Hydrodynamic Performance of a Hybrid System Combining a Fixed Breakwater and a Wave Energy Converter: An Experimental Study

Wei Peng,Jisheng Zhang,Renwen Chen,Yanjun Liu,Rui He,Yingnan Zhang,Xueer Yang

doi:10.3390/en13215740

Abstract

In this paper, a hybrid system integrating a fixed breakwater and an oscillating buoy type wave energy converter (WEC) is introduced. The energy converter is designed to extract the wave power by making use of the wave-induced heave motions of the three floating pontoons in front of the fixed breakwater. A preliminary experimental study is carried out to discuss the hydrodynamic performance of the hybrid system under the action of regular waves. A scale model was built in the laboratory at Hohai University, and the dissipative force from racks and gearboxes and the Ampere force from dynamos were employed as the power take-off (PTO) damping source. During the experiments, variations in numbers of key parameters, including the wave elevation, free response or damped motion of the floating pontoons, and the voltage output of the dynamos were simultaneously measured. Results indicate that the wave overtopping and breaking occurring on the upper surfaces of floating pontoons have a significant influence on the hydrodynamic performance of the system. For moderate and longer waves, the developed system proves to be effective in attenuating the incident energy, with less than 30% of the energy reflected back to the paddle. More importantly, the hydrodynamic efficiency of energy conversion for the present device can achieve approximately 19.6% at the lowest wave steepness in the model tests, implying that although the WEC model harnesses more energy in more energetic seas, the device may be more efficient for wave power extraction in a less energetic sea-state.

Highlights

The possibility of generating electrical power from water waves has been recognized since the late 18th century, and there are countless ideas for devices to extract the power
Thereby, there are two aspects to be considered for the developed hybrid system, namely, the wave attenuation and the wave energy extraction
When Hi /Li is equal to 0.06 or the wave height is large for shorter waves, the incident wave is nonlinear, and deformations of the water waves occur after interacting with the proposed breakwater–wave energy converter (WEC) system

Summary

Introduction

The possibility of generating electrical power from water waves has been recognized since the late 18th century, and there are countless ideas for devices to extract the power. A large number of concepts for wave energy conversion have been proposed, and thousands of wave energy extracting techniques have been patented in the world. Despite the large variation in design, wave energy converters (WECs) are generally categorized into either shoreline, nearshore, or offshore devices according to Energies 2020, 13, 5740; doi:10.3390/en13215740 www.mdpi.com/journal/energies. Developing shoreline WECs poses a number of challenges for engineers and researchers, e.g., lower wave power in shallow water, preservation of coastal scenery, and requirements on shoreline geometry and geology.

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Conclusion