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richard January 6, 2009 23:14

virtual geometry
Dear all

I have a large meshed gambit file composed of virtual edges, faces, volumes etc.. I want to include a separate wall on one of the faces. When I create a new face and try to subtract using the boolean option, I get the message unable to operate on non real geometry

So I try to change using the convert virtual geometry to real, However I get out of memory message. Is there any other way to convert the entire virtual geometry to real geometry ?


Uday January 7, 2009 00:13

Re: virtual geometry
Hello Richard

Well to get rid of the virtual geometry you need to delete the virtual volume first i.e. v_vols with lower geometry option off so your real volumes can be retained. Then in next step delete all the non real surfaces i.e. v_faces with lower geometry on so the nonreal edges and vertices are deleted.

Now you will get the real volume with real faces where you can try to do the boolean operations. Prior to that you can try to convert the geometry to real by convert from non real to real option.If its not working then you need to follow the above procedure.Make a note due deleting the virtual geometry procedure your mesh will be deleted.You need to remesh it.

The better way i feel is you can try it in Tgrid.

And about the memory issue there can be many issues like your mesh count etc. so try first the above things if you have any other problem we can discuss.

Uday Regards

richard January 7, 2009 02:32

Re: virtual geometry
Hi Uday

Appreciate your help. I did the following according to your instruction:

1. I deleted the virtual volume with geometry option off as you advised.

2. Then I deleted the virtual faces with geometry on.

However after step 1 I am left with just virtual edges and points.There doesnt seem to be any real volumes. After step 2 there is no geometry left

The real geometry data seems to be missing ? How can this be done using T grid ?



mAx January 7, 2009 04:10

Re: virtual geometry
try the split option, but you will need to split edge first, it will give you vertex. Then split face with those vertex, it will give you lines. And finally you will create wireframed surface with the lines. Split your volume with this surface. Hope it helps

Uday January 7, 2009 06:16

Re: virtual geometry
Hi Richard

I guess you have imported the mesh in gambit. If you have imported the mesh in gambit. Then it won't be possible to retrieve the geometry.

Now the easiest way out to find a soultion is Tgrid

In Tgrid once you read the mesh/case file you clear the volume mesh.


1)Mesh->clear---- Which deletes the volume mesh

2)Boundary->Create->Plane Surface-----Where in this window you can create a mesh plane (there no topological entities like volume or surface , You can see only surface mesh and this plane is nothing but a surface mesh of given size representing a plane of the given size which you can specify ) which cuts the surface mesh

3)In Plane surface option go for three point option you can click the three points where you want the surface-- once you select three points you can see a yellow square outline in the display i.e. in the surface mesh display

4)Push the button SCALE + which will increase the size of the plane and there its self you can specify the MESH SIZE (Specify the mesh size equal to the surface mesh size at that location)

5)CREATE the mesh plane Software will prompt you to choose the name of the surface.

6) Once the plane is created go to Boundary->Intersect Where you can intersect Surface mesh with the plane you have created.(The reason i asked you to keep the mesh size same was intersection you can see it now)

7)In this command you can choose the plane in one window and the surface mesh in other window OPERATION->INTERSECT push the button MARK and then say display(do not APPLY) you would see both surfaces and the probable intersection showing in yellow shade look that at only the intersected area it looks yellow and no node is left un-intersected you can even play with the tolerance if not perfectly intersecting.

8)once you get the assured of the tolerance level and every node is intersected say APPLY.

9)Now in Display grid see for multiple in surface mesh you can see the intersection.

10)one more operation is necessary before going to volume mesh you need only the punched part of the plane created so go to BOUNDARY->SEPERATE-> yo can seperate the plane by region

11)Delete the unwanted surface mesh

12)Now check for free face in display grid if there are no free faces MESH->TRI/TET->CONTROLS->INIT/MESH-> say non fluid TYPE as fluid one (As due to the surface we have created there would be two seperate zones and we want to treat both the zones as fluid) say ok

13)Now for Volume Mesh MESH->AUTO MESH->INIT & REFINE

14)Tgrid will create volume mesh in both domains and refine it and try to remove the swekness ..

I hope i have tried to expalin you step wise if you have any query write to me mail id

Give me the feed back.

Uday Regards

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