66 J.B. Hansen et al. Fig. 5.4 One percent mass change in node 10, 10 modes, 0.1 % noise on frequencies and 2 % noise on mode shapes matrix which has been clarified by researchers working with similar methods [5] and a solution using a so-called “weighted” pseudo-inverse has been suggested. Another important note regarding Fig. 5.3 is that the combination of the mode shape sensitivity and Bernal projection equation results in a sensitivity matrix holding more information and therefore leads to an improved damage vector. In the final simulation presented in this paper the frequencies and mode shape has been polluted with noise in the range of what can be expected from real measured data in order to create a realistic dataset. The solution using the combined equation, shown in the outermost right plot in Fig. 5.4, is proven to be quite robust even if the identified modal parameters contain noise. 5.4 Conclusions and Future Work The result of the simulations presented in this paper clearly states that the proposed method can detect mass change, position and magnitude, by using modal properties. Furthermore the technique exhibits sturdiness towards noise. The inverse issue will become the main subject of interest in the ongoing research. Due to practical reasons the mass detecting part of the technique, at this point, has been tested more extensively than the stiffness detecting part. The latter part, however, is expected to perform just as well as mass detecting part – at this point there is no immediate circumstance that suggests the opposite. References 1. Parloo E, Guillaume P, Van Overmeire M (2003) Damage assessment using mode shape sensitivities. Mech Syst Signal Process 17(3):499–518 2. Bernal D (2004) Modal scaling from known mass perturbations. J Eng Mech 130(9):1083–1088 3. Heylen RB, Lammens S, Sas P (1997) Modal analysis theory and testing. Faculty of Engineering, Department of Mechanical Engineering, Katholieke Universiteit Leuven, Leuven 4. SDTools – Vibration software and consulting. www.sdtools.com 5. Parloo E, Vanlanduit S, Guillaume P, Verboven P (2004) Increased reliability of reference-based damage identification techniques by using output-only data. J Sound Vib 270:813–832
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