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source: palm/trunk/SOURCE/pres.f90 @ 1925

Last change on this file since 1925 was 1919, checked in by raasch, 8 years ago
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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 1919 2016-05-27 14:51:23Z hellstea $
26	!
27	! 1918 2016-05-27 14:35:57Z raasch
28	! sum of divergence is also calculated when pres is called before the initial
29	! first time step,
30	! stearing is modified by using intermediate_timestep_count = 0 in order to
31	! determine if pres is called before the first initial timestep,
32	! bugfix: in case of Neumann conditions for pressure both at bottom and top,
33	! mean vertical velocity is also removed for the first time step
34	! bugfix for calculating divergences
35	!
36	! 1908 2016-05-25 17:22:32Z suehring
37	! New divergence for output into RUN_CONTROL file is calculated only at last
38	! Runge-Kutta step
39	!
40	! 1845 2016-04-08 08:29:13Z raasch
41	! nzb_2d replace by nzb_u\|v_inner
42	!
43	! 1799 2016-04-05 08:35:55Z gronemeier
44	! Bugfix: excluded third dimension from horizontal volume flow calculation
45	!
46	! 1762 2016-02-25 12:31:13Z hellstea
47	! Introduction of nested domain feature
48	!
49	! 1682 2015-10-07 23:56:08Z knoop
50	! Code annotations made doxygen readable
51	!
52	! 1575 2015-03-27 09:56:27Z raasch
53	! poismg_fast + respective module added, adjustments for psolver-queries
54	!
55	! 1342 2014-03-26 17:04:47Z kanani
56	! REAL constants defined as wp-kind
57	!
58	! 1320 2014-03-20 08:40:49Z raasch
59	! ONLY-attribute added to USE-statements,
60	! kind-parameters added to all INTEGER and REAL declaration statements,
61	! kinds are defined in new module kinds,
62	! old module precision_kind is removed,
63	! revision history before 2012 removed,
64	! comment fields (!:) to be used for variable explanations added to
65	! all variable declaration statements
66	!
67	! 1318 2014-03-17 13:35:16Z raasch
68	! module interfaces removed
69	!
70	! 1306 2014-03-13 14:30:59Z raasch
71	! second argument removed from routine poisfft
72	!
73	! 1257 2013-11-08 15:18:40Z raasch
74	! openacc loop and loop vector clauses removed, independent clauses added,
75	! end parallel replaced by end parallel loop
76	!
77	! 1221 2013-09-10 08:59:13Z raasch
78	! openACC porting of reduction operations, loops for calculating d are
79	! using the rflags_s_inner multiply flag instead of the nzb_s_inner loop index
80	!
81	! 1212 2013-08-15 08:46:27Z raasch
82	! call of poisfft_hybrid removed
83	!
84	! 1117 2013-03-27 11:15:36Z suehring
85	! Bugfix in OpenMP parallelization.
86	!
87	! 1113 2013-03-10 02:48:14Z raasch
88	! GPU-porting of several loops, some loops rearranged
89	!
90	! 1111 2013-03-08 23:54:10Z
91	! openACC statements added,
92	! ibc_p_b = 2 removed
93	!
94	! 1092 2013-02-02 11:24:22Z raasch
95	! unused variables removed
96	!
97	! 1036 2012-10-22 13:43:42Z raasch
98	! code put under GPL (PALM 3.9)
99	!
100	! 1003 2012-09-14 14:35:53Z raasch
101	! adjustment of array tend for cases with unequal subdomain sizes removed
102	!
103	! Revision 1.1 1997/07/24 11:24:44 raasch
104	! Initial revision
105	!
106	!
107	! Description:
108	! ------------
109	!> Compute the divergence of the provisional velocity field. Solve the Poisson
110	!> equation for the perturbation pressure. Compute the final velocities using
111	!> this perturbation pressure. Compute the remaining divergence.
112	!------------------------------------------------------------------------------!
113	SUBROUTINE pres
114
115
116	USE arrays_3d, &
117	ONLY: d, ddzu, ddzu_pres, ddzw, dzw, p, p_loc, tend, u, v, w
118
119	USE control_parameters, &
120	ONLY: bc_lr_cyc, bc_ns_cyc, conserve_volume_flow, dt_3d, &
121	gathered_size, ibc_p_b, ibc_p_t, intermediate_timestep_count, &
122	intermediate_timestep_count_max, mg_switch_to_pe0_level, &
123	nest_domain, nest_bound_l, nest_bound_n, nest_bound_r, &
124	nest_bound_s, on_device, outflow_l, outflow_n, outflow_r, &
125	outflow_s, psolver, subdomain_size, topography, volume_flow, &
126	volume_flow_area, volume_flow_initial
127
128	USE cpulog, &
129	ONLY: cpu_log, log_point, log_point_s
130
131	USE grid_variables, &
132	ONLY: ddx, ddy
133
134	USE indices, &
135	ONLY: nbgp, ngp_2dh_outer, nx, nxl, nxlg, nxl_mg, nxr, nxrg, nxr_mg, &
136	ny, nys, nysg, nys_mg, nyn, nyng, nyn_mg, nzb, nzb_s_inner, &
137	nzb_u_inner, nzb_v_inner, nzb_w_inner, nzt, nzt_mg, &
138	rflags_s_inner
139
140	USE kinds
141
142	USE pegrid
143
144	USE poisfft_mod, &
145	ONLY: poisfft
146
147	USE poismg_mod
148
149	USE statistics, &
150	ONLY: statistic_regions, sums_divnew_l, sums_divold_l, weight_pres, &
151	weight_substep
152
153	IMPLICIT NONE
154
155	INTEGER(iwp) :: i !<
156	INTEGER(iwp) :: j !<
157	INTEGER(iwp) :: k !<
158
159	REAL(wp) :: ddt_3d !<
160	REAL(wp) :: d_weight_pres !<
161	REAL(wp) :: localsum !<
162	REAL(wp) :: threadsum !<
163	REAL(wp) :: weight_pres_l !<
164
165	REAL(wp), DIMENSION(1:3) :: volume_flow_l !<
166	REAL(wp), DIMENSION(1:3) :: volume_flow_offset !<
167	REAL(wp), DIMENSION(1:nzt) :: w_l !<
168	REAL(wp), DIMENSION(1:nzt) :: w_l_l !<
169
170
171	CALL cpu_log( log_point(8), 'pres', 'start' )
172
173
174	!
175	!-- Calculate quantities to be used locally
176	ddt_3d = 1.0_wp / dt_3d
177	IF ( intermediate_timestep_count == 0 ) THEN
178	!
179	!-- If pres is called before initial time step
180	weight_pres_l = 1.0_wp
181	d_weight_pres = 1.0_wp
182	ELSE
183	weight_pres_l = weight_pres(intermediate_timestep_count)
184	d_weight_pres = 1.0_wp / weight_pres(intermediate_timestep_count)
185	ENDIF
186
187	!
188	!-- Multigrid method expects array d to have one ghost layer.
189	!--
190	IF ( psolver(1:9) == 'multigrid' ) THEN
191
192	DEALLOCATE( d )
193	ALLOCATE( d(nzb:nzt+1,nys-1:nyn+1,nxl-1:nxr+1) )
194
195	!
196	!-- Since p is later used to hold the weighted average of the substeps, it
197	!-- cannot be used in the iterative solver. Therefore, its initial value is
198	!-- stored on p_loc, which is then iteratively advanced in every substep.
199	IF ( intermediate_timestep_count <= 1 ) THEN
200	DO i = nxl-1, nxr+1
201	DO j = nys-1, nyn+1
202	DO k = nzb, nzt+1
203	p_loc(k,j,i) = p(k,j,i)
204	ENDDO
205	ENDDO
206	ENDDO
207	ENDIF
208
209	ELSEIF ( psolver == 'sor' .AND. intermediate_timestep_count <= 1 ) THEN
210
211	!
212	!-- Since p is later used to hold the weighted average of the substeps, it
213	!-- cannot be used in the iterative solver. Therefore, its initial value is
214	!-- stored on p_loc, which is then iteratively advanced in every substep.
215	p_loc = p
216
217	ENDIF
218
219	!
220	!-- Conserve the volume flow at the outflow in case of non-cyclic lateral
221	!-- boundary conditions
222	!-- WARNING: so far, this conservation does not work at the left/south
223	!-- boundary if the topography at the inflow differs from that at the
224	!-- outflow! For this case, volume_flow_area needs adjustment!
225	!
226	!-- Left/right
227	IF ( conserve_volume_flow .AND. ( outflow_l .OR. outflow_r ) ) THEN
228
229	volume_flow(1) = 0.0_wp
230	volume_flow_l(1) = 0.0_wp
231
232	IF ( outflow_l ) THEN
233	i = 0
234	ELSEIF ( outflow_r ) THEN
235	i = nx+1
236	ENDIF
237
238	DO j = nys, nyn
239	!
240	!-- Sum up the volume flow through the south/north boundary
241	DO k = nzb_u_inner(j,i)+1, nzt
242	volume_flow_l(1) = volume_flow_l(1) + u(k,j,i) * dzw(k)
243	ENDDO
244	ENDDO
245
246	#if defined( __parallel )
247	IF ( collective_wait ) CALL MPI_BARRIER( comm1dy, ierr )
248	CALL MPI_ALLREDUCE( volume_flow_l(1), volume_flow(1), 1, MPI_REAL, &
249	MPI_SUM, comm1dy, ierr )
250	#else
251	volume_flow = volume_flow_l
252	#endif
253	volume_flow_offset(1) = ( volume_flow_initial(1) - volume_flow(1) ) &
254	/ volume_flow_area(1)
255
256	DO j = nysg, nyng
257	DO k = nzb_u_inner(j,i)+1, nzt
258	u(k,j,i) = u(k,j,i) + volume_flow_offset(1)
259	ENDDO
260	ENDDO
261
262	ENDIF
263
264	!
265	!-- South/north
266	IF ( conserve_volume_flow .AND. ( outflow_n .OR. outflow_s ) ) THEN
267
268	volume_flow(2) = 0.0_wp
269	volume_flow_l(2) = 0.0_wp
270
271	IF ( outflow_s ) THEN
272	j = 0
273	ELSEIF ( outflow_n ) THEN
274	j = ny+1
275	ENDIF
276
277	DO i = nxl, nxr
278	!
279	!-- Sum up the volume flow through the south/north boundary
280	DO k = nzb_v_inner(j,i)+1, nzt
281	volume_flow_l(2) = volume_flow_l(2) + v(k,j,i) * dzw(k)
282	ENDDO
283	ENDDO
284
285	#if defined( __parallel )
286	IF ( collective_wait ) CALL MPI_BARRIER( comm1dx, ierr )
287	CALL MPI_ALLREDUCE( volume_flow_l(2), volume_flow(2), 1, MPI_REAL, &
288	MPI_SUM, comm1dx, ierr )
289	#else
290	volume_flow = volume_flow_l
291	#endif
292	volume_flow_offset(2) = ( volume_flow_initial(2) - volume_flow(2) ) &
293	/ volume_flow_area(2)
294
295	DO i = nxlg, nxrg
296	DO k = nzb_v_inner(j,i)+1, nzt
297	v(k,j,i) = v(k,j,i) + volume_flow_offset(2)
298	ENDDO
299	ENDDO
300
301	ENDIF
302
303	!
304	!-- Remove mean vertical velocity in case that Neumann conditions are
305	!-- used both at bottom and top boundary, and if not a nested domain.
306	!-- This cannot be done before the first initial time step because ngp_2dh_outer
307	!-- is not yet known then.
308	IF ( ibc_p_b == 1 .AND. ibc_p_t == 1 .AND. .NOT. nest_domain .AND. &
309	intermediate_timestep_count /= 0 ) &
310	THEN
311	w_l = 0.0_wp; w_l_l = 0.0_wp
312	DO i = nxl, nxr
313	DO j = nys, nyn
314	DO k = nzb_w_inner(j,i)+1, nzt
315	w_l_l(k) = w_l_l(k) + w(k,j,i)
316	ENDDO
317	ENDDO
318	ENDDO
319	#if defined( __parallel )
320	IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr )
321	CALL MPI_ALLREDUCE( w_l_l(1), w_l(1), nzt, MPI_REAL, MPI_SUM, &
322	comm2d, ierr )
323	#else
324	w_l = w_l_l
325	#endif
326	DO k = 1, nzt
327	w_l(k) = w_l(k) / ngp_2dh_outer(k,0)
328	ENDDO
329	DO i = nxlg, nxrg
330	DO j = nysg, nyng
331	DO k = nzb_w_inner(j,i)+1, nzt
332	w(k,j,i) = w(k,j,i) - w_l(k)
333	ENDDO
334	ENDDO
335	ENDDO
336	ENDIF
337
338	!
339	!-- Compute the divergence of the provisional velocity field.
340	CALL cpu_log( log_point_s(1), 'divergence', 'start' )
341
342	IF ( psolver(1:9) == 'multigrid' ) THEN
343	!$OMP PARALLEL DO SCHEDULE( STATIC )
344	DO i = nxl-1, nxr+1
345	DO j = nys-1, nyn+1
346	DO k = nzb, nzt+1
347	d(k,j,i) = 0.0_wp
348	ENDDO
349	ENDDO
350	ENDDO
351	ELSE
352	!$OMP PARALLEL DO SCHEDULE( STATIC )
353	!$acc kernels present( d )
354	DO i = nxl, nxr
355	DO j = nys, nyn
356	DO k = nzb+1, nzt
357	d(k,j,i) = 0.0_wp
358	ENDDO
359	ENDDO
360	ENDDO
361	!$acc end kernels
362	ENDIF
363
364	localsum = 0.0_wp
365	threadsum = 0.0_wp
366
367	#if defined( __ibm )
368	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
369	!$OMP DO SCHEDULE( STATIC )
370	DO i = nxl, nxr
371	DO j = nys, nyn
372	DO k = nzb_s_inner(j,i)+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
377	ENDDO
378	!
379	!-- Compute possible PE-sum of divergences for flow_statistics
380	DO k = nzb_s_inner(j,i)+1, nzt
381	threadsum = threadsum + ABS( d(k,j,i) )
382	ENDDO
383
384	ENDDO
385	ENDDO
386
387	IF ( intermediate_timestep_count == intermediate_timestep_count_max .OR. &
388	intermediate_timestep_count == 0 ) THEN
389	localsum = localsum + threadsum * dt_3d * weight_pres_l
390	ENDIF
391	!$OMP END PARALLEL
392	#else
393
394	!$OMP PARALLEL PRIVATE (i,j,k)
395	!$OMP DO SCHEDULE( STATIC )
396	!$acc kernels present( d, ddzw, rflags_s_inner, u, v, w )
397	!$acc loop collapse( 3 )
398	DO i = nxl, nxr
399	DO j = nys, nyn
400	DO k = 1, nzt
401	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
402	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
403	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) ) * ddt_3d &
404	* d_weight_pres * rflags_s_inner(k,j,i)
405	ENDDO
406	ENDDO
407	ENDDO
408	!$acc end kernels
409	!$OMP END PARALLEL
410
411	!
412	!-- Compute possible PE-sum of divergences for flow_statistics. Carry out
413	!-- computation only at last Runge-Kutta substep.
414	IF ( intermediate_timestep_count == intermediate_timestep_count_max .OR. &
415	intermediate_timestep_count == 0 ) THEN
416	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
417	!$OMP DO SCHEDULE( STATIC )
418	!$acc parallel loop collapse(3) present( d ) reduction(+:threadsum)
419	DO i = nxl, nxr
420	DO j = nys, nyn
421	DO k = nzb+1, nzt
422	threadsum = threadsum + ABS( d(k,j,i) )
423	ENDDO
424	ENDDO
425	ENDDO
426	!$acc end parallel loop
427	localsum = localsum + threadsum * dt_3d * weight_pres_l
428	!$OMP END PARALLEL
429	ENDIF
430	#endif
431
432	!
433	!-- For completeness, set the divergence sum of all statistic regions to those
434	!-- of the total domain
435	IF ( intermediate_timestep_count == intermediate_timestep_count_max .OR. &
436	intermediate_timestep_count == 0 ) THEN
437	sums_divold_l(0:statistic_regions) = localsum
438	ENDIF
439
440	CALL cpu_log( log_point_s(1), 'divergence', 'stop' )
441
442	!
443	!-- Compute the pressure perturbation solving the Poisson equation
444	IF ( psolver == 'poisfft' ) THEN
445
446	!
447	!-- Solve Poisson equation via FFT and solution of tridiagonal matrices
448	CALL poisfft( d )
449
450	!
451	!-- Store computed perturbation pressure and set boundary condition in
452	!-- z-direction
453	!$OMP PARALLEL DO
454	!$acc kernels present( d, tend )
455	DO i = nxl, nxr
456	DO j = nys, nyn
457	DO k = nzb+1, nzt
458	tend(k,j,i) = d(k,j,i)
459	ENDDO
460	ENDDO
461	ENDDO
462	!$acc end kernels
463
464	!
465	!-- Bottom boundary:
466	!-- This condition is only required for internal output. The pressure
467	!-- gradient (dp(nzb+1)-dp(nzb))/dz is not used anywhere else.
468	IF ( ibc_p_b == 1 ) THEN
469	!
470	!-- Neumann (dp/dz = 0)
471	!$OMP PARALLEL DO
472	!$acc kernels present( nzb_s_inner, tend )
473	DO i = nxlg, nxrg
474	DO j = nysg, nyng
475	tend(nzb_s_inner(j,i),j,i) = tend(nzb_s_inner(j,i)+1,j,i)
476	ENDDO
477	ENDDO
478	!$acc end kernels
479
480	ELSE
481	!
482	!-- Dirichlet
483	!$OMP PARALLEL DO
484	!$acc kernels present( tend )
485	DO i = nxlg, nxrg
486	DO j = nysg, nyng
487	tend(nzb_s_inner(j,i),j,i) = 0.0_wp
488	ENDDO
489	ENDDO
490	!$acc end kernels
491
492	ENDIF
493
494	!
495	!-- Top boundary
496	IF ( ibc_p_t == 1 ) THEN
497	!
498	!-- Neumann
499	!$OMP PARALLEL DO
500	!$acc kernels present( tend )
501	DO i = nxlg, nxrg
502	DO j = nysg, nyng
503	tend(nzt+1,j,i) = tend(nzt,j,i)
504	ENDDO
505	ENDDO
506	!$acc end kernels
507
508	ELSE
509	!
510	!-- Dirichlet
511	!$OMP PARALLEL DO
512	!$acc kernels present( tend )
513	DO i = nxlg, nxrg
514	DO j = nysg, nyng
515	tend(nzt+1,j,i) = 0.0_wp
516	ENDDO
517	ENDDO
518	!$acc end kernels
519
520	ENDIF
521
522	!
523	!-- Exchange boundaries for p
524	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
525	on_device = .TRUE. ! to be removed after complete porting
526	ELSE ! of ghost point exchange
527	!$acc update host( tend )
528	ENDIF
529	CALL exchange_horiz( tend, nbgp )
530	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
531	on_device = .FALSE. ! to be removed after complete porting
532	ELSE ! of ghost point exchange
533	!$acc update device( tend )
534	ENDIF
535
536	ELSEIF ( psolver == 'sor' ) THEN
537
538	!
539	!-- Solve Poisson equation for perturbation pressure using SOR-Red/Black
540	!-- scheme
541	CALL sor( d, ddzu_pres, ddzw, p_loc )
542	tend = p_loc
543
544	ELSEIF ( psolver(1:9) == 'multigrid' ) THEN
545
546	!
547	!-- Solve Poisson equation for perturbation pressure using Multigrid scheme,
548	!-- array tend is used to store the residuals, logical exchange_mg is used
549	!-- to discern data exchange in multigrid ( 1 ghostpoint ) and normal grid
550	!-- ( nbgp ghost points ).
551
552	!-- If the number of grid points of the gathered grid, which is collected
553	!-- on PE0, is larger than the number of grid points of an PE, than array
554	!-- tend will be enlarged.
555	IF ( gathered_size > subdomain_size ) THEN
556	DEALLOCATE( tend )
557	ALLOCATE( tend(nzb:nzt_mg(mg_switch_to_pe0_level)+1,nys_mg( &
558	mg_switch_to_pe0_level)-1:nyn_mg(mg_switch_to_pe0_level)+1,&
559	nxl_mg(mg_switch_to_pe0_level)-1:nxr_mg( &
560	mg_switch_to_pe0_level)+1) )
561	ENDIF
562
563	IF ( psolver == 'multigrid' ) THEN
564	CALL poismg( tend )
565	ELSE
566	CALL poismg_fast( tend )
567	ENDIF
568
569	IF ( gathered_size > subdomain_size ) THEN
570	DEALLOCATE( tend )
571	ALLOCATE( tend(nzb:nzt+1,nysg:nyng,nxlg:nxrg) )
572	ENDIF
573
574	!
575	!-- Restore perturbation pressure on tend because this array is used
576	!-- further below to correct the velocity fields
577	DO i = nxl-1, nxr+1
578	DO j = nys-1, nyn+1
579	DO k = nzb, nzt+1
580	tend(k,j,i) = p_loc(k,j,i)
581	ENDDO
582	ENDDO
583	ENDDO
584
585	ENDIF
586
587	!
588	!-- Store perturbation pressure on array p, used for pressure data output.
589	!-- Ghost layers are added in the output routines (except sor-method: see below)
590	IF ( intermediate_timestep_count <= 1 ) THEN
591	!$OMP PARALLEL PRIVATE (i,j,k)
592	!$OMP DO
593	!$acc kernels present( p, tend, weight_substep )
594	!$acc loop independent
595	DO i = nxl-1, nxr+1
596	!$acc loop independent
597	DO j = nys-1, nyn+1
598	!$acc loop independent
599	DO k = nzb, nzt+1
600	p(k,j,i) = tend(k,j,i) * &
601	weight_substep(intermediate_timestep_count)
602	ENDDO
603	ENDDO
604	ENDDO
605	!$acc end kernels
606	!$OMP END PARALLEL
607
608	ELSEIF ( intermediate_timestep_count > 1 ) THEN
609	!$OMP PARALLEL PRIVATE (i,j,k)
610	!$OMP DO
611	!$acc kernels present( p, tend, weight_substep )
612	!$acc loop independent
613	DO i = nxl-1, nxr+1
614	!$acc loop independent
615	DO j = nys-1, nyn+1
616	!$acc loop independent
617	DO k = nzb, nzt+1
618	p(k,j,i) = p(k,j,i) + tend(k,j,i) * &
619	weight_substep(intermediate_timestep_count)
620	ENDDO
621	ENDDO
622	ENDDO
623	!$acc end kernels
624	!$OMP END PARALLEL
625
626	ENDIF
627
628	!
629	!-- SOR-method needs ghost layers for the next timestep
630	IF ( psolver == 'sor' ) CALL exchange_horiz( p, nbgp )
631
632	!
633	!-- Correction of the provisional velocities with the current perturbation
634	!-- pressure just computed
635	IF ( conserve_volume_flow .AND. ( bc_lr_cyc .OR. bc_ns_cyc ) ) THEN
636	volume_flow_l(1) = 0.0_wp
637	volume_flow_l(2) = 0.0_wp
638	ENDIF
639
640	!$OMP PARALLEL PRIVATE (i,j,k)
641	!$OMP DO
642	!$acc kernels present( ddzu, nzb_u_inner, nzb_v_inner, nzb_w_inner, tend, u, v, w )
643	!$acc loop independent
644	DO i = nxl, nxr
645	!$acc loop independent
646	DO j = nys, nyn
647	!$acc loop independent
648	DO k = 1, nzt
649	IF ( k > nzb_w_inner(j,i) ) THEN
650	w(k,j,i) = w(k,j,i) - dt_3d * &
651	( tend(k+1,j,i) - tend(k,j,i) ) * ddzu(k+1) * &
652	weight_pres_l
653	ENDIF
654	ENDDO
655	!$acc loop independent
656	DO k = 1, nzt
657	IF ( k > nzb_u_inner(j,i) ) THEN
658	u(k,j,i) = u(k,j,i) - dt_3d * &
659	( tend(k,j,i) - tend(k,j,i-1) ) * ddx * &
660	weight_pres_l
661	ENDIF
662	ENDDO
663	!$acc loop independent
664	DO k = 1, nzt
665	IF ( k > nzb_v_inner(j,i) ) THEN
666	v(k,j,i) = v(k,j,i) - dt_3d * &
667	( tend(k,j,i) - tend(k,j-1,i) ) * ddy * &
668	weight_pres_l
669	ENDIF
670	ENDDO
671
672	ENDDO
673	ENDDO
674	!$acc end kernels
675	!$OMP END PARALLEL
676
677	!
678	!-- Sum up the volume flow through the right and north boundary
679	IF ( conserve_volume_flow .AND. bc_lr_cyc .AND. bc_ns_cyc .AND. &
680	nxr == nx ) THEN
681
682	!$OMP PARALLEL PRIVATE (j,k)
683	!$OMP DO
684	DO j = nys, nyn
685	!$OMP CRITICAL
686	DO k = nzb_u_inner(j,nx) + 1, nzt
687	volume_flow_l(1) = volume_flow_l(1) + u(k,j,nx) * dzw(k)
688	ENDDO
689	!$OMP END CRITICAL
690	ENDDO
691	!$OMP END PARALLEL
692
693	ENDIF
694
695	IF ( conserve_volume_flow .AND. bc_ns_cyc .AND. bc_lr_cyc .AND. &
696	nyn == ny ) THEN
697
698	!$OMP PARALLEL PRIVATE (i,k)
699	!$OMP DO
700	DO i = nxl, nxr
701	!$OMP CRITICAL
702	DO k = nzb_v_inner(ny,i) + 1, nzt
703	volume_flow_l(2) = volume_flow_l(2) + v(k,ny,i) * dzw(k)
704	ENDDO
705	!$OMP END CRITICAL
706	ENDDO
707	!$OMP END PARALLEL
708
709	ENDIF
710
711	!
712	!-- Conserve the volume flow
713	IF ( conserve_volume_flow .AND. ( bc_lr_cyc .AND. bc_ns_cyc ) ) THEN
714
715	#if defined( __parallel )
716	IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr )
717	CALL MPI_ALLREDUCE( volume_flow_l(1), volume_flow(1), 2, MPI_REAL, &
718	MPI_SUM, comm2d, ierr )
719	#else
720	volume_flow = volume_flow_l
721	#endif
722
723	volume_flow_offset(1:2) = ( volume_flow_initial(1:2) - volume_flow(1:2) ) / &
724	volume_flow_area(1:2)
725
726	!$OMP PARALLEL PRIVATE (i,j,k)
727	!$OMP DO
728	DO i = nxl, nxr
729	DO j = nys, nyn
730	DO k = nzb_u_inner(j,i) + 1, nzt
731	u(k,j,i) = u(k,j,i) + volume_flow_offset(1)
732	ENDDO
733	DO k = nzb_v_inner(j,i) + 1, nzt
734	v(k,j,i) = v(k,j,i) + volume_flow_offset(2)
735	ENDDO
736	ENDDO
737	ENDDO
738
739	!$OMP END PARALLEL
740
741	ENDIF
742
743	!
744	!-- Exchange of boundaries for the velocities
745	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
746	on_device = .TRUE. ! to be removed after complete porting
747	ELSE ! of ghost point exchange
748	!$acc update host( u, v, w )
749	ENDIF
750	CALL exchange_horiz( u, nbgp )
751	CALL exchange_horiz( v, nbgp )
752	CALL exchange_horiz( w, nbgp )
753	IF ( numprocs == 1 ) THEN ! workaround for single-core GPU runs
754	on_device = .FALSE. ! to be removed after complete porting
755	ELSE ! of ghost point exchange
756	!$acc update device( u, v, w )
757	ENDIF
758
759	!
760	!-- Compute the divergence of the corrected velocity field,
761	!-- A possible PE-sum is computed in flow_statistics. Carry out computation
762	!-- only at last Runge-Kutta step.
763	IF ( intermediate_timestep_count == intermediate_timestep_count_max .OR. &
764	intermediate_timestep_count == 0 ) THEN
765	CALL cpu_log( log_point_s(1), 'divergence', 'start' )
766	sums_divnew_l = 0.0_wp
767
768	!
769	!-- d must be reset to zero because it can contain nonzero values below the
770	!-- topography
771	IF ( topography /= 'flat' ) d = 0.0_wp
772
773	localsum = 0.0_wp
774	threadsum = 0.0_wp
775
776	!$OMP PARALLEL PRIVATE (i,j,k) FIRSTPRIVATE(threadsum) REDUCTION(+:localsum)
777	!$OMP DO SCHEDULE( STATIC )
778	#if defined( __ibm )
779	DO i = nxl, nxr
780	DO j = nys, nyn
781	DO k = nzb_s_inner(j,i)+1, nzt
782	d(k,j,i) = ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
783	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
784	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k)
785	ENDDO
786	DO k = nzb+1, nzt
787	threadsum = threadsum + ABS( d(k,j,i) )
788	ENDDO
789	ENDDO
790	ENDDO
791	#else
792	!$acc kernels present( d, ddzw, rflags_s_inner, u, v, w )
793	!$acc loop collapse( 3 )
794	DO i = nxl, nxr
795	DO j = nys, nyn
796	DO k = 1, nzt
797	d(k,j,i) = ( ( u(k,j,i+1) - u(k,j,i) ) * ddx + &
798	( v(k,j+1,i) - v(k,j,i) ) * ddy + &
799	( w(k,j,i) - w(k-1,j,i) ) * ddzw(k) &
800	) * rflags_s_inner(k,j,i)
801	ENDDO
802	ENDDO
803	ENDDO
804	!$acc end kernels
805	!
806	!-- Compute possible PE-sum of divergences for flow_statistics
807	!$acc parallel loop collapse(3) present( d ) reduction(+:threadsum)
808	DO i = nxl, nxr
809	DO j = nys, nyn
810	DO k = nzb+1, nzt
811	threadsum = threadsum + ABS( d(k,j,i) )
812	ENDDO
813	ENDDO
814	ENDDO
815	!$acc end parallel loop
816	#endif
817
818	localsum = localsum + threadsum
819	!$OMP END PARALLEL
820
821	!
822	!-- For completeness, set the divergence sum of all statistic regions to those
823	!-- of the total domain
824	sums_divnew_l(0:statistic_regions) = localsum
825
826	CALL cpu_log( log_point_s(1), 'divergence', 'stop' )
827
828	ENDIF
829
830	CALL cpu_log( log_point(8), 'pres', 'stop' )
831
832
833	END SUBROUTINE pres

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