Structural Health Monitoring Using Smart Sensors - ideals ...

same community, eliminating the need to globally transfer a large amount of data through
a long communication path.
While most of the derivation in NExT, ERA, and the DLV method can be directly
applicable to data from a local sensor community, the mass normalization constants, d j
or
i
, for the DLV method may need data at DOFs outside the community. To estimate d j
in
a local sensor community, the input force and the output response at that location need to
be available. i
needs mode shapes to be estimated for DOFs corresponding to the
location of the mass perturbation, as shown in Eq. (6.21). In addition, q ii
in Eq. (6.22)
may contain a large error if only a limited number of sensors in a local area is used. Gao
(2005) suggested that estimation of mass normalization constants be performed from
globally obtained data during initialization of the SHM system. Normalization constants
obtained during initialization are then converted to normalization constants for each
sensor community through the following equations:
d j
i
=
d j
j
ref
i
------------------
i
j
ref
(6.31)
j
i
=
j
---------------- j
ref
i
i
j
ref
(6.32)
and are the j -th mode mass normalization constants for the sensor community, i .
j
ref
i
and j
ref
i
are the j -th global mode shape’s components corresponding to the
i
i
reference sensor node of the i-th sensor community. j
ref
and j
ref
are components of j-
th mode shape determined in the i-th sensor community. These components correspond to
the reference sensor DOF of the community. In this way, mass normalization constants for
each sensor community can be estimated. Thus, monitoring is realized within local sensor
communities.
d j
i
j
i
DCS also describes how local sensor communities collaborate with each other to
judge structural damage, including redundancy to increase fault tolerance. Local sensor
communities are formed with overlap, so that more than one sensor community monitors
the same element. This overlap provides the means to deal with false-positive and falsenegative
damage detection. Information about localized damaged elements is exchanged
among local sensor communities. If damage localization in one sensor community
contradicts that in another community, measurement and analysis are repeated. If a
damaged element is detected and no inconsistency is reported, the base station is informed
of the damage (see Figure 6.1).
6.5 Stochastic Damage Locating Vector method
Recent algorithmic development of the Stochastic DLV (SDLV) method by Bernal
(2006) has the potential to improve the DCS for SHM by eliminating the need to estimate
normalization constants. The initialization phase of DCS involving either input force
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