Target Times

This week, we’re highlighting two commands that allow for greater flexibility in defining target times during your HydroGeoSphere simulations: target times and generate target times.

The target times command lets you specify a simple list of times that the model should hit during the simulation. This is particularly useful when you need to include additional target times that aren’t tied to boundary conditions or output times—avoiding the creation of unnecessary output, especially in scenarios like transient calibration.

The generate target times command goes a step further by generating a sequence of target times automatically. You can specify the start time (tstart) and end time (tend) for the series, and the command will add time steps (delta) with an increasing multiplier (tinc) until it reaches a maximum size (dtmax). This command is helpful when you need a more structured or dynamic set of target times without manually listing each one.

Both commands provide flexibility when defining time targets in your model, especially when working with complex calibration processes or simulations that require precise timing without generating excessive output.

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During model setup, grok creates an internal lists of target times that HGS is required to hit during a simulation. The target times list is derived primarily from times set as part of boundary condition specification and from output times. In addition, some other commands may also update the target time list. In some cases (e.g., transient calibration), it may be desirable to include additional target times in the simulation without having to include them through boundary conditions or output times (which can generate unnecessary output).

There are two commands to facilitate this: target times and generate target times

Target times

Target times is a simple list of times that you want the simulation to hit.

For example:

target times
1
5
12.6
300
end

Generate Target times

Generate target times provides a simple algorithm to generate target times based on a start/end time, a defined time step size and multiplier. New target times are generated from the start time tstart to the end time tend by repeatedly adding the time step delta, which is increased each step by the multiplier tinc until it reaches a maximum size of dtmax.

For example:

generate target times
1      ! tstart
0.1    ! delta
1.2    ! tinc
10     ! dtmax
100    ! dtend

Output times

Users may be interested in adding newly generated target times (i.e. via Generate target times) to the list of output times (i.e. times when geospatial model output is recorded for every node in the model domain using the command Output times…end). Unfortunately this can’t be done automatically, with the rationale behind this limitation being that the generated target time list can be extremely large, and could result in excessively large amount of data being written to output files.

Thankfully there is a relatively simple workaround. A full list of target times is written to the .eco file when grox.exe is run, and you can simply copy the target times back into the .grok file under the output times command. As an example, the Generate target times command listed above by would result in the following output in the .eco file (with the resulting target times listed under the 'Time' column):

Target times
-------------------------------------
 Step #    Timestep             Time 
   1      1.0000000          1.0000000    
   2      4.0000000          5.0000000    
   3      7.6000000          12.600000    
   4      287.40000          300.00000    
   5      9999700.0          10000000.    
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