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