101 lines
3.8 KiB
HTML
101 lines
3.8 KiB
HTML
<HTML>
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<CENTER><A HREF = "http://www.cfdem.com">LIGGGHTS WWW Site</A> - <A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LIGGGHTS Documentation</A> - <A HREF = "Section_commands.html#comm">LIGGGHTS Commands</A>
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</CENTER>
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<HR>
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<H3>fix multisphere command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>fix ID group-ID multisphere
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</PRE>
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<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
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</UL>
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<P><B>Examples:</B>
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</P>
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<P>fix ms all multisphere
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</P>
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<P><B>Description:</B>
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</P>
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<P>Treat one or more sets of atoms as independent rigid bodies. This
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means that each timestep the total force and torque on each rigid body
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is computed as the sum of the forces and torques on its constituent
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particles and the coordinates, velocities, and orientations of the
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atoms in each body are updated so that the body moves and rotates as a
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single entity. The integration that is performed by this command is
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euqivalent to <A HREF = "fix_rigid.html">fix_rigid</A>. However, the following
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implementation details are different:
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</P>
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<P>(1) Body data held by this fix is distributed across all processes, yielding
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better parallel scalabilty.
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</P>
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<P>(2) Bodies (particle clumps) can be added/inserted via
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<A HREF = "fix_insert_stream.html">fix_insert_stream</A>,
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<A HREF = "fix_insert_rate_region.html">fix_insert_rate_region</A> or
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<A HREF = "fix_insert_pack.html">fix_insert_pack</A> and are automatically added
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to this fix.
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</P>
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<P>(3) A body is removed from the simulation domain if any of it's particles
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is removed from the simulation according to the <A HREF = "boundary.html">boundary</A>
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settings or by any command that deleted particles (e.g.
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<A HREF = "delete_atoms.html">delete_atoms</A>).
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</P>
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<P>(4) By using this fix, gravity (<A HREF = "fix_gravity.html">fix_gravity</A>)
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will be handled correctly for for overlapping particle clumps.
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</P>
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<P>(5) This fix internally performs a <A HREF = "neigh_modify.html">neigh_modify</A> exclude
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command so that particles belonging to the same rigid body are excluded
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from the neighborlist build.
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</P>
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<P>IMPORTANT NOTE: You should not update the atoms in rigid bodies via
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other time-integration fixes (e.g. nve, nvt, npt), or you will be
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integrating their motion more than once each timestep.
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</P>
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<HR>
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<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
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</P>
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<P>No information about this fix is written to <A HREF = "restart.html">binary restart
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files</A>. This means you can currently not restart a simulation
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using multisphere particles.
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</P>
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<P>None of the <A HREF = "fix_modify.html">fix_modify</A> options are relevant to this
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fix. No global scalar or vector or per-atom quantities are stored by
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this fix for access by various <A HREF = "Section_howto.html#4_15">output
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commands</A>. No parameter of this fix can be
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used with the <I>start/stop</I> keywords of the <A HREF = "run.html">run</A> command.
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This fix is not invoked during <A HREF = "minimize.html">energy minimization</A>.
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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>Only one fix multisphere at a time is allowed.
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Heat transfer simulations are not possible when using this fix
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(e.g. <A HREF = "fix_heat_gran_conduction.html">fix heat/gran/conduction</A>)
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</P>
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<P>IMPORTANT NOTE: All fixes or computes gathering statistical output
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(such as e.g. <A HREF = "compute_com.html">compute com</A> or <A HREF = "fix_ave_time.html">fix ave/time</A>
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operate on a per-sphere rather than on a per-body basis.
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</P>
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<P>Currently, using fix multisphere requires <A HREF = "newton.html">newton</A> = off and
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<A HREF = "dimension.html">dimension</A> = 3.
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "fix_rigid.html">fix_rigid</A>
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<A HREF = "fix_particletemplate_sphere.html">fix_particletemplate_sphere</A>
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<A HREF = "neigh_modify.html">neigh_modify</A>
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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