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More improvements to the position and velocity of fragments to preven…
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…t out of control collision cascades
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@daminton
daminton committed Jan 9, 2023
1 parent d710c9a commit 1843972
Showing 1 changed file with 54 additions and 40 deletions.
94 changes: 54 additions & 40 deletions src/fraggle/fraggle_generate.f90
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Original file line number Diff line number Diff line change
Expand Up @@ -228,26 +228,34 @@ module subroutine fraggle_generate_pos_vec(collider)
! Arguments
class(collision_fraggle), intent(inout) :: collider !! Fraggle collision system object
! Internals
real(DP) :: dis, direction
real(DP) :: dis, direction, rdistance
real(DP), dimension(NDIM,2) :: fragment_cloud_center
real(DP), dimension(2) :: fragment_cloud_radius, rdistance
real(DP), dimension(2) :: fragment_cloud_radius
logical, dimension(collider%fragments%nbody) :: loverlap
real(DP), dimension(collider%fragments%nbody) :: mass_rscale
integer(I4B) :: i, j, loop
logical :: lcat, lhitandrun
integer(I4B) :: i, j, loop, istart
logical :: lsupercat, lhitandrun
integer(I4B), parameter :: MAXLOOP = 20000
real(DP), parameter :: rdistance_scale_factor = 0.20_DP ! Scale factor to apply to distance scaling of cloud centers in the event of overlap
! The distance is chosen to be close to the original locations of the impactors
! but far enough apart to prevent a collisional cascade between fragments
real(DP), parameter :: rdistance_scale_factor = 1.0_DP ! Scale factor to apply to distance scaling of cloud centers in the event of overlap
! The distance is chosen to be close to the original locations of the impactors
! but far enough apart to prevent a collisional cascade between fragments
real(DP), parameter :: cloud_size_scale_factor = 3.0_DP ! Scale factor to apply to the size of the cloud relative to the distance from the impact point.
! A larger value puts more space between fragments initially

associate(fragments => collider%fragments, impactors => collider%impactors, nfrag => collider%fragments%nbody)
lcat = (impactors%regime == COLLRESOLVE_REGIME_SUPERCATASTROPHIC)
lsupercat = (impactors%regime == COLLRESOLVE_REGIME_SUPERCATASTROPHIC)
lhitandrun = (impactors%regime == COLLRESOLVE_REGIME_HIT_AND_RUN)

! We will treat the first two fragments of the list as special cases.
! Place the first two bodies at the centers of the two fragment clouds, but be sure they are sufficiently far apart to avoid overlap
loverlap(:) = .true.
rdistance(:) = rdistance_scale_factor * impactors%radius(:)
if (lhitandrun) then
rdistance = impactors%radius(2)
else if (lsupercat) then
rdistance = 0.5_DP * sum(impactors%radius(:))
else
rdistance = 10 * impactors%radius(2)
end if
! Give the fragment positions a random value that is scaled with fragment mass so that the more massive bodies tend to be closer to the impact point
! Later, velocities will be scaled such that the farther away a fragment is placed from the impact point, the higher will its velocity be.
call random_number(mass_rscale)
Expand All @@ -260,40 +268,46 @@ module subroutine fraggle_generate_pos_vec(collider)
if (lhitandrun) then
fragment_cloud_radius(:) = impactors%radius(:)
fragment_cloud_center(:,1) = impactors%rc(:,1)
fragment_cloud_center(:,2) = impactors%rc(:,2) + rdistance(2) * impactors%bounce_unit(:)
fragment_cloud_center(:,2) = impactors%rc(:,2) + rdistance * impactors%bounce_unit(:)
else if (lsupercat) then
fragment_cloud_center(:,1) = impactors%rc(:,1) - rdistance * impactors%bounce_unit(:)
fragment_cloud_center(:,2) = impactors%rc(:,2) + rdistance * impactors%bounce_unit(:)
fragment_cloud_radius(:) = cloud_size_scale_factor * rdistance / 2.0_DP
else
fragment_cloud_center(:,1) = impactors%rc(:,1) - rdistance(1) * impactors%bounce_unit(:)
fragment_cloud_center(:,2) = impactors%rc(:,2) + rdistance(2) * impactors%bounce_unit(:)
fragment_cloud_radius(1) = 8 * .mag.(fragment_cloud_center(:,1) - impactors%rbimp(:))
fragment_cloud_radius(2) = 8 * .mag.(fragment_cloud_center(:,2) - impactors%rbimp(:))
fragment_cloud_center(:,1) = impactors%rbimp(:) - impactors%radius(1) * impactors%y_unit(:)
fragment_cloud_center(:,2) = impactors%rbimp(:) + impactors%radius(2) * impactors%y_unit(:)
fragment_cloud_radius(:) = cloud_size_scale_factor * rdistance
end if
fragments%rc(:,1) = fragment_cloud_center(:,1)
if (lsupercat) then
istart = 3
fragments%rc(:,2) = fragment_cloud_center(:,2)
else
istart = 2
end if

do concurrent(i = 1:nfrag, loverlap(i))
if (i <= 2) then
fragments%rc(:,i) = fragment_cloud_center(:,i)
else
! Make a random cloud
call random_number(fragments%rc(:,i))

! Make the fragment cloud symmertic about 0
fragments%rc(:,i) = 2 *(fragments%rc(:,i) - 0.5_DP)

j = fragments%origin_body(i)

! Scale the cloud size
fragments%rc(:,i) = fragment_cloud_radius(j) * mass_rscale(:) * .unit.fragments%rc(:,i)

! Shift to the cloud center coordinates
fragments%rc(:,i) = fragments%rc(:,i) + fragment_cloud_center(:,j)

! Make sure that the fragments are positioned away from the impact point
direction = dot_product(fragments%rc(:,i) - impactors%rbimp(:), fragment_cloud_center(:,j) - impactors%rbimp(:))
if (direction < 0.0_DP) then
fragments%rc(:,i) = fragments%rc(:,i) - fragment_cloud_center(:,j)
fragments%rc(:,i) = -fragments%rc(:,i) + fragment_cloud_center(:,j)
end if
do concurrent(i = istart:nfrag, loverlap(i))
! Make a random cloud
call random_number(fragments%rc(:,i))

! Make the fragment cloud symmertic about 0
fragments%rc(:,i) = 2 *(fragments%rc(:,i) - 0.5_DP)

j = fragments%origin_body(i)

! Scale the cloud size
fragments%rc(:,i) = fragment_cloud_radius(j) * mass_rscale(:) * .unit.fragments%rc(:,i)

! Shift to the cloud center coordinates
fragments%rc(:,i) = fragments%rc(:,i) + fragment_cloud_center(:,j)

! Make sure that the fragments are positioned away from the impact point
direction = dot_product(fragments%rc(:,i) - impactors%rbimp(:), fragment_cloud_center(:,j) - impactors%rbimp(:))
if (direction < 0.0_DP) then
fragments%rc(:,i) = fragments%rc(:,i) - fragment_cloud_center(:,j)
fragments%rc(:,i) = -fragments%rc(:,i) + fragment_cloud_center(:,j)
end if

end do

! Check for any overlapping bodies.
Expand All @@ -304,7 +318,7 @@ module subroutine fraggle_generate_pos_vec(collider)
loverlap(i) = loverlap(i) .or. (dis <= (fragments%radius(i) + fragments%radius(j)))
end do
end do
rdistance(:) = rdistance(:) * collider%fail_scale
rdistance = rdistance * collider%fail_scale
end do

call collision_util_shift_vector_to_origin(fragments%mass, fragments%rc)
Expand Down Expand Up @@ -443,7 +457,7 @@ module subroutine fraggle_generate_vel_vec(collider, nbody_system, param, lfailu
vmag = vesc * vscale(i)
rimp(:) = fragments%rc(:,i) - impactors%rbimp(:)
vimp_unit(:) = .unit. rimp(:)
fragments%vc(:,i) = vmag * vscale(i) * impactors%bounce_unit(:) * vsign(i) + vrot(:) + vmag * vimp_unit(:)
fragments%vc(:,i) = vmag * vscale(i) * vimp_unit(:) + vrot(:)
end if
end do

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