Failure risk assessment and dominant cause analysis of an integrated point-absorber wave energy converter in a semi-submersible wind–wave hybrid system

Integrated point-absorber wave energy converters in semi-submersible wind–wave hybrid systems are susceptible to low-frequency, high-consequence (LFHC) failures under extreme sea states. To reduce the masking of severe but infrequent failures in conventional failure mode and effects analysis (FMEA) aggregation, this study combines cloud-model-based linguistic quantification, Decision-Making Trial and Evaluation Laboratory (DEMATEL)-Criteria Importance Through Intercriteria Correlation (CRITIC)-minimum discrimination information principle (MDIP) weighting, and Cloud-VIKOR ranking. Potential failure modes are first identified using a product breakdown structure (PBS). To retain cause-level heterogeneity in occurrence and detection difficulty, 38 failure modes are expanded into 55 failure mode–cause evaluation units. Expert linguistic assessments are quantified using the cloud model, while DEMATEL–CRITIC–MDIP fuses the subjective interdependence and objective dispersion of risk criteria. Cloud-VIKOR is then used to prioritize critical failures, with a larger Q i indicating a higher risk priority. The results identify mechanical jamming, stability loss, hydraulic pipeline rupture, leakage/water ingress, and oil contamination as the major high-risk failure modes. Stability loss ranks second under Cloud-VIKOR but only thirteenth under the traditional risk priority number (RPN) method, confirming the higher sensitivity of the proposed framework to LFHC failures. Subsystem, component-, and cause-level analyses further show that high-risk failures mainly follow three patterns: single-dominant, primary–secondary progressive, and dual-factor coupled structures. The findings provide traceable risk insights for risk-informed decision making (RIDM)-oriented inspection, monitoring, preventive maintenance, and design improvement of integrated wave energy devices in wind–wave hybrid systems.