1) we know, some initial iterations are needed to get the smooth and equilibrium interface. the question is how to determine the number of iterations. And during the iteration, I think the interface also moves, maybe just a small distance?
2) which model does MICRESS use for anisotropic interfacial energy and mobility?
3)what is the meaning of INTEGER of randomization?
4) for diffusion, what does 'infinite' represent?
how to determine the initial iteration
Re: how to determine the initial iteration
Hi zhubq,
welcome to the MICRESS forum!
1.) The initial iterations are necessary because the initial grain structure typically is "sharp", and a diffuse interface has to be established.
If you have a planar interface, then the answer to the question how to determine the number of interations would be easy: You would just have to use a high enough number. As soon as there is a curvature, it gets more complicated, because the phase-field parameter is a non-conserved variable, and during initialisation solute redistribution is switched off. Because the stabilisation term, which enforces the interface profile, and curvature are not separated in our phase field model, curved initial grains will shrink and finally vanish if the number of iterations is too high. For single round particles we try to compensate for that, but in the general case this cannot be avoided.
In most cases, there will be no problem, if you use a small number (~10) of initial iterations. If you need to start with an exact given grain fraction, there is no other possibility than to do it by trial and error. On the other hand, to have a look on the bright side, the non-conserved phase-field variable during initialisation gives you the opportunity to fine-tune the initial grain fraction even if the "sharp" grain consists of only few grid cells...
2.) MICRESS uses different models for anisotropy. The simplest case is the cubic metallic anisotropy which in the 2D case consists of a 4-fold cosinus function (look here). Then, there is the more complex hexagonal symmetry which has been published (e.g. B. Böttger, J. Eiken, I. Steinbach: Phase field simulation of equiaxed solidification in technical alloys. Acta Materialia 54 (2006), pp. 2697-2704.), but which is currently under rework. Maybe, Janin can tell us more about that. Finally, there is a faceted model (look here) where each facet orientation can be specified explicitely and even an antifacet model (to be announced).
3.) If a MICRESS functionality makes use of a Random Number Generator, like for nucleation, this RNG has to be initialized with an arbitrary integer number. Otherwise, e.g., inserting a new nucleation type would change the random positions of all other types for a given MICRESS example. Essentially, the "randomization" is done to achieve reproducibility of the results.
4.) Infinite diffusion means that the composition in one phase is mixed completely, as if the diffusion coefficient was inifinite. If more than one grain of the given phase is present, only touching grains exchange there solute.
This option is very interesting, if diffusion coefficients vary by orders of magnitude, and only the lower ones are rate-determining. Then, this options greatly reduces the simulation time, because the internal diffusion time step can be significantly increased.
Best wishes
Bernd
welcome to the MICRESS forum!
1.) The initial iterations are necessary because the initial grain structure typically is "sharp", and a diffuse interface has to be established.
If you have a planar interface, then the answer to the question how to determine the number of interations would be easy: You would just have to use a high enough number. As soon as there is a curvature, it gets more complicated, because the phase-field parameter is a non-conserved variable, and during initialisation solute redistribution is switched off. Because the stabilisation term, which enforces the interface profile, and curvature are not separated in our phase field model, curved initial grains will shrink and finally vanish if the number of iterations is too high. For single round particles we try to compensate for that, but in the general case this cannot be avoided.
In most cases, there will be no problem, if you use a small number (~10) of initial iterations. If you need to start with an exact given grain fraction, there is no other possibility than to do it by trial and error. On the other hand, to have a look on the bright side, the non-conserved phase-field variable during initialisation gives you the opportunity to fine-tune the initial grain fraction even if the "sharp" grain consists of only few grid cells...
2.) MICRESS uses different models for anisotropy. The simplest case is the cubic metallic anisotropy which in the 2D case consists of a 4-fold cosinus function (look here). Then, there is the more complex hexagonal symmetry which has been published (e.g. B. Böttger, J. Eiken, I. Steinbach: Phase field simulation of equiaxed solidification in technical alloys. Acta Materialia 54 (2006), pp. 2697-2704.), but which is currently under rework. Maybe, Janin can tell us more about that. Finally, there is a faceted model (look here) where each facet orientation can be specified explicitely and even an antifacet model (to be announced).
3.) If a MICRESS functionality makes use of a Random Number Generator, like for nucleation, this RNG has to be initialized with an arbitrary integer number. Otherwise, e.g., inserting a new nucleation type would change the random positions of all other types for a given MICRESS example. Essentially, the "randomization" is done to achieve reproducibility of the results.
4.) Infinite diffusion means that the composition in one phase is mixed completely, as if the diffusion coefficient was inifinite. If more than one grain of the given phase is present, only touching grains exchange there solute.
This option is very interesting, if diffusion coefficients vary by orders of magnitude, and only the lower ones are rate-determining. Then, this options greatly reduces the simulation time, because the internal diffusion time step can be significantly increased.
Best wishes
Bernd