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Superadiabatic reduction (linear) timescale limiter #1008

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Merged
Debraheem merged 1 commit into from
Jun 2, 2026
Merged

Superadiabatic reduction (linear) timescale limiter #1008

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20 changes: 15 additions & 5 deletions star/defaults/controls.defaults
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Original file line number Diff line number Diff line change
Expand Up @@ -2746,11 +2746,8 @@
! ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

! Optional convective-turnover-time limiter for the throttle.
! When ``.true.``, multiplies the throttle excess
! ``(Gamma_factor - 1)`` by
!
! ``f_tau = 1 - exp(-dt / tau_conv)``
!
! When ``.true.``, relaxes the throttle using a fraction
! ``f_tau`` set by ``superad_reduction_turnover_limit_function``,
! where ``tau_conv = scale_height(k) / mlt_vc_old(k)`` is the
! local convective turnover time computed from the previous
! step's converged convective velocity. This reflects the
Expand All @@ -2776,6 +2773,19 @@

superad_reduction_use_turnover_limit = .false.

! superad_reduction_turnover_limit_function
! ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

! Functional form for the turnover-time relaxation fraction. Allowed
! values are:
!
! - ``'exponential'``: ``f_tau = 1 - exp(-dt/tau_conv)``
! - ``'linear'``: ``f_tau = min(dt/tau_conv, 1)``

! ::

superad_reduction_turnover_limit_function = 'exponential'

! superad_reduction_turnover_vc_floor_frac
! ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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5 changes: 4 additions & 1 deletion star/private/ctrls_io.f90
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Expand Up @@ -136,7 +136,8 @@ module ctrls_io
gradT_excess_min_center_he4, gradT_excess_max_logT, gradT_excess_min_log_tau_full_on, gradT_excess_max_log_tau_full_off, &
use_superad_reduction, superad_reduction_gamma_limit, superad_reduction_gamma_limit_scale, D_mix_zero_region_top_q, &
superad_reduction_gamma_inv_scale, superad_reduction_diff_grads_limit, superad_reduction_limit, &
superad_reduction_use_turnover_limit, superad_reduction_turnover_vc_floor_frac, &
superad_reduction_use_turnover_limit, superad_reduction_turnover_limit_function, &
superad_reduction_turnover_vc_floor_frac, &
make_gradr_sticky_in_solver_iters, min_logT_for_make_gradr_sticky_in_solver_iters, &
max_logT_for_mlt, thermohaline_coeff, thermohaline_option, mixing_length_alpha, remove_small_D_limit, &
alt_scale_height_flag, Henyey_MLT_y_param, Henyey_MLT_nu_param, no_MLT_below_shock, mlt_make_surface_no_mixing, &
Expand Down Expand Up @@ -1080,6 +1081,7 @@ subroutine store_controls(s, ierr)
s% superad_reduction_diff_grads_limit = superad_reduction_diff_grads_limit
s% superad_reduction_limit = superad_reduction_limit
s% superad_reduction_use_turnover_limit = superad_reduction_use_turnover_limit
s% superad_reduction_turnover_limit_function = superad_reduction_turnover_limit_function
s% superad_reduction_turnover_vc_floor_frac = superad_reduction_turnover_vc_floor_frac

s% max_logT_for_mlt = max_logT_for_mlt
Expand Down Expand Up @@ -2805,6 +2807,7 @@ subroutine set_controls_for_writing(s, ierr)
superad_reduction_diff_grads_limit = s% superad_reduction_diff_grads_limit
superad_reduction_limit = s% superad_reduction_limit
superad_reduction_use_turnover_limit = s% superad_reduction_use_turnover_limit
superad_reduction_turnover_limit_function = s% superad_reduction_turnover_limit_function
superad_reduction_turnover_vc_floor_frac = s% superad_reduction_turnover_vc_floor_frac

max_logT_for_mlt = s% max_logT_for_mlt
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7 changes: 6 additions & 1 deletion star/private/turb_support.f90
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Expand Up @@ -561,7 +561,12 @@ subroutine set_superad_reduction()
* s% csound_face(k)
vc_old_local = max(s% mlt_vc_old(k), vc_old_floor, 1d-30)
tau_conv = scale_height / vc_old_local
f_turnover = 1d0 - exp(-s% dt / tau_conv)
select case (trim(s% superad_reduction_turnover_limit_function))
case ('linear')
f_turnover = min(s% dt / tau_conv, 1d0)
case default
f_turnover = 1d0 - exp(-s% dt / tau_conv)
end select
Gamma_factor = Gamma_factor_old_local + &
f_turnover * (Gamma_factor - Gamma_factor_old_local)
end if
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1 change: 1 addition & 0 deletions star_data/private/star_controls.inc
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Expand Up @@ -307,6 +307,7 @@
superad_reduction_diff_grads_limit, &
superad_reduction_limit
logical :: superad_reduction_use_turnover_limit
character(len=strlen) :: superad_reduction_turnover_limit_function
real(dp) :: superad_reduction_turnover_vc_floor_frac

! mixing parameters
Expand Down
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