GGU-2D-TRANSIENT: "Start" menu item
After going to this menu item or, alternatively, by pressing [F5], the program models the specified system using the data provided The following dialog box appears first:
All results from the transient modelling are included in the output file. It is automatically given the "_t.plw" extension, because the GGU-PLGW evaluation program only displays files with this extension in the file selector box, for reasons of clarity.
Furthermore, the following check boxes and/or preferences can be used in the dialog box:
You define the end time ("End time") for the transient modelling (dimension as for permeability).
You define the time increment ("Time step value dtmax") of the transient modelling (dimension as for permeability). The program also includes a time increment control. If you have selected a time increment that is too large, the time increment will be halved during transient modelling until sufficient precision is achieved. If you have selected a very small time increment, the program is also capable of adjusting the increment by doubling. If this is not wished for because, e.g., you need values at certain times for later evaluation, simply deactivate the "If required increase time step via dtmax" check box.
Iteration is necessary for every time increment. If the deviation of the potentials between the iteration steps (i) and (i - 1) is smaller than the "Maximum deviation", the program will jump to the next time increment. Maximum deviation values of 0.0001 are generally sufficient.
You have the option of specifying a "Damping" value. During phreatic line modelling in complicated groundwater systems, oscillation around the actual solution can occur. This oscillation is damped by the damping factor. Values between 0.0 and 0.95 make the most sense. A value of 1.0 (complete damping) is nonsense and will therefore not be accepted by the program.
A flood of results is usually the consequence of transient modelling, with correspondingly large result files. Often, a small time increment must be selected in order to achieve sufficiently precise results. You can therefore specify in the "Data output" group box the times at which data output should follow.
During modelling, the program automatically proceeds to all times associated with boundary polygons, regardless of the selected time step. If you activate the "At all polygon course modelling points" check box, the results for all times will be given additionally to the usual input. So data output can either be at all polygon course output points, at a user-definable time [T], or at each desired (nth) time increment. These three options can also be combined with one another. It is conceivable, for example, to enter a very large value for data output "At each nth time step" and to temporally subdivide a boundary condition polygon such that output only occurs at the user-defined times.
Because long paths are shown shortened in the dialog box, the "Display entire file name" button can be clicked before commencing modelling. The name of the file containing the transient modelling data will then be displayed showing the complete path.
Once all data has been entered, start modelling by clicking "OK". During modelling, a dialog box appears with information on modelling progress. It is also provided with a "Cancel" button. If you press this button, modelling will not cease immediately, but instead you can edit specific program data such as maximum deviation, time step, etc. and then carry on modelling.
A record with the extension "_t.plw" is generated for the evaluation application during modelling. If, after commencing modelling, you open the GGU-PLGW program, you can check and evaluate the current results while modelling is still in progress. The "Animation" function is particularly impressive here; it can be executed parallel to the running modelling process.