git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@15299 f3b2605a-c512-4ea7-a41b-209d697bcdaa

doc/html/_sources/fix_wall_gran.txt

@@ -8,10 +8,15 @@ Syntax
 
 .. parsed-literal::
 
-   fix ID group-ID wall/gran Kn Kt gamma_n gamma_t xmu dampflag wallstyle args keyword values ...
+   fix ID group-ID wall/gran Kn Kt fstyle gamma_n gamma_t xmu dampflag wallstyle args keyword values ...
 
 * ID, group-ID are documented in :doc:`fix <fix>` command
 * wall/gran = style name of this fix command
+* fstyle = style of force interactions between particles and wall
+.. parsed-literal::
+
+     possible choices: hooke, hooke/history, hertz/history
+
 * Kn = elastic constant for normal particle repulsion (force/distance units or pressure units - see discussion below)
 * Kt = elastic constant for tangential contact (force/distance units or pressure units - see discussion below)
 * gamma_n = damping coefficient for collisions in normal direction (1/time units or 1/time-distance units - see discussion below)
@@ -46,9 +51,9 @@ Examples
 
 .. parsed-literal::
 
-   fix 1 all wall/gran 200000.0 NULL 50.0 NULL 0.5 0 xplane -10.0 10.0 
+   fix 1 all wall/gran hooke  200000.0 NULL 50.0 NULL 0.5 0 xplane -10.0 10.0 
-   fix 1 all wall/gran 200000.0 NULL 50.0 NULL 0.5 0 zplane 0.0 NULL 
+   fix 1 all wall/gran hooke/history 200000.0 NULL 50.0 NULL 0.5 0 zplane 0.0 NULL 
-   fix 2 all wall/gran 100000.0 20000.0 50.0 30.0 0.5 1 zcylinder 15.0 wiggle z 3.0 2.0
+   fix 2 all wall/gran hooke 100000.0 20000.0 50.0 30.0 0.5 1 zcylinder 15.0 wiggle z 3.0 2.0
 
 Description
 """""""""""
@@ -57,28 +62,28 @@ Bound the simulation domain of a granular system with a frictional
 wall.  All particles in the group interact with the wall when they are
 close enough to touch it.
 
-The first set of parameters (Kn, Kt, gamma_n, gamma_t, xmu, and
+The nature of the wall/particle interactions are determined by the
-dampflag) have the same meaning as those specified with the
+*fstyle* setting.  It can be any of the styles defined by the
-:doc:`pair_style granular <pair_gran>` force fields.  This means a NULL
+:doc:`pair_style granular <pair_gran>` commands.  Currently this is
-can be used for either Kt or gamma_t as described on that page.  If a
+*hooke*\ , *hooke/history*\ , or *hertz/history*\ .  The equation for the
-NULL is used for Kt, then a default value is used where Kt = 2/7 Kn.
+force between the wall and particles touching it is the same as the
-If a NULL is used for gamma_t, then a default value is used where
+corresponding equation on the :doc:`pair_style granular <pair_gran>` doc
-gamma_t = 1/2 gamma_n.
+page, in the limit of one of the two particles going to infinite
+radius and mass (flat wall).  I.e. delta = radius - r = overlap of
+particle with wall, m_eff = mass of particle, and sqrt(RiRj/Ri+Rj)
+becomes sqrt(radius of particle).  The units for Kn, Kt, gamma_n, and
+gamma_t are as described on that doc page.  The meaning of xmu and
+dampflag are also as described on that page.  Note that you can choose
+a different force styles and/or different values for the 6
+wall/particle coefficients than for particle/particle interactions.
+E.g. if you wish to model the wall as a different material.
 
-The nature of the wall/particle interactions are determined by which
+The parameters *Kn*\ , *Kt*\ , *gamma_n*\ , *gamma_t*\ , *xmu* and *dampflag*
-pair_style is used in your input script: *hooke*\ , *hooke/history*\ , or
+have the same meaning as those specified with the :doc:`pair_style granular <pair_gran>` commands.  This means a NULL can be used for
-*hertz/history*\ .  The equation for the force between the wall and
+either *Kt* or *gamma_t* as described on that page.  If a NULL is used
-particles touching it is the same as the corresponding equation on the
+for *Kt*\ , then a default value is used where *Kt* = 2/7 *Kn*\ .  If a
-:doc:`pair_style granular <pair_gran>` doc page, in the limit of one of
+NULL is used for *gamma_t*\ , then a default value is used where
-the two particles going to infinite radius and mass (flat wall).
+*gamma_t* = 1/2 *gamma_n*\ .
-I.e. delta = radius - r = overlap of particle with wall, m_eff = mass
-of particle, and sqrt(RiRj/Ri+Rj) becomes sqrt(radius of particle).
-The units for Kn, Kt, gamma_n, and gamma_t are as described on that
-doc page.  The meaning of xmu and dampflag are also as described on
-that page.  Note that you can choose different values for these 6
-wall/particle coefficients than for particle/particle interactions, if
-you wish your wall to interact differently with the particles, e.g. if
-the wall is a different material.
 
 .. note::
 
@@ -95,6 +100,12 @@ the wall is a different material.
    Kt, gamma_n, and gamma_s should be set sqrt(2.0) larger than they were
    previously.
 
+The effective mass *m_eff* in the formulas listed on the :doc:`pair_style granular <pair_gran>` doc page is the mass of the particle for
+particle/wall interactions (mass of wall is infinite).  If the
+particle is part of a rigid body, its mass is replaced by the mass of
+the rigid body in those formulas.  This is determined by searching for
+a :doc:`fix rigid <fix_rigid>` command (or its variants).
+
 The *wallstyle* can be planar or cylindrical.  The 3 planar options
 specify a pair of walls in a dimension.  Wall positions are given by
 *lo* and *hi*\ .  Either of the values can be specified as NULL if a

doc/html/_sources/pair_gran.txt

@@ -91,7 +91,7 @@ The other quantities in the equations are as follows:
 * gamma_n = viscoelastic damping constant for normal contact
 * gamma_t = viscoelastic damping constant for tangential contact
 * m_eff = Mi Mj / (Mi + Mj) = effective mass of 2 particles of mass Mi and Mj
-* Delta St = tangential displacement vector between 2 spherical particles       which is truncated to satisfy a frictional yield criterion
+* Delta St = tangential displacement vector between 2 particles       which is truncated to satisfy a frictional yield criterion
 * 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
@@ -170,6 +170,12 @@ holds, though the spring is no longer linear.
    for modeling of systems which can sustain very large tangential
    forces.
 
+The effective mass *m_eff* is given by the formula above for two
+isolated particles.  If either particle is part of a rigid body, its
+mass is replaced by the mass of the rigid body in the formula above.
+This is determined by searching for a :doc:`fix rigid <fix_rigid>`
+command (or its variants).
+
 For granular styles there are no additional coefficients to set for
 each pair of atom types via the :doc:`pair_coeff <pair_coeff>` command.
 All settings are global and are made via the pair_style command.

doc/html/fix_wall_gran.html

@@ -128,12 +128,18 @@
 <span id="index-0"></span><h1>fix wall/gran command</h1>
 <div class="section" id="syntax">
 <h2>Syntax</h2>
-<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">fix</span> <span class="n">ID</span> <span class="n">group</span><span class="o">-</span><span class="n">ID</span> <span class="n">wall</span><span class="o">/</span><span class="n">gran</span> <span class="n">Kn</span> <span class="n">Kt</span> <span class="n">gamma_n</span> <span class="n">gamma_t</span> <span class="n">xmu</span> <span class="n">dampflag</span> <span class="n">wallstyle</span> <span class="n">args</span> <span class="n">keyword</span> <span class="n">values</span> <span class="o">...</span>
+<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">fix</span> <span class="n">ID</span> <span class="n">group</span><span class="o">-</span><span class="n">ID</span> <span class="n">wall</span><span class="o">/</span><span class="n">gran</span> <span class="n">Kn</span> <span class="n">Kt</span> <span class="n">fstyle</span> <span class="n">gamma_n</span> <span class="n">gamma_t</span> <span class="n">xmu</span> <span class="n">dampflag</span> <span class="n">wallstyle</span> <span class="n">args</span> <span class="n">keyword</span> <span class="n">values</span> <span class="o">...</span>
 </pre></div>
 </div>
 <ul class="simple">
 <li>ID, group-ID are documented in <a class="reference internal" href="fix.html"><span class="doc">fix</span></a> command</li>
 <li>wall/gran = style name of this fix command</li>
+<li>fstyle = style of force interactions between particles and wall</li>
+</ul>
+<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">possible</span> <span class="n">choices</span><span class="p">:</span> <span class="n">hooke</span><span class="p">,</span> <span class="n">hooke</span><span class="o">/</span><span class="n">history</span><span class="p">,</span> <span class="n">hertz</span><span class="o">/</span><span class="n">history</span>
+</pre></div>
+</div>
+<ul class="simple">
 <li>Kn = elastic constant for normal particle repulsion (force/distance units or pressure units - see discussion below)</li>
 <li>Kt = elastic constant for tangential contact (force/distance units or pressure units - see discussion below)</li>
 <li>gamma_n = damping coefficient for collisions in normal direction (1/time units or 1/time-distance units - see discussion below)</li>
@@ -165,9 +171,9 @@
 </div>
 <div class="section" id="examples">
 <h2>Examples</h2>
-<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">fix</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">wall</span><span class="o">/</span><span class="n">gran</span> <span class="mf">200000.0</span> <span class="n">NULL</span> <span class="mf">50.0</span> <span class="n">NULL</span> <span class="mf">0.5</span> <span class="mi">0</span> <span class="n">xplane</span> <span class="o">-</span><span class="mf">10.0</span> <span class="mf">10.0</span>
+<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">fix</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">wall</span><span class="o">/</span><span class="n">gran</span> <span class="n">hooke</span>  <span class="mf">200000.0</span> <span class="n">NULL</span> <span class="mf">50.0</span> <span class="n">NULL</span> <span class="mf">0.5</span> <span class="mi">0</span> <span class="n">xplane</span> <span class="o">-</span><span class="mf">10.0</span> <span class="mf">10.0</span>
-<span class="n">fix</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">wall</span><span class="o">/</span><span class="n">gran</span> <span class="mf">200000.0</span> <span class="n">NULL</span> <span class="mf">50.0</span> <span class="n">NULL</span> <span class="mf">0.5</span> <span class="mi">0</span> <span class="n">zplane</span> <span class="mf">0.0</span> <span class="n">NULL</span>
+<span class="n">fix</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">wall</span><span class="o">/</span><span class="n">gran</span> <span class="n">hooke</span><span class="o">/</span><span class="n">history</span> <span class="mf">200000.0</span> <span class="n">NULL</span> <span class="mf">50.0</span> <span class="n">NULL</span> <span class="mf">0.5</span> <span class="mi">0</span> <span class="n">zplane</span> <span class="mf">0.0</span> <span class="n">NULL</span>
-<span class="n">fix</span> <span class="mi">2</span> <span class="nb">all</span> <span class="n">wall</span><span class="o">/</span><span class="n">gran</span> <span class="mf">100000.0</span> <span class="mf">20000.0</span> <span class="mf">50.0</span> <span class="mf">30.0</span> <span class="mf">0.5</span> <span class="mi">1</span> <span class="n">zcylinder</span> <span class="mf">15.0</span> <span class="n">wiggle</span> <span class="n">z</span> <span class="mf">3.0</span> <span class="mf">2.0</span>
+<span class="n">fix</span> <span class="mi">2</span> <span class="nb">all</span> <span class="n">wall</span><span class="o">/</span><span class="n">gran</span> <span class="n">hooke</span> <span class="mf">100000.0</span> <span class="mf">20000.0</span> <span class="mf">50.0</span> <span class="mf">30.0</span> <span class="mf">0.5</span> <span class="mi">1</span> <span class="n">zcylinder</span> <span class="mf">15.0</span> <span class="n">wiggle</span> <span class="n">z</span> <span class="mf">3.0</span> <span class="mf">2.0</span>
 </pre></div>
 </div>
 </div>
@@ -176,27 +182,27 @@
 <p>Bound the simulation domain of a granular system with a frictional
 wall.  All particles in the group interact with the wall when they are
 close enough to touch it.</p>
-<p>The first set of parameters (Kn, Kt, gamma_n, gamma_t, xmu, and
+<p>The nature of the wall/particle interactions are determined by the
-dampflag) have the same meaning as those specified with the
+<em>fstyle</em> setting.  It can be any of the styles defined by the
-<a class="reference internal" href="pair_gran.html"><span class="doc">pair_style granular</span></a> force fields.  This means a NULL
+<a class="reference internal" href="pair_gran.html"><span class="doc">pair_style granular</span></a> commands.  Currently this is
-can be used for either Kt or gamma_t as described on that page.  If a
+<em>hooke</em>, <em>hooke/history</em>, or <em>hertz/history</em>.  The equation for the
-NULL is used for Kt, then a default value is used where Kt = 2/7 Kn.
+force between the wall and particles touching it is the same as the
-If a NULL is used for gamma_t, then a default value is used where
+corresponding equation on the <a class="reference internal" href="pair_gran.html"><span class="doc">pair_style granular</span></a> doc
-gamma_t = 1/2 gamma_n.</p>
+page, in the limit of one of the two particles going to infinite
-<p>The nature of the wall/particle interactions are determined by which
+radius and mass (flat wall).  I.e. delta = radius - r = overlap of
-pair_style is used in your input script: <em>hooke</em>, <em>hooke/history</em>, or
+particle with wall, m_eff = mass of particle, and sqrt(RiRj/Ri+Rj)
-<em>hertz/history</em>.  The equation for the force between the wall and
+becomes sqrt(radius of particle).  The units for Kn, Kt, gamma_n, and
-particles touching it is the same as the corresponding equation on the
+gamma_t are as described on that doc page.  The meaning of xmu and
-<a class="reference internal" href="pair_gran.html"><span class="doc">pair_style granular</span></a> doc page, in the limit of one of
+dampflag are also as described on that page.  Note that you can choose
-the two particles going to infinite radius and mass (flat wall).
+a different force styles and/or different values for the 6
-I.e. delta = radius - r = overlap of particle with wall, m_eff = mass
+wall/particle coefficients than for particle/particle interactions.
-of particle, and sqrt(RiRj/Ri+Rj) becomes sqrt(radius of particle).
+E.g. if you wish to model the wall as a different material.</p>
-The units for Kn, Kt, gamma_n, and gamma_t are as described on that
+<p>The parameters <em>Kn</em>, <em>Kt</em>, <em>gamma_n</em>, <em>gamma_t</em>, <em>xmu</em> and <em>dampflag</em>
-doc page.  The meaning of xmu and dampflag are also as described on
+have the same meaning as those specified with the <a class="reference internal" href="pair_gran.html"><span class="doc">pair_style granular</span></a> commands.  This means a NULL can be used for
-that page.  Note that you can choose different values for these 6
+either <em>Kt</em> or <em>gamma_t</em> as described on that page.  If a NULL is used
-wall/particle coefficients than for particle/particle interactions, if
+for <em>Kt</em>, then a default value is used where <em>Kt</em> = 2/7 <em>Kn</em>.  If a
-you wish your wall to interact differently with the particles, e.g. if
+NULL is used for <em>gamma_t</em>, then a default value is used where
-the wall is a different material.</p>
+<em>gamma_t</em> = 1/2 <em>gamma_n</em>.</p>
 <div class="admonition note">
 <p class="first admonition-title">Note</p>
 <p class="last">As discussed on the doc page for <a class="reference internal" href="pair_gran.html"><span class="doc">pair_style granular</span></a>, versions of LAMMPS before 9Jan09 used a
@@ -212,6 +218,11 @@ common case of a monodisperse system with particles of diameter 1, Kn,
 Kt, gamma_n, and gamma_s should be set sqrt(2.0) larger than they were
 previously.</p>
 </div>
+<p>The effective mass <em>m_eff</em> in the formulas listed on the <a class="reference internal" href="pair_gran.html"><span class="doc">pair_style granular</span></a> doc page is the mass of the particle for
+particle/wall interactions (mass of wall is infinite).  If the
+particle is part of a rigid body, its mass is replaced by the mass of
+the rigid body in those formulas.  This is determined by searching for
+a <a class="reference internal" href="fix_rigid.html"><span class="doc">fix rigid</span></a> command (or its variants).</p>
 <p>The <em>wallstyle</em> can be planar or cylindrical.  The 3 planar options
 specify a pair of walls in a dimension.  Wall positions are given by
 <em>lo</em> and <em>hi</em>.  Either of the values can be specified as NULL if a

doc/html/pair_gran.html

@@ -205,7 +205,7 @@ if <em>dampflag</em> is set to 0.</p>
 <li>gamma_n = viscoelastic damping constant for normal contact</li>
 <li>gamma_t = viscoelastic damping constant for tangential contact</li>
 <li>m_eff = Mi Mj / (Mi + Mj) = effective mass of 2 particles of mass Mi and Mj</li>
-<li>Delta St = tangential displacement vector between 2 spherical particles       which is truncated to satisfy a frictional yield criterion</li>
+<li>Delta St = tangential displacement vector between 2 particles       which is truncated to satisfy a frictional yield criterion</li>
 <li>n_ij = unit vector along the line connecting the centers of the 2 particles</li>
 <li>Vn = normal component of the relative velocity of the 2 particles</li>
 <li>Vt = tangential component of the relative velocity of the 2 particles</li>
@@ -277,6 +277,11 @@ holds, though the spring is no longer linear.</p>
 for modeling of systems which can sustain very large tangential
 forces.</p>
 </div>
+<p>The effective mass <em>m_eff</em> is given by the formula above for two
+isolated particles.  If either particle is part of a rigid body, its
+mass is replaced by the mass of the rigid body in the formula above.
+This is determined by searching for a <a class="reference internal" href="fix_rigid.html"><span class="doc">fix rigid</span></a>
+command (or its variants).</p>
 <p>For granular styles there are no additional coefficients to set for
 each pair of atom types via the <a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a> command.
 All settings are global and are made via the pair_style command.

doc/src/fix_wall_gran.txt

@@ -10,10 +10,12 @@ fix wall/gran command :h3
 
 [Syntax:]
 
-fix ID group-ID wall/gran Kn Kt gamma_n gamma_t xmu dampflag wallstyle args keyword values ... :pre
+fix ID group-ID wall/gran Kn Kt fstyle gamma_n gamma_t xmu dampflag wallstyle args keyword values ... :pre
 
 ID, group-ID are documented in "fix"_fix.html command :ulb,l
 wall/gran = style name of this fix command :l
+fstyle = style of force interactions between particles and wall :l
+  possible choices: hooke, hooke/history, hertz/history :pre
 Kn = elastic constant for normal particle repulsion (force/distance units or pressure units - see discussion below) :l
 Kt = elastic constant for tangential contact (force/distance units or pressure units - see discussion below) :l
 gamma_n = damping coefficient for collisions in normal direction (1/time units or 1/time-distance units - see discussion below) :l
@@ -39,9 +41,9 @@ keyword = {wiggle} or {shear} :l
 
 [Examples:]
 
-fix 1 all wall/gran 200000.0 NULL 50.0 NULL 0.5 0 xplane -10.0 10.0 
+fix 1 all wall/gran hooke  200000.0 NULL 50.0 NULL 0.5 0 xplane -10.0 10.0 
-fix 1 all wall/gran 200000.0 NULL 50.0 NULL 0.5 0 zplane 0.0 NULL 
+fix 1 all wall/gran hooke/history 200000.0 NULL 50.0 NULL 0.5 0 zplane 0.0 NULL 
-fix 2 all wall/gran 100000.0 20000.0 50.0 30.0 0.5 1 zcylinder 15.0 wiggle z 3.0 2.0 :pre
+fix 2 all wall/gran hooke 100000.0 20000.0 50.0 30.0 0.5 1 zcylinder 15.0 wiggle z 3.0 2.0 :pre
 
 [Description:]
 
@@ -49,28 +51,29 @@ Bound the simulation domain of a granular system with a frictional
 wall.  All particles in the group interact with the wall when they are
 close enough to touch it.
 
-The first set of parameters (Kn, Kt, gamma_n, gamma_t, xmu, and
+The nature of the wall/particle interactions are determined by the
-dampflag) have the same meaning as those specified with the
+{fstyle} setting.  It can be any of the styles defined by the
-"pair_style granular"_pair_gran.html force fields.  This means a NULL
+"pair_style granular"_pair_gran.html commands.  Currently this is
-can be used for either Kt or gamma_t as described on that page.  If a
+{hooke}, {hooke/history}, or {hertz/history}.  The equation for the
-NULL is used for Kt, then a default value is used where Kt = 2/7 Kn.
+force between the wall and particles touching it is the same as the
-If a NULL is used for gamma_t, then a default value is used where
+corresponding equation on the "pair_style granular"_pair_gran.html doc
-gamma_t = 1/2 gamma_n.
+page, in the limit of one of the two particles going to infinite
+radius and mass (flat wall).  I.e. delta = radius - r = overlap of
+particle with wall, m_eff = mass of particle, and sqrt(RiRj/Ri+Rj)
+becomes sqrt(radius of particle).  The units for Kn, Kt, gamma_n, and
+gamma_t are as described on that doc page.  The meaning of xmu and
+dampflag are also as described on that page.  Note that you can choose
+a different force styles and/or different values for the 6
+wall/particle coefficients than for particle/particle interactions.
+E.g. if you wish to model the wall as a different material.
 
-The nature of the wall/particle interactions are determined by which
+The parameters {Kn}, {Kt}, {gamma_n}, {gamma_t}, {xmu} and {dampflag}
-pair_style is used in your input script: {hooke}, {hooke/history}, or
+have the same meaning as those specified with the "pair_style
-{hertz/history}.  The equation for the force between the wall and
+granular"_pair_gran.html commands.  This means a NULL can be used for
-particles touching it is the same as the corresponding equation on the
+either {Kt} or {gamma_t} as described on that page.  If a NULL is used
-"pair_style granular"_pair_gran.html doc page, in the limit of one of
+for {Kt}, then a default value is used where {Kt} = 2/7 {Kn}.  If a
-the two particles going to infinite radius and mass (flat wall).
+NULL is used for {gamma_t}, then a default value is used where
-I.e. delta = radius - r = overlap of particle with wall, m_eff = mass
+{gamma_t} = 1/2 {gamma_n}.
-of particle, and sqrt(RiRj/Ri+Rj) becomes sqrt(radius of particle).
-The units for Kn, Kt, gamma_n, and gamma_t are as described on that
-doc page.  The meaning of xmu and dampflag are also as described on
-that page.  Note that you can choose different values for these 6
-wall/particle coefficients than for particle/particle interactions, if
-you wish your wall to interact differently with the particles, e.g. if
-the wall is a different material.
 
 NOTE: As discussed on the doc page for "pair_style
 granular"_pair_gran.html, versions of LAMMPS before 9Jan09 used a
@@ -86,6 +89,13 @@ common case of a monodisperse system with particles of diameter 1, Kn,
 Kt, gamma_n, and gamma_s should be set sqrt(2.0) larger than they were
 previously.
 
+The effective mass {m_eff} in the formulas listed on the "pair_style
+granular"_pair_gran.html doc page is the mass of the particle for
+particle/wall interactions (mass of wall is infinite).  If the
+particle is part of a rigid body, its mass is replaced by the mass of
+the rigid body in those formulas.  This is determined by searching for
+a "fix rigid"_fix_rigid.html command (or its variants).
+
 The {wallstyle} can be planar or cylindrical.  The 3 planar options
 specify a pair of walls in a dimension.  Wall positions are given by
 {lo} and {hi}.  Either of the values can be specified as NULL if a

doc/src/pair_gran.txt

@@ -76,7 +76,7 @@ Kt = elastic constant for tangential contact
 gamma_n = viscoelastic damping constant for normal contact
 gamma_t = viscoelastic damping constant for tangential contact
 m_eff = Mi Mj / (Mi + Mj) = effective mass of 2 particles of mass Mi and Mj
-Delta St = tangential displacement vector between 2 spherical particles \
+Delta St = tangential displacement vector between 2 particles \
       which is truncated to satisfy a frictional yield criterion
 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
@@ -152,6 +152,12 @@ NOTE: Normally, xmu should be specified as a fractional value between
 for modeling of systems which can sustain very large tangential
 forces.
 
+The effective mass {m_eff} is given by the formula above for two
+isolated particles.  If either particle is part of a rigid body, its
+mass is replaced by the mass of the rigid body in the formula above.
+This is determined by searching for a "fix rigid"_fix_rigid.html
+command (or its variants).
+
 For granular styles there are no additional coefficients to set for
 each pair of atom types via the "pair_coeff"_pair_coeff.html command.
 All settings are global and are made via the pair_style command.