Re: bracket contact

Hi,

Without the spring, the pin can have free rigid body motions.

Even after contact is established, the pin could spin around its axle since there is no friction in the model.
In the initial state (before contact is established) the model is threefold singular. Any numerical disturbance in the first iterations could then send the pin 'into the universe' since it has no constraints againstY-translation, Z-translation or X-rotation.

The very weak spring will remove the singularity, while it still only introduces negligible forces in the converged state when displacements are small.

This method for suppressing singularities in the initial state of contact models is rather standard, and is used also in other models. In the section 'Constraints' under 'Introduction to Contact modeling' in the Structural Mechanics Module documentation a slightly more sophisticated version is described.

Thanks for the comment, we will extend the explanation of the spring in the next release of this model.

Regards,
Henrik