The WRASPA, or Wave-driven Resonant, Arcuate-action, Surging Power Absorber, is a hinged device which operates in Pitch-Surge. It is envisaged that the device will operate in water depths of 20-50m.
The device has been the subject of a joint research programme of design optimization, funded by the Joule Centre in Manchester, and conducted by Lancaster and Manchester Metropolitan Universities. We are now working to build a consortium to take forward the development of this device, so that it can be demonstrated at full scale. Current work centres around further improvements in collector shape and further developments of the novel control system for power conversion.
This diagram above and the top picture show the essentials of the practical device with one possible method of holding it in position, by placing its base unit, containing all the power conversion and control equipment, into a pre-installed seabed pile. Other methods are also envisaged, once the collector and Power Take Off designs are optimised. The diagram shows how in more recent embodiments, a “skirt” is extended down from the collector to protect the mechnism.
This photo shows the first shape - the rounded half-moon that had square corners and lower powers than the, later, rounded version seen in the videos.
The plotted "work loops" are from that model with x-axis (angular motion) and y-axis (torque) combining to give a loop area in Joules - torque load was varied to find the best operating position.
This device is built on some 30 years of experience in wave power at Lancaster University and is the brainchild of Bob Chaplin. (r.chaplin AT lancaster.ac.uk)
Details of this device were presented at 2 conferences in 2007:
- International Conference on Clean Electrical Power, Capri, May 2007: Abstract: "...The key to success in clean electrical power lies in a low lifetime-cost of power as delivered to the user. For wave power this must start with a compact, powerful and reliable wave energy converter, or WEC. Pitching-surge point-absorber WECs have the potential to generate average annual powers of around 1.5MW in North Atlantic conditions from relatively small devices. The paper reports very early work on one such device - WRASPA - in water depths greater than 20m including the effects of collector geometry on power output, based on both experimental and computational modelling. In particular, the progress towards optimum collector geometry will be described. Engineering designs for devices based on these findings will be outlined."
- European Wave and Tidal Energy Conference, Oporto, Sept 2007. "...2MW in North Atlantic conditions from relatively small devices that would be economically competitive with other technologies and would be relatively easy to install and maintain. The paper examines the factors governing the performance of such devices and outlines their underlying theory Preliminary laboratory test results from a 1/100 scale pilot design are presented. It is hoped that more extensive development work will follow these promising early results. Engineering designs for devices based on these findings are outlined. For more details or a copy of this paper please contact Bob Chaplin or George Aggidis.
Wave Energy Research Projects
surge rig 2006
Shows early tests with a plate collector moving in pure surge. Later tests – not shown – clearly showed that this resonant mechanism could deliver high power from a small device: it was absorbing more power than was incident on its own width.
Wraspa Mk2 rhm2
Shows a 1/100 scale tank test model in Lancaster’s own 2.5m wide tank. This is the rig currently in use with the power-take-off arrangement mounted above the water on the same “C” –shaped frame that carries the hinged collector. The collector body is the “rhm2” or the 2nd version of the basic rounded half-moon, the shape suggested by Prof. Michael French whose ideas have inspired the work at Lancaster over many years.
Wraspa Mk2 rhm2b
this clip shows the same rig working in waves – it should be noted that, at this stage. The power-take-off is not yet working. It will be used late in June to shows power capture in regular waves and in mixed seas.