Abstract
The Fabriconda wave energy converter is a submerged tube lying perpendicular to incoming wave fronts. The tube consists of a series of smaller fabric tubes, called cells, joined together longitudinally to form a larger central tube. The cells and central tube are flooded with water. Cross-sectional area changes with pressure due to the cells changing shape. The Fabriconda is therefore distensible, enabling it to extract energy from external waves. Waves induce a series of travelling bulges, and an internal oscillatory flow, in both the central tube and cells. If the speed of these bulges is close to the phase speed of the external wave, energy is progressively transferred to this flow. A power take-off system terminates the tube at the stern. A 1D mathematical model has been developed to predict the power captured by the Fabriconda, based on the application of the conservation of momentum and mass to the flow in both the central tube and cells. An analytical solution of this model has been found using an assumption of harmonic behaviour. A time-stepping finite difference solution was also derived and found to agree with the analytical solution. The results from these models have been compared with measurements. The cross sectional shape of the Fabriconda depends on the ratio between cell and central tube pressure, while the free bulge speed is dependent on the sum of the central tube and cell distensibilities. Both findings were supported by measurements. Measurements found that power generally peaked closer to the resonance frequency than predicted and was dependent on initial pressure. The effect of tube length on the frequency dependency of power capture and the presence of secondary peaks led to the conclusion that normal mode effects are significant to the Fabriconda's performance. This work has determined the operating principles of the Fabriconda and demonstrated that it can extract energy from waves. Predictions of full scale performance and commercial viability are not considered.