Re: [vmtk-users] vmtkmeshgenerator quality issues

[Luca A. <luc...@gm...>]

Hi Richard,

On Oct 2, 2012, at 5:08 PM, Richard Downe wrote:

> I have been attempting to use vmtk to generate meshes for use with fluent.
> Because the nature of my workflow involves geometric transformations of 
> segmented borders, my starting point is a point set (well, more 
> accurately, several disjoint structured grids).
> I have a program that generates a topologically sound triangular surface 
> with minimal triangle angle of 24 degrees, flow extensions added, and 
> caps removed at boundaries.
> 
> My coordinates are also spaced in meters, so my edge lengths are 
> typically on the order of 0.0002.
> After a few false starts, I have successfully been able to run 
> vmtkmeshgenerator on the STL file output by my initial triangulation, 
> and pipe it into vmtkmeshwriter to create a fluent file, and use a pipe 
> I wrote myself to identify the inlets based on proximity of the entities 
> to known locations of centerlines at boundaries.

Sounds like great work.

> The first surface I attempted ran in fluent fine.  2 subsequent, more 
> complex surfaces are causing fluent to fail in mysterious ways that are 
> almost certainly related to mesh quality.  I am invoking 
> vmtkmeshgenerator with -edgelength 0.0002 as the only argument.  Are 
> there known steps I can take to alleviate this/improve mesh quality?  
> There are clearly a large number of people using vmtk successfully, so I 
> can only assume I could be doing something better.  (When I examine the 
> mesh, fluent's quality rating is typically between 10 and 20, with a 
> maximum aspect ratio value of around 35).

I'd really need to look into the mesh, would it be possible for you to send
me the stl file?

> My current tack is to attempt to add the centerlines into the flow using 
> vmtkdistancetocenterlines, on the assumption that this will cause the 
> sizing function to generate more useful information, and thereby give me 
> better shaped tetrahedra -- but I could use advice, as I do somewhat 
> feel like I'm swinging in the dark.

Depending on the nature of your domain, it is possible that 0.0002 as an
element size ends up being inadequate for certain regions and overkill
for others, so the use of centerline information almost certainly helps.

However, I'd first take a look at the surface to see if it rings any bell.

Best,


Luca


> Thanks.
> --Richard
> 
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