Contact Issues

Hi all,

I can't seem to get this contact working.

When the clevis has a displacement applied, the simulation will run, and a result is reached.
When I try to to do the same but by applying a force, it does not work.

The attached file should help.

I want to be able to apply a 3kN force, and check the final displacement, rather than the other way around.
I have tried troubleshooting with a very small force, as the non-converging model seems to explode and flatten like a pancake.
IC Contact.liml


  • The model always has to be fully constrained or it won't find a static solution. At the first time step, before it makes contact, the cylinder is unconstrained.

    You can solve it by putting weak springs on it to keep it from flying away until the contact engages. I also reduced the (initial) time step size to help it use a smaller force initially.

    Here's an example that solves but the springs are a bit too stiff and provide significant reaction force. Reduce their stiffness and the time step size until the force on the springs is negligible.
    IC Contact.liml
  • Hello Victor

    I downloaded your example IC contact.liml and opend it in Mecway 8.0.
    When I run the solver i got an error message in the solver Output

    "*ERROR reading *SPRING: *SPRING card without data"

    Looking to the inp-file .
    <------showed a blank line here

    after removing the empty line ccx (outside Mecway) started, but the reults were not meaningful (model exploded)

    is there an issue with Mecway 8.0
  • Which version of CCX are you using?
  • 2.10
  • I don't know why CCX 2.10 didn't work. According to the manual, it's supposed to have a blank line. Maybe a CR/LF problem?

    CCX 2.13 requires a decimal point after the spring constant so it might fail because Mecway doesn't include that - maybe change the spring constant to something with decimal places to force it? I'll update Mecway to use this new format. It's also made the blank line optional, so it should be safe to delete.

    I used the CCX 2.11 that's included with Mecway.
  • the decimal point solved that issue in 2.13_MT , your 2.11 was working too

  • Thanks Victor, and Merry Christmas!

    Back to projects between family commitments and before setting off on holiday, now is the time...

    Can you explain why you have used 3 springs in the locations that you have?
  • The 3 springs are to constrain the 3 degrees of freedom of the cylinder. They have pin joints at their ends so you need several:
    • The spring parallel to Z prevents rigid body motion in the Z direction.
    • The spring parallel to X prevents rigid body motion in the X direction.
    • The 3rd, diagonal spring, together with the other two, prevents rotation about the Y axis.
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