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Assume un-aligned normals for rotational BCs

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Sterling Harper 2020-11-14 14:00:16 -07:00
parent c75790d3ac
commit a8ecb795a3
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24
docs/source/usersguide/geometry.rst
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@ -162,22 +162,26 @@ surface. To specify a vacuum boundary condition, simply change the
Reflective and periodic boundary conditions can be set with the strings
'reflective' and 'periodic'. Vacuum and reflective boundary conditions can be
applied to any type of surface. Periodic boundary conditions can be applied to
pairs of planar surfaces. For axis-aligned planes, matching periodic surfaces
can be determined automatically. For non-axis-aligned planes, it is necessary to
specify pairs explicitly using the :attr:`Surface.periodic_surface` attribute as
in the following example::
pairs of planar surfaces. If there are only two periodic surfaces they will be
matched automatically. Otherwise it is necessary to specify pairs explicitly
using the :attr:`Surface.periodic_surface` attribute as in the following
example::
p1 = openmc.Plane(a=0.3, b=5.0, d=1.0, boundary_type='periodic')
p2 = openmc.Plane(a=0.3, b=5.0, d=-1.0, boundary_type='periodic')
p1.periodic_surface = p2
Rotationally-periodic boundary conditions can be specified for a pair of
:class:`XPlane` and :class:`YPlane`; in that case, the
:attr:`Surface.periodic_surface` attribute must be specified manually as well.
Both rotational and translational periodic boundary conditions are specified in
the same fashion. If both planes have the same normal vector, a translational
periodicity is assumed; rotational periodicity is assumed otherwise. Currently,
only rotations about the :math:`z`-axis are supported.
.. caution:: When using rotationally-periodic boundary conditions, your geometry
must be defined in the first quadrant, i.e., above the y-plane and
to the right of the x-plane.
For a rotational periodic BC, the normal vectors of each surface must point
inwards---towards the valid geometry. For example, a :class:`XPlane` and
:class:`YPlane` would be valid for a 90-degree periodic rotation if the geometry
lies in the first quadrant of the Cartesian grid. If the geometry instead lies
in the fourth quadrant, the :class:`YPlane` must be replaced by a
:class:`Plane` with the normal vector pointing in the :math:`-y` direction.
.. _usersguide_cells: