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parameters (or iges)->geometry->mesh->cfd

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Old   January 12, 2007, 14:15
Default parameters (or iges)->geometry->mesh->cfd
  #1
nico
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Hello,

My question is about making the meshing process as smooth as possible. Taking as example a spheric body (blocking stategy is kept the same), i have two ways of inputing the geometry: *a simple text file where i can specify (say) 3 radiuses. this text file is either used in a 3d package or in the meshing software. (good option if model is simple) *i get the iges file of a spheric body (more complex shape) but still same blocking strategy.

What are the best ways to solve such problem? I am not looking for something completly automatic. An option would be to get a 3D parametric program (expensive), with the 3d model either defined by parameters (the text file) or an iges file. Complete model is then exported to mesher, geometry is opened (in Gridgen: database) and mesh strategy (in gridgen: gg file) or script is used to get the mesh.

What I am not sure about is, particurly in Gridgen, how well 2 different iges file are recognized. For example if i created a mesh with an iges file, i then get a new file (not simply modified), how much work will i have to do?

Regards, Nico

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Old   January 13, 2007, 18:26
Default Re: parameters (or iges)->geometry->mesh->cfd
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John Chawner
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Nico,

All things being equal, you'll be better off if a text file describing the geometry serves as input to a Gridgen Glyph script that creates the geometry (database) and then the grid. It's better this way because you'll have ultimate control.

You can accomplish the same goal with an IGES file, but there are a few caveats. Gridgen likes to see a few things remain constant from one IGES file to the next when you're swapping shape: 1) topology, 2) entity names, 3) parametrization. When this all works, the swapping of one shape for another is completely automatic.

When you can't meet the three conditions, you can import the grid without the database (thus breaking all parametric connections), import the new database, then project all the database constrained bits to the new database, and finally clean-up the rest.

There's still a third way to approach the problem and that is to script the mesh starting from an IGES. There are enough query commands in the Glyph Scripting Language that you should be able to figure out where all the pieces are and then how to mesh them. There are several examples of when this has been done. You can make this approach work better by making some assumptions about the CAD model: that certain components are in certain layers, for example.

Hope this helps.
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Old   January 15, 2007, 07:40
Default Re: parameters (or iges)->geometry->mesh->cfd
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nico
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Thanks for the reply,

I understand that the first option would be best (I dont need an iges file), unfortunately i would have to build surfaces is Gridgen, and Gridgen does not provide something good enough (I need to loft a surface between sections).

The only way seems to be careful about how the iges file is organised and setup.

Thanks again,

Nico
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