Umbilical Fatigue Analysis for a Wave Energy Converter: Preprint

Unique umbilical designs for wave energy converter (WEC), including the ability to handle significantly larger motions and loads over long deployments, are often required, where conventional marine umbilical designs for offshore oil and gas and offshore wind may not meet the design and cost needs of wave energy technologies. This study details a fatigue analysis of a dynamic power umbilical attached to a two-body floating point absorber WEC system, using the sea-states provided for the PacWave testing facilities. The six degrees of freedom motion time history for the WEC was simulated, and the motions of the attachment point for the umbilical on the WEC and respective sea-states were used to analyze the dynamic motions and fatigue of the connected power umbilical to predict the fatigue life. The results show that the fatigue damage observed is more significant in shallow water, and extensive fatigue damage may occur due to the larger curvature response of the umbilical. The umbilical configurations departing at 90 deg off incoming waves were found to have the highest fatigue life attributed to less extension or compression of the umbilical. However, additional bend stiffener/limiter features may be required to be incorporated into the buoyancy section and touchdown regions to minimize curvature induced fatigue.