Sine sweep excitation is frequently used to excite large structure for the identification of modal
parameters. The advantage of the technique lays in the possibility of speeding up the test procedure when
compared with the stepped sine approach still keeping the possibility to identify non-linearities if the
sweep rate is kept low. Even if some indication of the allowable sweep rate are recommended in a
standard (ISO 7626) practically all the theoretical work has been done on SDOF systems. In this work, the
authors will present some considerations on sweep sine excitation applied to a MDOF (8dof) system with
an unbalanced mass providing the excitation. The idea behind such model is related to the will to
extrapolate the rigid body dynamics of complex machinery with rotating unbalanced shafts. The MDOF
system allows to make considerations of the influence of the coupling between the DOFs, and to
understand the influence of the sweep rate on the different natural frequencies.
