Analytical Contact, Extrude to Revolve, Avoiding Line of 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.  With Extrude to Revolve and Revolve to Revolve contacts it is possible that the contact region could be along a line, resulting in a non-unique solution, in which case the contact will fail to be detected.

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

About the Model

The example model is a simple bumper test rig.  The test sled has an initial velocity of 20mph. 

The Bumper sheet body will contact the blue cylinder using an Extrusion to Revolution Analytical contact element.

The Bumper is the Extrusion defined with the sketch shown.  With this definition the bumper is perfectly flat in the YZ plane.

In the animation and plots below, we can see that the contact is not detected.

The image below shows the geometry just as the sheet bodies intersect.  As can be seen the overlap forms a rectangular area, meaning there is not a single point of contact and no unique normal.

Correcting the Contact Geometry

To avoid the degenerate condition of line-line contact we need to have curvature in both directions at the plane of contact.   There is already curvature on the Obstacle as it is a circle in the XY plane.

The Bumper profile is changed to an arc with a finite radius that is tangent to the original surface.  The radius of this arc will affect the Hertzian force calculation.  To emulate a flat surface, it should be a large value.  The images below show the arc set to 50mm, 100mm, and 1000mm.  At 1000mm the arc is matching the flat surface well.

The final animation shows the contact being detected as expected.