A PIV investigation of OWC operation in regular, polychromatic and irregular waves

Highlights

Experiments were performed in regular, polychromatic and irregular waves.

PIV velocity fields were generated in each wave type.

Methodology for the analysis of velocity fields in time domain was developed.

Histograms were used to compare device performance in different wave types.

The devices operation is similar in polychromatic and irregular waves.

Abstract

Model scale testing plays an essential role in the development and evaluation of wave energy converters and is generally performed in either regular or irregular waves. A less frequently used intermediate wave type is a polychromatic wave which has properties of both. This paper presents methodology for data processing and results from experiments in all three wave types using PIV to capture the velocity fields in and around an oscillating water column. Two methods for the merging of data in the time domain from multiple runs are presented for data sources with high and low sampling rates.

The operation of the OWC in regular, polychromatic and irregular waves was compared using a novel application of normalised histograms and revealed numerous differences including the frequency and size of vortices. A linear relationship was identified between total kinetic energy and energy contained within vortices in the irregular wave. Polychromatic waves successfully represented the power output of the device in irregular waves but more investigation is required into whether they can represent the impact of vortices on device operation. The techniques developed enable evaluation of WEC design changes using PIV in the time domain, and therefore in a more realistic sea state.

Keywords

  • Oscillating water column (OWC);
  • Particle image velocimetry (PIV);
  • Irregular waves;
  • Polychromatic waves;
  • Time-series analysis;
  • Wave energy

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