GGU-3D-TRANSIENT: "Model" menu item
- Matthias Jusko
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:
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 needed, use a time step bigger than 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. Independently of the selected time increment, the program automatically proceeds to all times associated with boundary polygons.
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 modelling 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.
After entering your modelling preferences close the above dialog box using the "OK" button. The system information will then be displayed first. The modelling results are saved in a ".plw3d" file. The complete path can be viewed after clicking the "Show complete file name" button. Modelling starts after closing the message box by pressing "OK".
During modelling, a dialog box appears with information on the 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 parameters such as maximum deviation, time step, etc. and then carry on modelling. If you bring modelling to an end the current time step is completed when you click "Safe cancel". You are provided with information on the modelling time and the size of the result file once modelling is complete.