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source: palm/trunk/SOURCE/pres.f90 @ 1575

Last change on this file since 1575 was 1575, checked in by raasch, 9 years ago
optimized multigrid method installed, new parameter seed_follows_topography for particle release, small adjustment in subjob for HLRN
Property svn:keywords set to `Id`
File size: 24.1 KB

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1	SUBROUTINE pres
2
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 1997-2014 Leibniz Universitaet Hannover
18	!--------------------------------------------------------------------------------!
19	!
20	! Current revisions:
21	! ------------------
22	! poismg_fast + respective module added, adjustments for psolver-queries
23	!
24	! Former revisions:
25	! -----------------
26	! $Id: pres.f90 1575 2015-03-27 09:56:27Z raasch $
27	!
28	! 1342 2014-03-26 17:04:47Z kanani
29	! REAL constants defined as wp-kind
30	!
31	! 1320 2014-03-20 08:40:49Z raasch
32	! ONLY-attribute added to USE-statements,
33	! kind-parameters added to all INTEGER and REAL declaration statements,
34	! kinds are defined in new module kinds,
35	! old module precision_kind is removed,
36	! revision history before 2012 removed,
37	! comment fields (!:) to be used for variable explanations added to
38	! all variable declaration statements
39	!
40	! 1318 2014-03-17 13:35:16Z raasch
41	! module interfaces removed
42	!
43	! 1306 2014-03-13 14:30:59Z raasch
44	! second argument removed from routine poisfft
45	!
46	! 1257 2013-11-08 15:18:40Z raasch
47	! openacc loop and loop vector clauses removed, independent clauses added,
48	! end parallel replaced by end parallel loop
49	!
50	! 1221 2013-09-10 08:59:13Z raasch
51	! openACC porting of reduction operations, loops for calculating d are
52	! using the rflags_s_inner multiply flag instead of the nzb_s_inner loop index
53	!
54	! 1212 2013-08-15 08:46:27Z raasch
55	! call of poisfft_hybrid removed
56	!
57	! 1117 2013-03-27 11:15:36Z suehring
58	! Bugfix in OpenMP parallelization.
59	!
60	! 1113 2013-03-10 02:48:14Z raasch
61	! GPU-porting of several loops, some loops rearranged
62	!
63	! 1111 2013-03-08 23:54:10Z
64	! openACC statements added,
65	! ibc_p_b = 2 removed
66	!
67	! 1092 2013-02-02 11:24:22Z raasch
68	! unused variables removed
69	!
70	! 1036 2012-10-22 13:43:42Z raasch
71	! code put under GPL (PALM 3.9)
72	!
73	! 1003 2012-09-14 14:35:53Z raasch
74	! adjustment of array tend for cases with unequal subdomain sizes removed
75	!
76	! Revision 1.1 1997/07/24 11:24:44 raasch
77	! Initial revision
78	!
79	!
80	! Description:
81	! ------------
82	! Compute the divergence of the provisional velocity field. Solve the Poisson
83	! equation for the perturbation pressure. Compute the final velocities using
84	! this perturbation pressure. Compute the remaining divergence.
85	!------------------------------------------------------------------------------!
86
87	USE arrays_3d, &
88	ONLY: d, ddzu, ddzu_pres, ddzw, dzw, p, p_loc, tend, u, v, w
89
90	USE control_parameters, &
91	ONLY: bc_lr_cyc, bc_ns_cyc, conserve_volume_flow, dt_3d, &
92	gathered_size, ibc_p_b, ibc_p_t, intermediate_timestep_count, &
93	mg_switch_to_pe0_level, on_device, outflow_l, outflow_n, &
94	outflow_r, outflow_s, psolver, simulated_time, subdomain_size, &
95	topography, volume_flow, volume_flow_area, volume_flow_initial
96
97	USE cpulog, &
98	ONLY: cpu_log, log_point, log_point_s
99
100	USE grid_variables, &
101	ONLY: ddx, ddy
102
103	USE indices, &
104	ONLY: nbgp, ngp_2dh_outer, nx, nxl, nxlg, nxl_mg, nxr, nxrg, nxr_mg, &
105	ny, nys, nysg, nys_mg, nyn, nyng, nyn_mg, nzb, nzb_s_inner, &
106	nzb_u_inner, nzb_v_inner, nzb_w_inner, nzb_2d, nzt, nzt_mg, &
107	rflags_s_inner
108
109	USE kinds
110
111	USE pegrid
112
113	USE poisfft_mod, &
114	ONLY: poisfft
115
116	USE poismg_mod
117
118	USE statistics, &
119	ONLY: statistic_regions, sums_divnew_l, sums_divold_l, weight_pres, &
120	weight_substep
121
122	IMPLICIT NONE
123
124	INTEGER(iwp) :: i !:
125	INTEGER(iwp) :: j !:
126	INTEGER(iwp) :: k !:
127
128	REAL(wp) :: ddt_3d !:
129	REAL(wp) :: localsum !:
130	REAL(wp) :: threadsum !:
131	REAL(wp) :: d_weight_pres !:
132
133	REAL(wp), DIMENSION(1:2) :: volume_flow_l !:
134	REAL(wp), DIMENSION(1:2) :: volume_flow_offset !:
135	REAL(wp), DIMENSION(1:nzt) :: w_l !:
136	REAL(wp), DIMENSION(1:nzt) :: w_l_l !:
137
138
139	CALL cpu_log( log_point(8), 'pres', 'start' )
140
141
142	ddt_3d = 1.0_wp / dt_3d
143	d_weight_pres = 1.0_wp / weight_pres(intermediate_timestep_count)
144
145	!
146	!-- Multigrid method expects array d to have one ghost layer.
147	!--
148	IF ( psolver(1:9) == 'multigrid' ) THEN
149
150	DEALLOCATE( d )
151	ALLOCATE( d(nzb:nzt+1,nys-1:nyn+1,nxl-1:nxr+1) )
152
153	!
154	!-- Since p is later used to hold the weighted average of the substeps, it
155	!-- cannot be used in the iterative solver. Therefore, its initial value is
156	!-- stored on p_loc, which is then iteratively advanced in every substep.
157	IF ( intermediate_timestep_count == 1 ) THEN
158	DO i = nxl-1, nxr+1
159	DO j = nys-1, nyn+1
160	DO k = nzb, nzt+1
161	p_loc(k,j,i) = p(k,j,i)
162	ENDDO
163	ENDDO
164	ENDDO
165	ENDIF
166
167	ELSEIF ( psolver == 'sor' .AND. intermediate_timestep_count == 1 ) THEN
168
169	!
170	!-- Since p is later used to hold the weighted average of the substeps, it
171	!-- cannot be used in the iterative solver. Therefore, its initial value is
172	!-- stored on p_loc, which is then iteratively advanced in every substep.
173	p_loc = p
174
175	ENDIF
176
177	!
178	!-- Conserve the volume flow at the outflow in case of non-cyclic lateral
179	!-- boundary conditions
180	!-- WARNING: so far, this conservation does not work at the left/south
181	!-- boundary if the topography at the inflow differs from that at the
182	!-- outflow! For this case, volume_flow_area needs adjustment!
183	!
184	!-- Left/right
185	IF ( conserve_volume_flow .AND. ( outflow_l .OR. outflow_r ) ) THEN
186
187	volume_flow(1) = 0.0_wp
188	volume_flow_l(1) = 0.0_wp
189
190	IF ( outflow_l ) THEN
191	i = 0
192	ELSEIF ( outflow_r ) THEN
193	i = nx+1
194	ENDIF
195
196	DO j = nys, nyn
197	!
198	!-- Sum up the volume flow through the south/north boundary
199	DO k = nzb_2d(j,i)+1, nzt
200	volume_flow_l(1) = volume_flow_l(1) + u(k,j,i) * dzw(k)
201	ENDDO
202	ENDDO
203
204	#if defined( __parallel )
205	IF ( collective_wait ) CALL MPI_BARRIER( comm1dy, ierr )
206	CALL MPI_ALLREDUCE( volume_flow_l(1), volume_flow(1), 1, MPI_REAL, &
207	MPI_SUM, comm1dy, ierr )
208	#else
209	volume_flow = volume_flow_l
210	#endif
211	volume_flow_offset(1) = ( volume_flow_initial(1) - volume_flow(1) ) &
212	/ volume_flow_area(1)
213
214	DO j = nysg, nyng
215	DO k = nzb_2d(j,i)+1, nzt
216	u(k,j,i) = u(k,j,i) + volume_flow_offset(1)
217	ENDDO
218	ENDDO
219
220	ENDIF
221
222	!
223	!-- South/north
224	IF ( conserve_volume_flow .AND. ( outflow_n .OR. outflow_s ) ) THEN
225
226	volume_flow(2) = 0.0_wp
227	volume_flow_l(2) = 0.0_wp
228
229	IF ( outflow_s ) THEN
230	j = 0
231	ELSEIF ( outflow_n ) THEN
232	j = ny+1
233	ENDIF
234
235	DO i = nxl, nxr
236	!
237	!-- Sum up the volume flow through the south/north boundary
238	DO k = nzb_2d(j,i)+1, nzt
239	volume_flow_l(2) = volume_flow_l(2) + v(k,j,i) * dzw(k)
240	ENDDO
241	ENDDO
242
243	#if defined( __parallel )
244	IF ( collective_wait ) CALL MPI_BARRIER( comm1dx, ierr )
245	CALL MPI_ALLREDUCE( volume_flow_l(2), volume_flow(2), 1, MPI_REAL, &
246	MPI_SUM, comm1dx, ierr )
247	#else
248	volume_flow = volume_flow_l
249	#endif
250	volume_flow_offset(2) = ( volume_flow_initial(2) - volume_flow(2) ) &
251	/ volume_flow_area(2)
252
253	DO i = nxlg, nxrg
254	DO k = nzb_v_inner(j,i)+1, nzt
255	v(k,j,i) = v(k,j,i) + volume_flow_offset(2)
256	ENDDO
257	ENDDO
258
259	ENDIF
260
261	!
262	!-- Remove mean vertical velocity
263	IF ( ibc_p_b == 1 .AND. ibc_p_t == 1 ) THEN
264	IF ( simulated_time > 0.0_wp ) THEN ! otherwise nzb_w_inner not yet known
265	w_l = 0.0_wp; w_l_l = 0.0_wp
266	DO i = nxl, nxr
267	DO j = nys, nyn
268	DO k = nzb_w_inner(j,i)+1, nzt
269	w_l_l(k) = w_l_l(k) + w(k,j,i)
270	ENDDO
271	ENDDO
272	ENDDO
273	#if defined( __parallel )
274	IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr )
275	CALL MPI_ALLREDUCE( w_l_l(1), w_l(1), nzt, MPI_REAL, MPI_SUM, &
276	comm2d, ierr )
277	#else
278	w_l = w_l_l
279	#endif
280	DO k = 1, nzt
281	w_l(k) = w_l(k) / ngp_2dh_outer(k,0)
282	ENDDO
283	DO i = nxlg, nxrg
284	DO j = nysg, nyng
285	DO k = nzb_w_inner(j,i)+1, nzt
286	w(k,j,i) = w(k,j,i) - w_l(k)
287	ENDDO
288	ENDDO
289	ENDDO
290	ENDIF
291	ENDIF
292
293	!
294	!-- Compute the divergence of the provisional velocity field.
295	CALL cpu_log( log_point_s(1), 'divergence', 'start' )
296
297	IF ( psolver(1:9) == 'multigrid' ) THEN
298	!$OMP PARALLEL DO SCHEDULE( STATIC )
299	DO i = nxl-1, nxr+1
300	DO j = nys-1, nyn+1
301	DO k = nzb, nzt+1
302	d(k,j,i) = 0.0_wp
303	ENDDO
304	ENDDO
305	ENDDO
306	ELSE
307	!$OMP PARALLEL DO SCHEDULE( STATIC )
308	!$acc kernels present( d )
309	DO i = nxl, nxr
310	DO j = nys, nyn
311	DO k = nzb+1, nzt
312	d(k,j,i) = 0.0_wp
313	ENDDO
314	ENDDO
315	ENDDO
316	!$acc end kernels
317	ENDIF
318
319	localsum = 0.0_wp
320	threadsum = 0.0_wp
321
322	#if defined( __ibm )
323	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
324	!$OMP DO SCHEDULE( STATIC )
325	DO i = nxl, nxr
326	DO j = nys, nyn
327	DO k = nzb_s_inner(j,i)+1, nzt
328	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
329	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
330	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) ) * ddt_3d &
331	* d_weight_pres
332	ENDDO
333	!
334	!-- Compute possible PE-sum of divergences for flow_statistics
335	DO k = nzb_s_inner(j,i)+1, nzt
336	threadsum = threadsum + ABS( d(k,j,i) )
337	ENDDO
338
339	ENDDO
340	ENDDO
341
342	localsum = localsum + threadsum * dt_3d * &
343	weight_pres(intermediate_timestep_count)
344
345	!$OMP END PARALLEL
346	#else
347
348	!$OMP PARALLEL PRIVATE (i,j,k)
349	!$OMP DO SCHEDULE( STATIC )
350	!$acc kernels present( d, ddzw, rflags_s_inner, u, v, w )
351	!$acc loop collapse( 3 )
352	DO i = nxl, nxr
353	DO j = nys, nyn
354	DO k = 1, nzt
355	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
356	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
357	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) ) * ddt_3d &
358	* d_weight_pres * rflags_s_inner(k,j,i)
359	ENDDO
360	ENDDO
361	ENDDO
362	!$acc end kernels
363	!$OMP END PARALLEL
364
365	!
366	!-- Compute possible PE-sum of divergences for flow_statistics
367	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
368	!$OMP DO SCHEDULE( STATIC )
369	!$acc parallel loop collapse(3) present( d ) reduction(+:threadsum)
370	DO i = nxl, nxr
371	DO j = nys, nyn
372	DO k = nzb+1, nzt
373	threadsum = threadsum + ABS( d(k,j,i) )
374	ENDDO
375	ENDDO
376	ENDDO
377	!$acc end parallel loop
378	localsum = localsum + threadsum * dt_3d * &
379	weight_pres(intermediate_timestep_count)
380	!$OMP END PARALLEL
381	#endif
382
383	!
384	!-- For completeness, set the divergence sum of all statistic regions to those
385	!-- of the total domain
386	sums_divold_l(0:statistic_regions) = localsum
387
388	CALL cpu_log( log_point_s(1), 'divergence', 'stop' )
389
390	!
391	!-- Compute the pressure perturbation solving the Poisson equation
392	IF ( psolver == 'poisfft' ) THEN
393
394	!
395	!-- Solve Poisson equation via FFT and solution of tridiagonal matrices
396	CALL poisfft( d )
397
398	!
399	!-- Store computed perturbation pressure and set boundary condition in
400	!-- z-direction
401	!$OMP PARALLEL DO
402	!$acc kernels present( d, tend )
403	DO i = nxl, nxr
404	DO j = nys, nyn
405	DO k = nzb+1, nzt
406	tend(k,j,i) = d(k,j,i)
407	ENDDO
408	ENDDO
409	ENDDO
410	!$acc end kernels
411
412	!
413	!-- Bottom boundary:
414	!-- This condition is only required for internal output. The pressure
415	!-- gradient (dp(nzb+1)-dp(nzb))/dz is not used anywhere else.
416	IF ( ibc_p_b == 1 ) THEN
417	!
418	!-- Neumann (dp/dz = 0)
419	!$OMP PARALLEL DO
420	!$acc kernels present( nzb_s_inner, tend )
421	DO i = nxlg, nxrg
422	DO j = nysg, nyng
423	tend(nzb_s_inner(j,i),j,i) = tend(nzb_s_inner(j,i)+1,j,i)
424	ENDDO
425	ENDDO
426	!$acc end kernels
427
428	ELSE
429	!
430	!-- Dirichlet
431	!$OMP PARALLEL DO
432	!$acc kernels present( tend )
433	DO i = nxlg, nxrg
434	DO j = nysg, nyng
435	tend(nzb_s_inner(j,i),j,i) = 0.0_wp
436	ENDDO
437	ENDDO
438	!$acc end kernels
439
440	ENDIF
441
442	!
443	!-- Top boundary
444	IF ( ibc_p_t == 1 ) THEN
445	!
446	!-- Neumann
447	!$OMP PARALLEL DO
448	!$acc kernels present( tend )
449	DO i = nxlg, nxrg
450	DO j = nysg, nyng
451	tend(nzt+1,j,i) = tend(nzt,j,i)
452	ENDDO
453	ENDDO
454	!$acc end kernels
455
456	ELSE
457	!
458	!-- Dirichlet
459	!$OMP PARALLEL DO
460	!$acc kernels present( tend )
461	DO i = nxlg, nxrg
462	DO j = nysg, nyng
463	tend(nzt+1,j,i) = 0.0_wp
464	ENDDO
465	ENDDO
466	!$acc end kernels
467
468	ENDIF
469
470	!
471	!-- Exchange boundaries for p
472	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
473	on_device = .TRUE. ! to be removed after complete porting
474	ELSE ! of ghost point exchange
475	!$acc update host( tend )
476	ENDIF
477	CALL exchange_horiz( tend, nbgp )
478	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
479	on_device = .FALSE. ! to be removed after complete porting
480	ELSE ! of ghost point exchange
481	!$acc update device( tend )
482	ENDIF
483
484	ELSEIF ( psolver == 'sor' ) THEN
485
486	!
487	!-- Solve Poisson equation for perturbation pressure using SOR-Red/Black
488	!-- scheme
489	CALL sor( d, ddzu_pres, ddzw, p_loc )
490	tend = p_loc
491
492	ELSEIF ( psolver(1:9) == 'multigrid' ) THEN
493
494	!
495	!-- Solve Poisson equation for perturbation pressure using Multigrid scheme,
496	!-- array tend is used to store the residuals, logical exchange_mg is used
497	!-- to discern data exchange in multigrid ( 1 ghostpoint ) and normal grid
498	!-- ( nbgp ghost points ).
499
500	!-- If the number of grid points of the gathered grid, which is collected
501	!-- on PE0, is larger than the number of grid points of an PE, than array
502	!-- tend will be enlarged.
503	IF ( gathered_size > subdomain_size ) THEN
504	DEALLOCATE( tend )
505	ALLOCATE( tend(nzb:nzt_mg(mg_switch_to_pe0_level)+1,nys_mg( &
506	mg_switch_to_pe0_level)-1:nyn_mg(mg_switch_to_pe0_level)+1,&
507	nxl_mg(mg_switch_to_pe0_level)-1:nxr_mg( &
508	mg_switch_to_pe0_level)+1) )
509	ENDIF
510
511	IF ( psolver == 'multigrid' ) THEN
512	CALL poismg( tend )
513	ELSE
514	CALL poismg_fast( tend )
515	ENDIF
516
517	IF ( gathered_size > subdomain_size ) THEN
518	DEALLOCATE( tend )
519	ALLOCATE( tend(nzb:nzt+1,nysg:nyng,nxlg:nxrg) )
520	ENDIF
521
522	!
523	!-- Restore perturbation pressure on tend because this array is used
524	!-- further below to correct the velocity fields
525	DO i = nxl-1, nxr+1
526	DO j = nys-1, nyn+1
527	DO k = nzb, nzt+1
528	tend(k,j,i) = p_loc(k,j,i)
529	ENDDO
530	ENDDO
531	ENDDO
532
533	ENDIF
534
535	!
536	!-- Store perturbation pressure on array p, used for pressure data output.
537	!-- Ghost layers are added in the output routines (except sor-method: see below)
538	IF ( intermediate_timestep_count == 1 ) THEN
539	!$OMP PARALLEL PRIVATE (i,j,k)
540	!$OMP DO
541	!$acc kernels present( p, tend, weight_substep )
542	!$acc loop independent
543	DO i = nxl-1, nxr+1
544	!$acc loop independent
545	DO j = nys-1, nyn+1
546	!$acc loop independent
547	DO k = nzb, nzt+1
548	p(k,j,i) = tend(k,j,i) * &
549	weight_substep(intermediate_timestep_count)
550	ENDDO
551	ENDDO
552	ENDDO
553	!$acc end kernels
554	!$OMP END PARALLEL
555
556	ELSE
557	!$OMP PARALLEL PRIVATE (i,j,k)
558	!$OMP DO
559	!$acc kernels present( p, tend, weight_substep )
560	!$acc loop independent
561	DO i = nxl-1, nxr+1
562	!$acc loop independent
563	DO j = nys-1, nyn+1
564	!$acc loop independent
565	DO k = nzb, nzt+1
566	p(k,j,i) = p(k,j,i) + tend(k,j,i) * &
567	weight_substep(intermediate_timestep_count)
568	ENDDO
569	ENDDO
570	ENDDO
571	!$acc end kernels
572	!$OMP END PARALLEL
573
574	ENDIF
575
576	!
577	!-- SOR-method needs ghost layers for the next timestep
578	IF ( psolver == 'sor' ) CALL exchange_horiz( p, nbgp )
579
580	!
581	!-- Correction of the provisional velocities with the current perturbation
582	!-- pressure just computed
583	IF ( conserve_volume_flow .AND. ( bc_lr_cyc .OR. bc_ns_cyc ) ) THEN
584	volume_flow_l(1) = 0.0_wp
585	volume_flow_l(2) = 0.0_wp
586	ENDIF
587
588	!$OMP PARALLEL PRIVATE (i,j,k)
589	!$OMP DO
590	!$acc kernels present( ddzu, nzb_u_inner, nzb_v_inner, nzb_w_inner, tend, u, v, w, weight_pres )
591	!$acc loop independent
592	DO i = nxl, nxr
593	!$acc loop independent
594	DO j = nys, nyn
595	!$acc loop independent
596	DO k = 1, nzt
597	IF ( k > nzb_w_inner(j,i) ) THEN
598	w(k,j,i) = w(k,j,i) - dt_3d * &
599	( tend(k+1,j,i) - tend(k,j,i) ) * ddzu(k+1) * &
600	weight_pres(intermediate_timestep_count)
601	ENDIF
602	ENDDO
603	!$acc loop independent
604	DO k = 1, nzt
605	IF ( k > nzb_u_inner(j,i) ) THEN
606	u(k,j,i) = u(k,j,i) - dt_3d * &
607	( tend(k,j,i) - tend(k,j,i-1) ) * ddx * &
608	weight_pres(intermediate_timestep_count)
609	ENDIF
610	ENDDO
611	!$acc loop independent
612	DO k = 1, nzt
613	IF ( k > nzb_v_inner(j,i) ) THEN
614	v(k,j,i) = v(k,j,i) - dt_3d * &
615	( tend(k,j,i) - tend(k,j-1,i) ) * ddy * &
616	weight_pres(intermediate_timestep_count)
617	ENDIF
618	ENDDO
619
620	ENDDO
621	ENDDO
622	!$acc end kernels
623	!$OMP END PARALLEL
624
625	!
626	!-- Sum up the volume flow through the right and north boundary
627	IF ( conserve_volume_flow .AND. bc_lr_cyc .AND. bc_ns_cyc .AND. &
628	nxr == nx ) THEN
629
630	!$OMP PARALLEL PRIVATE (j,k)
631	!$OMP DO
632	DO j = nys, nyn
633	!$OMP CRITICAL
634	DO k = nzb_2d(j,nx) + 1, nzt
635	volume_flow_l(1) = volume_flow_l(1) + u(k,j,nx) * dzw(k)
636	ENDDO
637	!$OMP END CRITICAL
638	ENDDO
639	!$OMP END PARALLEL
640
641	ENDIF
642
643	IF ( conserve_volume_flow .AND. bc_ns_cyc .AND. bc_lr_cyc .AND. &
644	nyn == ny ) THEN
645
646	!$OMP PARALLEL PRIVATE (i,k)
647	!$OMP DO
648	DO i = nxl, nxr
649	!$OMP CRITICAL
650	DO k = nzb_2d(ny,i) + 1, nzt
651	volume_flow_l(2) = volume_flow_l(2) + v(k,ny,i) * dzw(k)
652	ENDDO
653	!$OMP END CRITICAL
654	ENDDO
655	!$OMP END PARALLEL
656
657	ENDIF
658
659	!
660	!-- Conserve the volume flow
661	IF ( conserve_volume_flow .AND. ( bc_lr_cyc .AND. bc_ns_cyc ) ) THEN
662
663	#if defined( __parallel )
664	IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr )
665	CALL MPI_ALLREDUCE( volume_flow_l(1), volume_flow(1), 2, MPI_REAL, &
666	MPI_SUM, comm2d, ierr )
667	#else
668	volume_flow = volume_flow_l
669	#endif
670
671	volume_flow_offset = ( volume_flow_initial - volume_flow ) / &
672	volume_flow_area
673
674	!$OMP PARALLEL PRIVATE (i,j,k)
675	!$OMP DO
676	DO i = nxl, nxr
677	DO j = nys, nyn
678	DO k = nzb_u_inner(j,i) + 1, nzt
679	u(k,j,i) = u(k,j,i) + volume_flow_offset(1)
680	ENDDO
681	DO k = nzb_v_inner(j,i) + 1, nzt
682	v(k,j,i) = v(k,j,i) + volume_flow_offset(2)
683	ENDDO
684	ENDDO
685	ENDDO
686
687	!$OMP END PARALLEL
688
689	ENDIF
690
691	!
692	!-- Exchange of boundaries for the velocities
693	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
694	on_device = .TRUE. ! to be removed after complete porting
695	ELSE ! of ghost point exchange
696	!$acc update host( u, v, w )
697	ENDIF
698	CALL exchange_horiz( u, nbgp )
699	CALL exchange_horiz( v, nbgp )
700	CALL exchange_horiz( w, nbgp )
701	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
702	on_device = .FALSE. ! to be removed after complete porting
703	ELSE ! of ghost point exchange
704	!$acc update device( u, v, w )
705	ENDIF
706
707	!
708	!-- Compute the divergence of the corrected velocity field,
709	!-- a possible PE-sum is computed in flow_statistics
710	CALL cpu_log( log_point_s(1), 'divergence', 'start' )
711	sums_divnew_l = 0.0_wp
712
713	!
714	!-- d must be reset to zero because it can contain nonzero values below the
715	!-- topography
716	IF ( topography /= 'flat' ) d = 0.0_wp
717
718	localsum = 0.0_wp
719	threadsum = 0.0_wp
720
721	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
722	!$OMP DO SCHEDULE( STATIC )
723	#if defined( __ibm )
724	DO i = nxl, nxr
725	DO j = nys, nyn
726	DO k = nzb_s_inner(j,i)+1, nzt
727	d(k,j,i) = ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
728	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
729	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k)
730	ENDDO
731	DO k = nzb+1, nzt
732	threadsum = threadsum + ABS( d(k,j,i) )
733	ENDDO
734	ENDDO
735	ENDDO
736	#else
737	!$acc kernels present( d, ddzw, rflags_s_inner, u, v, w )
738	!$acc loop collapse( 3 )
739	DO i = nxl, nxr
740	DO j = nys, nyn
741	DO k = 1, nzt
742	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
743	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
744	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) &
745	) * rflags_s_inner(k,j,i)
746	ENDDO
747	ENDDO
748	ENDDO
749	!$acc end kernels
750	!
751	!-- Compute possible PE-sum of divergences for flow_statistics
752	!$acc parallel loop collapse(3) present( d ) reduction(+:threadsum)
753	DO i = nxl, nxr
754	DO j = nys, nyn
755	DO k = nzb+1, nzt
756	threadsum = threadsum + ABS( d(k,j,i) )
757	ENDDO
758	ENDDO
759	ENDDO
760	!$acc end parallel loop
761	#endif
762
763	localsum = localsum + threadsum
764	!$OMP END PARALLEL
765
766	!
767	!-- For completeness, set the divergence sum of all statistic regions to those
768	!-- of the total domain
769	sums_divnew_l(0:statistic_regions) = localsum
770
771	CALL cpu_log( log_point_s(1), 'divergence', 'stop' )
772
773	CALL cpu_log( log_point(8), 'pres', 'stop' )
774
775
776	END SUBROUTINE pres

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