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-   -   Grid check failed (non positive volumes). (http://www.cfd-online.com/Forums/fluent/45544-grid-check-failed-non-positive-volumes.html)

Muhammad Usman Qureshi July 28, 2007 12:09

Grid check failed (non positive volumes).
 
Hi,

When i check my 3D grid in Fluent it displays the following message

WARNING: non-positive volumes exist. WARNING: Grid check failed.

what should i do to remove these.

Many Thanks.


GTkid July 28, 2007 15:40

Re: Grid check failed (non positive volumes).
 
Hey Muhammad,

If you go into Gambit and examine the mesh you should find where the negative volumes exist. They will be the only ones at skewness of 1!

I'm not sure why these things happen but in Gambit sometimes if you do things in a certain order, it will crash or create negative volumes,(etc,etc,etc,etc) it really can be a nightmare.

You should save your work all the time and remesh the bad part again. I HAVE FOUND THAT SPLITTING THE BAD PART INTO SMALLER GOEMETRIES HELPS.

I expect you were using cooper or tgrid scheme or something like that.

Sorry there's not much else to say but I've experienced this lots of times and certainly the first thing I would do is remesh it in a different manner, then divide the geometry up if that doesn't work.

abbas July 29, 2007 08:36

Re: Grid check failed (non positive volumes).
 
hi you should divide your geometry and mesh theses little part and define intersection of parts as a interface in boundary condition panel in gambit software if minnimizing spacing no helpful. best regards.

farhan July 30, 2007 06:26

Re: Grid check failed (non positive volumes).
 
check cells for their right handedness. all the cells should be right handed. If not you can make them right handed in gridgen or gambit, whichever mesh generator u r using.

red lemon July 30, 2007 13:58

Re: Grid check failed (non positive volumes).
 
or use repair left handed faces TUI command in Fluent. But normally negative cells or inverted elements will require a local remesh rather than simple fix.

blue rose September 26, 2013 06:26

TO Mohammed
 
hi
It is because u have certain small regions in mesh which are not smooth, to avoid these problems after meshing ( before importing to fluent) run smooth grid option, then you will be able to see where the grid is negative. depending on it you have to adjust the edges and give proper associations ( edge, face) until the whole grid is positive. then import it in fluent, u will not find this particular problem then.


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