Rough Sea Trials of the RV Triton

Sponsors – Office of Naval Research, British Ministry of Defense

The British Research Vessel (R/V) Triton was developed by the British Navy to investigate design and performance issues associated with large-scale trimarans. The U.S. Navy assisted in the program by providing the funding and support for the Trials Instrumentation System (TIS), a comprehensive data acquisition system through the ship. In concert with these efforts, AITHER installed a network of optical fiber Bragg gratings (FBG) strain sensors. While potentially useful strain data was acquired by the fiber optic sensors, the main interest of this research program was to demonstrate the viability of such a system compared to electrical resistance foil strain gages, which are the primary sensor type in the structural monitoring portion of TIS.

The application of FBG sensors to the R/V Triton represented a number of new challenges for optical sensor technology. Two types of measurements were of interest to the sponsors: primary and secondary loads. Primary loads are the main bending loads of the ship requiring a large number of sensors to be monitored at relatively low speeds (~100 Hz). The secondary loads, however, are mainly slamming events due to wave impacts and must be sampled at a much higher rate (>1000 Hz) but with a lower number of sensors. For this program, a total of 35 FBG sensors were used to measure the primary loads on three separate fibers, and 16 FBG sensors were used for secondary loads on a single fiber. The primary load channels were configured as strain rosettes, shear gages, and axial gages. Eight axial gages were configured as strain isolating Flat-Pack sensors to provide temperature-compensated strain measurement. To interrogate all of the FBG sensors simultaneously, AITHER used its High Speed – Fiber Optic Interrogation System (HS-FOIS) with one fiber sampled at 1600 Hz and the other three fibers at 100 Hz. Rough sea trials of the system in the North Atlantic took place in February 2002. Data from these tests, a sample of which is shown below, demonstrates the unique advantages of FBG sensors and the HS-FOIS for large-scale, high-speed structural monitoring applications of Navy ships. For further information refer to the SPIE conference paper entitled, “Structural Load Monitoring of the R/V Triton Using Fiber Optic Sensors” under publications.