Effects of bottom profile of an oscillating water column device on its hydrodynamic characteristics

Highlights

The influence of different shapes of bottom profiles inside the OWC chamber on its efficiency is investigated.

An in depth investigation of air vent optimization for conventional flat bottom OWC is carried out.

The efficiency decreases with an increase in wave steepness, due to reflection from lip wall and bottom profile of the OWC.

The natural frequency of the system was observed to be unaltered for different bottom profile configurations.

The OWC with circular curve bottom profile exhibited a better performance in terms of its effective wave energy conversion.

Abstract

The oscillating water column, OWC device is one of the more promising devices for the extraction of energy from ocean waves. The present study mainly focuses on the influence of bottom profile configuration in the OWC on its hydrodynamic performance. Four different bottom profiles flat, circular curve of radius 300 mm, slope of 1:1 and 1:5 were tested in a wave flume. The said models were simultaneously subjected to both regular and random waves. The hydrodynamic performance was studied in terms of wave amplification factor, wave power absorption coefficient, hydrodynamic efficiency, lip wall pressure ratio (pressure at in front of lip wall/pressure due to incident wave) and air pressure ratio (air pressure/pressure due to incident wave). It is found that the natural period of the system was around 1.9 s. The OWC with circular curve bottom profile exhibited a better performance in terms of its effective wave energy conversion and wave amplification factor inside the chamber. The peak magnitude of hydrodynamic efficiency for circular curve bottom profile was 0.71. The performance of the OWC model is found to be better when closer to the natural period of the device.

Keywords

  • Oscillating water column;
  • Optimum air damping;
  • Bottom profile optimization;
  • Hydrodynamic efficiency;
  • Wave amplification;
  • Pressure ratio

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