Substructure decoupling as the identification of a set of disconnection forces

The objective of this paper is to achieve a better understanding of the substructure decoupling problem by analyzing different sets of disconnection forces. Substructure decoupling consists in the identification of a dynamic model of an unknown substructure embedded in a known structure (coupled structure). Disconnection forces can be imagined to be applied to the coupled structure in order to reproduce the dynamic behavior of the substructure to be identified. The disconnection forces are such as to cancel the effect of constraint forces exerted at the coupling DoFs of the unknown substructure by the remaining part of the structural system. Several sets of disconnection forces can be devised: the trivial set, consisting of disconnection forces acting at the coupling DoFs and opposite to the constraint forces; non trivial sets of disconnection forces acting at different DoFs but such as to cancel the effect of the constraint forces. Here, a procedure to determine disconnection forces is recalled in the framework of substructure decoupling. Different sets of disconnection forces are compared using both simulated and experimental data of a tree structure (known structure). Indications provided by disconnection forces are in agreement with the results of the decoupling procedure.