Modeling scenarios for using an Interface Resistance

There are two modeling scenarios for using an Interface Resistance simulation object, which can be termed "conduction interface" and "free face interface.”

Conduction interface methodology

This conduction interface methodology models the thermal effect of a mechanical interface (bolted or bonded for example). Use Interface Resistance to insert additional conductances in series with existing conductances. Note that because they share nodes, the selected elements would conduct heat even without the thermal coupling.

Start with two adjacent polygon bodies that are meshed with 3D elements that share nodes. A typical way to do this is to use Boolean operations to partition one polygon body into two polygon bodies at the interface and mesh the two polygon bodies, using meshing techniques that ensure the elements share nodes at the interface. Create a geometry group containing the shared partition surface and define it as a Surface Interface type. The conductances of the Surface Interface are added in series to the conductances of the 3D elements on either side of the shared surface.

A similar technique applies to two polygon faces sharing an edge, which are both meshed with 2D elements that share nodes along that edge. Select the shared polygon edge and use it to define an Edge Interface type. The conductance of the coupling will be added in series to the conductances of the 2D elements on either side of the shared polygon edge.

Free face interface methodology

The free face interface methodology is useful when you have already defined Radiation, Thermal Coupling — Convection, or another type of Thermal Coupling on a surface of a polygon body and wish to introduce an additional conductance or resistance between the polygon body and the face. There is no need to mesh the polygon face.

Similarly, the free face interface methodology may be used when you have defined a thermal coupling on an edge of a polygon face, and wish to introduce an additional conductance or resistance in series between the polygon face and the edge. There is no need to mesh the polygon edge.

Select a face of a polygon body meshed with 3D elements to define the Surface Interface type. In this case, the interface conductance is placed in series with the conductance spanning the 3D elements and the polygon face itself. For example, you can use this technique to establish a boundary condition or model radiation on a surface that is coated with a different material than the underlying solid.

A similar technique applies to the edge of a polygon face meshed with 2D elements. The interface conductance is placed in series with the conductance spanning the 2D elements and the polygon edge itself.

Duplicating the interface edge or face during the solution

During the solution, the solver duplicates the shared surface or edge and its corresponding nodes. In post processing, you can see the new surface or edge and the new nodes. The solver writes the ID of the new nodes and elements to the REPF file.

Example:

Relevant section of a sample REPF file containing IDs of duplicate nodes and elements

                    Edge Interface Resistance   Original Element           Duplicated Elements       887                          3719       875                          3827       873                          3803       ...                    Edge Interface Resistance   Original Node           Duplicated Nodes         2                           976         3                           977         6                           978       ...

The following example shows how this technique allows the solver to display the nodal temperature difference between the adjacent faces at the edge interface resistance. The lower edge of the bottom element is kept at 100 °C, and a heat load of 1000 W is applied to the upper edge of the top element.

		There is an edge interface between the two elements.The original nodes' IDs at the edge interface are 6 and 8 and the duplicated nodes' IDs are 121 and 122.
		No edge interface exists between the elements. The adjacent elements share nodes at the interface.

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