Help on the FEM-PD coupling with 3D Hex8 elements

[ValeMig16]

Dear All,
I am writing to kindly ask for your support on the below topic.

I have the final objective to perform an impact simulation, however, to due the extensive geometry, I am investigating the Arlequin FEM–PD coupling as a possible alternative. Before moving to the actual geometry, I started developing a smaller flat plate (3D) as an initial and simpler benchmark.
Following the FEM_Bar example, I first generated a 3D tetrahedral mesh and corresponding mesh_data and topo_data files. However, during FEM initialization I obtained the error: "Size of topology and polynomial degree does not match". Following this, I tried with 8-node hexahedral elements rather than 4-node tetrahedra.

The simulation seemed to proceed significantly further with the below steps all completed successfully.
mesh reading
neighborhood creation
overlap creation
FEM initialization
Arlequin activation
coupling pair search

Unfortunately, the error I encountered was "UndefVarError: Hexahedron not defined in PeriLab.Helpers".

Could you please help me to better understand whether the current Arlequin coupling is intended to support 3D HEX8 finite elements?
If not, I would like to know whether extending the current implementation to HEX8 elements is planned in future releases.

If it could be helpful, I have attached the files related to the HEX8 simulation.

Thank you once again for your time,
Best regards,
Valeria

mesh_data_hex8_3d_coupled.txt
prova.yaml
prova_2026_06_28_16_38_37.log
topo_data_hex8_3d_coupled.txt

[JTHesse]

Continued in #377