Identification of interface forces for inverse dynamic substructuring applications

Inverse dynamic substructuring, also called substructure decoupling, is the identification of the dynamic behaviour of a structural subsystem, starting from the known dynamic behaviour of both the coupled system and the remaining part of the structural system (residual subsystem). In direct decoupling, a fictitious subsystem that is the negative of the residual subsystem is added to the coupled system, and appropriate compatibility and equilibrium conditions are enforced at interface DoFs. The effect of the negative structure is to add a set of 'disconnection forces' to the forces acting on the coupled system. The disconnection forces are such as to cancel the effect of constraint forces at the coupling DoFs. Equivalently, one can imagine that disconnection forces are directly applied to the coupled structure. Therefore, the decoupling problem becomes a force identification problem. In this paper, to better understand ill-conditioning problems that arise in inverse dynamic substructuring, conditions are sought under which disconnection forces can be successfully identified.