Structural Health Monitoring Using Smart Sensors - ideals ...

1
Normalized accumulated stress
0.8
0.6
0.4
0.2
0
3 4 5 6 7 8 9 1011 7 8 9 10 111213 1415 1112 1314 151617 1819
Element ID
Figure 8.8. Normalized accumulated stress in sensor community 1, 2, and 3 (the SDLV
method).
by the three cluster head nodes. Element 8 is detected as an element with the normalized
accumulated stress smaller than the threshold value, 0.3.
The intermediate and final results of the two DLV methods such as singular values,
DLVs, and the normalized accumulated stress are also calculated on a PC based on the
centrally collected acceleration time histories. The results calculated on the Imote2 are the
same as those on the PC with the same precision of the data type.
The damage detection capability of the proposed SHM framework implemented on a
network of Imote2s has been demonstrated in this section. Further investigation of the
capabilities of the approach will be pursued in section 8.8 by replacing other elements of
the truss.
8.5 DCS logic
Upon completing calculation of the normalized accumulated stresses, the three cluster
heads exchange their damage detection results to perform the DCS logic given in Figure
7.22. The log of the associated session recorded on the base station is presented in Figures
8.9 and 8.10. These figures correspond to the damage detection results in Figures 8.7 and
8.8, respectively. Because no inconsistency is reported, retake flags are set to zero as
indicated by lines2, 9, and 16 in Figures 8.9 and 8.10. When no inconsistency is found, the
results are reported to the base station, and the Imote2s prepare to enter a sleep mode.
Though element 18 is identified as a damaged element by the mass perturbation DLV
method, this false-positive is likely to be avoided if sensor community 4 also monitors this
element because of the redundancy. When inconsistency is detected, the DCS algorithm is
repeatedly applied. Figure 8.11 shows the report to the base station when inconsistency is
observed. Sensor communities 3, 4, and 5 monitor the truss to detect damage at element
21. Sensor communities 3 and 4 organized by cluster head nodes 73 and 135 find
inconsistency. Sensor community 3 identifies element 16 as damaged, while sensor
community 4 does not. After all three cluster heads finish reporting, only sensor
communities 3 and 4 repeat acceleration measurement and data processing. The DCS
143