Risk analysis of an Autonomous Surface Craft for operation in harsh ocean environments

Risk analysis of an Autonomous Surface Craft (ASC) is a very important subject since it is closely related to the safety of an ASC operating in harsh ocean environments. In this study, we provide a detailed analysis of the primary disturbance of ocean waves and its influence on an ASC's roll motion. A conventional decoupled nonlinear roll motion model has been chosen and through experiments the roll motion model parameters are successfully identified. Using this model, we perform extensive simulations under different assumed wave conditions. Our analysis is based on the well-known erosion basin technique in phase plane. The safe region proportion has been defined to serve as a safety criterion. Through analysis, we find out that the safety of an ASC operating in the ocean is related to the wave amplitude and wave encounter frequency. This relationship provides a useful reference for risk analysis of an ASC. The results provided can be regarded as guidelines for an ASC's safety determination, and thus they are planned to be integrated into an ASC for its self safety awareness. The presented method can also be extended to other medium-size or large marine vessels for their operational safety analysis.