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<li class="toctree-l1"><a class="reference internal" href="Section_intro.html">1. Introduction</a></li>
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<li>pair_style body/rounded/polygon command</li>
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<div class="section" id="pair-style-body-rounded-polygon-command">
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<span id="index-0"></span><h1>pair_style body/rounded/polygon command<a class="headerlink" href="#pair-style-body-rounded-polygon-command" title="Permalink to this headline">¶</a></h1>
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<div class="section" id="syntax">
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<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>pair_style body/rounded/polygon cutoff_global cutoff_inner delta_ua c_n
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</pre></div>
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</div>
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<ul class="simple">
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<li>cutoff_global = global cutoff for COM interactions (distance units)</li>
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<li>cutoff_inner = cutoff for vertex-vertex and vertex-edge interactions (distance units)</li>
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<li>delta_ua = characteristic contact length (distance units)</li>
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<li>c_n = normal friction coefficient (energy time/distance^2)</li>
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</ul>
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</div>
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<div class="section" id="examples">
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<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>pair_style body/rounded/polygon 6.0 0.5 0.5 0.1
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pair_coeff 1 1 1.0 100.0 12.0
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</pre></div>
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</div>
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<div class="section" id="description">
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<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
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<p>Style <em>body/rounded/polygon</em> implements the pairwise body/body
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interactions between 2D convex polygons, as described
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in <a class="reference internal" href="#fraige"><span>Fraige</span></a>. This pair style is designed for use with
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the “rounded/polygon” body style, which is specified as
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an argument to the “atom-style body/rounded/polygon” command.
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See the <a class="reference internal" href="body.html"><em>body</em></a> doc page for more details about the body
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styles LAMMPS supports.</p>
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<p>The “rounded/polygon” style treats a body particle as a discrete
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element model (DEM) polygon composed of N vertices.
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The coordinates of a body particle are its center-of-mass (COM).
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The initial position of the vertices are specified the data file.
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The current implementation follows the multiple contact points model as
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described in <a class="reference internal" href="#fraige"><span>Fraige</span></a>, but neglects and the contact history
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the tangential contact forces for now.</p>
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<p>The parameters <em>delta_ua</em> and <em>c_n</em> are the characteristic contact length
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and the normal friction coefficient, respectively. See Eqs. (1) and (5)
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in <a class="reference internal" href="#fraige"><span>Fraige</span></a> for more details.</p>
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<p>For style <em>body/rounded/polygon</em>, the following coefficients
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must be defined for each pair of atoms types via the <a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a>
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command as in the examples above:</p>
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<ul class="simple">
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<li>sigma = vertex rounded diameter (distance units)</li>
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<li>k_n = normal repulsion strength (energy/distance^2)</li>
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<li>k_na = normal attraction strength (energy/distance^2)</li>
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<li>cutoff = cutoff for COM interactions (distance units)</li>
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</ul>
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<p>The last parameter is optional. If not specified, the global
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cutoff specified in the pair_style command is used.</p>
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<p>Note that the current implementation assumes that the edge length
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of the polygons (L) should be at least twice greater than
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the vertex rounded radius (sigma) so as to distinguish vertex-vertex from
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vertex-edge contacts.</p>
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<div class="admonition note">
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<p class="first admonition-title">Note</p>
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<p class="last">Because this pair style requires the body velocities to compute
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the friction component of the forces, users should specify
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<em>comm_modify vel yes</em> in the input script with this pair style.</p>
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</div>
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<hr class="docutils" />
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<p><strong>Mixing, shift, table, tail correction, restart, rRESPA info</strong>:</p>
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<p>For atom type pairs I,J and I != J, the epsilon and sigma coefficients
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and cutoff distance for all of this pair style can be mixed. The
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default mix value is <em>geometric</em>. See the “pair_modify” command for
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details.</p>
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<p>This pair style does not support the <a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a>
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shift, table, and tail options.</p>
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<p>This pair style does not write its information to <a class="reference internal" href="restart.html"><em>binary restart files</em></a>.</p>
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<p>This pair style can only be used via the <em>pair</em> keyword of the
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<a class="reference internal" href="run_style.html"><em>run_style respa</em></a> command. It does not support the
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<em>inner</em>, <em>middle</em>, <em>outer</em> keywords.</p>
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</div>
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<hr class="docutils" />
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<div class="section" id="restrictions">
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<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
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<p>This style is part of the BODY package. It is only enabled if LAMMPS
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was built with that package. See the <span class="xref std std-ref">Making LAMMPS</span> section for more info.</p>
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<p>Defining particles to be bodies so they participate in body/body or
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body/particle interactions requires the use of the <a class="reference internal" href="atom_style.html"><em>atom_style body</em></a> command.</p>
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</div>
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<div class="section" id="related-commands">
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<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
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<p><a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a></p>
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<p><strong>Default:</strong> none</p>
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<p id="fraige"><strong>(Fraige)</strong> F. Y. Fraige, P. A. Langston, A. J. Matchett, J. Dodds,
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Particuology, 6, 455 (2008).</p>
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