1 | SUBROUTINE timestep |
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2 | |
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3 | !------------------------------------------------------------------------------! |
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4 | ! Current revisions: |
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5 | ! ----------------- |
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6 | ! |
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7 | ! |
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8 | ! Former revisions: |
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9 | ! ----------------- |
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10 | ! $Id: timestep.f90 708 2011-03-29 12:34:54Z raasch $ |
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11 | ! |
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12 | ! 707 2011-03-29 11:39:40Z raasch |
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13 | ! bc_lr/ns replaced by bc_lr/ns_cyc |
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14 | ! |
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15 | ! 667 2010-12-23 12:06:00Z suehring/gryschka |
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16 | ! Exchange of terminate_coupled between ocean and atmosphere via PE0 |
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17 | ! Minimum grid spacing dxyz2_min(k) is now calculated using dzw instead of dzu |
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18 | ! |
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19 | ! 622 2010-12-10 08:08:13Z raasch |
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20 | ! optional barriers included in order to speed up collective operations |
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21 | ! |
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22 | ! 343 2009-06-24 12:59:09Z maronga |
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23 | ! Additional timestep criterion in case of simulations with plant canopy |
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24 | ! Output of messages replaced by message handling routine. |
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25 | ! |
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26 | ! 222 2009-01-12 16:04:16Z letzel |
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27 | ! Implementation of a MPI-1 Coupling: replaced myid with target_id |
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28 | ! Bugfix for nonparallel execution |
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29 | ! |
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30 | ! 108 2007-08-24 15:10:38Z letzel |
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31 | ! modifications to terminate coupled runs |
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32 | ! |
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33 | ! RCS Log replace by Id keyword, revision history cleaned up |
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34 | ! |
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35 | ! Revision 1.21 2006/02/23 12:59:44 raasch |
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36 | ! nt_anz renamed current_timestep_number |
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37 | ! |
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38 | ! Revision 1.1 1997/08/11 06:26:19 raasch |
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39 | ! Initial revision |
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40 | ! |
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41 | ! |
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42 | ! Description: |
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43 | ! ------------ |
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44 | ! Compute the time step under consideration of the FCL and diffusion criterion. |
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45 | !------------------------------------------------------------------------------! |
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46 | |
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47 | USE arrays_3d |
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48 | USE control_parameters |
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49 | USE cpulog |
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50 | USE grid_variables |
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51 | USE indices |
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52 | USE interfaces |
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53 | USE pegrid |
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54 | USE statistics |
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55 | |
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56 | IMPLICIT NONE |
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57 | |
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58 | INTEGER :: i, j, k |
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59 | |
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60 | REAL :: div, dt_diff, dt_diff_l, dt_plant_canopy, & |
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61 | dt_plant_canopy_l, & |
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62 | dt_plant_canopy_u, dt_plant_canopy_v, dt_plant_canopy_w, & |
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63 | dt_u, dt_v, dt_w, lad_max, percent_change, & |
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64 | u_gtrans_l, vabs_max, value, v_gtrans_l |
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65 | |
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66 | REAL, DIMENSION(2) :: uv_gtrans, uv_gtrans_l |
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67 | REAL, DIMENSION(nzb+1:nzt) :: dxyz2_min |
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68 | |
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69 | |
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70 | |
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71 | CALL cpu_log( log_point(12), 'calculate_timestep', 'start' ) |
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72 | |
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73 | ! |
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74 | !-- Determine the maxima of the velocity components. |
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75 | CALL global_min_max( nzb, nzt+1, nysg, nyng, nxlg, nxrg, u, 'abs', & |
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76 | u_max, u_max_ijk ) |
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77 | CALL global_min_max( nzb, nzt+1, nysg, nyng, nxlg, nxrg, v, 'abs', & |
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78 | v_max, v_max_ijk ) |
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79 | CALL global_min_max( nzb, nzt+1, nysg, nyng, nxlg, nxrg, w, 'abs', & |
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80 | w_max, w_max_ijk ) |
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81 | |
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82 | ! |
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83 | !-- In case maxima of the horizontal velocity components have been found at the |
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84 | !-- bottom boundary (k=nzb), the corresponding maximum at level k=1 is chosen |
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85 | !-- if the Dirichlet-boundary condition ('mirror') has been set. This is |
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86 | !-- necessary, because otherwise in case of Galilei-transform a far too large |
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87 | !-- velocity (having the respective opposite sign) would be used for the time |
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88 | !-- step determination (almost double the mean flow velocity). |
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89 | IF ( ibc_uv_b == 0 ) THEN |
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90 | IF ( u_max_ijk(1) == nzb ) THEN |
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91 | u_max = -u_max |
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92 | u_max_ijk(1) = nzb + 1 |
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93 | ENDIF |
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94 | IF ( v_max_ijk(1) == nzb ) THEN |
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95 | v_max = -v_max |
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96 | v_max_ijk(1) = nzb + 1 |
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97 | ENDIF |
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98 | ENDIF |
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99 | |
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100 | ! |
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101 | !-- In case of Galilei-transform not using the geostrophic wind as translation |
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102 | !-- velocity, compute the volume-averaged horizontal velocity components, which |
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103 | !-- will then be subtracted from the horizontal wind for the time step and |
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104 | !-- horizontal advection routines. |
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105 | IF ( galilei_transformation .AND. .NOT. use_ug_for_galilei_tr ) THEN |
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106 | IF ( flow_statistics_called ) THEN |
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107 | ! |
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108 | !-- Horizontal averages already existent, just need to average them |
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109 | !-- vertically. |
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110 | u_gtrans = 0.0 |
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111 | v_gtrans = 0.0 |
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112 | DO k = nzb+1, nzt |
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113 | u_gtrans = u_gtrans + hom(k,1,1,0) |
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114 | v_gtrans = v_gtrans + hom(k,1,2,0) |
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115 | ENDDO |
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116 | u_gtrans = u_gtrans / REAL( nzt - nzb ) |
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117 | v_gtrans = v_gtrans / REAL( nzt - nzb ) |
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118 | ELSE |
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119 | ! |
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120 | !-- Averaging over the entire model domain. |
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121 | uv_gtrans_l = 0.0 |
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122 | DO i = nxl, nxr |
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123 | DO j = nys, nyn |
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124 | DO k = nzb+1, nzt |
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125 | uv_gtrans_l(1) = uv_gtrans_l(1) + u(k,j,i) |
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126 | uv_gtrans_l(2) = uv_gtrans_l(2) + v(k,j,i) |
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127 | ENDDO |
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128 | ENDDO |
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129 | ENDDO |
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130 | uv_gtrans_l = uv_gtrans_l / REAL( (nxr-nxl+1)*(nyn-nys+1)*(nzt-nzb) ) |
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131 | #if defined( __parallel ) |
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132 | IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr ) |
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133 | CALL MPI_ALLREDUCE( uv_gtrans_l, uv_gtrans, 2, MPI_REAL, MPI_SUM, & |
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134 | comm2d, ierr ) |
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135 | u_gtrans = uv_gtrans(1) / REAL( numprocs ) |
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136 | v_gtrans = uv_gtrans(2) / REAL( numprocs ) |
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137 | #else |
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138 | u_gtrans = uv_gtrans_l(1) |
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139 | v_gtrans = uv_gtrans_l(2) |
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140 | #endif |
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141 | ENDIF |
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142 | ENDIF |
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143 | |
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144 | IF ( .NOT. dt_fixed ) THEN |
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145 | ! |
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146 | !-- Variable time step: |
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147 | ! |
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148 | !-- For each component, compute the maximum time step according to the |
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149 | !-- FCL-criterion. |
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150 | dt_u = dx / ( ABS( u_max - u_gtrans ) + 1.0E-10 ) |
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151 | dt_v = dy / ( ABS( v_max - v_gtrans ) + 1.0E-10 ) |
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152 | dt_w = dzu(MAX( 1, w_max_ijk(1) )) / ( ABS( w_max ) + 1.0E-10 ) |
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153 | |
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154 | ! |
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155 | !-- Compute time step according to the diffusion criterion. |
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156 | !-- First calculate minimum grid spacing which only depends on index k |
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157 | !-- Note: also at k=nzb+1 a full grid length is being assumed, although |
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158 | !-- in the Prandtl-layer friction term only dz/2 is used. |
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159 | !-- Experience from the old model seems to justify this. |
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160 | dt_diff_l = 999999.0 |
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161 | |
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162 | DO k = nzb+1, nzt |
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163 | dxyz2_min(k) = MIN( dx2, dy2, dzw(k)*dzw(k) ) * 0.125 |
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164 | ENDDO |
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165 | |
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166 | !$OMP PARALLEL private(i,j,k,value) reduction(MIN: dt_diff_l) |
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167 | !$OMP DO |
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168 | DO i = nxl, nxr |
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169 | DO j = nys, nyn |
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170 | DO k = nzb+1, nzt |
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171 | value = dxyz2_min(k) / ( MAX( kh(k,j,i), km(k,j,i) ) + 1E-20 ) |
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172 | |
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173 | dt_diff_l = MIN( value, dt_diff_l ) |
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174 | ENDDO |
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175 | ENDDO |
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176 | ENDDO |
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177 | !$OMP END PARALLEL |
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178 | #if defined( __parallel ) |
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179 | IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr ) |
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180 | CALL MPI_ALLREDUCE( dt_diff_l, dt_diff, 1, MPI_REAL, MPI_MIN, comm2d, & |
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181 | ierr ) |
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182 | #else |
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183 | dt_diff = dt_diff_l |
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184 | #endif |
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185 | |
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186 | ! |
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187 | !-- In case of non-cyclic lateral boundaries, the diffusion time step |
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188 | !-- may be further restricted by the lateral damping layer (damping only |
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189 | !-- along x and y) |
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190 | IF ( .NOT. bc_lr_cyc ) THEN |
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191 | dt_diff = MIN( dt_diff, 0.125 * dx2 / ( km_damp_max + 1E-20 ) ) |
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192 | ELSEIF ( .NOT. bc_ns_cyc ) THEN |
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193 | dt_diff = MIN( dt_diff, 0.125 * dy2 / ( km_damp_max + 1E-20 ) ) |
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194 | ENDIF |
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195 | |
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196 | ! |
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197 | !-- Additional timestep criterion with plant canopies: |
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198 | !-- it is not allowed to extract more than the available momentum |
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199 | IF ( plant_canopy ) THEN |
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200 | |
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201 | dt_plant_canopy_l = 0.0 |
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202 | DO i = nxl, nxr |
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203 | DO j = nys, nyn |
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204 | DO k = nzb+1, nzt |
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205 | dt_plant_canopy_u = cdc(k,j,i) * lad_u(k,j,i) * & |
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206 | SQRT( u(k,j,i)**2 + & |
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207 | ( ( v(k,j,i-1) + & |
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208 | v(k,j,i) + & |
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209 | v(k,j+1,i) + & |
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210 | v(k,j+1,i-1) ) & |
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211 | / 4.0 )**2 + & |
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212 | ( ( w(k-1,j,i-1) + & |
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213 | w(k-1,j,i) + & |
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214 | w(k,j,i-1) + & |
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215 | w(k,j,i) ) & |
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216 | / 4.0 )**2 ) |
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217 | IF ( dt_plant_canopy_u > dt_plant_canopy_l ) THEN |
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218 | dt_plant_canopy_l = dt_plant_canopy_u |
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219 | ENDIF |
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220 | dt_plant_canopy_v = cdc(k,j,i) * lad_v(k,j,i) * & |
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221 | SQRT( ( ( u(k,j-1,i) + & |
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222 | u(k,j-1,i+1) + & |
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223 | u(k,j,i) + & |
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224 | u(k,j,i+1) ) & |
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225 | / 4.0 )**2 + & |
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226 | v(k,j,i)**2 + & |
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227 | ( ( w(k-1,j-1,i) + & |
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228 | w(k-1,j,i) + & |
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229 | w(k,j-1,i) + & |
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230 | w(k,j,i) ) & |
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231 | / 4.0 )**2 ) |
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232 | IF ( dt_plant_canopy_v > dt_plant_canopy_l ) THEN |
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233 | dt_plant_canopy_l = dt_plant_canopy_v |
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234 | ENDIF |
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235 | dt_plant_canopy_w = cdc(k,j,i) * lad_w(k,j,i) * & |
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236 | SQRT( ( ( u(k,j,i) + & |
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237 | u(k,j,i+1) + & |
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238 | u(k+1,j,i) + & |
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239 | u(k+1,j,i+1) ) & |
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240 | / 4.0 )**2 + & |
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241 | ( ( v(k,j,i) + & |
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242 | v(k,j+1,i) + & |
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243 | v(k+1,j,i) + & |
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244 | v(k+1,j+1,i) ) & |
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245 | / 4.0 )**2 + & |
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246 | w(k,j,i)**2 ) |
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247 | IF ( dt_plant_canopy_w > dt_plant_canopy_l ) THEN |
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248 | dt_plant_canopy_l = dt_plant_canopy_w |
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249 | ENDIF |
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250 | ENDDO |
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251 | ENDDO |
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252 | ENDDO |
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253 | |
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254 | IF ( dt_plant_canopy_l > 0.0 ) THEN |
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255 | ! |
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256 | !-- Invert dt_plant_canopy_l and apply a security timestep factor 0.1 |
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257 | dt_plant_canopy_l = 0.1 / dt_plant_canopy_l |
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258 | ELSE |
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259 | ! |
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260 | !-- In case of inhomogeneous plant canopy, some processors may have no |
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261 | !-- canopy at all. Then use dt_max as dummy instead. |
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262 | dt_plant_canopy_l = dt_max |
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263 | ENDIF |
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264 | |
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265 | ! |
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266 | !-- Determine the global minumum |
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267 | #if defined( __parallel ) |
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268 | IF ( collective_wait ) CALL MPI_BARRIER( comm2d, ierr ) |
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269 | CALL MPI_ALLREDUCE( dt_plant_canopy_l, dt_plant_canopy, 1, MPI_REAL, & |
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270 | MPI_MIN, comm2d, ierr ) |
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271 | #else |
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272 | dt_plant_canopy = dt_plant_canopy_l |
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273 | #endif |
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274 | |
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275 | ELSE |
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276 | ! |
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277 | !-- Use dt_diff as dummy value to avoid extra IF branches further below |
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278 | dt_plant_canopy = dt_diff |
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279 | |
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280 | ENDIF |
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281 | |
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282 | ! |
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283 | !-- The time step is the minimum of the 3-4 components and the diffusion time |
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284 | !-- step minus a reduction to be on the safe side. Factor 0.5 is necessary |
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285 | !-- since the leap-frog scheme always progresses by 2 * delta t. |
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286 | !-- The user has to set the cfl_factor small enough to ensure that the |
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287 | !-- divergences do not become too large. |
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288 | !-- The time step must not exceed the maximum allowed value. |
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289 | IF ( timestep_scheme(1:5) == 'runge' ) THEN |
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290 | dt_3d = cfl_factor * MIN( dt_diff, dt_plant_canopy, dt_u, dt_v, dt_w ) |
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291 | ELSE |
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292 | dt_3d = cfl_factor * 0.5 * & |
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293 | MIN( dt_diff, dt_plant_canopy, dt_u, dt_v, dt_w ) |
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294 | ENDIF |
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295 | dt_3d = MIN( dt_3d, dt_max ) |
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296 | |
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297 | ! |
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298 | !-- Remember the restricting time step criterion for later output. |
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299 | IF ( MIN( dt_u, dt_v, dt_w ) < MIN( dt_diff, dt_plant_canopy ) ) THEN |
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300 | timestep_reason = 'A' |
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301 | ELSEIF ( dt_plant_canopy < dt_diff ) THEN |
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302 | timestep_reason = 'C' |
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303 | ELSE |
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304 | timestep_reason = 'D' |
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305 | ENDIF |
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306 | |
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307 | ! |
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308 | !-- Set flag if the time step becomes too small. |
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309 | IF ( dt_3d < ( 0.00001 * dt_max ) ) THEN |
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310 | stop_dt = .TRUE. |
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311 | |
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312 | WRITE( message_string, * ) 'Time step has reached minimum limit.', & |
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313 | '&dt = ', dt_3d, ' s Simulation is terminated.', & |
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314 | '&old_dt = ', old_dt, ' s', & |
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315 | '&dt_u = ', dt_u, ' s', & |
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316 | '&dt_v = ', dt_v, ' s', & |
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317 | '&dt_w = ', dt_w, ' s', & |
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318 | '&dt_diff = ', dt_diff, ' s', & |
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319 | '&dt_plant_canopy = ', dt_plant_canopy, ' s', & |
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320 | '&u_max = ', u_max, ' m/s k=', u_max_ijk(1), & |
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321 | ' j=', u_max_ijk(2), ' i=', u_max_ijk(3), & |
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322 | '&v_max = ', v_max, ' m/s k=', v_max_ijk(1), & |
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323 | ' j=', v_max_ijk(2), ' i=', v_max_ijk(3), & |
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324 | '&w_max = ', w_max, ' m/s k=', w_max_ijk(1), & |
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325 | ' j=', w_max_ijk(2), ' i=', w_max_ijk(3) |
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326 | CALL message( 'timestep', 'PA0312', 0, 1, 0, 6, 0 ) |
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327 | ! |
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328 | !-- In case of coupled runs inform the remote model of the termination |
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329 | !-- and its reason, provided the remote model has not already been |
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330 | !-- informed of another termination reason (terminate_coupled > 0) before. |
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331 | #if defined( __parallel ) |
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332 | IF ( coupling_mode /= 'uncoupled' .AND. terminate_coupled == 0 ) THEN |
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333 | terminate_coupled = 2 |
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334 | IF ( myid == 0 ) THEN |
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335 | CALL MPI_SENDRECV( & |
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336 | terminate_coupled, 1, MPI_INTEGER, target_id, 0, & |
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337 | terminate_coupled_remote, 1, MPI_INTEGER, target_id, 0, & |
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338 | comm_inter, status, ierr ) |
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339 | ENDIF |
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340 | CALL MPI_BCAST( terminate_coupled_remote, 1, MPI_INTEGER, 0, comm2d, ierr) |
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341 | ENDIF |
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342 | #endif |
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343 | ENDIF |
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344 | |
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345 | ! |
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346 | !-- Ensure a smooth value (two significant digits) of the timestep. For |
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347 | !-- other schemes than Runge-Kutta, the following restrictions appear: |
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348 | !-- The current timestep is only then changed, if the change relative to |
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349 | !-- its previous value exceeds +5 % or -2 %. In case of a timestep |
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350 | !-- reduction, at least 30 iterations have to be performed before a timestep |
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351 | !-- enlargement is permitted again. |
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352 | percent_change = dt_3d / old_dt - 1.0 |
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353 | IF ( percent_change > 0.05 .OR. percent_change < -0.02 .OR. & |
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354 | timestep_scheme(1:5) == 'runge' ) THEN |
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355 | |
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356 | ! |
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357 | !-- Time step enlargement by no more than 2 %. |
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358 | IF ( percent_change > 0.0 .AND. simulated_time /= 0.0 .AND. & |
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359 | timestep_scheme(1:5) /= 'runge' ) THEN |
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360 | dt_3d = 1.02 * old_dt |
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361 | ENDIF |
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362 | |
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363 | ! |
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364 | !-- A relatively smooth value of the time step is ensured by taking |
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365 | !-- only the first two significant digits. |
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366 | div = 1000.0 |
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367 | DO WHILE ( dt_3d < div ) |
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368 | div = div / 10.0 |
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369 | ENDDO |
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370 | dt_3d = NINT( dt_3d * 100.0 / div ) * div / 100.0 |
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371 | |
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372 | ! |
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373 | !-- Now the time step can be adjusted. |
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374 | IF ( percent_change < 0.0 .OR. timestep_scheme(1:5) == 'runge' ) & |
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375 | THEN |
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376 | ! |
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377 | !-- Time step reduction. |
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378 | old_dt = dt_3d |
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379 | dt_changed = .TRUE. |
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380 | ELSE |
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381 | ! |
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382 | !-- For other timestep schemes , the time step is only enlarged |
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383 | !-- after at least 30 iterations since the previous time step |
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384 | !-- change or, of course, after model initialization. |
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385 | IF ( current_timestep_number >= last_dt_change + 30 .OR. & |
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386 | simulated_time == 0.0 ) THEN |
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387 | old_dt = dt_3d |
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388 | dt_changed = .TRUE. |
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389 | ELSE |
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390 | dt_3d = old_dt |
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391 | dt_changed = .FALSE. |
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392 | ENDIF |
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393 | |
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394 | ENDIF |
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395 | ELSE |
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396 | ! |
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397 | !-- No time step change since the difference is too small. |
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398 | dt_3d = old_dt |
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399 | dt_changed = .FALSE. |
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400 | ENDIF |
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401 | |
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402 | IF ( dt_changed ) last_dt_change = current_timestep_number |
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403 | |
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404 | ENDIF |
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405 | CALL cpu_log( log_point(12), 'calculate_timestep', 'stop' ) |
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406 | |
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407 | END SUBROUTINE timestep |
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