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-   -   Removing Invalid Cells? (http://www.cfd-online.com/Forums/star-ccm/76908-removing-invalid-cells.html)

syd June 8, 2010 08:27

Removing Invalid Cells?
 
Hi everyone!

I have a problem: I'm simulating a sailboat, but, everytime I mesh it, there's always some invalid cells (in the mast), no matter how small I choose the base size and local meshing parameters.

I can't modify the CAD files which I am importing, so I guess there's no way I won't have some invalid cells...

Now, if I try to run a solution after removing these invalid cells, will it diverge?

Thank you all!

f-w June 8, 2010 14:18

Quote:

Originally Posted by syd (Post 262093)
Now, if I try to run a solution after removing these invalid cells, will it diverge?

Only one way to tell ... but make sure you are not removing too many. When you do this, you are basically changing the geometry, since the neighboring cells' faces get symmetry planes assigned to them.

On a side note: you should be catching and correcting bad cells at surface mesh level, so they won't make your life harder later on. You can do this manually or automatically with the surface repair tool (look it up in the manual).

syd June 8, 2010 17:45

Quote:

Originally Posted by f-w (Post 262138)
Only one way to tell ... but make sure you are not removing too many. When you do this, you are basically changing the geometry, since the neighboring cells' faces get symmetry planes assigned to them.

On a side note: you should be catching and correcting bad cells at surface mesh level, so they won't make your life harder later on. You can do this manually or automatically with the surface repair tool (look it up in the manual).


thanks.

anyway, I removed few cells, let's say a dozen more or less...

I'll also try to wrap the surface before remeshing, I want to see if this helps...

Vinicius June 8, 2010 18:09

You can turn on the cell quality remediation in the physics continua and remove the invalid cells with a rigth click on the region, and choosing remove invalid cells option.

f-w June 9, 2010 13:00

Quote:

Originally Posted by Vinicius (Post 262165)
You can turn on the cell quality remediation in the physics continua and remove the invalid cells with a rigth click on the region, and choosing remove invalid cells option.

From past experience, cell quality remediation doesn't always work (especially on invalid, rather than poor-quality cells); plus, it slows down your simulation because after each iteration, computations are made to find these cells.

abdul099 July 6, 2010 09:45

In my experience, a lot of problems with invalid cells are caused by a shitty CAD geometry.

As f-w said, you can try to repair the surface before generating a volume mesh. In my experience, it is the best to do it manually (if the errors are not too much), and to start with the imported surface. If it has a good quality, the surface remesher has less problems and the overall mesh quality could be increased. Got to "Representations", Right-click on "Imported surface", choose "Repair Surface". The use of the surface repair should be explained in the tutorials.

If there will still be a lot invalid cells, you should go a step back and check if your geometry is suitable for CFD and your mesh settings are suitable for this geometry. You should make sure, there are no unimportant small geometry features and/or mesh settings are appropriate to capture all geometry feature.

Best regards


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