General questions regaring the new grid refinement functionality
- This topic has 2 replies, 2 voices, and was last updated 2 weeks, 5 days ago by .
-
Posts
-
First of all congratulations on the great job!
I have a couple of questions regarding the new grid refinement functionality that I am sure could help others as well.
1) When running the sphere3D example, the refined geometry gives an error message and states that there are some material 0 voxels although the simulation runs properly. This is also happening to a custom simulation I created and the refinement region definition does not seem to be easy to understand when analyzing the code. I know you are working on the documentation and perhaps this could be explained in depth.
2) Has the behavior of this functionality been validated or is it still in progress?
3) Will there be a problem if the refinement region captures half of a solid? Meaning that there are some solid boundaries in the interface between the refined and coarse grids, for example when refining the volume around the cylinder at the cylinder3D example, some of the lateral walls will be included in the refinement region and these walls will be part of the interface between both grids.
4) Does this functionality work with the turbulence models already available in openlb?
Thank you so much and keep up the good work, the development process of the software looks great.
1) You can ignore the geometry error here. This is a remnant of the current geometry validity conventions (e.g. that a material 0 (inactive) cell must not directly border a fluid (material 1) cell) only holding for uniform grids. You can remove the check method until we have a resolution-transparent geometry model in a future release, if this message bothers you.
The current release of the refinement module is a prototype that requires deep OpenLB knowledge to transfer to other cases. We are working on a user-friendly way to generate the refined meshes but this will take time.
2) Validation is in progress. In any case, grid refinement should always be evaluated for the specific application and LB models as it is a very active and unsettled topic. E.g. any refinement introduces an additional error source that can only be ignored after careful consideration and numerical tests.
3) This is a good example for the difficulty of refinement in LBM: It depends. A simple approach is to only couple bulk cells (as refinement schemes are commonly evaluated only in the bulk). For 3D Schäfer-Turek (cylinder3d), not coupling the wall cells suffices in my experience.
4) It should if the non-equilibrium is in fact obtained as the difference between current populations and their second-order equilibrium. If this doesn’t hold the coupling needs to be adapted.
Please also note that the public version implements a simplified version of the vertex-centered scheme by Lagrava (it uses very simplified spatial interpolations). A full version as well as support for cell-centered couplings are in the works.
The work on grid refinement is currently limited mostly by the number of developers working on this, if you are interested I’d be happy for any help.
- You must be logged in to reply to this topic.