Combine visco_plastic and grain_size model

Hello everyone, I 'm running a subduction model.
At first, I use the visco_plastic model because PeierlsCreep is available in this model.
Later I found that the grain size in this model is fixed, and grain size evolution seems only available in grain_size model.
When I set up the material model, I hope that the function of grain size evolution and visco-plastic are both available in one model.
Can this combination be directly completed in the settings of the prm file? Or do I need to modify the source file? How should I combine these two models for use?

Thanks a lot!
Jane

Hi Jane,

You are right that this would be useful functionality, unfortunately it is currently not possible without modifying the code itself. We have implemented some preliminary steps towards making grain size evolution available in other material models, but that is not complete yet. If you want to implement something on your own, you can take a look at PRs Create grain size evolution reaction model by gassmoeller · Pull Request #5991 · geodynamics/aspect · GitHub, add grain size to composite viscoplastic by bobmyhill · Pull Request #5972 · geodynamics/aspect · GitHub, allow variable grain size in diffusion creep by bobmyhill · Pull Request #5960 · geodynamics/aspect · GitHub, which contain the most relevant changes.

As far as I remember what is left to do is to include the grain size evolution reaction model into the visco plastic material model (like it is done in the grain size model), and to include the variable grain size as input into the visco plastic rheology (so that the diffusion creep viscosity can be adjusted accordingly). Not terribly difficult, but also more than a 5 line change, in particular we need to make sure the visco plastic material model continues to work as before if no grain size evolution is active.

Contributions in this direction are of course welcome, but if you want to give it a try, let us know early so we can develop this together (avoiding duplicate work, or having to rewrite a working code to make it fit into the broader picture).

Best,
Rene

Hi Rene,

Thank you for your detailed response and for pointing me toward the relevant PRs! The information you provided is really helpful.

I’ll give it a try and work on combining the grain size evolution with the visco-plastic material model myself. If I run into any issues or need further clarification, I’ll reach out so we can coordinate and ensure the implementation fits well into the broader structure.

I really appreciate your guidance and the ongoing efforts to improve ASPECT!

Best,
Jane