Efficient thermal analysis of hot structures using new finite elements

Hybrid structures, for example metallic multiwall TPS, sandwiches or hot structures, consist of layers with different thermal conductivity. In addition, radiation and convection can occur within these layers. Analysis of these internal heat transfer mechanisms and the design of hybrid structures require three-dimensional models leading to a high modelling effort. With a new layer-wise theory for heat conduction of hybrid structures this effort can be drastically reduced. Hybrid structures are idealized as structures with homogeneous layers characterised by different thermal conductivities. For layers with internal radiation exchange and convection an equivalent thermal conductivity is used. By means of two heat transfer equilibrium conditions the nodal degrees of freedom become independent of the number of layers. A four noded finite shell element QUADLLT based on the new theory has been developed. This 2D finite element enables the calculation of three-dimensional temperature distribution within hybrid structures. Comparison with 3D analysis and test results shows good agreement. The present finite element formulation is capable of linear steady-state thermal problems and can be expanded for application to non-linear transient thermal problems.