Finite Element Analysis

[Madhavan Lakshmiraghavan]

Travis,

Converting a mesh in STL format to one in IGES format is non-trivial.  The IGES
format is based on a completely different representation of a surface/solid as
compared to STL.  However, if you can somehow (using vtk or otherwise - will
get to that shortly) eliminate the bad polygons in your STL file, then taking
that to ANSYS is trivial.  An STL file contains all the info needed in an ANSYS
input file. So its a breeze.

Now, coming o the question of how you eliminate the bad polygons and get a
"good" mesh, thats the tough part. vtk offers some tools (vtkDecimate,
vtkSmootherPolyDataFilter, vtkPolyDataConnectivityFilter etc.) that may help,
but you may also have to look around on the internet because, vtk may not be
sufficient for this purpose.  You see, the mesh-quality demands of FEM are in
many cases, more stringent than those for graphic visualization.  Check the
meshing research corner at http://www.andrew.cmu.edu/user/sowen/mesh.html for a
list of freeware software that are available out there.

Good luck.

M.L. Raghavan, Ph.D.
Dartmouth College.


--- vtk at yifan.net wrote:
Hi:

I am a newbie of VTK and FEM, but right now I have to build a program which can
read CT slices (DICOM file), and construct a 3D model (in VTK) of the bone,
then export this 3D model to a Finite Element Analysis program (e.g. ANSYS).

I use DICOM2 to convert dicom file to raw format, and then I use
vtkVolume16Reader reads the raw data, and  then use vtkMarchingCubes to
construct the 3D model.

my question are:

1: VTK can export STL files, but ANSYS can not import STL files, so if there is
a tool can convert STL file to IGES or other formats?  or if there is a better
way to do this?

2: As I mentioned before, I am not familiar with finite element analysis
programs, so if I use vtkMarchingCubes to construct the 3D model, (assuming I
can export this 3D model to finite
element progran, e.g. ANSYS), if the finite element program  can regard this 3D
model as a "good" model?

3: so far the result 3D model is not good, cause the original CT slices are not
very clear, especially at the bone connection area.  so, how can I "clean" the
original slices? any graphic libraries available?
--- end of quote ---


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