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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 1343 2014-03-26 17:07:58Z keck $
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 statistics, &
117	ONLY: statistic_regions, sums_divnew_l, sums_divold_l, weight_pres, &
118	weight_substep
119
120	IMPLICIT NONE
121
122	INTEGER(iwp) :: i !:
123	INTEGER(iwp) :: j !:
124	INTEGER(iwp) :: k !:
125
126	REAL(wp) :: ddt_3d !:
127	REAL(wp) :: localsum !:
128	REAL(wp) :: threadsum !:
129	REAL(wp) :: d_weight_pres !:
130
131	REAL(wp), DIMENSION(1:2) :: volume_flow_l !:
132	REAL(wp), DIMENSION(1:2) :: volume_flow_offset !:
133	REAL(wp), DIMENSION(1:nzt) :: w_l !:
134	REAL(wp), DIMENSION(1:nzt) :: w_l_l !:
135
136
137	CALL cpu_log( log_point(8), 'pres', 'start' )
138
139
140	ddt_3d = 1.0_wp / dt_3d
141	d_weight_pres = 1.0_wp / weight_pres(intermediate_timestep_count)
142
143	!
144	!-- Multigrid method expects array d to have one ghost layer.
145	!--
146	IF ( psolver == 'multigrid' ) THEN
147
148	DEALLOCATE( d )
149	ALLOCATE( d(nzb:nzt+1,nys-1:nyn+1,nxl-1:nxr+1) )
150
151	!
152	!-- Since p is later used to hold the weighted average of the substeps, it
153	!-- cannot be used in the iterative solver. Therefore, its initial value is
154	!-- stored on p_loc, which is then iteratively advanced in every substep.
155	IF ( intermediate_timestep_count == 1 ) THEN
156	DO i = nxl-1, nxr+1
157	DO j = nys-1, nyn+1
158	DO k = nzb, nzt+1
159	p_loc(k,j,i) = p(k,j,i)
160	ENDDO
161	ENDDO
162	ENDDO
163	ENDIF
164
165	ELSEIF ( psolver == 'sor' .AND. intermediate_timestep_count == 1 ) THEN
166
167	!
168	!-- Since p is later used to hold the weighted average of the substeps, it
169	!-- cannot be used in the iterative solver. Therefore, its initial value is
170	!-- stored on p_loc, which is then iteratively advanced in every substep.
171	p_loc = p
172
173	ENDIF
174
175	!
176	!-- Conserve the volume flow at the outflow in case of non-cyclic lateral
177	!-- boundary conditions
178	!-- WARNING: so far, this conservation does not work at the left/south
179	!-- boundary if the topography at the inflow differs from that at the
180	!-- outflow! For this case, volume_flow_area needs adjustment!
181	!
182	!-- Left/right
183	IF ( conserve_volume_flow .AND. ( outflow_l .OR. outflow_r ) ) THEN
184
185	volume_flow(1) = 0.0_wp
186	volume_flow_l(1) = 0.0_wp
187
188	IF ( outflow_l ) THEN
189	i = 0
190	ELSEIF ( outflow_r ) THEN
191	i = nx+1
192	ENDIF
193
194	DO j = nys, nyn
195	!
196	!-- Sum up the volume flow through the south/north boundary
197	DO k = nzb_2d(j,i)+1, nzt
198	volume_flow_l(1) = volume_flow_l(1) + u(k,j,i) * dzw(k)
199	ENDDO
200	ENDDO
201
202	#if defined( __parallel )
203	IF ( collective_wait ) CALL MPI_BARRIER( comm1dy, ierr )
204	CALL MPI_ALLREDUCE( volume_flow_l(1), volume_flow(1), 1, MPI_REAL, &
205	MPI_SUM, comm1dy, ierr )
206	#else
207	volume_flow = volume_flow_l
208	#endif
209	volume_flow_offset(1) = ( volume_flow_initial(1) - volume_flow(1) ) &
210	/ volume_flow_area(1)
211
212	DO j = nysg, nyng
213	DO k = nzb_2d(j,i)+1, nzt
214	u(k,j,i) = u(k,j,i) + volume_flow_offset(1)
215	ENDDO
216	ENDDO
217
218	ENDIF
219
220	!
221	!-- South/north
222	IF ( conserve_volume_flow .AND. ( outflow_n .OR. outflow_s ) ) THEN
223
224	volume_flow(2) = 0.0_wp
225	volume_flow_l(2) = 0.0_wp
226
227	IF ( outflow_s ) THEN
228	j = 0
229	ELSEIF ( outflow_n ) THEN
230	j = ny+1
231	ENDIF
232
233	DO i = nxl, nxr
234	!
235	!-- Sum up the volume flow through the south/north boundary
236	DO k = nzb_2d(j,i)+1, nzt
237	volume_flow_l(2) = volume_flow_l(2) + v(k,j,i) * dzw(k)
238	ENDDO
239	ENDDO
240
241	#if defined( __parallel )
242	IF ( collective_wait ) CALL MPI_BARRIER( comm1dx, ierr )
243	CALL MPI_ALLREDUCE( volume_flow_l(2), volume_flow(2), 1, MPI_REAL, &
244	MPI_SUM, comm1dx, ierr )
245	#else
246	volume_flow = volume_flow_l
247	#endif
248	volume_flow_offset(2) = ( volume_flow_initial(2) - volume_flow(2) ) &
249	/ volume_flow_area(2)
250
251	DO i = nxlg, nxrg
252	DO k = nzb_v_inner(j,i)+1, nzt
253	v(k,j,i) = v(k,j,i) + volume_flow_offset(2)
254	ENDDO
255	ENDDO
256
257	ENDIF
258
259	!
260	!-- Remove mean vertical velocity
261	IF ( ibc_p_b == 1 .AND. ibc_p_t == 1 ) THEN
262	IF ( simulated_time > 0.0_wp ) THEN ! otherwise nzb_w_inner not yet known
263	w_l = 0.0_wp; w_l_l = 0.0_wp
264	DO i = nxl, nxr
265	DO j = nys, nyn
266	DO k = nzb_w_inner(j,i)+1, nzt
267	w_l_l(k) = w_l_l(k) + w(k,j,i)
268	ENDDO
269	ENDDO
270	ENDDO
271	#if defined( __parallel )
272	IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr )
273	CALL MPI_ALLREDUCE( w_l_l(1), w_l(1), nzt, MPI_REAL, MPI_SUM, &
274	comm2d, ierr )
275	#else
276	w_l = w_l_l
277	#endif
278	DO k = 1, nzt
279	w_l(k) = w_l(k) / ngp_2dh_outer(k,0)
280	ENDDO
281	DO i = nxlg, nxrg
282	DO j = nysg, nyng
283	DO k = nzb_w_inner(j,i)+1, nzt
284	w(k,j,i) = w(k,j,i) - w_l(k)
285	ENDDO
286	ENDDO
287	ENDDO
288	ENDIF
289	ENDIF
290
291	!
292	!-- Compute the divergence of the provisional velocity field.
293	CALL cpu_log( log_point_s(1), 'divergence', 'start' )
294
295	IF ( psolver == 'multigrid' ) THEN
296	!$OMP PARALLEL DO SCHEDULE( STATIC )
297	DO i = nxl-1, nxr+1
298	DO j = nys-1, nyn+1
299	DO k = nzb, nzt+1
300	d(k,j,i) = 0.0_wp
301	ENDDO
302	ENDDO
303	ENDDO
304	ELSE
305	!$OMP PARALLEL DO SCHEDULE( STATIC )
306	!$acc kernels present( d )
307	DO i = nxl, nxr
308	DO j = nys, nyn
309	DO k = nzb+1, nzt
310	d(k,j,i) = 0.0_wp
311	ENDDO
312	ENDDO
313	ENDDO
314	!$acc end kernels
315	ENDIF
316
317	localsum = 0.0_wp
318	threadsum = 0.0_wp
319
320	#if defined( __ibm )
321	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
322	!$OMP DO SCHEDULE( STATIC )
323	DO i = nxl, nxr
324	DO j = nys, nyn
325	DO k = nzb_s_inner(j,i)+1, nzt
326	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
327	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
328	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) ) * ddt_3d &
329	* d_weight_pres
330	ENDDO
331	!
332	!-- Compute possible PE-sum of divergences for flow_statistics
333	DO k = nzb_s_inner(j,i)+1, nzt
334	threadsum = threadsum + ABS( d(k,j,i) )
335	ENDDO
336
337	ENDDO
338	ENDDO
339
340	localsum = localsum + threadsum * dt_3d * &
341	weight_pres(intermediate_timestep_count)
342
343	!$OMP END PARALLEL
344	#else
345
346	!$OMP PARALLEL PRIVATE (i,j,k)
347	!$OMP DO SCHEDULE( STATIC )
348	!$acc kernels present( d, ddzw, rflags_s_inner, u, v, w )
349	!$acc loop collapse( 3 )
350	DO i = nxl, nxr
351	DO j = nys, nyn
352	DO k = 1, nzt
353	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
354	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
355	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) ) * ddt_3d &
356	* d_weight_pres * rflags_s_inner(k,j,i)
357	ENDDO
358	ENDDO
359	ENDDO
360	!$acc end kernels
361	!$OMP END PARALLEL
362
363	!
364	!-- Compute possible PE-sum of divergences for flow_statistics
365	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
366	!$OMP DO SCHEDULE( STATIC )
367	!$acc parallel loop collapse(3) present( d ) reduction(+:threadsum)
368	DO i = nxl, nxr
369	DO j = nys, nyn
370	DO k = nzb+1, nzt
371	threadsum = threadsum + ABS( d(k,j,i) )
372	ENDDO
373	ENDDO
374	ENDDO
375	!$acc end parallel loop
376	localsum = localsum + threadsum * dt_3d * &
377	weight_pres(intermediate_timestep_count)
378	!$OMP END PARALLEL
379	#endif
380
381	!
382	!-- For completeness, set the divergence sum of all statistic regions to those
383	!-- of the total domain
384	sums_divold_l(0:statistic_regions) = localsum
385
386	CALL cpu_log( log_point_s(1), 'divergence', 'stop' )
387
388	!
389	!-- Compute the pressure perturbation solving the Poisson equation
390	IF ( psolver(1:7) == 'poisfft' ) THEN
391
392	!
393	!-- Solve Poisson equation via FFT and solution of tridiagonal matrices
394	IF ( psolver == 'poisfft' ) THEN
395
396	CALL poisfft( d )
397
398	ENDIF
399
400	!
401	!-- Store computed perturbation pressure and set boundary condition in
402	!-- z-direction
403	!$OMP PARALLEL DO
404	!$acc kernels present( d, tend )
405	DO i = nxl, nxr
406	DO j = nys, nyn
407	DO k = nzb+1, nzt
408	tend(k,j,i) = d(k,j,i)
409	ENDDO
410	ENDDO
411	ENDDO
412	!$acc end kernels
413
414	!
415	!-- Bottom boundary:
416	!-- This condition is only required for internal output. The pressure
417	!-- gradient (dp(nzb+1)-dp(nzb))/dz is not used anywhere else.
418	IF ( ibc_p_b == 1 ) THEN
419	!
420	!-- Neumann (dp/dz = 0)
421	!$OMP PARALLEL DO
422	!$acc kernels present( nzb_s_inner, tend )
423	DO i = nxlg, nxrg
424	DO j = nysg, nyng
425	tend(nzb_s_inner(j,i),j,i) = tend(nzb_s_inner(j,i)+1,j,i)
426	ENDDO
427	ENDDO
428	!$acc end kernels
429
430	ELSE
431	!
432	!-- Dirichlet
433	!$OMP PARALLEL DO
434	!$acc kernels present( tend )
435	DO i = nxlg, nxrg
436	DO j = nysg, nyng
437	tend(nzb_s_inner(j,i),j,i) = 0.0_wp
438	ENDDO
439	ENDDO
440	!$acc end kernels
441
442	ENDIF
443
444	!
445	!-- Top boundary
446	IF ( ibc_p_t == 1 ) THEN
447	!
448	!-- Neumann
449	!$OMP PARALLEL DO
450	!$acc kernels present( tend )
451	DO i = nxlg, nxrg
452	DO j = nysg, nyng
453	tend(nzt+1,j,i) = tend(nzt,j,i)
454	ENDDO
455	ENDDO
456	!$acc end kernels
457
458	ELSE
459	!
460	!-- Dirichlet
461	!$OMP PARALLEL DO
462	!$acc kernels present( tend )
463	DO i = nxlg, nxrg
464	DO j = nysg, nyng
465	tend(nzt+1,j,i) = 0.0_wp
466	ENDDO
467	ENDDO
468	!$acc end kernels
469
470	ENDIF
471
472	!
473	!-- Exchange boundaries for p
474	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
475	on_device = .TRUE. ! to be removed after complete porting
476	ELSE ! of ghost point exchange
477	!$acc update host( tend )
478	ENDIF
479	CALL exchange_horiz( tend, nbgp )
480	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
481	on_device = .FALSE. ! to be removed after complete porting
482	ELSE ! of ghost point exchange
483	!$acc update device( tend )
484	ENDIF
485
486	ELSEIF ( psolver == 'sor' ) THEN
487
488	!
489	!-- Solve Poisson equation for perturbation pressure using SOR-Red/Black
490	!-- scheme
491	CALL sor( d, ddzu_pres, ddzw, p_loc )
492	tend = p_loc
493
494	ELSEIF ( psolver == 'multigrid' ) THEN
495
496	!
497	!-- Solve Poisson equation for perturbation pressure using Multigrid scheme,
498	!-- array tend is used to store the residuals, logical exchange_mg is used
499	!-- to discern data exchange in multigrid ( 1 ghostpoint ) and normal grid
500	!-- ( nbgp ghost points ).
501
502	!-- If the number of grid points of the gathered grid, which is collected
503	!-- on PE0, is larger than the number of grid points of an PE, than array
504	!-- tend will be enlarged.
505	IF ( gathered_size > subdomain_size ) THEN
506	DEALLOCATE( tend )
507	ALLOCATE( tend(nzb:nzt_mg(mg_switch_to_pe0_level)+1,nys_mg( &
508	mg_switch_to_pe0_level)-1:nyn_mg(mg_switch_to_pe0_level)+1,&
509	nxl_mg(mg_switch_to_pe0_level)-1:nxr_mg( &
510	mg_switch_to_pe0_level)+1) )
511	ENDIF
512
513	CALL poismg( tend )
514
515	IF ( gathered_size > subdomain_size ) THEN
516	DEALLOCATE( tend )
517	ALLOCATE( tend(nzb:nzt+1,nysg:nyng,nxlg:nxrg) )
518	ENDIF
519
520	!
521	!-- Restore perturbation pressure on tend because this array is used
522	!-- further below to correct the velocity fields
523	DO i = nxl-1, nxr+1
524	DO j = nys-1, nyn+1
525	DO k = nzb, nzt+1
526	tend(k,j,i) = p_loc(k,j,i)
527	ENDDO
528	ENDDO
529	ENDDO
530
531	ENDIF
532
533	!
534	!-- Store perturbation pressure on array p, used for pressure data output.
535	!-- Ghost layers are added in the output routines (except sor-method: see below)
536	IF ( intermediate_timestep_count == 1 ) THEN
537	!$OMP PARALLEL PRIVATE (i,j,k)
538	!$OMP DO
539	!$acc kernels present( p, tend, weight_substep )
540	!$acc loop independent
541	DO i = nxl-1, nxr+1
542	!$acc loop independent
543	DO j = nys-1, nyn+1
544	!$acc loop independent
545	DO k = nzb, nzt+1
546	p(k,j,i) = tend(k,j,i) * &
547	weight_substep(intermediate_timestep_count)
548	ENDDO
549	ENDDO
550	ENDDO
551	!$acc end kernels
552	!$OMP END PARALLEL
553
554	ELSE
555	!$OMP PARALLEL PRIVATE (i,j,k)
556	!$OMP DO
557	!$acc kernels present( p, tend, weight_substep )
558	!$acc loop independent
559	DO i = nxl-1, nxr+1
560	!$acc loop independent
561	DO j = nys-1, nyn+1
562	!$acc loop independent
563	DO k = nzb, nzt+1
564	p(k,j,i) = p(k,j,i) + tend(k,j,i) * &
565	weight_substep(intermediate_timestep_count)
566	ENDDO
567	ENDDO
568	ENDDO
569	!$acc end kernels
570	!$OMP END PARALLEL
571
572	ENDIF
573
574	!
575	!-- SOR-method needs ghost layers for the next timestep
576	IF ( psolver == 'sor' ) CALL exchange_horiz( p, nbgp )
577
578	!
579	!-- Correction of the provisional velocities with the current perturbation
580	!-- pressure just computed
581	IF ( conserve_volume_flow .AND. ( bc_lr_cyc .OR. bc_ns_cyc ) ) THEN
582	volume_flow_l(1) = 0.0_wp
583	volume_flow_l(2) = 0.0_wp
584	ENDIF
585
586	!$OMP PARALLEL PRIVATE (i,j,k)
587	!$OMP DO
588	!$acc kernels present( ddzu, nzb_u_inner, nzb_v_inner, nzb_w_inner, tend, u, v, w, weight_pres )
589	!$acc loop independent
590	DO i = nxl, nxr
591	!$acc loop independent
592	DO j = nys, nyn
593	!$acc loop independent
594	DO k = 1, nzt
595	IF ( k > nzb_w_inner(j,i) ) THEN
596	w(k,j,i) = w(k,j,i) - dt_3d * &
597	( tend(k+1,j,i) - tend(k,j,i) ) * ddzu(k+1) * &
598	weight_pres(intermediate_timestep_count)
599	ENDIF
600	ENDDO
601	!$acc loop independent
602	DO k = 1, nzt
603	IF ( k > nzb_u_inner(j,i) ) THEN
604	u(k,j,i) = u(k,j,i) - dt_3d * &
605	( tend(k,j,i) - tend(k,j,i-1) ) * ddx * &
606	weight_pres(intermediate_timestep_count)
607	ENDIF
608	ENDDO
609	!$acc loop independent
610	DO k = 1, nzt
611	IF ( k > nzb_v_inner(j,i) ) THEN
612	v(k,j,i) = v(k,j,i) - dt_3d * &
613	( tend(k,j,i) - tend(k,j-1,i) ) * ddy * &
614	weight_pres(intermediate_timestep_count)
615	ENDIF
616	ENDDO
617
618	ENDDO
619	ENDDO
620	!$acc end kernels
621	!$OMP END PARALLEL
622
623	!
624	!-- Sum up the volume flow through the right and north boundary
625	IF ( conserve_volume_flow .AND. bc_lr_cyc .AND. bc_ns_cyc .AND. &
626	nxr == nx ) THEN
627
628	!$OMP PARALLEL PRIVATE (j,k)
629	!$OMP DO
630	DO j = nys, nyn
631	!$OMP CRITICAL
632	DO k = nzb_2d(j,nx) + 1, nzt
633	volume_flow_l(1) = volume_flow_l(1) + u(k,j,nx) * dzw(k)
634	ENDDO
635	!$OMP END CRITICAL
636	ENDDO
637	!$OMP END PARALLEL
638
639	ENDIF
640
641	IF ( conserve_volume_flow .AND. bc_ns_cyc .AND. bc_lr_cyc .AND. &
642	nyn == ny ) THEN
643
644	!$OMP PARALLEL PRIVATE (i,k)
645	!$OMP DO
646	DO i = nxl, nxr
647	!$OMP CRITICAL
648	DO k = nzb_2d(ny,i) + 1, nzt
649	volume_flow_l(2) = volume_flow_l(2) + v(k,ny,i) * dzw(k)
650	ENDDO
651	!$OMP END CRITICAL
652	ENDDO
653	!$OMP END PARALLEL
654
655	ENDIF
656
657	!
658	!-- Conserve the volume flow
659	IF ( conserve_volume_flow .AND. ( bc_lr_cyc .AND. bc_ns_cyc ) ) THEN
660
661	#if defined( __parallel )
662	IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr )
663	CALL MPI_ALLREDUCE( volume_flow_l(1), volume_flow(1), 2, MPI_REAL, &
664	MPI_SUM, comm2d, ierr )
665	#else
666	volume_flow = volume_flow_l
667	#endif
668
669	volume_flow_offset = ( volume_flow_initial - volume_flow ) / &
670	volume_flow_area
671
672	!$OMP PARALLEL PRIVATE (i,j,k)
673	!$OMP DO
674	DO i = nxl, nxr
675	DO j = nys, nyn
676	DO k = nzb_u_inner(j,i) + 1, nzt
677	u(k,j,i) = u(k,j,i) + volume_flow_offset(1)
678	ENDDO
679	DO k = nzb_v_inner(j,i) + 1, nzt
680	v(k,j,i) = v(k,j,i) + volume_flow_offset(2)
681	ENDDO
682	ENDDO
683	ENDDO
684
685	!$OMP END PARALLEL
686
687	ENDIF
688
689	!
690	!-- Exchange of boundaries for the velocities
691	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
692	on_device = .TRUE. ! to be removed after complete porting
693	ELSE ! of ghost point exchange
694	!$acc update host( u, v, w )
695	ENDIF
696	CALL exchange_horiz( u, nbgp )
697	CALL exchange_horiz( v, nbgp )
698	CALL exchange_horiz( w, nbgp )
699	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
700	on_device = .FALSE. ! to be removed after complete porting
701	ELSE ! of ghost point exchange
702	!$acc update device( u, v, w )
703	ENDIF
704
705	!
706	!-- Compute the divergence of the corrected velocity field,
707	!-- a possible PE-sum is computed in flow_statistics
708	CALL cpu_log( log_point_s(1), 'divergence', 'start' )
709	sums_divnew_l = 0.0_wp
710
711	!
712	!-- d must be reset to zero because it can contain nonzero values below the
713	!-- topography
714	IF ( topography /= 'flat' ) d = 0.0_wp
715
716	localsum = 0.0_wp
717	threadsum = 0.0_wp
718
719	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
720	!$OMP DO SCHEDULE( STATIC )
721	#if defined( __ibm )
722	DO i = nxl, nxr
723	DO j = nys, nyn
724	DO k = nzb_s_inner(j,i)+1, nzt
725	d(k,j,i) = ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
726	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
727	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k)
728	ENDDO
729	DO k = nzb+1, nzt
730	threadsum = threadsum + ABS( d(k,j,i) )
731	ENDDO
732	ENDDO
733	ENDDO
734	#else
735	!$acc kernels present( d, ddzw, rflags_s_inner, u, v, w )
736	!$acc loop collapse( 3 )
737	DO i = nxl, nxr
738	DO j = nys, nyn
739	DO k = 1, nzt
740	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
741	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
742	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) &
743	) * rflags_s_inner(k,j,i)
744	ENDDO
745	ENDDO
746	ENDDO
747	!$acc end kernels
748	!
749	!-- Compute possible PE-sum of divergences for flow_statistics
750	!$acc parallel loop collapse(3) present( d ) reduction(+:threadsum)
751	DO i = nxl, nxr
752	DO j = nys, nyn
753	DO k = nzb+1, nzt
754	threadsum = threadsum + ABS( d(k,j,i) )
755	ENDDO
756	ENDDO
757	ENDDO
758	!$acc end parallel loop
759	#endif
760
761	localsum = localsum + threadsum
762	!$OMP END PARALLEL
763
764	!
765	!-- For completeness, set the divergence sum of all statistic regions to those
766	!-- of the total domain
767	sums_divnew_l(0:statistic_regions) = localsum
768
769	CALL cpu_log( log_point_s(1), 'divergence', 'stop' )
770
771	CALL cpu_log( log_point(8), 'pres', 'stop' )
772
773
774	END SUBROUTINE pres

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