Homec4science
Diffusion lammps (lammm-devel) Browse

lammps/doc/pair_style_gran.txt
89753028d731lammm-devel

Last Change
Raw File

pair_style_gran.txt
View Options

"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)
:line
pair_style gran/hertizian command :h3
pair_style gran/history command :h3
pair_style gran/no_history command :h3
[Syntax:]
pair_style style Kn gamma_n xmu dampflag :pre
style = {gran/hertzian} or {gran/history} or {gran/no_history} :ulb,l
Kn = spring constant for particle repulsion :l
(mg/d units where m is mass, g is the gravitational constant, d is diameter of a particle) :pre
gamma_n = damping coefficient for normal direction collisions (sqrt(g/d) units) :l
xmu = static yield criterion :l
dampflag = flag (0/1) for whether to (no/yes) include tangential damping :l,ule
[Examples:]
pair_style gran/history 200000.0 0.5 1.0 1 :pre
[Description:]
The {gran} styles use the following formula "(Silbert)"_#Silbert for
frictional force between two granular particles that are a distance r
apart when r is less than the contact distance d.
:c,image(Eqs/pair_granular.jpg)
The 1st term is a normal force and the 2nd term is a tangential force.
The other quantites are as follows:
delta = d - r
f(x) = 1 for Hookean contacts used in pair styles {history} and {no_history}
f(x) = sqrt(x) for pair style {hertzian}
Kn = elastic constant for normal contact
Kt = elastic constant for tangential contact = 2/7 of Kn
gamma_n = viscoelastic constants for normal contact
gamma_t = viscoelastic constants for tangential contact = 1/2 of gamma_n
m_eff = Mi Mj / (Mi + Mj) = effective mass of 2 particles of mass Mi and Mj
Delta St = tangential displacement vector between the 2 spherical particles \
which is truncated to satisfy a frictional yield criterion
n = a unit vector along the line connecting the centers of the 2 particles
Vn = normal component of the relative velocity of the 2 particles
Vt = tangential component of the relative velocity of the 2 particles :ul
The Kn and gamma_n coefficients are set as parameters to the
pair_style command. Xmu is also specified which is the upper limit of
the tangential force through the Coulomb criterion Ft = xmu*Fn. The
tangential force between 2 particles grows according to a tangential
spring and dash-pot model until Ft/Fn = xmu and then is held at Ft =
Fn*xmu until the particles lose contact.
For granular styles there are no individual atom type coefficients
that can be set. All global settings are made via the pair_style
command.
See the citation for more discussion of the granular potentials.
[Restrictions:] none
All of these styles are part of the "granular" package. It is only
enabled if LAMMPS was built with that package. See the "Making
LAMMPS"_Section_start.html#2_2 section for more info.
You must use "atom style"_atom_style.html {granular} with these pair
styles.
[Related commands:]
"pair_coeff"_pair_coeff.html
[Default:] none
:line
:link(Silbert)
[(Silbert)] Silbert, Ertas, Grest, Halsey, Levine, Plimpton, Phys Rev
E, 64, p 051302 (2001).
c4science · Help