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git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@2170 f3b2605a-c512-4ea7-a41b-209d697bcdaa

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sjplimp 2008-10-10 22:54:00 +00:00
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44
doc/pair_gran.html
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@ -21,15 +21,13 @@
</PRE>
<UL><LI>style = <I>gran/hertzian</I> or <I>gran/history</I> or <I>gran/no_history</I>
<LI>Kn = spring constant for particle repulsion
<LI>Kn = spring constant for particle repulsion (force/distance units)
<PRE> (mg/d units where m is mass, g is the gravitational constant, d is diameter of a particle)
</PRE>
<LI>gamma_n = damping coefficient for normal direction collisions (sqrt(g/d) units)
<LI>gamma_n = damping coefficient for normal direction collisions (1/time units)
<LI>xmu = static yield criterion
<LI>xmu = static yield criterion (unitless)
<LI>dampflag = flag (0/1) for whether to (no/yes) include tangential damping
<LI>dampflag = 0 or 1 if tangential damping force is excluded or included
</UL>
<P><B>Examples:</B>
</P>
@ -39,32 +37,42 @@
</P>
<P>The <I>gran</I> styles use the following formula <A HREF = "#Silbert">(Silbert)</A> for
frictional force between two granular particles that are a distance r
apart when r is less than the contact distance d.
apart when r is less than the contact distance d = Ri + Rj, where Ri
and Rj are the radii of the two particles:
</P>
<CENTER><IMG SRC = "Eqs/pair_granular.jpg">
</CENTER>
<P>The 1st term is a normal force and the 2nd term is a tangential force.
The other quantities are as follows:
The normal force has 2 parts: a contact force and a damping force.
The tangential force also has 2 parts: a shear force and a damping
force. The shear force is included in pair styles <I>history</I> and
<I>Hertzian</I>, but is not included in pair style <I>no_history</I>. The
tangential damping force is not included if <I>dampflag</I> is set to 0.
The other quantities in the equation are as follows:
</P>
<UL><LI>delta = d - r
<LI>f(x) = 1 for Hookean contacts used in pair styles <I>history</I> and <I>no_history</I>
<LI>f(x) = sqrt(x) for pair style <I>hertzian</I>
<LI>f(x) = 1 for Hookean contact used in pair styles <I>history</I> and <I>no_history</I>
<LI>f(x) = sqrt(x) for Hertzian contact used in pair style <I>hertzian</I>
<LI>Kn = elastic constant for normal contact
<LI>Kt = elastic constant for tangential contact = 2/7 of Kn
<LI>gamma_n = viscoelastic constants for normal contact
<LI>gamma_t = viscoelastic constants for tangential contact = 1/2 of gamma_n
<LI>gamma_n = viscoelastic damping constant for normal contact
<LI>gamma_t = viscoelastic damping constant for tangential contact = 1/2 of gamma_n
<LI>m_eff = Mi Mj / (Mi + Mj) = effective mass of 2 particles of mass Mi and Mj
<LI>Delta St = tangential displacement vector between the 2 spherical particles which is truncated to satisfy a frictional yield criterion
<LI>n = a unit vector along the line connecting the centers of the 2 particles
<LI>n_ij = unit vector along the line connecting the centers of the 2 particles
<LI>Vn = normal component of the relative velocity of the 2 particles
<LI>Vt = tangential component of the relative velocity of the 2 particles
</UL>
<P>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.
pair_style command. You can also think of Kn as being in mg/d units
where m is mass, g is the gravitational constant, and d is the
characteristic diameter of a particle.
</P>
<P>Xmu is also specified in the pair_style command and 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 is then
held at Ft = Fn*xmu until the particles lose contact.
</P>
<P>For granular styles there are no individual atom type coefficients
that can be set via the <A HREF = "pair_coeff.html">pair_coeff</A> command. All

43
doc/pair_gran.txt
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@ -15,11 +15,10 @@ pair_style gran/no_history command :h3
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
Kn = spring constant for particle repulsion (force/distance units) :l
gamma_n = damping coefficient for normal direction collisions (1/time units) :l
xmu = static yield criterion (unitless) :l
dampflag = 0 or 1 if tangential damping force is excluded or included :l,ule
[Examples:]
@ -29,33 +28,43 @@ pair_style gran/history 200000.0 0.5 1.0 1 :pre
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.
apart when r is less than the contact distance d = Ri + Rj, where Ri
and Rj are the radii of the two particles:
:c,image(Eqs/pair_granular.jpg)
The 1st term is a normal force and the 2nd term is a tangential force.
The other quantities are as follows:
The normal force has 2 parts: a contact force and a damping force.
The tangential force also has 2 parts: a shear force and a damping
force. The shear force is included in pair styles {history} and
{Hertzian}, but is not included in pair style {no_history}. The
tangential damping force is not included if {dampflag} is set to 0.
The other quantities in the equation 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}
f(x) = 1 for Hookean contact used in pair styles {history} and {no_history}
f(x) = sqrt(x) for Hertzian contact used in 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
gamma_n = viscoelastic damping constant for normal contact
gamma_t = viscoelastic damping constant 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
n_ij = 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.
pair_style command. You can also think of Kn as being in mg/d units
where m is mass, g is the gravitational constant, and d is the
characteristic diameter of a particle.
Xmu is also specified in the pair_style command and 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 is then
held at Ft = Fn*xmu until the particles lose contact.
For granular styles there are no individual atom type coefficients
that can be set via the "pair_coeff"_pair_coeff.html command. All