In Situ Measurement of Sloshing Impact on LNG Insulation Panel by using High Speed Fiber Optics

The sloshing impact induced strain exerted on the insulation panel of a liquefied natural gas (LNG) tank was measured in situ by using a fiber-optic Bragg reflector and a wavelength interrogator. To prevent the catastrophic failure of the LNG vessel caused by sloshing impact on the insulation panel, continuous monitoring and dynamic analysis of the induced strain are required. In this study, two different fiber-optic systems are developed based on (1) edge filter type and (2) arrayed waveguide grating type. Bragg reflection sensors were embedded inside the reinforced polyurethane foam insulating panel, which was used to cover the inner surface of the LNG tank. Initially, an edge filter type fiber-optic system is attempted for measuring strain for high speed applications. Another type of fiber-optic system, arrayed waveguide grating, is developed. By incorporating an arrayed waveguide grating device for the interrogation of the reflected wavelength from the Bragg reflector, a dynamic strain of 4000 µε occurring within a duration of 10 ms was able to be measured in real time. The accuracy of the measured data was confirmed by comparing it to the data obtained by means of a high speed camera.