source: palm/trunk/SOURCE/lpm_boundary_conds.f90 @ 2701

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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 1997-2017 Leibniz Universitaet Hannover
18!------------------------------------------------------------------------------!
19!
20! Current revisions:
21! -----------------
22!
23!
24! Former revisions:
25! -----------------
26! $Id: lpm_boundary_conds.f90 2701 2017-12-15 15:40:50Z suehring $
27! Particle reflections at downward-facing walls implemented. Moreover,
28! reflections are adjusted to revised particle grid box location.
29! (responsible Philipp Thiele)
30!
31! 2698 2017-12-14 18:46:24Z suehring
32! Changed particle box locations: center of particle box now coincides
33! with scalar grid point of same index.
34! Renamed module and subroutines: lpm_pack_arrays_mod -> lpm_pack_and_sort_mod
35! lpm_pack_all_arrays -> lpm_sort_in_subboxes, lpm_pack_arrays -> lpm_pack
36! lpm_sort -> lpm_sort_timeloop_done
37!
38! 2318 2017-07-20 17:27:44Z suehring
39! Get topography top index via Function call
40!
41! 2317 2017-07-20 17:27:19Z suehring
42!
43! 2232 2017-05-30 17:47:52Z suehring
44! Adjustments to new topography and surface concept
45! Rename character range into location, as range is an intrinsic.
46!
47! 2000 2016-08-20 18:09:15Z knoop
48! Forced header and separation lines into 80 columns
49!
50! 1929 2016-06-09 16:25:25Z suehring
51! Rewritten wall reflection
52!
53! 1822 2016-04-07 07:49:42Z hoffmann
54! Tails removed. Unused variables removed.
55!
56! 1682 2015-10-07 23:56:08Z knoop
57! Code annotations made doxygen readable
58!
59! 1359 2014-04-11 17:15:14Z hoffmann
60! New particle structure integrated.
61! Kind definition added to all floating point numbers.
62!
63! 1320 2014-03-20 08:40:49Z raasch
64! ONLY-attribute added to USE-statements,
65! kind-parameters added to all INTEGER and REAL declaration statements,
66! kinds are defined in new module kinds,
67! revision history before 2012 removed,
68! comment fields (!:) to be used for variable explanations added to
69! all variable declaration statements
70!
71! 1036 2012-10-22 13:43:42Z raasch
72! code put under GPL (PALM 3.9)
73!
74! 849 2012-03-15 10:35:09Z raasch
75! routine renamed lpm_boundary_conds, bottom and top boundary conditions
76! included (former part of advec_particles)
77!
78! 824 2012-02-17 09:09:57Z raasch
79! particle attributes speed_x|y|z_sgs renamed rvar1|2|3
80!
81! Initial version (2007/03/09)
82!
83! Description:
84! ------------
85!> Boundary conditions for the Lagrangian particles.
86!> The routine consists of two different parts. One handles the bottom (flat)
87!> and top boundary. In this part, also particles which exceeded their lifetime
88!> are deleted.
89!> The other part handles the reflection of particles from vertical walls.
90!> This part was developed by Jin Zhang during 2006-2007.
91!>
92!> To do: Code structure for finding the t_index values and for checking the
93!> -----  reflection conditions is basically the same for all four cases, so it
94!>        should be possible to further simplify/shorten it.
95!>
96!> THE WALLS PART OF THIS ROUTINE HAS NOT BEEN TESTED FOR OCEAN RUNS SO FAR!!!!
97!> (see offset_ocean_*)
98!------------------------------------------------------------------------------!
99 SUBROUTINE lpm_boundary_conds( location , i, j, k )
100 
101
102    USE arrays_3d,                                                             &
103        ONLY:  zu, zw
104
105    USE control_parameters,                                                    &
106        ONLY:  dz, message_string, particle_maximum_age
107
108    USE cpulog,                                                                &
109        ONLY:  cpu_log, log_point_s
110
111    USE grid_variables,                                                        &
112        ONLY:  ddx, dx, ddy, dy
113
114    USE indices,                                                               &
115        ONLY:  nxl, nxr, nyn, nys, nz, nzb, wall_flags_0,nyng,nysg
116
117    USE kinds
118
119    USE particle_attributes,                                                   &
120        ONLY:  deleted_particles, ibc_par_b, ibc_par_t, number_of_particles,   &
121               particles, particle_type, offset_ocean_nzt_m1,                  &
122               use_sgs_for_particles
123
124    USE pegrid
125
126    IMPLICIT NONE
127
128    CHARACTER (LEN=*) ::  location     !<
129   
130    INTEGER(iwp), INTENT(IN) ::  i !<
131    INTEGER(iwp), INTENT(IN) ::  j !<
132    INTEGER(iwp), INTENT(IN) ::  k !<
133   
134    INTEGER(iwp) ::  inc            !< dummy for sorting algorithmus
135    INTEGER(iwp) ::  ir             !< dummy for sorting algorithmus
136    INTEGER(iwp) ::  i1             !< grid index (x) of old particle position
137    INTEGER(iwp) ::  i2             !< grid index (x) of current particle position
138    INTEGER(iwp) ::  i3             !< grid index (x) of intermediate particle position
139    INTEGER(iwp) ::  jr             !< dummy for sorting algorithmus
140    INTEGER(iwp) ::  j1             !< grid index (y) of old particle position
141    INTEGER(iwp) ::  j2             !< grid index (y) of current particle position
142    INTEGER(iwp) ::  j3             !< grid index (y) of intermediate particle position
143    INTEGER(iwp) ::  k1             !< grid index (z) of old particle position
144    INTEGER(iwp) ::  k2             !< grid index (z) of current particle position
145    INTEGER(iwp) ::  k3             !< grid index (z) of intermediate particle position
146    INTEGER(iwp) ::  n              !< particle number
147    INTEGER(iwp) ::  t_index        !< running index for intermediate particle timesteps in reflection algorithmus
148    INTEGER(iwp) ::  t_index_number !< number of intermediate particle timesteps in reflection algorithmus
149    INTEGER(iwp) ::  tmp_x          !< dummy for sorting algorithm
150    INTEGER(iwp) ::  tmp_y          !< dummy for sorting algorithm
151    INTEGER(iwp) ::  tmp_z          !< dummy for sorting algorithm
152
153    INTEGER(iwp), DIMENSION(0:10) :: x_ind(0:10) = 0 !< index array (x) of intermediate particle positions
154    INTEGER(iwp), DIMENSION(0:10) :: y_ind(0:10) = 0 !< index array (y) of intermediate particle positions
155    INTEGER(iwp), DIMENSION(0:10) :: z_ind(0:10) = 0 !< index array (z) of intermediate particle positions
156   
157    LOGICAL  ::  cross_wall_x    !< flag to check if particle reflection along x is necessary
158    LOGICAL  ::  cross_wall_y    !< flag to check if particle reflection along y is necessary
159    LOGICAL  ::  cross_wall_z    !< flag to check if particle reflection along z is necessary
160    LOGICAL  ::  reflect_x       !< flag to check if particle is already reflected along x
161    LOGICAL  ::  reflect_y       !< flag to check if particle is already reflected along y
162    LOGICAL  ::  reflect_z       !< flag to check if particle is already reflected along z
163    LOGICAL  ::  tmp_reach_x     !< dummy for sorting algorithmus
164    LOGICAL  ::  tmp_reach_y     !< dummy for sorting algorithmus
165    LOGICAL  ::  tmp_reach_z     !< dummy for sorting algorithmus
166    LOGICAL  ::  x_wall_reached  !< flag to check if particle has already reached wall
167    LOGICAL  ::  y_wall_reached  !< flag to check if particle has already reached wall
168    LOGICAL  ::  z_wall_reached  !< flag to check if particle has already reached wall
169
170    LOGICAL, DIMENSION(0:10) ::  reach_x  !< flag to check if particle is at a yz-wall
171    LOGICAL, DIMENSION(0:10) ::  reach_y  !< flag to check if particle is at a xz-wall
172    LOGICAL, DIMENSION(0:10) ::  reach_z  !< flag to check if particle is at a xy-wall
173
174    REAL(wp) ::  dt_particle    !< particle timestep
175    REAL(wp) ::  dum            !< dummy argument
176    REAL(wp) ::  eps = 1E-10_wp !< security number to check if particle has reached a wall
177    REAL(wp) ::  pos_x          !< intermediate particle position (x)
178    REAL(wp) ::  pos_x_old      !< particle position (x) at previous particle timestep
179    REAL(wp) ::  pos_y          !< intermediate particle position (y)
180    REAL(wp) ::  pos_y_old      !< particle position (y) at previous particle timestep
181    REAL(wp) ::  pos_z          !< intermediate particle position (z)
182    REAL(wp) ::  pos_z_old      !< particle position (z) at previous particle timestep
183    REAL(wp) ::  prt_x          !< current particle position (x)
184    REAL(wp) ::  prt_y          !< current particle position (y)
185    REAL(wp) ::  prt_z          !< current particle position (z)
186    REAL(wp) ::  t_old          !< previous reflection time
187    REAL(wp) ::  tmp_t          !< dummy for sorting algorithmus
188    REAL(wp) ::  xwall          !< location of wall in x
189    REAL(wp) ::  ywall          !< location of wall in y
190    REAL(wp) ::  zwall          !< location of wall in z
191
192    REAL(wp), DIMENSION(0:10) ::  t  !< reflection time
193
194
195    IF ( location == 'bottom/top' )  THEN
196
197!
198!--    Apply boundary conditions to those particles that have crossed the top or
199!--    bottom boundary and delete those particles, which are older than allowed
200       DO  n = 1, number_of_particles
201
202!
203!--       Stop if particles have moved further than the length of one
204!--       PE subdomain (newly released particles have age = age_m!)
205          IF ( particles(n)%age /= particles(n)%age_m )  THEN
206             IF ( ABS(particles(n)%speed_x) >                                  &
207                  ((nxr-nxl+2)*dx)/(particles(n)%age-particles(n)%age_m)  .OR. &
208                  ABS(particles(n)%speed_y) >                                  &
209                  ((nyn-nys+2)*dy)/(particles(n)%age-particles(n)%age_m) )  THEN
210
211                  WRITE( message_string, * )  'particle too fast.  n = ',  n
212                  CALL message( 'lpm_boundary_conds', 'PA0148', 2, 2, -1, 6, 1 )
213             ENDIF
214          ENDIF
215
216          IF ( particles(n)%age > particle_maximum_age  .AND.  &
217               particles(n)%particle_mask )                              &
218          THEN
219             particles(n)%particle_mask  = .FALSE.
220             deleted_particles = deleted_particles + 1
221          ENDIF
222
223          IF ( particles(n)%z >= zu(nz)  .AND.  particles(n)%particle_mask )  THEN
224             IF ( ibc_par_t == 1 )  THEN
225!
226!--             Particle absorption
227                particles(n)%particle_mask  = .FALSE.
228                deleted_particles = deleted_particles + 1
229             ELSEIF ( ibc_par_t == 2 )  THEN
230!
231!--             Particle reflection
232                particles(n)%z       = 2.0_wp * zu(nz) - particles(n)%z
233                particles(n)%speed_z = -particles(n)%speed_z
234                IF ( use_sgs_for_particles  .AND. &
235                     particles(n)%rvar3 > 0.0_wp )  THEN
236                   particles(n)%rvar3 = -particles(n)%rvar3
237                ENDIF
238             ENDIF
239          ENDIF
240         
241          IF ( particles(n)%z < zw(0)  .AND.  particles(n)%particle_mask )  THEN
242             IF ( ibc_par_b == 1 )  THEN
243!
244!--             Particle absorption
245                particles(n)%particle_mask  = .FALSE.
246                deleted_particles = deleted_particles + 1
247             ELSEIF ( ibc_par_b == 2 )  THEN
248!
249!--             Particle reflection
250                particles(n)%z       = 2.0_wp * zw(0) - 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       ENDDO
259
260    ELSEIF ( location == 'walls' )  THEN
261
262
263       CALL cpu_log( log_point_s(48), 'lpm_wall_reflect', 'start' )
264
265       DO  n = 1, number_of_particles
266!
267!--       Recalculate particle timestep
268          dt_particle = particles(n)%age - particles(n)%age_m
269!
270!--       Obtain x/y indices for current particle position
271          i2 = particles(n)%x * ddx
272          j2 = particles(n)%y * ddy
273          IF (zw(k)   < particles(n)%z ) k2 = k + 1
274          IF (zw(k-1) > particles(n)%z ) k2 = k - 1 
275!
276!--       Save current particle positions
277          prt_x = particles(n)%x
278          prt_y = particles(n)%y
279          prt_z = particles(n)%z
280!
281!--       Recalculate old particle positions
282          pos_x_old = particles(n)%x - particles(n)%speed_x * dt_particle
283          pos_y_old = particles(n)%y - particles(n)%speed_y * dt_particle
284          pos_z_old = particles(n)%z - particles(n)%speed_z * dt_particle
285!
286!--       Obtain x/y indices for old particle positions
287          i1 = i
288          j1 = j
289          k1 = k
290!
291!--       Determine horizontal as well as vertical walls at which particle can
292!--       be potentially reflected.
293!--       Start with walls aligned in yz layer.
294!--       Wall to the right
295          IF ( prt_x > pos_x_old )  THEN
296             xwall = ( i1 + 1 ) * dx
297!
298!--       Wall to the left
299          ELSE
300             xwall = i1 * dx
301          ENDIF
302!
303!--       Walls aligned in xz layer
304!--       Wall to the north
305          IF ( prt_y > pos_y_old )  THEN
306             ywall = ( j1 +1 ) * dy
307!--       Wall to the south
308          ELSE
309             ywall = j1 * dy
310          ENDIF
311
312          IF ( prt_z > pos_z_old ) THEN
313             zwall = zw(k)
314          ELSE
315             zwall = zw(k-1)
316          ENDIF     
317!
318!--       Initialize flags to check if particle reflection is necessary
319          cross_wall_x = .FALSE.
320          cross_wall_y = .FALSE.
321          cross_wall_z = .FALSE.
322!
323!--       Initialize flags to check if a wall is reached
324          reach_x      = .FALSE.
325          reach_y      = .FALSE.
326          reach_z      = .FALSE.
327!
328!--       Initialize flags to check if a particle was already reflected
329          reflect_x    = .FALSE.
330          reflect_y    = .FALSE.
331          reflect_z    = .FALSE.
332!
333!--       Initialize flags to check if a wall is already crossed.
334!--       ( Required to obtain correct indices. )
335          x_wall_reached = .FALSE.
336          y_wall_reached = .FALSE.
337          z_wall_reached = .FALSE.
338!
339!--       Initialize time array
340          t     = 0.0_wp
341!
342!--       Check if particle can reach any wall. This case, calculate the
343!--       fractional time needed to reach this wall. Store this fractional
344!--       timestep in array t. Moreover, store indices for these grid
345!--       boxes where the respective wall belongs to. 
346!--       Start with x-direction.
347          t_index    = 1
348          t(t_index) = ( xwall - pos_x_old )                                   &
349                     / MERGE( MAX( prt_x - pos_x_old,  1E-30_wp ),             &
350                              MIN( prt_x - pos_x_old, -1E-30_wp ),             &
351                              prt_x > pos_x_old )
352          x_ind(t_index)   = i2
353          y_ind(t_index)   = j1
354          z_ind(t_index)   = k1
355          reach_x(t_index) = .TRUE.
356          reach_y(t_index) = .FALSE.
357          reach_z(t_index) = .FALSE.
358!
359!--       Store these values only if particle really reaches any wall. t must
360!--       be in a interval between [0:1].
361          IF ( t(t_index) <= 1.0_wp .AND. t(t_index) >= 0.0_wp )  THEN
362             t_index      = t_index + 1
363             cross_wall_x = .TRUE.
364          ENDIF
365!
366!--       y-direction
367          t(t_index) = ( ywall - pos_y_old )                                   &
368                     / MERGE( MAX( prt_y - pos_y_old,  1E-30_wp ),             &
369                              MIN( prt_y - pos_y_old, -1E-30_wp ),             &
370                              prt_y > pos_y_old )
371          x_ind(t_index)   = i1
372          y_ind(t_index)   = j2
373          z_ind(t_index)   = k1
374          reach_x(t_index) = .FALSE.
375          reach_y(t_index) = .TRUE.
376          reach_z(t_index) = .FALSE.
377          IF ( t(t_index) <= 1.0_wp .AND. t(t_index) >= 0.0_wp )  THEN
378             t_index      = t_index + 1
379             cross_wall_y = .TRUE.
380          ENDIF
381!
382!--       z-direction
383          t(t_index) = (zwall - pos_z_old )                                    &
384                     / MERGE( MAX( prt_z - pos_z_old,  1E-30_wp ),             &
385                              MIN( prt_z - pos_z_old, -1E-30_wp ),             &
386                              prt_z > pos_z_old )
387                     
388          x_ind(t_index)   = i1
389          y_ind(t_index)   = j1
390          z_ind(t_index)   = k2
391          reach_x(t_index) = .FALSE.
392          reach_y(t_index) = .FALSE.
393          reach_z(t_index) = .TRUE.
394          IF( t(t_index) <= 1.0_wp .AND. t(t_index) >= 0.0_wp) THEN
395             t_index      = t_index + 1
396             cross_wall_z = .TRUE.
397          ENDIF
398         
399          t_index_number = t_index - 1
400!
401!--       Carry out reflection only if particle reaches any wall
402          IF ( cross_wall_x .OR. cross_wall_y .OR. cross_wall_z )  THEN
403!
404!--          Sort fractional timesteps in ascending order. Also sort the
405!--          corresponding indices and flag according to the time interval a 
406!--          particle reaches the respective wall.
407             inc = 1
408             jr  = 1
409             DO WHILE ( inc <= t_index_number )
410                inc = 3 * inc + 1
411             ENDDO
412
413             DO WHILE ( inc > 1 )
414                inc = inc / 3
415                DO  ir = inc+1, t_index_number
416                   tmp_t       = t(ir)
417                   tmp_x       = x_ind(ir)
418                   tmp_y       = y_ind(ir)
419                   tmp_z       = z_ind(ir)
420                   tmp_reach_x = reach_x(ir)
421                   tmp_reach_y = reach_y(ir)
422                   tmp_reach_z = reach_z(ir)
423                   jr    = ir
424                   DO WHILE ( t(jr-inc) > tmp_t )
425                      t(jr)       = t(jr-inc)
426                      x_ind(jr)   = x_ind(jr-inc)
427                      y_ind(jr)   = y_ind(jr-inc)
428                      z_ind(jr)   = z_ind(jr-inc)
429                      reach_x(jr) = reach_x(jr-inc)
430                      reach_y(jr) = reach_y(jr-inc)
431                      reach_z(jr) = reach_z(jr-inc)
432                      jr    = jr - inc
433                      IF ( jr <= inc )  EXIT
434                   ENDDO
435                   t(jr)       = tmp_t
436                   x_ind(jr)   = tmp_x
437                   y_ind(jr)   = tmp_y
438                   z_ind(jr)   = tmp_z
439                   reach_x(jr) = tmp_reach_x
440                   reach_y(jr) = tmp_reach_y
441                   reach_z(jr) = tmp_reach_z
442                ENDDO
443             ENDDO
444!
445!--          Initialize temporary particle positions
446             pos_x = pos_x_old
447             pos_y = pos_y_old
448             pos_z = pos_z_old
449!
450!--          Loop over all times a particle possibly moves into a new grid box
451             t_old = 0.0_wp
452             DO t_index = 1, t_index_number
453!           
454!--             Calculate intermediate particle position according to the
455!--             timesteps a particle reaches any wall.
456                pos_x = pos_x + ( t(t_index) - t_old ) * dt_particle           &
457                                                       * particles(n)%speed_x
458                pos_y = pos_y + ( t(t_index) - t_old ) * dt_particle           &
459                                                       * particles(n)%speed_y
460                pos_z = pos_z + ( t(t_index) - t_old ) * dt_particle           &
461                                                       * particles(n)%speed_z
462!
463!--             Obtain x/y grid indices for intermediate particle position from
464!--             sorted index array
465                i3 = x_ind(t_index)
466                j3 = y_ind(t_index)
467                k3 = z_ind(t_index)
468!
469!--             Check which wall is already reached
470                IF ( .NOT. x_wall_reached )  x_wall_reached = reach_x(t_index) 
471                IF ( .NOT. y_wall_reached )  y_wall_reached = reach_y(t_index)
472                IF ( .NOT. z_wall_reached )  z_wall_reached = reach_z(t_index)
473!
474!--             Check if a particle needs to be reflected at any yz-wall. If
475!--             necessary, carry out reflection. Please note, a security
476!--             constant is required, as the particle position does not
477!--             necessarily exactly match the wall location due to rounding
478!--             errors.
479                IF ( reach_x(t_index)                      .AND.               & 
480                     ABS( pos_x - xwall ) < eps            .AND.               &
481                     .NOT. BTEST(wall_flags_0(k3,j3,i3),0) .AND.               &
482                     .NOT. reflect_x )  THEN
483!
484!
485!--                Reflection in x-direction.
486!--                Ensure correct reflection by MIN/MAX functions, depending on
487!--                direction of particle transport.
488!--                Due to rounding errors pos_x does not exactly match the wall
489!--                location, leading to erroneous reflection.             
490                   pos_x = MERGE( MIN( 2.0_wp * xwall - pos_x, xwall ),        &
491                                  MAX( 2.0_wp * xwall - pos_x, xwall ),        &
492                                  particles(n)%x > xwall )
493!
494!--                Change sign of particle speed                     
495                   particles(n)%speed_x = - particles(n)%speed_x
496!
497!--                Also change sign of subgrid-scale particle speed
498                   particles(n)%rvar1 = - particles(n)%rvar1
499!
500!--                Set flag that reflection along x is already done
501                   reflect_x          = .TRUE.
502!
503!--                As the particle does not cross any further yz-wall during
504!--                this timestep, set further x-indices to the current one.
505                   x_ind(t_index:t_index_number) = i1
506!
507!--             If particle already reached the wall but was not reflected,
508!--             set further x-indices to the new one.
509                ELSEIF ( x_wall_reached .AND. .NOT. reflect_x )  THEN
510                    x_ind(t_index:t_index_number) = i2
511                ENDIF !particle reflection in x direction done
512
513!
514!--             Check if a particle needs to be reflected at any xz-wall. If
515!--             necessary, carry out reflection. Please note, a security
516!--             constant is required, as the particle position does not
517!--             necessarily exactly match the wall location due to rounding
518!--             errors.
519                WRITE(9,*) 'wall_test_y nysg:',nysg ,' y: ',particles(n)%y,' j3: ',j3,'nyng:', nyng 
520                FLUSH(9)
521                WRITE(9,*) BTEST(wall_flags_0(k3,j3,i3),0) 
522                FLUSH(9)
523                IF ( reach_y(t_index)                      .AND.               & 
524                     ABS( pos_y - ywall ) < eps            .AND.               &
525                     .NOT. BTEST(wall_flags_0(k3,j3,i3),0) .AND.               &
526                     .NOT. reflect_y )  THEN
527!
528!
529!--                Reflection in y-direction.
530!--                Ensure correct reflection by MIN/MAX functions, depending on
531!--                direction of particle transport.
532!--                Due to rounding errors pos_y does not exactly match the wall
533!--                location, leading to erroneous reflection.             
534                   pos_y = MERGE( MIN( 2.0_wp * ywall - pos_y, ywall ),        &
535                                  MAX( 2.0_wp * ywall - pos_y, ywall ),        &
536                                  particles(n)%y > ywall )
537!
538!--                Change sign of particle speed                     
539                   particles(n)%speed_y = - particles(n)%speed_y
540!
541!--                Also change sign of subgrid-scale particle speed
542                   particles(n)%rvar2 = - particles(n)%rvar2
543!
544!--                Set flag that reflection along y is already done
545                   reflect_y          = .TRUE.
546!
547!--                As the particle does not cross any further xz-wall during
548!--                this timestep, set further y-indices to the current one.
549                   y_ind(t_index:t_index_number) = j1
550!
551!--             If particle already reached the wall but was not reflected,
552!--             set further y-indices to the new one.
553                ELSEIF ( y_wall_reached .AND. .NOT. reflect_y )  THEN
554                    y_ind(t_index:t_index_number) = j2
555                ENDIF !particle reflection in y direction done
556               
557!
558!--             Check if a particle needs to be reflected at any xy-wall. If
559!--             necessary, carry out reflection. Please note, a security
560!--             constant is required, as the particle position does not
561!--             necessarily exactly match the wall location due to rounding
562!--             errors.
563                IF ( reach_z(t_index)                      .AND.               & 
564                     ABS( pos_z - zwall ) < eps            .AND.               &
565                     .NOT. BTEST(wall_flags_0(k3,j3,i3),0) .AND.               &
566                     .NOT. reflect_z )  THEN
567!
568!
569!--                Reflection in z-direction.
570!--                Ensure correct reflection by MIN/MAX functions, depending on
571!--                direction of particle transport.
572!--                Due to rounding errors pos_z does not exactly match the wall
573!--                location, leading to erroneous reflection.             
574                   pos_z = MERGE( MIN( 2.0_wp * zwall - pos_z, zwall ),        &
575                                  MAX( 2.0_wp * zwall - pos_z, zwall ),        &
576                                  particles(n)%z > zwall )
577!
578!--                Change sign of particle speed                     
579                   particles(n)%speed_z = - particles(n)%speed_z
580!
581!--                Also change sign of subgrid-scale particle speed
582                   particles(n)%rvar3 = - particles(n)%rvar3
583!
584!--                Set flag that reflection along z is already done
585                   reflect_z          = .TRUE.
586!
587!--                As the particle does not cross any further xy-wall during
588!--                this timestep, set further z-indices to the current one.
589                   z_ind(t_index:t_index_number) = k1
590!
591!--             If particle already reached the wall but was not reflected,
592!--             set further z-indices to the new one.
593                ELSEIF ( z_wall_reached .AND. .NOT. reflect_z )  THEN
594                    z_ind(t_index:t_index_number) = k2
595                ENDIF !particle reflection in z direction done               
596               
597!
598!--             Swap time
599                t_old = t(t_index)
600
601             ENDDO
602!
603!--          If a particle was reflected, calculate final position from last
604!--          intermediate position.
605             IF ( reflect_x .OR. reflect_y .OR. reflect_z )  THEN
606
607                particles(n)%x = pos_x + ( 1.0_wp - t_old ) * dt_particle      &
608                                                         * particles(n)%speed_x
609                particles(n)%y = pos_y + ( 1.0_wp - t_old ) * dt_particle      &
610                                                         * particles(n)%speed_y
611                particles(n)%z = pos_z + ( 1.0_wp - t_old ) * dt_particle      &
612                                                         * particles(n)%speed_z
613
614             ENDIF
615
616          ENDIF
617
618       ENDDO
619
620       CALL cpu_log( log_point_s(48), 'lpm_wall_reflect', 'stop' )
621
622    ENDIF
623
624 END SUBROUTINE lpm_boundary_conds
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