[jonmec]

Hello ....

I´m a new user and I´m trying to run my case in Parallel way.

I´ve already decomposed my case, but I had problems when I tried to start a LAM ....

please, someone help me!

what is the comand to start LAM?

[cedric_duprat]

Hi Jonathas

OpenFoam User Guide
3.4 Running applications in parallel
3.4.2 Running a decomposed cas
3.4.2.1 Starting a LAM multicomputer (U-82)

regards,
cedric

[gwierink]

Hi everyone,

I want to run my case in parallel, first with just two nodes on my laptop. When I try to decompose the case with decomposePar I get the error

/*---------------------------------------------------------------------------*\
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 1.4.1 |
| \ / A nd | Web: http://www.openfoam.org |
| \/ M anipulation | |
\*---------------------------------------------------------------------------*/

Exec : decomposePar . bubbleCellpar
Date : Nov 05 2008
Time : 12:10:41
Host :
PID : 15597
Root : /home/gijsbert/OpenFOAM/run
Case : bubbleCellpar
Nprocs : 1
Create time

Time = 0
Create mesh


Calculating distribution of cells
Selecting decompositionMethod simple


--> FOAM FATAL ERROR : Wrong number of processor divisions in geomDecomp:
Number of domains : 2
Wanted decomposition : (2 2 1)

From function geomDecomp::geomDecomp(const dictionary& decompositionDict)
in file geomDecomp/geomDecomp.C at line 53.

FOAM exiting


My composeParDict looks like this:

numberOfSubdomains 2;

method simple;

simpleCoeffs
{
n (1 2 1);
delta 0.001;
}

hierarchicalCoeffs
{
n (1 1 1);
delta 0.001;
order xyz;
}

metisCoeffs
{
processorWeights
(
1
1
);
}

manualCoeffs
{
dataFile "";
}

distributed no;

roots
(
);


From the error output it looks like I only use 1 processor while I try to divide the case over two. Can anyone help me on this problem?

Thank you in advance

[sivakumar]

hi,
can u tell me how many processor u r going to use????

[sivakumar]

hey man,
go to u r decomposeParDict in system file, in that
simpleCoeffs
{
n (2 1 1);
delta 0.001;
}
...

then
metisCoeffs
{
processorWeights
(
1
1
);

just do this changes then try to decompose
i hope it will work.

by
siva

[dmoroian]

Hello Gijsbert,
It looks to me that you've chosen to have 2 partitions, and the splitting algorithm is simple. However, you specified that the algorithm should split in 2 along x, 2 along y, and 1 along z, which makes 4 partitions.
Although you show the correct setting:

simpleCoeffs
{
n (1 2 1);
delta 0.001;
}

the decomposePar sees differently:

Wanted decomposition : (2 2 1)

so you probably modified in the wrong file...

I hope this is helpful,
Dragos

[gwierink]

Hi guys,

Many thanks for your replies.

@ siva:
I am trying to decompose my case to use the two cores of my dual core laptop, just to try if it runs. Soon I will get a quadcore, so I want to be able to do parallel runs. For that I copied the /system/decomposeParDict from the interFoam/damBreak tutorial into my case file and modified it to have 2 processors and a decomposition of (2 2 1). But somehow during the actual decomposition it does not work.

@ Dragos:
As described above I have modified the /system/decomposeParDict file in case directory and, as you write, during the decomposition that file is appearently not read, or read elsewhere.

Any ideas? Does decomposePar look for decomposeParDict in a different place than I think perhaps?

Rgds, Gijsbert

[sivakumar]

hi,
u have 2 processor, but u r splitting u r geometry it to 4, so the the command it will not work.
in that

simpleCoeffs
{
n (1 2 1);
delta 0.001;
}

this is the right way,
if u tried, still u r getting the problem
attach u r problem here, " i mean what the computer says"

may be we can have a look.

by siva

[gwierink]

Hi siva,

Thank you for your reply. I did edit the decomposeParDict as you suggested, but apparently it did not want to save although I did do Ctrl+S. Perhaps it is most fool proof to actually close decomposeParDict before decomposing the case, so that it is saved for sure and no weird things happen. When I tried again today, everything worked fine! So I just ran my first parallel case successfully. Thanks for your quick replies.

Cheers, Gijs

[eduardasilva]

Hello all,

I have been running some cases with simpleFoam in a cylinder using parallel implementations in a Quad core processor. I would like to better understand when does the parallel communication occur between the 4 subdomains. Are the governing equations being solved in subdomain 1 and then being send to sudomain 2? How significant is it to use an implicit coupling method rather than an explicit one?

Thanks in advance,
Eduarda

[prapanj]

Edura,

The communication occurs at the end of each time step. All 4 processors have a copy of the program(binary). The binary can identify the processor number in which it is present. Using this, the processor understands what part of the domain it has to solve. It uses the flow field values along the boundaries of the adjacent subdomains(which are in adjacent processors) as its own boundary conditions. So after each timestep, the flow field values along the edges of the subdomains are exchanged. At the end of the simulations, the subdomains are composed back together to form the domain.

I have mentioned just one way of doing it. For better efficiency, cells may be distributed among processors in a round-robin too. But I hope you get a gist of what happens.

Refer this book : Parallel computing , by Barry Wilkinson and Michael Allen.

[hellorishi]

Hello All,

Does somebody have an example of decomposePar file using the "distributed yes;" and "roots" options?

I would like to use two nodes of a cluster to run OpenFOAM-1.5.x in parallel. I would like to use /tmp or /scratch of local cluster disks, instead of using the mounted ~/ to store the data.
I have enabled passwordless ssh.

Thanks in advance,
Rishi

[tomislav_maric]

I'm trying to run damBreak tutorial in parallel on a HP 6820s dual core laptop. I've found this thread:

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

that states it's worth the trouble. I change the number of sub domains in "decomposeParDict" to 2. I'm using simple decomposition and set the coefficient "n" to (2 1 1). The "decomposePar" runs fine, telling me the number of processors is 1 (nProc: 1, with dual core?).

As a result I have two new directories: "processor0" and "processor1" with "0" and "constant" as their subdirectories. checkMesh tells me I have 2268 cells split in two on each "processor". The problem happens when I run "paraFoam -case processor0" (as read from page 64 in OF U-guide). Paraview starts fine, but when I try to import mesh data and click the Apply button, it shuts down and I get this error in console:

*** An error occurred in MPI_Bsend
*** before MPI was initialized
*** MPI_ERRORS_ARE_FATAL (goodbye)
[icarus:12344] Abort before MPI_INIT completed successfully; not able to guarantee that all other processes were killed!


I have NO clue about parallel runs (or cpu architecture and its inner works) and I'm running most of my cases on this laptop so I wanted to speed things up at least a bit. What does this error mean? Also if I try

"mpirun -np 1 interFoam -parallel > log &"

it won't work, but

"mpirun -np 2 interFoam -parallel > log &"

runs fine (the results are written in directories "processor0" and "processor1"). Now, my question is: why does decomposePar tell me that I have nProc: 1 (number of processors 1) and creates processor0 and processor1 directories, while mpirun works only with the argument -np 2? Am I doing something wrong?

[mattijs]

The MPI_BSend message sounds like a bug. Probably some boundary condition that does an extraneous parallel communication even when not running parallel. Try reconstructPar + postprocessing on the undecomposed case instead.

2) the "nProc:1" message I assume comes from the header. decomposePar runs on one processor only. It can decompose for any number of processors as given in the decomposeParDict.

[tomislav_maric]

Originally Posted by mattijs

The MPI_BSend message sounds like a bug. Probably some boundary condition that does an extraneous parallel communication even when not running parallel. Try reconstructPar + postprocessing on the undecomposed case instead.

Thank You, I've tried it already and I've seen that it works fine on the damBreak case. I was worried because I have a case that's pretty expensive and I wanted to try a parallel run on my laptop first.

Originally Posted by mattijs

2) the "nProc:1" message I assume comes from the header. decomposePar runs on one processor only. It can decompose for any number of processors as given in the decomposeParDict.

I guess it creates "processor0" and "processor1" for two mesh sub-domains divided for one processor, but two cores? Again, I don't know enough details of comp. architecture to understand this yet, the important thing is that it seems to be working fine for two days now. I'm running interFoam on a pretty heavy case, without complaints, so far.

Thank You,

Tomislav

[azb162]

Hi Foamers,

I have been trying to run biconic25-55Run35 tutorial on two processors.
I have used the simple decomposition scheme in the decomposepar utility to
decompose the mesh. When I run the decomposed case, it runs for a few time steps (5-10) and then it crashes. Can somebody help me debug this problem.

thanks ...