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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
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<HR>
<H3>fix lb/viscous command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>fix ID group-ID lb/viscous
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
<LI>lb/viscous = style name of this fix command
</UL>
<P><B>Examples:</B>
</P>
<P>fix 1 flow lb/viscous
</P>
<P><B>Description:</B>
</P>
<P>This fix is similar to the <A HREF = "fix_viscous.html">fix viscous</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 HREF = "fix_lb_fluid.html">fix
lb/fluid</A> command (which applies an equal and
opposite force to the fluid).
</P>
<P>IMPORTANT NOTE: This fix should only be used in conjunction with one
of the built in LAMMPS integrators; it should not be used with the
<A HREF = "fix_lb_pc.html">fix lb/pc</A> or <A HREF = "fix_lb_rigid_pc_sphere.html">fix
lb/rigid/pc/sphere</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>
<HR>
<P>For further details, as well as descriptions and results of several
test runs, see <A HREF = "#Mackay">Mackay et al.</A>. Please include a citation to
this paper if this fix is used in work contributing to published
research.
</P>
<HR>
<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
</P>
<P>As described in the <A HREF = "fix_viscous.html">fix viscous</A> documentation:
</P>
<P>"No information about this fix is written to <A HREF = "restart.html">binary restart
files</A>. None of the <A HREF = "fix_modify.html">fix_modify</A> options
are relevant to this fix. No global or per-atom quantities are stored
by this fix for access by various <A HREF = "Section_howto.html#howto_15">output
commands</A>. No parameter of this fix can
be used with the <I>start/stop</I> keywords of the <A HREF = "run.html">run</A> command.
</P>
<P>The forces due to this fix are imposed during an energy minimization,
invoked by the <A HREF = "minimize.html">minimize</A> command. This fix should only
be used with damped dynamics minimizers that allow for
non-conservative forces. See the <A HREF = "min_style.html">min_style</A> command
for details."
</P>
<P><B>Restrictions:</B>
</P>
<P>This fix is part of the USER-LB package. It is only enabled if LAMMPS
was built with that package. See the <A HREF = "Section_start.html#start_3">Making
LAMMPS</A> section for more info.
</P>
<P>Can only be used if a lattice-Boltzmann fluid has been created via the
<A HREF = "fix_lb_fluid.html">fix lb/fluid</A> command, and must come after this
command.
</P>
<P>This fix should not be used if either the <A HREF = "fix_lb_pc.html">fix lb/pc</A>
or <A HREF = "fix_lb_rigid_pc_sphere.html">fix lb/rigid/pc/sphere</A> integrator is
used.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "fix_lb_fluid.html">fix lb/fluid</A>, <A HREF = "fix_lb_pc.html">fix lb/pc</A>, <A HREF = "fix_lb_rigid_pc_sphere.html">fix
lb/rigid/pc/sphere</A>
</P>
<P><B>Default:</B> none
</P>
<HR>
<A NAME = "Mackay"></A>
<P><B>(Mackay et al.)</B> 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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