On Mar 19, 2007, at 10:17 PM, Chris Calebrese wrote:
I’m trying to create objects in 3D, specifically a cylinder, within
a larger mesh. The object will be static and will be solid (for
example it will not permit diffusion, while the surrounding medium
will). Below I have created an object in 3D inside of a
rectangular mesh, where the position of the object is defined by
the value of pillar=1 (concept taken from one of the level set
examples). Because the mesh is square, the edges will
“pixilated.” Is there a better way to define a cylinder or other
smooth, non-planar face within a larger mesh (perhaps create an
irregular grid?).
Hi Chris,
A mesh where the cell faces lie directly on the interface will gain
accuracy because the boundary between the
two regions has better definition, but you lose some accuracy due to
using an unstructured mesh. The relative cost
I am not sure about.
The best way to create a mesh where the faces are on the boundary is
with Gmsh.
The are three options for doing this:
1) Gmsh will make a circle within a square in 2D and mesh it. The
interface between the two regions will then have faces along it. You
could then use the
extruder from <http://matdl-osi.org/fipy/wiki/SurfaceOfSphere> to
extrude it into 3D. The actually link for extrude.py is <http://matdl-
osi.org/fipy/attachment/wiki/SurfaceOfSphere/extrude.py?format=raw>.
I am not sure whether the extruder can create layers. Jon,
can the extruder create layers or is it just one layer as used for
the spherical problem? Looking at the code it only seems to
be one layer. I imagine this could be extended to multiple layers
without too much difficulty.
2) The other option would be to create the volume objects in gmsh and
mesh it directly. Actually, this may be the more straight forward
than option 1. The GmshImporter3D should do the trick once the mesh
has been created.
3) What you did. It may be inaccurate, but it depends what you are
looking for in your solution.
We have just updated the gmsh importer to read the new (2.0) gmsh
file format so you'll need to checkout trunk if you use version 2.0
of gmsh.
Hope this helps.
Cheers
--
Daniel Wheeler
