Models for accounting/eliminating rotational DOFs in distributed structural modification

Predicting the effects of distributed modifications is becoming increasingly important in mechanical manufacturing, as a basic step for further optimization purposes. However an actual shortcoming is encountered for the difficulty of describing separately the original and modifying structures providing the behaviour of the modified system. In fact, unlike lumped modifications, when coupling together the finite element model of the modifying structure with the FRF model of the original one, one must consider the rotational DOFs at the interface between the two structures. Due to the difficulty of measuring rotational DOFs and to the impossibility of providing and measuring lumped moments, either condensation or expansion is required before coupling the structures together. This paper analyzes and compares few possible options to provide an efficient formulation in case of distributed modifications, suggesting the use of PZT sensors to provide rotational DOFs.