×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Ansys Mechanical / Workbench Spherical Constraint

Ansys Mechanical / Workbench Spherical Constraint

Ansys Mechanical / Workbench Spherical Constraint

(OP)
I'm analysing a structure which has a cylinder and both the rod ends have spherical constraints. Free rotation x,y,z but can react translational loads in x,y,z. These spherical constraints are not grounded and are within the structure itself. When I use a body to body spherical contact the analysis does not run. Further reading tells me this is because solid elements need to be further constrained or the spherical contact surface has can infinetly rotate. However as it is body to body I can't put any global constraints at the contact surface.

Does anyone have any suggestions?

RE: Ansys Mechanical / Workbench Spherical Constraint

Do you have weak springs activated?

Rick Fischer
Principal Engineer
Argonne National Laboratory

RE: Ansys Mechanical / Workbench Spherical Constraint

(OP)
What would you suggest regarding weak springs? Should I also have large deflections on?

I have managed to set up a model using contacts, but it is very expensive with regards to running time.

RE: Ansys Mechanical / Workbench Spherical Constraint

What so you mean by "the analysis does not run?" Does it fail to run with an error message or start but fail due to non-convergence? What warnings and error messages are generated?

Generally, a model in a static structural analysis needs to be tied down somewhere of you get solution problems, typically a deflection limit exceeded or negative pivot ratios. Presumably the thing you are modeling is tied down somehow, so start with that. You can do this with a zero deflection, a fixed boundary condition, or a fixed joint. I would turn on both weak springs and large deflections. Large deflections is especially important of something is rotating.

I've found the easiest way to hose up a model with joints is to get the coordinate system wrong. Make sure the origin is at the center of the sphere and that it makes physical sense with respect to your model.

Rick Fischer
Principal Engineer
Argonne National Laboratory

RE: Ansys Mechanical / Workbench Spherical Constraint

(OP)
Thanks for your help. Prior to your post I turned on large deflections, weak springs and indeed the local axis of the spherical is central to the local axis of the spherical constraint. I'm awaiting results...

Globally the boundary conditions are correct. The problem is with the body to body contact being underconstrained, this was the problem with the first few runs as stated in the error message. Hopefully this latest run will work and the local and global reactions should prove this.

Thanks for your input.

RE: Ansys Mechanical / Workbench Spherical Constraint

(OP)
After a few ways of modelling this I managed to get accurate results. However, as first anticipated I was not able to use the body - body to spherical constraint. Instead I set up a local axis at the spherical node, transformed it to the cylinder line of action and used a remote displacement for the correct rotation and translation, taking the physical cylinder out the model. It yielded reaction forces as expected. Thanks for your help.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources