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<div class="section" id="fix-lb-viscous-command">
<span id="index-0"></span><h1>fix lb/viscous 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">lb</span><span class="o">/</span><span class="n">viscous</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>lb/viscous = style name of this fix command</li>
</ul>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<p>fix 1 flow lb/viscous</p>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>This fix is similar to the <a class="reference internal" href="fix_viscous.html"><span class="doc">fix viscous</span></a> command, and
is to be used in place of that command when a lattice-Boltzmann fluid
is present, and the user wishes to integrate the particle motion using
one of the built in LAMMPS integrators.</p>
<p>This fix adds a force, F = - Gamma*(velocity-fluid_velocity), to each
atom, where Gamma is the force coupling constant described in the <a class="reference internal" href="fix_lb_fluid.html"><span class="doc">fix lb/fluid</span></a> command (which applies an equal and
opposite force to the fluid).</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">This fix should only be used in conjunction with one of the
built in LAMMPS integrators; it should not be used with the <a class="reference internal" href="fix_lb_pc.html"><span class="doc">fix lb/pc</span></a> or <a class="reference internal" href="fix_lb_rigid_pc_sphere.html"><span class="doc">fix lb/rigid/pc/sphere</span></a> integrators, which
already include the hydrodynamic forces. These latter fixes should
only be used if the force coupling constant has been set by the user
(instead of using the default value); if the default force coupling
value is used, then this fix provides the only method for adding the
hydrodynamic forces to the particles.</p>
</div>
<hr class="docutils" />
<p>For further details, as well as descriptions and results of several
test runs, see <a class="reference internal" href="#mackay"><span class="std std-ref">Mackay et al.</span></a>. Please include a citation to
this paper if this fix is used in work contributing to published
research.</p>
</div>
<hr class="docutils" />
<div class="section" id="restart-fix-modify-output-run-start-stop-minimize-info">
<h2>Restart, fix_modify, output, run start/stop, minimize info</h2>
<p>As described in the <a class="reference internal" href="fix_viscous.html"><span class="doc">fix viscous</span></a> documentation:</p>
<p>&#8220;No information about this fix is written to <a class="reference internal" href="restart.html"><span class="doc">binary restart files</span></a>. None of the <a class="reference internal" href="fix_modify.html"><span class="doc">fix_modify</span></a> options
are relevant to this fix. No global or per-atom quantities are stored
by this fix for access by various <a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">output commands</span></a>. No parameter of this fix can
be used with the <em>start/stop</em> keywords of the <a class="reference internal" href="run.html"><span class="doc">run</span></a> command.</p>
<p>The forces due to this fix are imposed during an energy minimization,
invoked by the <a class="reference internal" href="minimize.html"><span class="doc">minimize</span></a> command. This fix should only
be used with damped dynamics minimizers that allow for
non-conservative forces. See the <a class="reference internal" href="min_style.html"><span class="doc">min_style</span></a> command
for details.&#8221;</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<p>This fix is part of the USER-LB package. It is only enabled if LAMMPS
was built with that package. See the <a class="reference internal" href="Section_start.html#start-3"><span class="std std-ref">Making LAMMPS</span></a> section for more info.</p>
<p>Can only be used if a lattice-Boltzmann fluid has been created via the
<a class="reference internal" href="fix_lb_fluid.html"><span class="doc">fix lb/fluid</span></a> command, and must come after this
command.</p>
<p>This fix should not be used if either the <a class="reference internal" href="fix_lb_pc.html"><span class="doc">fix lb/pc</span></a>
or <a class="reference internal" href="fix_lb_rigid_pc_sphere.html"><span class="doc">fix lb/rigid/pc/sphere</span></a> integrator is
used.</p>
</div>
<div class="section" id="related-commands">
<h2>Related commands</h2>
<p><a class="reference internal" href="fix_lb_fluid.html"><span class="doc">fix lb/fluid</span></a>, <a class="reference internal" href="fix_lb_pc.html"><span class="doc">fix lb/pc</span></a>, <a class="reference internal" href="fix_lb_rigid_pc_sphere.html"><span class="doc">fix lb/rigid/pc/sphere</span></a></p>
<p><strong>Default:</strong> none</p>
<hr class="docutils" />
<p id="mackay"><strong>(Mackay et al.)</strong> Mackay, F. E., Ollila, S.T.T., and Denniston, C., Hydrodynamic Forces Implemented into LAMMPS through a lattice-Boltzmann fluid, Computer Physics Communications 184 (2013) 2021-2031.</p>
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