Constraint equations to join rotating shafts in Calculix

barrti

Greetings
In a recent post today I started experimenting with mpcs to join the rotation of two shafts (beam elements) using dynamic analysis. It worked for small rotations in the mw solver. Because I will experience large rotations I will need to use the ccx nonlinear dynamic solver. Thanks to Victor for explaining this.

This brings me to my current question. How do you write an Mpc using ccx solver in mecway, to join the rotation of the two shafts at right angles? Is it possible to write an Mpc between the two end nodes of the two beams?

I tried to look at ccx documentation but I could not sort it out.

Regards
Barrti

Victor

This is tricky. I don't really know how to do that, or even if you can. *EQUATION only does linear equations, so if you connect displacements, they'll have the same problem of not rotating properly with large rotations. *MPC does nonlinear equations but you can't define them yourself without recompiling CCX, and the built-in ones don't seem to connect rotations.

Are you sure you need large rotations? You're presumably not trying to model a complete revolution of the driveshaft? I'd expect you could capture vibration and elastic deformation using only small rotations. Also, rotational DOF can tolerate bigger rotation angles than translational DOF because a linear change in angle is still a rotation, not a translation.

barrti

Victor
Thanks for that. I'm glad that it wasn't some obvious thing that I just missed!

I should be fine given that shaft rotation as you explain will be tolerated to a larger extent with a linear analysis. I should be able to do a separate analysis that handles large geometry changes.
Thanks again for explaining.
Regards
Tim