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-   -   [ICEM] ICEM CFD Build Topology (http://www.cfd-online.com/Forums/ansys-meshing/97273-icem-cfd-build-topology.html)

Dave442 February 13, 2012 18:11

ICEM CFD Build Topology
 
Hi all,

I am newish to ICEM CFD and I am working with .stl data for the first time. I have a .stl file which I can import into ICEM and use to generate curves and surfaces. The resulting topology appears to be in good agreement with the .stl mesh, which is great!

In my experience, however, generating a single surface from a faceted surface results in some amount of error. I have been reading the manual, however, and I cant seem to figure out whether it is possible to quantify exactly how much detail is lost during the build topology procedure. Is it based purely on the specified tolerance?

Any advice would be greatly appreciated!

Thanks,
Dave

PSYMN February 14, 2012 10:40

Build topology doesn't lose detail, it simply "joins" entities within that tolerance...

The joining is done at the topological level, the STL facets are not changed.

Just keep the tolerance smaller than your local mesh size and it won't be a problem.

Dave442 February 14, 2012 12:28

Hi Simon,

Thanks for the response. I understand the build topology function better now.

Much appreciated!

Dave

robboflea July 24, 2013 08:23

I have a question related to the build topology tool and Simon's post.

Let's say for example that when importing a stp file the build topology gives me a correct color for the edges from a tolerance greater than 0.01mm.

However my minimum mesh size can be much smaller than that. Now my understanding was that, after using build topology with a tolerance of 0.01 all double edges appearing with higher tolerances are merged. After this the model is completely closed and it is possible then to mesh it careless of the smallest element size dimension. But this conflicts with Simon's suggestion to set the tolerance smaller than the minimum element size.

Or am I wrong and the right way to repair the geometry is to use as simon suggested a tolerance smaller than the smallest element size and then manually remove all double edges?

In both cases should the surfaces associated with the modified edges be deleted and rebuilt from the newly moved edges?

Thanks a lot for your help in advance

Rob

Quote:

Originally Posted by PSYMN (Post 344368)
Build topology doesn't lose detail, it simply "joins" entities within that tolerance...

The joining is done at the topological level, the STL facets are not changed.

Just keep the tolerance smaller than your local mesh size and it won't be a problem.


harsh_999 October 27, 2013 07:09

Hi all,
I've a same Q as Rob has asked
In my case,I've kept build topology tolerance as 0.05
I've assigned in part mesh setup a minimum size limit for each part which is >0.05
Is this a correct approach?
Please help
Thanks

Far October 27, 2013 10:13

Quote:

Originally Posted by harsh_999 (Post 459225)
Hi all,
I've a same Q as Rob has asked
In my case,I've kept build topology tolerance as 0.05
I've assigned in part mesh setup a minimum size limit for each part which is >0.05
Is this a correct approach?
Please help
Thanks

check the model that you are not losing any important details. rule of thumb : tolerance = 1/10 of the min curve length in model.

lcaBR March 27, 2014 13:40

Hi guys! Sorry to revive this topic, but I have a similar question regarding aspects of build topology.

I've got this geometry which has an outlet surface. If I set a build topology tolerance of 1, the edge of this surface gets red, as it should be, once this boundary is connected to another surface.

However, if I set a tolerance of 0.0001, the edge(s) gets yellow, therefore meaning a gap exists there. Why 0.0001? Because my minimum element size is supposed to be 0.001 (Boundary Layer elements), and there is this suggestion of using tolerance = 1/10th of the minimum element size.

Question is: will I have trouble using the tolerance equals to 1, as this value gets me connected edges (red edges)? If so, the solution would be to make another geometry more precisely on CAD?

kad March 27, 2014 16:32

Your build topology tolerance might be in the range of your model tolerance. Try reducing the model tolerance under settings->model.


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