Issue with convergence with similar meshes

[lango]

Elmer beginner here, I've been playing around with a box case to get the hang of it. Files are below.

Issue I have is, if I change the mesh to a similar but less uniform version, the simulation goes from working perfectly to diverging. Everything else is kept the same and both meshes were generated the same way from the same geometry, only change was in the minimum element size when meshing. The attached case has the working mesh, the one that diverges is in the separate file.

The result that works is as expected, the force in the bottom displaces it uniformly, as in the left of the image. The diverged case goes a bit wild.

results.png

(409.97 KiB) Not downloaded yet

What could be causing such different behaviour from similar meshes? Am I missing something obvious?

[kevinarden]

Elastic solvers are very dependent on mesh quality. The linear tet is never used for, linear triangles are also not used.
Inconsistent terms in the interpolation functions of linear elements make shear strains much different from zero. The non-zero artificial shear strains absorb much energy making the element stiffer. To alleviate shear locking you can: 1) use finer mesh of standard linear elements; 2) use standard high-order elements; 3) use incompatible (non standard) elements designed for anti shear locking.

Hexahedron elements and quads are preferred, if tets and triangles are necessary they must be higher order elements. You were probably just on the edge of converging with the first mesh.

Also in elastic solvers iterative solutions are not necessary, you can use direct methods.

[lango]

Thank you for the suggestion!

Couldn't get better results with higher order, but direct method did the trick for me.