Contact edge tolerance capability

[bwspenc]

For node-face contact to function correctly in situations where a node is right on the edge of a surface, it is necessary to allow for contact to be enforced between a node and a face even though the node is off the face by a slight amount. This is typically referred to as an edge tolerance or tangential tolerance, and the distance that the edge is extended can either be a user-supplied parameter or computed automatically based on typical face dimensions.

We need this to solve a problem with thermal contact between two surfaces that have a symmetry plane. This is also important for mechanical contact in similar scenarios.

[bwspenc]

In 8014b62:

Contact bug fix

In the competition between two faces, the wrong variable was being
used for the distance from one of the faces.  Instead of using the
distance for that face, we were always using 0.  I fixed that and
restructured the logic for better code readability. Addresses #852

[bwspenc]

In 9d56af2:

Fix bug in contact search

Contact distance calculation was wrong.  -Wshadow would have caught this.
Addresses #852

[friedmud]

Hmmm... are you sure you weren't seeing that warning in debug mode? I thought we did -Wall for debug mode.

Are you suggesting we make that warning an error?

[bwspenc]

I'm pretty sure -Wall does not enable shadow variable checking with gcc. You need to explicitly include -Wshadow to get that. I manually added -Wshadow and recompiled just this file, and got a whole ton of shadow variable warnings coming from packages we depend on (libmesh, mtwist), as well as headers in Moose. Most (all?) of them are from having a variable and a method having the same name, which is not actually a problem. I looked into this a while back, and I don't think we can pick and choose which types of shadow variables should trigger warnings. To answer your question, yes, I think that adding -Wshadow would be really good thing, but we would probably have to do a lot of cleanup work to be able to enable it. It is probably worth the effort because shadow variables can produce very nasty, hard to find bugs.

[bwspenc]

In 3cd5575:

Contact search refactor

1) Added option for the user to prescribe a tangential distance over
   which the face is virtually extended.  If this option is used,
   contact is enforced between a node and a face if the node is off
   the edge of the face and the tangential distance off the face
   is smaller than the specified tolerance.  This is essential for
   using node-face contact with symmetry planes or for enforcing
   contact between two bodies with matching edges.  This is
   optionally enabled by specifying "tangential_tolerance" in the
   scope of anything that creates a PenetrationLocator.

2) Refactor search algorithm to remove all calls to
   elem.contains_point.  These called expensive inverse maps, and
   were causing the node to be paired with the wrong face in some
   situations and causing a sign error in the penetration distance if
   the node was close to the surface.

3) Improve speed and robustness in handling of cases where the
   contact point is on a ridge between two faces.

4) Make contact on triangular faces work.

Addresses #852

[friedmud]

Wow - tons of good work here Ben.

[bwspenc]

In 25dd127:

Bug fix in penetration locator addresses #852

[bwspenc]

In 99e0439:

Use get_node_index() method on libmesh Elem class

Temporary workaround can be removed now that libmesh is updated.
Addresses #852

[bwspenc]

In 19c0b49:

Test new PenetrationAux diagnostics

Modify existing tests that use PenetrationAux to request
the full set of diagnostics.  Addresses #852

[bwspenc]

In f270f4e:

Handle ridge and peak cases more robustly in PenetrationLocator

Addresses #852

[bwspenc]

In fa2afaf:

Add 2d tests of PenetrationLocator with moving contact surfaces

These tests exercise PenetrationLocator in 2d with moving meshes in a
variety of situations.  There are two variants of each of these
tests: one with a zero tangential tolerance, and one with a nonzero
tangential tolerance (tt in the name).

Addresses #852

[bwspenc]

In 19e3a84:

Add moving 2d penetration locator tests with quadratic elements

Addresses #852

[bwspenc]

In 86cf4d0:

Fix bug in penetration locator addresses #852

[bwspenc]

In 7effd61:

Fix another PenetrationLocator bug uncovered by testing addresses #852