4 Hybrid Substructure Assembly Techniques for Efficient and Robust. . . 43 0 0.5 1 1.5 2 2.5 Magnitude (abs) 10-3 101 102 -1080 -720 -360 0 360 720 1080 Phase (deg) Exact SPA PEM Bode Diagram Frequency (Hz) (a) 0 0.5 1 1.5 Magnitude (abs) 10-3 101 102 -2160 -1440 -720 0 720 1440 Phase (deg) Exact SPA PEM Bode Diagram Frequency (Hz) (b) Fig. 4.5 An FRF describing the sound pressure due to structural excitation of ATB for the identification in (a) and the hybrid assembly in (b), comparing SPA and PEM Table 4.3 Required offline costs a different number of in- and outputs nIO and different model orders n nIO|n 2|4 2|50 30|4 ETFE 0.2 s 0.2 s 10.5s SPA 5.7 s 5.6 s 1220.7 SID 5.1 s 857.6 s 40,000 s PEM 5.8 s 1090.8 s 86,520 s 4.4.2 Efficiency Identification—Offline Costs In the context of the initial optimization problem, the time required to perform the identification is denoted as offline costs. These are briefly mentioned here, since an important observation can be made (Table 4.3). The effect of a higher order has no impact on the required time for non-parametric approaches. For both, SID and PEM the step from order 4 to order 50 increases the required computation time by a factor of roughly 20. It can be observed that the number of in- and outputs has a dramatic impact on the required identification time for the state-space based methods. This is foremost due to the way the data is handled. As described in Sect. 4.3.1, the results from independent excitations are stacked to form the input time series Uand Y. This lengthens the input time series and results in an impractical computation time. Assembly: Online Costs The evaluation of the assembly equation requires different mathematical operations for SSS and FBS. Table 4.4 shows the required time to evaluate an assembly at nf frequencies withnc coupled oscillators. The basis for this evaluation was a model of the ATB with 100 arbitrarily chosen in- and outputs of order 50. The results show that based on the chosen example, no method is preferable since the required computation time is in general similar.
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