how does the REFINE_BOXES in input file work?

[陈奕纯]

Here's the attribute from the fila example in IB:

StandardTagAndInitialize {
   tagging_method = "GRADIENT_DETECTOR","REFINE_BOXES"
   RefineBoxes {
      level_0 = [( 0,2*N - 1),(             N - 1,        2*N - 1)]
      level_1 = [( 0,REF_RATIO  *2*N - 1),( REF_RATIO  *N - 1,REF_RATIO  *2*N - 1)]
      level_2 = [( 0,REF_RATIO^2*2*N - 1),( REF_RATIO^2*N - 1,REF_RATIO^2*2*N - 1)]
   }
}

I'm confused about the refine box area. How does the RefineBoxes work?

For example, I have an area with NxN grid. I would like to put a square refine box that is one level higher at the center of the area and the box width is half the the domain width, how should i set up this attribute?

[Boyce Griffith]

On Jun 17, 2025, at 5:34 AM, 陈奕纯 <a1185...@gmail.com> wrote:

Here's the attribute from the fila example in IB:

StandardTagAndInitialize {
   tagging_method = "GRADIENT_DETECTOR","REFINE_BOXES"
   RefineBoxes {
      level_0 = [( 0,2*N - 1),(             N - 1,        2*N - 1)]
      level_1 = [( 0,REF_RATIO  *2*N - 1),( REF_RATIO  *N - 1,REF_RATIO  *2*N - 1)]
      level_2 = [( 0,REF_RATIO^2*2*N - 1),( REF_RATIO^2*N - 1,REF_RATIO^2*2*N - 1)]
   }
}

I'm confused about the refine box area. How does the RefineBoxes work?

REFINE_BOXES indicates that specific regions of each level should be marked for refinement. Cells that are marked for refinement on level l are guaranteed to be covered by finer grid cells on level l+1. The grid generation algorithm may also introduce additional fine grid cells.

Note that the indexing is different on different levels. E.g. if you have an NxN box on level 0 and a refinement ratio r, then you have an (r*N)x(r*N) box on level 1.

For example, I have an area with NxN grid. I would like to put a square refine box that is one level higher at the center of the area and the box width is half the the domain width, how should i set up this attribute?

You would want to set up boxes that go from the lower corner of the region to the upper corner of the region. If the lower-left corner of the computational domain is (0,0), then you would do something like:

level_0 = [ (N/4 , 3*N/4 - 1) , (N/4 , 3*N/4 - 1) ]

In general, you would do something like: level_0 = [(x_start,x_end) , (y_start,y_end)].

You also can list multiple boxes for refinement to get more complicated refined regions. See, for instance, IBAMR example navier_stokes/ex0.

— Boyce

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