Tips for a Successful Diffusion Simulation

For example, if you have an alloy with five or six elements, first run a simulation with only the main elements. When this simulation works, you can then add more elements as necessary.

If you start with a high accuracy setting, then computing the simulation takes much longer, and problems are more likely. Check the profiles and the overall mass balance, and if the accuracy is insufficient then you can improve the accuracy values.

To change the accuracy:

In Console Mode use SET_ACCURACY and increase or decrease Max relative error and Max absolute error.

In Graphical Mode the setting is on the Diffusion Calculator in the section Time step control.

If you get large fluctuations in the composition or phase boundary profiles, then you can try modifying the grid or the time step of the simulation. You can increase the time step by lowering the accuracy if automatic time step control is used (the default).

If you increase the tolerated relative and/or absolute error then the automatic time step control increases the time step.

In Console Mode use the SET_ACCURACY command.

In Graphical Mode the setting is on the Diffusion Calculator in the section Time step control.

The composition or phase boundary profiles can often also be improved if the partial differential equations (PDEs) are integrated fully implicitly (i.e. Euler backward).

To integrate the PDEs in this way:

In Console Mode use SET_SIMULATION_CONDITION to set the parameter Degree of Implicity when Integrating PDEs to a value of 1.

In Graphical Mode, the setting is on the Diffusion Calculator on the Options tab. Under Simulation Conditions, you can try a different Time integration method. The default method is Trapezoidal, which is equivalent to a 0.5 numerical setting in Console Mode. If you choose Euler backward, this is equivalent to a 1.0 numerical setting in Console Mode.

If your Console Mode simulation fails to converge, then debugging may give you some clues about the source of the failure. To receive more detailed information about what is happening during the simulation use the command DEBUGGING.