Waves to Drive a Direct Rotor for Unidirectional Rotation

Abstract

Ocean waves constitute a massive source of renewable energy. However, ocean wave energy is highly underutilized. In the present work, a new approach for wave energy harvesting is discussed. A direct-drive rotor is employed as a key component of a wave energy converter (WEC). The rotor absorbs wave energy and performs unidirectional rotary motion. This approach is in contrast to the overly dominant existing technologies that utilize wave-driven oscillation (either linear or angular, e.g., heave, surge or pitch) for energy conversion. It is also different from the very few existing technologies that use direct-drive rotors to realize unidirectional rotary motion. The focus of this work is on characterization of some rotor designs using numerical tools. The tools include a wave model and a drag force model. Simple circular tubes are used as blades in a basic rotor design. This basic design demonstrates strong potential for unidirectional rotary motion at a proper rotor submersion level and under various wave conditions. Two improved designs are yielded from the basic design. In one improved design, the original circular tubes are replaced with semicircular tubes as new blades. In another design, the semicircular tubes are further modified to become one-way foldable. The two improvements significantly enhance the rotors’ unidirectional rotary motion in waves, which has been verified by numerical experiments. Broad ranges of wave parameters and the submersion level have been numerically explored on the two improved rotor designs in conjunction with dimensional analysis.