Rigid Body Elements in Elmer?

[btjhedin]

I would like to run linear elastic models in Elmer mixing 3d elements and 1d elements in form of rigid beams.

I have multiple bodies and couple them with rigid beams simulating bolt joints. In commercial software like Nastran, there is RBE2 and RBE3, where all nodes belonging to the element have directly coupled degrees of freedom. Usually, there is one master node, and a number of slave nodes, where the slave nodes have the same translation and rotation as the master node (or something similar).

I have managed to run elastic models meshed with 3d elements with good results.

1. The first question, can you use a mesh which mixes elements of different types?
2. Is there a rigid body element solver (or something with the same functionality) in Elmer?
3. Do I have to write my own solver, and in such case, how? (I have read the ElmerProgrammersTutorial.pdf, but I could use a few more hints)

Best regards,
Tommy

[raback]

Hi

1) Basically you could have an equation defined on different elements, it just requires some development in the code...
2) No.
3) I'm afraid so. Ask hints as you face them. The main challenge is how to couple the different dimensionalities in an implicit manner i.e. 1).

-Peter

[btjhedin]

I guess that what I really want to do is to add some terms to the global stiffness matrix.

Will that work if I use different solvers, or do I have to modify the ElasticSolver to read my special 1d elements?

[raback]

Hi

Yes, I think you have to express everything in form of single matrix equation in order to have decent performance. There are some tools that aid you to play with matrices. Of course it might be better to start with some specific solver but it is not impossible that something generic could be coined too.

-Peter