Adaptive Mesh Refinement

Enabling Adaptive Mesh Refinement

Like Static Mesh Refinement, no configuration option is needed to enable AMR. You need to set the refinement parameters in the input file. For example,

<mesh>
...
refinement     = adaptive
numlevels      = 4
deref_count    = 5

This means the finer levels are created up to 4 levels (= the root level + 3 finer levels). The deref_count parameter means that at least 5 timesteps are required to be flagged for derefinement before a MeshBlock is actually derefined. This suppresses destruction of newly-refined MeshBlocks immediately after refinement.

The AMR Condition Function

Then a function to check whether a MeshBlock should be refined or derefined must be defined and enrolled in the Problem Generator. For example, in src/pgen/dmr.cpp,

int RefinementCondition(MeshBlock *pmb)
{
  AthenaArray<Real> &w = pmb->phydro->w;
  Real maxeps=0.0;
  int k=pmb->ks;
  for(int j=pmb->js; j<=pmb->je; j++) {
    for(int i=pmb->is; i<=pmb->ie; i++) {
      Real epsr= (std::abs(w(IDN,k,j,i+1)-2.0*w(IDN,k,j,i)+w(IDN,k,j,i-1))
                 +std::abs(w(IDN,k,j+1,i)-2.0*w(IDN,k,j,i)+w(IDN,k,j-1,i)))/w(IDN,k,j,i);
      Real epsp= (std::abs(w(IEN,k,j,i+1)-2.0*w(IEN,k,j,i)+w(IEN,k,j,i-1))
                 +std::abs(w(IEN,k,j+1,i)-2.0*w(IEN,k,j,i)+w(IEN,k,j-1,i)))/w(IEN,k,j,i);
      Real eps = std::max(epsr, epsp);
      maxeps = std::max(maxeps, eps);
    }
  }
  if(maxeps > 0.01) return 1;
  if(maxeps < 0.005) return -1;
  return 0;
}