|Simulation of an Anaconda device in the sea. Click to enlarge.|
Engineers at the University of Southampton (UK) are embarking on a program of large-scale laboratory experiments and mathematical studies to try to advance the development of a simple wave energy converter concept that promises wave-generated electricity at lower cost. The project is supported with more than £430,232 (US$852,233) in funding from the Engineering and Physical Sciences Research Council (EPSRC), and is in collaboration with the inventors and the developer of the device.
Called the Anaconda, the device is a large distensible rubber tube that is closed at both ends and filled with water. It is designed to be anchored just below the sea’s surface, with one end facing the oncoming waves.
A wave hitting the end squeezes it and causes a bulge wave to form inside the tube. A bulge wave is a wave of pressure produced when a fluid oscillates forwards and backwards inside a distensible tube. The bulge wave travels at a speed that is determined by the geometry and material properties of the tube.
Inside the tube, the bulge waves are accompanied by a periodically reversing flow. One way of extracting power from the Anaconda is to use a pair of duck-bill valves to convert this into a rectified flow past a turbine between high and low pressure reservoirs. Power produced is fed to shore via a cable.
Because it is made of rubber, the Anaconda is much lighter than other wave energy devices (which are primarily made of metal) and dispenses with the need for hydraulic rams, hinges and articulated joints. This reduces capital and maintenance costs and scope for breakdowns.
The Anaconda was invented by Francis Farley (an experimental physicist) and Rod Rainey (of Atkins Oil and Gas). Their website on the Anaconda is at http://www.bulgewave.com. Manufacturing rights for the Anaconda now belong to Checkmate SeaEnergy, part of the Checkmate Group.
The Anaconda concept has only been proven at very small laboratory-scale, so questions about its potential performance still need to be answered. Using tubes with diameters of 0.25 and 0.5 meters, the University of Southampton experiments will assess the Anaconda’s behaviour in regular, irregular and extreme waves.
Parameters measured will include internal pressures, changes in tube shape and the forces that mooring cables would be subjected to. As well as providing insights into the device’s hydrodynamic behaviour, the data will form the basis of a novel mathematical model that can estimate exactly how much power a full-scale Anaconda would produce.
The mathematical studies undertaken by the EPSRC-funded project are novel because the Anaconda’s response to pressures induced by surface waves is much more complex than that of a ship or an offshore structure. It has many more degrees of freedom, and motions of each kind (vertical and horizontal bending, bulging, stretching, ovalling, twisting) all interact because of the compliant nature of the rubber.
When built, each full-scale Anaconda device would be 200 meters long and 7 metres in diameter, and deployed in water depths of between 40 and 100 meters. Initial assessments indicate that the Anaconda would be rated at a power output of 1MW (roughly the electricity consumption of 2,000 UK houses) and might be able to generate power at a cost of 6p (US$0.12) per kWh or less. Although around twice as much as the cost of electricity generated from traditional coal-fired power stations, this compares very favorably with generation costs for other leading wave energy concepts.
A one-third scale model of the Anaconda could be built next year for sea testing and we could see the first full-size device deployed off the UK coast in around five years’ time.—Professor John Chaplin, leader of the EPSRC-funded project
The Anaconda is one of the new concepts identified by the Carbon Trust’s Marine Energy Accelerator initiative as having potential to deliver breakthrough reductions in the cost of energy.
Together with tidal energy, it is estimated that wave power could supply up to 20% of the UK’s current electricity demand.
Francis J.M. Farley and R.C.T. Rainey (2006) Anaconda: The bulge wave sea energy converter
J.R. Chaplin, F.J.M Farley, M.E. Prentice, R.C.T. Rainey, S.J. Rimmer & A.T. Roach (2007) Development of the Anaconda all-rubber WEC, European Wave & Tidal Energy Conference
J.R.Chaplin & G. Hearn, Southampton University, The Hydrodyanamics of a Distensible Wave Energy Converter, EPSRC study grant award details