forked from lijiext/lammps
88 lines
2.5 KiB
Plaintext
88 lines
2.5 KiB
Plaintext
.. index:: fix lb/momentum
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fix lb/momentum 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/momentum nevery keyword values ...
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* ID, group-ID are documented in the :doc:`fix <fix>` command
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* lb/momentum = style name of this fix command
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* nevery = adjust the momentum every this many timesteps
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* zero or more keyword/value pairs may be appended
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* keyword = *linear*
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.. parsed-literal::
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*linear* values = xflag yflag zflag
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xflag,yflag,zflag = 0/1 to exclude/include each dimension.
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Examples
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""""""""
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.. parsed-literal::
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fix 1 sphere lb/momentum
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fix 1 all lb/momentum linear 1 1 0
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Description
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"""""""""""
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This fix is based on the :doc:`fix momentum <fix_momentum>` command, and
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was created to be used in place of that command, when a
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lattice-Boltzmann fluid is present.
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Zero the total linear momentum of the system, including both the atoms
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specified by group-ID and the lattice-Boltzmann fluid every nevery
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timesteps. This is accomplished by adjusting the particle velocities
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and the fluid velocities at each lattice site.
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.. note::
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This fix only considers the linear momentum of the system.
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By default, the subtraction is performed for each dimension. This can
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be changed by specifying the keyword *linear*\ , along with a set of
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three flags set to 0/1 in order to exclude/ include the corresponding
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dimension.
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Restart, fix_modify, output, run start/stop, minimize info
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""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
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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 <4_15>`. No parameter of this fix can be
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used with the *start/stop* keywords of the :doc:`run <run>` command.
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This fix is not invoked during :doc:`energy minimization <minimize>`.
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Restrictions
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""""""""""""
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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 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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Related commands
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""""""""""""""""
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:doc:`fix momentum <fix_momentum>`, :doc:`fix lb/fluid <fix_lb_fluid>`
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Default
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"""""""
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Zeros the total system linear momentum in each dimension.
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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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