23/2017 - 09:08

Hi mschramm,

thanks a lot for the explanation. I really needed that.
Is there a small typo in the last line? As far as I understood it schould be:
--> bond_coeff 1 gamma Kn Kt 2 Kn_max Kt_max temp_max