1. A method for performing dynamic analysis of a system, the method comprising sub-structuring of said system into a plurality of sub-structures modelling said sub-structures into sub-structure models and modelling interfaces between said sub-structure models combining said sub-structure models at the interfaces into a combined system solving the combined system wherein said modelling comprises performing a generalised eigenvector analysis on a discretised model of at least a subassembly of at least two sub-structures.