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IB: abort if an immersed boundary marks no cell anywhere #1914

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IB: abort if an immersed boundary marks no cell anywhere #1914

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42 changes: 42 additions & 0 deletions src/simulation/m_ibm.fpp
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Original file line number Diff line number Diff line change
Expand Up @@ -115,6 +115,7 @@ contains
$:GPU_UPDATE(device='[ib_markers%sf]')
call s_apply_ib_patches(ib_markers)
$:GPU_UPDATE(host='[ib_markers%sf]')
call s_check_every_patch_marked()
do i = 1, num_ibs
if (patch_ib(i)%moving_ibm /= 0) call s_compute_centroid_offset(i) ! offsets are computed after IB markers are generated
$:GPU_UPDATE(device='[patch_ib(i)]')
Expand Down Expand Up @@ -1677,6 +1678,47 @@ contains

end subroutine s_get_neighborhood_idx

!> Abort if any immersed boundary marked no cell anywhere in the domain.
!!
!! A rank is given a patch when the patch CENTROID falls in its share of the domain, but for an STL
!! the centroid and the geometry are independent: the body is placed by model_translate, and a case
!! may legitimately leave the centroid at the origin. Ownership is then decided at a point the body
!! does not occupy, and the owning rank marks only whatever of the geometry its own subdomain happens
!! to reach. That shrinks as the decomposition is refined, so a body can erode and finally vanish --
!! contributing no markers, no ghost points, and a force of exactly zero every step -- with nothing
!! reported. Marker generation is a pure function of geometry and grid, so a result that depends on
!! the rank count is always wrong.
!!
!! Measured on a two-body case, identical deck, only the rank count changed, with a patch at the
!! origin as a control: the control held 30191 cells at 64, 128 and 512 ranks, while a patch eight
!! chords away went 19115 -> 12667 -> 0.
!!
!! One reduction per patch at setup. It cannot see partial erosion -- that needs the marked volume,
!! which is not available here -- but it turns the total loss into an immediate, specific error.
impure subroutine s_check_every_patch_marked()

integer(kind=8) :: cnt_loc, cnt_glb
integer :: gid, i, j, k

do gid = 1, num_gbl_ibs
cnt_loc = 0_8
do k = 0, p
do j = 0, n
do i = 0, m
Comment on lines +1703 to +1707
if (ib_markers%sf(i, j, k) == gid) cnt_loc = cnt_loc + 1_8
end do
end do
end do
cnt_glb = cnt_loc
#ifdef MFC_MPI
if (num_procs > 1) call s_mpi_allreduce_integer_sum(cnt_loc, cnt_glb)
#endif
@:PROHIBIT(cnt_glb == 0_8, &
& "An immersed boundary marked no cell anywhere: its centroid decides which rank "// "owns it, so a body placed elsewhere with model_translate is handed to a rank that "// "does not hold it. Set patch_ib%x/y/z_centroid to where the body actually is.")
end do

end subroutine s_check_every_patch_marked

subroutine s_update_ib_lookup()

integer :: i
Expand Down
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