Computer Aided Design (CAD) and Computer Aided Engineering (CAE) are two significantly different disciplines, and hence they require different shape models representations. As a result, models generated by CAD systems often need to be submitted to shape transformations for Finite Element Analysis (FEA). In this paper, a new approach is proposed to ease integration between CAD and CAE also outlining some patents. It is based on new shape representation called 'mixed shape representation' that supports simultaneously a B-Rep (manifold and non-manifold) and a polyhedral representation to create a robust link between the CAD and CAE environments. Both representations are maintained through the same topology description called the High Level Topology (HLT), which represents a common requirement for simulation model preparation. An innovative approach to FE model preparation based on the mixed representation is presented in this paper. Thus a set of necessary tools is associated to the mixed shape representation, which contributes to reduce, as much as possible, the time of a model preparation process.