A. Culla, W. D’Ambrogio, A. Fregolent and A. Schiavone Fig. 29 Inertance H55 of the unknown subsystemAusing compatibility at the coupling DoFs and equilibrium at the coupling DoF 2 and at the internal Dof 1: fitted (blue); after decoupling (red) 0 5 10 15 100 102 Frequency [Hz] Magnitude [(m/s2)/N ] Fig. 30 Inertance H66 of the unknown subsystemAusing compatibility at the coupling DoFs and equilibrium at the coupling DoF 3 and at the internal Dof 1: fitted (blue); after decoupling (red) 0 5 10 15 100 102 Frequency [Hz] Magnitude [(m/s2)/N ] The best results (see Figs. 28 and 30) are obtained when the coupling DoF 2 is not considered as equilibrium DoF, thus implying that the drive point inertance H22 of the coupled system is not necessary. Probably this FRFs is affected by some systematic errors due to unmeasured rotational DoFs or to non linearities not accounted in the model. 4 Discussion In this paper, FRFs acquired on a lumped parameter benchmark system with translational DoFs are used to check coupling and decoupling procedures and to look for additional issues (systematic errors, inconsistencies, etc.) that are not observed when using simulated data. The use of a lumped parameter benchmark should avoid problems due to unmeasured coupling DoFs and problems due to modal truncation. In practice, the used benchmark (version 2) allows small transverse motion: therefore, some coupling DoFs are not measured; furthermore, due to the transverse sensitivity of the accelerometers, additional modes are observed in the measured FRFs which can pro108
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