Fig. 10 C 11 H and C 12 H resulting from the coupling of A1 and A2 with the sub-structure B C 11 H and C 12 H resulting from the coupling of A1 and A2 with the sub-structure B, with the addition of masses in A 4 CONCLUSIONS In this paper the authors have presented three formulations for the uncoupling of sub-structures, something that may be of considerable interest, for instance when trying to model complex joints. The formulation that presented the best results requires measurements at the connection points of the structures; unfortunately, this may not always be possible in practice. Any of the three formulations revealed to be numerically unstable due to the inversion of difference matrices. This problem has been investigated in this study and improvements have been obtained when adding point masses to the remaining substructures other than the one to be characterized. Those added masses move the natural frequencies, allowing to understand the problems that are happening and as already said, improving the results. Together with the use of modal identification methods, the uncoupling techniques may be of interest in various situations. Experimental implementation still has to be further investigated, as the accurate measurement of rotations is quite difficult to obtain. REFERENCES [1] D'Ambrogio, W., Fregolent, A. "Sensitivity of decoupling techniques to uncertainties in the properties" Proceedings of "Noise and Vibration Engineering" (ISMA 2008), Leuven, Belgium, pp. 3737-3749, 2008. 200 400 600 800 1000 1200 1400 1600 1800 2000 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 Receptance [dB] (ref. 1 m/N) Frequency [Hz] Hc11 Hcc11-1% 200 400 600 800 1000 1200 1400 1600 1800 2000 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 Receptance [dB] (ref. 1 m/N) Frequency [Hz] Hc12 Hcc12-1% 200 400 600 800 1000 1200 1400 1600 1800 2000 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 Receptance [dB] (ref. 1 m/N) Frequency [Hz] Hc11-1% Hcc11-1% 200 400 600 800 1000 1200 1400 1600 1800 2000 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 Receptance [dB] (ref. 1 m/N) Frequency [Hz] Hc12-1% Hcc12-1% 391 Fig. 11
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