Wave energy capture: The focusing of wave-induced flow through a submerged surface

Abstract

A submerged impervious horizontal disk is positioned near the free surface. Piercing this body is a tubular section, having an opening flush with the top surface and extending completely through the body. Waves passing over this surface will induce an oscillating fluid flow within this tubular section. The magnitude of the oscillation is dependent upon the structure's dimensions relative to environmental conditions such as the wave period, the wave height and submergence depth, as well as the extent to which surface waves are focused within this region. Both the numerical and experimental results of this phenomenon, which are pertinent to the development of a new wave energy converter, are described. The flow within the opening of the submerged surface is modeled by use of the Green function method within the confines of linear potential theory. The numerical predictions are compared with the experimental data. Monochromatic waves propagate over the submerged surface of a free-standing disk model, i.e., placed away from any flume walls. The wave-induced flow through the submerged surface is measured by two different sensors: an electromagnetic flow sensor and a particle image velocimetry laser. Wave elevation is recorded using capacitive-type wave gauges. Phasing of wave elevation to the vertical velocity through the tubular section is also discussed. Of the parameters that were varied decreasing the submergence depth of the disk resulted in the most significant increase in vertical wave-induced velocity.