Smoothing experimental data in dynamic substructuring of built up systems To cancel the effect of the additional springs from the FRFs of the subsystems, a local structural modification procedure is used. Results are shown in Figs. 13 and 14. Fig. 13 Inertance H22 of subsystemB before and after cancelling the effect of additional springs: before (blue) and after (red) spring cancellation. 0 5 10 15 10−2 100 102 Frequency [Hz] Magnitude [(m/s2)/N ] Fig. 14 Inertance H55 of subsystemA before and after cancelling the effect of additional springs: before (blue) and after (red) spring cancellation. 0 5 10 15 10−2 100 102 Frequency [Hz] Magnitude [(m/s2)/N ] To have an idea about the theoretical natural frequencies of the different (sub)systems, the physical parameters shown in Table 1 are used. In Table 3, these values are compared with those obtained by curve fitting the experimental measurements and (in case of subsystems A and B) removing the effects of additional springs. It can be noticed that the largest relative error occurs for the third frequency of the subsystemB, partly due to additional spring removal and for the third frequency of the coupled systemAB. Moreover, additional frequencies can be recognised in the experimental coupled system, but not in the 4 DoFs lumped model. This is due to lateral motion not controlled by the benchmark version 2 (without rail guides). 101
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