Snatch loading of a single taut moored floating wave energy converter due to focussed wave groups

This paper concerns experimental measurements of the interaction of a taut moored floating body, representing a wave energy converter in survivability mode, with extreme waves. Focussed wave groups, based initially on NewWave theory, are used to generate the extreme waves, with crest amplitude exceeding the mooring׳s design capacity. Two data sets are presented and discussed. In the first the influence of wave steepness on model response and mooring load is investigated using non-breaking focussed wave groups. In the second the influence of wave breaking location is investigated using a plunging breaking wave. Both data sets exhibit snatch loading as the extension of the mooring is exceeded. The magnitude of this loading is not found to be strongly dependent on wave steepness, while the following motion response of the body is. Breaking location has a much greater effect than wave steepness on the magnitude of the mooring load, while significant influence of the body motion and displacement on the mooring load is demonstrated. Evidence is provided that the use of individual focussed wave groups is inadequate to assess fully the extreme loads experienced by a taut moored WEC due to the demonstrated dependence of mooring load on the body׳s motion and displacement.