Fiber optic structural health monitoring system: rough sea trials testing of the RV Triton

Abstract

Systems Planning and Analysis, Inc., under sponsorship from the United States Navy, Office of Naval Research (ONR), has developed a structural health monitoring system for large-scale structures, based on fiber Bragg grating (FBG) sensors. The application of this new structural health monitoring system to US Navy vessels will reduce maintenance costs by allowing for scheduling of need-based maintenance, increase fleet operational availability, and ship survivability by providing ship operators real-time information concerning the state of the ship structure. Central to the monitoring system is an instrumentation unit capable of detecting signals from hundreds of FBG sensors with sampling rates approaching 2 kHz. The instrumentation is based on SPA's proprietary Digital Spatial Wavelength Domain Multiplexing (DSWDM) technology developed under this effort. DSWDM technology is electro-optics based and has been shown to provide significantly higher sampling rates than comparative FBG interrogation technologies. The baseline system interrogates more than 120 sensors along eight fiber channels. The prototype High Speed-Fiber Optic Interrogation System (HS-FOIS) also possesses a number of advantages intrinsic to optical fiber sensors as compared to conventional strain sensor systems. These advantages include extremely low installed weight and volume, immunity to electromagnetic interference and corrosive environments, and low signal attenuation and drift. This paper describes the installation and testing of a large-scale fiber optic sensor network on the British Trimaran Research Vessel (RV) Triton. In this on-going project with the Naval Surface Warfare Center, Carderock Division (NSWCCD) and the British Defence Science and Technology Laboratory (formerly DERA), Systems Planning and Analysis, Inc. (SPA) recently completed the installation and at-sea testing of an integrated hardware/software structural monitoring system. The rough sea trials of the RV Triton was conducted in early February 2002 in the North Atlantic. This paper describes the fiber optic Bragg grating sensor network comprising of 51 sensors, the interrogating system, and the processing algorithms used to simultaneously record strain data at both high- and low-speed frequencies, including triggering of the high-speed channels. This paper also details the sensor layout and installation process with emphasis on lessons learned during this procedure. The test procedure and sample data results are presented. Finally, conclusions on the presented data and implications of the structural health monitoring system for future naval vessels are discussed.