Study Of Key Technology On Ship Hull Structural Health Monitoring With Fiber Bragg Grating

Ship hull structures usually sail in complex and harsh environment. Due to the various kinds of loads and surroundings eroding the hull structures continuously, the strength and functions of hull would be damaged and destroyed. Even more, it would cause the tremendous loss of people and properties. So the need for health monitoring of ship hulls are recognized more necessarily. Fiber Bragg Grating (FBG) sensor is a new kind of fiber optic sensors. In addition to small size,immunity to electromagnetic fields and resistance to the harsh corrosive environment in a ship hull, FBG has the advantage that a large number of them can be included in a single fiber (multiplexed). It therefore is suited for ship hulls monitoring. In this dissertation, centering on the sensing system and signal analysis and processing system of the ship hull structures health monitoring system, the key technologies were mainly studied. Main works are shown as follows:1. The cross sensitivity problem of strain and temperature of FBG was studied and the"reference grating method"was chose for temperature compensation method in ship hull structures health monitoring system. The reflection spectrum characteristics of FBG under transverse stress and the strain transferring performance of surface FBG sensor were analyzed. On this basis, the FBG encapsulation structure was designed which was suitable for the ship structure and navigation environment.2. The placement scheme of FBG sensors for strength bending moment measuring in ship and submersible was investigated with finite element analysis technology and theoretical approach. A new FBG sensor optimal placement rule for wave slamming loads monitoring was proposed. The fast and high accuracy method of FBG sensor optimal placement was achieved with a self-adaptive particle swarm optimization and chaos search algorithm.3. The FBG sensor networks and the interrogation system combining the tunable Fabry-Perot filter and interferometer method were designed for the ship hull monitoring system. The dynamic digital interrogation was mainly studied based on unbalanced Mach-Zehnder interferometer and phase generated carrier mehtod. The experiment results showed that the dynamic strain resolution of the interrogation system was 0.165με/Hz at 500Hz.4. The digital filter technology for processing the ship strength bending moment signal was introduced simply. The parameters estimation technology for wave slamming loads was mainly studied. The frequency parameter estimation method based on continuous wavelet transform and the amplitude parameter estimation method based matched filter were proposed and the unbiased and valid estimation was accomplished.5. The fatigue life evaluation technology of ship hull structures was studied. The judgment procedure for fatigue damage was designed based on statistically processing the random loads. Three kinds of key technology, the fatigue life model,stress cycle count method and fatigue damage accumulation criterion, were mainly researched.6. According to the T joint structure in ship hull structure, a static damage identification method based on measuring strain of FBG network was presented. The damage severity identification was implemented with support vector machine. According to micro fatigue crack, a dynamic damage identification method based on vibration signal wavelet packet decomposition and statistical process control theory was put forward. The damage location and damage severity were identified using intelligent algorithm.The main creative contributions of this dissertation are as follows:1. The FBG sensor optimal placement rule for wave slamming loads monitoring was proposed, and the sensors placement problem was solved with particle swarm optimization with self-adaptive inertia weight and chaos search algorithm.2. The damage identification method based on FBG strain network and support vector machine was used for T joint structure in ship hull structure.3. The damage indicator, namely sum of relative varitation ratio ,was constructed based on the wavelet packet node energy of vibration signals. The damage identification method for micro fatigue crack is proposed with the damage indicator and statistical process control theory. This method could eliminate the influence of measurement noise.4. The parameters evaluation methods for wave slamming load signal with continuous wavelet transform and matched filter was put forwards.