Analytical Contact, Extrude to Revolve, Avoiding Edge Contact

Background

Analytical contacts provide a fast, efficient, and accurate way to model contact between sheet bodies created using extrusions, revolutions, and sweeps.  Between the two sheet bodies there needs to be a unique normal for the contact to be detected and force properly applied.  If contact occurs at the edge of the sheet body, there will no longer be a normal and hence no contact force will be generated.

This example provides a simple demonstration of this situation and a method to resolve it.

About the Model

The example model is a simple bumper test rig.  It is the same model used in the FAQ “Analytical Contact, Extrude to Revolve, Avoiding Line of Contact” with a few adjustments:

• The Sled body is taller, and the bumper has been moved down to create a significant overturning moment when the bumper strikes the obstacle.
• The Sled is supported on the Base with contact elements; hence it is free to leave the ground.  In the prior model, the Sled as on a Slider joint with the Base.

• The Bumper in the initial configuration of this model has a curvature to avoid the contact region being a line/area.

In the animation with Contact Force Vector, we can see that the Bumper contacts the Obstacle, the point of contact moves up the Bumper surface, and then passes through once the contact point reaches the top of the Bumper.

Correcting the Contact Geometry

To avoid the contact passing through the Bumper we need to insure there is a normal once the edge is reached.  Instead of having the Bumper geometry end at the edge of the arc, we need to add a small tangent arc at the ends of the Bumper profile.  

The final animation shows the contact being detected as expected.