[Gmsh] Remeshing of deformed meshes and tracking of subdomains

[Christophe Geuzaine]

Hi Tim,

> On 29 May 2020, at 17:30, Tim Furlan <tim.furlan at tu-dortmund.de> wrote:
> 
> Dear gmsh users and developers,
> 
> i am dealing with high-deformation FEM simulations involving contact. I would like to replace the deformed mesh with a new one after a certain number of steps (potentially many times during one simulation). I use Abaqus as the FEM solver if it matters, and use the python api of gmsh.
> 
> For the remeshing, i create geometrical surfaces for all faces of my elements on the boundary of the domain. This means also creating lines for all element edges and keeping track of them, since they might occur more than once and with different directions.
> 
> I need to track certain subdomains (e.g. parts of the surface) to impose the boundary conditions, and the solution i came up with is to compound the corresponding surface faces and their respective boundaries (to allow both refinement and coarsening). To do this, i need to split the boundaries of the subdomains in a lot of segments (so that they end when a domain ends).
> 
> Tracking the subdomains only through physical tags seems unfeasible since the subdomain boundaries are then only preserved inaccurately.
> 

It's indeed a "classical" problem. I don't think there's a definitive answer about whether it's better to change/reconstruct the CAD and/or deform/untangle/adapt the mesh.

> I feel that i might be missing an easier way to do what i want. I looked into the tutorials and found the following options:
> 
> - The createGeometry() command is able to create geometry from a mesh (basically doing what i do by hand i guess?). However, i did not find an easy way to track boundary conditions using this, as i can not rely on identifying them by feature angles. Is there any way to obtain the elements the resulting entities are derived from?
> 
> - The tutorial on meshing of discrete curves looks like it follows a similar approach. However, i was unable to extend this approach to 3d surfaces. Is it possible to define discrete entities for the different parts of the body surface i want to remesh instead of using compounds? I was especially confused with how to handle e.g. element edges that belong to multiple surface parts.
> 

You should be able to do this indeed, i.e. define discrete surfaces after deformation and remesh those.  Maybe send a small example?

It might be better to open an issue on the gitlab for this, so that we can track progress.

Christophe


> I would appreciate any input on a more elegant/efficient way to solve the problem.
> 
> 
> Kind regard and thanks in advance
> 
> Tim
> 
> 
> 
> 
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— 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine