Connecting shells and solid elements by liaison_mail
[under construction .... not finished yet ... ]
To start with, this contribution mainly focuses on the use of Salome and Code Aster, not on the results and the mechanical justifications of the code that has been used. So no guarantee that the results will be correct up to the fifth decimal place, which they are not. I do hope though that this information is useful. For me it has been, because I had to think about some commands and look through the documentation and learn from that. In case of mistakes, errors or remarks, please notify me, or better, you are invited to correct or edit them yourself. Enjoy.
I stole a lot of ideas from the CaeLinux and Code Aster forums. So thank you for all who posted on this topic. This contribution is heavily based on the examples ssls101m and ssls101m in the atest directory
[As usual, the files that define the geometry, mesh and command files can be found at the end of this contribution.]
The geometry of the construction
- a number of method to establish a connection between shells to solid elements can be used:
- the Arlequin method
- use a region of solid nodes; this causes a rigid body between the interface of the shells and solids
- liason_mail, since version CAster 10.1.xx
As usual the geometry is quite simple in order not to disturb the issue we would like to show with other difficulties. The first part consists of a beam of height 23 [mm] and a cross section of 3*8 [mm2]. This part is modeled by solid elements. On top of this another beam of height 17 [mm] is added. The width of this beam is 8 [mm]. This part is modeled by shell elements, ie. only the 2D dimensions -height and width- are modeled here. The thickness of 1 [mm] is defined in the Aster command file.
The geometry is defined in a python script (for download see end of this contribution) and can be loaded into Salome Geometry module by File --> Load script (or ctrl T in the object browser window). Right click Refresh or push F5 after loading if necessary.
- x direction is out-of-plane of the shell
- z direction is in the main direction of the construction
The mesh of the construction
For we command file in Code Aster we need various parts (or groups in Salome) to apply boundary conditions, forces, material properties and such. These groups are depicted in the image above:
- the bottom and top surface of the block FBbot and FBtop,
- the solid element region block,
- the shell elements shell and
- the two vertices on top edge of the shell elements: Nforce
Again, the mesh of the construction is defined in a python script.
First, a mesh with linear elements has been used (tetra4 and tria3 elements) that can be used with DKT modelisation. Later a quadratic mesh with tetra10 and tria6 elements have been employed. This will provide us with a better converging solution, but makes the command file a bit more complex because we need to modify the tria6 to a tria7 mesh for coque_3d finite elements. The coque_3d element has an extra node at the centre of it.
Relevant part of the command file
The boundary conditions are applied on FBbot: all displacements of this surface are restricted. The forces are applied on the two nodes Nforce in the out-of-plane or x direction and the magnitude is 10 N each, ie. 20 N in total. The material properties of both the shell and solid elements are steel.