Holistic risk assessment of oscillating water column devices using a hybrid hexagon and Pythagorean fuzzy multi-criteria approach

Wave energy converters (WECs) such as Oscillating Water Column (OWC) devices hold great promise for renewable energy generation, but their long-term reliability under harsh marine conditions remains a critical challenge. This paper addresses the risk assessment gap for OWC systems by introducing a novel integrated framework that bridges technical reliability with economic viability. The proposed Hexagon Risk Assessment methodology extends traditional Failure Modes and Effects Analysis (FMEA) by incorporating six evaluation criteria (including exposure, detectability, control measures, and economic impact) rather than the standard three. These criteria are weighted and aggregated using a Pythagorean fuzzy multi-criteria decision-making (MCDM) approach, providing a robust prioritisation of failure modes. Compared to previous FMEA-based or single-method studies, the Hexagon methodology offers a more comprehensive evaluation of OWC risks, capturing complex environmental and operational uncertainties. Applied to a representative case study reflecting real-world operational constraints, the methodology successfully identified the most critical failure modes, with aging degradation, resonance tuning failure, and extreme weather events emerging as top risks. Among the evaluated criteria, severity, exposure, and economic impact were found to have the greatest influence on overall risk prioritisation. The results confirm that this holistic risk assessment approach can enhance maintenance planning and design optimisation for wave energy systems, ultimately supporting cost-reduction strategies necessary for commercial deployment.