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source: palm/trunk/SOURCE/timestep.f90 @ 1076

Last change on this file since 1076 was 1054, checked in by hoffmann, 12 years ago
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[1]	1	SUBROUTINE timestep
	2
[1036]	3	!--------------------------------------------------------------------------------!
	4	! This file is part of PALM.
	5	!
	6	! PALM is free software: you can redistribute it and/or modify it under the terms
	7	! of the GNU General Public License as published by the Free Software Foundation,
	8	! either version 3 of the License, or (at your option) any later version.
	9	!
	10	! PALM is distributed in the hope that it will be useful, but WITHOUT ANY
	11	! WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
	12	! A PARTICULAR PURPOSE. See the GNU General Public License for more details.
	13	!
	14	! You should have received a copy of the GNU General Public License along with
	15	! PALM. If not, see <http://www.gnu.org/licenses/>.
	16	!
	17	! Copyright 1997-2012 Leibniz University Hannover
	18	!--------------------------------------------------------------------------------!
	19	!
[258]	20	! Current revisions:
[866]	21	! ------------------
[316]	22	!
[1]	23	! Former revisions:
	24	! -----------------
[3]	25	! $Id: timestep.f90 1054 2012-11-13 17:30:09Z hoffmann $
[110]	26	!
[1054]	27	! 1053 2012-11-13 17:11:03Z hoffmann
	28	! timestep is reduced in two-moment cloud scheme according to the maximum
	29	! terminal velocity of rain drops
	30	!
[1037]	31	! 1036 2012-10-22 13:43:42Z raasch
	32	! code put under GPL (PALM 3.9)
	33	!
[1002]	34	! 1001 2012-09-13 14:08:46Z raasch
	35	! all actions concerning leapfrog scheme removed
	36	!
[979]	37	! 978 2012-08-09 08:28:32Z fricke
	38	! restriction of the outflow damping layer in the diffusion criterion removed
	39	!
[867]	40	! 866 2012-03-28 06:44:41Z raasch
	41	! bugfix for timestep calculation in case of Galilei transformation,
	42	! special treatment in case of mirror velocity boundary condition removed
	43	!
[708]	44	! 707 2011-03-29 11:39:40Z raasch
	45	! bc_lr/ns replaced by bc_lr/ns_cyc
	46	!
[668]	47	! 667 2010-12-23 12:06:00Z suehring/gryschka
	48	! Exchange of terminate_coupled between ocean and atmosphere via PE0
	49	! Minimum grid spacing dxyz2_min(k) is now calculated using dzw instead of dzu
	50	!
[623]	51	! 622 2010-12-10 08:08:13Z raasch
	52	! optional barriers included in order to speed up collective operations
	53	!
[392]	54	! 343 2009-06-24 12:59:09Z maronga
	55	! Additional timestep criterion in case of simulations with plant canopy
	56	! Output of messages replaced by message handling routine.
	57	!
[226]	58	! 222 2009-01-12 16:04:16Z letzel
	59	! Implementation of a MPI-1 Coupling: replaced myid with target_id
	60	! Bugfix for nonparallel execution
	61	!
[110]	62	! 108 2007-08-24 15:10:38Z letzel
	63	! modifications to terminate coupled runs
	64	!
[3]	65	! RCS Log replace by Id keyword, revision history cleaned up
	66	!
[1]	67	! Revision 1.21 2006/02/23 12:59:44 raasch
	68	! nt_anz renamed current_timestep_number
	69	!
	70	! Revision 1.1 1997/08/11 06:26:19 raasch
	71	! Initial revision
	72	!
	73	!
	74	! Description:
	75	! ------------
	76	! Compute the time step under consideration of the FCL and diffusion criterion.
	77	!------------------------------------------------------------------------------!
	78
	79	USE arrays_3d
[1053]	80	USE cloud_parameters
[1]	81	USE control_parameters
	82	USE cpulog
	83	USE grid_variables
	84	USE indices
	85	USE interfaces
	86	USE pegrid
	87	USE statistics
	88
	89	IMPLICIT NONE
	90
[866]	91	INTEGER :: i, j, k, u_max_cfl_ijk(3), v_max_cfl_ijk(3)
[1]	92
[318]	93	REAL :: div, dt_diff, dt_diff_l, dt_plant_canopy, &
	94	dt_plant_canopy_l, &
	95	dt_plant_canopy_u, dt_plant_canopy_v, dt_plant_canopy_w, &
[1001]	96	dt_u, dt_v, dt_w, lad_max, &
[866]	97	u_gtrans_l, u_max_cfl, vabs_max, value, v_gtrans_l, v_max_cfl
[1]	98
	99	REAL, DIMENSION(2) :: uv_gtrans, uv_gtrans_l
	100	REAL, DIMENSION(nzb+1:nzt) :: dxyz2_min
	101
[667]	102
	103
[1]	104	CALL cpu_log( log_point(12), 'calculate_timestep', 'start' )
	105
	106	!
	107	!-- In case of Galilei-transform not using the geostrophic wind as translation
	108	!-- velocity, compute the volume-averaged horizontal velocity components, which
	109	!-- will then be subtracted from the horizontal wind for the time step and
	110	!-- horizontal advection routines.
	111	IF ( galilei_transformation .AND. .NOT. use_ug_for_galilei_tr ) THEN
	112	IF ( flow_statistics_called ) THEN
	113	!
	114	!-- Horizontal averages already existent, just need to average them
	115	!-- vertically.
	116	u_gtrans = 0.0
	117	v_gtrans = 0.0
	118	DO k = nzb+1, nzt
	119	u_gtrans = u_gtrans + hom(k,1,1,0)
	120	v_gtrans = v_gtrans + hom(k,1,2,0)
	121	ENDDO
	122	u_gtrans = u_gtrans / REAL( nzt - nzb )
	123	v_gtrans = v_gtrans / REAL( nzt - nzb )
	124	ELSE
	125	!
	126	!-- Averaging over the entire model domain.
	127	uv_gtrans_l = 0.0
	128	DO i = nxl, nxr
	129	DO j = nys, nyn
	130	DO k = nzb+1, nzt
	131	uv_gtrans_l(1) = uv_gtrans_l(1) + u(k,j,i)
	132	uv_gtrans_l(2) = uv_gtrans_l(2) + v(k,j,i)
	133	ENDDO
	134	ENDDO
	135	ENDDO
	136	uv_gtrans_l = uv_gtrans_l / REAL( (nxr-nxl+1)(nyn-nys+1)(nzt-nzb) )
	137	#if defined( __parallel )
[622]	138	IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr )
[1]	139	CALL MPI_ALLREDUCE( uv_gtrans_l, uv_gtrans, 2, MPI_REAL, MPI_SUM, &
	140	comm2d, ierr )
	141	u_gtrans = uv_gtrans(1) / REAL( numprocs )
	142	v_gtrans = uv_gtrans(2) / REAL( numprocs )
	143	#else
	144	u_gtrans = uv_gtrans_l(1)
	145	v_gtrans = uv_gtrans_l(2)
	146	#endif
	147	ENDIF
	148	ENDIF
	149
[866]	150	!
	151	!-- Determine the maxima of the velocity components.
	152	CALL global_min_max( nzb, nzt+1, nysg, nyng, nxlg, nxrg, u, 'abs', 0.0, &
	153	u_max, u_max_ijk )
	154	CALL global_min_max( nzb, nzt+1, nysg, nyng, nxlg, nxrg, v, 'abs', 0.0, &
	155	v_max, v_max_ijk )
	156	CALL global_min_max( nzb, nzt+1, nysg, nyng, nxlg, nxrg, w, 'abs', 0.0, &
	157	w_max, w_max_ijk )
	158
	159	!
	160	!-- In case of Galilei transformation, the horizontal velocity maxima have
	161	!-- to be calculated from the transformed horizontal velocities
	162	IF ( galilei_transformation ) THEN
	163	CALL global_min_max( nzb, nzt+1, nysg, nyng, nxlg, nxrg, u, 'absoff', &
	164	u_gtrans, u_max_cfl, u_max_cfl_ijk )
	165	CALL global_min_max( nzb, nzt+1, nysg, nyng, nxlg, nxrg, v, 'absoff', &
	166	v_gtrans, v_max_cfl, v_max_cfl_ijk )
	167	ELSE
	168	u_max_cfl = u_max
	169	v_max_cfl = v_max
	170	u_max_cfl_ijk = u_max_ijk
	171	v_max_cfl_ijk = v_max_ijk
	172	ENDIF
	173
	174
[1]	175	IF ( .NOT. dt_fixed ) THEN
	176	!
	177	!-- Variable time step:
	178	!
	179	!-- For each component, compute the maximum time step according to the
[866]	180	!-- CFL-criterion.
	181	dt_u = dx / ( ABS( u_max_cfl ) + 1.0E-10 )
	182	dt_v = dy / ( ABS( v_max_cfl ) + 1.0E-10 )
[1]	183	dt_w = dzu(MAX( 1, w_max_ijk(1) )) / ( ABS( w_max ) + 1.0E-10 )
	184
	185	!
	186	!-- Compute time step according to the diffusion criterion.
	187	!-- First calculate minimum grid spacing which only depends on index k
	188	!-- Note: also at k=nzb+1 a full grid length is being assumed, although
	189	!-- in the Prandtl-layer friction term only dz/2 is used.
	190	!-- Experience from the old model seems to justify this.
	191	dt_diff_l = 999999.0
	192
	193	DO k = nzb+1, nzt
[667]	194	dxyz2_min(k) = MIN( dx2, dy2, dzw(k)dzw(k) ) 0.125
[1]	195	ENDDO
	196
	197	!$OMP PARALLEL private(i,j,k,value) reduction(MIN: dt_diff_l)
	198	!$OMP DO
	199	DO i = nxl, nxr
	200	DO j = nys, nyn
	201	DO k = nzb+1, nzt
	202	value = dxyz2_min(k) / ( MAX( kh(k,j,i), km(k,j,i) ) + 1E-20 )
	203
	204	dt_diff_l = MIN( value, dt_diff_l )
	205	ENDDO
	206	ENDDO
	207	ENDDO
	208	!$OMP END PARALLEL
	209	#if defined( __parallel )
[622]	210	IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr )
[1]	211	CALL MPI_ALLREDUCE( dt_diff_l, dt_diff, 1, MPI_REAL, MPI_MIN, comm2d, &
	212	ierr )
	213	#else
	214	dt_diff = dt_diff_l
	215	#endif
	216
	217	!
[316]	218	!-- Additional timestep criterion with plant canopies:
	219	!-- it is not allowed to extract more than the available momentum
	220	IF ( plant_canopy ) THEN
[318]	221
	222	dt_plant_canopy_l = 0.0
	223	DO i = nxl, nxr
	224	DO j = nys, nyn
	225	DO k = nzb+1, nzt
	226	dt_plant_canopy_u = cdc(k,j,i) * lad_u(k,j,i) * &
	227	SQRT( u(k,j,i)**2 + &
	228	( ( v(k,j,i-1) + &
	229	v(k,j,i) + &
	230	v(k,j+1,i) + &
	231	v(k,j+1,i-1) ) &
	232	/ 4.0 )**2 + &
	233	( ( w(k-1,j,i-1) + &
	234	w(k-1,j,i) + &
	235	w(k,j,i-1) + &
	236	w(k,j,i) ) &
	237	/ 4.0 )**2 )
	238	IF ( dt_plant_canopy_u > dt_plant_canopy_l ) THEN
	239	dt_plant_canopy_l = dt_plant_canopy_u
	240	ENDIF
	241	dt_plant_canopy_v = cdc(k,j,i) * lad_v(k,j,i) * &
	242	SQRT( ( ( u(k,j-1,i) + &
	243	u(k,j-1,i+1) + &
	244	u(k,j,i) + &
	245	u(k,j,i+1) ) &
	246	/ 4.0 )**2 + &
	247	v(k,j,i)**2 + &
	248	( ( w(k-1,j-1,i) + &
	249	w(k-1,j,i) + &
	250	w(k,j-1,i) + &
	251	w(k,j,i) ) &
	252	/ 4.0 )**2 )
	253	IF ( dt_plant_canopy_v > dt_plant_canopy_l ) THEN
	254	dt_plant_canopy_l = dt_plant_canopy_v
	255	ENDIF
	256	dt_plant_canopy_w = cdc(k,j,i) * lad_w(k,j,i) * &
	257	SQRT( ( ( u(k,j,i) + &
	258	u(k,j,i+1) + &
	259	u(k+1,j,i) + &
	260	u(k+1,j,i+1) ) &
	261	/ 4.0 )**2 + &
	262	( ( v(k,j,i) + &
	263	v(k,j+1,i) + &
	264	v(k+1,j,i) + &
	265	v(k+1,j+1,i) ) &
	266	/ 4.0 )**2 + &
	267	w(k,j,i)**2 )
	268	IF ( dt_plant_canopy_w > dt_plant_canopy_l ) THEN
	269	dt_plant_canopy_l = dt_plant_canopy_w
	270	ENDIF
	271	ENDDO
	272	ENDDO
	273	ENDDO
	274
	275	IF ( dt_plant_canopy_l > 0.0 ) THEN
[320]	276	!
	277	!-- Invert dt_plant_canopy_l and apply a security timestep factor 0.1
[318]	278	dt_plant_canopy_l = 0.1 / dt_plant_canopy_l
[320]	279	ELSE
	280	!
	281	!-- In case of inhomogeneous plant canopy, some processors may have no
	282	!-- canopy at all. Then use dt_max as dummy instead.
	283	dt_plant_canopy_l = dt_max
[318]	284	ENDIF
[320]	285
[316]	286	!
[318]	287	!-- Determine the global minumum
	288	#if defined( __parallel )
[622]	289	IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr )
[866]	290	CALL MPI_ALLREDUCE( dt_plant_canopy_l, dt_plant_canopy, 1, MPI_REAL, &
[318]	291	MPI_MIN, comm2d, ierr )
	292	#else
	293	dt_plant_canopy = dt_plant_canopy_l
	294	#endif
[316]	295
	296	ELSE
	297	!
	298	!-- Use dt_diff as dummy value to avoid extra IF branches further below
	299	dt_plant_canopy = dt_diff
	300
	301	ENDIF
	302
	303	!
	304	!-- The time step is the minimum of the 3-4 components and the diffusion time
[1001]	305	!-- step minus a reduction (cfl_factor) to be on the safe side.
[1]	306	!-- The time step must not exceed the maximum allowed value.
[1053]	307	dt_3d = cfl_factor * MIN( dt_diff, dt_plant_canopy, dt_u, dt_v, dt_w, &
	308	dt_precipitation )
[1]	309	dt_3d = MIN( dt_3d, dt_max )
	310
	311	!
	312	!-- Remember the restricting time step criterion for later output.
[316]	313	IF ( MIN( dt_u, dt_v, dt_w ) < MIN( dt_diff, dt_plant_canopy ) ) THEN
[1]	314	timestep_reason = 'A'
[316]	315	ELSEIF ( dt_plant_canopy < dt_diff ) THEN
	316	timestep_reason = 'C'
[1]	317	ELSE
	318	timestep_reason = 'D'
	319	ENDIF
	320
	321	!
	322	!-- Set flag if the time step becomes too small.
	323	IF ( dt_3d < ( 0.00001 * dt_max ) ) THEN
	324	stop_dt = .TRUE.
[108]	325
[320]	326	WRITE( message_string, * ) 'Time step has reached minimum limit.', &
	327	'&dt = ', dt_3d, ' s Simulation is terminated.', &
	328	'&old_dt = ', old_dt, ' s', &
	329	'&dt_u = ', dt_u, ' s', &
	330	'&dt_v = ', dt_v, ' s', &
	331	'&dt_w = ', dt_w, ' s', &
	332	'&dt_diff = ', dt_diff, ' s', &
	333	'&dt_plant_canopy = ', dt_plant_canopy, ' s', &
[866]	334	'&u_max_cfl = ', u_max_cfl, ' m/s k=', u_max_cfl_ijk(1), &
[320]	335	' j=', u_max_ijk(2), ' i=', u_max_ijk(3), &
[866]	336	'&v_max_cfl = ', v_max_cfl, ' m/s k=', v_max_cfl_ijk(1), &
[320]	337	' j=', v_max_ijk(2), ' i=', v_max_ijk(3), &
[866]	338	'&w_max = ', w_max, ' m/s k=', w_max_ijk(1), &
[320]	339	' j=', w_max_ijk(2), ' i=', w_max_ijk(3)
[258]	340	CALL message( 'timestep', 'PA0312', 0, 1, 0, 6, 0 )
[108]	341	!
	342	!-- In case of coupled runs inform the remote model of the termination
	343	!-- and its reason, provided the remote model has not already been
	344	!-- informed of another termination reason (terminate_coupled > 0) before.
[222]	345	#if defined( __parallel )
[108]	346	IF ( coupling_mode /= 'uncoupled' .AND. terminate_coupled == 0 ) THEN
	347	terminate_coupled = 2
[667]	348	IF ( myid == 0 ) THEN
	349	CALL MPI_SENDRECV( &
	350	terminate_coupled, 1, MPI_INTEGER, target_id, 0, &
	351	terminate_coupled_remote, 1, MPI_INTEGER, target_id, 0, &
	352	comm_inter, status, ierr )
	353	ENDIF
	354	CALL MPI_BCAST( terminate_coupled_remote, 1, MPI_INTEGER, 0, comm2d, ierr)
[108]	355	ENDIF
[222]	356	#endif
[1]	357	ENDIF
	358
	359	!
[1001]	360	!-- Ensure a smooth value (two significant digits) of the timestep.
	361	div = 1000.0
	362	DO WHILE ( dt_3d < div )
	363	div = div / 10.0
	364	ENDDO
	365	dt_3d = NINT( dt_3d * 100.0 / div ) * div / 100.0
[1]	366
	367	!
[1001]	368	!-- Adjust the time step
	369	old_dt = dt_3d
[1]	370
[1001]	371	ENDIF
[1]	372
	373	CALL cpu_log( log_point(12), 'calculate_timestep', 'stop' )
	374
	375	END SUBROUTINE timestep

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