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Fixed-dt runs: keep the clock on t_step*dt so restarts continue bitwise #1951

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Merged
sbryngelson merged 2 commits into from
Oct 8, 2026
+22 −15
Merged

Fixed-dt runs: keep the clock on t_step*dt so restarts continue bitwise #1951

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d282849
Fixed-dt runs: keep the clock on t_step*dt so restarts continue bitwise
sbryngelson Oct 7, 2026
00c3622
Merge branch 'master' into fix-fixed-dt-time-restart
sbryngelson Oct 8, 2026
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3 changes: 1 addition & 2 deletions src/simulation/m_global_parameters.fpp
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Expand Up @@ -286,8 +286,7 @@ module m_global_parameters
!> @{
!> @}

real(wp) :: mytime !< Current simulation time
real(wp) :: finaltime !< Final simulation time
real(wp) :: mytime !< Current simulation time
type(pres_field), allocatable, dimension(:) :: pb_ts
type(pres_field), allocatable, dimension(:) :: mv_ts

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17 changes: 10 additions & 7 deletions src/simulation/m_start_up.fpp
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Expand Up @@ -601,16 +601,13 @@ contains
end if
end if

! Land exactly on t_stop. A fixed dt already lands on t_step_stop by step count; trimming it to t_step_stop*dt - mytime
! would only change the run's last dt by round-off, which a run continuing past that step does not see
if (cfl_dt) then
if ((mytime + dt) >= t_stop) then
dt = t_stop - mytime
$:GPU_UPDATE(device='[dt]')
end if
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else
if ((mytime + dt) >= finaltime) then
dt = finaltime - mytime
$:GPU_UPDATE(device='[dt]')
end if
end if

if (cfl_dt) then
Expand Down Expand Up @@ -652,8 +649,14 @@ contains
call s_tvd_rk(t_step, time_avg, time_stepper)
end if

! Advance time after RK so source terms see current-step time
mytime = mytime + dt
! Advance time after RK so source terms see current-step time. With a fixed dt, use the same t_step*dt a restart
! starts from (p_main): a running sum drifts from it (1290 ulps by step 27000), so a restarted run would see the
! prescribed IB kinematics, inflow ramps and forcing at slightly different times than the run it continues
if (cfl_dt) then
mytime = mytime + dt
else
mytime = (t_step + 1)*dt
end if
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if (relax) call s_infinite_relaxation_k(q_cons_ts(1)%vf)

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16 changes: 11 additions & 5 deletions src/simulation/m_time_steppers.fpp
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Expand Up @@ -564,7 +564,7 @@ contains
if (ib) then
! check if any IBMS are moving, and if so, update the markers, ghost points, levelsets, and levelset norms
if (moving_immersed_boundary_flag) then
call s_propagate_immersed_boundaries(s)
call s_propagate_immersed_boundaries(s, t_step)
end if

! update the ghost fluid properties point values based on IB state
Expand Down Expand Up @@ -831,9 +831,9 @@ contains
end subroutine s_apply_synthetic_turbulence_force

!> Update immersed boundary positions and velocities at the current Runge-Kutta stage
subroutine s_propagate_immersed_boundaries(s)
subroutine s_propagate_immersed_boundaries(s, t_step)

integer, intent(in) :: s
integer, intent(in) :: s, t_step
integer :: i
integer :: gbl_id ! used for analytic ib patch motion
real(wp) :: t_stage ! time of the state produced by RK stage s (used by prescribed kinematics)
Expand All @@ -842,8 +842,14 @@ contains

if (moving_immersed_boundary_flag) call s_compute_ib_forces(q_prim_vf, fluid_pp)

t_stage = mytime + dt
if (time_stepper == time_stepper_rk3 .and. s == 2) t_stage = mytime + 0.5_wp*dt
if (cfl_dt) then
t_stage = mytime + dt
if (time_stepper == time_stepper_rk3 .and. s == 2) t_stage = mytime + 0.5_wp*dt
else
! The same t_step*dt form a restart evaluates the kinematics at, so a restart sees bitwise the same body
t_stage = (t_step + 1)*dt
if (time_stepper == time_stepper_rk3 .and. s == 2) t_stage = (t_step + 0.5_wp)*dt
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end if

$:GPU_PARALLEL_LOOP(private='[i, gbl_id]', copyin='[s, t_stage]')
do i = 1, num_ibs
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1 change: 0 additions & 1 deletion src/simulation/p_main.fpp
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Expand Up @@ -54,7 +54,6 @@ program p_main
else
mytime = t_step*dt
end if
finaltime = t_step_stop*dt
end if

call nvtxEndRange ! INIT
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