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-   -   GGI -> AMI stability (http://www.cfd-online.com/Forums/openfoam-solving/103789-ggi-ami-stability.html)

jiejie June 27, 2012 01:47

GGI -> AMI stability
 
Dear Foamers

I set up my rotating propeller case with both GGI and AMI interface in OF1.6-ext and OF2.1.1 respectively. I started using GGI prior to AMI. There was no problem when I ran the simulation with GGI. Then, I setup the case with AMI using the same mesh. The simulation keeps blowing up. Since I set the "adjustTimeStep" to yes, I found OpenFOAM kept reducing the delta time till the simulation crushed.

May I ask how everyone sets up the fvScheme and fvSolution files with AMI? I just used the default from the propeller case in OF2.1.1. I experienced the same unstable simulation with the GGI in OF1.6-ext. The simulation became stable after I changed schemes in fvSolution and fvScheme.

Thank you much much.

Jie

dogan November 26, 2012 11:29

GGI to AMI
 
Hello Jiejie
first of all, i would like to say you that i am not capable to answer your question, because i am really very new in using OpenFOAM. in fact, i wanted to ask you a question about ggi and ami. I am using OpenFOAM 2.1.x, and unfortunately, this version does not have the GGI algorithm. I have found the ERCOFTAC centrifugal test case on web, which is ready to run just for practice, but it is using the GGI algorithm, and i don't have the extended version to run it. so my question is that, is it possible to convert GGI to AMI? if the answer is yes, can you tell me the main steps how to do it?
thank you very much,
dogan

jiejie November 26, 2012 19:36

Quote:

Originally Posted by dogan (Post 394228)
Hello Jiejie
so my question is that, is it possible to convert GGI to AMI? if the answer is yes, can you tell me the main steps how to do it?
thank you very much,
dogan

Hi dogan

I would like to know the answer to this question as well. Just in my opinion (I am not sure whether I am correct), you can try to use a text editor to replace GGI in the corresponding files (e.g. boundary, u, p ...) with AMI. Then, run it and see whether it works. As GGI is from the extended project and AMI is from the SGI release, I don't think it can be converted easily.

Jiejie

dogan April 30, 2013 08:18

Hi again jiejie,

you were right, i tried to convert GGI to AMI, but i didn't succed it. So that i decided to use OpenFoam 1.6extended instead of 2.1.x. So that, regarding the use of GGI, i have some questions.

In my case, i am supposed to do a simulation of a centrifugal pump. My first approach is to calculate it steady state (with MRFSimpleFoam solver), which i have already done it.

And secondly i have to do it transient where i need to use the pimpleDyMFoam solver. in this point my problem is setting up the case for a transient simulation.

I have created the dynamicMeshDict which is as follows:

dynamicFvMeshLib "libtopoChangerFvMesh.so";
dynamicFvMesh mixerGgiFvMesh;

mixerGgiFvMeshCoeffs
{
coordinateSystem
{
type cylindrical;
origin (0 0 0);
axis (0 0 1);
direction (1 0 0);
}

rpm 151.844;

slider
{
moving ( GEOM-SIDE-1 );
static ( GEOM-SIDE-2 );
}
}


and then i changed the BC of rotational wall from fixedValue to movingWallVelocity. and moreover i defined the movingCells in the cellZones file. but still my calculation crashes after a couple of timesteps even though my timesteps are small enough (1e-8). If you have any idea regarding this problem, could you please help me.

best regards

Dogan

timo_IHS April 30, 2013 10:31

Hi Dogan,

for starting I would use (more) 1st order for time and div-scheme.
pimpleDyMFoam gave me a strange pressure oscillation for the first time step(s) at every (re)start. Try transientSimpleDyMFoam from 1.6-ext, which you can compile for 2.1.

Best

dogan April 30, 2013 13:00

Hi Timo,
thanks for replying. in my calculation, i tried backward for time, and gauss upwind for the div schemes, but anyway it crashed after 20 time steps. so that i thought whether i set it up correctly or not.

I also checked the tutorials from both OF2.1.x and OF 1.6 ext, but i can not find any solver with the name transientSimpleDyMFoam. Because of my mesh quality, i have to use for sure GGI algorithm which is available in 1.6 ext but not available in 2.1.x. So that i will use 1.6 ext, but i can find only the pimpleDyMFoam and icoDyMFoam tutorials available for a transient simulation.

i read it somewhere but i am not sure about that: do i need to use moveMesh command before i start my simulation with pimpleDyMFoam, or after setting up the case, should i directly start the simulation with pimpleDyMFoam (or any other transient solver).
I hope you can help me in this matter.

best regards
Dogan

hakonbar April 30, 2013 14:23

Hi dogan,

Did you remember to split the baffles before running pimpleDyMFoam? The command for that is:

mergeOrSplitBaffles -split -overwrite

Also, the dynamicMeshDict for an AMI case looks a bit different than the one you posted, which I guess is from a GGI. The "propeller" tutorial inside "incompressible/pimpleDyMFoam" is great for learning to use AMI.

dogan May 2, 2013 10:14

Hi Håkon,

thanks for replying.

i tried splitting buffles but it didn't work anyway.
i set the time step to 10e-8 and started the simulation. it runs for 20 time steps, but then i can see the time steps are getting smaller smaller (runTimeModifiable was set true) and then it crashes. i don't know what the source of the problem may be?

and by the way, i am using OF 1.6. ext for this simulation, so it is with ggi algorithm.

do you have any other idea which setting should i change?

Thanks and regards

Dogan

hakonbar May 2, 2013 13:02

Sorry, I've never used GGI myself, so I really don't know what else to try. Best of luck on your simulations, though, and I hope you work it out!

dogan May 3, 2013 10:59

Thanks anyway... i hope i figure it out...

renyun0511 May 9, 2013 23:18

Hi, dogan,

I'm using of 1.6-ext to do the transient simulation of a centrifugal pump, too. I'd like to ask you that did you solve your problem? Because I came across with the worse problem, here is the links:

http://www.cfd-online.com/Forums/ope...exception.html

You said that you defined the movingCells in the cellZones, I don't know how to do it? Does it need special command to transfer the rotating part to cellZones? my rotating part is impeller, and I found it was in the cellZones after I transfered the mesh file to OpenFOAM-1.6-ext. So, did I need to define it with movingCells in cellZones?

Thanks!

Yun Ren

Quote:

and then i changed the BC of rotational wall from fixedValue to movingWallVelocity. and moreover i defined the movingCells in the cellZones file. but still my calculation crashes after a couple of timesteps even though my timesteps are small enough (1e-8). If you have any idea regarding this problem, could you please help me.



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