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source: palm/trunk/SOURCE/pres.f90 @ 1827

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1	!> @file pres.f90
2	!--------------------------------------------------------------------------------!
3	! This file is part of PALM.
4	!
5	! PALM is free software: you can redistribute it and/or modify it under the terms
6	! of the GNU General Public License as published by the Free Software Foundation,
7	! either version 3 of the License, or (at your option) any later version.
8	!
9	! PALM is distributed in the hope that it will be useful, but WITHOUT ANY
10	! WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
11	! A PARTICULAR PURPOSE. See the GNU General Public License for more details.
12	!
13	! You should have received a copy of the GNU General Public License along with
14	! PALM. If not, see <http://www.gnu.org/licenses/>.
15	!
16	! Copyright 1997-2016 Leibniz Universitaet Hannover
17	!--------------------------------------------------------------------------------!
18	!
19	! Current revisions:
20	! ------------------
21	!
22	!
23	! Former revisions:
24	! -----------------
25	! $Id: pres.f90 1818 2016-04-06 15:53:27Z maronga $
26	!
27	! 1799 2016-04-05 08:35:55Z gronemeier
28	! Bugfix: excluded third dimension from horizontal volume flow calculation
29	!
30	! 1762 2016-02-25 12:31:13Z hellstea
31	! Introduction of nested domain feature
32	!
33	! 1682 2015-10-07 23:56:08Z knoop
34	! Code annotations made doxygen readable
35	!
36	! 1575 2015-03-27 09:56:27Z raasch
37	! poismg_fast + respective module added, adjustments for psolver-queries
38	!
39	! 1342 2014-03-26 17:04:47Z kanani
40	! REAL constants defined as wp-kind
41	!
42	! 1320 2014-03-20 08:40:49Z raasch
43	! ONLY-attribute added to USE-statements,
44	! kind-parameters added to all INTEGER and REAL declaration statements,
45	! kinds are defined in new module kinds,
46	! old module precision_kind is removed,
47	! revision history before 2012 removed,
48	! comment fields (!:) to be used for variable explanations added to
49	! all variable declaration statements
50	!
51	! 1318 2014-03-17 13:35:16Z raasch
52	! module interfaces removed
53	!
54	! 1306 2014-03-13 14:30:59Z raasch
55	! second argument removed from routine poisfft
56	!
57	! 1257 2013-11-08 15:18:40Z raasch
58	! openacc loop and loop vector clauses removed, independent clauses added,
59	! end parallel replaced by end parallel loop
60	!
61	! 1221 2013-09-10 08:59:13Z raasch
62	! openACC porting of reduction operations, loops for calculating d are
63	! using the rflags_s_inner multiply flag instead of the nzb_s_inner loop index
64	!
65	! 1212 2013-08-15 08:46:27Z raasch
66	! call of poisfft_hybrid removed
67	!
68	! 1117 2013-03-27 11:15:36Z suehring
69	! Bugfix in OpenMP parallelization.
70	!
71	! 1113 2013-03-10 02:48:14Z raasch
72	! GPU-porting of several loops, some loops rearranged
73	!
74	! 1111 2013-03-08 23:54:10Z
75	! openACC statements added,
76	! ibc_p_b = 2 removed
77	!
78	! 1092 2013-02-02 11:24:22Z raasch
79	! unused variables removed
80	!
81	! 1036 2012-10-22 13:43:42Z raasch
82	! code put under GPL (PALM 3.9)
83	!
84	! 1003 2012-09-14 14:35:53Z raasch
85	! adjustment of array tend for cases with unequal subdomain sizes removed
86	!
87	! Revision 1.1 1997/07/24 11:24:44 raasch
88	! Initial revision
89	!
90	!
91	! Description:
92	! ------------
93	!> Compute the divergence of the provisional velocity field. Solve the Poisson
94	!> equation for the perturbation pressure. Compute the final velocities using
95	!> this perturbation pressure. Compute the remaining divergence.
96	!------------------------------------------------------------------------------!
97	SUBROUTINE pres
98
99
100	USE arrays_3d, &
101	ONLY: d, ddzu, ddzu_pres, ddzw, dzw, p, p_loc, tend, u, v, w
102
103	USE control_parameters, &
104	ONLY: bc_lr_cyc, bc_ns_cyc, conserve_volume_flow, dt_3d, &
105	gathered_size, ibc_p_b, ibc_p_t, intermediate_timestep_count, &
106	mg_switch_to_pe0_level, nest_domain, nest_bound_l, &
107	nest_bound_n, nest_bound_r, nest_bound_s, on_device, outflow_l, &
108	outflow_n, outflow_r, outflow_s, psolver, simulated_time, &
109	subdomain_size, topography, volume_flow, volume_flow_area, &
110	volume_flow_initial
111
112	USE cpulog, &
113	ONLY: cpu_log, log_point, log_point_s
114
115	USE grid_variables, &
116	ONLY: ddx, ddy
117
118	USE indices, &
119	ONLY: nbgp, ngp_2dh_outer, nx, nxl, nxlg, nxl_mg, nxr, nxrg, nxr_mg, &
120	ny, nys, nysg, nys_mg, nyn, nyng, nyn_mg, nzb, nzb_s_inner, &
121	nzb_u_inner, nzb_v_inner, nzb_w_inner, nzb_2d, nzt, nzt_mg, &
122	rflags_s_inner
123
124	USE kinds
125
126	USE pegrid
127
128	USE poisfft_mod, &
129	ONLY: poisfft
130
131	USE poismg_mod
132
133	USE statistics, &
134	ONLY: statistic_regions, sums_divnew_l, sums_divold_l, weight_pres, &
135	weight_substep
136
137	IMPLICIT NONE
138
139	INTEGER(iwp) :: i !<
140	INTEGER(iwp) :: j !<
141	INTEGER(iwp) :: k !<
142
143	REAL(wp) :: ddt_3d !<
144	REAL(wp) :: localsum !<
145	REAL(wp) :: threadsum !<
146	REAL(wp) :: d_weight_pres !<
147
148	REAL(wp), DIMENSION(1:3) :: volume_flow_l !<
149	REAL(wp), DIMENSION(1:3) :: volume_flow_offset !<
150	REAL(wp), DIMENSION(1:nzt) :: w_l !<
151	REAL(wp), DIMENSION(1:nzt) :: w_l_l !<
152
153
154	CALL cpu_log( log_point(8), 'pres', 'start' )
155
156
157	ddt_3d = 1.0_wp / dt_3d
158	d_weight_pres = 1.0_wp / weight_pres(intermediate_timestep_count)
159
160	!
161	!-- Multigrid method expects array d to have one ghost layer.
162	!--
163	IF ( psolver(1:9) == 'multigrid' ) THEN
164
165	DEALLOCATE( d )
166	ALLOCATE( d(nzb:nzt+1,nys-1:nyn+1,nxl-1:nxr+1) )
167
168	!
169	!-- Since p is later used to hold the weighted average of the substeps, it
170	!-- cannot be used in the iterative solver. Therefore, its initial value is
171	!-- stored on p_loc, which is then iteratively advanced in every substep.
172	IF ( intermediate_timestep_count <= 1 ) THEN
173	DO i = nxl-1, nxr+1
174	DO j = nys-1, nyn+1
175	DO k = nzb, nzt+1
176	p_loc(k,j,i) = p(k,j,i)
177	ENDDO
178	ENDDO
179	ENDDO
180	ENDIF
181
182	ELSEIF ( psolver == 'sor' .AND. intermediate_timestep_count == 1 ) THEN
183
184	!
185	!-- Since p is later used to hold the weighted average of the substeps, it
186	!-- cannot be used in the iterative solver. Therefore, its initial value is
187	!-- stored on p_loc, which is then iteratively advanced in every substep.
188	p_loc = p
189
190	ENDIF
191
192	!
193	!-- Conserve the volume flow at the outflow in case of non-cyclic lateral
194	!-- boundary conditions
195	!-- WARNING: so far, this conservation does not work at the left/south
196	!-- boundary if the topography at the inflow differs from that at the
197	!-- outflow! For this case, volume_flow_area needs adjustment!
198	!
199	!-- Left/right
200	IF ( conserve_volume_flow .AND. ( outflow_l .OR. outflow_r ) ) THEN
201
202	volume_flow(1) = 0.0_wp
203	volume_flow_l(1) = 0.0_wp
204
205	IF ( outflow_l ) THEN
206	i = 0
207	ELSEIF ( outflow_r ) THEN
208	i = nx+1
209	ENDIF
210
211	DO j = nys, nyn
212	!
213	!-- Sum up the volume flow through the south/north boundary
214	DO k = nzb_2d(j,i)+1, nzt
215	volume_flow_l(1) = volume_flow_l(1) + u(k,j,i) * dzw(k)
216	ENDDO
217	ENDDO
218
219	#if defined( __parallel )
220	IF ( collective_wait ) CALL MPI_BARRIER( comm1dy, ierr )
221	CALL MPI_ALLREDUCE( volume_flow_l(1), volume_flow(1), 1, MPI_REAL, &
222	MPI_SUM, comm1dy, ierr )
223	#else
224	volume_flow = volume_flow_l
225	#endif
226	volume_flow_offset(1) = ( volume_flow_initial(1) - volume_flow(1) ) &
227	/ volume_flow_area(1)
228
229	DO j = nysg, nyng
230	DO k = nzb_2d(j,i)+1, nzt
231	u(k,j,i) = u(k,j,i) + volume_flow_offset(1)
232	ENDDO
233	ENDDO
234
235	ENDIF
236
237	!
238	!-- South/north
239	IF ( conserve_volume_flow .AND. ( outflow_n .OR. outflow_s ) ) THEN
240
241	volume_flow(2) = 0.0_wp
242	volume_flow_l(2) = 0.0_wp
243
244	IF ( outflow_s ) THEN
245	j = 0
246	ELSEIF ( outflow_n ) THEN
247	j = ny+1
248	ENDIF
249
250	DO i = nxl, nxr
251	!
252	!-- Sum up the volume flow through the south/north boundary
253	DO k = nzb_2d(j,i)+1, nzt
254	volume_flow_l(2) = volume_flow_l(2) + v(k,j,i) * dzw(k)
255	ENDDO
256	ENDDO
257
258	#if defined( __parallel )
259	IF ( collective_wait ) CALL MPI_BARRIER( comm1dx, ierr )
260	CALL MPI_ALLREDUCE( volume_flow_l(2), volume_flow(2), 1, MPI_REAL, &
261	MPI_SUM, comm1dx, ierr )
262	#else
263	volume_flow = volume_flow_l
264	#endif
265	volume_flow_offset(2) = ( volume_flow_initial(2) - volume_flow(2) ) &
266	/ volume_flow_area(2)
267
268	DO i = nxlg, nxrg
269	DO k = nzb_v_inner(j,i)+1, nzt
270	v(k,j,i) = v(k,j,i) + volume_flow_offset(2)
271	ENDDO
272	ENDDO
273
274	ENDIF
275
276	!
277	!-- Remove mean vertical velocity in case that Neumann conditions are
278	!-- used both at bottom and top boundary, and if not a nested domain
279	IF ( ibc_p_b == 1 .AND. ibc_p_t == 1 .AND. .NOT. nest_domain) THEN
280	IF ( simulated_time > 0.0_wp ) THEN ! otherwise nzb_w_inner not yet known
281	w_l = 0.0_wp; w_l_l = 0.0_wp
282	DO i = nxl, nxr
283	DO j = nys, nyn
284	DO k = nzb_w_inner(j,i)+1, nzt
285	w_l_l(k) = w_l_l(k) + w(k,j,i)
286	ENDDO
287	ENDDO
288	ENDDO
289	#if defined( __parallel )
290	IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr )
291	CALL MPI_ALLREDUCE( w_l_l(1), w_l(1), nzt, MPI_REAL, MPI_SUM, &
292	comm2d, ierr )
293	#else
294	w_l = w_l_l
295	#endif
296	DO k = 1, nzt
297	w_l(k) = w_l(k) / ngp_2dh_outer(k,0)
298	ENDDO
299	DO i = nxlg, nxrg
300	DO j = nysg, nyng
301	DO k = nzb_w_inner(j,i)+1, nzt
302	w(k,j,i) = w(k,j,i) - w_l(k)
303	ENDDO
304	ENDDO
305	ENDDO
306	ENDIF
307	ENDIF
308
309	!
310	!-- Compute the divergence of the provisional velocity field.
311	CALL cpu_log( log_point_s(1), 'divergence', 'start' )
312
313	IF ( psolver(1:9) == 'multigrid' ) THEN
314	!$OMP PARALLEL DO SCHEDULE( STATIC )
315	DO i = nxl-1, nxr+1
316	DO j = nys-1, nyn+1
317	DO k = nzb, nzt+1
318	d(k,j,i) = 0.0_wp
319	ENDDO
320	ENDDO
321	ENDDO
322	ELSE
323	!$OMP PARALLEL DO SCHEDULE( STATIC )
324	!$acc kernels present( d )
325	DO i = nxl, nxr
326	DO j = nys, nyn
327	DO k = nzb+1, nzt
328	d(k,j,i) = 0.0_wp
329	ENDDO
330	ENDDO
331	ENDDO
332	!$acc end kernels
333	ENDIF
334
335	localsum = 0.0_wp
336	threadsum = 0.0_wp
337
338	#if defined( __ibm )
339	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
340	!$OMP DO SCHEDULE( STATIC )
341	DO i = nxl, nxr
342	DO j = nys, nyn
343	DO k = nzb_s_inner(j,i)+1, nzt
344	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
345	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
346	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) ) * ddt_3d &
347	* d_weight_pres
348	ENDDO
349	!
350	!-- Compute possible PE-sum of divergences for flow_statistics
351	DO k = nzb_s_inner(j,i)+1, nzt
352	threadsum = threadsum + ABS( d(k,j,i) )
353	ENDDO
354
355	ENDDO
356	ENDDO
357
358	localsum = localsum + threadsum * dt_3d * &
359	weight_pres(intermediate_timestep_count)
360
361	!$OMP END PARALLEL
362	#else
363
364	!$OMP PARALLEL PRIVATE (i,j,k)
365	!$OMP DO SCHEDULE( STATIC )
366	!$acc kernels present( d, ddzw, rflags_s_inner, u, v, w )
367	!$acc loop collapse( 3 )
368	DO i = nxl, nxr
369	DO j = nys, nyn
370	DO k = 1, nzt
371	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
372	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
373	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) ) * ddt_3d &
374	* d_weight_pres * rflags_s_inner(k,j,i)
375	ENDDO
376	ENDDO
377	ENDDO
378	!$acc end kernels
379	!$OMP END PARALLEL
380
381	!
382	!-- Compute possible PE-sum of divergences for flow_statistics
383	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
384	!$OMP DO SCHEDULE( STATIC )
385	!$acc parallel loop collapse(3) present( d ) reduction(+:threadsum)
386	DO i = nxl, nxr
387	DO j = nys, nyn
388	DO k = nzb+1, nzt
389	threadsum = threadsum + ABS( d(k,j,i) )
390	ENDDO
391	ENDDO
392	ENDDO
393	!$acc end parallel loop
394	localsum = localsum + threadsum * dt_3d * &
395	weight_pres(intermediate_timestep_count)
396	!$OMP END PARALLEL
397	#endif
398
399	!
400	!-- For completeness, set the divergence sum of all statistic regions to those
401	!-- of the total domain
402	sums_divold_l(0:statistic_regions) = localsum
403
404	CALL cpu_log( log_point_s(1), 'divergence', 'stop' )
405
406	!
407	!-- Compute the pressure perturbation solving the Poisson equation
408	IF ( psolver == 'poisfft' ) THEN
409
410	!
411	!-- Solve Poisson equation via FFT and solution of tridiagonal matrices
412	CALL poisfft( d )
413
414	!
415	!-- Store computed perturbation pressure and set boundary condition in
416	!-- z-direction
417	!$OMP PARALLEL DO
418	!$acc kernels present( d, tend )
419	DO i = nxl, nxr
420	DO j = nys, nyn
421	DO k = nzb+1, nzt
422	tend(k,j,i) = d(k,j,i)
423	ENDDO
424	ENDDO
425	ENDDO
426	!$acc end kernels
427
428	!
429	!-- Bottom boundary:
430	!-- This condition is only required for internal output. The pressure
431	!-- gradient (dp(nzb+1)-dp(nzb))/dz is not used anywhere else.
432	IF ( ibc_p_b == 1 ) THEN
433	!
434	!-- Neumann (dp/dz = 0)
435	!$OMP PARALLEL DO
436	!$acc kernels present( nzb_s_inner, tend )
437	DO i = nxlg, nxrg
438	DO j = nysg, nyng
439	tend(nzb_s_inner(j,i),j,i) = tend(nzb_s_inner(j,i)+1,j,i)
440	ENDDO
441	ENDDO
442	!$acc end kernels
443
444	ELSE
445	!
446	!-- Dirichlet
447	!$OMP PARALLEL DO
448	!$acc kernels present( tend )
449	DO i = nxlg, nxrg
450	DO j = nysg, nyng
451	tend(nzb_s_inner(j,i),j,i) = 0.0_wp
452	ENDDO
453	ENDDO
454	!$acc end kernels
455
456	ENDIF
457
458	!
459	!-- Top boundary
460	IF ( ibc_p_t == 1 ) THEN
461	!
462	!-- Neumann
463	!$OMP PARALLEL DO
464	!$acc kernels present( tend )
465	DO i = nxlg, nxrg
466	DO j = nysg, nyng
467	tend(nzt+1,j,i) = tend(nzt,j,i)
468	ENDDO
469	ENDDO
470	!$acc end kernels
471
472	ELSE
473	!
474	!-- Dirichlet
475	!$OMP PARALLEL DO
476	!$acc kernels present( tend )
477	DO i = nxlg, nxrg
478	DO j = nysg, nyng
479	tend(nzt+1,j,i) = 0.0_wp
480	ENDDO
481	ENDDO
482	!$acc end kernels
483
484	ENDIF
485
486	!
487	!-- Exchange boundaries for p
488	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
489	on_device = .TRUE. ! to be removed after complete porting
490	ELSE ! of ghost point exchange
491	!$acc update host( tend )
492	ENDIF
493	CALL exchange_horiz( tend, nbgp )
494	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
495	on_device = .FALSE. ! to be removed after complete porting
496	ELSE ! of ghost point exchange
497	!$acc update device( tend )
498	ENDIF
499
500	ELSEIF ( psolver == 'sor' ) THEN
501
502	!
503	!-- Solve Poisson equation for perturbation pressure using SOR-Red/Black
504	!-- scheme
505	CALL sor( d, ddzu_pres, ddzw, p_loc )
506	tend = p_loc
507
508	ELSEIF ( psolver(1:9) == 'multigrid' ) THEN
509
510	!
511	!-- Solve Poisson equation for perturbation pressure using Multigrid scheme,
512	!-- array tend is used to store the residuals, logical exchange_mg is used
513	!-- to discern data exchange in multigrid ( 1 ghostpoint ) and normal grid
514	!-- ( nbgp ghost points ).
515
516	!-- If the number of grid points of the gathered grid, which is collected
517	!-- on PE0, is larger than the number of grid points of an PE, than array
518	!-- tend will be enlarged.
519	IF ( gathered_size > subdomain_size ) THEN
520	DEALLOCATE( tend )
521	ALLOCATE( tend(nzb:nzt_mg(mg_switch_to_pe0_level)+1,nys_mg( &
522	mg_switch_to_pe0_level)-1:nyn_mg(mg_switch_to_pe0_level)+1,&
523	nxl_mg(mg_switch_to_pe0_level)-1:nxr_mg( &
524	mg_switch_to_pe0_level)+1) )
525	ENDIF
526
527	IF ( psolver == 'multigrid' ) THEN
528	CALL poismg( tend )
529	ELSE
530	CALL poismg_fast( tend )
531	ENDIF
532
533	IF ( gathered_size > subdomain_size ) THEN
534	DEALLOCATE( tend )
535	ALLOCATE( tend(nzb:nzt+1,nysg:nyng,nxlg:nxrg) )
536	ENDIF
537
538	!
539	!-- Restore perturbation pressure on tend because this array is used
540	!-- further below to correct the velocity fields
541	DO i = nxl-1, nxr+1
542	DO j = nys-1, nyn+1
543	DO k = nzb, nzt+1
544	tend(k,j,i) = p_loc(k,j,i)
545	ENDDO
546	ENDDO
547	ENDDO
548
549	ENDIF
550
551	!
552	!-- Store perturbation pressure on array p, used for pressure data output.
553	!-- Ghost layers are added in the output routines (except sor-method: see below)
554	IF ( intermediate_timestep_count == 1 ) THEN
555	!$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	!$acc loop independent
563	DO k = nzb, nzt+1
564	p(k,j,i) = tend(k,j,i) * &
565	weight_substep(intermediate_timestep_count)
566	ENDDO
567	ENDDO
568	ENDDO
569	!$acc end kernels
570	!$OMP END PARALLEL
571
572	ELSEIF ( intermediate_timestep_count > 1 ) THEN
573	!$OMP PARALLEL PRIVATE (i,j,k)
574	!$OMP DO
575	!$acc kernels present( p, tend, weight_substep )
576	!$acc loop independent
577	DO i = nxl-1, nxr+1
578	!$acc loop independent
579	DO j = nys-1, nyn+1
580	!$acc loop independent
581	DO k = nzb, nzt+1
582	p(k,j,i) = p(k,j,i) + tend(k,j,i) * &
583	weight_substep(intermediate_timestep_count)
584	ENDDO
585	ENDDO
586	ENDDO
587	!$acc end kernels
588	!$OMP END PARALLEL
589
590	ENDIF
591
592	!
593	!-- SOR-method needs ghost layers for the next timestep
594	IF ( psolver == 'sor' ) CALL exchange_horiz( p, nbgp )
595
596	!
597	!-- Correction of the provisional velocities with the current perturbation
598	!-- pressure just computed
599	IF ( conserve_volume_flow .AND. ( bc_lr_cyc .OR. bc_ns_cyc ) ) THEN
600	volume_flow_l(1) = 0.0_wp
601	volume_flow_l(2) = 0.0_wp
602	ENDIF
603
604	!$OMP PARALLEL PRIVATE (i,j,k)
605	!$OMP DO
606	!$acc kernels present( ddzu, nzb_u_inner, nzb_v_inner, nzb_w_inner, tend, u, v, w, weight_pres )
607	!$acc loop independent
608	DO i = nxl, nxr
609	!$acc loop independent
610	DO j = nys, nyn
611	!$acc loop independent
612	DO k = 1, nzt
613	IF ( k > nzb_w_inner(j,i) ) THEN
614	w(k,j,i) = w(k,j,i) - dt_3d * &
615	( tend(k+1,j,i) - tend(k,j,i) ) * ddzu(k+1) * &
616	weight_pres(intermediate_timestep_count)
617	ENDIF
618	ENDDO
619	!$acc loop independent
620	DO k = 1, nzt
621	IF ( k > nzb_u_inner(j,i) ) THEN
622	u(k,j,i) = u(k,j,i) - dt_3d * &
623	( tend(k,j,i) - tend(k,j,i-1) ) * ddx * &
624	weight_pres(intermediate_timestep_count)
625	ENDIF
626	ENDDO
627	!$acc loop independent
628	DO k = 1, nzt
629	IF ( k > nzb_v_inner(j,i) ) THEN
630	v(k,j,i) = v(k,j,i) - dt_3d * &
631	( tend(k,j,i) - tend(k,j-1,i) ) * ddy * &
632	weight_pres(intermediate_timestep_count)
633	ENDIF
634	ENDDO
635
636	ENDDO
637	ENDDO
638	!$acc end kernels
639	!$OMP END PARALLEL
640
641	!
642	!-- Sum up the volume flow through the right and north boundary
643	IF ( conserve_volume_flow .AND. bc_lr_cyc .AND. bc_ns_cyc .AND. &
644	nxr == nx ) THEN
645
646	!$OMP PARALLEL PRIVATE (j,k)
647	!$OMP DO
648	DO j = nys, nyn
649	!$OMP CRITICAL
650	DO k = nzb_2d(j,nx) + 1, nzt
651	volume_flow_l(1) = volume_flow_l(1) + u(k,j,nx) * dzw(k)
652	ENDDO
653	!$OMP END CRITICAL
654	ENDDO
655	!$OMP END PARALLEL
656
657	ENDIF
658
659	IF ( conserve_volume_flow .AND. bc_ns_cyc .AND. bc_lr_cyc .AND. &
660	nyn == ny ) THEN
661
662	!$OMP PARALLEL PRIVATE (i,k)
663	!$OMP DO
664	DO i = nxl, nxr
665	!$OMP CRITICAL
666	DO k = nzb_2d(ny,i) + 1, nzt
667	volume_flow_l(2) = volume_flow_l(2) + v(k,ny,i) * dzw(k)
668	ENDDO
669	!$OMP END CRITICAL
670	ENDDO
671	!$OMP END PARALLEL
672
673	ENDIF
674
675	!
676	!-- Conserve the volume flow
677	IF ( conserve_volume_flow .AND. ( bc_lr_cyc .AND. bc_ns_cyc ) ) THEN
678
679	#if defined( __parallel )
680	IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr )
681	CALL MPI_ALLREDUCE( volume_flow_l(1), volume_flow(1), 2, MPI_REAL, &
682	MPI_SUM, comm2d, ierr )
683	#else
684	volume_flow = volume_flow_l
685	#endif
686
687	volume_flow_offset(1:2) = ( volume_flow_initial(1:2) - volume_flow(1:2) ) / &
688	volume_flow_area(1:2)
689
690	!$OMP PARALLEL PRIVATE (i,j,k)
691	!$OMP DO
692	DO i = nxl, nxr
693	DO j = nys, nyn
694	DO k = nzb_u_inner(j,i) + 1, nzt
695	u(k,j,i) = u(k,j,i) + volume_flow_offset(1)
696	ENDDO
697	DO k = nzb_v_inner(j,i) + 1, nzt
698	v(k,j,i) = v(k,j,i) + volume_flow_offset(2)
699	ENDDO
700	ENDDO
701	ENDDO
702
703	!$OMP END PARALLEL
704
705	ENDIF
706
707	!
708	!-- Exchange of boundaries for the velocities
709	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
710	on_device = .TRUE. ! to be removed after complete porting
711	ELSE ! of ghost point exchange
712	!$acc update host( u, v, w )
713	ENDIF
714	CALL exchange_horiz( u, nbgp )
715	CALL exchange_horiz( v, nbgp )
716	CALL exchange_horiz( w, nbgp )
717	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
718	on_device = .FALSE. ! to be removed after complete porting
719	ELSE ! of ghost point exchange
720	!$acc update device( u, v, w )
721	ENDIF
722
723	!
724	!-- Compute the divergence of the corrected velocity field,
725	!-- a possible PE-sum is computed in flow_statistics
726	CALL cpu_log( log_point_s(1), 'divergence', 'start' )
727	sums_divnew_l = 0.0_wp
728
729	!
730	!-- d must be reset to zero because it can contain nonzero values below the
731	!-- topography
732	IF ( topography /= 'flat' ) d = 0.0_wp
733
734	localsum = 0.0_wp
735	threadsum = 0.0_wp
736
737	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
738	!$OMP DO SCHEDULE( STATIC )
739	#if defined( __ibm )
740	DO i = nxl, nxr
741	DO j = nys, nyn
742	DO k = nzb_s_inner(j,i)+1, nzt
743	d(k,j,i) = ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
744	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
745	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k)
746	ENDDO
747	DO k = nzb+1, nzt
748	threadsum = threadsum + ABS( d(k,j,i) )
749	ENDDO
750	ENDDO
751	ENDDO
752	#else
753	!$acc kernels present( d, ddzw, rflags_s_inner, u, v, w )
754	!$acc loop collapse( 3 )
755	DO i = nxl, nxr
756	DO j = nys, nyn
757	DO k = 1, nzt
758	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
759	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
760	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) &
761	) * rflags_s_inner(k,j,i)
762	ENDDO
763	ENDDO
764	ENDDO
765	!$acc end kernels
766	!
767	!-- Compute possible PE-sum of divergences for flow_statistics
768	!$acc parallel loop collapse(3) present( d ) reduction(+:threadsum)
769	DO i = nxl, nxr
770	DO j = nys, nyn
771	DO k = nzb+1, nzt
772	threadsum = threadsum + ABS( d(k,j,i) )
773	ENDDO
774	ENDDO
775	ENDDO
776	!$acc end parallel loop
777	#endif
778
779	localsum = localsum + threadsum
780	!$OMP END PARALLEL
781
782	!
783	!-- For completeness, set the divergence sum of all statistic regions to those
784	!-- of the total domain
785	sums_divnew_l(0:statistic_regions) = localsum
786
787	CALL cpu_log( log_point_s(1), 'divergence', 'stop' )
788
789	CALL cpu_log( log_point(8), 'pres', 'stop' )
790
791
792	END SUBROUTINE pres

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