| Summary: | Traditional naval vessels with steel structures have the benefit of large safety factors and
a distinct material endurance limit. However, as performance requirements and budget
constraints rise, the demand for lighter weight vessels increases. Reducing the mass of
vessels is commonly achieved by the use of aluminum or composite structures, which
requires closer attention to be paid to crack initiation and propagation. It is rarely
feasible to require a lengthy inspection process that removes the vessel from service for
an extended amount of time. Structural health monitoring (SHM), involving continuous
measurement of the structural response to an energy source, has been proposed as a step
towards condition-based maintenance. Furthermore, using a passive monitoring system
with an array of sensors has several advantages: monitoring can take place in real-time
using only ambient noise vibrations and neither deployment of an active source nor visual
access to the inspected areas are required.
Passive SHM on a naval vessel is not without challenge. The structures of ships are
typically geometrically complex, causing scattering, multiple reflections, and mode
conversion of the propagating waves in the vessel. And rather than a distinct and
predictable input produced by controlled active sources, the vibration sources are hull
impacts, smaller waves, and even onboard machinery and activity. This research
summarizes findings from data collected onboard a Navy vessel and presents
recommendations data processing techniques. The intent is to present a robust method of
passive structural health monitoring for such a vessel using only ambient vibrations
recordings.
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