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