Meshing volumes/surfaces with holes with salome

Hi all,

I want to run some external flow calculations, and so far I'm using GMSH as a meshing tool. I'm not really happy with it, for several reasons :
1)creating a geometry is very long and complicated (I created the same geometry in gmsh and in salome just to see the difference. With gmsh it took me more than an hour, with salome only ten minutes)
2)when importing a geometry from salome (or any other cad software), some of the functions don't work (like any transformation on the geometry like translation, symmetry,... or the functions to refine the mesh at some specific places (transfinite algo using bump/progression))
3)I can't create a proper hexaedral mesh, defining the number of points I want on a line or the dimension of the cells. all I was able to do was to create quadrangles, but what I get was totally different from proper rectangles
4)gmsh tends to create non symmetric meshes

I first tried salome, but I had problems as soon as I wanted to mesh faces or volumes with holes (that's all what I work with for external flows...), so I came to use GMSH, but I start to meet its limitations...
Now I would like to know if it is possible (doing some magical manipulation) to mesh easily surface/volume with holes.
I also found that salome had some problems as soon as the size of the domain or of the mesh wanted was big, and I also work with big meshes (not less than a million cells for each case), so is it just me doing something wrong or is it a known limitation of salome ? (I'm using salome 4.1.4 and gmsh 2.3.1 because that's what was in my caelinux distribution 2009).

If salome is not able to meet my expectations, do you have any idea of a powerful tool for geometry & meshing ?

I'm waiting for any idea that could help me !!

Alicia

The thread is old, but somebody may find this helpful:
CIMNE GiD is indeed a very nice mesher and up to certain point a viable CAD, but the latest Linux version cannot import STEP. About the limitation to 1000 nodes, it's true if you use it without any license, but you can ask in an e-formular on their site for a one-month free license for students (they only ask you your name and other stuff, nothing serious) which makes it fully functional. If you reach the ned of the license, usually they will give you other period. Oh, one more thing, a good part of the code is accesible, but it's by no means under GPL or any of those licenses we adore.I had a good experience using GiD, I'm sorry to say that some features are better in GiD than in Salome, specially refining (Salome supports though more file and mesh types and has more meshing algorithms).
You can also try Engrid, many openfoamers recomend it. It supports hexaedral meshes, refining and other things that I don't know because I never used it. There's a tutorial about using it together with Blender, and that's what scares me (really, I once made a circle in Blender after half an hour of struggling, got tired and open it sporadically to see if providence makes appear an intuitive toolbar).
And yes, in my mighty 32bit Sempron, computing a big mesh or more than 1million cells can last like an hour or even more. GiD and Gmsh are faster in that aspect, but I think it has to do also with the fact that Salome optimizes by default the mesh, whereas the other two don't.
In Gmsh you control the mesh size by assigning characteristic lengths to points, so you may add dummy points where you need better refinement, it's not difficult but certainly not intuitive, and it's the only way to refine the mesh.
One advice that helped me in geometry generation: I do as much as I can of the geoemtry outside the mesher with a dedicated CAD. When it comes to 3D Linux is still a bit backwards, but if you can get a copy of a Rhino3D 2.0 (it's of 2001) you can make it run with Wine perfectly and it will solve all your problems when it comes to geometry generation, including importing and exporting a lot of filetypes. It's quite easy to use, if you know AutoCad then you'll grab this fairly fast, as the command names and structures are almost equal.<br /><br />Post edited by: CAVT, at: 2010/08/27 05:47

CAVT wrote:

In Gmsh you control the mesh size by assigning characteristic lengths to points, so you may add dummy points where you need better refinement, it's not difficult but certainly not intuitive, and it's the only way to refine the mesh.

I may be leading this conversation astray, but what does assigning a 'characteristic length' to a point mean?! Only in GMSH have I come across such a contradiction of basic geometrical principles! One reason why I tried it, found its scripting structure and logic and menus so bizarre and so I generally avoid it. Would you care to explain to a GMSH skeptic please? I would like to use it, but I keep shunning it for the reasons I mentioned earlier...

Thank you.
JMB

JMB wrote:

CAVT wrote:

In Gmsh you control the mesh size by assigning characteristic lengths to points, so you may add dummy points where you need better refinement, it's not difficult but certainly not intuitive, and it's the only way to refine the mesh.

I may be leading this conversation astray, but what does assigning a 'characteristic length' to a point mean?! Only in GMSH have I come across such a contradiction of basic geometrical principles! One reason why I tried it, found its scripting structure and logic and menus so bizarre and so I generally avoid it. Would you care to explain to a GMSH skeptic please? I would like to use it, but I keep shunning it for the reasons I mentioned earlier...

Thank you.
JMB

Ok, but since I'm no expert in it at all, the info I give here is to be used under adult supervision .
The characteristic length is the element size, and it can be assigned only to points, i.e. the element size along a straight line (for example) will be determined by the interpolation of the characteristic lengths of each point at each extreme. Then you may extend the concept to surfaces and volumes. That's why I said you need to define dummy points where you want better refinement (or coarsening). Anyway, the secret of Gmsh relies not on the GUI but on editing the .geo, which defines the geometry and mesh characteristics. Everytime you import a geometry from another format, to have control over it it's necessary to save it as a .geo file.
Ah, almost forgot, besides defining characteristic lengths for each point, there's a general characteristic length defineable in the mesh options GUI.
All what I know from Gmsh I know it from these tutorials, which are fairly good (the first one specially):
amcg.ese.ic.ac.uk/index.php?title=Local:Gmsh_tutorial
vimeo.com/3287369
geuz.org/gmsh/screencasts/