Investigating of Helmholtz wave energy converter

Highlights

In this article, a novel wave energy converter that uses the Helmholtz resonance frequency is introduced.

The main focus of the current study is to understand the mechanism of wave amplification at Helmholtz resonance frequency in a basin and experimentally investigate the geometry of an ideal wave pool in a wave tank utilizing the theoretical method previously done on tidal Helmholtz resonance.

The application of the theory of Helmholtz resonance used for wind-driven ocean waves was explored in 1/25th scale and 1/7th scale model through experiments, and in both cases the experiment supports the theoretical work which previously done for tidal Helmholtz mode.

The results of the current study can be used to optimize the design of HWEC devices for extracting wave energy.

The HWEC has a simple design, contains no moving parts except for PTO unit, requires low cast material, possesses a relatively small form factor, and the coastal location would lead to low power transition costs after conversion to electricity.

Abstract

This study examines a new concept of wave energy conversion inspired by natural wave pools which are able to trap ocean wave energy into a basin. A novel wave energy converter that uses the Helmholtz resonance frequency is introduced. This device which is called Helmholtz wave energy converter (HWEC) amplifies the oscillation amplitude of a fluid in a basin that is connected to the sea through a narrow channel. The main focus of the current study is to understand the mechanism of wave amplification at Helmholtz resonance frequency in a basin and experimentally investigate the geometry of an ideal wave pool in a wave tank utilizing the theoretical method previously has been done on tidal Helmholtz resonance. The geometry causes amplification in oscillating fluid velocity within the channel at the Helmholtz frequency. Geometric characteristics of HWEC were experimentally studied to determine the dimensions of the basin for inducing Helmholtz resonance. A 1/25th and a 1/7th scale models were used to correlate the Helmholtz frequency with the device geometry. In addition, the effects of the device’s basin length and angle of winglets at the inlet of the channel were explored. Furthermore, Particle image velocimetry (PIV) technique was used to determine the velocity fields through the channel of the 1/25th scale model. The results suggest that reducing the angle of the winglets leads to fewer higher order harmonics resulting in better performance of the device in extracting the energy of the incoming waves. It is also shown that the alignment of the axis of the device relative to the incoming waves plays an important role in the overall efficiency of the device. The results of the current study can be used to optimize the design of HWEC devices for extracting wave energy. Moreover, the results reveal that resonance in the channel results in amplification of wave height relative to incoming waves and the corresponding wave power available for absorption. Appropriate location of the power take-off (PTO) in the channel can be empirically determined using PIV data. However this work does not examine the effect of the PTO in the device’s energy absorption performance.

Keywords

  • Helmholtz resonance mode;
  • Wave energy converter;
  • Power take-off;
  • Particle image velocimetry (PIV);
  • Wave power absorption

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