!> @file timestep.f90 !------------------------------------------------------------------------------! ! This file is part of the PALM model system. ! ! PALM is free software: you can redistribute it and/or modify it under the ! terms of the GNU General Public License as published by the Free Software ! Foundation, either version 3 of the License, or (at your option) any later ! version. ! ! PALM is distributed in the hope that it will be useful, but WITHOUT ANY ! WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR ! A PARTICULAR PURPOSE. See the GNU General Public License for more details. ! ! You should have received a copy of the GNU General Public License along with ! PALM. If not, see . ! ! Copyright 1997-2018 Leibniz Universitaet Hannover !------------------------------------------------------------------------------! ! ! Current revisions: ! ------------------ ! ! ! Former revisions: ! ----------------- ! $Id: timestep.f90 2718 2018-01-02 08:49:38Z scharf $ ! Corrected "Former revisions" section ! ! 2696 2017-12-14 17:12:51Z kanani ! Change in file header (GPL part) ! ! 2365 2017-08-21 14:59:59Z kanani ! Vertical grid nesting: Sync fine and coarse grid timestep (SadiqHuq) ! ! 2258 2017-06-08 07:55:13Z suehring ! Bugfix, add pre-preprocessor directives to enable non-parrallel mode ! ! 2168 2017-03-06 13:08:38Z suehring ! ! 2130 2017-01-24 16:25:39Z raasch ! bugfix: in case of nested runs the stop condition in case of too small ! timesteps is communicated to all parent/child processes, ! some formatting done ! ! 2118 2017-01-17 16:38:49Z raasch ! OpenACC directives and related part of code removed ! ! 2000 2016-08-20 18:09:15Z knoop ! Forced header and separation lines into 80 columns ! ! 1849 2016-04-08 11:33:18Z hoffmann ! Adapted for modularization of microphysics ! ! 1682 2015-10-07 23:56:08Z knoop ! Code annotations made doxygen readable ! ! 1484 2014-10-21 10:53:05Z kanani ! Changes due to new module structure of the plant canopy model: ! calculations and parameters related to the plant canopy model removed ! (the limitation of the canopy drag, i.e. that the canopy drag itself should ! not change the sign of the velocity components, is now assured for in the ! calculation of the canopy tendency terms in subroutine plant_canopy_model) ! ! 1342 2014-03-26 17:04:47Z kanani ! REAL constants defined as wp-kind ! ! 1322 2014-03-20 16:38:49Z raasch ! REAL functions provided with KIND-attribute ! ! 1320 2014-03-20 08:40:49Z raasch ! ONLY-attribute added to USE-statements, ! kind-parameters added to all INTEGER and REAL declaration statements, ! kinds are defined in new module kinds, ! old module precision_kind is removed, ! revision history before 2012 removed, ! comment fields (!:) to be used for variable explanations added to ! all variable declaration statements ! ! 1257 2013-11-08 15:18:40Z raasch ! openacc porting ! bugfix for calculation of advective timestep in case of vertically stretched ! grids ! ! 1092 2013-02-02 11:24:22Z raasch ! unused variables removed ! ! 1053 2012-11-13 17:11:03Z hoffmann ! timestep is reduced in two-moment cloud scheme according to the maximum ! terminal velocity of rain drops ! ! 1036 2012-10-22 13:43:42Z raasch ! code put under GPL (PALM 3.9) ! ! 1001 2012-09-13 14:08:46Z raasch ! all actions concerning leapfrog scheme removed ! ! 978 2012-08-09 08:28:32Z fricke ! restriction of the outflow damping layer in the diffusion criterion removed ! ! 866 2012-03-28 06:44:41Z raasch ! bugfix for timestep calculation in case of Galilei transformation, ! special treatment in case of mirror velocity boundary condition removed ! ! Revision 1.1 1997/08/11 06:26:19 raasch ! Initial revision ! ! ! Description: ! ------------ !> Compute the time step under consideration of the FCL and diffusion criterion. !------------------------------------------------------------------------------! SUBROUTINE timestep USE arrays_3d, & ONLY: dzu, dzw, kh, km, u, v, w USE control_parameters, & ONLY: cfl_factor, coupling_mode, dt_3d, dt_fixed, dt_max, & galilei_transformation, old_dt, message_string, & stop_dt, terminate_coupled, terminate_coupled_remote, & timestep_reason, u_gtrans, use_ug_for_galilei_tr, v_gtrans USE cpulog, & ONLY: cpu_log, log_point USE grid_variables, & ONLY: dx, dx2, dy, dy2 USE indices, & ONLY: nxl, nxlg, nxr, nxrg, nyn, nyng, nys, nysg, nzb, nzt USE interfaces USE kinds USE microphysics_mod, & ONLY: dt_precipitation USE pegrid USE pmc_interface, & ONLY: nested_run USE statistics, & ONLY: flow_statistics_called, hom, u_max, u_max_ijk, v_max, v_max_ijk,& w_max, w_max_ijk USE vertical_nesting_mod, & ONLY: vnested, vnest_timestep_sync IMPLICIT NONE INTEGER(iwp) :: i !< INTEGER(iwp) :: j !< INTEGER(iwp) :: k !< LOGICAL :: stop_dt_local !< local switch for controlling the time stepping REAL(wp) :: div !< REAL(wp) :: dt_diff !< REAL(wp) :: dt_diff_l !< REAL(wp) :: dt_u !< REAL(wp) :: dt_u_l !< REAL(wp) :: dt_v !< REAL(wp) :: dt_v_l !< REAL(wp) :: dt_w !< REAL(wp) :: dt_w_l !< REAL(wp) :: u_gtrans_l !< REAL(wp) :: u_max_l !< REAL(wp) :: u_min_l !< REAL(wp) :: value !< REAL(wp) :: v_gtrans_l !< REAL(wp) :: v_max_l !< REAL(wp) :: v_min_l !< REAL(wp) :: w_max_l !< REAL(wp) :: w_min_l !< REAL(wp), DIMENSION(2) :: uv_gtrans !< REAL(wp), DIMENSION(2) :: uv_gtrans_l !< REAL(wp), DIMENSION(3) :: reduce !< REAL(wp), DIMENSION(3) :: reduce_l !< REAL(wp), DIMENSION(nzb+1:nzt) :: dxyz2_min !< CALL cpu_log( log_point(12), 'calculate_timestep', 'start' ) ! !-- In case of Galilei-transform not using the geostrophic wind as translation !-- velocity, compute the volume-averaged horizontal velocity components, which !-- will then be subtracted from the horizontal wind for the time step and !-- horizontal advection routines. IF ( galilei_transformation .AND. .NOT. use_ug_for_galilei_tr ) THEN IF ( flow_statistics_called ) THEN ! !-- Horizontal averages already existent, just need to average them !-- vertically. u_gtrans = 0.0_wp v_gtrans = 0.0_wp DO k = nzb+1, nzt u_gtrans = u_gtrans + hom(k,1,1,0) v_gtrans = v_gtrans + hom(k,1,2,0) ENDDO u_gtrans = u_gtrans / REAL( nzt - nzb, KIND=wp ) v_gtrans = v_gtrans / REAL( nzt - nzb, KIND=wp ) ELSE ! !-- Averaging over the entire model domain. u_gtrans_l = 0.0_wp v_gtrans_l = 0.0_wp DO i = nxl, nxr DO j = nys, nyn DO k = nzb+1, nzt u_gtrans_l = u_gtrans_l + u(k,j,i) v_gtrans_l = v_gtrans_l + v(k,j,i) ENDDO ENDDO ENDDO uv_gtrans_l(1) = u_gtrans_l / & REAL( (nxr-nxl+1)*(nyn-nys+1)*(nzt-nzb), KIND=wp ) uv_gtrans_l(2) = v_gtrans_l / & REAL( (nxr-nxl+1)*(nyn-nys+1)*(nzt-nzb), KIND=wp ) #if defined( __parallel ) IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr ) CALL MPI_ALLREDUCE( uv_gtrans_l, uv_gtrans, 2, MPI_REAL, MPI_SUM, & comm2d, ierr ) u_gtrans = uv_gtrans(1) / REAL( numprocs, KIND=wp ) v_gtrans = uv_gtrans(2) / REAL( numprocs, KIND=wp ) #else u_gtrans = uv_gtrans_l(1) v_gtrans = uv_gtrans_l(2) #endif ENDIF ENDIF ! !-- Determine the maxima of the velocity components, including their !-- grid index positions. CALL global_min_max( nzb, nzt+1, nysg, nyng, nxlg, nxrg, u, 'abs', 0.0_wp, & u_max, u_max_ijk ) CALL global_min_max( nzb, nzt+1, nysg, nyng, nxlg, nxrg, v, 'abs', 0.0_wp, & v_max, v_max_ijk ) CALL global_min_max( nzb, nzt+1, nysg, nyng, nxlg, nxrg, w, 'abs', 0.0_wp, & w_max, w_max_ijk ) IF ( .NOT. dt_fixed ) THEN ! !-- Variable time step: !-- Calculate the maximum time step according to the CFL-criterion, !-- individually for each velocity component dt_u_l = 999999.9_wp dt_v_l = 999999.9_wp dt_w_l = 999999.9_wp DO i = nxl, nxr DO j = nys, nyn DO k = nzb+1, nzt dt_u_l = MIN( dt_u_l, ( dx / & ( ABS( u(k,j,i) - u_gtrans ) + 1.0E-10_wp ) ) ) dt_v_l = MIN( dt_v_l, ( dy / & ( ABS( v(k,j,i) - v_gtrans ) + 1.0E-10_wp ) ) ) dt_w_l = MIN( dt_w_l, ( dzu(k) / & ( ABS( w(k,j,i) ) + 1.0E-10_wp ) ) ) ENDDO ENDDO ENDDO #if defined( __parallel ) reduce_l(1) = dt_u_l reduce_l(2) = dt_v_l reduce_l(3) = dt_w_l IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr ) CALL MPI_ALLREDUCE( reduce_l, reduce, 3, MPI_REAL, MPI_MIN, comm2d, ierr ) dt_u = reduce(1) dt_v = reduce(2) dt_w = reduce(3) #else dt_u = dt_u_l dt_v = dt_v_l dt_w = dt_w_l #endif ! !-- Compute time step according to the diffusion criterion. !-- First calculate minimum grid spacing which only depends on index k dt_diff_l = 999999.0_wp DO k = nzb+1, nzt dxyz2_min(k) = MIN( dx2, dy2, dzw(k)*dzw(k) ) * 0.125_wp ENDDO !$OMP PARALLEL private(i,j,k,value) reduction(MIN: dt_diff_l) !$OMP DO DO i = nxl, nxr DO j = nys, nyn DO k = nzb+1, nzt dt_diff_l = MIN( dt_diff_l, dxyz2_min(k) / & ( MAX( kh(k,j,i), km(k,j,i) ) + 1E-20_wp ) ) ENDDO ENDDO ENDDO !$OMP END PARALLEL #if defined( __parallel ) IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr ) CALL MPI_ALLREDUCE( dt_diff_l, dt_diff, 1, MPI_REAL, MPI_MIN, comm2d, & ierr ) #else dt_diff = dt_diff_l #endif ! !-- The time step is the minimum of the 3-4 components and the diffusion time !-- step minus a reduction (cfl_factor) to be on the safe side. !-- The time step must not exceed the maximum allowed value. dt_3d = cfl_factor * MIN( dt_diff, dt_u, dt_v, dt_w, dt_precipitation ) dt_3d = MIN( dt_3d, dt_max ) ! !-- Remember the restricting time step criterion for later output. IF ( MIN( dt_u, dt_v, dt_w ) < dt_diff ) THEN timestep_reason = 'A' ELSE timestep_reason = 'D' ENDIF ! !-- Set flag if the time step becomes too small. IF ( dt_3d < ( 0.00001_wp * dt_max ) ) THEN stop_dt = .TRUE. WRITE( message_string, * ) 'Time step has reached minimum limit.', & '&dt = ', dt_3d, ' s Simulation is terminated.', & '&old_dt = ', old_dt, ' s', & '&dt_u = ', dt_u, ' s', & '&dt_v = ', dt_v, ' s', & '&dt_w = ', dt_w, ' s', & '&dt_diff = ', dt_diff, ' s', & '&u_max = ', u_max, ' m/s k=', u_max_ijk(1), & ' j=', u_max_ijk(2), ' i=', u_max_ijk(3), & '&v_max = ', v_max, ' m/s k=', v_max_ijk(1), & ' j=', v_max_ijk(2), ' i=', v_max_ijk(3), & '&w_max = ', w_max, ' m/s k=', w_max_ijk(1), & ' j=', w_max_ijk(2), ' i=', w_max_ijk(3) CALL message( 'timestep', 'PA0312', 0, 1, 0, 6, 0 ) ! !-- In case of coupled runs inform the remote model of the termination !-- and its reason, provided the remote model has not already been !-- informed of another termination reason (terminate_coupled > 0) before. #if defined( __parallel ) IF ( coupling_mode /= 'uncoupled' .AND. terminate_coupled == 0 ) THEN terminate_coupled = 2 IF ( myid == 0 ) THEN CALL MPI_SENDRECV( & terminate_coupled, 1, MPI_INTEGER, target_id, 0, & terminate_coupled_remote, 1, MPI_INTEGER, target_id, 0, & comm_inter, status, ierr ) ENDIF CALL MPI_BCAST( terminate_coupled_remote, 1, MPI_INTEGER, 0, & comm2d, ierr) ENDIF #endif ENDIF ! !-- In case of nested runs all parent/child processes have to terminate if !-- one process has set the stop flag, i.e. they need to set the stop flag !-- too. IF ( nested_run ) THEN stop_dt_local = stop_dt #if defined( __parallel ) CALL MPI_ALLREDUCE( stop_dt_local, stop_dt, 1, MPI_LOGICAL, MPI_LOR, & MPI_COMM_WORLD, ierr ) #endif ENDIF ! !-- Ensure a smooth value (two significant digits) of the timestep. div = 1000.0_wp DO WHILE ( dt_3d < div ) div = div / 10.0_wp ENDDO dt_3d = NINT( dt_3d * 100.0_wp / div ) * div / 100.0_wp ! !-- Adjust the time step old_dt = dt_3d ENDIF ! !-- Vertical nesting: coarse and fine grid timestep has to be identical IF ( vnested ) CALL vnest_timestep_sync CALL cpu_log( log_point(12), 'calculate_timestep', 'stop' ) END SUBROUTINE timestep