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lammps/doc/_sources/fix_lb_viscous.txt
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fix_lb_viscous.txt
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.. index:: fix lb/viscous
fix lb/viscous command
======================
Syntax
""""""
.. parsed-literal::
fix ID group-ID lb/viscous
* ID, group-ID are documented in :doc:`fix <fix>` command
* lb/viscous = style name of this fix command
Examples
""""""""
fix 1 flow lb/viscous
Description
"""""""""""
This fix is similar to the :doc:`fix viscous <fix_viscous>` 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.
This fix adds a force, F = - Gamma*(velocity-fluid_velocity), to each
atom, where Gamma is the force coupling constant described in the :doc:`fix lb/fluid <fix_lb_fluid>` command (which applies an equal and
opposite force to the fluid).
.. note::
This fix should only be used in conjunction with one of the
built in LAMMPS integrators; it should not be used with the :doc:`fix lb/pc <fix_lb_pc>` or :doc:`fix lb/rigid/pc/sphere <fix_lb_rigid_pc_sphere>` 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.
----------
For further details, as well as descriptions and results of several
test runs, see :ref:`Mackay et al. <Mackay>`. Please include a citation to
this paper if this fix is used in work contributing to published
research.
----------
Restart, fix_modify, output, run start/stop, minimize info
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
As described in the :doc:`fix viscous <fix_viscous>` documentation:
"No information about this fix is written to :doc:`binary restart files <restart>`. None of the :doc:`fix_modify <fix_modify>` options
are relevant to this fix. No global or per-atom quantities are stored
by this fix for access by various :ref:`output commands <howto_15>`. No parameter of this fix can
be used with the *start/stop* keywords of the :doc:`run <run>` command.
The forces due to this fix are imposed during an energy minimization,
invoked by the :doc:`minimize <minimize>` command. This fix should only
be used with damped dynamics minimizers that allow for
non-conservative forces. See the :doc:`min_style <min_style>` command
for details."
Restrictions
""""""""""""
This fix is part of the USER-LB package. It is only enabled if LAMMPS
was built with that package. See the :ref:`Making LAMMPS <start_3>` section for more info.
Can only be used if a lattice-Boltzmann fluid has been created via the
:doc:`fix lb/fluid <fix_lb_fluid>` command, and must come after this
command.
This fix should not be used if either the :doc:`fix lb/pc <fix_lb_pc>`
or :doc:`fix lb/rigid/pc/sphere <fix_lb_rigid_pc_sphere>` integrator is
used.
Related commands
""""""""""""""""
:doc:`fix lb/fluid <fix_lb_fluid>`, :doc:`fix lb/pc <fix_lb_pc>`, :doc:`fix lb/rigid/pc/sphere <fix_lb_rigid_pc_sphere>`
**Default:** none
----------
.. _Mackay:
**(Mackay et al.)** 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.
.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm
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