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View Full Version : Re: FEA: File translation: Amira to Patran



mviceconti63
01-14-2003, 02:39 AM
Sometime is easy to confuse the file format with its content. Most
CAE programs work with surfaces described as mathematical entities,
typically NURBS or Bezier splines. On the contrary, segmentation
programs usually generate a facet description of the surface, where
the surface is represented by a collection of triangular tiles.
some file formats support both types of representation of the
surface, but each program usually supports only one representation.

The real issue is that converting a facet description into a NURBS
description is a quite complex issue, which requires specialised
programs such as Raindrop Geomagic. From what you says it appears
that Mimics now supports such conversion; as far as I know Amira does
not (but you should check). If you can conver the tiles surface into
a spline surface, than you can export in IGES format and read it in
Patran.

The alternative is to force the segmentation program to generate
triangles as equilateral as possible, and then to force Patran to
read them as a surface mesh, typically by writing them in a FEM
format, such as Nastran input file. Patran can use a surface mesh to
initialise a solid mesh. OF course the mesh size and the mesh
conditioning are governed by the mesh and the conditioning of the
initial surface mesh, so the whole game is much more difficult.

Sorry for not providing you a trivial answer, but as you see it is
not a trivial question.

ciao

Marco


ps: I have a vague memory of a tetrahedral mesh support inside
Amira. Try to check it maybe you can create the mesh directly inside
Amira itself.


>Hello All,
>
>We have just begun to explore the possibility of pairing MRI images and FEA
>and have run into some roadblocks. Here's our situation, and I'm hoping
>someone can help by offering any guidance. One application of Amira is 3D
>surface reconstruction from MR (or CT) images. The problem is getting
>surfaces out of Amira and into Patran which is the FEA pre-processor we
>have to work with.
>
>I'm hoping anyone who could figure out how to convert such images into a
>format that Patran can accept (or anyone familiar with using Amira files
>for FEA) can offer some advise.
>
> We have tried a few things such as using Solid Edge, Solid Works, and
>Unigraphics as an intermediary but this hasn't produced the desired
>surface. Perhaps there are settings that could easily be changed?
>
>These are the relevant file types that Amira can export:
>DXF
>STL
>VRML
>PSI
>Unv (Ideas)
>
>To my knowlege, these are the files types that Patran can import:
>IGES (*.igs)
>Patran NEUTRAL (*.out)
>STEP (*.st(p))
>ACIS
>Parasolid xmt
>Cadds 5
>Catia
>Euclid 3
>Pro/E
>Unigraphics
>Express Neutral
>
>For example, the *.igs files we have created in a different surface
>reconstruction program (Mimics) have seemed to work the best with Patran:
>is it possible to convert a *.dxf(3D) file to *.igs using some intermediary
>program?
>
>Thanks in advance for you help,
>Rebecca Shearn
>
>----------------------------------------
>Biomedical Engineer
>
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MARCO VICECONTI, PhD (viceconti@tecno.ior.it)
Laboratorio di Tecnologia Medica tel. 39-051-6366865
Istituti Ortopedici Rizzoli fax. 39-051-6366863
via di barbiano 1/10, 40136 - Bologna, Italy

Tiger! Tiger! Burning bright in the forest of the night,
what immortal hand or eye could frame thy fearful symmetry?
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