Abstract : The international Rosetta mission will study in depth 67P/Churyumov-Gerasimenko's nucleus global structure and the onset of its activity during the pre-perihelion phase. Numerical simulations towards realistic models of comet nuclei will facilitate the inversion procedures and the interpretation of the data obtained during the rendez-vous of the mission. New aspects of comet nuclei formation and evolution simulations have been developed by our teams to better describe the physical processes of the origins and evolution of these small bodies. Cometesimal aggregation simulations taking into account the evolution of the cohesive energy by sintering processes during accretion in the Kuiper belt can be used to interpret the layered structure and surface features observed for previous comets  and quantify the tensile strengths of these objects. Simulations have been done using up to 50000 cometesimals with sizes ranging from tens to hundreds of meters. A layering of the cohesive strength of the comet nuclei material naturally occurs leading to the presence of a high cohesive core surrounded by less cohesive outer layers. Thermal evolution models of comet nuclei have been rather successful in describing the more recent evolution of these objects. A new quasi-3D approach for non-spherically shaped comet nuclei has been developed for the case of 67P/Churyumov-Gerasimenko's nucleus to analyse the effect of irregular shapes (non-spherical, mountain-like and depression-like features) on its thermal evolution, on the local dust crust formation and the onset of its activity . The results of such simulations are used to derive generic cometary nuclei models to be implemented in the analyses processes of the CONSERT experiment on-board Rosetta that will study the internal dielectric properties and heterogeneities of the nucleus. Support from CNES and Europlanet is acknowledged.  Belton et al., Icarus 187, 332 (2007)  Lasue et al., PSS, submitted.