SUMMARY

As performance requirements and budget constraints rise, the demands for lighter weight naval vessels increase. Traditional vessels with steel structures have the benefit of large safety factors and a high material endurance limit. However, the use of aluminum structures requires closer attention to be paid to crack initiation and propagation. It is not 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, 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 real-time, does not require deployment of an active source, and does not necessitate access to the inspected area. 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 as 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 on sensor placement and data reduction. The intent is to present a robust method of passive structural health monitoring and life prediction for such a vessel using only ambient vibrations recordings.