Bulge wave energy conversion – Rubber snake anaconda

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					 Bulge wave energy conversion – Rubber snake anaconda

                                              Author, Swati A Patil, M. Tech. (Env. Engg.)
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         The ‘ANACONDA’ named after the species of aquatic boas is a new concept for
wave energy conversion (WEC). It is just a rubber tube; full of water, closed at both ends and
anchored below the sea surface with one end facing the oncoming waves. As a long sea wave
passes this tube, squeezing it, it starts a bulge wave, which passes down the tube walls
gathering energy from the ocean wave as it goes. Continuous energy gathering is caused by
resonance between bulge wave frequency and sea wave and this energy is stored in the rubber
as P.E. As bulge wave travels it increases progressively in size and at the end of the tube the
energy is converted to a surge of water which drives a turbine in the power take off.
‘ANACONDA’ has good energy capture, low capital cost and low maintenance as it uses
rubber and very few parts unlike other WEC devices. It produces environmental friendly
1    Bulge wave energy conversion

                                                                                         Chapter 1

    Marine renewable energy as a infinite source of energy can be a reliable alternative for fossil
    fuels particularly in the UK with high potential wave energy in the Britain marine
    environment. Wide variety of wave energy converters has been developed in last decades and
    presenting more economical and reliable technologies is also under process. The ‘Anaconda’
    a full-rubber Wave Energy Converter (WEC) operates in a completely new way, transferring
    energy from water waves to bulge waves in a giant water-filled submerged rubber tube,
    aligned head-to-sea. Initial researches have shown that it offers advantages of low capital and
    operational costs, because of its extreme simplicity and the unique durability of rubber. [1]

    Besides the importance of the design process of a wave energy converter, it is very vital to
    decide about the grouping of the devices in a wave farm. To have an optimum power output
    from the wave farm and minimum environmental impacts on marine environment and
    shoreline, it is necessary to evaluate the layout and the configuration of wave farm by
    laboratorial tests or computer simulations. [2]

    Renewable energy is recognized as a pollution-free source of power generation in the world
    and it is under rapid development in different fields such as wind, wave, solar and etc. One of
    the main sources of renewable energy can be derived from ocean waves. Numerous wave
    energy converters have been invented and designed for locations from the shore to deep
    water. These devices should be deployed in an arranged array to be more efficient and cost
    effective. The effect of each device on its surroundings will affect the efficiency of other
    devices in the wave farm. Therefore the device spacing and geometric configuration has
    effect on power output of each individual device. Wave device and wave-wave interaction
    also makes the prediction of output wave characteristics more complicated.[2]

    ‘Anaconda’ as a new floating wave energy converter has recently introduced by scientists. As
    the potentially most-efficient wave energy converter. In this dissertation a brief
    Introduction of Anaconda and its outstanding advantages are presented.[1]                                                                             1
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    1.1: WAVE ENERGY.

    Ocean waves arise from transferring the energy from the sun to wind and then water. Solar
    energy causes wind which blows over the ocean surface, converting wind energy to wave
    energy. This wave energy can travel thousands of kilometers with little energy loss.
    Furthermore, waves are a huge source of power with a predictable intensity that isaccurately
    predictable several days before their arrival. Wave energy is more predictable than wind or
    solar energy. Fig. 1.1 presents wave power levels in kW/m of wave crest. Kilo Watt per meter
    (kW/m) is the typical units for measuring wave energy. Estimates show approximately 8,000-
    80,000 TWh/yr or 1-10 TW of wave energy in the entire oceans, and on average, each wave
    crest transmits 10-50 kW/m, Muetze (2006).from the waves can be used to convert into other
    forms of energy.

    Fig 1.1: Approximate global distribution of wave power levels in kW/m of wave front,
    Muetze (2006).[4]

    In the UK many investigations focus on the potential for future exploitation of the marine
    energy resource. Also development of new and improved devices for efficient and sustainable
    power generation and supply has been planned by comprehensive studies in the country.                                                                       2
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                                                                                    Chapter 2
                       WAVE ENERGY CONVERTERS.
    The different wave energy converters are:
       1. Pelamis
       2. Wave Dragon Type
       3. Anaconda

    2.1: PELAMIS.

         Fig2.1: Photographic picture of Pelamis. [2]
    This type of energy converter is made up of metal like steel or aluminum. It has four
    compartments and is a long structure, this has certain disadvantages as it has risk of breakage
    and maintenance cost is high.                                                                          3
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    2.2: WAVE DRAGON:

         Fig 2.2: Photographic picture of wave dragon [2]

    It is a type of energy converter which is made up of rubber but the disadvantage is that this
    converter is floating on the surface and it will effect on the navigation.

    Impact of wave energy converters:
    •Noise- it will produce noise but the noise is less as compared to the wind mill.
    •Change of migration route for marine mammals
    •Visual effect
    •Navigation – navigation of ship is disturbed.                                                                        4
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                                                                                     Chapter 3

                          ANACONDA –TECHNOLOGY.
    Anaconda is a new wave energy converter system based on bulge waves traveling Along a
    distensible rubber tube. The Anaconda is named after the long and enormous South American
    snake that hunts for its prey in water. It is the largest snake that Spends most of its time in
    water environments.

    Waves are formed by winds blowing over the water surface, which make the water particles
    adopt circular motions. This motion carries kinetic energy, the amount of which is
    determined by the speed and duration of the wind, the length of sea it blows over, the water
    depth, sea bed conditions and also interactions with the tides. [4]

    Waves only occur in the volume of water closest to the water surface, whereas in tides, the
    entire water body moves from the surface to the seabed. In Tides, the energy is due to a net
    movement of water, but in Waves, the water acts as a carrier for energy, moving it in some
    directions but it does not undergo a net movement itself. Waves are formed by the wind – the
    stronger the wind and the longer the distance over which it blows, the larger the waves and
    the more energy they carry. [4]

    Essentially, it is very large water filled distensible rubber tube floating just beneath the sea
    surface at right angles to the waves, with a power take off at the stern. As a wave passes the
    bulge tube is lifted with the surrounding. Water and causes bulge waves to be excited which
    passes down the tube’s diameter like a pulse in an artery, gathering energy from the sea wave
    as it goes. Continuous energy gathering results from resonance between the bulge wave and
    the sea wave. Energy from the sea wave is stored in the rubber as it stretches. 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 surge drives a turbine in
    the power take off after the flow has been smoothed.[6]                                                                           5
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    Wave energy occurs due to movements of water near the surface of the sea. Waves are
    formed by winds blowing over the water surface, which make the water particles adopt
    circular motions. This motion carries kinetic energy, the amount of which is determined by
    the speed and duration of the wind, the length of sea it blows over, the water depth, sea bed
    conditions.                                                                                  .

    Waves only occur in the volume of water closest to the water surface, whereas in tides, the
    entire water body moves from the surface to the sea bed. In Tides, the energy is due to a net
    movement of water, but in Waves, the water acts as a carrier for energy, moving it in some
    directions but it does not undergo a net movement itself.

    It has been known for many years that bulge waves can propagate along a fluid-filled elastic
    tube – they are like sound waves, except that the elasticity of the tube walls increases the
    effective compressibility of the fluid, slowing the wave. The best-known example is
    physiological: the pressure pulse from the heart propagates relatively slowly along the
    arteries (much more slowly than the speed of sound in blood), because of the elasticity of the
    artery wall. ANACONDA is a giant water-filled rubber tube, in which the natural
    propagation speed of bulge waves is matched to the speed of the water waves to be captured.
    There is then a resonant amplification of the bulge wave, and the water wave energy is
    captured as a bulge wave.

    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 reservoir are at different heights.

    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 chambers so the
    total. Volume of the two reservoir remain same.                                                                         6
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    Anaconda wave energy converter - sketches of the device in waves travelling from left to
    right, at four phases of the motion, with a power take-off system at the downwave end.
    Arrows indicate the direction of the oscillatory internal flow.

    Waves are formed by the wind – the stronger the wind and the longer the distance over which
    it blows, the larger the waves and the more energy they carry. For that reason waves on the
    West Coast of the UK tend to contain more energy than the East Coast. Essentially, it is very
    large water filled distensible rubber tube floating just beneath the sea surface at right angles
    to the waves, with a power take off at the stern.

    The figure shows how bulge wave is produced and moves along a floating tube in the sea. In
    the picture the waves come from the left. The arrows show the flow direction of water inside
    the tube. The bulge wave in the tube and the waves in the sea have the same velocity; and the
    wave energy is gradually transferred to the tube.

    Fig3.2: Bulge waves [3]                                                                            7
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    The wave squeezes the tube at the bow and starts a bulge running. But as it runs the
    wave runs after it, squeezing more and more, causing the bulge gets bigger and
    bigger. The bulge moves in front of the wave where the slope of the water (pressure
    gradient) is highest. In fact the bulge surfs on the front of the wave.
    A good example of bulge waves in a distensible tube is the pressure pulse which
    travels along the arteries.
    Squeezing a filled rubber tube will make a local bulge in it and this bulge can
    propagate along the tube at a speed of ‘c’ given by

    E is the tensile modulus of the rubber, d the diameter of the tube, h its wall thickness
    and ρ is the density of water.

    The speed of the bulge can be controlled by choosing the dimensions of the tube and
    the properties of the rubber.

    The bulge wave is a wave of pressure, associated with a longitudinal oscillation of fluid,
    forwards and backwards within the tube. The water flows forwards when the pressure is high,
    and the water is flowing backwards when the pressure is low. Aresonant interaction will
    happen when the bulge in the tube travels at the same speed as the wave and the bulge grows
    linearly along the tube and carries energy.In resonance, the energy in the bulge grows as the
    square of the distance from the bow. Off resonance, the bulge grows initially and after
    reaching a maximum, decreases; this cause fluctuations in the power output.

    The pressure oscillation at the end of a tube one wavelength long is three times the incoming
    sea wave. The energy in the tube is proportional to the tube area. The capturedenergy is
    related to the energy per meter of wave front in the sea by “capture width” (CW) parameter.
    In fact the device collects all the energy in the sea from a wave frontage equal to the capture
    width. The predicted capture width for different wave period has been illustrated. The
    maximum capture width is about 50 m. as an average over the wave spectrum in the sea, the
    mean capture width equal to 20 m can be expected for a tube 7m diameter and 156m length
    (Farley and Rainey 2006).                                                                          8
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    In typical Atlantic conditions, the wave energy in the sea is 50 KW/m, so the energy captured
    in 20m width would be about 1 MW.
    Comparing with other wave energy converters, the bulge wave tube has the highest capture
    width. This advantage can give a privilege to Anaconda in economic competition with other
    wave energy converters.

    Fig3.2: Full view of anaconda [2]                                                                        9
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     So far the device has only been proven at very small scale in the laboratory. So the next step
     will be to use rubber tubes that are bigger: 0.25 meters and 0.5 meters in diameter. A full
     scale Anaconda would be huge. 200 meters long (656 feet), 7 meters in diameter (23 feet),
     and it would be deployed in the ocean at water depths of 40 to 100 meters (130 to 330 feet).
     The thickness of the device of above-mentioned dimensions comes out to be around 15cm at
     the tail end. At the front portion its still less. The average thickness comes out to be around 8-
     10cm. Electricity productions for one unit is estimated at 1 megawatt, enough to power 2,000
     UK houses.

                                  FIG 3.3: Anaconda used in groups [2]                                                                             10
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                                                                                       Chapter 4


     The economics of ‘ANACONDA’ have shown to be very promising. It has shown a great
     potential compared to other WEC’s. The economics of the device depend on the price of the
     rubber, per unit of elastic energy stored in it over its lifetime, in p/kWh. This must be less
     than the selling price of the electricity produced over the device lifetime, again measured in
     p/kWh. The material used is rubber.

     Rubber has good durability. Despite their harsh treatment and the extremely hostile
     environment, they last many years. This is partly because the fatigue life of rubber is
     extremely long, as is shown by the example of a car tyre, which can last for 100,000 km =
     100,000,000 revolutions = 108 cycles, which comfortably exceeds the number of waves
     encountered by a WEC in 10 years.

     The flexibility of rubber also offers unique advantages in handling and safety. It is easy to
     transport and install, because it can be rolled up and carried as deck cargo, and it poses no
     danger to shipping, even if it breaks free from its moorings. From the point of view of rubber
     engineering, the power take-off system does not dominate the capital costs, because the
     material used is all-inextensible, as in a dracone. To use the rubber most effectively the tube
     will have a composite wall, partly rubber and partly inextensible polymer-coated fabric, the
     weight of rubber required for a 1 MW installation will then be only a few hundred tonnes.

     Special type of rubber like the Hypathalon type or some other depending upon properties like
     elasticity, durability, better adaptability in water, may be used. Waterproof coating can also
     be done for better performance. It doesn’t affect the elasticity or performance of the device. It
     is the main tube, which dominates the capital cost, because the rubber in it is required to store
     energy. In a bulge wave device, the stored elastic energy in the rubber in one wavelength of
     tube (approximately equal to the length of ANACONDA) equals the electrical power output                                                                            11
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     over one period. Thus the elastic energy stored in the whole device over its lifetime is
     approximately equal to its lifetime electrical energy output.
     Below is the comparison of costs of ‘ANACONDA’ with some other WEC devices based on
     preliminary estimates: These figures show that Anaconda is cost effective WEC.

                           Device                            Cost per KW electrical energy
                OTEC (Ocean Thermal Energy                           7000-12000 US$

                          Pelamis                                    5000-7000 US$
                          Anaconda                                   1000-2000 US$                                                                      12
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                                                                                      Chapter 5

     1. Simple system:
     As already mentioned this device has only a rubber tube and a power take of system consisting
     of turbine and other components. It has only a single moving part and veryfew metallic parts as
     Compared to other WEC devices.

     2. Good Energy Capture:
     As shown earlier this device has shown very good energy capture that far exceeds other WEC

     3. Good Survivor:
     As the main body is a rubber tube and no complicated machinery, it proves to be a good survivor
     in the sea.

     4. Low Maintenance:
     Compared to other WEC devices it requires very less maintenance owing to its simple system.

     5. Low Cost Energy:
     As already seen in economics the cost of this device is very low as compared to other WEC devices.
     Also the maintenance costs are very less.

     6. Closed System:
     This is also a major advantage where Anaconda holds an upper hand over the other WEC devices.
     It is a closed system. The water circulates inside the closed rubber tube.Nothing is sent outside or no
     water or marine animals enter into the system. Marine animals are not going to affect the functioning
     of this device and they themselves are also not going to get harmed.

     7. Pollution Free:
     This device provides clean and environmental friendly energy. It creates no pollution like as it
     has no emissions.                                                                           13
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                                                                                    Chapter 6

                    PRESENT - STATUS OF ANACONDA

            The concept is protected by a UK patent and there is plenty of time for international
     applications. There is confidence that research programme will resolve all the remaining
     scientific issues regarding power capture and power take-off. The development programme
     (a) Develop a bottom-mounted version of about 1.5 m diameter, suitable for installation on a
     beach, average power output about 50 kW. The power take-off is simpler in this case,
     because the seabed provides a reference, and such a device could pump water to the shore. As
     well as a demonstrator of the technology, the device could have a niche market, perhaps in

     (b) Develop a floating version of (a), designed to produce electricity. This means solving the
     problem of a power take-off without a seabed reference, and designing an electrical and a
     mooring system. The device would be primarily a demonstrator, but again could have a niche

     (c) Full-scale device as when built, each full-scale anaconda device would be 200 meters long
     and 7 meters in diameter, and deployed in water depths of between 40 and 100 meters.[4]                                                                         14
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                                                                                 Chapter 7


     The potential for producing energy from waves has been recognized for many years. Any
     coast where the wave strength is over 25KW per meter has the potential for an Anaconda
             3/4 of the globe is covered by water.
             India is surrounded by water on three sides.
             Countries like UK, US, South Africa could be hugely benefited.
     It would also be possible to produce smaller versions of Anaconda that could be co-located
     with offshore wind farms.                                                                     15
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                                                                                        Chapter 8

                                TAKE A BITE OF CO2.[8]

            The Anaconda could make a valuable contribution to environmental protection by
     encouraging the use of wave power. A giant rubber anaconda could be a step on the road to
     meeting a large chunk of our energy needs using carbon-free, wave-generated electricity.
     Because it is made of rubber rather than metal, the Anaconda is much lighter than other wave
     energy devices and dispenses with the need for hydraulic rams, hinges and articulated joints.
     This reduces capital and maintenance costs and scope for breakdowns.

            The device has already been given a significant vote of confidence by the Carbon
     Trust. The Anaconda has been chosen as one of only two technologies to take part in the
     Trust's marine accelerator programme, which aims to push new low-carbon technology ideas
     closer commercial reality. It has the potential to be robust and quite easy and cheap to
     manufacture. When we look at some of the severe offshore conditions that wave and tidal
     devices have to face, then we realize that a structure like this could be quite cheap.                                                                        16
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                                                                                    Chapter 9

                                    CONCLUSIONS. [8]

        •   Though the device has only been proven at very small scale but its method of
            operation and construction mean that it has enormous potential, which exceeds all
            other wave energy converters and many other renewable energy sources.

        •   It has the potential to save millions of tonnes of carbon dioxide production around the

        •   ANACONDA can produce clean and environmentally friendly power.

        •    This technology will surely help reduce our dependence on non-renewable sources
            and enable us to create a sustainable future for anyone.

        •   Its key advantage is its survivability. If the worst comes to the worst it'll only be
            washed up on the beach and you can patch it up and put it back out there.                                                                         17
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        1. Farley, F.J.M. and Rainey, R.C.T. ANACONDA: the bulgewave sea energy
            converter. Unpublished note, available on
        2. Chaplin, J.R., Farley F.J.M. and Rainey, R.C.T. Power Conversion in the
            ANACONDA WEC available on
        3. Chemical Weekly Magazine, July 2008 issue
        4. http://
        8.                                                        18

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Description: Ocean Eneargy - Wave Energy