[Gmsh] An idea

[Christophe Geuzaine]

CEM ALBUKREK wrote:
> Hello Christophe,
> 
> I have been using Gmsh successfully to build complex tet meshes as input 
> to OpenFOAM. To give you a sense of the complexity attached is a picture 
> of a typical surface mesh, which is an assembly of NAS and STL files 
> combined into one closed volume using some scripts I developed. You have 
> warned on your website that GMSH is not so good at large meshes from 
> STL's; what threshold (# of tets) did you have in mind? I am able to go 
> as far as the 32 bit memory allows me to at this point. May be the trick 
> is the application of effective surface mesh smoothing techniques before 
> moving onto volume meshing...
> 
> One issue with CFD is that one can march an unsteady (varying time) 
> simulation only as fast as the smallest tetrahedron allows; i.e.
> 
> velocity * time_step <= tet size
> 
> for each one of the tetrahedra.
> 
> Sometimes small elements are unavoidable no matter how great a surface 
> mesh one puts together. One way around the problem is to blindly erase 
> the tetrahedra smaller than a threshold and run the flow simulation 
> around these tiny blockages, which are too small to affect the bulk 
> flow. I would like to implement a little sub-routine to do the same 
> thing with GMSH. For instance we have the mesh quality filters for beta, 
> gamma & theta. In a similar fashion I would like to put one for the size 
> (or volume) and also be able to click delete. Do you see any problem 
> with this? 


Hi Cem - You could do this interactively:

1) select a size range for the elements in Options->Mesh->Visibility

2) in the mesh menu select "Delete"

3) select all the visible elements with the mouse (Ctrl+LeftButton to
start a rectangular selection area, LeftButton to finish)




> May be FEM solvers could benefit from this kind of feature as 
> well knowing tiny bubbles are not uncommon in molded plastics and cast 
> metals.
> 
> What do you think?
> 
> -- 
> CEM M. ALBUKREK, PhD
> Computer Aided Engineering Design Consultant
> Tel: (857) 234-1035
> 
> ------------------------------------------------------------------------
> 
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-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine