Complete rework of relinearisation options
Posted: Tue Oct 10, 2017 6:23 pm
Dear MICRESS users,
For the MICRESS 6.400 release, the existing relinearisation options have been strongly reworked and complemented by additional options. Updating relinearisation data is often very time-consuming, and the user needs to decide how often and at which scope such an updating is necessary - eventually he will have to decide by weighting simulation time vs. exactness and numerical stability.
In general, when using TC-coupling to thermodynamic databases, quasi-equilibrium conditions at the interface are calculated which needs access to the database and to the Thermo-Calc (TQ) calculation engine, and which is time-consuming. Afterwards, depending on the chosen updating scheme, these data are extrapolated and used for a certain time before updating is performed. While the way how the updating frequency is controlled has not changed recently (two independent inputs for all interfaces and each phase interaction, either at constant intervals ("manual"), time-dependent intervals ("from_file") or after a certain temperature change ("automatic")), the focus here is on the scope or spatial reference where the linearisation are calculated and valid for.
All in all, 5 such options are now available which can be specified following the "database" keyword in the phase diagram input data of each phase interaction, 3 of which were already part of version 6.300. Default is "local" linearisation which means that each interface cell bears its own set of linearisation data. The option "global" means that each interface between two specific grains will get its own data set, which strongly reduced the effort of updating. In order to increase "locality" and exactness, this spatial scope can be narrowed by "globalF" to each interconnected segment ("fragment") of the interface region for a specific grain pair.
As new option, "globalG" connects one set of linearisation data to all interfaces between two phases, so that it comes close to a "linearized phase diagram", or more precisely the "linTQ" mode with the important difference that the data are automatically calculated and updated based on the average interface compositions and temperature. Nevertheless, this mode should be regarded as a fully global description. In combination with the idea of interconnected segments, the "globalGF" mode finally defines common linearisation data for interconnected segments ("fragments") of phase interfaces which may span several grain interfaces belonging to the same phase pair.
In terms of "locality", the following order can be defined:
"local" > "globalF" > "global" > "globalGF" > "globalG"
In general, the spatial scope given by these options corresponds as well to the region where the common linearisation data is valid as well as the region where the average interface composition is retrieved for calculation of updated linearisation data.
In multi-phase regions (triple junctions), this procedure may lead to local inconsistencies between the different phase interfaces, because they use linearisation data sets which may have been averaged based on different spatial regions (as the integration area for each interface also includes dual interface regions). If necessary, this problem can be avoided using the option "database_consistent" which separates the triple point areas from the dual interface regions both in terms of the range of averaging of interface compositions as in terms of the range of validity of the linearisation data.
"database_consistent" is only available globally for all interfaces and essentially splits the relinearisation areas into smaller consistent blocks. If different option collide at the triple junctions, the one with the highest "locality" will inherit its properties to the other coexisting interfaces to keep consistency in all cases.
For the MICRESS 6.400 release, the existing relinearisation options have been strongly reworked and complemented by additional options. Updating relinearisation data is often very time-consuming, and the user needs to decide how often and at which scope such an updating is necessary - eventually he will have to decide by weighting simulation time vs. exactness and numerical stability.
In general, when using TC-coupling to thermodynamic databases, quasi-equilibrium conditions at the interface are calculated which needs access to the database and to the Thermo-Calc (TQ) calculation engine, and which is time-consuming. Afterwards, depending on the chosen updating scheme, these data are extrapolated and used for a certain time before updating is performed. While the way how the updating frequency is controlled has not changed recently (two independent inputs for all interfaces and each phase interaction, either at constant intervals ("manual"), time-dependent intervals ("from_file") or after a certain temperature change ("automatic")), the focus here is on the scope or spatial reference where the linearisation are calculated and valid for.
All in all, 5 such options are now available which can be specified following the "database" keyword in the phase diagram input data of each phase interaction, 3 of which were already part of version 6.300. Default is "local" linearisation which means that each interface cell bears its own set of linearisation data. The option "global" means that each interface between two specific grains will get its own data set, which strongly reduced the effort of updating. In order to increase "locality" and exactness, this spatial scope can be narrowed by "globalF" to each interconnected segment ("fragment") of the interface region for a specific grain pair.
As new option, "globalG" connects one set of linearisation data to all interfaces between two phases, so that it comes close to a "linearized phase diagram", or more precisely the "linTQ" mode with the important difference that the data are automatically calculated and updated based on the average interface compositions and temperature. Nevertheless, this mode should be regarded as a fully global description. In combination with the idea of interconnected segments, the "globalGF" mode finally defines common linearisation data for interconnected segments ("fragments") of phase interfaces which may span several grain interfaces belonging to the same phase pair.
In terms of "locality", the following order can be defined:
"local" > "globalF" > "global" > "globalGF" > "globalG"
In general, the spatial scope given by these options corresponds as well to the region where the common linearisation data is valid as well as the region where the average interface composition is retrieved for calculation of updated linearisation data.
In multi-phase regions (triple junctions), this procedure may lead to local inconsistencies between the different phase interfaces, because they use linearisation data sets which may have been averaged based on different spatial regions (as the integration area for each interface also includes dual interface regions). If necessary, this problem can be avoided using the option "database_consistent" which separates the triple point areas from the dual interface regions both in terms of the range of averaging of interface compositions as in terms of the range of validity of the linearisation data.
"database_consistent" is only available globally for all interfaces and essentially splits the relinearisation areas into smaller consistent blocks. If different option collide at the triple junctions, the one with the highest "locality" will inherit its properties to the other coexisting interfaces to keep consistency in all cases.