time_step_controller.f90

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module time_step_controller
  use num_types, only : rp
  use logger, only : neko_log, log_size
  use json_module, only : json_file
  use json_utils, only : json_get_or_default
  implicit none
  private
 
  type, public :: time_step_controller_t
     logical :: if_variable_dt
     real(kind=rp) :: set_cfl
     real(kind=rp) :: max_dt
     integer :: max_update_frequency
     integer :: dt_last_change
     real(kind=rp) :: alpha !coefficient of running average
     real(kind=rp) :: max_dt_increase_factor, min_dt_decrease_factor
   contains
     procedure, pass(this) :: init => time_step_controller_init
     procedure, pass(this) :: set_dt => time_step_controller_set_dt
 
  end type time_step_controller_t
 
contains
 
  subroutine time_step_controller_init(this, params)
    class(time_step_controller_t), intent(inout) :: this
    type(json_file), intent(inout) :: params
 
    this%dt_last_change = 0
    call json_get_or_default(params, 'case.variable_timestep',&
                                    this%if_variable_dt, .false.)
    call json_get_or_default(params, 'case.target_cfl',&
                                    this%set_cfl, 0.4_rp)
    call json_get_or_default(params, 'case.max_timestep',&
                                    this%max_dt, huge(0.0_rp))
    call json_get_or_default(params, 'case.cfl_max_update_frequency',&
                                    this%max_update_frequency, 0)
    call json_get_or_default(params, 'case.cfl_running_avg_coeff',&
                                    this%alpha, 0.5_rp)
    call json_get_or_default(params, 'case.max_dt_increase_factor',&
                                    this%max_dt_increase_factor, 1.2_rp)
    call json_get_or_default(params, 'case.min_dt_decrease_factor',&
                                    this%min_dt_decrease_factor, 0.5_rp)
 
  end subroutine time_step_controller_init
 
  subroutine time_step_controller_set_dt(this, dt, cfl, cfl_avrg, tstep)
    implicit none
    class(time_step_controller_t), intent(inout) :: this
    real(kind=rp), intent(inout) :: dt
    real(kind=rp), intent(in) :: cfl
    real(kind=rp), intent(inout) :: cfl_avrg
    real(kind=rp) :: dt_old, scaling_factor
    character(len=LOG_SIZE) :: log_buf
    integer, intent(in):: tstep
 
    if (this%if_variable_dt .eqv. .true.) then
       if (tstep .eq. 1) then
          ! set the first dt for desired cfl
          dt = min(this%set_cfl/cfl*dt, this%max_dt)
       else
          ! Calculate the average of cfl over the desired interval
          cfl_avrg = this%alpha * cfl + (1-this%alpha) * cfl_avrg
 
          if (abs(cfl_avrg - this%set_cfl) .ge. 0.2*this%set_cfl .and. &
             this%dt_last_change .ge. this%max_update_frequency) then
 
             if (this%set_cfl/cfl .ge. 1) then
                ! increase of time step
                scaling_factor = min(this%max_dt_increase_factor, this%set_cfl/cfl)
             else
                ! reduction of time step
                scaling_factor = max(this%min_dt_decrease_factor, this%set_cfl/cfl)
             end if
 
             dt_old = dt
             dt = scaling_factor * dt_old
             dt = min(dt, this%max_dt)
 
             write(log_buf, '(A,E15.7,1x,A,E15.7)') 'Avrg CFL:', cfl_avrg, &
                         'set_cfl:', this%set_cfl
             call neko_log%message(log_buf)
 
             write(log_buf, '(A,E15.7,1x,A,E15.7)') 'old dt:', dt_old, &
                         'new dt:', dt
             call neko_log%message(log_buf)
 
             this%dt_last_change = 0
 
          else
             this%dt_last_change = this%dt_last_change + 1
          end if
       end if
 
    end if
 
  end subroutine time_step_controller_set_dt
 
 
 
 
end module time_step_controller