For transient calculations with the SITRA module, an ASCII file with the name out66 is generated after each simulation. The first row of this file contains the various parameters of the transient calculation (for a steady-state calculation, these parameters equal 0). This is followed by a block with the last calculated potential heads or pressure values (in the order of the internal node numbering) and a block with the last calculated concentrations/temperatures (if a transport calculation was carried out). This 'slimmed-down' version of the out66 file is generated automatically with each calculation run with SITRA.

If a transient calculation has already been performed and "Save for continuation (out66)" of the transient calculation has been selected, a detailed version of the out66 file is saved, which contains additional data required to continue transient calculations.

To continue the transient calculation, the user must rename the file out66 into null.

If a null file is available, you have several possibilities for using it:

• The potential/pressure heads and concentrations or temperatures from the null file can be used as starting values for an iteration (saturated/unsaturated calculation or density-dependent calculation), or selected as initial potential / pressure heads or initial concentrations / temperatures for a transient calculation. Only the 'slimmed down' form of the out66 file, renamed to null, is required for this.

• If a continuation of the transient calculation with the data of the null file is desired (warm start), the detailed form of the out66 file (renamed to null) is required. In this case, the time steps are calculated as follows:

If nmax time steps were calculated in the first run (nmax is the second to last parameter of the 1st line of the null file), then the time steps nmax+1, nmax+2, ... are calculated when the calculation is continued. The transient time steps of the continued calculation then begin with the last calculated time of the previous time steps.

• If the transient calculation is to be continued with a different transient input file, the parameter nmax of the previous calculation run must be changed to '-1' in the 1st line of the null file. Then, for the continuation of the transient calculation a new transient input file should be used. The starting time (0.0) of the new calculation then corresponds to the last calculated time of the previous calculation used to generate the warm start data. The transient times of the new calculation therefore start at 0.0. This procedure has the advantage that the data for already calculated time steps in the transient input file does not need to be included for the continuation.

Result files