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updated rules for rounded body particles

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This commit is contained in:
Steve Plimpton
2020-07-14 13:25:17 -06:00
parent fd2b5b1cd8
commit 449d7be8f8
1 changed files with 37 additions and 18 deletions
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55
doc/src/Howto_body.rst
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@ -6,16 +6,18 @@ Body particles
In LAMMPS, body particles are generalized finite-size particles.
Individual body particles can represent complex entities, such as
surface meshes of discrete points, collections of sub-particles,
deformable objects, etc. Note that other kinds of finite-size spherical
and aspherical particles are also supported by LAMMPS, such as spheres,
ellipsoids, line segments, and triangles, but they are simpler entities
than body particles. See the :doc:`Howto spherical <Howto_spherical>`
doc page for a general overview of all these particle types.
deformable objects, etc. Note that other kinds of finite-size
spherical and aspherical particles are also supported by LAMMPS, such
as spheres, ellipsoids, line segments, and triangles, but they are
simpler entities that body particles. See the :doc:`Howto spherical
<Howto_spherical>` doc page for a general overview of all these
particle types.
Body particles are used via the :doc:`atom_style body <atom_style>`
command. It takes a body style as an argument. The current body
styles supported by LAMMPS are as follows. The name in the first
column is used as the *bstyle* argument for the :doc:`atom_style body <atom_style>` command.
column is used as the *bstyle* argument for the :doc:`atom_style body
<atom_style>` command.
+----------------------+---------------------------------------------------+
| *nparticle* | rigid body with N sub-particles |
@ -56,10 +58,10 @@ interactions, building neighbor lists, migrating particles between
processors, output of particles to a dump file, etc. This means that
interactions between pairs of bodies or between a body and non-body
(point) particle need to be encoded in an appropriate pair style. If
such a pair style were to mimic the :doc:`fix rigid <fix_rigid>` model,
it would need to loop over the entire collection of interactions
between pairs of simple particles within the two bodies, each time a
single body/body interaction was computed.
such a pair style were to mimic the :doc:`fix rigid <fix_rigid>`
model, it would need to loop over the entire collection of
interactions between pairs of simple particles within the two bodies,
each time a single body/body interaction was computed.
Thus it only makes sense to use body particles and develop such a pair
style, when particle/particle interactions are more complex than what
@ -213,6 +215,12 @@ particle. These floating-point values can be listed on as many lines
as you wish; see the :doc:`read_data <read_data>` command for more
details.
.. note::
It is important that the vertices for each polygonal body particle be
listed in order around its perimeter, so that edges can be inferred.
LAMMPS does not check that this is the case.
The 6 moments of inertia (ixx,iyy,izz,ixy,ixz,iyz) should be the
values consistent with the current orientation of the rigid body
around its center of mass. The values are with respect to the
@ -335,15 +343,23 @@ different for each body particle. These floating-point values can be
listed on as many lines as you wish; see the :doc:`read_data
<read_data>` command for more details.
Note that vertices are numbered from 0 to N-1 inclusive. The 2
vertices in each edge can be in any order. Faces can be triangles or
quadrilaterals. In both cases 4 vertices must be specified. For a
Note that vertices are numbered from 0 to N-1 inclusive. The order of
the 2 vertices in each edge does not matter. Faces can be triangles
or quadrilaterals. In both cases 4 vertices must be specified. For a
triangle the 4th vertex is -1. The 4 vertices within each triangle or
quadrilateral face should be ordered by the right-hand rule so that
the normal vector of the face points outwards from the center of mass.
For polyhedron with faces with more than 4 vertices, you should
split the complex face into multiple simple faces, each of
which is a triangle or quadrilateral.
For polyhedron with faces with more than 4 vertices, you should split
the complex face into multiple simple faces, each of which is a
triangle or quadrilateral.
.. note::
If a face is a quadrilateral then its 4 vertices must be co-planar.
LAMMPS does not check that this is the case. If you have a quad-face
of a polyhedron that is not planar (e.g. a cube whose vertices have
been randomly displaced), then you should represent the single quad
face as two triangle faces instead.
The 6 moments of inertia (ixx,iyy,izz,ixy,ixz,iyz) should be the
values consistent with the current orientation of the rigid body
@ -400,7 +416,7 @@ by circles of diameter 0.5, is specified as follows:
.. parsed-literal::
1 3 13
2 0 0
2 1 1
0 1.33333 1.33333 0 0 0
-2 0 0
2 0 0
@ -411,11 +427,14 @@ A sphere whose diameter is 3.0 and mass 1.0, is specified as follows:
.. parsed-literal::
1 3 10
1 0 0
1 1 1
0.9 0.9 0.9 0 0 0
0 0 0
3.0
The number of edges and faces for a rod or sphere must be listed,
but is ignored.
The :doc:`pair_style body/rounded/polhedron
<pair_body_rounded_polyhedron>` command can be used with this body
style to compute body/body interactions. The :doc:`fix