The Hydrodynamics of Deformable Flexible Fabric Structures for Wave Energy Conversion

Host Institution: University of Plymouth

Principle Investigator: Professor Deborah Greaves

Whereas tidal stream technology is relatively advanced, the wave energy industry is still in a nascent stage of development with a wide range of different design concepts for extracting wave energy being developed. A winning technology has yet to be identified and there may well be more than one. It is within this framework that the theme of 'Novel, future, concepts for marine energy generation' is listed within the EPSRC SUPERGEN Marine challenge 2 Marine energy (Wave and Tidal) technology for 2050. Addressing this theme, we propose a new concept for wave energy conversion that uses a novel hydrodynamic action and is constructed from low cost material leading to significant reduction in cost and size of device in comparison with others.

A significant drawback of wave energy converters acting as heaving point absorbers is the mismatch between the typical wave period of the wave climate and the resonant natural period of motion response. This means that devices have to be large in order to operate optimally in swell waves. To overcome these limitations, control systems may be used in order to modify the motion response to suit the wave climate, but this can be complex and expensive.

In this project, we investigate an alternative approach in which the device's geometry responds to hydrodynamic loading. In its simplest form, the concept is a floating wedge-shaped body that has a spring-loaded hinge at its apex that closes as the device sinks and opens as it rises in a breathing action. In the proposed project an axisymmetric form will be investigated; comprising a sealed bag that shrinks and swells without hinges. This breathing action makes it possible to install a power take-off inside the device that requires no external reference. This distinguishes it from other heaving point absorbers. The breathing action can be used to pump air through a reversible flow (Wells) turbine into a second container of fixed volume. No other mechanical parts are needed because the pressure change in the fixed volume generates a spring force which contributes to the restoring force on the device. The concept can be designed so that the breathing system resonates at the heaving frequency.

The proposed project will assess the hydrodynamics of the breathing action within a new device concept called the Squid, by developing an optimisation tool using semi-analytical and numerical models and by performing a series of physical experiments. Both still water tests in the flume at the University of Southampton and wave tests in the ocean basin within the new COaST Laboratory at Plymouth University will be carried out and used to investigate the characteristics of the new concept and to validate the numerical model optimisation tool.