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source: palm/trunk/SOURCE/lpm_boundary_conds.f90 @ 3196

Last change on this file since 3196 was 3189, checked in by Giersch, 6 years ago
Interpolation to particle position revised, indent revised, bugfix in calculation of the x/y indices for current particle position
Property svn:keywords set to `Id`
File size: 27.3 KB

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1	!> @file lpm_boundary_conds.f90
2	!------------------------------------------------------------------------------!
3	! This file is part of the PALM model system.
4	!
5	! PALM is free software: you can redistribute it and/or modify it under the
6	! terms of the GNU General Public License as published by the Free Software
7	! Foundation, either version 3 of the License, or (at your option) any later
8	! 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 1997-2018 Leibniz Universitaet Hannover
18	!------------------------------------------------------------------------------!
19	!
20	! Current revisions:
21	! -----------------
22	!
23	!
24	! Former revisions:
25	! -----------------
26	! $Id: lpm_boundary_conds.f90 3189 2018-08-06 13:18:55Z maronga $
27	! Bugfix in calculation of the x/y indices for current particle postion
28	!
29	! 3067 2018-06-12 14:04:34Z suehring
30	! Remove write statements
31	!
32	! 2801 2018-02-14 16:01:55Z thiele
33	! Introduce particle transfer in nested models.
34	!
35	! 2718 2018-01-02 08:49:38Z maronga
36	! Corrected "Former revisions" section
37	!
38	! 2701 2017-12-15 15:40:50Z suehring
39	! Changes from last commit documented
40	!
41	! 2698 2017-12-14 18:46:24Z suehring
42	! Particle reflections at downward-facing walls implemented. Moreover,
43	! reflections are adjusted to revised particle grid box location.
44	! (responsible Philipp Thiele)
45	!
46	! 2696 2017-12-14 17:12:51Z kanani
47	! Change in file header (GPL part)
48	!
49	! 2606 2017-11-10 10:36:31Z schwenkel
50	! Changed particle box locations: center of particle box now coincides
51	! with scalar grid point of same index.
52	! Renamed module and subroutines: lpm_pack_arrays_mod -> lpm_pack_and_sort_mod
53	! lpm_pack_all_arrays -> lpm_sort_in_subboxes, lpm_pack_arrays -> lpm_pack
54	! lpm_sort -> lpm_sort_timeloop_done
55	!
56	! 2318 2017-07-20 17:27:44Z suehring
57	! Get topography top index via Function call
58	!
59	! 2317 2017-07-20 17:27:19Z suehring
60	!
61	! 2232 2017-05-30 17:47:52Z suehring
62	! Adjustments to new topography and surface concept
63	! Rename character range into location, as range is an intrinsic.
64	!
65	! 2000 2016-08-20 18:09:15Z knoop
66	! Forced header and separation lines into 80 columns
67	!
68	! 1929 2016-06-09 16:25:25Z suehring
69	! Rewritten wall reflection
70	!
71	! 1822 2016-04-07 07:49:42Z hoffmann
72	! Tails removed. Unused variables removed.
73	!
74	! 1682 2015-10-07 23:56:08Z knoop
75	! Code annotations made doxygen readable
76	!
77	! 1359 2014-04-11 17:15:14Z hoffmann
78	! New particle structure integrated.
79	! Kind definition added to all floating point numbers.
80	!
81	! 1320 2014-03-20 08:40:49Z raasch
82	! ONLY-attribute added to USE-statements,
83	! kind-parameters added to all INTEGER and REAL declaration statements,
84	! kinds are defined in new module kinds,
85	! revision history before 2012 removed,
86	! comment fields (!:) to be used for variable explanations added to
87	! all variable declaration statements
88	!
89	! 1036 2012-10-22 13:43:42Z raasch
90	! code put under GPL (PALM 3.9)
91	!
92	! 849 2012-03-15 10:35:09Z raasch
93	! routine renamed lpm_boundary_conds, bottom and top boundary conditions
94	! included (former part of advec_particles)
95	!
96	! 824 2012-02-17 09:09:57Z raasch
97	! particle attributes speed_x\|y\|z_sgs renamed rvar1\|2\|3
98	!
99	! Initial version (2007/03/09)
100	!
101	! Description:
102	! ------------
103	!> Boundary conditions for the Lagrangian particles.
104	!> The routine consists of two different parts. One handles the bottom (flat)
105	!> and top boundary. In this part, also particles which exceeded their lifetime
106	!> are deleted.
107	!> The other part handles the reflection of particles from vertical walls.
108	!> This part was developed by Jin Zhang during 2006-2007.
109	!>
110	!> To do: Code structure for finding the t_index values and for checking the
111	!> ----- reflection conditions is basically the same for all four cases, so it
112	!> should be possible to further simplify/shorten it.
113	!>
114	!> THE WALLS PART OF THIS ROUTINE HAS NOT BEEN TESTED FOR OCEAN RUNS SO FAR!!!!
115	!> (see offset_ocean_*)
116	!------------------------------------------------------------------------------!
117	SUBROUTINE lpm_boundary_conds( location , i, j, k )
118
119
120	USE arrays_3d, &
121	ONLY: zu, zw
122
123	USE control_parameters, &
124	ONLY: dz, message_string, particle_maximum_age
125
126	USE cpulog, &
127	ONLY: cpu_log, log_point_s
128
129	USE grid_variables, &
130	ONLY: ddx, dx, ddy, dy
131
132	USE indices, &
133	ONLY: nxl, nxr, nyn, nys, nz, nzb, wall_flags_0,nyng,nysg
134
135	USE kinds
136
137	USE particle_attributes, &
138	ONLY: deleted_particles, ibc_par_b, ibc_par_t, number_of_particles, &
139	particles, particle_type, offset_ocean_nzt_m1, &
140	use_sgs_for_particles
141
142	USE pegrid
143
144	IMPLICIT NONE
145
146	CHARACTER (LEN=*) :: location !<
147
148	INTEGER(iwp), INTENT(IN) :: i !<
149	INTEGER(iwp), INTENT(IN) :: j !<
150	INTEGER(iwp), INTENT(IN) :: k !<
151
152	INTEGER(iwp) :: inc !< dummy for sorting algorithmus
153	INTEGER(iwp) :: ir !< dummy for sorting algorithmus
154	INTEGER(iwp) :: i1 !< grid index (x) of old particle position
155	INTEGER(iwp) :: i2 !< grid index (x) of current particle position
156	INTEGER(iwp) :: i3 !< grid index (x) of intermediate particle position
157	INTEGER(iwp) :: jr !< dummy for sorting algorithmus
158	INTEGER(iwp) :: j1 !< grid index (y) of old particle position
159	INTEGER(iwp) :: j2 !< grid index (y) of current particle position
160	INTEGER(iwp) :: j3 !< grid index (y) of intermediate particle position
161	INTEGER(iwp) :: k1 !< grid index (z) of old particle position
162	INTEGER(iwp) :: k2 !< grid index (z) of current particle position
163	INTEGER(iwp) :: k3 !< grid index (z) of intermediate particle position
164	INTEGER(iwp) :: n !< particle number
165	INTEGER(iwp) :: t_index !< running index for intermediate particle timesteps in reflection algorithmus
166	INTEGER(iwp) :: t_index_number !< number of intermediate particle timesteps in reflection algorithmus
167	INTEGER(iwp) :: tmp_x !< dummy for sorting algorithm
168	INTEGER(iwp) :: tmp_y !< dummy for sorting algorithm
169	INTEGER(iwp) :: tmp_z !< dummy for sorting algorithm
170
171	INTEGER(iwp), DIMENSION(0:10) :: x_ind(0:10) = 0 !< index array (x) of intermediate particle positions
172	INTEGER(iwp), DIMENSION(0:10) :: y_ind(0:10) = 0 !< index array (y) of intermediate particle positions
173	INTEGER(iwp), DIMENSION(0:10) :: z_ind(0:10) = 0 !< index array (z) of intermediate particle positions
174
175	LOGICAL :: cross_wall_x !< flag to check if particle reflection along x is necessary
176	LOGICAL :: cross_wall_y !< flag to check if particle reflection along y is necessary
177	LOGICAL :: cross_wall_z !< flag to check if particle reflection along z is necessary
178	LOGICAL :: reflect_x !< flag to check if particle is already reflected along x
179	LOGICAL :: reflect_y !< flag to check if particle is already reflected along y
180	LOGICAL :: reflect_z !< flag to check if particle is already reflected along z
181	LOGICAL :: tmp_reach_x !< dummy for sorting algorithmus
182	LOGICAL :: tmp_reach_y !< dummy for sorting algorithmus
183	LOGICAL :: tmp_reach_z !< dummy for sorting algorithmus
184	LOGICAL :: x_wall_reached !< flag to check if particle has already reached wall
185	LOGICAL :: y_wall_reached !< flag to check if particle has already reached wall
186	LOGICAL :: z_wall_reached !< flag to check if particle has already reached wall
187
188	LOGICAL, DIMENSION(0:10) :: reach_x !< flag to check if particle is at a yz-wall
189	LOGICAL, DIMENSION(0:10) :: reach_y !< flag to check if particle is at a xz-wall
190	LOGICAL, DIMENSION(0:10) :: reach_z !< flag to check if particle is at a xy-wall
191
192	REAL(wp) :: dt_particle !< particle timestep
193	REAL(wp) :: dum !< dummy argument
194	REAL(wp) :: eps = 1E-10_wp !< security number to check if particle has reached a wall
195	REAL(wp) :: pos_x !< intermediate particle position (x)
196	REAL(wp) :: pos_x_old !< particle position (x) at previous particle timestep
197	REAL(wp) :: pos_y !< intermediate particle position (y)
198	REAL(wp) :: pos_y_old !< particle position (y) at previous particle timestep
199	REAL(wp) :: pos_z !< intermediate particle position (z)
200	REAL(wp) :: pos_z_old !< particle position (z) at previous particle timestep
201	REAL(wp) :: prt_x !< current particle position (x)
202	REAL(wp) :: prt_y !< current particle position (y)
203	REAL(wp) :: prt_z !< current particle position (z)
204	REAL(wp) :: t_old !< previous reflection time
205	REAL(wp) :: tmp_t !< dummy for sorting algorithmus
206	REAL(wp) :: xwall !< location of wall in x
207	REAL(wp) :: ywall !< location of wall in y
208	REAL(wp) :: zwall !< location of wall in z
209
210	REAL(wp), DIMENSION(0:10) :: t !< reflection time
211
212
213	IF ( location == 'bottom/top' ) THEN
214
215	!
216	!-- Apply boundary conditions to those particles that have crossed the top or
217	!-- bottom boundary and delete those particles, which are older than allowed
218	DO n = 1, number_of_particles
219
220	!
221	!-- Stop if particles have moved further than the length of one
222	!-- PE subdomain (newly released particles have age = age_m!)
223	IF ( particles(n)%age /= particles(n)%age_m ) THEN
224	IF ( ABS(particles(n)%speed_x) > &
225	((nxr-nxl+2)*dx)/(particles(n)%age-particles(n)%age_m) .OR. &
226	ABS(particles(n)%speed_y) > &
227	((nyn-nys+2)*dy)/(particles(n)%age-particles(n)%age_m) ) THEN
228
229	WRITE( message_string, * ) 'particle too fast. n = ', n
230	CALL message( 'lpm_boundary_conds', 'PA0148', 2, 2, -1, 6, 1 )
231	ENDIF
232	ENDIF
233
234	IF ( particles(n)%age > particle_maximum_age .AND. &
235	particles(n)%particle_mask ) &
236	THEN
237	particles(n)%particle_mask = .FALSE.
238	deleted_particles = deleted_particles + 1
239	ENDIF
240
241	IF ( particles(n)%z >= zw(nz) .AND. particles(n)%particle_mask ) THEN
242	IF ( ibc_par_t == 1 ) THEN
243	!
244	!-- Particle absorption
245	particles(n)%particle_mask = .FALSE.
246	deleted_particles = deleted_particles + 1
247	ELSEIF ( ibc_par_t == 2 ) THEN
248	!
249	!-- Particle reflection
250	particles(n)%z = 2.0_wp * zw(nz) - particles(n)%z
251	particles(n)%speed_z = -particles(n)%speed_z
252	IF ( use_sgs_for_particles .AND. &
253	particles(n)%rvar3 > 0.0_wp ) THEN
254	particles(n)%rvar3 = -particles(n)%rvar3
255	ENDIF
256	ENDIF
257	ENDIF
258
259	IF ( particles(n)%z < zw(0) .AND. particles(n)%particle_mask ) THEN
260	IF ( ibc_par_b == 1 ) THEN
261	!
262	!-- Particle absorption
263	particles(n)%particle_mask = .FALSE.
264	deleted_particles = deleted_particles + 1
265	ELSEIF ( ibc_par_b == 2 ) THEN
266	!
267	!-- Particle reflection
268	particles(n)%z = 2.0_wp * zw(0) - particles(n)%z
269	particles(n)%speed_z = -particles(n)%speed_z
270	IF ( use_sgs_for_particles .AND. &
271	particles(n)%rvar3 < 0.0_wp ) THEN
272	particles(n)%rvar3 = -particles(n)%rvar3
273	ENDIF
274	ENDIF
275	ENDIF
276	ENDDO
277
278	ELSEIF ( location == 'walls' ) THEN
279
280
281	CALL cpu_log( log_point_s(48), 'lpm_wall_reflect', 'start' )
282
283	DO n = 1, number_of_particles
284	!
285	!-- Recalculate particle timestep
286	dt_particle = particles(n)%age - particles(n)%age_m
287	!
288	!-- Obtain x/y indices for current particle position
289	i2 = particles(n)%x * ddx
290	j2 = particles(n)%y * ddy
291	IF (zw(k) < particles(n)%z ) k2 = k + 1
292	IF (zw(k) > particles(n)%z .AND. zw(k-1) < particles(n)%z ) k2 = k
293	IF (zw(k-1) > particles(n)%z ) k2 = k - 1
294	!
295	!-- Save current particle positions
296	prt_x = particles(n)%x
297	prt_y = particles(n)%y
298	prt_z = particles(n)%z
299	!
300	!-- Recalculate old particle positions
301	pos_x_old = particles(n)%x - particles(n)%speed_x * dt_particle
302	pos_y_old = particles(n)%y - particles(n)%speed_y * dt_particle
303	pos_z_old = particles(n)%z - particles(n)%speed_z * dt_particle
304	!
305	!-- Obtain x/y indices for old particle positions
306	i1 = i
307	j1 = j
308	k1 = k
309	!
310	!-- Determine horizontal as well as vertical walls at which particle can
311	!-- be potentially reflected.
312	!-- Start with walls aligned in yz layer.
313	!-- Wall to the right
314	IF ( prt_x > pos_x_old ) THEN
315	xwall = ( i1 + 1 ) * dx
316	!
317	!-- Wall to the left
318	ELSE
319	xwall = i1 * dx
320	ENDIF
321	!
322	!-- Walls aligned in xz layer
323	!-- Wall to the north
324	IF ( prt_y > pos_y_old ) THEN
325	ywall = ( j1 +1 ) * dy
326	!-- Wall to the south
327	ELSE
328	ywall = j1 * dy
329	ENDIF
330
331	IF ( prt_z > pos_z_old ) THEN
332	zwall = zw(k)
333	ELSE
334	zwall = zw(k-1)
335	ENDIF
336	!
337	!-- Initialize flags to check if particle reflection is necessary
338	cross_wall_x = .FALSE.
339	cross_wall_y = .FALSE.
340	cross_wall_z = .FALSE.
341	!
342	!-- Initialize flags to check if a wall is reached
343	reach_x = .FALSE.
344	reach_y = .FALSE.
345	reach_z = .FALSE.
346	!
347	!-- Initialize flags to check if a particle was already reflected
348	reflect_x = .FALSE.
349	reflect_y = .FALSE.
350	reflect_z = .FALSE.
351	!
352	!-- Initialize flags to check if a wall is already crossed.
353	!-- ( Required to obtain correct indices. )
354	x_wall_reached = .FALSE.
355	y_wall_reached = .FALSE.
356	z_wall_reached = .FALSE.
357	!
358	!-- Initialize time array
359	t = 0.0_wp
360	!
361	!-- Check if particle can reach any wall. This case, calculate the
362	!-- fractional time needed to reach this wall. Store this fractional
363	!-- timestep in array t. Moreover, store indices for these grid
364	!-- boxes where the respective wall belongs to.
365	!-- Start with x-direction.
366	t_index = 1
367	t(t_index) = ( xwall - pos_x_old ) &
368	/ MERGE( MAX( prt_x - pos_x_old, 1E-30_wp ), &
369	MIN( prt_x - pos_x_old, -1E-30_wp ), &
370	prt_x > pos_x_old )
371	x_ind(t_index) = i2
372	y_ind(t_index) = j1
373	z_ind(t_index) = k1
374	reach_x(t_index) = .TRUE.
375	reach_y(t_index) = .FALSE.
376	reach_z(t_index) = .FALSE.
377	!
378	!-- Store these values only if particle really reaches any wall. t must
379	!-- be in a interval between [0:1].
380	IF ( t(t_index) <= 1.0_wp .AND. t(t_index) >= 0.0_wp ) THEN
381	t_index = t_index + 1
382	cross_wall_x = .TRUE.
383	ENDIF
384	!
385	!-- y-direction
386	t(t_index) = ( ywall - pos_y_old ) &
387	/ MERGE( MAX( prt_y - pos_y_old, 1E-30_wp ), &
388	MIN( prt_y - pos_y_old, -1E-30_wp ), &
389	prt_y > pos_y_old )
390	x_ind(t_index) = i1
391	y_ind(t_index) = j2
392	z_ind(t_index) = k1
393	reach_x(t_index) = .FALSE.
394	reach_y(t_index) = .TRUE.
395	reach_z(t_index) = .FALSE.
396	IF ( t(t_index) <= 1.0_wp .AND. t(t_index) >= 0.0_wp ) THEN
397	t_index = t_index + 1
398	cross_wall_y = .TRUE.
399	ENDIF
400	!
401	!-- z-direction
402	t(t_index) = (zwall - pos_z_old ) &
403	/ MERGE( MAX( prt_z - pos_z_old, 1E-30_wp ), &
404	MIN( prt_z - pos_z_old, -1E-30_wp ), &
405	prt_z > pos_z_old )
406
407	x_ind(t_index) = i1
408	y_ind(t_index) = j1
409	z_ind(t_index) = k2
410	reach_x(t_index) = .FALSE.
411	reach_y(t_index) = .FALSE.
412	reach_z(t_index) = .TRUE.
413	IF( t(t_index) <= 1.0_wp .AND. t(t_index) >= 0.0_wp) THEN
414	t_index = t_index + 1
415	cross_wall_z = .TRUE.
416	ENDIF
417
418	t_index_number = t_index - 1
419	!
420	!-- Carry out reflection only if particle reaches any wall
421	IF ( cross_wall_x .OR. cross_wall_y .OR. cross_wall_z ) THEN
422	!
423	!-- Sort fractional timesteps in ascending order. Also sort the
424	!-- corresponding indices and flag according to the time interval a
425	!-- particle reaches the respective wall.
426	inc = 1
427	jr = 1
428	DO WHILE ( inc <= t_index_number )
429	inc = 3 * inc + 1
430	ENDDO
431
432	DO WHILE ( inc > 1 )
433	inc = inc / 3
434	DO ir = inc+1, t_index_number
435	tmp_t = t(ir)
436	tmp_x = x_ind(ir)
437	tmp_y = y_ind(ir)
438	tmp_z = z_ind(ir)
439	tmp_reach_x = reach_x(ir)
440	tmp_reach_y = reach_y(ir)
441	tmp_reach_z = reach_z(ir)
442	jr = ir
443	DO WHILE ( t(jr-inc) > tmp_t )
444	t(jr) = t(jr-inc)
445	x_ind(jr) = x_ind(jr-inc)
446	y_ind(jr) = y_ind(jr-inc)
447	z_ind(jr) = z_ind(jr-inc)
448	reach_x(jr) = reach_x(jr-inc)
449	reach_y(jr) = reach_y(jr-inc)
450	reach_z(jr) = reach_z(jr-inc)
451	jr = jr - inc
452	IF ( jr <= inc ) EXIT
453	ENDDO
454	t(jr) = tmp_t
455	x_ind(jr) = tmp_x
456	y_ind(jr) = tmp_y
457	z_ind(jr) = tmp_z
458	reach_x(jr) = tmp_reach_x
459	reach_y(jr) = tmp_reach_y
460	reach_z(jr) = tmp_reach_z
461	ENDDO
462	ENDDO
463	!
464	!-- Initialize temporary particle positions
465	pos_x = pos_x_old
466	pos_y = pos_y_old
467	pos_z = pos_z_old
468	!
469	!-- Loop over all times a particle possibly moves into a new grid box
470	t_old = 0.0_wp
471	DO t_index = 1, t_index_number
472	!
473	!-- Calculate intermediate particle position according to the
474	!-- timesteps a particle reaches any wall.
475	pos_x = pos_x + ( t(t_index) - t_old ) * dt_particle &
476	* particles(n)%speed_x
477	pos_y = pos_y + ( t(t_index) - t_old ) * dt_particle &
478	* particles(n)%speed_y
479	pos_z = pos_z + ( t(t_index) - t_old ) * dt_particle &
480	* particles(n)%speed_z
481	!
482	!-- Obtain x/y grid indices for intermediate particle position from
483	!-- sorted index array
484	i3 = x_ind(t_index)
485	j3 = y_ind(t_index)
486	k3 = z_ind(t_index)
487	!
488	!-- Check which wall is already reached
489	IF ( .NOT. x_wall_reached ) x_wall_reached = reach_x(t_index)
490	IF ( .NOT. y_wall_reached ) y_wall_reached = reach_y(t_index)
491	IF ( .NOT. z_wall_reached ) z_wall_reached = reach_z(t_index)
492	!
493	!-- Check if a particle needs to be reflected at any yz-wall. If
494	!-- necessary, carry out reflection. Please note, a security
495	!-- constant is required, as the particle position does not
496	!-- necessarily exactly match the wall location due to rounding
497	!-- errors.
498	IF ( reach_x(t_index) .AND. &
499	ABS( pos_x - xwall ) < eps .AND. &
500	.NOT. BTEST(wall_flags_0(k3,j3,i3),0) .AND. &
501	.NOT. reflect_x ) THEN
502	!
503	!
504	!-- Reflection in x-direction.
505	!-- Ensure correct reflection by MIN/MAX functions, depending on
506	!-- direction of particle transport.
507	!-- Due to rounding errors pos_x does not exactly match the wall
508	!-- location, leading to erroneous reflection.
509	pos_x = MERGE( MIN( 2.0_wp * xwall - pos_x, xwall ), &
510	MAX( 2.0_wp * xwall - pos_x, xwall ), &
511	particles(n)%x > xwall )
512	!
513	!-- Change sign of particle speed
514	particles(n)%speed_x = - particles(n)%speed_x
515	!
516	!-- Also change sign of subgrid-scale particle speed
517	particles(n)%rvar1 = - particles(n)%rvar1
518	!
519	!-- Set flag that reflection along x is already done
520	reflect_x = .TRUE.
521	!
522	!-- As the particle does not cross any further yz-wall during
523	!-- this timestep, set further x-indices to the current one.
524	x_ind(t_index:t_index_number) = i1
525	!
526	!-- If particle already reached the wall but was not reflected,
527	!-- set further x-indices to the new one.
528	ELSEIF ( x_wall_reached .AND. .NOT. reflect_x ) THEN
529	x_ind(t_index:t_index_number) = i2
530	ENDIF !particle reflection in x direction done
531
532	!
533	!-- Check if a particle needs to be reflected at any xz-wall. If
534	!-- necessary, carry out reflection. Please note, a security
535	!-- constant is required, as the particle position does not
536	!-- necessarily exactly match the wall location due to rounding
537	!-- errors.
538	IF ( reach_y(t_index) .AND. &
539	ABS( pos_y - ywall ) < eps .AND. &
540	.NOT. BTEST(wall_flags_0(k3,j3,i3),0) .AND. &
541	.NOT. reflect_y ) THEN
542	!
543	!
544	!-- Reflection in y-direction.
545	!-- Ensure correct reflection by MIN/MAX functions, depending on
546	!-- direction of particle transport.
547	!-- Due to rounding errors pos_y does not exactly match the wall
548	!-- location, leading to erroneous reflection.
549	pos_y = MERGE( MIN( 2.0_wp * ywall - pos_y, ywall ), &
550	MAX( 2.0_wp * ywall - pos_y, ywall ), &
551	particles(n)%y > ywall )
552	!
553	!-- Change sign of particle speed
554	particles(n)%speed_y = - particles(n)%speed_y
555	!
556	!-- Also change sign of subgrid-scale particle speed
557	particles(n)%rvar2 = - particles(n)%rvar2
558	!
559	!-- Set flag that reflection along y is already done
560	reflect_y = .TRUE.
561	!
562	!-- As the particle does not cross any further xz-wall during
563	!-- this timestep, set further y-indices to the current one.
564	y_ind(t_index:t_index_number) = j1
565	!
566	!-- If particle already reached the wall but was not reflected,
567	!-- set further y-indices to the new one.
568	ELSEIF ( y_wall_reached .AND. .NOT. reflect_y ) THEN
569	y_ind(t_index:t_index_number) = j2
570	ENDIF !particle reflection in y direction done
571
572	!
573	!-- Check if a particle needs to be reflected at any xy-wall. If
574	!-- necessary, carry out reflection. Please note, a security
575	!-- constant is required, as the particle position does not
576	!-- necessarily exactly match the wall location due to rounding
577	!-- errors.
578	IF ( reach_z(t_index) .AND. &
579	ABS( pos_z - zwall ) < eps .AND. &
580	.NOT. BTEST(wall_flags_0(k3,j3,i3),0) .AND. &
581	.NOT. reflect_z ) THEN
582	!
583	!
584	!-- Reflection in z-direction.
585	!-- Ensure correct reflection by MIN/MAX functions, depending on
586	!-- direction of particle transport.
587	!-- Due to rounding errors pos_z does not exactly match the wall
588	!-- location, leading to erroneous reflection.
589	pos_z = MERGE( MIN( 2.0_wp * zwall - pos_z, zwall ), &
590	MAX( 2.0_wp * zwall - pos_z, zwall ), &
591	particles(n)%z > zwall )
592	!
593	!-- Change sign of particle speed
594	particles(n)%speed_z = - particles(n)%speed_z
595	!
596	!-- Also change sign of subgrid-scale particle speed
597	particles(n)%rvar3 = - particles(n)%rvar3
598	!
599	!-- Set flag that reflection along z is already done
600	reflect_z = .TRUE.
601	!
602	!-- As the particle does not cross any further xy-wall during
603	!-- this timestep, set further z-indices to the current one.
604	z_ind(t_index:t_index_number) = k1
605	!
606	!-- If particle already reached the wall but was not reflected,
607	!-- set further z-indices to the new one.
608	ELSEIF ( z_wall_reached .AND. .NOT. reflect_z ) THEN
609	z_ind(t_index:t_index_number) = k2
610	ENDIF !particle reflection in z direction done
611
612	!
613	!-- Swap time
614	t_old = t(t_index)
615
616	ENDDO
617	!
618	!-- If a particle was reflected, calculate final position from last
619	!-- intermediate position.
620	IF ( reflect_x .OR. reflect_y .OR. reflect_z ) THEN
621
622	particles(n)%x = pos_x + ( 1.0_wp - t_old ) * dt_particle &
623	* particles(n)%speed_x
624	particles(n)%y = pos_y + ( 1.0_wp - t_old ) * dt_particle &
625	* particles(n)%speed_y
626	particles(n)%z = pos_z + ( 1.0_wp - t_old ) * dt_particle &
627	* particles(n)%speed_z
628
629	ENDIF
630
631	ENDIF
632
633	ENDDO
634
635	CALL cpu_log( log_point_s(48), 'lpm_wall_reflect', 'stop' )
636
637	ENDIF
638
639	END SUBROUTINE lpm_boundary_conds

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