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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	!
23	!
24	! Former revisions:
25	! -----------------
26	! $Id: pres.f90 1576 2015-03-27 10:23:30Z hoffmann $
27	!
28	! 1575 2015-03-27 09:56:27Z raasch
29	! poismg_fast + respective module added, adjustments for psolver-queries
30	!
31	! 1342 2014-03-26 17:04:47Z kanani
32	! REAL constants defined as wp-kind
33	!
34	! 1320 2014-03-20 08:40:49Z raasch
35	! ONLY-attribute added to USE-statements,
36	! kind-parameters added to all INTEGER and REAL declaration statements,
37	! kinds are defined in new module kinds,
38	! old module precision_kind is removed,
39	! revision history before 2012 removed,
40	! comment fields (!:) to be used for variable explanations added to
41	! all variable declaration statements
42	!
43	! 1318 2014-03-17 13:35:16Z raasch
44	! module interfaces removed
45	!
46	! 1306 2014-03-13 14:30:59Z raasch
47	! second argument removed from routine poisfft
48	!
49	! 1257 2013-11-08 15:18:40Z raasch
50	! openacc loop and loop vector clauses removed, independent clauses added,
51	! end parallel replaced by end parallel loop
52	!
53	! 1221 2013-09-10 08:59:13Z raasch
54	! openACC porting of reduction operations, loops for calculating d are
55	! using the rflags_s_inner multiply flag instead of the nzb_s_inner loop index
56	!
57	! 1212 2013-08-15 08:46:27Z raasch
58	! call of poisfft_hybrid removed
59	!
60	! 1117 2013-03-27 11:15:36Z suehring
61	! Bugfix in OpenMP parallelization.
62	!
63	! 1113 2013-03-10 02:48:14Z raasch
64	! GPU-porting of several loops, some loops rearranged
65	!
66	! 1111 2013-03-08 23:54:10Z
67	! openACC statements added,
68	! ibc_p_b = 2 removed
69	!
70	! 1092 2013-02-02 11:24:22Z raasch
71	! unused variables removed
72	!
73	! 1036 2012-10-22 13:43:42Z raasch
74	! code put under GPL (PALM 3.9)
75	!
76	! 1003 2012-09-14 14:35:53Z raasch
77	! adjustment of array tend for cases with unequal subdomain sizes removed
78	!
79	! Revision 1.1 1997/07/24 11:24:44 raasch
80	! Initial revision
81	!
82	!
83	! Description:
84	! ------------
85	! Compute the divergence of the provisional velocity field. Solve the Poisson
86	! equation for the perturbation pressure. Compute the final velocities using
87	! this perturbation pressure. Compute the remaining divergence.
88	!------------------------------------------------------------------------------!
89
90	USE arrays_3d, &
91	ONLY: d, ddzu, ddzu_pres, ddzw, dzw, p, p_loc, tend, u, v, w
92
93	USE control_parameters, &
94	ONLY: bc_lr_cyc, bc_ns_cyc, conserve_volume_flow, dt_3d, &
95	gathered_size, ibc_p_b, ibc_p_t, intermediate_timestep_count, &
96	mg_switch_to_pe0_level, on_device, outflow_l, outflow_n, &
97	outflow_r, outflow_s, psolver, simulated_time, subdomain_size, &
98	topography, volume_flow, volume_flow_area, volume_flow_initial
99
100	USE cpulog, &
101	ONLY: cpu_log, log_point, log_point_s
102
103	USE grid_variables, &
104	ONLY: ddx, ddy
105
106	USE indices, &
107	ONLY: nbgp, ngp_2dh_outer, nx, nxl, nxlg, nxl_mg, nxr, nxrg, nxr_mg, &
108	ny, nys, nysg, nys_mg, nyn, nyng, nyn_mg, nzb, nzb_s_inner, &
109	nzb_u_inner, nzb_v_inner, nzb_w_inner, nzb_2d, nzt, nzt_mg, &
110	rflags_s_inner
111
112	USE kinds
113
114	USE pegrid
115
116	USE poisfft_mod, &
117	ONLY: poisfft
118
119	USE poismg_mod
120
121	USE statistics, &
122	ONLY: statistic_regions, sums_divnew_l, sums_divold_l, weight_pres, &
123	weight_substep
124
125	IMPLICIT NONE
126
127	INTEGER(iwp) :: i !:
128	INTEGER(iwp) :: j !:
129	INTEGER(iwp) :: k !:
130
131	REAL(wp) :: ddt_3d !:
132	REAL(wp) :: localsum !:
133	REAL(wp) :: threadsum !:
134	REAL(wp) :: d_weight_pres !:
135
136	REAL(wp), DIMENSION(1:2) :: volume_flow_l !:
137	REAL(wp), DIMENSION(1:2) :: volume_flow_offset !:
138	REAL(wp), DIMENSION(1:nzt) :: w_l !:
139	REAL(wp), DIMENSION(1:nzt) :: w_l_l !:
140
141
142	CALL cpu_log( log_point(8), 'pres', 'start' )
143
144
145	ddt_3d = 1.0_wp / dt_3d
146	d_weight_pres = 1.0_wp / weight_pres(intermediate_timestep_count)
147
148	!
149	!-- Multigrid method expects array d to have one ghost layer.
150	!--
151	IF ( psolver(1:9) == 'multigrid' ) THEN
152
153	DEALLOCATE( d )
154	ALLOCATE( d(nzb:nzt+1,nys-1:nyn+1,nxl-1:nxr+1) )
155
156	!
157	!-- Since p is later used to hold the weighted average of the substeps, it
158	!-- cannot be used in the iterative solver. Therefore, its initial value is
159	!-- stored on p_loc, which is then iteratively advanced in every substep.
160	IF ( intermediate_timestep_count == 1 ) THEN
161	DO i = nxl-1, nxr+1
162	DO j = nys-1, nyn+1
163	DO k = nzb, nzt+1
164	p_loc(k,j,i) = p(k,j,i)
165	ENDDO
166	ENDDO
167	ENDDO
168	ENDIF
169
170	ELSEIF ( psolver == 'sor' .AND. intermediate_timestep_count == 1 ) THEN
171
172	!
173	!-- Since p is later used to hold the weighted average of the substeps, it
174	!-- cannot be used in the iterative solver. Therefore, its initial value is
175	!-- stored on p_loc, which is then iteratively advanced in every substep.
176	p_loc = p
177
178	ENDIF
179
180	!
181	!-- Conserve the volume flow at the outflow in case of non-cyclic lateral
182	!-- boundary conditions
183	!-- WARNING: so far, this conservation does not work at the left/south
184	!-- boundary if the topography at the inflow differs from that at the
185	!-- outflow! For this case, volume_flow_area needs adjustment!
186	!
187	!-- Left/right
188	IF ( conserve_volume_flow .AND. ( outflow_l .OR. outflow_r ) ) THEN
189
190	volume_flow(1) = 0.0_wp
191	volume_flow_l(1) = 0.0_wp
192
193	IF ( outflow_l ) THEN
194	i = 0
195	ELSEIF ( outflow_r ) THEN
196	i = nx+1
197	ENDIF
198
199	DO j = nys, nyn
200	!
201	!-- Sum up the volume flow through the south/north boundary
202	DO k = nzb_2d(j,i)+1, nzt
203	volume_flow_l(1) = volume_flow_l(1) + u(k,j,i) * dzw(k)
204	ENDDO
205	ENDDO
206
207	#if defined( __parallel )
208	IF ( collective_wait ) CALL MPI_BARRIER( comm1dy, ierr )
209	CALL MPI_ALLREDUCE( volume_flow_l(1), volume_flow(1), 1, MPI_REAL, &
210	MPI_SUM, comm1dy, ierr )
211	#else
212	volume_flow = volume_flow_l
213	#endif
214	volume_flow_offset(1) = ( volume_flow_initial(1) - volume_flow(1) ) &
215	/ volume_flow_area(1)
216
217	DO j = nysg, nyng
218	DO k = nzb_2d(j,i)+1, nzt
219	u(k,j,i) = u(k,j,i) + volume_flow_offset(1)
220	ENDDO
221	ENDDO
222
223	ENDIF
224
225	!
226	!-- South/north
227	IF ( conserve_volume_flow .AND. ( outflow_n .OR. outflow_s ) ) THEN
228
229	volume_flow(2) = 0.0_wp
230	volume_flow_l(2) = 0.0_wp
231
232	IF ( outflow_s ) THEN
233	j = 0
234	ELSEIF ( outflow_n ) THEN
235	j = ny+1
236	ENDIF
237
238	DO i = nxl, nxr
239	!
240	!-- Sum up the volume flow through the south/north boundary
241	DO k = nzb_2d(j,i)+1, nzt
242	volume_flow_l(2) = volume_flow_l(2) + v(k,j,i) * dzw(k)
243	ENDDO
244	ENDDO
245
246	#if defined( __parallel )
247	IF ( collective_wait ) CALL MPI_BARRIER( comm1dx, ierr )
248	CALL MPI_ALLREDUCE( volume_flow_l(2), volume_flow(2), 1, MPI_REAL, &
249	MPI_SUM, comm1dx, ierr )
250	#else
251	volume_flow = volume_flow_l
252	#endif
253	volume_flow_offset(2) = ( volume_flow_initial(2) - volume_flow(2) ) &
254	/ volume_flow_area(2)
255
256	DO i = nxlg, nxrg
257	DO k = nzb_v_inner(j,i)+1, nzt
258	v(k,j,i) = v(k,j,i) + volume_flow_offset(2)
259	ENDDO
260	ENDDO
261
262	ENDIF
263
264	!
265	!-- Remove mean vertical velocity
266	IF ( ibc_p_b == 1 .AND. ibc_p_t == 1 ) THEN
267	IF ( simulated_time > 0.0_wp ) THEN ! otherwise nzb_w_inner not yet known
268	w_l = 0.0_wp; w_l_l = 0.0_wp
269	DO i = nxl, nxr
270	DO j = nys, nyn
271	DO k = nzb_w_inner(j,i)+1, nzt
272	w_l_l(k) = w_l_l(k) + w(k,j,i)
273	ENDDO
274	ENDDO
275	ENDDO
276	#if defined( __parallel )
277	IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr )
278	CALL MPI_ALLREDUCE( w_l_l(1), w_l(1), nzt, MPI_REAL, MPI_SUM, &
279	comm2d, ierr )
280	#else
281	w_l = w_l_l
282	#endif
283	DO k = 1, nzt
284	w_l(k) = w_l(k) / ngp_2dh_outer(k,0)
285	ENDDO
286	DO i = nxlg, nxrg
287	DO j = nysg, nyng
288	DO k = nzb_w_inner(j,i)+1, nzt
289	w(k,j,i) = w(k,j,i) - w_l(k)
290	ENDDO
291	ENDDO
292	ENDDO
293	ENDIF
294	ENDIF
295
296	!
297	!-- Compute the divergence of the provisional velocity field.
298	CALL cpu_log( log_point_s(1), 'divergence', 'start' )
299
300	IF ( psolver(1:9) == 'multigrid' ) THEN
301	!$OMP PARALLEL DO SCHEDULE( STATIC )
302	DO i = nxl-1, nxr+1
303	DO j = nys-1, nyn+1
304	DO k = nzb, nzt+1
305	d(k,j,i) = 0.0_wp
306	ENDDO
307	ENDDO
308	ENDDO
309	ELSE
310	!$OMP PARALLEL DO SCHEDULE( STATIC )
311	!$acc kernels present( d )
312	DO i = nxl, nxr
313	DO j = nys, nyn
314	DO k = nzb+1, nzt
315	d(k,j,i) = 0.0_wp
316	ENDDO
317	ENDDO
318	ENDDO
319	!$acc end kernels
320	ENDIF
321
322	localsum = 0.0_wp
323	threadsum = 0.0_wp
324
325	#if defined( __ibm )
326	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
327	!$OMP DO SCHEDULE( STATIC )
328	DO i = nxl, nxr
329	DO j = nys, nyn
330	DO k = nzb_s_inner(j,i)+1, nzt
331	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
332	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
333	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) ) * ddt_3d &
334	* d_weight_pres
335	ENDDO
336	!
337	!-- Compute possible PE-sum of divergences for flow_statistics
338	DO k = nzb_s_inner(j,i)+1, nzt
339	threadsum = threadsum + ABS( d(k,j,i) )
340	ENDDO
341
342	ENDDO
343	ENDDO
344
345	localsum = localsum + threadsum * dt_3d * &
346	weight_pres(intermediate_timestep_count)
347
348	!$OMP END PARALLEL
349	#else
350
351	!$OMP PARALLEL PRIVATE (i,j,k)
352	!$OMP DO SCHEDULE( STATIC )
353	!$acc kernels present( d, ddzw, rflags_s_inner, u, v, w )
354	!$acc loop collapse( 3 )
355	DO i = nxl, nxr
356	DO j = nys, nyn
357	DO k = 1, nzt
358	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
359	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
360	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) ) * ddt_3d &
361	* d_weight_pres * rflags_s_inner(k,j,i)
362	ENDDO
363	ENDDO
364	ENDDO
365	!$acc end kernels
366	!$OMP END PARALLEL
367
368	!
369	!-- Compute possible PE-sum of divergences for flow_statistics
370	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
371	!$OMP DO SCHEDULE( STATIC )
372	!$acc parallel loop collapse(3) present( d ) reduction(+:threadsum)
373	DO i = nxl, nxr
374	DO j = nys, nyn
375	DO k = nzb+1, nzt
376	threadsum = threadsum + ABS( d(k,j,i) )
377	ENDDO
378	ENDDO
379	ENDDO
380	!$acc end parallel loop
381	localsum = localsum + threadsum * dt_3d * &
382	weight_pres(intermediate_timestep_count)
383	!$OMP END PARALLEL
384	#endif
385
386	!
387	!-- For completeness, set the divergence sum of all statistic regions to those
388	!-- of the total domain
389	sums_divold_l(0:statistic_regions) = localsum
390
391	CALL cpu_log( log_point_s(1), 'divergence', 'stop' )
392
393	!
394	!-- Compute the pressure perturbation solving the Poisson equation
395	IF ( psolver == 'poisfft' ) THEN
396
397	!
398	!-- Solve Poisson equation via FFT and solution of tridiagonal matrices
399	CALL poisfft( d )
400
401	!
402	!-- Store computed perturbation pressure and set boundary condition in
403	!-- z-direction
404	!$OMP PARALLEL DO
405	!$acc kernels present( d, tend )
406	DO i = nxl, nxr
407	DO j = nys, nyn
408	DO k = nzb+1, nzt
409	tend(k,j,i) = d(k,j,i)
410	ENDDO
411	ENDDO
412	ENDDO
413	!$acc end kernels
414
415	!
416	!-- Bottom boundary:
417	!-- This condition is only required for internal output. The pressure
418	!-- gradient (dp(nzb+1)-dp(nzb))/dz is not used anywhere else.
419	IF ( ibc_p_b == 1 ) THEN
420	!
421	!-- Neumann (dp/dz = 0)
422	!$OMP PARALLEL DO
423	!$acc kernels present( nzb_s_inner, tend )
424	DO i = nxlg, nxrg
425	DO j = nysg, nyng
426	tend(nzb_s_inner(j,i),j,i) = tend(nzb_s_inner(j,i)+1,j,i)
427	ENDDO
428	ENDDO
429	!$acc end kernels
430
431	ELSE
432	!
433	!-- Dirichlet
434	!$OMP PARALLEL DO
435	!$acc kernels present( tend )
436	DO i = nxlg, nxrg
437	DO j = nysg, nyng
438	tend(nzb_s_inner(j,i),j,i) = 0.0_wp
439	ENDDO
440	ENDDO
441	!$acc end kernels
442
443	ENDIF
444
445	!
446	!-- Top boundary
447	IF ( ibc_p_t == 1 ) THEN
448	!
449	!-- Neumann
450	!$OMP PARALLEL DO
451	!$acc kernels present( tend )
452	DO i = nxlg, nxrg
453	DO j = nysg, nyng
454	tend(nzt+1,j,i) = tend(nzt,j,i)
455	ENDDO
456	ENDDO
457	!$acc end kernels
458
459	ELSE
460	!
461	!-- Dirichlet
462	!$OMP PARALLEL DO
463	!$acc kernels present( tend )
464	DO i = nxlg, nxrg
465	DO j = nysg, nyng
466	tend(nzt+1,j,i) = 0.0_wp
467	ENDDO
468	ENDDO
469	!$acc end kernels
470
471	ENDIF
472
473	!
474	!-- Exchange boundaries for p
475	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
476	on_device = .TRUE. ! to be removed after complete porting
477	ELSE ! of ghost point exchange
478	!$acc update host( tend )
479	ENDIF
480	CALL exchange_horiz( tend, nbgp )
481	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
482	on_device = .FALSE. ! to be removed after complete porting
483	ELSE ! of ghost point exchange
484	!$acc update device( tend )
485	ENDIF
486
487	ELSEIF ( psolver == 'sor' ) THEN
488
489	!
490	!-- Solve Poisson equation for perturbation pressure using SOR-Red/Black
491	!-- scheme
492	CALL sor( d, ddzu_pres, ddzw, p_loc )
493	tend = p_loc
494
495	ELSEIF ( psolver(1:9) == 'multigrid' ) THEN
496
497	!
498	!-- Solve Poisson equation for perturbation pressure using Multigrid scheme,
499	!-- array tend is used to store the residuals, logical exchange_mg is used
500	!-- to discern data exchange in multigrid ( 1 ghostpoint ) and normal grid
501	!-- ( nbgp ghost points ).
502
503	!-- If the number of grid points of the gathered grid, which is collected
504	!-- on PE0, is larger than the number of grid points of an PE, than array
505	!-- tend will be enlarged.
506	IF ( gathered_size > subdomain_size ) THEN
507	DEALLOCATE( tend )
508	ALLOCATE( tend(nzb:nzt_mg(mg_switch_to_pe0_level)+1,nys_mg( &
509	mg_switch_to_pe0_level)-1:nyn_mg(mg_switch_to_pe0_level)+1,&
510	nxl_mg(mg_switch_to_pe0_level)-1:nxr_mg( &
511	mg_switch_to_pe0_level)+1) )
512	ENDIF
513
514	IF ( psolver == 'multigrid' ) THEN
515	CALL poismg( tend )
516	ELSE
517	CALL poismg_fast( tend )
518	ENDIF
519
520	IF ( gathered_size > subdomain_size ) THEN
521	DEALLOCATE( tend )
522	ALLOCATE( tend(nzb:nzt+1,nysg:nyng,nxlg:nxrg) )
523	ENDIF
524
525	!
526	!-- Restore perturbation pressure on tend because this array is used
527	!-- further below to correct the velocity fields
528	DO i = nxl-1, nxr+1
529	DO j = nys-1, nyn+1
530	DO k = nzb, nzt+1
531	tend(k,j,i) = p_loc(k,j,i)
532	ENDDO
533	ENDDO
534	ENDDO
535
536	ENDIF
537
538	!
539	!-- Store perturbation pressure on array p, used for pressure data output.
540	!-- Ghost layers are added in the output routines (except sor-method: see below)
541	IF ( intermediate_timestep_count == 1 ) THEN
542	!$OMP PARALLEL PRIVATE (i,j,k)
543	!$OMP DO
544	!$acc kernels present( p, tend, weight_substep )
545	!$acc loop independent
546	DO i = nxl-1, nxr+1
547	!$acc loop independent
548	DO j = nys-1, nyn+1
549	!$acc loop independent
550	DO k = nzb, nzt+1
551	p(k,j,i) = tend(k,j,i) * &
552	weight_substep(intermediate_timestep_count)
553	ENDDO
554	ENDDO
555	ENDDO
556	!$acc end kernels
557	!$OMP END PARALLEL
558
559	ELSE
560	!$OMP PARALLEL PRIVATE (i,j,k)
561	!$OMP DO
562	!$acc kernels present( p, tend, weight_substep )
563	!$acc loop independent
564	DO i = nxl-1, nxr+1
565	!$acc loop independent
566	DO j = nys-1, nyn+1
567	!$acc loop independent
568	DO k = nzb, nzt+1
569	p(k,j,i) = p(k,j,i) + tend(k,j,i) * &
570	weight_substep(intermediate_timestep_count)
571	ENDDO
572	ENDDO
573	ENDDO
574	!$acc end kernels
575	!$OMP END PARALLEL
576
577	ENDIF
578
579	!
580	!-- SOR-method needs ghost layers for the next timestep
581	IF ( psolver == 'sor' ) CALL exchange_horiz( p, nbgp )
582
583	!
584	!-- Correction of the provisional velocities with the current perturbation
585	!-- pressure just computed
586	IF ( conserve_volume_flow .AND. ( bc_lr_cyc .OR. bc_ns_cyc ) ) THEN
587	volume_flow_l(1) = 0.0_wp
588	volume_flow_l(2) = 0.0_wp
589	ENDIF
590
591	!$OMP PARALLEL PRIVATE (i,j,k)
592	!$OMP DO
593	!$acc kernels present( ddzu, nzb_u_inner, nzb_v_inner, nzb_w_inner, tend, u, v, w, weight_pres )
594	!$acc loop independent
595	DO i = nxl, nxr
596	!$acc loop independent
597	DO j = nys, nyn
598	!$acc loop independent
599	DO k = 1, nzt
600	IF ( k > nzb_w_inner(j,i) ) THEN
601	w(k,j,i) = w(k,j,i) - dt_3d * &
602	( tend(k+1,j,i) - tend(k,j,i) ) * ddzu(k+1) * &
603	weight_pres(intermediate_timestep_count)
604	ENDIF
605	ENDDO
606	!$acc loop independent
607	DO k = 1, nzt
608	IF ( k > nzb_u_inner(j,i) ) THEN
609	u(k,j,i) = u(k,j,i) - dt_3d * &
610	( tend(k,j,i) - tend(k,j,i-1) ) * ddx * &
611	weight_pres(intermediate_timestep_count)
612	ENDIF
613	ENDDO
614	!$acc loop independent
615	DO k = 1, nzt
616	IF ( k > nzb_v_inner(j,i) ) THEN
617	v(k,j,i) = v(k,j,i) - dt_3d * &
618	( tend(k,j,i) - tend(k,j-1,i) ) * ddy * &
619	weight_pres(intermediate_timestep_count)
620	ENDIF
621	ENDDO
622
623	ENDDO
624	ENDDO
625	!$acc end kernels
626	!$OMP END PARALLEL
627
628	!
629	!-- Sum up the volume flow through the right and north boundary
630	IF ( conserve_volume_flow .AND. bc_lr_cyc .AND. bc_ns_cyc .AND. &
631	nxr == nx ) THEN
632
633	!$OMP PARALLEL PRIVATE (j,k)
634	!$OMP DO
635	DO j = nys, nyn
636	!$OMP CRITICAL
637	DO k = nzb_2d(j,nx) + 1, nzt
638	volume_flow_l(1) = volume_flow_l(1) + u(k,j,nx) * dzw(k)
639	ENDDO
640	!$OMP END CRITICAL
641	ENDDO
642	!$OMP END PARALLEL
643
644	ENDIF
645
646	IF ( conserve_volume_flow .AND. bc_ns_cyc .AND. bc_lr_cyc .AND. &
647	nyn == ny ) THEN
648
649	!$OMP PARALLEL PRIVATE (i,k)
650	!$OMP DO
651	DO i = nxl, nxr
652	!$OMP CRITICAL
653	DO k = nzb_2d(ny,i) + 1, nzt
654	volume_flow_l(2) = volume_flow_l(2) + v(k,ny,i) * dzw(k)
655	ENDDO
656	!$OMP END CRITICAL
657	ENDDO
658	!$OMP END PARALLEL
659
660	ENDIF
661
662	!
663	!-- Conserve the volume flow
664	IF ( conserve_volume_flow .AND. ( bc_lr_cyc .AND. bc_ns_cyc ) ) THEN
665
666	#if defined( __parallel )
667	IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr )
668	CALL MPI_ALLREDUCE( volume_flow_l(1), volume_flow(1), 2, MPI_REAL, &
669	MPI_SUM, comm2d, ierr )
670	#else
671	volume_flow = volume_flow_l
672	#endif
673
674	volume_flow_offset = ( volume_flow_initial - volume_flow ) / &
675	volume_flow_area
676
677	!$OMP PARALLEL PRIVATE (i,j,k)
678	!$OMP DO
679	DO i = nxl, nxr
680	DO j = nys, nyn
681	DO k = nzb_u_inner(j,i) + 1, nzt
682	u(k,j,i) = u(k,j,i) + volume_flow_offset(1)
683	ENDDO
684	DO k = nzb_v_inner(j,i) + 1, nzt
685	v(k,j,i) = v(k,j,i) + volume_flow_offset(2)
686	ENDDO
687	ENDDO
688	ENDDO
689
690	!$OMP END PARALLEL
691
692	ENDIF
693
694	!
695	!-- Exchange of boundaries for the velocities
696	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
697	on_device = .TRUE. ! to be removed after complete porting
698	ELSE ! of ghost point exchange
699	!$acc update host( u, v, w )
700	ENDIF
701	CALL exchange_horiz( u, nbgp )
702	CALL exchange_horiz( v, nbgp )
703	CALL exchange_horiz( w, nbgp )
704	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
705	on_device = .FALSE. ! to be removed after complete porting
706	ELSE ! of ghost point exchange
707	!$acc update device( u, v, w )
708	ENDIF
709
710	!
711	!-- Compute the divergence of the corrected velocity field,
712	!-- a possible PE-sum is computed in flow_statistics
713	CALL cpu_log( log_point_s(1), 'divergence', 'start' )
714	sums_divnew_l = 0.0_wp
715
716	!
717	!-- d must be reset to zero because it can contain nonzero values below the
718	!-- topography
719	IF ( topography /= 'flat' ) d = 0.0_wp
720
721	localsum = 0.0_wp
722	threadsum = 0.0_wp
723
724	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
725	!$OMP DO SCHEDULE( STATIC )
726	#if defined( __ibm )
727	DO i = nxl, nxr
728	DO j = nys, nyn
729	DO k = nzb_s_inner(j,i)+1, nzt
730	d(k,j,i) = ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
731	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
732	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k)
733	ENDDO
734	DO k = nzb+1, nzt
735	threadsum = threadsum + ABS( d(k,j,i) )
736	ENDDO
737	ENDDO
738	ENDDO
739	#else
740	!$acc kernels present( d, ddzw, rflags_s_inner, u, v, w )
741	!$acc loop collapse( 3 )
742	DO i = nxl, nxr
743	DO j = nys, nyn
744	DO k = 1, nzt
745	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
746	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
747	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) &
748	) * rflags_s_inner(k,j,i)
749	ENDDO
750	ENDDO
751	ENDDO
752	!$acc end kernels
753	!
754	!-- Compute possible PE-sum of divergences for flow_statistics
755	!$acc parallel loop collapse(3) present( d ) reduction(+:threadsum)
756	DO i = nxl, nxr
757	DO j = nys, nyn
758	DO k = nzb+1, nzt
759	threadsum = threadsum + ABS( d(k,j,i) )
760	ENDDO
761	ENDDO
762	ENDDO
763	!$acc end parallel loop
764	#endif
765
766	localsum = localsum + threadsum
767	!$OMP END PARALLEL
768
769	!
770	!-- For completeness, set the divergence sum of all statistic regions to those
771	!-- of the total domain
772	sums_divnew_l(0:statistic_regions) = localsum
773
774	CALL cpu_log( log_point_s(1), 'divergence', 'stop' )
775
776	CALL cpu_log( log_point(8), 'pres', 'stop' )
777
778
779	END SUBROUTINE pres

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