New layerwise theories and finite elements for efficient thermal analysis of hybrid structures

Abstract

Hybrid structures, for example metallic multiwall thermal protection systems, 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 layerwise 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 assumed. By means of two heat transfer equilibrium conditions the nodal degrees of freedom become independent of the number of layers. Two four-noded finite shell elements QUADLLT and QUADQLT based on the new theory have been developed. These 2D finite elements enable the calculation of three-dimensional temperature distributions within hybrid structures. Comparison with 3D analysis and test results shows good agreement.