2D Simulations - General Tab

In this tab, you can enter general information regarding the 2D model.

2D model information

The model name will default to the name of the active simulation in Flood Modeller, but this can be edited and a model description can also be entered (click in the ‘description’ field to enter free text). The log filename for the 2D simulation can also be given; free text can be entered directly into the field or click the ‘browse’ button to open standard windows file explorer. If no log name is given, the tool will automatically create a log file with the same name and in the same location as the input (XML) file.

1D linking

Check-boxes are provided to include a link to a 1D river simulation or/and a 1D urban simulation. For each, a new tab then appears to fill out the 1D simulation details, together with referencing the link-line or link-element shapefile defining the connection.

Run timing

There are various timing options to select from for the run of your 2D model. The default is ‘Normal’ : this will run the model from start to finish based on the ‘Start time’ and ‘Finish time’ given.

Start and Finish times can be entered as relative values, e.g. start at 1 hour and finish 3 hours later (i.e. at 4 hours), by clicking in the relevant field and entering the desired times. Note the ‘Time unit’ drop-down box allows you to choose between seconds, minutes, hours and days. The ‘Start time’ must be earlier than the ‘Finish time’ (and therefore you may need to adjust the ‘Finish time’ prior to adjusting the ‘Start time’ )

Alternatively, by clicking on the ‘-> Absolute’ button, times and dates can be given for both. To adjust the times, click on the relevant part of the time shown (i.e. hours, minutes or seconds) to highlight that part. The new time can be entered directly or adjusted using the arrow keys on your keyboard or the arrow keys shows on screen:

To adjust dates, click the relevant part of the date shown (i.e. day, month or year) to highlight that part. A new day or year can be entered manually or adjusted using the arrow keys on your keyboard, and the month can be adjusted using the arrow keys on your keyboard. Alternatively, click the calendar button to browse to the date required. Click ‘-> Relative’ to return to entering relative start and end times instead.

The ‘Use Time Zero’ button allows you to enter the absolute time (i.e. time and date) of the time that will be considered to be zero by the tool. For example, if you set “time zero” to 9 am and choose a relative ‘Start time’ of 1 hour, the model will run from 1 hour after “time zero”, i.e. from 10 am. Setting a “time zero” is not necessary if absolute times are given for the ‘Start time’ and ‘End time’ . Click ‘No Time Zero’ to return to not setting a “time zero” for the run.

Alternatives to the ‘Normal’ timing option are ‘Run to peak’ and ‘Run to Steady State’ . These are selected via radial button. If ‘Run to peak’ is selected, the model will run from the given start time until the time of the peak flow. As such, no end time is required by the user (this will default at -1.00 and not be editable). A ‘Start time’ (and “time zero”, if relevant) should be set in the way outlined above.

If ‘Run to Steady State’ is selected, the panel on the right-hand side will become enabled:

You can choose the run to stop on convergence of the volume: this feature is designed to reduce computation time. When performing a pseudo steady-state simulation, the model will be simulated until the flow into the model equals the flow out of the model and the model volume remains steady. The ‘Run to Steady State’ feature allows the user to specify one or more convergence criteria and run the model with no fixed end time. This causes the solver to run the simulation until it has reached a pseudo steady-state condition at which point it exits the simulation.

The method works by determining the domain volume at the current time and comparing this to the volume calculated ‘Comparison period’ minutes prior to the current time. If the new volume has differed by less than a certain tolerance value, the model is deemed to have reached a pseudo steady-state (i.e. the volume has converged).

If ‘Volume comparison’ has been selected, this tolerance value is ‘Tolerance’ percent of the current volume. If ‘Total inflow comparison’ has been selected, the tolerance value is ‘Tolerance’ percent of the current total inflow. If ‘smallest inflow comparison’ has been selected, the tolerance value is ‘Tolerance’ percent of the current smallest inflow.

Use the check boxes marked ‘Volume comparison’ , ‘Total inflow comparison’ and ‘Smallest inflow comparison’ to select one or multiple options. Note that at least one box must be checked in order to proceed. A percentage tolerance must be given in each case: these default to 0.1% but can be edited by clicking in the relevant field to update the number.

If multiple comparisons have been selected, the simulation will run until the new volume differs by less than the smallest of the tolerance values. The ‘Comparison period’ specifies the number of minutes prior to the current time at which the solver should be looking when comparing the current volume with the previous. This defaults to 18 minutes but can be increased. The comparison period should not be smaller than 18 minutes and a window will pop up if a value less than 18 is entered:

The ‘Minimum run time’ specifies the number of minutes the simulation runs for before any volume comparisons are made. The default value for this is 36 minutes, although this can be increased. The ‘Minimum run time’ must be greater than the comparison period plus 18 minutes, and you will be prompted to adjust the value if it is too small:

General options

A number of options relating to the model can be set up here. These include:

• Action on water reaching model boundary – this defaults to ‘none’ . A drop-down box provides the options of ‘Give warning’ or ‘Stop run’

• Attempt to correct negative depths – check box to be selected as necessary. Note this setting is only applicable to ADI domains and will be ignored for any TVD domains set up (a prompt box will warn you of this if ‘Attempt to correct negative depths’ is selected)

• Generate spatial diagnostic output – check box that is selected as default but can be unselected.

Fields are also provided to enter parameters to flag a mass error check. This will be performed after a certain number of seconds and with a defined tolerance: both of these values can be entered directly into the relevant field.