Decoupling of a substructure from modal data of the complete structure

In this paper the decoupling problem, i.e. the identification of the modal properties of a substructure that is part of a larger structure, is considered. The dynamic behaviour of the whole structure, in terms of modal properties, is assumed to be known, together with the physical (finite element) model of the second substructure. The decoupling procedure recalls the modal based structural modification procedure. Typically, the theoretical model of the known substructure has many more degrees of freedom than those experimentally measured on the whole structure. Therefore, an expansion of the experimental degrees of freedom is necessary to match theoretical and experimental data. The paper highlights the difficulties involved with the decoupling operation.