[rucky96]

Hi,

I was trying to solve the problem of a magnetically confined conductive fluid in a periodic cylinder. The results for a serial simulation gives resonable results... But when I run the simulation for 2 processors one can distinguish 2 zones in the cylinder (one per processor). If I am using 3 one can distinguish 3 zones. Same for 4.

I suppose that there is a problem in the comunication between the cells at the boundaries of each processors zone. I am using scotch method.

I tried (it did not work):

1. Change the method to simple.
2. Add a correctBoundaryConditions() in the equation for B in mhdFoam.

I suppose that the problem is in the solver that I am using (a mhdFoam slightly modified). mhdFoam works well with parallelization. But when one wants to add a external magnetic field one has to modify the equation for B (with , is the same for all t).

• Induction equation in mhdFoam looks like:
  

          while (bpiso.correct())
          {
              fvVectorMatrix BEqn // the magnetic induction equation, calculates the magnetic field taking into account the influence of the velocity.
              (
                  fvm::ddt(B)
                + fvm::div(phi, B)
                - fvm::laplacian(DB, B)
                - fvc::div(phiB, U)
              );
  
              BEqn.solve();
              phiB = fvc::flux(B);//phiB is calculated at faces.
              
              while (bpiso.correctNonOrthogonal())
              {
                  fvScalarMatrix pBEqn //A Poisson equation is derived for the fictitious magnetic pressure pB and solved
                  (
                      fvm::laplacian(pB) == fvc::div(phiB)
                  );
  
                  pBEqn.solve();
  
                  if (bpiso.finalNonOrthogonalIter()) //The variable distribution is then employed to correct the phiB values
                  {
                      phiB -= pBEqn.flux();
                  }
                  
              }// The loop exits after the prescribed iterations stated in the fvSolution file.
              #include "magneticFieldErr.H" //print magnetic field divergence deviation from null value
          }

• My induction equation in modified mhdFoam looks like
  

          #include "readBFixed.H"
          while (bpiso.correct())
          {
              fvVectorMatrix BVbleEqn
              (
                  fvm::ddt(BVble)
                + fvm::div(phi,BVble)
                + fvc::div(phi,BFixed)
                - fvc::div(phiBVble,U)
                - fvc::div(phiBFixed,U)
                - fvm::laplacian(lambda,BVble)
                - fvc::laplacian(lambda,BFixed)
              );
              
              BVbleEqn.solve();
              phiBVble = fvc::flux(BVble);
  
              while (bpiso.correctNonOrthogonal())
              {
                  fvScalarMatrix pBVbleEqn
                  (
                      fvm::laplacian(pBVble) == fvc::div(phiBVble)
                  );
  
                  pBVbleEqn.solve();
  
                  if (bpiso.finalNonOrthogonalIter())
                  {
                      phiBVble -= pBVbleEqn.flux();
                  }
              }
              #include "magneticFieldErr.H"
  
              BVble.correctBoundaryConditions();          
          }
          B=BVble+BFixed;
          phiB = fvc::flux(B);

Maybe the problem is to sum B=BVble+BFixed in this way??

3p.png

2p.png

[rucky96]

I tried the same case with the OF series solver for MHD. I used the same configuration and the same magnetic field profile but without an external magnetic field source at t> 0, that is, it is an MHD decay. The result has been the same as with the modified solver.

I have tried the same thing in a box with periodic conditions on the sides and I have not seen anything unusual.

It seems that the quality of the parallelization in OF depends on how simple the mesh is. If it is a bit complicated it seems that parallelization does not work so well. If this is true is an OF internal issue and I cannot do anything.

Am I right?

[HPE]

yes you can. submit an issue ticket in gitlab repo.

[rucky96]

Hi HPE,

Thanks for answering. I do not understand what you mean

[HPE]

My apologies. I wrote that while I was in bed.

>> If this is true is an OF internal issue and I cannot do anything.

I meant that if you think that there is an internal issue in OF, you can submit a bug ticket in gitlab repository, so that the developers can have a look at the issue, and evaluate it for you.