## CalculiX Free Rotation Axis 3D Model Large Displacement

About the development of the FEM module/workbench.

Moderator: bernd

dbar
Posts: 3
Joined: Wed Oct 03, 2018 7:56 am

### CalculiX Free Rotation Axis 3D Model Large Displacement

Hello Everyone,

I'm struggling on how to applied on cylindrical face on a 3D model (no beam no shell) a free rotation condition.

My model is a simply 3D mechanical part tetra mesh with a single hole inside. There is no other part or element. And I want this hole as a rotation axis like a revolute joint.

Angle amplitude around this axis will be about plus or minus 90°. So calculation will be performed with NLGEOM. And analysis is *DYNAMIC.

It is planned to couple this Calculix model with a fluid calculation analysis on SU2.

I'm used to commercial FEM soft where it is click and play for creating this kind of boundary condition. But here tried things that I saw on forum or video tutorial and none of them respond to my problem. Also I cannot tried on an another software because my coupling soft only works with Calculix.

The only way I'm seeing is to add another part like a 3D pin and add contact conditions between them.

I really would like to avoid this kind of solution in order to not slowdown solving time due to convergence issue. I would like something fast to solve.

fandaL
Posts: 325
Joined: Thu Jul 24, 2014 8:29 am

### Re: CalculiX Free Rotation Axis 3D Model Large Displacement

Look at transformation tool
FEM/Model/Mechanical Constraints/Constraint transform
It should prescribe different coordinate system for nodes at the selected face, so that boundary condition on that nodes will be in local coordinate system

Check also the ccx manual for the *TRANSFORM card http://www.feacluster.com/CalculiX/ccx_ ... de318.html
bernd
Posts: 7890
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

### Re: CalculiX Free Rotation Axis 3D Model Large Displacement

dbar
Posts: 3
Joined: Wed Oct 03, 2018 7:56 am

### Re: CalculiX Free Rotation Axis 3D Model Large Displacement

Thank you fandaL

I did try *transform card : Adding a local cylindrical coordinate system at the center of my hole and then apply DOF conditions with rotation coordinate free (2nd DOF) on the hole.

It seemed work for small angle but when I try to reach high angle like 45° or more I had some weird deformation around the hole on the mesh plus, the rotation was not free to move. I had also some resisting reaction force on the hole.

I tried exactly the same condition as this tutorial : https://www.youtube.com/watch?v=8nwY23Gm4hU

anyway thank you for suggestion
dbar
Posts: 3
Joined: Wed Oct 03, 2018 7:56 am

### Re: CalculiX Free Rotation Axis 3D Model Large Displacement

I found a way to add free rotation condition around an axis without adding part to create hinge contact.

For those interested you should proceed as following:

Create a rigid body on the hole or surface representing you rotation axis. REF NODE and ROT NODE should be the same ass below. If REF NODE is not specified rotation doesn't really works.
*NODE
4883,0,0,0
*RIGID BODY,NSET=cl,REF NODE=4883,ROT NODE=4883

And then on boundary card free axis for rotation you want on rigid body node. In example below Z axis is free.
*BOUNDARY
4883,1,1,0
4883,2,2,0