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source: palm/trunk/SOURCE/pres.f90 @ 1268

Last change on this file since 1268 was 1258, checked in by raasch, 11 years ago
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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 1997-2012 Leibniz University Hannover
18	!--------------------------------------------------------------------------------!
19	!
20	! Current revisions:
21	! ------------------
22	!
23	!
24	! Former revisions:
25	! -----------------
26	! $Id: pres.f90 1258 2013-11-08 16:09:09Z heinze $
27	!
28	! 1257 2013-11-08 15:18:40Z raasch
29	! openacc loop and loop vector clauses removed, independent clauses added,
30	! end parallel replaced by end parallel loop
31	!
32	! 1221 2013-09-10 08:59:13Z raasch
33	! openACC porting of reduction operations, loops for calculating d are
34	! using the rflags_s_inner multiply flag instead of the nzb_s_inner loop index
35	!
36	! 1212 2013-08-15 08:46:27Z raasch
37	! call of poisfft_hybrid removed
38	!
39	! 1117 2013-03-27 11:15:36Z suehring
40	! Bugfix in OpenMP parallelization.
41	!
42	! 1113 2013-03-10 02:48:14Z raasch
43	! GPU-porting of several loops, some loops rearranged
44	!
45	! 1111 2013-03-08 23:54:10Z
46	! openACC statements added,
47	! ibc_p_b = 2 removed
48	!
49	! 1092 2013-02-02 11:24:22Z raasch
50	! unused variables removed
51	!
52	! 1036 2012-10-22 13:43:42Z raasch
53	! code put under GPL (PALM 3.9)
54	!
55	! 1003 2012-09-14 14:35:53Z raasch
56	! adjustment of array tend for cases with unequal subdomain sizes removed
57	!
58	! 778 2011-11-07 14:18:25Z fricke
59	! New allocation of tend when multigrid is used and the collected field on PE0
60	! has more grid points than the subdomain of an PE.
61	!
62	! 719 2011-04-06 13:05:23Z gryschka
63	! Bugfix in volume flow control for double cyclic boundary conditions
64	!
65	! 709 2011-03-30 09:31:40Z raasch
66	! formatting adjustments
67	!
68	! 707 2011-03-29 11:39:40Z raasch
69	! Calculation of weighted average of p is now handled in the same way
70	! regardless of the number of ghost layers (advection scheme),
71	! multigrid and sor method are using p_loc for iterative advancements of
72	! pressure,
73	! localsum calculation modified for proper OpenMP reduction,
74	! bc_lr/ns replaced by bc_lr/ns_cyc
75	!
76	! 693 2011-03-08 09:..:..Z raasch
77	! bugfix: weighting coefficient added to ibm branch
78	!
79	! 680 2011-02-04 23:16:06Z gryschka
80	! bugfix: collective_wait
81	!
82	! 675 2011-01-19 10:56:55Z suehring
83	! Removed bugfix while copying tend.
84	!
85	! 673 2011-01-18 16:19:48Z suehring
86	! Weighting coefficients added for right computation of the pressure during
87	! Runge-Kutta substeps.
88	!
89	! 667 2010-12-23 12:06:00Z suehring/gryschka
90	! New allocation of tend when ws-scheme and multigrid is used. This is due to
91	! reasons of perforance of the data_exchange. The same is done with p after
92	! poismg is called.
93	! nxl-1, nxr+1, nys-1, nyn+1 replaced by nxlg, nxrg, nysg, nyng when no
94	! multigrid is used. Calls of exchange_horiz are modified.
95	! bugfix: After pressure correction no volume flow correction in case of
96	! non-cyclic boundary conditions
97	! (has to be done only before pressure correction)
98	! Call of SOR routine is referenced with ddzu_pres.
99	!
100	! 622 2010-12-10 08:08:13Z raasch
101	! optional barriers included in order to speed up collective operations
102	!
103	! 151 2008-03-07 13:42:18Z raasch
104	! Bugfix in volume flow control for non-cyclic boundary conditions
105	!
106	! 106 2007-08-16 14:30:26Z raasch
107	! Volume flow conservation added for the remaining three outflow boundaries
108	!
109	! 85 2007-05-11 09:35:14Z raasch
110	! Division through dt_3d replaced by multiplication of the inverse.
111	! For performance optimisation, this is done in the loop calculating the
112	! divergence instead of using a seperate loop.
113	!
114	! 75 2007-03-22 09:54:05Z raasch
115	! Volume flow control for non-cyclic boundary conditions added (currently only
116	! for the north boundary!!), 2nd+3rd argument removed from exchange horiz,
117	! mean vertical velocity is removed in case of Neumann boundary conditions
118	! both at the bottom and the top
119	!
120	! RCS Log replace by Id keyword, revision history cleaned up
121	!
122	! Revision 1.25 2006/04/26 13:26:12 raasch
123	! OpenMP optimization (+localsum, threadsum)
124	!
125	! Revision 1.1 1997/07/24 11:24:44 raasch
126	! Initial revision
127	!
128	!
129	! Description:
130	! ------------
131	! Compute the divergence of the provisional velocity field. Solve the Poisson
132	! equation for the perturbation pressure. Compute the final velocities using
133	! this perturbation pressure. Compute the remaining divergence.
134	!------------------------------------------------------------------------------!
135
136	USE arrays_3d
137	USE constants
138	USE control_parameters
139	USE cpulog
140	USE grid_variables
141	USE indices
142	USE interfaces
143	USE pegrid
144	USE poisfft_mod
145	USE statistics
146
147	IMPLICIT NONE
148
149	INTEGER :: i, j, k
150
151	REAL :: ddt_3d, localsum, threadsum, d_weight_pres
152
153	REAL, DIMENSION(1:2) :: volume_flow_l, volume_flow_offset
154	REAL, DIMENSION(1:nzt) :: w_l, w_l_l
155
156
157	CALL cpu_log( log_point(8), 'pres', 'start' )
158
159
160	ddt_3d = 1.0 / dt_3d
161	d_weight_pres = 1.0 / weight_pres(intermediate_timestep_count)
162
163	!
164	!-- Multigrid method expects array d to have one ghost layer.
165	!--
166	IF ( psolver == 'multigrid' ) THEN
167
168	DEALLOCATE( d )
169	ALLOCATE( d(nzb:nzt+1,nys-1:nyn+1,nxl-1:nxr+1) )
170
171	!
172	!-- Since p is later used to hold the weighted average of the substeps, it
173	!-- cannot be used in the iterative solver. Therefore, its initial value is
174	!-- stored on p_loc, which is then iteratively advanced in every substep.
175	IF ( intermediate_timestep_count == 1 ) THEN
176	DO i = nxl-1, nxr+1
177	DO j = nys-1, nyn+1
178	DO k = nzb, nzt+1
179	p_loc(k,j,i) = p(k,j,i)
180	ENDDO
181	ENDDO
182	ENDDO
183	ENDIF
184
185	ELSEIF ( psolver == 'sor' .AND. intermediate_timestep_count == 1 ) THEN
186
187	!
188	!-- Since p is later used to hold the weighted average of the substeps, it
189	!-- cannot be used in the iterative solver. Therefore, its initial value is
190	!-- stored on p_loc, which is then iteratively advanced in every substep.
191	p_loc = p
192
193	ENDIF
194
195	!
196	!-- Conserve the volume flow at the outflow in case of non-cyclic lateral
197	!-- boundary conditions
198	!-- WARNING: so far, this conservation does not work at the left/south
199	!-- boundary if the topography at the inflow differs from that at the
200	!-- outflow! For this case, volume_flow_area needs adjustment!
201	!
202	!-- Left/right
203	IF ( conserve_volume_flow .AND. ( outflow_l .OR. outflow_r ) ) THEN
204
205	volume_flow(1) = 0.0
206	volume_flow_l(1) = 0.0
207
208	IF ( outflow_l ) THEN
209	i = 0
210	ELSEIF ( outflow_r ) THEN
211	i = nx+1
212	ENDIF
213
214	DO j = nys, nyn
215	!
216	!-- Sum up the volume flow through the south/north boundary
217	DO k = nzb_2d(j,i)+1, nzt
218	volume_flow_l(1) = volume_flow_l(1) + u(k,j,i) * dzw(k)
219	ENDDO
220	ENDDO
221
222	#if defined( __parallel )
223	IF ( collective_wait ) CALL MPI_BARRIER( comm1dy, ierr )
224	CALL MPI_ALLREDUCE( volume_flow_l(1), volume_flow(1), 1, MPI_REAL, &
225	MPI_SUM, comm1dy, ierr )
226	#else
227	volume_flow = volume_flow_l
228	#endif
229	volume_flow_offset(1) = ( volume_flow_initial(1) - volume_flow(1) ) &
230	/ volume_flow_area(1)
231
232	DO j = nysg, nyng
233	DO k = nzb_2d(j,i)+1, nzt
234	u(k,j,i) = u(k,j,i) + volume_flow_offset(1)
235	ENDDO
236	ENDDO
237
238	ENDIF
239
240	!
241	!-- South/north
242	IF ( conserve_volume_flow .AND. ( outflow_n .OR. outflow_s ) ) THEN
243
244	volume_flow(2) = 0.0
245	volume_flow_l(2) = 0.0
246
247	IF ( outflow_s ) THEN
248	j = 0
249	ELSEIF ( outflow_n ) THEN
250	j = ny+1
251	ENDIF
252
253	DO i = nxl, nxr
254	!
255	!-- Sum up the volume flow through the south/north boundary
256	DO k = nzb_2d(j,i)+1, nzt
257	volume_flow_l(2) = volume_flow_l(2) + v(k,j,i) * dzw(k)
258	ENDDO
259	ENDDO
260
261	#if defined( __parallel )
262	IF ( collective_wait ) CALL MPI_BARRIER( comm1dx, ierr )
263	CALL MPI_ALLREDUCE( volume_flow_l(2), volume_flow(2), 1, MPI_REAL, &
264	MPI_SUM, comm1dx, ierr )
265	#else
266	volume_flow = volume_flow_l
267	#endif
268	volume_flow_offset(2) = ( volume_flow_initial(2) - volume_flow(2) ) &
269	/ volume_flow_area(2)
270
271	DO i = nxlg, nxrg
272	DO k = nzb_v_inner(j,i)+1, nzt
273	v(k,j,i) = v(k,j,i) + volume_flow_offset(2)
274	ENDDO
275	ENDDO
276
277	ENDIF
278
279	!
280	!-- Remove mean vertical velocity
281	IF ( ibc_p_b == 1 .AND. ibc_p_t == 1 ) THEN
282	IF ( simulated_time > 0.0 ) THEN ! otherwise nzb_w_inner not yet known
283	w_l = 0.0; w_l_l = 0.0
284	DO i = nxl, nxr
285	DO j = nys, nyn
286	DO k = nzb_w_inner(j,i)+1, nzt
287	w_l_l(k) = w_l_l(k) + w(k,j,i)
288	ENDDO
289	ENDDO
290	ENDDO
291	#if defined( __parallel )
292	IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr )
293	CALL MPI_ALLREDUCE( w_l_l(1), w_l(1), nzt, MPI_REAL, MPI_SUM, &
294	comm2d, ierr )
295	#else
296	w_l = w_l_l
297	#endif
298	DO k = 1, nzt
299	w_l(k) = w_l(k) / ngp_2dh_outer(k,0)
300	ENDDO
301	DO i = nxlg, nxrg
302	DO j = nysg, nyng
303	DO k = nzb_w_inner(j,i)+1, nzt
304	w(k,j,i) = w(k,j,i) - w_l(k)
305	ENDDO
306	ENDDO
307	ENDDO
308	ENDIF
309	ENDIF
310
311	!
312	!-- Compute the divergence of the provisional velocity field.
313	CALL cpu_log( log_point_s(1), 'divergence', 'start' )
314
315	IF ( psolver == 'multigrid' ) THEN
316	!$OMP PARALLEL DO SCHEDULE( STATIC )
317	DO i = nxl-1, nxr+1
318	DO j = nys-1, nyn+1
319	DO k = nzb, nzt+1
320	d(k,j,i) = 0.0
321	ENDDO
322	ENDDO
323	ENDDO
324	ELSE
325	!$OMP PARALLEL DO SCHEDULE( STATIC )
326	!$acc kernels present( d )
327	DO i = nxl, nxr
328	DO j = nys, nyn
329	DO k = nzb+1, nzt
330	d(k,j,i) = 0.0
331	ENDDO
332	ENDDO
333	ENDDO
334	!$acc end kernels
335	ENDIF
336
337	localsum = 0.0
338	threadsum = 0.0
339
340	#if defined( __ibm )
341	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
342	!$OMP DO SCHEDULE( STATIC )
343	DO i = nxl, nxr
344	DO j = nys, nyn
345	DO k = nzb_s_inner(j,i)+1, nzt
346	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
347	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
348	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) ) * ddt_3d &
349	* d_weight_pres
350	ENDDO
351	!
352	!-- Compute possible PE-sum of divergences for flow_statistics
353	DO k = nzb_s_inner(j,i)+1, nzt
354	threadsum = threadsum + ABS( d(k,j,i) )
355	ENDDO
356
357	ENDDO
358	ENDDO
359
360	localsum = localsum + threadsum * dt_3d * &
361	weight_pres(intermediate_timestep_count)
362
363	!$OMP END PARALLEL
364	#else
365
366	!$OMP PARALLEL PRIVATE (i,j,k)
367	!$OMP DO SCHEDULE( STATIC )
368	!$acc kernels present( d, ddzw, rflags_s_inner, u, v, w )
369	!$acc loop collapse( 3 )
370	DO i = nxl, nxr
371	DO j = nys, nyn
372	DO k = 1, nzt
373	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
374	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
375	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) ) * ddt_3d &
376	* d_weight_pres * rflags_s_inner(k,j,i)
377	ENDDO
378	ENDDO
379	ENDDO
380	!$acc end kernels
381	!$OMP END PARALLEL
382
383	!
384	!-- Compute possible PE-sum of divergences for flow_statistics
385	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
386	!$OMP DO SCHEDULE( STATIC )
387	!$acc parallel loop collapse(3) present( d ) reduction(+:threadsum)
388	DO i = nxl, nxr
389	DO j = nys, nyn
390	DO k = nzb+1, nzt
391	threadsum = threadsum + ABS( d(k,j,i) )
392	ENDDO
393	ENDDO
394	ENDDO
395	!$acc end parallel loop
396	localsum = localsum + threadsum * dt_3d * &
397	weight_pres(intermediate_timestep_count)
398	!$OMP END PARALLEL
399	#endif
400
401	!
402	!-- For completeness, set the divergence sum of all statistic regions to those
403	!-- of the total domain
404	sums_divold_l(0:statistic_regions) = localsum
405
406	CALL cpu_log( log_point_s(1), 'divergence', 'stop' )
407
408	!
409	!-- Compute the pressure perturbation solving the Poisson equation
410	IF ( psolver(1:7) == 'poisfft' ) THEN
411
412	!
413	!-- Solve Poisson equation via FFT and solution of tridiagonal matrices
414	IF ( psolver == 'poisfft' ) THEN
415
416	CALL poisfft( d, tend )
417
418	ENDIF
419
420	!
421	!-- Store computed perturbation pressure and set boundary condition in
422	!-- z-direction
423	!$OMP PARALLEL DO
424	!$acc kernels present( d, tend )
425	DO i = nxl, nxr
426	DO j = nys, nyn
427	DO k = nzb+1, nzt
428	tend(k,j,i) = d(k,j,i)
429	ENDDO
430	ENDDO
431	ENDDO
432	!$acc end kernels
433
434	!
435	!-- Bottom boundary:
436	!-- This condition is only required for internal output. The pressure
437	!-- gradient (dp(nzb+1)-dp(nzb))/dz is not used anywhere else.
438	IF ( ibc_p_b == 1 ) THEN
439	!
440	!-- Neumann (dp/dz = 0)
441	!$OMP PARALLEL DO
442	!$acc kernels present( nzb_s_inner, tend )
443	DO i = nxlg, nxrg
444	DO j = nysg, nyng
445	tend(nzb_s_inner(j,i),j,i) = tend(nzb_s_inner(j,i)+1,j,i)
446	ENDDO
447	ENDDO
448	!$acc end kernels
449
450	ELSE
451	!
452	!-- Dirichlet
453	!$OMP PARALLEL DO
454	!$acc kernels present( tend )
455	DO i = nxlg, nxrg
456	DO j = nysg, nyng
457	tend(nzb_s_inner(j,i),j,i) = 0.0
458	ENDDO
459	ENDDO
460	!$acc end kernels
461
462	ENDIF
463
464	!
465	!-- Top boundary
466	IF ( ibc_p_t == 1 ) THEN
467	!
468	!-- Neumann
469	!$OMP PARALLEL DO
470	!$acc kernels present( tend )
471	DO i = nxlg, nxrg
472	DO j = nysg, nyng
473	tend(nzt+1,j,i) = tend(nzt,j,i)
474	ENDDO
475	ENDDO
476	!$acc end kernels
477
478	ELSE
479	!
480	!-- Dirichlet
481	!$OMP PARALLEL DO
482	!$acc kernels present( tend )
483	DO i = nxlg, nxrg
484	DO j = nysg, nyng
485	tend(nzt+1,j,i) = 0.0
486	ENDDO
487	ENDDO
488	!$acc end kernels
489
490	ENDIF
491
492	!
493	!-- Exchange boundaries for p
494	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
495	on_device = .TRUE. ! to be removed after complete porting
496	ELSE ! of ghost point exchange
497	!$acc update host( tend )
498	ENDIF
499	CALL exchange_horiz( tend, nbgp )
500	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
501	on_device = .FALSE. ! to be removed after complete porting
502	ELSE ! of ghost point exchange
503	!$acc update device( tend )
504	ENDIF
505
506	ELSEIF ( psolver == 'sor' ) THEN
507
508	!
509	!-- Solve Poisson equation for perturbation pressure using SOR-Red/Black
510	!-- scheme
511	CALL sor( d, ddzu_pres, ddzw, p_loc )
512	tend = p_loc
513
514	ELSEIF ( psolver == 'multigrid' ) THEN
515
516	!
517	!-- Solve Poisson equation for perturbation pressure using Multigrid scheme,
518	!-- array tend is used to store the residuals, logical exchange_mg is used
519	!-- to discern data exchange in multigrid ( 1 ghostpoint ) and normal grid
520	!-- ( nbgp ghost points ).
521
522	!-- If the number of grid points of the gathered grid, which is collected
523	!-- on PE0, is larger than the number of grid points of an PE, than array
524	!-- tend will be enlarged.
525	IF ( gathered_size > subdomain_size ) THEN
526	DEALLOCATE( tend )
527	ALLOCATE( tend(nzb:nzt_mg(mg_switch_to_pe0_level)+1,nys_mg( &
528	mg_switch_to_pe0_level)-1:nyn_mg(mg_switch_to_pe0_level)+1,&
529	nxl_mg(mg_switch_to_pe0_level)-1:nxr_mg( &
530	mg_switch_to_pe0_level)+1) )
531	ENDIF
532
533	CALL poismg( tend )
534
535	IF ( gathered_size > subdomain_size ) THEN
536	DEALLOCATE( tend )
537	ALLOCATE( tend(nzb:nzt+1,nysg:nyng,nxlg:nxrg) )
538	ENDIF
539
540	!
541	!-- Restore perturbation pressure on tend because this array is used
542	!-- further below to correct the velocity fields
543	DO i = nxl-1, nxr+1
544	DO j = nys-1, nyn+1
545	DO k = nzb, nzt+1
546	tend(k,j,i) = p_loc(k,j,i)
547	ENDDO
548	ENDDO
549	ENDDO
550
551	ENDIF
552
553	!
554	!-- Store perturbation pressure on array p, used for pressure data output.
555	!-- Ghost layers are added in the output routines (except sor-method: see below)
556	IF ( intermediate_timestep_count == 1 ) THEN
557	!$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	!$acc loop independent
565	DO k = nzb, nzt+1
566	p(k,j,i) = tend(k,j,i) * &
567	weight_substep(intermediate_timestep_count)
568	ENDDO
569	ENDDO
570	ENDDO
571	!$acc end kernels
572	!$OMP END PARALLEL
573
574	ELSE
575	!$OMP PARALLEL PRIVATE (i,j,k)
576	!$OMP DO
577	!$acc kernels present( p, tend, weight_substep )
578	!$acc loop independent
579	DO i = nxl-1, nxr+1
580	!$acc loop independent
581	DO j = nys-1, nyn+1
582	!$acc loop independent
583	DO k = nzb, nzt+1
584	p(k,j,i) = p(k,j,i) + tend(k,j,i) * &
585	weight_substep(intermediate_timestep_count)
586	ENDDO
587	ENDDO
588	ENDDO
589	!$acc end kernels
590	!$OMP END PARALLEL
591
592	ENDIF
593
594	!
595	!-- SOR-method needs ghost layers for the next timestep
596	IF ( psolver == 'sor' ) CALL exchange_horiz( p, nbgp )
597
598	!
599	!-- Correction of the provisional velocities with the current perturbation
600	!-- pressure just computed
601	IF ( conserve_volume_flow .AND. ( bc_lr_cyc .OR. bc_ns_cyc ) ) THEN
602	volume_flow_l(1) = 0.0
603	volume_flow_l(2) = 0.0
604	ENDIF
605
606	!$OMP PARALLEL PRIVATE (i,j,k)
607	!$OMP DO
608	!$acc kernels present( ddzu, nzb_u_inner, nzb_v_inner, nzb_w_inner, tend, u, v, w, weight_pres )
609	!$acc loop independent
610	DO i = nxl, nxr
611	!$acc loop independent
612	DO j = nys, nyn
613	!$acc loop independent
614	DO k = 1, nzt
615	IF ( k > nzb_w_inner(j,i) ) THEN
616	w(k,j,i) = w(k,j,i) - dt_3d * &
617	( tend(k+1,j,i) - tend(k,j,i) ) * ddzu(k+1) * &
618	weight_pres(intermediate_timestep_count)
619	ENDIF
620	ENDDO
621	!$acc loop independent
622	DO k = 1, nzt
623	IF ( k > nzb_u_inner(j,i) ) THEN
624	u(k,j,i) = u(k,j,i) - dt_3d * &
625	( tend(k,j,i) - tend(k,j,i-1) ) * ddx * &
626	weight_pres(intermediate_timestep_count)
627	ENDIF
628	ENDDO
629	!$acc loop independent
630	DO k = 1, nzt
631	IF ( k > nzb_v_inner(j,i) ) THEN
632	v(k,j,i) = v(k,j,i) - dt_3d * &
633	( tend(k,j,i) - tend(k,j-1,i) ) * ddy * &
634	weight_pres(intermediate_timestep_count)
635	ENDIF
636	ENDDO
637
638	ENDDO
639	ENDDO
640	!$acc end kernels
641	!$OMP END PARALLEL
642
643	!
644	!-- Sum up the volume flow through the right and north boundary
645	IF ( conserve_volume_flow .AND. bc_lr_cyc .AND. bc_ns_cyc .AND. &
646	nxr == nx ) THEN
647
648	!$OMP PARALLEL PRIVATE (j,k)
649	!$OMP DO
650	DO j = nys, nyn
651	!$OMP CRITICAL
652	DO k = nzb_2d(j,nx) + 1, nzt
653	volume_flow_l(1) = volume_flow_l(1) + u(k,j,nx) * dzw(k)
654	ENDDO
655	!$OMP END CRITICAL
656	ENDDO
657	!$OMP END PARALLEL
658
659	ENDIF
660
661	IF ( conserve_volume_flow .AND. bc_ns_cyc .AND. bc_lr_cyc .AND. &
662	nyn == ny ) THEN
663
664	!$OMP PARALLEL PRIVATE (i,k)
665	!$OMP DO
666	DO i = nxl, nxr
667	!$OMP CRITICAL
668	DO k = nzb_2d(ny,i) + 1, nzt
669	volume_flow_l(2) = volume_flow_l(2) + v(k,ny,i) * dzw(k)
670	ENDDO
671	!$OMP END CRITICAL
672	ENDDO
673	!$OMP END PARALLEL
674
675	ENDIF
676
677	!
678	!-- Conserve the volume flow
679	IF ( conserve_volume_flow .AND. ( bc_lr_cyc .AND. bc_ns_cyc ) ) THEN
680
681	#if defined( __parallel )
682	IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr )
683	CALL MPI_ALLREDUCE( volume_flow_l(1), volume_flow(1), 2, MPI_REAL, &
684	MPI_SUM, comm2d, ierr )
685	#else
686	volume_flow = volume_flow_l
687	#endif
688
689	volume_flow_offset = ( volume_flow_initial - volume_flow ) / &
690	volume_flow_area
691
692	!$OMP PARALLEL PRIVATE (i,j,k)
693	!$OMP DO
694	DO i = nxl, nxr
695	DO j = nys, nyn
696	DO k = nzb_u_inner(j,i) + 1, nzt
697	u(k,j,i) = u(k,j,i) + volume_flow_offset(1)
698	ENDDO
699	DO k = nzb_v_inner(j,i) + 1, nzt
700	v(k,j,i) = v(k,j,i) + volume_flow_offset(2)
701	ENDDO
702	ENDDO
703	ENDDO
704
705	!$OMP END PARALLEL
706
707	ENDIF
708
709	!
710	!-- Exchange of boundaries for the velocities
711	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
712	on_device = .TRUE. ! to be removed after complete porting
713	ELSE ! of ghost point exchange
714	!$acc update host( u, v, w )
715	ENDIF
716	CALL exchange_horiz( u, nbgp )
717	CALL exchange_horiz( v, nbgp )
718	CALL exchange_horiz( w, nbgp )
719	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
720	on_device = .FALSE. ! to be removed after complete porting
721	ELSE ! of ghost point exchange
722	!$acc update device( u, v, w )
723	ENDIF
724
725	!
726	!-- Compute the divergence of the corrected velocity field,
727	!-- a possible PE-sum is computed in flow_statistics
728	CALL cpu_log( log_point_s(1), 'divergence', 'start' )
729	sums_divnew_l = 0.0
730
731	!
732	!-- d must be reset to zero because it can contain nonzero values below the
733	!-- topography
734	IF ( topography /= 'flat' ) d = 0.0
735
736	localsum = 0.0
737	threadsum = 0.0
738
739	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
740	!$OMP DO SCHEDULE( STATIC )
741	#if defined( __ibm )
742	DO i = nxl, nxr
743	DO j = nys, nyn
744	DO k = nzb_s_inner(j,i)+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	ENDDO
749	DO k = nzb+1, nzt
750	threadsum = threadsum + ABS( d(k,j,i) )
751	ENDDO
752	ENDDO
753	ENDDO
754	#else
755	!$acc kernels present( d, ddzw, rflags_s_inner, u, v, w )
756	!$acc loop collapse( 3 )
757	DO i = nxl, nxr
758	DO j = nys, nyn
759	DO k = 1, nzt
760	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
761	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
762	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) &
763	) * rflags_s_inner(k,j,i)
764	ENDDO
765	ENDDO
766	ENDDO
767	!$acc end kernels
768	!
769	!-- Compute possible PE-sum of divergences for flow_statistics
770	!$acc parallel loop collapse(3) present( d ) reduction(+:threadsum)
771	DO i = nxl, nxr
772	DO j = nys, nyn
773	DO k = nzb+1, nzt
774	threadsum = threadsum + ABS( d(k,j,i) )
775	ENDDO
776	ENDDO
777	ENDDO
778	!$acc end parallel loop
779	#endif
780
781	localsum = localsum + threadsum
782	!$OMP END PARALLEL
783
784	!
785	!-- For completeness, set the divergence sum of all statistic regions to those
786	!-- of the total domain
787	sums_divnew_l(0:statistic_regions) = localsum
788
789	CALL cpu_log( log_point_s(1), 'divergence', 'stop' )
790
791	CALL cpu_log( log_point(8), 'pres', 'stop' )
792
793
794	END SUBROUTINE pres

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