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timesteps [2012/07/01 15:40] 134.93.180.188timesteps [2024/03/07 09:11] (current) enviadmin
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 In former versions, the main time step was fixed to 10s. It has turned out that this time step can be too large for certain cases which causes troubles in form of numerical instabilities. Therefore, ENVI-met provides now a dynamic adaptation of the main time step. The criteria for time step selection is the height of the sun. In former versions, the main time step was fixed to 10s. It has turned out that this time step can be too large for certain cases which causes troubles in form of numerical instabilities. Therefore, ENVI-met provides now a dynamic adaptation of the main time step. The criteria for time step selection is the height of the sun.
  
-**We highly recommend the usage of this feature. It is a default setting now.** +Smaller time steps are normally required when the solar input is high, whereas bigger ones can be used in the morning or evening. The solar height is divided into **3 intervals**, defined by 2 boundary values of the sun height ''heightA'' and ''heightB''.
- +
-Smaller time steps are normally required when the solar input is high, whereas bigger ones can be used in the morning or evening. The solar height is divided into 3 intervals, defined by 2 boundary values of the sun height heightA and heightB.+
  
 The intervals are: The intervals are:
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   * Interval 3 (class 2 timestep): ''heightB'' <= Sun height   * Interval 3 (class 2 timestep): ''heightB'' <= Sun height
  
-You can assign individual time steps to each of the intervals. Normally, the time step for interval 3 should be the smallest as this time interval is active when the sun height is at its maximum. Also, you can change the boundary values for switching between the intervals. +You can assign individual time steps to each of the intervals. Normally, the time step for interval 3 should be the smallest as this time interval is active when the sun height is at its maximum. Also, you can change the boundary values for switching between the interval. Both can be achieved in the ENVI-guide.
- +
-<file> +
-00:[TIMESTEPS] _______________________Dynamic Time steps +
-01:Sun height for switching dt(0) -> dt(1)       =40 +
-02:Sun height for switching dt(1) -> dt(2)       =50 +
-03:Time step (s) for interval 1 dt(0)            =10.+
-04:Time step (s) for interval 2 dt(1)            =5.0 +
-05:Time step (s) for interval 3 dt(2)            =2.0 +
-</file> +
-  +
-**In addition, during the first 30 minutes of model simulation, the main time step is always set to the class 2 timestep to improve numerical stability during the model spin-up phase.** +
- +
-===== What do the lines mean? ===== +
- +
-=== 01,02: Sun heights for switching between the intervals (Default 40° and 50°)=== +
-As said above, these are the values for height A and heightB defining the sun height threshold values switching between the time step intervals.\\ +
-The first value is the boundary between interval 1 and 2, the second one between interval 2 and 3. +
- +
-=== 03,04,05: Time steps for the 3 intervals (Default 10s, 5s, 2s)=== +
-The assigned time steps for the sun height intervals. +
- +
- +
-\\+
  
  
-===== ===== 
-Using dynamic time steps is the default setting in ENVI-met.\\ 
-You can overwrite it, be unselecting the "use dynamic time steps" option in the "Advanced Settings" tab (**add link**) and then clicking  "Apply Changes"