Appendix G: Mesh Editing
Cubit
provides a set of capabilities to take an existing mesh and edit it by modifying
its mesh connectivity, nodal position, or genesis data. CAD solid model
geometry is not necessary. This capability is useful for design studies,
or adding detail to a model based on new understanding of the relevant features
and physics. It also provides a graphical alternative to many GJoin
and Grepos capabilities.
Import the mesh as
mesh based geometry, or import the
CAD solid model and then import
the mesh and automatically associate it to the solid model.
In either case, all of the
genesis
entities are retained. After editing, the mesh can be
re-exported, and the retained entities are exported as well. Blocks,
as well as nodesets
and sidesets can be edited by adding or removing individual geometric
or mesh entities.
You can import and export
only part of a model, if desired, by specifying the blocks to be imported
or exported. The mesh-based model can be unmerged on import, to facilitate
editing just part of the mesh. ( mesh
import, and mesh
export.)
In order to retain the geometric
topology in the exported mesh, file, set the nodeset associativity on.
This works when exporting mesh from either mesh based geometry or solid
model geometry. To force a collection of mesh entities to become a geometric
entity upon re-import, place them in a common nodeset or sideset. E.g.
If the model in Cubit is merged,
you can disconnect a piece of the mesh by
unmerging the geometry. This piece can be manipulated separately,
then re-merged
with the rest of the model.
Meshed geometry can be merged,
providing the mesh and geometry of the two objects have the same topology.
If the node positions are different, they will be aligned during the merge
process. E.g.
If you have disconnected,
meshed volumes, but the positions of the nodes and edges match, you can
imprint the model using virtual geometry based on the mesh; see the new
imprint mesh command. After doing so, the model
may be merged normally. If you are going to remesh a volume, it can be
important to imprint it before deleting its mesh. E.g.
If one or both of the volumes
is unmeshed, it is still possible to imprint them manually using virtual
geometry. (If both are ACIS-based unmeshed volumes, then use automatic
solid model imprinting.)
This manual virtual geometry imprinting can be tedious for large models,
but will be automated in future Cubit versions. For a meshed volume, the
basic idea is to partition
it with its own mesh so that it's topology matches the other volume. For
an unmeshed volume, the basic idea is to partition
it with geometry. This geometry can be its own geometry, the geometry
of another (meshed) volume, or new
geometry created bottom-up from the positions of some mesh or geometry.
Be sure to partition in a bottom up fasion, partitioning all of the curves
before partitioning the surfaces. It is not yet possible for the user
to partition volumes. The following is an example of the manual process.
Mesh-based geometry, and geometry
that is meshed, can be moved
or otherwise transformed
within Cubit. Mesh (including mesh-based geometry) can also be scaled
on input or output by specifying a
transformation.
You can create new pieces
of geometry, either mesh-based or solid-model based geometry. Mesh-based
and solid-model based geometry can be imprinted and merged with each other,
as described above.
You can change the element
order of blocks. The new element type will be used when the mesh is
exported.
You can refine the mesh by
dicing, refinement
or by deleting the mesh, resizing, and remeshing.
You can reposition the mesh
by smoothing. Model Acquisition
Manipulating Topology and
Connectivity:
Imprinting and Merging and Unmerging
vol 1 int 4
mesh vol 1
export mesh 'plain_brick.g'
set nodeset associativity on
export mesh 'assoc_brick.g'
reset
# only one surface
import mesh geom 'plain_brick.g' feature_angle 0
reset
# six surfaces
import mesh geom 'assoc_brick.g' feature_angle 0
brick wid 10
body 2 move 10 0 0
vol all interval 4
mesh volume all
surface 6 smooth scheme randomize
smooth surface 6
display
merge all
unmerge all
draw volume 2
brick wid 10
body 2 move 10 5 0
vol all size 2
mesh vol all
imprint mesh volume all
merge all
brick wid 10
brick wid 10
body 2 move 10 5 0
vol 1 int 6
mesh vol 1
# partition the meshed surface
partition create surface 6 edge 396 398 400 402 404 405
# partition the unmeshed surface
# it is important to partition the curves first
partition create curve 15 vertex 2
partition create curve 19 vertex 5
partition create surface 10 curve 12
# merge
merge all
Options for mesh transfer
In order to get both objects meshed
with compatible meshes, you can transfer the mesh from one object to another
by
copying the mesh, or exporting an interface mesh and importing it onto
another geometry. It is possible to delete the mesh of a mesh-based volume,
then import a new mesh onto it. When importing a mesh, part of the geometry
may be already meshed, in which case the meshes will be merged.
Geometry (and Mesh) Manipulation
Mesh Manipulation