Ultrasonic waves for the inspection of underwater waveguide structures

Abstract

The non destructive inspection of immersed structures is popular as it minimizes unexpected and costly failures of important marine structures. In this paper we present a non-contact laser/immersion transducer technique for the inspection of underwater waveguide structures. The technique uses laser pulses to generate leaky guided waves and conventional immersion transducers to detect these waves. To prove the feasibility of the proposed methodology, a laser operating at 532 nm is used to excite leaky guided waves in a plate subjected to different damage scenarios. The plate is immersed in water at constant temperature and damage is first simulated using different weights located in the region of interest, i.e. between the point of the laser illumination and the immersion transducers. Damage is also simulated by engraving a series of notches on the face of the plate exposed to the probing system. The waveforms are then processed using the joint time-frequency analysis of the Gabor wavelet transform, statistical features and advanced signal processing techniques to identify and locate the presence of the defects. The findings show that the probing system and the signal processing algorithm used are able to detect differences between pristine and damaged conditions.