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Old   August 4, 2009, 07:15
Default Two regions, problem ?
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Hello,

I have created two blocks which are side by side. CheckMesh outputs the following message:

*Number of regions: 2
The mesh has multiple regions which are not connected by any face.
<<Writing region information to "constant/cellToRegion"

Is it essential to connect them for solving ? Or is it unimportant ?


I think it is important, maybe anybody has some arguments why not..


How is it possible to connect these two Blocks ? With mergePairs ?

Last edited by dipling; August 4, 2009 at 07:47.
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Old   August 4, 2009, 09:33
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For understanding i attached a draft...

block 1 dimension [x y z ] --> [0-10 ; 0-10 ; 0-50] hex (20 20 40)
block 2 dimension [x y z] --> [0-5; 0-5; -7 - 0] hex (15 15 10)
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File Type: jpg blocks.jpg (15.8 KB, 64 views)
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Old   August 5, 2009, 02:15
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Henrik Rusche
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Dipling,

yes, it is important to have a single region if you want the flow to go across.

yes, mergePairs is the keyword to use.

Henrik
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Old   September 3, 2009, 08:00
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michel elsner
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Hello all,

I have the same Problem like Dipling.
I merged my Meshes (rotor and stator) to use the interDyMFoam solver. When I run checkMesh I still have two faces which are not connected. Is it important for the ggi? I thought ggi will correct this, but all what I tried ends with floating point exception while velocity magnitude is rapidly increasing . Does anybody have some ideas for me?

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Michél
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Old   September 3, 2009, 08:16
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Christof Benz
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hi michel,

i think ggi connects these 2 parts befor the fluxes are estimate. have a look at the tutorials in $FOAM_TUTORIALS/icoDyMFoam/mixer...
maybe this can help.

Christof
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Old   September 3, 2009, 08:54
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michel elsner
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hi Christof,

thank you first for your very fast reply
I looked a few times in that case to find out what I am doing wrong. I followed the steps like openfoamwiki describes about the ggi. I made two Meshes - Rotor and Stator (both has the same radius) and named the sliding patches insideSlider and outsideSlider. When I merged them the the rotor is circulating like I want. But from the beginning the velocity magnitude is increasing and the timesteps will become smaller and smaller (it looks like Courant Number mean: 9.60502e-05 max: 159.58 velocity magnitude: 6.73986e+81 deltaT = 1.41308e-85 GGI pair (outsideSlider, insideSlider) : 1.84927e+78 3.18538e+78 Diff = 1.77211e+75 or 0.0958272 % Time = 0.000650347) even if the rotation of the rotor is set to 0 in the dynamicMeshDict???

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Michel
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Old   September 3, 2009, 09:12
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Christof Benz
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i dont know much about ggi because i dont use it up to now.
it seems to me, that ggi goes right because there are no failure. maybe your boundary conditions?
check this.

can you upload your case?

Christof
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Old   September 3, 2009, 10:38
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michel elsner
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here is the case. sets(insideZone / outsideZone), points, faces, etc. in constant I deleted because of the size. I also attached the checkMesh log in the archive. Maybe someone find out what is wrong. thank you.

Michel
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Old   September 7, 2009, 17:23
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Steve Hansel
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Quote:
Originally Posted by holzmichel View Post
hi Christof,

thank you first for your very fast reply
I looked a few times in that case to find out what I am doing wrong. I followed the steps like openfoamwiki describes about the ggi. I made two Meshes - Rotor and Stator (both has the same radius) and named the sliding patches insideSlider and outsideSlider. When I merged them the the rotor is circulating like I want. But from the beginning the velocity magnitude is increasing and the timesteps will become smaller and smaller (it looks like Courant Number mean: 9.60502e-05 max: 159.58 velocity magnitude: 6.73986e+81 deltaT = 1.41308e-85 GGI pair (outsideSlider, insideSlider) : 1.84927e+78 3.18538e+78 Diff = 1.77211e+75 or 0.0958272 % Time = 0.000650347) even if the rotation of the rotor is set to 0 in the dynamicMeshDict???

Regards
Michel
I'm not sure about your application, but having the rotor and stator the same radius would cause problems in my tests. I actually rotate one of the meshes and if they are actually the same size, then as one rotates, it crosses into the other's area. (Due to the circle being made out of flat sides.) I leave 0.0005 m between the rotor and stator, but that number depends on the mesh size and diameter. If your mesh is turning, you will need to allow a little space between them.
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Old   September 14, 2009, 05:26
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michel elsner
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Hello Steve,

thanks for your help. I tried your suggestion but the same error is given.
Maybe some other reasons for this problem.

Regards
Michél
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Old   September 14, 2009, 10:51
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Steve Hansel
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Holdmichel, set your update rate to a small number so you get many snapshots and try to continue the simulation. Maybe you will be able to tell where the velocity is starting to go wrong. I'm curious to know if it's on the moving interface or the edge of your test area.

I generally use zero velocity sides on my test areas to keep things under control. (Fixed velocity inlet, and a fixed pressure outlet.)
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Old   September 16, 2009, 03:57
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michel elsner
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well my case do not have an inlet and outlet. I want to transport the fluid in the case with the rotor. When I set dt very small like 1*10-7 or higher like 5*10-3 it makes no difference of the increasing of the velocity. I tried to set the rpm of the rotor to 0 to have no velocity but there the velocity also increase. it is really strange and makes no sense. I will try your idea to find it out and hope I will have a success.

Regards

Michél
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