Wave energy absorption by a floating air bag

TL;DR

This paper investigates a floating air bag device that harnesses wave energy by expanding and contracting, with numerical predictions matching small-scale experiments, highlighting its unique resonance and response properties.

Contribution

The study introduces a novel wave energy device using a floating air bag, analyzing its dynamic response and resonance characteristics influenced by compressibility and air volume adjustments.

Findings

The device's heave resonance period exceeds that of rigid counterparts.

Adjusting air volume alters the device's shape and response.

Turbine damping affects dynamic response without shape change.

Abstract

A floating air bag, ballasted in water, expands and contracts as it heaves under wave action. Connecting the bag to a secondary volume via a turbine transforms the bag into a device capable of generating useful energy from the waves. Small-scale measurements of the device reveal some interesting properties, which are successfully predicted numerically. Owing to its compressibility, the device can have a heave resonance period longer than that of a rigid device of the same shape and size, without any phase control. Furthermore, varying the amount of air in the bag is found to change its shape and hence its dynamic response, while varying the turbine damping or the air volume ratio changes the dynamic response without changing the shape.