Experimental study of mooring forces on the multi-float WEC M4 in large waves with buoy and elastic cables

A wind semi-sub platform with hinged floats for omnidirectional swell wave energy conversion

“…It should be noted that in extreme steep waves, the wave floats will be intermittently overtopped and partially submerged based on experience for the multi-float wave energy converter M4, limiting the pitch motion and providing a passive end stop to rotation, e.g. Stansby et al (2022b), and this is obviously not captured in a linear wave diffraction-radiation model.…”

“…Experimental analysis for M4 in focussed waves has also shown response to be remarkably linear in large waves with weak higher-order effects (Santo et al 2017). Measured mooring forces were, however, highly nonlinear (Stansby et al 2019(Stansby et al , 2022b, but not considered here where a small spring stiffness is added in the horizontal directions for station keeping. In large steep waves, the float decks were intermittently overtopped and partially submerged causing sloshing and energy dissipation, capping the pitch motion, acting as an end stop (Stansby et al 2022b).…”

“…Measured mooring forces were, however, highly nonlinear (Stansby et al 2019(Stansby et al , 2022b, but not considered here where a small spring stiffness is added in the horizontal directions for station keeping. In large steep waves, the float decks were intermittently overtopped and partially submerged causing sloshing and energy dissipation, capping the pitch motion, acting as an end stop (Stansby et al 2022b). In these cases, the wave PTO is disengaged.…”

“…There is the advantage that wind platform pitch is reduced in large waves, but with quite large relative pitch motions, e.g. 22°with H s 6 m. In practice, the extent of pitch motion is limited by overtopping of the wave floats, to about 40°for a wave energy converter (Stansby and Carpintero Moreno 2020;Stansby et al 2022b).…”