External Boundary Conditions

[alahyari]

Hi all,

I'm trying to implement external boundary conditions, and I'm facing a rather strange problem. Let's say I have external BCs on all my boundaries, so I set amrex::BCRec bcs to amrex::BCType::ext_dir for all components in all directions. Then, according to the instructions, I wrote the following function to fill the boundary cell:

void external_bc(amrex::Box const& bx, 
	       amrex::Array4<amrex::Real> const& q,
	       const int dcomp, 
	       const int numcomp,
	       amrex::GeometryData const& geom, 
	       const amrex::Real time,
	       const amrex::BCRec* bcr, 
	       const int bcomp, 
	       const int orig_comp)
{
    \* check bcr values in lower end and higher end of each direction and 
       if equal to "amrex::BCType::ext_dir", fill the boundary cells accordingly */
}

at which the pointer function bcfill of type UserFillBox points to, which is then passed to an amrex::PhysBCFunct object of type amrex::CpuBndryFuncFab for filling the patches (see below for lev=0).

if (lev == 0)
    {
        // current level multifab and time in case for sub-time-stepping
        amrex::Vector<amrex::MultiFab*> smf;
        amrex::Vector<amrex::Real> stime;
        get_data(0, time, smf, stime);

        amrex::CpuBndryFuncFab bndry_func(bcfill);
        amrex::PhysBCFunct<amrex::CpuBndryFuncFab> physbc(geom[lev], bcs, bndry_func);

        amrex::FillPatchSingleLevel(mf, time, smf, stime, 0, 0, nv, geom[lev], physbc, 0);
    }

So far, everything's good. But, when external_bc function is called, the const amrex::BCRec* bcr does not seem to be consistent with the original amrex::BCRec bcs. When I check the bcr values, it seems only the lower end of each direction is amrex::BCType::ext_dir and the higher ends are amrex::BCType::int_dir for some reason. I double checked the bcs values right before being passed to the amrex::PhysBCFunct object and all is fine. Am I missing anything? Has anyone encountered a similar issue?

Thank you in advance.

[WeiqunZhang]

I think everything is fine. The bcr passed to your external_bc is not the original BCRec for the whole domain. It's the BC for that box. For boxes with higher ends not touching the physical domain, the value there will not be external dirichlet.

[alahyari]

Oh, gosh! That does make sense. Thank you @WeiqunZhang