TECHNOLOGY AREAS: Ground/Sea Vehicles, Materials/Processes

ACQUISITION PROGRAM: PMS 501, Littoral Combat Ship, ACAT 1

OBJECTIVE: Develop an approach that will provide analysis and trending algorithms with sufficient flexibility to function with current and future Structural Health Monitoring (SHM) sensors to support a real-time, situational awareness capability required by ship operators and the long-term, oversight awareness required by maintainers of future, aluminum, naval, ship structures.

DESCRIPTION: The Navy is moving toward the use of light-weight, aluminum, high-speed naval ship structures with targeted service lives of 30 years. The ability of the ship�s force to understand the impacts of structural "wear and tear" over time without having to resort to labor-intensive and time-consuming projection-calculations or laboratory sampling and testing is of paramount interest. These methods do not clearly articulate or anticipate the impacting operational variables such as load, material condition, sea-state, weather, etc. Additionally, it is not uncommon for both naval and commercial ships to plan their travel routes to be mindful of weather concerns so as not to further add to the "wear and tear" of the ship�s structure over time. To address these and other issues, it is envisioned that future SHM systems will be able to monitor and record data from hundreds of sensors and will provide the operators with real-time knowledge of how the ship is operating as compared to its identified Safe Operating Envelope (SOE). Initially, the SHM system suite of sensors will be simple conventional strain gages, accelerometers and possibly some thermocouples. Eventually, as technology become available and/or matures, the suite of sensors will likely grow to include technologies such as, but not limited to, fiber optic strain gages, MEMs devices and a variety of active and passive acoustic emission sensors. There could also be a pairing of sensors to provide an elevated level of status for many areas of the structure. In addition to normal stress/strain data there will be temperature data, data for changes due to corrosion as well as crack initiation and growth, and the change in the state of sensitization if the material is aluminum. One of the key challenges to achieving this goal is in the conversion of data (strain, temperature, acceleration, etc.) to information (describing the fatigue state of a structure, etc). Using conventional analysis tools on a vast data stream will only produce a burdensome array of results that cannot be displayed on a single computer screen or easily interpreted in real time by ship�s force.

This topic seeks the development of an innovative and non-traditional approaches to quantitatively collect, analyze and present data to enable existing and future ship�s force or even shore-based support facilities to address emerging problems and assess areas of impact to the ship�s structural integrity and, if applicable, it�s operational capability. This technology will allow the ship to optimize its operational profile based on dynamic, real-time, ship-specific data. The goal is to quickly generate useful information that supports decisions by the maintainers and operators. As the tool progresses in development, ship sensors might be identified that could provide additional ship performance data that impacts the structural integrity of the ship. For this reason and to be able to interface with any and future data acquisition systems, the approach proposed should employ the use of open architecture principles as practicable. For the purposes of demonstration, the proposed tool shall be able to interface with the Integrated Condition Assessment System (ICAS). This system provides a ship to shore link that can be used to send data to shore based analysts. This will support long term strategies that match structural inspections with planned industrial availabilities.

PHASE I: Demonstrate the feasibility of an approach for an automated structural integrity assesement and analysis tool for shipboard or shore-based support activity using representative strain, acceleration and ship motion time history data from naval sea trials (Ref 1). Establish validation goals and metrics to analyze the feasibility of the proposed solution(s). Provide a Phase II development approach and schedule that contains discrete milestones for product development.

PHASE II: Finalize the design approach and fabricate a prototype system based on the results in Phase I. In a laboratory environment, use representative inputs/data to demonstrate the viability of the prototype product. Develop testing procedures to measure the effectiveness of the tool. Provide a detailed concept of operation and projected capabilities, prototype descriptions, interface specifications, operating sequences, emergency procedures, logistics support plan, system cost estimates (both acquisition and lifecycle), and manning/Human Systems Interface (H.S.I.) requirements. As applicable, plan for software certification, validation and method of implementation into a future ship support environment.

PHASE III: Expanding the concept developed in Phase I and II, work with the Navy and Industry to certify and implement this technology onto a future surface combatant requiring a SHM capability. As needed, support the creation of appropriate infrastructure for handling, analyzing, and archiving the data and analysis.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The use of aluminum and advance material structures is prevalent in commercial shipping where the same concerns exist regarding the long-life operation of these assets. Any structural monitoring system analysis tools developed for Navy ships will have direct commercial applications in ferries and cargo ships as well as possible applications in both military and civilian aviation.

REFERENCES:
1. Representative strain, acceleration and ship motion time history data from naval sea trials (available upon request).

2. H. Sohn. C.R. Farrar, F. M. Hemez, D. D. Shunk, S. W. Stinemates, B. R. Nadler and J. J. Czarnecki, "A Review of Structural Health Monitoring Literature form 1996-2001," Los Alamos National Laboratory report LA-13976-MS (2004). http://www.lanl.gov/projects/ei/shm/publications.shtml

3. J. A. Brandon, "Some insights into the dynamics of defective structures", Proceedings of the Institution of Mechanical Engineers, Part C Journal of Mechanical Engineering Science 212 (1998) 441�454.

4. H. W. Park, H. Sohn, K. H. Law, C. R. Farrar, "Time reversal active sensing for health monitoring of a composite plate", Journal of Sound and Vibration 302 (2007) 50�56.

5. J. M. Nichols, S. T. Trickey, M. Seaver, S. R. Motley, E. D. Eisner, "Using ambient vibrations to detect loosening of a composite-to-metal bolted joint in the presence of strong temperature fluctuations", Journal of Vibration and Acoustics 129 (2007) 710-717.

6. G. Wang, K. Pran, G. Sagvolden, G. B. Havsgard, A. E. Jensen, G. A. Johnson and S. T. Vohra, "Ship Hull Structure Monitoring Using Fiber Optic Sensors", Smart Material Structures 10 (2001) 472�478.

KEYWORDS: structure; monitoring; aluminum; collection; analysis; SHM

** TOPIC AUTHOR (TPOC) **

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