The Anaconda technology is based on the propagation of internal bulge-waves through a flexible, water-filled tube. The tube is intended to sit just below the water surface and is aligned perpendicular to the oncoming wave front (Figure 1). Dynamic pressure variations applied to the flexible tube by incident ocean waves change the cross-section of the tube at frequencies which initiate an internal bulge-wave. This wave propagates inside the tube in phase with the external ocean wave. The bulge-wave continues to extract energy from the external ocean wave as it grows towards the stern power take off (PTO). The speed of the bulge propagation along the tube is determined by the distensibility of the tube. If this speed is close to the phase velocity of the waves, then there is a resonance and optimised energy transfer between the two. Distensibility is the property relating to the stretching or swelling of the tube and the key control parameter needed to optimise this energy transfer. It is defined as a function of tube working diameter, thickness, percentage of rubber to inextensible material in the circumference and Young’s Modulus of materials.
The Anaconda technology embodies a complex hydro-elastic problem directly coupling power performance and survivability in both extreme conditions and fatigue conditions as a result of millions of duty cycles during operational conditions. The governing design parameters of the bulge-wave tube’s dynamic response to wave excitation influence this balance between cost, power performance and survivability. Determining how to select the particular design parameters to address this balance and demonstrate economic potential is a key target outcome of current development work.
The use of a wave absorbing mode based on flexible materials is a radical change from other families of WEC devices, with potential for step-change improvements in areas that impact overall LCOE:
- A self-referencing primary absorber based on flexible materials avoids the need for any articulated joints, reference bodies and/or end stops associated with rigid wave activated bodies. This offers potential step changes in reliability and survivability.
- The inflated structure permits the use of new installation and maintenance principles for marine operations offering potentially radical changes to installation and O&M costs.
- The bulge-wave principle for converting wave energy is entirely novel and has been patented by CSL. While impressive energy production and broad-bandedness has been measured experimentally, the full energy production potential is only just beginning to be understood. A key advantage also is that at the point of conversion, only relatively simple damping strategies are required to convert the available power, with no need for more complicated control strategies or reactive forces.
- There is potential for a step change in structural weights and material costs, especially given the future innovation potential in the primary bulge tube design.
- There is a drastic reduction in the criticality of structural failure modes of the primary absorber, relative to large steel structural failures.
The novelty of the Anaconda technology presents substantial opportunities to reduce LCOE of wave energy technology through the significant amount of learning which can be achieved during the continued development and understanding of this concept. This is in contrast to rigid body structures where there are well-established analysis, design and construction techniques but often more limited learning potential in delivering on a pathway to the WES target unit cost of energy.