| 1 | SUBROUTINE adapt_timestep(grid, config_flags) |
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| 2 | |
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| 3 | !-------------------------------------------------------------------------- |
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| 4 | !<DESCRIPTION> |
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| 5 | !<pre> |
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| 6 | ! |
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| 7 | ! This routine sets the time step based on the cfl condition. It's used to |
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| 8 | ! dynamically adapt the timestep as the model runs. |
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| 9 | ! |
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| 10 | ! T. Hutchinson, WSI |
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| 11 | ! March 2007 |
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| 12 | ! |
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| 13 | !</pre> |
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| 14 | !</DESCRIPTION> |
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| 15 | !-------------------------------------------------------------------------- |
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| 16 | |
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| 17 | ! Driver layer modules |
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| 18 | USE module_domain |
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| 19 | USE module_configure |
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| 20 | USE module_dm |
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| 21 | USE module_bc_em |
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| 22 | |
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| 23 | IMPLICIT NONE |
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| 24 | |
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| 25 | TYPE(domain) , TARGET , INTENT(INOUT) :: grid |
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| 26 | TYPE (grid_config_rec_type) , INTENT(IN) :: config_flags |
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| 27 | |
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| 28 | LOGICAL :: use_last2 |
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| 29 | REAL :: curr_secs |
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| 30 | REAL :: max_increase_factor |
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| 31 | REAL :: time_to_output, & |
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| 32 | time_to_bc |
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| 33 | INTEGER :: idex=0, jdex=0 |
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| 34 | INTEGER :: rc |
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| 35 | TYPE(WRFU_TimeInterval) :: tmpTimeInterval, dtInterval |
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| 36 | INTEGER :: num_small_steps |
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| 37 | integer :: tile |
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| 38 | LOGICAL :: stepping_to_bc |
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| 39 | INTEGER :: bc_time, output_time |
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| 40 | double precision :: dt |
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| 41 | INTEGER, PARAMETER :: precision = 100 |
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| 42 | INTEGER :: dt_num, dt_den, dt_whole |
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| 43 | REAL :: factor |
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| 44 | INTEGER :: num, den |
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| 45 | TYPE(WRFU_TimeInterval) :: last_dtInterval |
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| 46 | REAL :: real_time |
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| 47 | |
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| 48 | ! |
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| 49 | ! If use_last2 is true, this routine will use the time step |
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| 50 | ! from 2 steps ago to compute the next time step. This |
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| 51 | ! is used along with step_to_output and step_to_bc |
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| 52 | |
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| 53 | use_last2 = .FALSE. |
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| 54 | |
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| 55 | ! |
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| 56 | ! For nests, we only want to change nests' time steps when the time is |
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| 57 | ! conincident with the parent's time. So, if dtbc is not |
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| 58 | ! zero, simply return and leave the last time step in place. |
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| 59 | ! |
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| 60 | if (config_flags%nested) then |
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| 61 | if (abs(grid%dtbc) > 0.0001) then |
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| 62 | return |
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| 63 | endif |
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| 64 | endif |
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| 65 | |
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| 66 | last_dtInterval = grid%last_dtInterval |
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| 67 | |
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| 68 | ! |
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| 69 | ! Get current time |
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| 70 | ! |
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| 71 | |
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| 72 | tmpTimeInterval = domain_get_current_time ( grid ) - & |
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| 73 | domain_get_start_time ( grid ) |
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| 74 | |
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| 75 | ! |
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| 76 | ! Calculate current time in seconds since beginning of model run. |
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| 77 | ! Unfortunately, ESMF does not seem to have a way to return |
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| 78 | ! floating point seconds based on a TimeInterval. So, we will |
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| 79 | ! calculate it here--but, this is not clean!! |
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| 80 | ! |
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| 81 | curr_secs = real_time(tmpTimeInterval) |
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| 82 | |
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| 83 | ! |
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| 84 | ! Calculate the maximum allowable increase in the time step given |
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| 85 | ! the user input max_step_increase_pct value and the nest ratio. |
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| 86 | ! |
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| 87 | if (config_flags%nested) then |
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| 88 | max_increase_factor = 1. + & |
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| 89 | grid%parent_time_step_ratio * grid%max_step_increase_pct / 100. |
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| 90 | else |
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| 91 | max_increase_factor = 1. + grid%max_step_increase_pct / 100. |
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| 92 | endif |
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| 93 | |
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| 94 | ! |
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| 95 | ! If this is the first time step of the model run (indicated by current_time |
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| 96 | ! eq start_time), then set the time step to the input starting_time_step. |
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| 97 | ! |
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| 98 | ! Else, calculate the time step based on cfl. |
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| 99 | ! |
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| 100 | if (domain_get_current_time ( grid ) .eq. domain_get_start_time ( grid )) then |
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| 101 | CALL WRFU_TimeIntervalSet(dtInterval, Sn=grid%starting_time_step, Sd=1) |
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| 102 | curr_secs = 0 |
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| 103 | CALL WRFU_TimeIntervalSet(last_dtInterval, Sn=0, Sd=1) |
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| 104 | |
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| 105 | else |
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| 106 | if (grid%max_cfl_val < 0.001) then |
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| 107 | ! |
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| 108 | ! If the max_cfl_val is small, then we increase dtInterval the maximum |
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| 109 | ! amount allowable. |
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| 110 | ! |
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| 111 | num = INT(max_increase_factor * precision + 0.5) |
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| 112 | den = precision |
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| 113 | dtInterval = last_dtInterval * num / den |
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| 114 | |
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| 115 | else |
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| 116 | ! |
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| 117 | ! If the max_cfl_val is greater than the user input target cfl, we |
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| 118 | ! reduce the time step, |
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| 119 | ! else, we increase it. |
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| 120 | ! |
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| 121 | if (grid%max_cfl_val .gt. grid%target_cfl) then |
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| 122 | ! |
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| 123 | ! If we are reducing the time step, we go below target cfl by half the |
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| 124 | ! difference between max and target (or 75% of the last time step, |
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| 125 | ! which ever is greater). |
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| 126 | ! This tends to keep the model more stable. |
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| 127 | ! |
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| 128 | |
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| 129 | factor = MAX ( 0.75 , ( (grid%target_cfl - 0.5 * & |
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| 130 | (grid%max_cfl_val - grid%target_cfl) ) / grid%max_cfl_val ) ) |
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| 131 | num = INT(factor * precision + 0.5) |
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| 132 | den = precision |
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| 133 | |
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| 134 | dtInterval = last_dtInterval * num / den |
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| 135 | |
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| 136 | else |
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| 137 | ! |
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| 138 | ! Linearly increase dtInterval (we'll limit below) |
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| 139 | ! |
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| 140 | |
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| 141 | factor = grid%target_cfl / grid%max_cfl_val |
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| 142 | num = INT(factor * precision + 0.5) |
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| 143 | den = precision |
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| 144 | dtInterval = last_dtInterval * num / den |
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| 145 | endif |
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| 146 | |
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| 147 | endif |
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| 148 | |
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| 149 | endif |
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| 150 | |
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| 151 | ! Limit the increase of dtInterval to the specified input limit |
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| 152 | |
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| 153 | num = NINT( max_increase_factor * precision ) |
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| 154 | den = precision |
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| 155 | tmpTimeInterval = last_dtInterval * num / den |
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| 156 | if ( (domain_get_current_time ( grid ) .ne. domain_get_start_time ( grid )) & |
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| 157 | .and. (dtInterval .gt. tmpTimeInterval ) ) then |
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| 158 | dtInterval = tmpTimeInterval |
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| 159 | endif |
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| 160 | |
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| 161 | ! |
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| 162 | ! Here, we round off dtInterval to nearest 1/100. This prevents |
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| 163 | ! the denominator from getting too large and causing overflow. |
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| 164 | ! |
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| 165 | dt = real_time(dtInterval) |
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| 166 | num = NINT(dt * precision) |
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| 167 | den = precision |
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| 168 | CALL WRFU_TimeIntervalSet(dtInterval, Sn=num, Sd=den) |
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| 169 | |
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| 170 | ! Limit the maximum dtInterval based on user input |
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| 171 | |
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| 172 | CALL WRFU_TimeIntervalSet(tmpTimeInterval, Sn=grid%max_time_step, Sd=1) |
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| 173 | if (dtInterval .gt. tmpTimeInterval ) then |
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| 174 | dtInterval = tmpTimeInterval |
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| 175 | endif |
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| 176 | |
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| 177 | ! Limit the minimum dtInterval based on user input. |
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| 178 | |
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| 179 | CALL WRFU_TimeIntervalSet(tmpTimeInterval, Sn=grid%min_time_step, Sd=1) |
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| 180 | if (dtInterval .lt. tmpTimeInterval ) then |
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| 181 | dtInterval = tmpTimeInterval |
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| 182 | endif |
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| 183 | |
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| 184 | ! |
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| 185 | ! Now, if this is a nest, we round down the time step to the nearest |
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| 186 | ! value that divides evenly into the parent time step. |
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| 187 | ! |
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| 188 | if (config_flags%nested) then |
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| 189 | ! We'll calculate real numbers to get the number of small steps: |
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| 190 | |
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| 191 | dt = real_time(dtInterval) |
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| 192 | |
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| 193 | num_small_steps = CEILING( grid%parents(1)%ptr%dt / dt ) |
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| 194 | |
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| 195 | #ifdef DM_PARALLEL |
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| 196 | call wrf_dm_maxval(num_small_steps, idex, jdex) |
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| 197 | #endif |
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| 198 | dtInterval = domain_get_time_step(grid%parents(1)%ptr) / & |
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| 199 | num_small_steps |
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| 200 | endif |
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| 201 | |
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| 202 | ! |
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| 203 | ! Setup the values for several variables from the tile with the |
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| 204 | ! minimum dt. |
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| 205 | ! |
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| 206 | dt = real_time(dtInterval) |
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| 207 | |
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| 208 | #ifdef DM_PARALLEL |
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| 209 | call wrf_dm_mintile_double(dt, tile) |
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| 210 | CALL WRFU_TimeIntervalGet(dtInterval,Sn=dt_num,Sd=dt_den,S=dt_whole) |
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| 211 | call wrf_dm_tile_val_int(dt_num, tile) |
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| 212 | call wrf_dm_tile_val_int(dt_den, tile) |
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| 213 | call wrf_dm_tile_val_int(dt_whole, tile) |
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| 214 | CALL WRFU_TimeIntervalSet(dtInterval, Sn = dt_whole*dt_den + dt_num, Sd = dt_den) |
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| 215 | |
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| 216 | call wrf_dm_maxtile_real(grid%max_cfl_val, tile) |
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| 217 | call wrf_dm_maxtile_real(grid%max_vert_cfl, tile) |
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| 218 | call wrf_dm_maxtile_real(grid%max_horiz_cfl, tile) |
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| 219 | #endif |
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| 220 | |
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| 221 | ! |
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| 222 | ! Assure that we fall on a BC time. Due to a bug in WRF, the time |
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| 223 | ! step must fall on the boundary times. |
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| 224 | ! |
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| 225 | |
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| 226 | time_to_bc = grid%interval_seconds - grid%dtbc |
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| 227 | num = INT(time_to_bc * precision + 0.5) |
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| 228 | den = precision |
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| 229 | CALL WRFU_TimeIntervalSet(tmpTimeInterval, Sn=num, Sd=den) |
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| 230 | |
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| 231 | if ( ( tmpTimeInterval .LT. dtInterval * 2 ) .and. & |
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| 232 | ( tmpTimeInterval .GT. dtInterval ) ) then |
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| 233 | dtInterval = tmpTimeInterval / 2 |
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| 234 | |
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| 235 | use_last2 = .TRUE. |
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| 236 | stepping_to_bc = .true. |
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| 237 | |
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| 238 | elseif (tmpTimeInterval .LE. dtInterval) then |
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| 239 | |
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| 240 | bc_time = NINT ( (curr_secs + time_to_bc) / ( grid%interval_seconds ) ) & |
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| 241 | * ( grid%interval_seconds ) |
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| 242 | CALL WRFU_TimeIntervalSet(tmpTimeInterval, S=bc_time) |
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| 243 | dtInterval = tmpTimeInterval - & |
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| 244 | (domain_get_current_time(grid) - domain_get_start_time(grid)) |
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| 245 | |
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| 246 | use_last2 = .TRUE. |
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| 247 | stepping_to_bc = .true. |
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| 248 | else |
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| 249 | stepping_to_bc = .false. |
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| 250 | endif |
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| 251 | |
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| 252 | ! |
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| 253 | ! If the user has requested that we step to output, then |
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| 254 | ! assure that we fall on an output time. We look out two time steps to |
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| 255 | ! avoid having a very short time step. Very short time steps can cause model |
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| 256 | ! instability. |
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| 257 | ! |
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| 258 | |
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| 259 | if ((grid%step_to_output_time) .and. (.not. stepping_to_bc) .and. & |
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| 260 | (.not. config_flags%nested)) then |
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| 261 | |
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| 262 | time_to_output = grid%history_interval*60 - & |
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| 263 | mod(curr_secs, grid%history_interval*60.0) |
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| 264 | num = INT(time_to_output * precision + 0.5) |
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| 265 | den = precision |
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| 266 | call WRFU_TimeIntervalSet(tmpTimeInterval, Sn=num, Sd=den) |
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| 267 | |
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| 268 | if ( ( tmpTimeInterval .LT. dtInterval * 2 ) .and. & |
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| 269 | ( tmpTimeInterval .GT. dtInterval ) ) then |
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| 270 | dtInterval = tmpTimeInterval / 2 |
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| 271 | use_last2 = .TRUE. |
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| 272 | |
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| 273 | elseif (tmpTimeInterval .LE. dtInterval) then |
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| 274 | ! |
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| 275 | ! We will do some tricks here to assure that we fall exactly on an |
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| 276 | ! output time. Without the tricks, round-off error causes problems! |
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| 277 | ! |
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| 278 | |
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| 279 | ! |
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| 280 | ! Calculate output time. We round to nearest history time to assure |
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| 281 | ! we don't have any rounding error. |
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| 282 | ! |
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| 283 | output_time = NINT ( (curr_secs + time_to_output) / & |
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| 284 | ( grid%history_interval * 60 ) ) * (grid%history_interval * 60) |
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| 285 | CALL WRFU_TimeIntervalSet(tmpTimeInterval, S=output_time) |
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| 286 | dtInterval = tmpTimeInterval - & |
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| 287 | (domain_get_current_time(grid) - domain_get_start_time(grid)) |
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| 288 | |
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| 289 | use_last2 = .TRUE. |
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| 290 | endif |
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| 291 | endif |
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| 292 | |
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| 293 | if (use_last2) then |
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| 294 | grid%last_dtInterval = last_dtInterval |
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| 295 | else |
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| 296 | grid%last_dtInterval = dtInterval |
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| 297 | endif |
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| 298 | |
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| 299 | grid%dt = real_time(dtInterval) |
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| 300 | |
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| 301 | grid%last_max_vert_cfl = grid%max_vert_cfl |
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| 302 | |
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| 303 | ! |
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| 304 | ! Update the clock based on the new time step |
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| 305 | ! |
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| 306 | CALL WRFU_ClockSet ( grid%domain_clock, & |
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| 307 | timeStep=dtInterval, & |
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| 308 | rc=rc ) |
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| 309 | |
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| 310 | ! |
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| 311 | ! Lateral boundary weight recomputation based on time step. |
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| 312 | ! |
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| 313 | CALL lbc_fcx_gcx ( grid%fcx , grid%gcx , grid%spec_bdy_width , & |
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| 314 | grid%spec_zone , grid%relax_zone , grid%dt , config_flags%spec_exp , & |
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| 315 | config_flags%specified , config_flags%nested ) |
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| 316 | |
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| 317 | END SUBROUTINE adapt_timestep |
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| 318 | |
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| 319 | FUNCTION real_time( timeinterval ) RESULT ( out_time ) |
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| 320 | |
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| 321 | USE module_domain |
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| 322 | |
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| 323 | IMPLICIT NONE |
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| 324 | |
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| 325 | ! This function returns a floating point time from an input time interval |
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| 326 | ! |
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| 327 | ! Unfortunately, the ESMF did not provide this functionality. |
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| 328 | ! |
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| 329 | ! Be careful with the output because, due to rounding, the time is only |
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| 330 | ! approximate. |
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| 331 | ! |
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| 332 | ! Todd Hutchinson, WSI |
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| 333 | ! 4/17/2007 |
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| 334 | |
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| 335 | ! !RETURN VALUE: |
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| 336 | REAL :: out_time |
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| 337 | INTEGER :: dt_num, dt_den, dt_whole |
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| 338 | |
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| 339 | ! !ARGUMENTS: |
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| 340 | TYPE(WRFU_TimeInterval), intent(INOUT) :: timeinterval |
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| 341 | |
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| 342 | CALL WRFU_TimeIntervalGet(timeinterval,Sn=dt_num,Sd=dt_den,S=dt_whole) |
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| 343 | if (ABS(dt_den) < 1) then |
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| 344 | out_time = dt_whole |
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| 345 | else |
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| 346 | out_time = dt_whole + dt_num / REAL(dt_den) |
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| 347 | endif |
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| 348 | END FUNCTION |
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