Applying Moments to line 3 beam using ccx and nonlinear 3d dynamic

barrtibarrti
Greetings
Its probably too late here but I cant get this model to run. What am I missing? Every time I add a moment to a node on the shaft on the x-axis to rotate the shaft, the software fails to find a solution.

Comments

  • VictorVictor
    I'll look again later but you might need to use a force couple on an additional element instead. Force on the wheel works.
  • VictorVictor
    edited October 2017
    I'm not sure why this happened but adding a dummy element with zero density to the node with the moment makes it solve.

    I also turned on automatic time stepping which helps it get further into the solution but it only rotates about 45 degrees.
  • barrtibarrti
    Thanks Victor

    That is very wierd? Do u think that this is a ccx bug/peculiarity?

    Maybe the arm you added gives the moment something to push on:)

    Some searching of the Calculix ccx info on beam elements:

    http://web.mit.edu/calculix_v2.7/CalculiX/ccx_2.7/doc/ccx/node53.html

    About a page into this link they talk about knots:
    "In addition, a knot is also generated if

    -a rotational degree of freedom in the node is constrained through a SPC or MPC. In this case, the knot introduces the necessary rotational degrees of freedom.

    -a bending moment or torque is defined in the nodes. Here too, the rigid body introduces the necessary rotational degrees of freedom."

    Just a guess - is it possible that this has something to do with it?

    I did get it to run to completion by using auto timestep with 100,000 steps. Took about 5mins. I also used a gentler torque ramp

    Thanks again.

    Regards
  • VictorVictor
    I think you're probably onto it with the knots. I don't understand them well enough to say though. Generally, all the 6-dof elements in CCX are a bit flimsy and it sometimes fails in surprising ways. I've seen the geometry of connections between elements determine success or failure of the solver on shells too.
  • barrtibarrti
    Victor,
    Thanks for that. FEA is an art often it seems!

    Cheers
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