Page 138 - TransAT_Tutorial_Manual

TransAT Tutorial Manual 4.1. Dam Break

4.1.5.5 Initial Conditions
In TransAT, the user has the possibility to create custom initial conditions. For two–phase flow
simulations especially, the initial gas–liquid interface topology has to be specified by the user. In
this case, this is achieved in TransAT using an XML file initialconditions.xml.

For this specific case, the only variables that are being initialized are simply the ones that are
solved for, i.e. velocity, pressure, and the Level-Set function which defines the topology of the
gas–liquid interface.

At the initial time step, pressure and velocity are set to 0 throughout the domain.

As for the two phases, they are initially confined in two distinct areas. The liquid is confined
in a rectangular area and the gas occupies the rest of the domain. The interface between the
two fluids is defined by the Level-Set function which is positive for one fluid and negative for
the other. To create the initial interface, a rectangular shape is defined in the Levet-set node of
initialconditions.xml.

To be able to use custom initial conditions in this case, the file initialconditions.xml has to be
placed in the project folder. For this case, a ready-made initial conditions file available in the
TransAT Tutorials folder will be used to initialise variables over the domain. More information
can be found on the generation of custom initial conditions in the Custom Initial Conditions
chapter of the TransAT User Manual .

• Click Files in the top left corner then select Save to save the settings of the simulation

• Copy the file initialconditions.xml from the folder
Public/Documents/TransAT5.7/Tutorials/4.1 - dam break to your project folder.

The simulation must now be re-loaded to take into account the initial conditions settings set in
initialconditions.xml.

• Click Files in the top left corner then select Open Project
• Select the project file of the simulation e.g. dam break.stt.

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Ascomp AG Switzerland 128 Version 5.7