We’ve already said that Anaconda uses an entirely new way of harvesting wave energy. Essentially, it is a very large (perhaps 200m long and 5m diameter) water filled distensible rubber tube floating just beneath the ocean surface at right angles to the waves, with a power take off at the stern. As a long wave passes the bulge tube is lifted with the surrounding water and this causes a bulge wave to be excited which passes down the tube’s walls like a pulse in an artery, gathering energy from the ocean wave as it goes. Continuous energy gathering is caused by resonance between the bulge wave frequency and the sea wave’s so energy is drawn in towards the tube from the width of the sea wave crest as it progresses along the tube . Energy from the sea wave is stored in the rubber as potential energy by it being stretched (in a sea wave it is stored as potential energy due to gravity). The bulge wave travels just in front of the wave rather like a surfer, picking up energy as it increases progressively in size. At the end of the tube the bulge wave energy is converted to a surge of water which drives a turbine in the power take off after the flow has been smoothed.

It is a closed circuit system so issues with ingestion of marine animals will not arise. Because it is under the surface and rubber can be formulated to be non polluting, environmental impact will be minimal.

The idea of the excitation of bulge waves is novel and is the essential intellectual property from which comes many of Anaconda’s advantages over other WECs. A more detailed description of the theory of the device is included in a paper delivered to the 7th European Wave and Tidal Energy Conference in September 2007. To read this, click here.

Initial model tests carried out at Southampton University have shown correlation between actual results and those of the theory. The interaction of the bulge tube with the surrounding sea waves is very complex and is the subject of an Engineering and Physical Sciences Research Council grant funded study lead by by Professor John Chaplin, Fluid Dynamics, which we are sponsoring. The study will result in a detailed numerical model of the bulge tube being developed and will help us to optimise tube efficiency in real sea conditions. Follow this link to learn more.

Water from each bulge wave flows under pressure into the upper reservoir of the Power Take Off through a one way valve. Energy storage is due to potential energy against gravity because the reservoirs are at different heights. The space above the free surface in each reservoir is occupied by a variable volume air bag. These are interconnected and used to maintain a positive pressure in the system. Pressure compensation due to the system pressure being higher then the surrounding sea allows the water to flow under gravity trough the turbine and into the lower chamber. As water leaves the upper chamber, air from the lower chamber’s air bag goes in the opposite direction to fill the upper chamber’s so the total volume of the two reservoirs remains the same. The water is then drawn back into the bulge tube through the other one way valve during the low pressure phase of the bulge wave. Since they are inter-connected, pre-pressurisation of the bulge tube is achieved by the compensation system used in the PTO. This allows the bulge tube to contract beyond its resting state without becoming flaccid. Another benefit of the pre-pressurisation is that it keeps the distensible portion of the bulge tube in tension, greatly increasing its fatigue life. Pressurisation also affects tuning to the sea wave length. Reactor mass is provided by the water in the PTO and there is an additional keel weight which is also used for stability.