Regarding Constraints and rigid body motion

[Varun Tanikella]

I am doing a static structural analysis for a nonlinear geometry (a bearing) to be specific a clutch release bearing. I have results for the project that I am doing with one warning saying that one or more bodies may not be constrained only if the weak springs option is on. But, with the weak springs option is off I do not have any warnings with the same results.

What is your comment/ opinion on this? Is it really important to consider this warning?

There is convergence as well.

I have tried all the possible ways regarding the constraints problem with the model which did not work.

I have even tried to check the reaction forces. I think there is something wrong with the constraints only.

Your suggestions are valuable and thank you in advance.

 

[rb1957]

if part of your model is attached to "the rest of the world" by springs, I think you need to add a rigid body constraint to the sprung portion, all 6 dof (at a node) and check that these aren't taking load.

another day in paradise, or is paradise one day closer ?

 

[ThomasH]

Hi

My first question is, what does the "weak spring option" do? It probably has to do with the constraints and since those are essential I would start there.

I suppose it is a setting in the software you use. What is the software?

Thomas

 

[NRP99]

In the context of ANSYS, weak springs are added to the model when the the parts in assembly are attached to each other with only contact. Body attached to each other with only contact and no other constraint causes the body to fly away in space when loads are applied and leading to rigid body motion and non-convergence. Weak springs restrict this by applying the weak force opposite to force creating rigid body motion. This way weak springs provide numerical stability to the under constrained model. But results should be carefully checked for. If reaction forces at the weak spring locations are more than other reaction forces, springs are affecting the result and the model is ill constrained and you need to reapply proper boundary conditions/constraint.

If model is already properly constrained, there is no need of weak springs. I guess the warning should pop up when weak spring option off for under constrained model.