Acoustic Emission Monitoring of S.A. Agulhas II: Parametric Analysis and Correlation with Global Strain

Abstract

The long-term structural integrity of ships operating in harsh environments depends on the ability to detect and interpret early signs of fatigue damage under service conditions. Among available non-destructive techniques, Acoustic Emission (AE) monitoring has shown significant potential for detecting crack activity and local degradation processes in real time. However, the interpretation of AE data in full-scale environments remains complex, as ship structures are subjected to continuously varying mechanical, operational and environmental conditions. Demonstrating AE feasibility in realistic ship environments is therefore critical to advancing its integration within structural health monitoring frameworks. This study presents results from an AE monitoring campaign conducted on board the Polar Supply and Research Vessel S. A. Agulhas II (SAAII) shown in Figure 1 (left), owned by the Department of Forestry, Fisheries and the Environment of South Africa. Two groups of AE sensors were installed: one on the port side near a visually inspected fatigue crack, as shown in Figure 1 (right), and one on the starboard side in a region with a previously repaired crack. This configuration enabled a relative assessment of AE behavior between an active and a repaired region subjected to comparable loading conditions during a single voyage. In total, more than four million AE signals were collected, approximately 80% of which originated from the port-side sensor group, with amplitudes predominantly between 50 and 70 dB and exhibiting AE characteristics consistent with those observed in previous laboratory experiments. The monitoring campaign additionally benchmarked the insights from AE measurements in combination with global structural measurements, including strain gauges and accelerometers, whilst considering the ship route and weather information. This combination of data enables an evaluation of how AE activity correlates to operational and environmental parameters. The study reflects on aspects of sensor deployment, data acquisition, and correlation strategies with other measurements, demonstrating the feasibility and practical considerations of integrating AE monitoring within a multimodal sensing framework for in-service structural monitoring of steel ship structures.