Whether you want to use the exact gas cloud resulting from a dispersion simulation to conduct an explosion simulation, or simply stop and restart a simulation, you need a complete snapshot of the simulation to achieve this. Such a snapshot is called a dump file and it is written by FLACS as rd<JOBID>.nxxx, where xxx is the number of dump file which you define yourself.
When working with dump files, you write results of a simulation at a given time or other trigger, and then load these results in another simulation.

Writing dump files

You can create a dump file at any time during a simulation by using a runtime simulation control file cc<JOBID>.dat3. To generate the cc-file you have to activate the Dump/load settings by right-clicking into the scenario menu and ticking off the corresponding line.

Right-click on one of the scenario menu window titles or the background area to open the selection of visible scenario menu sections.

The corresponding section will show up in the CASD scenario menu, initially with a single data row. You can add as many rows as you wish, or delete rows, by right-clicking into the section.

On each row you can select the variable to be set by clicking on the default parameter and selecting it from the pull-down list with all possible values. The most common way to dump the results is at defined time; you achieve this by using the combination of an NDUMP and a TDUMP setting, where the first parameter defines the dump file number and the second defines the time (in simulation time seconds) when you want to dump the results.

For example, the parameters below will write a dump file rd<JOBID>.n001 holding a snapshot of the results at 600 seconds of simulated time. For each dump file number defined by the NDUMP parameter, you need to define the criterion for dumping the results on the following row.

Two other ways to trigger dumping are at a given iteration and at a given fuel level. You define these by using the two parameters IDUMP and FDUMP, respectively, in the same way as described for dumping results at a specific time.

The runtime simulation control file cc<JOBID>.dat3 can be edited while the simulation is running. Therefore, it is possible modify the settings described above during the simulation, based on its results. You can either modify the cc-file from CASD as described above, or you can open the cc-file with a text editor and add the dump settings you need.

Note that you can only dump results at future simulation times. That is, if the simulated time is 250 seconds you can only dump results at events occurring after this time.

Loading dump files

Once you have obtained a dump file of the simulation results you want to use, you can load these results at the start of your new simulation. The results dumped from the first simulation will be seen as initial conditions for the second simulation. For example, a gas cloud as the result dumped from a dispersion simulation can be the initial condition loaded by an explosion simulation.

Loading the dumped file into a new simulation is triggered in a similar way to writing the dump (see the section above on Writing dump files): instead of NDUMP for writing, you use to NLOAD to read the dump file with the given number at the start of a new simulation.

For example, the setting below will read the dump file with the same job number as the scenario being edited and having dump number 001, i.e. rd<JOBID>.n001.

The FLACS utility rdfile

Dump files are written with the resolution of the grid used in the dumped simulation. When reading the dumped results in the start-up of a new simulation, the grid resolution might be different. This is often the case when using a dispersion result to start an explosion simulation. In this case you need to adapt the dumped result to the grid resolution of the new simulation. This can be done using the FLACS utility rdfile.

Currently, you can only run the rdfile utility from the command line. The easiest way to do this is from a command window. You can open the Command Window by clicking on its icon in the RunManager tool bar or the Tools menu in RunManager.

Opening a command window from the RunManager: through the icon (left) or in the Tools menu.

In the command window, first of all type rdfile and press Enter to confirm that the utility is accessible and to get some guidelines on its usage.

The simplest command to adapt a dump file using rdfile from the command window is

rdfile rd<JOB-In>.nxxx rd<JOB-Out>.nyyy

where JOB-In is the job number of the simulation from which you dumped the results and JOB-Out is the job number of the new simulation you intend to run. The number xxx and yyy correspond to the number of the dump files. There are various options which you can use while adapting rd-files. These options are explained in the usage text that is displayed when you type rdfile in the command window.

An example of common usage of rdfile is to adapt the first (i.e. xxx=001) dispersion dump-file with scenario number 010100 to the grid resolution of an explosion simulation with scenario number 020100:

rdfile rd010100.n001 rd020100.n001 time=0 iter=0 force

Here time=0 and iter=0 set the simulation time and iteration number, respectively, back to zero. The option force will overwrite an existing output file with the same name.