Thermal Contact Solver

Thermal analysis is performed first using initial contact status.

An iterative solution process is developed to solve fully coupled nonlinear thermal structural problem, as shown in Figure 1. Nonlinear structural analysis is employed to find contact status. Thermal conductance at the contact interface is calculated based on contact clearance or pressure, or based on user-defined values. Coupling is essential because the contact status is used to determine thermal conductance. Temperature results from thermal analysis are used as convergence criteria.

Thermal conductance across contact interface can be based on user-defined values, clearance, or pressure. The PGAPHT and PCONTHT entries can be used to define the thermal conductivity values.
Note:
  1. For thermal contact problems with CGAP/CGAPG, PGAPHT is required. The PGAPHT entry should have the same PID as PGAP. For problems with CONTACT and PCONT, the PCONTHT entry should be used and it requires the same PID as PCONT.
  2. Thermal conductivity based on the AUTO option (KCHTC/KCHT fields on PCONTHT/PGAPHT entries) can be used in thermal analysis to allow OptiStruct to automatically determine the conductivity values based on the conductivity of surrounding elements. AUTO conductivity is chosen in such a way that it works as a perfect conductor for closed gap/contact and insulator for open gap/contact.
  3. For problems without PCONT, PCONTHT is not required. Thermal conductivity is internally calculated by the AUTO method.
  4. High conductance at the interface is automatically enforced for FREEZE contact.
  5. In Heat transfer analysis with Contact (except for FREEZE contact), the slave set ID (SSID) should not be defined as a GRID set.


    Figure 1. Fully Coupled Contact-based Thermal-Structural Analysis

Theoretically, while higher conductance values enforce a perfect conductor, excessively high values may cause poor conditioning of the conductivity matrix. If such effects are observed, it may be beneficial to reduce the value of conductance, or use conductance based contact clearance and pressure.

Clearance based Thermal Conductance (TCID on PCONTHT/PGAPHT, via TABLED#)

The clearance based conductance values can be specified one the TABLED# entries (which should start from zero clearance). Conductance is linearly interpolated within the range on the TABLED# entry. It is extrapolated to zero outside the range. The typical conductance values vary.


Figure 2. Thermal Conductance based on Contact Clearance

Pressure based Thermal Conductance (TPID on PCONTHT, via TABLED#)

The pressure based conductance values can be specified one the TABLED# entries. The typical conductivity values vary.


Figure 3. Thermal Conductance based on Contact Pressure

Clearance and Pressure based Thermal Conductance (TCID and TPID on PCONTHT, via TABLED#)

The clearance and pressure based conductance values can be specified on the TABLED# entries. The typical conductance values vary.


Figure 4. Thermal Conductance based on Contact Clearance and Pressure
Typical thermal conductance values increase as the clearance between the master and slave decreases. In the case of contact pressure, the thermal conductance increases with a corresponding increase in pressure.
Note: Shell elements are considered to be membranes in Heat Transfer Analysis. Composite properties are homogenized (1 degree of freedom per grid). The temperature distribution through the thickness of shell elements is not calculated. Only nodal temperature is determined.

Thermal Contact with FREEZE Status

For thermal contact with FREEZE status, the actual contact status (open or closed) based on geometry will be used in heat transfer analysis.