Input file order dependence when applying ThermalContact for two variables

[sapitts]

Reason

I am using the ThermalContact action to model the transfer of both temperature and electrical potential between two mesh blocks. These two blocks are separately meshed so that mechanical contact can be used and the different displacements of the disparate materials can be captured (hence no use of interface kernels). This approach of using the ThermalContact action to model electrical potential transfer between different blocks follows that of recently published work.

The temperature field solution is dependent on the order of the input file blocks in the ThermalContact action: Placing the electrical potential block first seems to allow both field variables to 'diffuse' across the boundary. Placing the thermal block first appears to render the boundary adiabatic and only allows the electrical potential to transfer through out the mesh. Images from two identical simulations, where the only difference is the order of the input file blocks, are given below.

This order-dependent behavior is unexpected, and I am uncertain if always placing the electrical potential ThermalContact blocks first will continue to allow both variables to transfer across the mesh boundary.

Design

Determination of if this behavior is anticipated or not, and documentation or code changes dependent on that decision.

Impact

Reduce confusion for users and increase code reliability

[sapitts]

Pinging @bwspenc @dschwen @cticenhour for input please

[sapitts]

Input file to reproduce the behavior: example_thermalcontact_input.txt