Experimental and numerical study of a novel unidirectional mechanical power take-off system for two-body wave energy converters

Abstract

This paper presents the numerical and experimental evaluations of a new power take-off system to be used in two body point absorber wave energy converters. The proposed power take-off uses a ball screw mechanism to convert the reciprocating motion of the converter bodies, into a unidirectional rotary motion. The unidirectional motion eventually rotates a generator and produces electricity. The increase in the power absorption of the proposed unidirectional mechanism compared to the bidirectional mechanism is investigated. A dry test mechanism is developed to mimic the oceanic conditions to measure the power take-off performance. This mechanism measures the force required to oscillate the power take-off at various frequencies, power take-off linear speeds, output angular velocities, and generated voltages. The performance of the power take-off is then monitored under various external electrical loads. Several experiments are also conducted to investigate the effect of Coulomb and viscous friction on the performance of the system. The experimental results show that the power take-off efficiency is about 65% at a nut speed of 10 cm/s. The results also show that using the unidirectional mechanism leads to an 18% increase in power absorption at a frequency of 1 Hz, compared to using a bidirectional mechanism.

Keywords

• Power take-off system
• Wave energy converter
• Point absorber
• Unidirectional power take-off