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-   -   Help con BC (http://www.cfd-online.com/Forums/openfoam-solving/59239-help-con-bc.html)

mlarenas January 3, 2008 11:04

Hi, Im new using OpenFoam. I d
 
Hi, Im new using OpenFoam. I dont have much experience in CFD neither... just doing some work for university.
Currently, Im modelling a big hole in a surface (copper open mine, about 4 kms long) and at this point I need to impose atmospheric conditions for the wind. Here is the mesh:

http://img176.imageshack.us/my.php?image=meshsd8.png

The problem is when I set 'inlet' condition for the circular boundary, the next error appears:

Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow.
Total flux : 4.2258e+06
Specified mass inflow : 7.50341e+07
Specified mass outflow : 7.85048e+07
Adjustable mass outflow : 0

I have to impose a constant field of velocity on the boundary, and I as far as I understand, the error says there is no conservation of flow.
On top, I set 'symmetryPlane' condition and 'wall' to the ground.

Im still using icoFoam, just to get familiar with the libraries and parameters.

So.. the main question is.. what are the best BC for this problem? I appreciate any help http://www.cfd-online.com/OpenFOAM_D...part/happy.gif

Sorry for my english... Im from Chile.

dmoroian January 3, 2008 12:09

Hi Manuel, Did you try to do
 
Hi Manuel,
Did you try to do what the solver suggests: run potentialFoam to initialize the outflow?

Dragos

mlarenas January 3, 2008 14:06

I dont know what it exactly me
 
I dont know what it exactly means... can you tell me what to do plz?

If I run potentialFoam with the same conditions, same as before I get:

Create mesh for time = 0

Reading field p

Reading field U


Calculating potential flow


--> FOAM FATAL ERROR : Continuity error cannot be removed by adjusting the outflow.
Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow.
Total flux : 1e-300
Specified mass inflow : 7.50341e+07
Specified mass outflow : 7.85048e+07
Adjustable mass outflow : 0


From function adjustPhi(surfaceScalarField& phi, const volVectorField& U,const volScalarField& p
in file cfdTools/general/adjustPhi/adjustPhi.C at line 111.

FOAM exiting

I dont understand what Im doing wrong http://www.cfd-online.com/OpenFOAM_D...lipart/sad.gif

dmoroian January 3, 2008 17:08

Hello again Manuel, Would it
 
Hello again Manuel,
Would it be possible for me to have a look at your case (download it from some website)?

Dragos

mlarenas January 3, 2008 23:17

I would really appreciate your
 
I would really appreciate your help, Im sending it tomorrow, it is in the office. You need the complete folder right? Ill upload it on a website at night... thx!!

Manuel

mlarenas January 4, 2008 09:26

OK, I sent to your email the U
 
OK, I sent to your email the URL with the folder 'chuqui', the complete case.
Thx again!!

dmoroian January 4, 2008 11:09

Hi Manuel, I just looked brie
 
Hi Manuel,
I just looked briefly through your case and ... I could not find any outlet boundary condition. It is always a must to have an outlet if you have an inlet... hmm unless you have a mass sink somewhere in your domain.
Where are you supposed to have an outlet?

Dragos

mlarenas January 4, 2008 11:30

What Im trying to model is the
 
What Im trying to model is the flow of wind... so I supposed that imposing constant condition on boundary for velocity... the flow would just 'pass' through the Mine doing some strange behavior... is that so bad? http://www.cfd-online.com/OpenFOAM_D...lipart/sad.gif

That's why I asked about the BC's for this problem, how can I simulate just the flow of wind through the surface?

By the way, I tried to set the 'top' boundary as outlet, but most part of the wind went there... so ugly...

I tried to split the 'inlet_velocity' face (to make the inlet & outlet surface), but as you see the mesh is complicated & I dont know how to do that...

Any suggestions?

dmoroian January 4, 2008 12:25

Ok, so if I understand correct
 
Ok, so if I understand correctly you want to simulate the flow over an irregular surface (the bottom of your domain). If this is true, then one solution is to split in 2 the cylindrical surface that is right now an inlet, and transform it into an inlet and an outlet. This implies that you know already the direction of the flow.
I don't know how to do the split with OpenFOAM utilities, but I suspect you have used Gambit to produce the mesh, and there, you can do the splitting very easy.

Dragos

mlarenas January 4, 2008 12:39

That's exactly what I said htt
 
That's exactly what I said http://www.cfd-online.com/OpenFOAM_D...part/happy.gif and yes, the mesh was made in Gambit (not by me) but then exported to Fluent to make the .msh archive. I tried to read in Gambit that file... but I couldnt... some compatibility problems I think. So, if you suggest to make the splitting.. Ill put my efforts there.
Thanks!

mlarenas January 4, 2008 14:24

Nop, definitely I couldnt http
 
Nop, definitely I couldnt http://www.cfd-online.com/OpenFOAM_D...lipart/sad.gif nobody here uses here Fluent or Gambit... could you do the splitting for me plz? I uploaded the msh file... so if you could... that would be great! and I promise not to bother you anymore http://www.cfd-online.com/OpenFOAM_D...part/happy.gif

Manuel

dmoroian January 4, 2008 16:56

I'll try, but I cannot do it n
 
I'll try, but I cannot do it now. Most probably on Monday.
Also I need to know how to split. Can you make a sketch showing which side will be the inlet and which the outlet?

Dragos

mlarenas January 7, 2008 08:28

OK, here you are: http://im
 
OK, here you are:

http://img292.imageshack.us/img292/2425/mesh2ut0.png

They told me that wind flows from north to south in the morning and all the way around at night. So, I made the simplest split; two approximately symmetric hemispheres according to the real orientation. It doesn't really matters which of the them you choose as 'inlet', I think we can change it anyways in OpenFoam.

Thanks again!!
Manuel

yingfeng January 10, 2008 15:02

Manuel, Correct me if I am
 
Manuel,

Correct me if I am wrong. I have never done any wind simulation. But can't you set a fixedValue boundary condition at the top, something like uniform value (5,0,0) assuming your top surface normal is the z axis. Then the deep hole wall as well as the bottom will have fixed zero velocity.

This would be like the cavity example in the tutorial.

Yingfeng

mlarenas January 10, 2008 16:29

Hm... but I need to simulate w
 
Hm... but I need to simulate wind coming from outside and passing over the mine... in the cavity is just an internal flow. Am I right?

Manuel


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