forked from lijiext/lammps
86 lines
3.0 KiB
Plaintext
86 lines
3.0 KiB
Plaintext
|
"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).
|