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Unstructured grid problem

Jon Hardwick, modified 4 Years ago.

Unstructured grid problem

Youngling Posts: 0 Join Date: 9/3/14 Recent Posts
Hi all,

I have been trying to create a new unstructured grid using a combination on MATLAB and RGFGRID, when I load the grid in to Delta Shell I get the following error:

** ERROR : 88 small flow links discarded. Run remove small flow links or increase trhs.

Can anyone help? (Or let me know what trhs is?)

Many Thanks

Arthur van Dam, modified 4 Years ago.

RE: Unstructured grid problem (Answer)

Youngling Posts: 17 Join Date: 3/3/11 Recent Posts
This is a known issue and will be improved in an upcoming release.

The explanation of the error is below.
Please refer to Fig. 7.2 in your D-Flow FM User Manual, it depicts the topology of unstructured grids and the staggered data on top of it. Each pair of cells is connected by a so called 'flow link' between the two pressure points. In some locations, the length of this flow link may be close to zero, which will then be discarded in further computations. It can be resolved by merging these neighbouring grid cells into a single cell.

The current resolution is: re-open the grid in RGFGRID again, and run the command "Operations > Grid > Merge blunt triangles".

In case even that does not work, please send your grid ( file to
Liv Herdman, modified 4 Years ago.

RE: Unstructured grid problem

Youngling Posts: 9 Join Date: 6/15/15 Recent Posts
I am having a similar problem with small flow links. I do not want to allow 5 sided cells and thus the operation to merge circumcenters in RGFGRID does not work. Please advise on other ways to address the small flow link problem. I only have 2 small flow links so a manual solution would be fine, however I am unable to identify the location of the problem cells. The grid file does not appear to store flow link information.