In the section "Phase interaction data" of the input file you have to specify the maximal driving force which is allowed for the corresponding phase interaction. Higher driving forces which occur in interfaces of this phase interaction are automatically cut off smoothly.
Cutting off the driving force is only necessary in few cases. One such case would be if you start a simulation with an initial high undercooling (like with nucleation), which would cause numerical problems in this initial state if the spacial resolution is insufficient. But if you are not interested in the initial behaviour to be correctly simulated you can afford to use a coarse resolution and to suppress the numerical problems by cutting off the high driving force at the beginning. At a later stage this cut-off will no longer affect the results because the interface is nearer to local equilibrium. Specifying a huge value for the maximal driving force switches off this option.
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original message from Bernd
Maximal driving force allowed
Problems with a too low dGMax value
Hi all,
I want to add a further comment with respect to the consequences of a too low value of the maximal driving force allowed. I experienced a problem in a multicomponent Ni-based example where I had chosen dGMax to be 10 J/cm3 for the liquid-fcc interface. I found problems with single grid cells which, at the end of solidification, did not get completely solid. I found out that the reason was the high curvature contribution in such single cells, when various phases are involved which additionally block diffusion. Effectively, under these conditions, the maximal driving force of 10 J/cm3 was not sufficient to overcome the local curvature. Increasing dGMax to 15 J/cm3 immediately solved the problem!
You should consider that when you think about a reasonable value for dGMax or if you encounter problems with complete solidification!
Bernd
I want to add a further comment with respect to the consequences of a too low value of the maximal driving force allowed. I experienced a problem in a multicomponent Ni-based example where I had chosen dGMax to be 10 J/cm3 for the liquid-fcc interface. I found problems with single grid cells which, at the end of solidification, did not get completely solid. I found out that the reason was the high curvature contribution in such single cells, when various phases are involved which additionally block diffusion. Effectively, under these conditions, the maximal driving force of 10 J/cm3 was not sufficient to overcome the local curvature. Increasing dGMax to 15 J/cm3 immediately solved the problem!
You should consider that when you think about a reasonable value for dGMax or if you encounter problems with complete solidification!
Bernd