Guided wave propagation and interaction with ice layers in marine structures

Reliable and autonomous monitoring systems have been increasingly considered to enhance metal and composite-based maritime structures. The main goal is to continuously assess the overall condition of the structure using several nodes of sensors to ensure safety and cost-effective maintenance during the lifetime. To achieve the detection of small emerging flaws, ultrasound wave propagation in thin sheets is successfully adopted to interrogate both metallic and composite structures. However, ships are operating in water environment and even in polar regions, making the correct extraction of damage parameters from ultrasound signals quite challenging. An interesting and practically important aspect deals with icing problems, where thin layers of ice emerge in direct contact with the ship’s hull. This may lead to misinterpretations of measured signals, inducing false alarms and potentially missing damage detection. Guided wave propagation should be investigated in this contribution accounting for these aspects to prevent misleading interpretation. A finite element model has been considered including ice models to address the effect of an emerging ice layer on wave propagation using both pitch-catch and pulse-echo approaches. Numerical results show that reflections generated at the discontinuity raise with the thickness and length of ice layer. The ice accretion affects the transmitted energy, whose result is even more visible in the direct propagation analysis. The outcomes definitely prove the ability of guided waves to detect ice and the modeling is well suited for preliminary design of further experiments.