Experimental performance assessment of geometric hull designs for the E-Motions wave energy converter

Abstract

E-Motions is a low-cost and versatile/adaptable wave energy converter conceived towards harnessing energy from wave/wind-induced roll oscillations of floating platforms. This paper focuses on a recently conducted parametric physical modelling stage with three hull designs (half-cylinder, half-sphere and trapezoidal prism), which features a disruptive Power Take-Off reproduction. Free decay, inclining and free-fall tests denoted a good agreement between the physical model's properties and the estimates. Parametric regular waves tests yielded data regarding reflection and transmission coefficients, while large peak-to-peak roll amplitudes (nearly 80°) were measured for the half-cylinder and, to a lesser extent, the half-sphere. Peak reduction was observed under resonant conditions, with the introduction of the Power Take-Off, to which adds a motion phase difference between it and the floating platform. On power output, the half-cylinder and half-sphere yielded the highest capture width ratios and power values per metre of device (nearly 0.8 kW/m, in prototype values) and per displaced volume (up to 0.08 kW/m3). Albeit sufficient for supporting some marine activities, these values can be bolstered, in the future, either through alternative mass/damping combinations or stacking various rows of generators. Maximum mean-to-max power ratios reached a value of 11, within the standard literature range, from literature.