Power conversion in the Anaconda WEC

The Anaconda all-rubber 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 indications are that it offers advantages of low capital and operational costs, owing to its extreme simplicity and the unique durability of rubber (see www.bulgewave.com). This paper presents briefly the results of the first series of laboratory tests carried out on a model of the device, providing evidence of a capture width of between 3 and 4 diameters over a wide range of frequencies. Secondly we discuss a concept for a simple power take-off system

Ringing of vertical cylinder in waves

This paper analyses the results of two series of experiments concerned with the response of a single vertical cylinder in the inertia regime in steep non-breaking waves. We recorded first the loading on a cylinder when it was held stationary, and secondly, its response in the same waves when it was pivoted just above the floor of the wave flume, and supported at the top by springs in the horizontal plane. Spring stiffnesses were set to achieve natural frequencies (measured in still water) in the range between 3 and 11 times the dominant wave frequency. The experiments were repeated with cylinders of three different diameters.Peak loading on stationary cylinders was found to exceed the predictions of a Morison model (based on kinematics computed from a numerical model of the measured waves), though improvements were achieved through the inclusion of slender-body terms. Measured ringing responses are generally in good agreement with those computed on a quasi-static basis from the measured loading history, but in some conditions, particularly at low frequency ratios, there is clearly some feedback from the motion to the excitation. Peak accelerations in the steepest waves are found to be limited approximately to those that would occur if the maximum loading were applied as a step change. Particular attention is given to a rapid cycle of loading that occurs after the crest has passed the cylinder's axis, and to images of the flow around the cylinder at the water surface.<br/

Transient motion of a vertical cylinder: Measurements and computations of the free surface

In recent years there have been concerns in the offshore oil industry over the violent motions of the water surfaceproduced around a vertical cylinder by relatively large steep waves (say height/diameter = 1, height/length =0.1)

Laboratory testing the Anaconda

Laboratory measurements are presented of the performance of the Anaconda, a wave energy converter comprising a submerged water-filled distensible tube aligned with the incident waves. Experiments were carried out at a scale of around 1:25 with a 250mm diameter tube, 7m long, constructed of rubber and fabric, terminating in a linear power take-off of adjustable impedance.The paper presents some basic theory that leads to predictions of distensibility and bulge wave speed in a pressurised compound rubber and fabric tube, including the effects of inelastic sectors in the circumference, longitudinal tension, and the surrounding fluid. Results are shown to agree closely with measurements in still water.The theory is developed further to provide a model for the propagation of bulges and power conversion in the Anaconda. In the presence of external water waves the theory identifies three distinct internal wave components and provides theoretical estimates of power capture. For the first time, these and other predictions of the behaviour of the Anaconda, a device unlike almost all other marine systems, are shown to be in remarkably close agreement with measurements

Development of the Anaconda all-rubber WEC

The ANACONDA all-rubber WEC operates in a completely new way, capturing water waves as “bulge waves” in a giant water-filled rubber tube, aligned head-to-sea. It offers new possibilities for low capital and operational costs, based on the unique durability of rubber, and the single moving part (a conventional medium-head unidirectional water turbine). See www.bulgewave.com. Avon Fabrications LLP have recently taken an exclusive license to manufacture the device, which has been selected by the Carbon Trust for the Marine Energy Accelerator programme. Initial model tests show good capture width and wide bandwidth. 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/kW-hr. This must be less than the selling price of the electricity produced over the device lifetime, again measured in p/kW-hr. On this basis the economics of ANACONDA are very promising

Design rules for the avoidance of subharmonic oscillations in large floating offshore structures

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